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• 4181. [Article] Validation of Molecular Markers Associated with Perpetual Flowering (PF) and Soluble Solids Content (SSC) in Strawberry (Fragaria xananassa Duch. ex Rozier)

  Strawberry is economically the most important berry crop grown worldwide and breeders are continuously striving to develop improved cultivars. So far, marker assisted breeding (MAB) in strawberry has been ...

  Citation × Citation Citation Abstract Copy Title: Validation of Molecular Markers Associated with Perpetual Flowering (PF) and Soluble Solids Content (SSC) in Strawberry (Fragaria xananassa Duch. ex Rozier) Author: Salinas, Natalia R. Strawberry is economically the most important berry crop grown worldwide and breeders are continuously striving to develop improved cultivars. So far, marker assisted breeding (MAB) in strawberry has been limited to the private sector. However, loci controlling some traits of economic importance such as perpetual flowering (PF) and soluble solids content (SSC) associated with fruit sweetness were recently mapped in the cultivated strawberry, a prerequisite to enabling MAB. The first objective of this research was to investigate usefulness of markers linked to the FaPFRU locus controlling PF in 'Capitola' and strawberry germplasm containing the same F. virginiana subsp. glauca source collected by Bringhurst in Utah’s Wasatch Mountains through 'Tribute' and 'Seascape', and from other sources such as 'Pan American' through 'Fort-Laramie', and an unknown source through 'Sarian'. The second objective was to assess the ability of an SSC-associated simple sequence repeat (SSR) marker for predicting high soluble solids content in different environments in strawberry. Five SSR markers (EMFvi136, Bx89, Bx215, Bx56 and Bx63) that are linked to PF on linkage group IVb were used to genotype 893 strawberry individuals. Based on Mendel's Law of Inheritance, parentage was confirmed for most seedlings. Those that had unlikely genotypes or alleles were identified in each of the mapping and breeding populations from Michigan State University (MSU) and those of the USDA-ARS in Corvallis (ORUS). Off type frequencies in breeding populations were 17.1%, on average. Furthermore, multiple genotypes of parents were identified and included: 'Fort Laramie' and FRA 1701 in the MSU breeding programs and 'Tillamook' and 'Puget Reliance' in the ORUS program. Genotype of the FRA 1701 used as parent was different between both programs. Six alleles were associated with PF in the entire dataset: EMFvi136_167, Bx89_251, Bx89_262, Bx215_129 and Bx56_209. However, none of these alleles were present in the FRA 1701-derived progeny and could not be used to predict PF. Since Bx215 mapped closest to the FaPFRU locus, we used repeated rounds of ANOVA to identify combinations of alleles at this SSR that best explained the PF trait in the breeding populations. The presence of 129 and absence of 160 increased predictivity of PF from 63% to ~80% while the absence of 129, 123, 127 and 134 predicted OF in 100% of the germplasm where the original source of PF was that obtained from the F. virginiana subsp. glauca from the Wasatch Mountains through 'Capitola', 'Seascape' and 'Tribute'. In 'Sarian'-derived germplasm, other alleles, 123 and 134 or 127, were predictive of PF. Establishing allele composition at each subgenome using microsatellite allele dose and configuration establishment MADCE for Bx215, Bx56 and Bx63 identified the associated alleles as shared among three or four of the subgenomes, thus unable to predict PF based on allele presence in all PF individuals. Absence of these alleles was more predictive of once flowering and could be used to eliminate those individuals and therefore increase the proportion of PF progeny to evaluate. Determining haplotypes in this region and evaluating haplotype association with PF could be much more accurate in predicting PF than allele presence or absence and should be investigated. Soluble solid content-associated EMFv006 was used to genotype 602 individuals. Alleles and genotypes associated with low (209, 215), medium (207, 213, 217) and high SSC (219, 221) were obtained. Plants with the 213:219 EMFvi006 genotype always had higher SSC than those with the 213:209 or 213:215 genotypes in all states except for California. When converted to functional alleles and analyzed by ANOVA in each of the states, a consistent increase in SSC mean was observed between genotypes with the lower SSC types and the higher SSC genotypes in each of the states and years. Heritability (H²) was low (0.02-0.09) in all states but NH_12 indicating that this trait is highly influenced by environmental conditions. The proportion of phenotypic variance (PVE) was high in comparison with those of H² in all states except for CA_12 and ranged from 0.65 in MI_11 to 0.86 in NH_12, indicating that most of the genotypic variance observed can be explained by this locus that can strongly predict differences in SSC content. Much of the variability seen in the SSC trait in this study could be explained by differences in environments and fruit ripening at the time of harvest and their effects on SSC as SSC is very sensitive to environmental factors such as temperature and harvest date. It may be necessary to develop a more standardized protocol of measuring SSC across states and years to obtain more reliable SSC data for each individual. Most importantly, this study illustrates the usefulness of introgressing novel alleles from wild accessions into the cultivated gene pool. Both alleles consistently associated with high SSC, 219 and 221, originated from wild F. virginiana parents (FRA 1701-I1, and FRA 1701, respectively) from the "supercore" and were not present in any of the F. ×ananassa cultivars genotyped in this study except for an old European selection, 'Jucunda', of unknown pedigree. Based on the results obtained in this study, breeders may be able to select progeny with desired flowering type and increased soluble solid content after evaluating the alleles present in their parental material. Title: Validation of Molecular Markers Associated with Perpetual Flowering (PF) and Soluble Solids Content (SSC) in Strawberry (Fragaria xananassa Duch. ex Rozier) Author: Salinas, Natalia R. Strawberry is economically the most important berry crop grown worldwide and breeders are continuously striving to develop improved cultivars. So far, marker assisted breeding (MAB) in strawberry has been limited to the private sector. However, loci controlling some traits of economic importance such as perpetual flowering (PF) and soluble solids content (SSC) associated with fruit sweetness were recently mapped in the cultivated strawberry, a prerequisite to enabling MAB. The first objective of this research was to investigate usefulness of markers linked to the FaPFRU locus controlling PF in 'Capitola' and strawberry germplasm containing the same F. virginiana subsp. glauca source collected by Bringhurst in Utah’s Wasatch Mountains through 'Tribute' and 'Seascape', and from other sources such as 'Pan American' through 'Fort-Laramie', and an unknown source through 'Sarian'. The second objective was to assess the ability of an SSC-associated simple sequence repeat (SSR) marker for predicting high soluble solids content in different environments in strawberry. Five SSR markers (EMFvi136, Bx89, Bx215, Bx56 and Bx63) that are linked to PF on linkage group IVb were used to genotype 893 strawberry individuals. Based on Mendel's Law of Inheritance, parentage was confirmed for most seedlings. Those that had unlikely genotypes or alleles were identified in each of the mapping and breeding populations from Michigan State University (MSU) and those of the USDA-ARS in Corvallis (ORUS). Off type frequencies in breeding populations were 17.1%, on average. Furthermore, multiple genotypes of parents were identified and included: 'Fort Laramie' and FRA 1701 in the MSU breeding programs and 'Tillamook' and 'Puget Reliance' in the ORUS program. Genotype of the FRA 1701 used as parent was different between both programs. Six alleles were associated with PF in the entire dataset: EMFvi136_167, Bx89_251, Bx89_262, Bx215_129 and Bx56_209. However, none of these alleles were present in the FRA 1701-derived progeny and could not be used to predict PF. Since Bx215 mapped closest to the FaPFRU locus, we used repeated rounds of ANOVA to identify combinations of alleles at this SSR that best explained the PF trait in the breeding populations. The presence of 129 and absence of 160 increased predictivity of PF from 63% to ~80% while the absence of 129, 123, 127 and 134 predicted OF in 100% of the germplasm where the original source of PF was that obtained from the F. virginiana subsp. glauca from the Wasatch Mountains through 'Capitola', 'Seascape' and 'Tribute'. In 'Sarian'-derived germplasm, other alleles, 123 and 134 or 127, were predictive of PF. Establishing allele composition at each subgenome using microsatellite allele dose and configuration establishment MADCE for Bx215, Bx56 and Bx63 identified the associated alleles as shared among three or four of the subgenomes, thus unable to predict PF based on allele presence in all PF individuals. Absence of these alleles was more predictive of once flowering and could be used to eliminate those individuals and therefore increase the proportion of PF progeny to evaluate. Determining haplotypes in this region and evaluating haplotype association with PF could be much more accurate in predicting PF than allele presence or absence and should be investigated. Soluble solid content-associated EMFv006 was used to genotype 602 individuals. Alleles and genotypes associated with low (209, 215), medium (207, 213, 217) and high SSC (219, 221) were obtained. Plants with the 213:219 EMFvi006 genotype always had higher SSC than those with the 213:209 or 213:215 genotypes in all states except for California. When converted to functional alleles and analyzed by ANOVA in each of the states, a consistent increase in SSC mean was observed between genotypes with the lower SSC types and the higher SSC genotypes in each of the states and years. Heritability (H²) was low (0.02-0.09) in all states but NH_12 indicating that this trait is highly influenced by environmental conditions. The proportion of phenotypic variance (PVE) was high in comparison with those of H² in all states except for CA_12 and ranged from 0.65 in MI_11 to 0.86 in NH_12, indicating that most of the genotypic variance observed can be explained by this locus that can strongly predict differences in SSC content. Much of the variability seen in the SSC trait in this study could be explained by differences in environments and fruit ripening at the time of harvest and their effects on SSC as SSC is very sensitive to environmental factors such as temperature and harvest date. It may be necessary to develop a more standardized protocol of measuring SSC across states and years to obtain more reliable SSC data for each individual. Most importantly, this study illustrates the usefulness of introgressing novel alleles from wild accessions into the cultivated gene pool. Both alleles consistently associated with high SSC, 219 and 221, originated from wild F. virginiana parents (FRA 1701-I1, and FRA 1701, respectively) from the "supercore" and were not present in any of the F. ×ananassa cultivars genotyped in this study except for an old European selection, 'Jucunda', of unknown pedigree. Based on the results obtained in this study, breeders may be able to select progeny with desired flowering type and increased soluble solid content after evaluating the alleles present in their parental material. Close

• 4182. [Article] The Factors Affecting the Diets of Groundfish in the Gulf of Alaska : Ecological and Modeling Considerations

  Marine systems undergo changes in community composition over time as a result of a variety of environmental and anthropogenic factors. Understanding these community changes and the factors that drive them ...

  Citation × Citation Citation Abstract Copy Title: The Factors Affecting the Diets of Groundfish in the Gulf of Alaska : Ecological and Modeling Considerations Author: Thompson, Kevin A. Marine systems undergo changes in community composition over time as a result of a variety of environmental and anthropogenic factors. Understanding these community changes and the factors that drive them is critical for ecosystem management of marine resources. The Gulf of Alaska (GOA) is a large marine ecosystem that includes a variety of species that support large scale fisheries. This is also a system in which large scale community shifts, or regime shifts, have occurred due to the Pacific Decadal Oscillation (PDO) and fishing pressure. Given the economic and conservation importance of this marine system, the GOA has been modeled using a variety of multispecies, or ecosystem, models. While this work has been critical in understanding the ecosystem dynamics of the GOA and helped generate management recommendations for commercial species, these models often make assumptions regarding trophic-dynamics, particularly that predator-prey relationships follow a standard functional response and do not change through time in response to environmental variables. However, empirical evidence suggests that a predator's diet can be influenced by a variety of factors, abiotic and biotic, at large and small spatial scales. Our overall objective was to investigate the potential impact environmental variables may have in structuring this ecosystem by using statistical analyses of diets and an ecosystem modeling framework. We focused on three commercially and ecologically important groundfish predators: Pacific Cod (Gadus macrocephalus), Pacific Halibut (Hippoglossus stenolepis), and Sablefish (Anoplopoma fimbria). We also focused on a key prey species, Walleye Pollock (Gadus chalcogrammus), and used environmental data collected during trawl surveys and PDO data generated for the entire North Pacific region. The first study completed was focused solely on the consumption of Walleye Pollock, a critical fishery species and ecosystem link. We used data from trawl surveys to determine the potential influence of local environmental variables on the predation rate of Walleye Pollock in the system by these groundfish. Using an information-theoretic approach, we found that predator length was positively related to Walleye Pollock presence and proportion of total diet weight in all predators. Increased temperatures positively affected consumption of Walleye Pollock by Pacific Halibut, but not the other predators. We found evidence for a number of inter-predator effects of co-occurring predators, both positive (facultative) and negative (competitive). Observed prey density was not statistically significant with respect to consumption for these predators, suggesting that trawls sample the environment differently than Walleye Pollock predators or species interactions are more complex than those used in previous multispecies models. In our second study, we considered the entire diet of these predators, rather than one key prey. Furthermore, because PDO had been described as leading to community changes in the system previously, we hypothesized that it could also be driving shifts in diets in the three groundfish predators we studied. We used a multivariate statistical approach to compare the diets of these predators by PDO state (warm or cold years) and also included local environmental covariates. Overall, we found that diets observed in PDO cold years were significantly different than diets in fish in warm years. In general, predators were found to be consuming more Walleye Pollock and euphausiids in warm years, and more benthic invertebrates and other forage fish in cold years. Local environmental covariates contributed to the diets observed in these predators, however no general pattern was observed. Our results also show the benefit of using diet data from large scale monitoring efforts as indicators of community shifts in a large marine ecosystem through time. Ultimately, we used our statistical analyses regarding diet and PDO state to drive a modeling exercise using alternate representations of the diets of the predators in the GOA. We investigated the potential impact of shifting diets in groundfish in an ecosystem-modeling framework, using Ecopath trophic-mass balance models. We changed the diets of key groundfish predators in the model based on our previous results for three alternative model parametrizations; 1) average conditions over the time period, 2) cold PDO state, and 3) warm PDO state. We noted a number of differences in model estimated ecosystem indices. Biomass accumulation estimates indicated that some ecologically and commercially important species groups would be expected to greatly diverge in population size if models were based on data from warm vs. cold PDO years compared to the averaged climatic state. In general, predator overlap was at its lowest in the cold year model, as predators had more diverse diets and therefore predation was more diffuse in the system in general. These results indicate the potential importance of environmental context when collecting diet data to be used in ecosystem models designed to provide fishery management recommendations. As ecosystem models are used more commonly, taking the time to investigate the factors that structure diets and how predation changes due to environment can yield more representative, and potentially more accurate biomass projections and recommendations for the GOA and likely many other managed marine ecosystems. Title: The Factors Affecting the Diets of Groundfish in the Gulf of Alaska : Ecological and Modeling Considerations Author: Thompson, Kevin A. Marine systems undergo changes in community composition over time as a result of a variety of environmental and anthropogenic factors. Understanding these community changes and the factors that drive them is critical for ecosystem management of marine resources. The Gulf of Alaska (GOA) is a large marine ecosystem that includes a variety of species that support large scale fisheries. This is also a system in which large scale community shifts, or regime shifts, have occurred due to the Pacific Decadal Oscillation (PDO) and fishing pressure. Given the economic and conservation importance of this marine system, the GOA has been modeled using a variety of multispecies, or ecosystem, models. While this work has been critical in understanding the ecosystem dynamics of the GOA and helped generate management recommendations for commercial species, these models often make assumptions regarding trophic-dynamics, particularly that predator-prey relationships follow a standard functional response and do not change through time in response to environmental variables. However, empirical evidence suggests that a predator's diet can be influenced by a variety of factors, abiotic and biotic, at large and small spatial scales. Our overall objective was to investigate the potential impact environmental variables may have in structuring this ecosystem by using statistical analyses of diets and an ecosystem modeling framework. We focused on three commercially and ecologically important groundfish predators: Pacific Cod (Gadus macrocephalus), Pacific Halibut (Hippoglossus stenolepis), and Sablefish (Anoplopoma fimbria). We also focused on a key prey species, Walleye Pollock (Gadus chalcogrammus), and used environmental data collected during trawl surveys and PDO data generated for the entire North Pacific region. The first study completed was focused solely on the consumption of Walleye Pollock, a critical fishery species and ecosystem link. We used data from trawl surveys to determine the potential influence of local environmental variables on the predation rate of Walleye Pollock in the system by these groundfish. Using an information-theoretic approach, we found that predator length was positively related to Walleye Pollock presence and proportion of total diet weight in all predators. Increased temperatures positively affected consumption of Walleye Pollock by Pacific Halibut, but not the other predators. We found evidence for a number of inter-predator effects of co-occurring predators, both positive (facultative) and negative (competitive). Observed prey density was not statistically significant with respect to consumption for these predators, suggesting that trawls sample the environment differently than Walleye Pollock predators or species interactions are more complex than those used in previous multispecies models. In our second study, we considered the entire diet of these predators, rather than one key prey. Furthermore, because PDO had been described as leading to community changes in the system previously, we hypothesized that it could also be driving shifts in diets in the three groundfish predators we studied. We used a multivariate statistical approach to compare the diets of these predators by PDO state (warm or cold years) and also included local environmental covariates. Overall, we found that diets observed in PDO cold years were significantly different than diets in fish in warm years. In general, predators were found to be consuming more Walleye Pollock and euphausiids in warm years, and more benthic invertebrates and other forage fish in cold years. Local environmental covariates contributed to the diets observed in these predators, however no general pattern was observed. Our results also show the benefit of using diet data from large scale monitoring efforts as indicators of community shifts in a large marine ecosystem through time. Ultimately, we used our statistical analyses regarding diet and PDO state to drive a modeling exercise using alternate representations of the diets of the predators in the GOA. We investigated the potential impact of shifting diets in groundfish in an ecosystem-modeling framework, using Ecopath trophic-mass balance models. We changed the diets of key groundfish predators in the model based on our previous results for three alternative model parametrizations; 1) average conditions over the time period, 2) cold PDO state, and 3) warm PDO state. We noted a number of differences in model estimated ecosystem indices. Biomass accumulation estimates indicated that some ecologically and commercially important species groups would be expected to greatly diverge in population size if models were based on data from warm vs. cold PDO years compared to the averaged climatic state. In general, predator overlap was at its lowest in the cold year model, as predators had more diverse diets and therefore predation was more diffuse in the system in general. These results indicate the potential importance of environmental context when collecting diet data to be used in ecosystem models designed to provide fishery management recommendations. As ecosystem models are used more commonly, taking the time to investigate the factors that structure diets and how predation changes due to environment can yield more representative, and potentially more accurate biomass projections and recommendations for the GOA and likely many other managed marine ecosystems. Close

• 4183. [Article] Cover crop effects on root rot of sweet corn and soil properties

  Root rot of sweet corn in western Oregon and Washington is a significant disease that can reduce yield of intolerant cultivars of processed sweet corn by fifty percent. Root rot is caused by a complex ...

  Citation × Citation Citation Abstract Copy Title: Cover crop effects on root rot of sweet corn and soil properties Author: Miyazoe, Mikio Root rot of sweet corn in western Oregon and Washington is a significant disease that can reduce yield of intolerant cultivars of processed sweet corn by fifty percent. Root rot is caused by a complex of soilborne organisms, including Drechslera sp., Phoma terrestris, and Pythium arrhenomanes. Processors have adopted tolerant cultivars but farmers continue to seek cultural management strategies that reduce inoculum potential. High rate manure and compost amendments (16.8 - 56.0 Mg ha⁻¹) suppress root rot of corn through general suppression but this practice is not agronomically viable. General suppression is typically associated with high rates of organic amendment and high microbial (FDA) activity. Processed vegetable farmers currently grow winter cover crops to improve soil and water quality and are interested in identifying cover crops that suppress root rot of corn and increase yield. High biomass cover crops can yield up to 12 Mg ha⁻¹ dry matter; this rate of organic amendment may or may not be sufficient to generate general suppression. However, specific cover crops, such as species and cultivars of crucifers and oats, have been shown to more suppressive than other cover crop species and cultivars against specific soilborne diseases. Oat is grown as a winter cover crop in the Willamette Valley and contains avenecin, a chemical that has been shown to have activity against pathogen propagules. In addition, in previous work in containers oat cover crops suppressed root rot of sweet corn. However, there is a concern that oat cover crops immobilize N and reduce corn yield. The objectives of this research were to 1) identify high biomass cover crops with agronomic potential for western Oregon processed vegetable cropping systems, 2) evaluate the impact of high biomass cover crops on root rot severity and yield of sweet corn, 3) determine whether there is a correlation between dry matter, soil microbial activity and root rot severity and 4) determine whether cover crops immobilize nitrogen and reduce corn yield. Research station field trials were conducted in 2003-04, 2004-05 and 2005-06 at the Oregon State University vegetable research farm in Corvallis, Oregon and an on-farm experiment was conducted in 2004-05 at Kenagy Family Farm in Albany, Oregon. Oat 'Saia' winter-killed in 2005-06 and mustard mix 'Caliente' winter-killed every winter except 2004-05, when winter temperatures never dropped below -7 °C. Rape 'Dwarf Essex', mustard 'Braco', and arugula are reliably winter-hardy. All mustard cover crop species are susceptible to white mold caused by Sclerotinia sclerotiorum, causal agent of white mold of snap bean. Oat (Avena sativa) is susceptible to barley yellow dwarf virus (BYDV), an important pathogen of grass seed crops. Mustard cover crops could contaminate cruciferous seed crops. All of the cover crop species evaluated demonstrated some potential to suppress root rot of corn. Oat 'Saia' was the most consistently suppressive; it suppressed root rot in 4 of 6 experiments. Sudangrass was suppressive in the only year it was evaluated as well as in container experiments in previous work. In general, cover crops increased or had no impact on shoot and root dry matter in greenhouse bioassays. There was only one significant cover crop treatment effect on yield; in 2006, the oat treatment increased yield by 11.6% compared to the fallow. Overall, cover crop aboveground dry matter (DM) ranged from 4.2 Mg ha⁻¹ (summer R 2003) to 12.2 Mg ha⁻¹ (winter O 2004). Overall, there was a significant relationship between cover crop DM and radicle rot severity in greenhouse bioassay but not in field experiment. Cover crop treatments consistently increased soil microbial activity. Overall, there was a significant negative correlation between microbial activity and root rot severity in greenhouse bioassays early after cover crop incorporation, but the correlation weakened over time and ultimately was lost by about 80 days after incorporation. The C:N of oat and rape residues was 51 and 21, respectively. Soil nitrogen was immobilized by both the oat and rape cover crops, but oat immobilized more N than rape. Corn grown in the oat treatment soils had lower SPAD values, but it is not clear whether foliar N was sufficiently low to reduce yield potential. There was no consistent trend in above- or below-ground corn dry matter after oat incorporation over the three years. In 2006, the oat treatment had no significant effect on corn DM but increased yield by 11.1%. More work is required to better understand the impact of oat cover crop N immobilization on corn N status and yield. Oat 'Saia' has the potential to suppress root rot of sweet corn and maintain or increase corn productivity. However, this oat cultivar is not reliably winter-hardy and is susceptible to BYDV. Future research should screen Avena species and/or cultivars for improved winter hardiness, BYDV resistance, and root rot suppressive potential. Title: Cover crop effects on root rot of sweet corn and soil properties Author: Miyazoe, Mikio Root rot of sweet corn in western Oregon and Washington is a significant disease that can reduce yield of intolerant cultivars of processed sweet corn by fifty percent. Root rot is caused by a complex of soilborne organisms, including Drechslera sp., Phoma terrestris, and Pythium arrhenomanes. Processors have adopted tolerant cultivars but farmers continue to seek cultural management strategies that reduce inoculum potential. High rate manure and compost amendments (16.8 - 56.0 Mg ha⁻¹) suppress root rot of corn through general suppression but this practice is not agronomically viable. General suppression is typically associated with high rates of organic amendment and high microbial (FDA) activity. Processed vegetable farmers currently grow winter cover crops to improve soil and water quality and are interested in identifying cover crops that suppress root rot of corn and increase yield. High biomass cover crops can yield up to 12 Mg ha⁻¹ dry matter; this rate of organic amendment may or may not be sufficient to generate general suppression. However, specific cover crops, such as species and cultivars of crucifers and oats, have been shown to more suppressive than other cover crop species and cultivars against specific soilborne diseases. Oat is grown as a winter cover crop in the Willamette Valley and contains avenecin, a chemical that has been shown to have activity against pathogen propagules. In addition, in previous work in containers oat cover crops suppressed root rot of sweet corn. However, there is a concern that oat cover crops immobilize N and reduce corn yield. The objectives of this research were to 1) identify high biomass cover crops with agronomic potential for western Oregon processed vegetable cropping systems, 2) evaluate the impact of high biomass cover crops on root rot severity and yield of sweet corn, 3) determine whether there is a correlation between dry matter, soil microbial activity and root rot severity and 4) determine whether cover crops immobilize nitrogen and reduce corn yield. Research station field trials were conducted in 2003-04, 2004-05 and 2005-06 at the Oregon State University vegetable research farm in Corvallis, Oregon and an on-farm experiment was conducted in 2004-05 at Kenagy Family Farm in Albany, Oregon. Oat 'Saia' winter-killed in 2005-06 and mustard mix 'Caliente' winter-killed every winter except 2004-05, when winter temperatures never dropped below -7 °C. Rape 'Dwarf Essex', mustard 'Braco', and arugula are reliably winter-hardy. All mustard cover crop species are susceptible to white mold caused by Sclerotinia sclerotiorum, causal agent of white mold of snap bean. Oat (Avena sativa) is susceptible to barley yellow dwarf virus (BYDV), an important pathogen of grass seed crops. Mustard cover crops could contaminate cruciferous seed crops. All of the cover crop species evaluated demonstrated some potential to suppress root rot of corn. Oat 'Saia' was the most consistently suppressive; it suppressed root rot in 4 of 6 experiments. Sudangrass was suppressive in the only year it was evaluated as well as in container experiments in previous work. In general, cover crops increased or had no impact on shoot and root dry matter in greenhouse bioassays. There was only one significant cover crop treatment effect on yield; in 2006, the oat treatment increased yield by 11.6% compared to the fallow. Overall, cover crop aboveground dry matter (DM) ranged from 4.2 Mg ha⁻¹ (summer R 2003) to 12.2 Mg ha⁻¹ (winter O 2004). Overall, there was a significant relationship between cover crop DM and radicle rot severity in greenhouse bioassay but not in field experiment. Cover crop treatments consistently increased soil microbial activity. Overall, there was a significant negative correlation between microbial activity and root rot severity in greenhouse bioassays early after cover crop incorporation, but the correlation weakened over time and ultimately was lost by about 80 days after incorporation. The C:N of oat and rape residues was 51 and 21, respectively. Soil nitrogen was immobilized by both the oat and rape cover crops, but oat immobilized more N than rape. Corn grown in the oat treatment soils had lower SPAD values, but it is not clear whether foliar N was sufficiently low to reduce yield potential. There was no consistent trend in above- or below-ground corn dry matter after oat incorporation over the three years. In 2006, the oat treatment had no significant effect on corn DM but increased yield by 11.1%. More work is required to better understand the impact of oat cover crop N immobilization on corn N status and yield. Oat 'Saia' has the potential to suppress root rot of sweet corn and maintain or increase corn productivity. However, this oat cultivar is not reliably winter-hardy and is susceptible to BYDV. Future research should screen Avena species and/or cultivars for improved winter hardiness, BYDV resistance, and root rot suppressive potential. Close

• 4184. [Article] Potentiation of acute carbon tetrachloride hepatotoxicity by dietary exposure to chlorophenothane (DDT) in rats

  There has been no toxicologic proof that the long-term, low-level exposure of man to chlorophenothane (DDT) is linked with an increased susceptibility to toxicity or disease. Acute pretreatment of rats ...

  Citation × Citation Citation Abstract Copy Title: Potentiation of acute carbon tetrachloride hepatotoxicity by dietary exposure to chlorophenothane (DDT) in rats Author: Koeferl, Michael Tallyn There has been no toxicologic proof that the long-term, low-level exposure of man to chlorophenothane (DDT) is linked with an increased susceptibility to toxicity or disease. Acute pretreatment of rats with 75-100 mg/kg DDT has been demonstrated to potentiate CCI₄-induced hepatotoxicity in that species (McLean and McLean, 1966). Since the hepatotoxic response to CC1₄ is similar among mammalian species, it was believed man's response could also be altered by prior exposure to DDT. Chronic pretreatment of rats with DDT more closely duplicates man's exposure situation, which is mainly dietary. Therefore, this present investigation was undertaken to quantify the DDT-CCI₄ hepatotoxic interaction in rats from the standpoint of a chronic dietary exposure to DDT. Chronic and acute pretreatments with DDT were compared for their relative effects on acute CC1₄ hepatotoxicity. Subgroups of rats fed DDT at concentrations of 6-65 ppm for three weeks and 65 ppm for 24 weeks attained body burdens of DDT and its metabolites ranging from 6.1 to 30.6 ppm, compared to 0 ppm (no detectable) for controls. In the acute study, subgroups of rats were dosed with 35-150 mg/kg DDT by gavage 24 hours prior to CC1₄ exposure. Doses of CC1₄ ranging from 0.125 to 1.0 mi./kg were administered by gavage. All pretreatments with DDT, chronic or acute, resulted in a potentiated elevation of serum transaminase (SGPT and SGOT) activities following treatment with CC1₄. The degree of potentiation was dose-related to CCI₄ and to the total DDT body burden. In a temporal study, the onset of the potentiated response was noted six hours after CC1₄. All of the above-mentioned results were confirmed by histopathology. Plasma BSP disappearance, dose-response and temporal studies were conducted in control and DDT-fed rat groups, utilizing the BSP test as an index of hepatic functional impairment, CC1₄-induced BSP retention was greatly potentiated by prior dietary exposure to DDT. This potentiation effect was obscured at a dose of 2.0 ml/kg CC1₄, due to the severe hepatic damage produced by this dose of CCI₄ given alone. The onset and development of the potentiated hepatic dysfunction paralleled that of the parenchymal cell destruction. The potentiated CC1₄-induced increases in SGOT activity and centrilobularly-oriented coagulative necrosis in the DDT-fed animals were prevented by spinal cord transection at the level of the seventh cervical vertebra. Chronic DDT pretreatment did not enhance CC1₄ uptake into the blood or livers of intact rats, and this was ruled out as a possible mechanism for the potentiation effect. Cord-sectioning did enhance tissue CC1₄ uptake, yet these animals were protected against CC1₄-induced central necrosis. Neither cord-sectioning nor the resultant hypothermia reduced the microsomal cytochrome P-450 content in control or DDT-fed rats. Hypothermia depressed the in vitro N-demethylation of ethylmorphine, so that oxidative drug metabolism was probably also decreased in vivo in the cordotomized animals. Maximal blood and liver concentrations of CC1₄ were measured between 2-4 hours in the intact control and DDT-fed groups. These tissue CC1₄ concentrations decreased more rapidly between 4-12 hours in the DDT-fed rats, thus suggesting an increased rate of CC1₄ metabolism could have occurred at this time in vivo in these animals. Unlike the other indices of hepatic damage, the cytochrome P-450 response preceded rather than followed the hepatocellular destruction. About 75% of the induced cytochrome P-450 concentration in the DDTfed rats was destroyed within six hours after CC1₄, at which time the onset of potentiated hepatic damage was detected. In the controls, the cytochrome P-450 concentration regenerated from a low value at 18 hours to normal by 48 hours after CC1₄. Hepatic regeneration was impaired in the DDT-fed rats, since the cytochrome P-450 concentration continued to decline between 24-48 hours. The amount of cytochrome P-450 destruction appeared to correlate with the degree of hepatic damage observed. Lower absolute concentrations of cytochrome P-450 were measured in controls 24 hours after dosing with 0.125-2.0 ml/kg CC1₄. More cytochrome P-450 was destroyed in the DDT-fed group, however, as a result of the induced microsomal concentrations of this cytochrome present initially before CC1₄ was given. Thus, the CCI₄- cytochrome P-450 interaction could play an integral role in the potentiation phenomenon, as McLean and McLean (1969) have suggested. Liver weight increased in a dose-related manner to CC1₄ in both control and DDT-fed groups, but the response was greater in controls. In the control animals, the liver weight increased rapidly to a maximal value at 18 hours, but returned to normal by 48 hours after CC1₄. Although the onset of the response was slower in the DDT-fed rats, the liver weight continued to increase at 48 hours. Rectal temperatures declined between 6-24 hours only in the DDT-fed animals. The pharmacologic agents SKF 525-A (drug metabolism inhibitor) and lead (porphyrin biosynthesis inhibitor) were utilized to assess the role of cytochrome P-450 in potentiation. SKF 525-A provided protection against the potentiated CC1₄-induced centrilobular necrosis at 11 hours after CC1₄. This protection could not be positively ascribed to SKF 525-A binding with cytochrome P-450 or inhibiting CC1₄ metabolism, since SKF 525-A has been reported to alter the gastrointestinal absorption of CC1₄ (Marchand, McLean and Plaa, 1970). Lead significantly reduced the effect of prior DDT feeding in potentiating CC1₄ hepatotoxicity, but this protection did not result from a lowered microsomal cytochrome P-450 content. Thus, the role of cytochrome P-450 in the potentiation effect remains to be conclusively elucidated. Mecamylamine pretreatment was used to determine the importance of the sympathomimetic properties of DDT in potentiation. This ganglionic blocking agent produced an insignificant tendency to decrease the potentiated CC1₄- induced BSP retention. However, the histologic evidence of protection against CC1₄ -induced hepatic necrosis was not apparent in mecamylamine-pretreated animals. Thus, the central sympathetic nervous system stimulatory effects of DDT are probably not directly involved in potentiation. The basis for extrapolation of these results from rat to man could be the total DDT body burden, which was similar in these rats (6.1 -30.6 ppm) to that estimated for man, e.g., 10 ppm by Durham (1965). Since rats and man respond similarly to CC1₄, these results indicate that man's chronic exposure to DDT could render him highly susceptible to a secondary exposure to CC1₄. Title: Potentiation of acute carbon tetrachloride hepatotoxicity by dietary exposure to chlorophenothane (DDT) in rats Author: Koeferl, Michael Tallyn There has been no toxicologic proof that the long-term, low-level exposure of man to chlorophenothane (DDT) is linked with an increased susceptibility to toxicity or disease. Acute pretreatment of rats with 75-100 mg/kg DDT has been demonstrated to potentiate CCI₄-induced hepatotoxicity in that species (McLean and McLean, 1966). Since the hepatotoxic response to CC1₄ is similar among mammalian species, it was believed man's response could also be altered by prior exposure to DDT. Chronic pretreatment of rats with DDT more closely duplicates man's exposure situation, which is mainly dietary. Therefore, this present investigation was undertaken to quantify the DDT-CCI₄ hepatotoxic interaction in rats from the standpoint of a chronic dietary exposure to DDT. Chronic and acute pretreatments with DDT were compared for their relative effects on acute CC1₄ hepatotoxicity. Subgroups of rats fed DDT at concentrations of 6-65 ppm for three weeks and 65 ppm for 24 weeks attained body burdens of DDT and its metabolites ranging from 6.1 to 30.6 ppm, compared to 0 ppm (no detectable) for controls. In the acute study, subgroups of rats were dosed with 35-150 mg/kg DDT by gavage 24 hours prior to CC1₄ exposure. Doses of CC1₄ ranging from 0.125 to 1.0 mi./kg were administered by gavage. All pretreatments with DDT, chronic or acute, resulted in a potentiated elevation of serum transaminase (SGPT and SGOT) activities following treatment with CC1₄. The degree of potentiation was dose-related to CCI₄ and to the total DDT body burden. In a temporal study, the onset of the potentiated response was noted six hours after CC1₄. All of the above-mentioned results were confirmed by histopathology. Plasma BSP disappearance, dose-response and temporal studies were conducted in control and DDT-fed rat groups, utilizing the BSP test as an index of hepatic functional impairment, CC1₄-induced BSP retention was greatly potentiated by prior dietary exposure to DDT. This potentiation effect was obscured at a dose of 2.0 ml/kg CC1₄, due to the severe hepatic damage produced by this dose of CCI₄ given alone. The onset and development of the potentiated hepatic dysfunction paralleled that of the parenchymal cell destruction. The potentiated CC1₄-induced increases in SGOT activity and centrilobularly-oriented coagulative necrosis in the DDT-fed animals were prevented by spinal cord transection at the level of the seventh cervical vertebra. Chronic DDT pretreatment did not enhance CC1₄ uptake into the blood or livers of intact rats, and this was ruled out as a possible mechanism for the potentiation effect. Cord-sectioning did enhance tissue CC1₄ uptake, yet these animals were protected against CC1₄-induced central necrosis. Neither cord-sectioning nor the resultant hypothermia reduced the microsomal cytochrome P-450 content in control or DDT-fed rats. Hypothermia depressed the in vitro N-demethylation of ethylmorphine, so that oxidative drug metabolism was probably also decreased in vivo in the cordotomized animals. Maximal blood and liver concentrations of CC1₄ were measured between 2-4 hours in the intact control and DDT-fed groups. These tissue CC1₄ concentrations decreased more rapidly between 4-12 hours in the DDT-fed rats, thus suggesting an increased rate of CC1₄ metabolism could have occurred at this time in vivo in these animals. Unlike the other indices of hepatic damage, the cytochrome P-450 response preceded rather than followed the hepatocellular destruction. About 75% of the induced cytochrome P-450 concentration in the DDTfed rats was destroyed within six hours after CC1₄, at which time the onset of potentiated hepatic damage was detected. In the controls, the cytochrome P-450 concentration regenerated from a low value at 18 hours to normal by 48 hours after CC1₄. Hepatic regeneration was impaired in the DDT-fed rats, since the cytochrome P-450 concentration continued to decline between 24-48 hours. The amount of cytochrome P-450 destruction appeared to correlate with the degree of hepatic damage observed. Lower absolute concentrations of cytochrome P-450 were measured in controls 24 hours after dosing with 0.125-2.0 ml/kg CC1₄. More cytochrome P-450 was destroyed in the DDT-fed group, however, as a result of the induced microsomal concentrations of this cytochrome present initially before CC1₄ was given. Thus, the CCI₄- cytochrome P-450 interaction could play an integral role in the potentiation phenomenon, as McLean and McLean (1969) have suggested. Liver weight increased in a dose-related manner to CC1₄ in both control and DDT-fed groups, but the response was greater in controls. In the control animals, the liver weight increased rapidly to a maximal value at 18 hours, but returned to normal by 48 hours after CC1₄. Although the onset of the response was slower in the DDT-fed rats, the liver weight continued to increase at 48 hours. Rectal temperatures declined between 6-24 hours only in the DDT-fed animals. The pharmacologic agents SKF 525-A (drug metabolism inhibitor) and lead (porphyrin biosynthesis inhibitor) were utilized to assess the role of cytochrome P-450 in potentiation. SKF 525-A provided protection against the potentiated CC1₄-induced centrilobular necrosis at 11 hours after CC1₄. This protection could not be positively ascribed to SKF 525-A binding with cytochrome P-450 or inhibiting CC1₄ metabolism, since SKF 525-A has been reported to alter the gastrointestinal absorption of CC1₄ (Marchand, McLean and Plaa, 1970). Lead significantly reduced the effect of prior DDT feeding in potentiating CC1₄ hepatotoxicity, but this protection did not result from a lowered microsomal cytochrome P-450 content. Thus, the role of cytochrome P-450 in the potentiation effect remains to be conclusively elucidated. Mecamylamine pretreatment was used to determine the importance of the sympathomimetic properties of DDT in potentiation. This ganglionic blocking agent produced an insignificant tendency to decrease the potentiated CC1₄- induced BSP retention. However, the histologic evidence of protection against CC1₄ -induced hepatic necrosis was not apparent in mecamylamine-pretreated animals. Thus, the central sympathetic nervous system stimulatory effects of DDT are probably not directly involved in potentiation. The basis for extrapolation of these results from rat to man could be the total DDT body burden, which was similar in these rats (6.1 -30.6 ppm) to that estimated for man, e.g., 10 ppm by Durham (1965). Since rats and man respond similarly to CC1₄, these results indicate that man's chronic exposure to DDT could render him highly susceptible to a secondary exposure to CC1₄. Close

• 4185. [Article] Magma dynamics and evolution in continental arcs : insights from the Central Andes

  Constraining the magma evolution and dynamics that lead to the eruption of large volume continental arc systems is fundamental to our understanding of continental crust formation. An investigation into ...

  Citation × Citation Citation Abstract Copy Title: Magma dynamics and evolution in continental arcs : insights from the Central Andes Author: Grocke, Stephanie B. Constraining the magma evolution and dynamics that lead to the eruption of large volume continental arc systems is fundamental to our understanding of continental crust formation. An investigation into the magmagenesis that results in the formation of the Central Volcanic Zone (CVZ) in the Andes of South America, situated atop overthickened continental crust (<80 km thick), provides insights into large volume silicic magma reservoirs and how they evolve prior to their potentially catastrophic explosive eruption on the Earth’s surface. A focused case study of the Cerro Guacha Caldera Complex (CGCC), a nested volcanic system in the Altiplano-Puna Volcanic Complex of SW Bolivia, puts constraints on the progressive stages of development of the magmatic underpinnings of the caldera complex. Whole rock data, in conjunction with matrix glass, mineral compositions and melt inclusions, are used to infer processes that gave rise to the formation of the Guacha II Caldera, the younger of two main collapse features, formed from the supereruption of the Tara Ignimbrite (>800 km³ DRE) at 3.49 ± 0.01 Ma. The eruptive history of the Guacha II Caldera from pre-caldera to post-caldera is fully represented, allowing magma dynamics associated with a complete caldera cycle, from pre-climactic (catastrophic caldera-forming) magma accumulation through to post-climactic effusions that are part of the resurgent history of the caldera, to be examined. Analysis of the high-K, calcalkaline suite of andesite to high Si-rhyolite Tara pyroclastic deposits provides insights into the storage conditions and magma dynamics leading up to a supervolcanic eruption. The Tara eruptive products define a liquid line of descent from the basal andesite lava (62 wt % SiO₂) to the high-silica rhyolite post-collapse Chajnantor Dome lava (78 wt.% SiO₂), with major and trace element trends consistent with fractionation of quartz, plagioclase, orthopyroxene, hornblende, sanidine, biotite, and Fe-Ti oxides. Isotope ratios span a significant range in ⁸⁷Sr/⁸⁶Sr (0.709 to 0.713) and a relatively narrow range in ¹⁴³Nd/¹⁴⁴Nd (0.512179 to 0.512297) and δ¹⁸O[subscript (qtz)] (+8.68 to +8.43‰). These data require AFC processes to explain both the isotope and trace element compositions in the Tara magmas. Geothermobarometry reveals pre-eruptive temperatures (~800 - 950 °C), pressures (~200 MPa), and H₂O contents (~5 wt%) that suggest storage of a large-volume rhyodacite magma reservoir between 5 and 9 km depth in the upper crust. Analyses of quartz-hosted melt inclusions from pumices in the climactic plinian and ignimbrite phase of eruption reveal that pre-eruptive H₂O contents in the plinian pumice overlap with those in the ignimbrite pumice (2.2 to 6.0 and 2.1 to 5.4 wt.% H₂O, respectively). The ignimbrite magma, however, contains higher CO₂ (<630 versus <300 ppm) suggesting a vertically arranged pre-climactic magma column from 7.5 km to 4 km depth, which is in agreement with the geothermobarometry from mineral analysis. Andesite recharge can account for significant compositional heterogeneities identified in the Tara magmas. Variations in trace element concentrations from melt inclusions from each of the three eruptive phases also suggest that the large-volume pre-climactic reservoir, as well as the remnant magma, contained significant chemical heterogeneities due to variations in the degree of crystal fractionation and the influence of recharge magma. Based on Ti diffusion in quartz, we estimate that the recharge event occurred within <100 years of eruption and may signal the onset of the pressurization of the system that led to eruption. The following petrogenetic model is proposed for the Tara magmatic system: andesite recharge magma ascended into a large-volume rhyodacite magma reservoir in the upper crust, where it cooled and crystallized to form a small volume of rhyolite, crystal-poor, residual melt. Andesite erupted onto what is now the Guacha II caldera-floor, and was followed by an explosive plinian eruption that produced a rhyolite pumice fall deposit outside the caldera to the east and south. Based on melt inclusions, the plinian eruption tapped a less-evolved, crystal poor (~10 vol.%), more roofward liquid that syneruptively mixed with the highly crystalline (<30 vol.%), large volume rhyodacite magma reservoir. Caldera collapse was accompanied by an explosive eruption of the large-volume rhyodacite magma reservoir and subsequent column collapse, resulting in a pyroclastic flow that produced the >800 km³ Tara ignimbrite. Extrusion of three post-caldera domes followed caldera collapse. Subtle differences between these domes invoke separate coexisting "pods" of magma that evolved independently from one another from the remnant magma that is represented by the ignimbrite. Analyses of quartz-hosted melt inclusions from the post-collapse Chajnantor Dome suggest that the highly-differentiated remnant magma contained no detectable CO₂ and low H₂O contents, representative of a degassed magma. The eruptive transition during the climactic eruption was not controlled by the volatile budget of the melt but more likely by external factors such as vent geometry and conduit evolution. Post climactic effusive volcanism reflects the degassed nature of the remnant magma. Using a suite of volcanic rocks from the CVZ, we quantify the effect of assimilation of continental crust on magmatic oxygen fugacity (ƒO₂). We use several proxies to estimate the ƒO₂ recorded by lavas, pumice and scoria: 1) whole rock Fe³⁺/ΣFe ratios, 2) Fe³⁺/ΣFe ratios in quartz-hosted melt inclusions, and 3) Fe-Ti oxide oxybarometry. Samples span a range of crustal contribution, as indicated by their radiogenic isotope compositions (⁸⁷Sr/⁸⁶Sr = 0.705-0.713), and cover the full suite of magma compositions erupted during the Neogene history of the arc (52 - 74 wt.% SiO₂). Some samples show excellent agreement across multiple ƒO₂ proxies. In other cases, where pumices show evidence of alteration in hand-sample for example, the ƒO₂ recorded by bulk Fe³⁺/ΣFe ratios is two orders of magnitude more oxidized than corresponding ratios from melt inclusions or Fe-Ti oxides. This suggests modification of whole rock Fe³⁺/ΣFe ratios, but not melt inclusion Fe³⁺/ΣFe ratios, by syn- or post-eruptive processes and that care must be taken when relying on bulk techniques to determine magmatic ƒO₂. We cannot resolve any oxidation due to crystal fractionation in our sample suite. Crustal assimilation, however, can oxidize arc magmas. The increase in ƒO₂ due to crustal assimilation reaches, but does not exceed, ~1 log unit - even in the Andes, where crustal assimilation is extreme. Title: Magma dynamics and evolution in continental arcs : insights from the Central Andes Author: Grocke, Stephanie B. Constraining the magma evolution and dynamics that lead to the eruption of large volume continental arc systems is fundamental to our understanding of continental crust formation. An investigation into the magmagenesis that results in the formation of the Central Volcanic Zone (CVZ) in the Andes of South America, situated atop overthickened continental crust (<80 km thick), provides insights into large volume silicic magma reservoirs and how they evolve prior to their potentially catastrophic explosive eruption on the Earth’s surface. A focused case study of the Cerro Guacha Caldera Complex (CGCC), a nested volcanic system in the Altiplano-Puna Volcanic Complex of SW Bolivia, puts constraints on the progressive stages of development of the magmatic underpinnings of the caldera complex. Whole rock data, in conjunction with matrix glass, mineral compositions and melt inclusions, are used to infer processes that gave rise to the formation of the Guacha II Caldera, the younger of two main collapse features, formed from the supereruption of the Tara Ignimbrite (>800 km³ DRE) at 3.49 ± 0.01 Ma. The eruptive history of the Guacha II Caldera from pre-caldera to post-caldera is fully represented, allowing magma dynamics associated with a complete caldera cycle, from pre-climactic (catastrophic caldera-forming) magma accumulation through to post-climactic effusions that are part of the resurgent history of the caldera, to be examined. Analysis of the high-K, calcalkaline suite of andesite to high Si-rhyolite Tara pyroclastic deposits provides insights into the storage conditions and magma dynamics leading up to a supervolcanic eruption. The Tara eruptive products define a liquid line of descent from the basal andesite lava (62 wt % SiO₂) to the high-silica rhyolite post-collapse Chajnantor Dome lava (78 wt.% SiO₂), with major and trace element trends consistent with fractionation of quartz, plagioclase, orthopyroxene, hornblende, sanidine, biotite, and Fe-Ti oxides. Isotope ratios span a significant range in ⁸⁷Sr/⁸⁶Sr (0.709 to 0.713) and a relatively narrow range in ¹⁴³Nd/¹⁴⁴Nd (0.512179 to 0.512297) and δ¹⁸O[subscript (qtz)] (+8.68 to +8.43‰). These data require AFC processes to explain both the isotope and trace element compositions in the Tara magmas. Geothermobarometry reveals pre-eruptive temperatures (~800 - 950 °C), pressures (~200 MPa), and H₂O contents (~5 wt%) that suggest storage of a large-volume rhyodacite magma reservoir between 5 and 9 km depth in the upper crust. Analyses of quartz-hosted melt inclusions from pumices in the climactic plinian and ignimbrite phase of eruption reveal that pre-eruptive H₂O contents in the plinian pumice overlap with those in the ignimbrite pumice (2.2 to 6.0 and 2.1 to 5.4 wt.% H₂O, respectively). The ignimbrite magma, however, contains higher CO₂ (<630 versus <300 ppm) suggesting a vertically arranged pre-climactic magma column from 7.5 km to 4 km depth, which is in agreement with the geothermobarometry from mineral analysis. Andesite recharge can account for significant compositional heterogeneities identified in the Tara magmas. Variations in trace element concentrations from melt inclusions from each of the three eruptive phases also suggest that the large-volume pre-climactic reservoir, as well as the remnant magma, contained significant chemical heterogeneities due to variations in the degree of crystal fractionation and the influence of recharge magma. Based on Ti diffusion in quartz, we estimate that the recharge event occurred within <100 years of eruption and may signal the onset of the pressurization of the system that led to eruption. The following petrogenetic model is proposed for the Tara magmatic system: andesite recharge magma ascended into a large-volume rhyodacite magma reservoir in the upper crust, where it cooled and crystallized to form a small volume of rhyolite, crystal-poor, residual melt. Andesite erupted onto what is now the Guacha II caldera-floor, and was followed by an explosive plinian eruption that produced a rhyolite pumice fall deposit outside the caldera to the east and south. Based on melt inclusions, the plinian eruption tapped a less-evolved, crystal poor (~10 vol.%), more roofward liquid that syneruptively mixed with the highly crystalline (<30 vol.%), large volume rhyodacite magma reservoir. Caldera collapse was accompanied by an explosive eruption of the large-volume rhyodacite magma reservoir and subsequent column collapse, resulting in a pyroclastic flow that produced the >800 km³ Tara ignimbrite. Extrusion of three post-caldera domes followed caldera collapse. Subtle differences between these domes invoke separate coexisting "pods" of magma that evolved independently from one another from the remnant magma that is represented by the ignimbrite. Analyses of quartz-hosted melt inclusions from the post-collapse Chajnantor Dome suggest that the highly-differentiated remnant magma contained no detectable CO₂ and low H₂O contents, representative of a degassed magma. The eruptive transition during the climactic eruption was not controlled by the volatile budget of the melt but more likely by external factors such as vent geometry and conduit evolution. Post climactic effusive volcanism reflects the degassed nature of the remnant magma. Using a suite of volcanic rocks from the CVZ, we quantify the effect of assimilation of continental crust on magmatic oxygen fugacity (ƒO₂). We use several proxies to estimate the ƒO₂ recorded by lavas, pumice and scoria: 1) whole rock Fe³⁺/ΣFe ratios, 2) Fe³⁺/ΣFe ratios in quartz-hosted melt inclusions, and 3) Fe-Ti oxide oxybarometry. Samples span a range of crustal contribution, as indicated by their radiogenic isotope compositions (⁸⁷Sr/⁸⁶Sr = 0.705-0.713), and cover the full suite of magma compositions erupted during the Neogene history of the arc (52 - 74 wt.% SiO₂). Some samples show excellent agreement across multiple ƒO₂ proxies. In other cases, where pumices show evidence of alteration in hand-sample for example, the ƒO₂ recorded by bulk Fe³⁺/ΣFe ratios is two orders of magnitude more oxidized than corresponding ratios from melt inclusions or Fe-Ti oxides. This suggests modification of whole rock Fe³⁺/ΣFe ratios, but not melt inclusion Fe³⁺/ΣFe ratios, by syn- or post-eruptive processes and that care must be taken when relying on bulk techniques to determine magmatic ƒO₂. We cannot resolve any oxidation due to crystal fractionation in our sample suite. Crustal assimilation, however, can oxidize arc magmas. The increase in ƒO₂ due to crustal assimilation reaches, but does not exceed, ~1 log unit - even in the Andes, where crustal assimilation is extreme. Close

• 4186. [Article] Coastal sand dunes of Oregon and Washington

  In Part I the environment of the coastal dunes of Oregon and Washington is analyzed. Most of the substratum is a narrow foreland or terrace, in part submerged, that borders the mountain front. Temperature ...

  Citation × Citation Citation Abstract Copy Title: Coastal sand dunes of Oregon and Washington Author: Cooper, William Skinner, 1884- In Part I the environment of the coastal dunes of Oregon and Washington is analyzed. Most of the substratum is a narrow foreland or terrace, in part submerged, that borders the mountain front. Temperature is relatively low in summer and rarely reaches the freezing point in winter. Winter precipitation is heavy, and there is almost no snow; there is a pronounced deficiency in precipitation in summer. The summer wind is a very constant afternoon sea breeze from north to northwest; winter winds are variable but include frequent southwest gales. Longshore currents are governed by the seasonal winds, moving southward in summer and northward in winter. The regional vegetation is dense, tall conifer forest. The influence of man has been comparatively slight: in prehistoric times the starting of forest fires; in historic time moderate disturbance due to grazing and recent efforts to control the movement of the sand. Part II deals with forms and processes. The simplest combination of elements comprises sand, wind, and water. Interaction of these produces two patterns. In the transverse-ridge pattern the individual unit is a ridge essentially normal to the summer wind and moving with it; it is asymmetric in profile with gentle windward slope and steep leeward slope (slipface). Origin and maintenance of this profile are explained in accordance with principles developed in the field of aerodynamics, and conclusions arrived at deductively are confirmed by slow-motion photography of smoke streams on the dunes. The oblique-ridge pattern occurs only where there is full exposure to both seasonal winds, plenty of space, and plenty of sand. These conditions are met only in Region III (Coos Bay dune sheet). The units are much more massive than the transverse ridges and are essentially stationary. Their trend lies between the means of summer and winter winds. A theoretical explanation of their origin and maintenance is presented, and the oblique ridges and the "longitudinal dunes" of certain desert regions are compared. Neither transverse nor oblique ridge is found in stabilized condition. The factor vegetation added to the other three-sand, wind, and water-promotes stabilization. On a prograding shore, successive beach ridges are quickly captured and fixed, and retain their initial form indefinitely. On a retrograding shore the processes are exceedingly complex and involve repeated stabilization and rejuvenation. Two cases are presented: flat shore, with and without abundant sand supply; stabilized dune masses undergoing erosion. In the latter case, the commoner, development involves the following phases: trough blowout, merging of troughs, reduction to deflation base, and precipitation ridge, which may in time become completely stabilized while still retaining its characteristic form. In places sheltered from one or the other of the seasonal winds, usually the summer wind, giant parabola dunes, which may likewise become fixed by vegetation, develop. Part III is a description of the dune localities of the Oregon-Washington coast and an account of their history. Forty per cent of this coast bears dunes of greater or lesser magnitude. Thirty dune localities are grouped in four regions. Region I includes four localities north of Tillamook Head, Oregon, making a continuous strip 53 km long, that bears the parallel beach-dune-ridge pattern associated with progradation. The forms in Regions II, III, and IV, heterogeneous and complex, are those characteristic of retrograding shores. The two principal stabilized forms are the precipitation ridge and the parabola dune. In Regions II, III, and IV the existing features came into being mainly during the last grand period of sea-level rise, and the seaward portions of massive parabola complexes have been sliced away in varying degree by the advancing sea. The beach-ridge dunes of Region I were formed during the period of comparatively stable sea level, with a probable small net lowering, which followed the maximum of sea advance and has extended to the present. Progradation here during this period, in contrast with almost none south of Tillamook Head, has been possible because of the ample bed load carried to the coast by the Columbia River. South of Tillamook Head there is, in a number of well-distributed localities, evidence of three episodes of advance. The first is represented by the strip of thoroughly stabilized dunes that nearly everywhere forms the inner marginal part of the dune complexes. This episode reached its culmination before the sea had attained its maximum of advance-attested by the slicing away of portions of completely stabilized masses. The second advance for the most part fell short of the first, though in a few places it overpassed the limits of the latter; present condition ranges from complete stabilization to vigorous activity. The third episode is represented by active dunes with open access to the shore. In certain localities there are only an inner strip of stabilized dunes and an outer zone of active dunes. It is assumed that in these the visible effects of the second and third episodes have merged. An earlier cycle of dune development, similar to the modern one in character and extent, is proved by eolian sediments containing altered podzolic soils, which make a minor part of the mantle of unconsolidated materials that lies upon the rock platform of the 30-m terrace. The dunes of which these masses are remnants were formed during the next-to-the-last grand period of submergence. Development of the dunes of Regions II, III, and IV, associated with the grand period of submergence, is assigned to the period of deglaciation that followed the Wisconsin maximum, and mainly to the period of rapid deglaciation that began after the Valders-Mankato advance. The beach-ridge dunes of Region I, on the other hand, have developed in their entirety in the time since sea-level rise was succeeded by stability. By analogy, the earlier cycle of dune development was associated with the waning phase of Illinoian glaciation, and it may be assumed that similar dune cycles were associated with the earlier glaciations of the Pleistocene. Title: Coastal sand dunes of Oregon and Washington Author: Cooper, William Skinner, 1884- In Part I the environment of the coastal dunes of Oregon and Washington is analyzed. Most of the substratum is a narrow foreland or terrace, in part submerged, that borders the mountain front. Temperature is relatively low in summer and rarely reaches the freezing point in winter. Winter precipitation is heavy, and there is almost no snow; there is a pronounced deficiency in precipitation in summer. The summer wind is a very constant afternoon sea breeze from north to northwest; winter winds are variable but include frequent southwest gales. Longshore currents are governed by the seasonal winds, moving southward in summer and northward in winter. The regional vegetation is dense, tall conifer forest. The influence of man has been comparatively slight: in prehistoric times the starting of forest fires; in historic time moderate disturbance due to grazing and recent efforts to control the movement of the sand. Part II deals with forms and processes. The simplest combination of elements comprises sand, wind, and water. Interaction of these produces two patterns. In the transverse-ridge pattern the individual unit is a ridge essentially normal to the summer wind and moving with it; it is asymmetric in profile with gentle windward slope and steep leeward slope (slipface). Origin and maintenance of this profile are explained in accordance with principles developed in the field of aerodynamics, and conclusions arrived at deductively are confirmed by slow-motion photography of smoke streams on the dunes. The oblique-ridge pattern occurs only where there is full exposure to both seasonal winds, plenty of space, and plenty of sand. These conditions are met only in Region III (Coos Bay dune sheet). The units are much more massive than the transverse ridges and are essentially stationary. Their trend lies between the means of summer and winter winds. A theoretical explanation of their origin and maintenance is presented, and the oblique ridges and the "longitudinal dunes" of certain desert regions are compared. Neither transverse nor oblique ridge is found in stabilized condition. The factor vegetation added to the other three-sand, wind, and water-promotes stabilization. On a prograding shore, successive beach ridges are quickly captured and fixed, and retain their initial form indefinitely. On a retrograding shore the processes are exceedingly complex and involve repeated stabilization and rejuvenation. Two cases are presented: flat shore, with and without abundant sand supply; stabilized dune masses undergoing erosion. In the latter case, the commoner, development involves the following phases: trough blowout, merging of troughs, reduction to deflation base, and precipitation ridge, which may in time become completely stabilized while still retaining its characteristic form. In places sheltered from one or the other of the seasonal winds, usually the summer wind, giant parabola dunes, which may likewise become fixed by vegetation, develop. Part III is a description of the dune localities of the Oregon-Washington coast and an account of their history. Forty per cent of this coast bears dunes of greater or lesser magnitude. Thirty dune localities are grouped in four regions. Region I includes four localities north of Tillamook Head, Oregon, making a continuous strip 53 km long, that bears the parallel beach-dune-ridge pattern associated with progradation. The forms in Regions II, III, and IV, heterogeneous and complex, are those characteristic of retrograding shores. The two principal stabilized forms are the precipitation ridge and the parabola dune. In Regions II, III, and IV the existing features came into being mainly during the last grand period of sea-level rise, and the seaward portions of massive parabola complexes have been sliced away in varying degree by the advancing sea. The beach-ridge dunes of Region I were formed during the period of comparatively stable sea level, with a probable small net lowering, which followed the maximum of sea advance and has extended to the present. Progradation here during this period, in contrast with almost none south of Tillamook Head, has been possible because of the ample bed load carried to the coast by the Columbia River. South of Tillamook Head there is, in a number of well-distributed localities, evidence of three episodes of advance. The first is represented by the strip of thoroughly stabilized dunes that nearly everywhere forms the inner marginal part of the dune complexes. This episode reached its culmination before the sea had attained its maximum of advance-attested by the slicing away of portions of completely stabilized masses. The second advance for the most part fell short of the first, though in a few places it overpassed the limits of the latter; present condition ranges from complete stabilization to vigorous activity. The third episode is represented by active dunes with open access to the shore. In certain localities there are only an inner strip of stabilized dunes and an outer zone of active dunes. It is assumed that in these the visible effects of the second and third episodes have merged. An earlier cycle of dune development, similar to the modern one in character and extent, is proved by eolian sediments containing altered podzolic soils, which make a minor part of the mantle of unconsolidated materials that lies upon the rock platform of the 30-m terrace. The dunes of which these masses are remnants were formed during the next-to-the-last grand period of submergence. Development of the dunes of Regions II, III, and IV, associated with the grand period of submergence, is assigned to the period of deglaciation that followed the Wisconsin maximum, and mainly to the period of rapid deglaciation that began after the Valders-Mankato advance. The beach-ridge dunes of Region I, on the other hand, have developed in their entirety in the time since sea-level rise was succeeded by stability. By analogy, the earlier cycle of dune development was associated with the waning phase of Illinoian glaciation, and it may be assumed that similar dune cycles were associated with the earlier glaciations of the Pleistocene. Close

• 4187. [Article] The late holocene atmospheric methane budget reconstructed from ice cores

  Ice cores are considered the gold standard for recording past climate and biogeochemical changes. However, gas records derived from ice core analysis have until now been largely limited to centennial ...

  Citation × Citation Citation Abstract Copy Title: The late holocene atmospheric methane budget reconstructed from ice cores Author: Mitchell, Logan E. Ice cores are considered the gold standard for recording past climate and biogeochemical changes. However, gas records derived from ice core analysis have until now been largely limited to centennial and longer timescales because sufficient temporal resolution and analytical precision have been lacking, except during rare times when atmospheric concentrations changed rapidly. In this thesis I used a newly developed methane measurement line to make high-resolution, high-precision measurements of methane during the late Holocene (2800 years BP to present). This new measurement line is capable of an analytical precision of < 3 ppb using ~120 g samples whereas the previous highest resolution measurements attained a precision of ± 4.1 ppb using 500-1500g samples [MacFarling Meure et al., 2006]. The reduced sample size requirements as well as automation of a significant portion of the analysis process have enabled me to make >1500 discrete ice core methane measurements and construct the highest resolution records of methane available over the late Holocene. Ice core samples came from the recently completed West Antarctic Ice Sheet (WAIS) Divide ice core which has as one of its primary scientific objectives to produce the highest resolution records of greenhouse gases, and from the Greenland Ice Sheet Project (GISP2) ice core which is a proven paleoclimate archive. My thesis has the following three components. I first used a shallow ice core from WAIS Divide (WDC05A) to produce a 1000 year long methane record with a ~9 year temporal resolution. This record confirmed the existence of multidecadal scale variations that were first observed in the Law Dome, Antarctica ice core. I then explored a range of paleoclimate archives for possible mechanistic connections with methane concentrations on multidecadal timescales. In addition, I present a detailed description of the analytical methods used to obtain high-precision measurements of methane including the effects of solubility and a new chronology for the WDC05A ice core. I found that, in general, the correlations with paleoclimate proxies for temperature and precipitation were low over a range of geographic regions. Of these, the highest correlations were found from 1400-1600 C.E. during the onset of the Little Ice Age and with a drought index in the headwater region of the major East Asian rivers. Large population losses in Asia and the Americas are also coincident with methane concentration decreases indicating that anthropogenic activities may have been impacting multidecadal scale methane variability. In the second component I extended the WAIS Divide record back to 2800 years B.P. and also measured methane from GISP2D over this time interval. These records allowed me to examine the methane Inter-Polar Difference (IPD) which is created by greater northern hemispheric sources. The IPD provides an important constraint on changes in the latitudinal distribution of sources. We used this constraint and an 8-box global methane chemical transport model to examine the Early Anthropogenic Hypothesis which posits that humans began influencing climate thousands of years ago by increasing greenhouse gas emissions and preventing the onset of the next ice age. I found that most of the increase in methane sources over this time came from tropical regions with a smaller contribution coming from the extratropical northern hemisphere. Based on previous modeling estimates of natural methane source changes, I found that the increase in the southern hemisphere tropical methane emissions was likely natural and that the northern hemispheric increase in methane emissions was likely due to anthropogenic activities. These results also provide new constraints on the total magnitude of pre-industrial anthropogenic methane emissions, which I found to be between the high and low estimates that have been previously published in the literature. For the final component of my thesis I assembled a coalition of scientists to investigate the effects of layering on the process of air enclosure in ice at WAIS Divide. Air bubbles are trapped in ice 60-100m below the surface of an ice sheet as snow compacts into solid ice in a region that is known as the Lock-In Zone (LIZ). The details of this process are not known and in the absence of direct measurements previous researchers have assumed it to be a smooth process. This project utilized high-resolution methane and air content measurements as well as density of ice, δ¹⁵N of N₂, and bubble number density measurements to show that air entrapment is affected by high frequency (mm scale) layering in the density of ice within the LIZ. I show that previous parameterizations of the bubble closure process in firn models have not accounted for this variability and present a new parameterization which does. This has implications for interpreting rapid changes in trace gases measured in ice cores since variable bubble closure will impact the smoothing of those records. In particular it is essential to understand the details of this process as new high resolution ice core records from Antarctica and Greenland examine the relative timing between greenhouse gases and rapid climate changes. Title: The late holocene atmospheric methane budget reconstructed from ice cores Author: Mitchell, Logan E. Ice cores are considered the gold standard for recording past climate and biogeochemical changes. However, gas records derived from ice core analysis have until now been largely limited to centennial and longer timescales because sufficient temporal resolution and analytical precision have been lacking, except during rare times when atmospheric concentrations changed rapidly. In this thesis I used a newly developed methane measurement line to make high-resolution, high-precision measurements of methane during the late Holocene (2800 years BP to present). This new measurement line is capable of an analytical precision of < 3 ppb using ~120 g samples whereas the previous highest resolution measurements attained a precision of ± 4.1 ppb using 500-1500g samples [MacFarling Meure et al., 2006]. The reduced sample size requirements as well as automation of a significant portion of the analysis process have enabled me to make >1500 discrete ice core methane measurements and construct the highest resolution records of methane available over the late Holocene. Ice core samples came from the recently completed West Antarctic Ice Sheet (WAIS) Divide ice core which has as one of its primary scientific objectives to produce the highest resolution records of greenhouse gases, and from the Greenland Ice Sheet Project (GISP2) ice core which is a proven paleoclimate archive. My thesis has the following three components. I first used a shallow ice core from WAIS Divide (WDC05A) to produce a 1000 year long methane record with a ~9 year temporal resolution. This record confirmed the existence of multidecadal scale variations that were first observed in the Law Dome, Antarctica ice core. I then explored a range of paleoclimate archives for possible mechanistic connections with methane concentrations on multidecadal timescales. In addition, I present a detailed description of the analytical methods used to obtain high-precision measurements of methane including the effects of solubility and a new chronology for the WDC05A ice core. I found that, in general, the correlations with paleoclimate proxies for temperature and precipitation were low over a range of geographic regions. Of these, the highest correlations were found from 1400-1600 C.E. during the onset of the Little Ice Age and with a drought index in the headwater region of the major East Asian rivers. Large population losses in Asia and the Americas are also coincident with methane concentration decreases indicating that anthropogenic activities may have been impacting multidecadal scale methane variability. In the second component I extended the WAIS Divide record back to 2800 years B.P. and also measured methane from GISP2D over this time interval. These records allowed me to examine the methane Inter-Polar Difference (IPD) which is created by greater northern hemispheric sources. The IPD provides an important constraint on changes in the latitudinal distribution of sources. We used this constraint and an 8-box global methane chemical transport model to examine the Early Anthropogenic Hypothesis which posits that humans began influencing climate thousands of years ago by increasing greenhouse gas emissions and preventing the onset of the next ice age. I found that most of the increase in methane sources over this time came from tropical regions with a smaller contribution coming from the extratropical northern hemisphere. Based on previous modeling estimates of natural methane source changes, I found that the increase in the southern hemisphere tropical methane emissions was likely natural and that the northern hemispheric increase in methane emissions was likely due to anthropogenic activities. These results also provide new constraints on the total magnitude of pre-industrial anthropogenic methane emissions, which I found to be between the high and low estimates that have been previously published in the literature. For the final component of my thesis I assembled a coalition of scientists to investigate the effects of layering on the process of air enclosure in ice at WAIS Divide. Air bubbles are trapped in ice 60-100m below the surface of an ice sheet as snow compacts into solid ice in a region that is known as the Lock-In Zone (LIZ). The details of this process are not known and in the absence of direct measurements previous researchers have assumed it to be a smooth process. This project utilized high-resolution methane and air content measurements as well as density of ice, δ¹⁵N of N₂, and bubble number density measurements to show that air entrapment is affected by high frequency (mm scale) layering in the density of ice within the LIZ. I show that previous parameterizations of the bubble closure process in firn models have not accounted for this variability and present a new parameterization which does. This has implications for interpreting rapid changes in trace gases measured in ice cores since variable bubble closure will impact the smoothing of those records. In particular it is essential to understand the details of this process as new high resolution ice core records from Antarctica and Greenland examine the relative timing between greenhouse gases and rapid climate changes. Close

• 4188. [Article] Insights into the Geochemical Evolution of the Youngest Toba Tuff (Sumatra, Indonesia) Magma Chamber Through the Lens of Zircon-hosted Melt Inclusions

  Supervolcanic eruptions are among the most catastrophic phenomena on Earth, erupting 100s-1000s of cubic kilometers of magma, and producing devastating local effects and global climate perturbations. The ...

  Citation × Citation Citation Abstract Copy Title: Insights into the Geochemical Evolution of the Youngest Toba Tuff (Sumatra, Indonesia) Magma Chamber Through the Lens of Zircon-hosted Melt Inclusions Author: Lerner, Allan (Allan Henry) Supervolcanic eruptions are among the most catastrophic phenomena on Earth, erupting 100s-1000s of cubic kilometers of magma, and producing devastating local effects and global climate perturbations. The largest supervolcanic eruption of the last 28 Ma was the 74 ka Youngest Toba Tuff (YTT) eruption from Sumatra, Indonesia, which erupted 2,800 – 5,300 km³ of magma and may have pushed the human species to the brink of extinction. Despite the global significance of such events, the magmatic evolution that builds to super-eruptions remains poorly understood. The mineral zircon provides a unique potential to gain multidimensional insights into the pre-eruptive evolution of magma chambers by combining mineral and melt inclusion chemistry with U-series mineral dating. We combine zircon U-Th dating and trace element chemistry with zircon-hosted melt inclusion chemistries and volatile abundances to investigate the magmatic evolution preceding the YTT eruption To begin, we present the first detailed study of the susceptibility of zircon-hosted inclusions to syn- or post-entrapment modification of melt compositions. We conclude that boundary layer effects are negligible in even very small zircon-hosted inclusions owing to the slow growth rate of zircon crystals. Post-entrapment crystallization (PEC) of the zircon host phase is also a trivial concern, owing to the low Zr content of most melts. PEC of other daughter phases is recognized (< ~2% amphibole and sanidine), but these effects are also minor relative to melt inclusions in many major-phase minerals. The diffusive exchange of water from zircon-hosted melt inclusions is modeled to occur in less than 10 ka, and requilibration may occur within decades-centuries. Therefore, water contents of zircon-hosted inclusions represent late-stage storage conditions rather than long-term records of magmatic water. Zircon-hosted inclusions should remain diffusively sealed to all melt species, apart from H⁺, He, and Li⁺, over typical magmatic system timescales (104-105 yrs). Therefore, we conclude that zircon is a robust, albeit small, melt inclusion host and entrapped inclusions will be largely representative of the melt environments in which they formed. We then apply the multidimensional utility of zircon to gain insights into the pre-eruptive evolution of the YTT magmatic system. YTT zircon grains have U-Th crystallization ages spanning from the ~74 ka eruption age to > 375 ka, reinforcing earlier findings that the YTT system was long-lived. A progressive increase of U in zircon growth zones from < 500 to ~1,500 ppm indicates that the YTT system, or a portion of it, became highly fractionated between 130-200 ka. A lull in zircon formation between ~110-130 ka is contemporaneous with a previously recognized increase in chemical diversity of allanite, possibly reflecting a period of enhanced thermal input into the system. We identify two main populations of zircon-hosted melt inclusions. A low-MgO type is chemically evolved (> 280 ppm Rb, ~125 ppm Ba, 25-30 ppm Sr, < 0.03 wt% MgO) and has high water contents (3.8-5.7 wt% H₂O), consistent with formation and storage in a highly fractionated crystal mush ~4-9 km deep. A high-MgO type (250-260 ppm Rb, 160-450 ppm Ba, 35-55 ppm Sr, 0.04-0.07 wt% MgO) has compositions similar to matrix glasses, and is typically less hydrous (0.5-3.5 wt% H₂O), suggesting shallow (< 3 km) formation, storage, and syn-eruptive degassing in a less evolved melt. Melt inclusions dated via U-Th measurements of their entrapping zircon zones show no clear temporal differences between the two MgO populations. Rather, melt inclusions entrapped throughout the entire YTT history have relatively invariant major element compositions, and also have no discernible temporal trends in volatile abundances. We largely attribute these findings to the narrow stability field in which zircon crystallize, which inherently limits the compositional range of zircon-hosted inclusions. Zircon-hosted melt inclusions (particularly the high-MgO type) of many ages occur within sealed reentrant melt-channels. This suggests that melt inclusions in YTT zircon grains commonly formed as the system re-established zircon saturation following periods of zircon dissolution during thermal recharge events. A number of zircon grains have melt channels actively open to the grain exterior, which are rimmed with 1-3 μm of cathodoluminescence-bright (low-U) zircon growth. These dissolution/regrowth features are texturally similar to dissolution zones and high-temperature overgrowths described previously in YTT quartz; collectively, these textures provide evidence of a major thermal perturbation(s) 10s-100s of years before the YTT eruption. We conclude that high-T, mafic recharge events occurred throughout the pre-eruptive YTT evolution, and suggest that one or more large recharge events triggered the cataclysmic 74 ka YTT eruption. Title: Insights into the Geochemical Evolution of the Youngest Toba Tuff (Sumatra, Indonesia) Magma Chamber Through the Lens of Zircon-hosted Melt Inclusions Author: Lerner, Allan (Allan Henry) Supervolcanic eruptions are among the most catastrophic phenomena on Earth, erupting 100s-1000s of cubic kilometers of magma, and producing devastating local effects and global climate perturbations. The largest supervolcanic eruption of the last 28 Ma was the 74 ka Youngest Toba Tuff (YTT) eruption from Sumatra, Indonesia, which erupted 2,800 – 5,300 km³ of magma and may have pushed the human species to the brink of extinction. Despite the global significance of such events, the magmatic evolution that builds to super-eruptions remains poorly understood. The mineral zircon provides a unique potential to gain multidimensional insights into the pre-eruptive evolution of magma chambers by combining mineral and melt inclusion chemistry with U-series mineral dating. We combine zircon U-Th dating and trace element chemistry with zircon-hosted melt inclusion chemistries and volatile abundances to investigate the magmatic evolution preceding the YTT eruption To begin, we present the first detailed study of the susceptibility of zircon-hosted inclusions to syn- or post-entrapment modification of melt compositions. We conclude that boundary layer effects are negligible in even very small zircon-hosted inclusions owing to the slow growth rate of zircon crystals. Post-entrapment crystallization (PEC) of the zircon host phase is also a trivial concern, owing to the low Zr content of most melts. PEC of other daughter phases is recognized (< ~2% amphibole and sanidine), but these effects are also minor relative to melt inclusions in many major-phase minerals. The diffusive exchange of water from zircon-hosted melt inclusions is modeled to occur in less than 10 ka, and requilibration may occur within decades-centuries. Therefore, water contents of zircon-hosted inclusions represent late-stage storage conditions rather than long-term records of magmatic water. Zircon-hosted inclusions should remain diffusively sealed to all melt species, apart from H⁺, He, and Li⁺, over typical magmatic system timescales (104-105 yrs). Therefore, we conclude that zircon is a robust, albeit small, melt inclusion host and entrapped inclusions will be largely representative of the melt environments in which they formed. We then apply the multidimensional utility of zircon to gain insights into the pre-eruptive evolution of the YTT magmatic system. YTT zircon grains have U-Th crystallization ages spanning from the ~74 ka eruption age to > 375 ka, reinforcing earlier findings that the YTT system was long-lived. A progressive increase of U in zircon growth zones from < 500 to ~1,500 ppm indicates that the YTT system, or a portion of it, became highly fractionated between 130-200 ka. A lull in zircon formation between ~110-130 ka is contemporaneous with a previously recognized increase in chemical diversity of allanite, possibly reflecting a period of enhanced thermal input into the system. We identify two main populations of zircon-hosted melt inclusions. A low-MgO type is chemically evolved (> 280 ppm Rb, ~125 ppm Ba, 25-30 ppm Sr, < 0.03 wt% MgO) and has high water contents (3.8-5.7 wt% H₂O), consistent with formation and storage in a highly fractionated crystal mush ~4-9 km deep. A high-MgO type (250-260 ppm Rb, 160-450 ppm Ba, 35-55 ppm Sr, 0.04-0.07 wt% MgO) has compositions similar to matrix glasses, and is typically less hydrous (0.5-3.5 wt% H₂O), suggesting shallow (< 3 km) formation, storage, and syn-eruptive degassing in a less evolved melt. Melt inclusions dated via U-Th measurements of their entrapping zircon zones show no clear temporal differences between the two MgO populations. Rather, melt inclusions entrapped throughout the entire YTT history have relatively invariant major element compositions, and also have no discernible temporal trends in volatile abundances. We largely attribute these findings to the narrow stability field in which zircon crystallize, which inherently limits the compositional range of zircon-hosted inclusions. Zircon-hosted melt inclusions (particularly the high-MgO type) of many ages occur within sealed reentrant melt-channels. This suggests that melt inclusions in YTT zircon grains commonly formed as the system re-established zircon saturation following periods of zircon dissolution during thermal recharge events. A number of zircon grains have melt channels actively open to the grain exterior, which are rimmed with 1-3 μm of cathodoluminescence-bright (low-U) zircon growth. These dissolution/regrowth features are texturally similar to dissolution zones and high-temperature overgrowths described previously in YTT quartz; collectively, these textures provide evidence of a major thermal perturbation(s) 10s-100s of years before the YTT eruption. We conclude that high-T, mafic recharge events occurred throughout the pre-eruptive YTT evolution, and suggest that one or more large recharge events triggered the cataclysmic 74 ka YTT eruption. Close

• 4189. [Article] Cooperative product development between researchers and commercial fishermen to find applications for ocean condition forecasting technology

  This is a case study of the cooperative development of an ocean condition forecasting tool by Oregon commercial fishermen, Oregon State University (OSU) scientists, and OSU student software engineers. ...

  Citation × Citation Citation Abstract Copy Title: Cooperative product development between researchers and commercial fishermen to find applications for ocean condition forecasting technology Author: Duncan, Colin (Colin S.) This is a case study of the cooperative development of an ocean condition forecasting tool by Oregon commercial fishermen, Oregon State University (OSU) scientists, and OSU student software engineers. Ocean condition forecasting models developed by OSU scientists were used to create an online tool to assist decision-making for fishermen. This tool is loosely based on the NANOOS Visualization System (NVS), a publically available product of the Northwest Association of Networked Ocean Observing Systems (NANOOS). The new tool was designed using data gathered from Oregon commercial fishermen in semi-structured interviews and group meetings. These interviews and meetings explored the ways that the fishing community uses ocean condition information to inform fishing tactics. Similar interviews with scientists explored why and how the scientific community creates tools like NVS. Interviews were also conducted with the software engineers who built the tool in an attempt to examine the product design process itself. Resulting findings were used to build a prototype tool that matches the capabilities of the scientific and development communities with the needs of the fishing community. This study also gathered observations on fishermen's, scientists', and developers’ motives for cooperation in research and product development. Research in the fishing community indicated that fishermen make use of a wide variety of information, and in a diversity of ways. For example, predictions of sea surface temperature were of particular interest to tuna, swordfish, and salmon fishermen, while crabbers placed an emphasis on the speed and direction of ocean currents. There was general interest in wave models, particularly at the entrance to harbors, given the impact of wave action on vessel safety. Fishermen expressed interest in accurate representations of bathymetry, as well as in subsurface currents. Interface issues with the tool were also important. Fishermen stressed that simplicity and intuitive ease-of-use be balanced with richness of information. For example, fishermen expressed a preference for distance to be expressed in nautical miles rather than in the kilometers that are currently the default NVS setting. While they praised NVS for providing them with access to information on a wide variety of ocean conditions, the multiplicity of models available on NVS and the manner in which they were arranged could sometimes be confusing. Fishermen mentioned that they often use tools like NVS at sea, where the dynamic nature of the environment (i.e., on boat in constant motion) raises interface issues generally not present ashore. There was also concern about connectivity for an internet-based tool at sea, distant from internet or cellular connections. This research uncovered important details about the cooperative design process. Fishermen, in particular, expressed mixed feelings about cooperation with the scientific community, especially with respect to the perceived role scientists play in fisheries regulation. Fishermen also stated that the scientific community failed to value fishermen's knowledge. However, given the non-regulatory nature of this project, fishermen expressed cautious optimism. This research also uncovered practical considerations for cooperation between fishermen and scientists. For example, the best time for meetings and interviews with fishermen was October, November, and early December, during a lull in fishing activity that generally precedes the opening of the winter crab season. Early in the crab season, as well as late spring, were particularly bad times as the fishermen were generally busy. Fishermen's schedules may be irregular, dependent on fisheries regulations and on ocean conditions that may be highly uncertain. Scientists, by contrast, may have highly inflexible schedules, with numerous commitments booked months into the future. As a result, coordination between these two groups may prove challenging, and require creative thinking to maneuver around. Scientists expressed enthusiasm for using their ocean models to benefit the fishing community, as this demonstrated the applicability of their research to areas outside of academia. In the words of one participating scientist, "You want people to use the research that you’re doing." The idea of cooperation also met with a favorable response, but the value of middlemen who could intermediate between the communities was stressed. Lack of time was cited as a barrier to direct interaction, as was the perception that end-user interaction was a more appropriate job for social scientists, rather than oceanographers. The student software engineers who formed the tool's product development team also appreciated having a go-between to research the needs of the fishermen, "digest" the field data, and contribute findings to the design process. This freed the product development team to focus on its own strength (writing code), with the intermediary arranging occasional interactions with fishermen or scientists as necessary. However, the design team members did stress that as the new tool developed, direct interaction with fishermen would become more necessary. It may be that as the cooperative product development process continues the role of the intermediary may change. Those who study this in the future may find themselves facilitating and observing direct communication between participating fishermen, scientists, and development team members, rather than acting as the main channel of communication as has thus far been the case. This research has laid the groundwork for continuing development of a useful tool for Oregon's fishermen. It has also contributed to a mutually beneficial channel of communication between the fishing and scientific communities. Lessons learned about fishermen, scientists, and product designers can inform future iterations of the cooperative design process, as well as provide a basis for cooperation in other areas of research. However, these lessons and new channels of communication are only as valuable as the willingness to follow through with the cooperative development process. If the new tool never gets beyond the proof-of-concept stage, it may actually serve to worsen relations between the fishing and academic communities. According to one scientist, "If the project stops here, the fishermen will chalk this up to one more academic 'teaser' or failure." Fishermen, scientists, and development team members have all invested time, energy, and goodwill into this project. All three groups stand to realize that investment if the project succeeds, and to loose it if the project fails. True success in this project arguably means that the cooperative development process will be alive and benefiting the participants when this thesis is gathering dust on a shelf. Title: Cooperative product development between researchers and commercial fishermen to find applications for ocean condition forecasting technology Author: Duncan, Colin (Colin S.) This is a case study of the cooperative development of an ocean condition forecasting tool by Oregon commercial fishermen, Oregon State University (OSU) scientists, and OSU student software engineers. Ocean condition forecasting models developed by OSU scientists were used to create an online tool to assist decision-making for fishermen. This tool is loosely based on the NANOOS Visualization System (NVS), a publically available product of the Northwest Association of Networked Ocean Observing Systems (NANOOS). The new tool was designed using data gathered from Oregon commercial fishermen in semi-structured interviews and group meetings. These interviews and meetings explored the ways that the fishing community uses ocean condition information to inform fishing tactics. Similar interviews with scientists explored why and how the scientific community creates tools like NVS. Interviews were also conducted with the software engineers who built the tool in an attempt to examine the product design process itself. Resulting findings were used to build a prototype tool that matches the capabilities of the scientific and development communities with the needs of the fishing community. This study also gathered observations on fishermen's, scientists', and developers’ motives for cooperation in research and product development. Research in the fishing community indicated that fishermen make use of a wide variety of information, and in a diversity of ways. For example, predictions of sea surface temperature were of particular interest to tuna, swordfish, and salmon fishermen, while crabbers placed an emphasis on the speed and direction of ocean currents. There was general interest in wave models, particularly at the entrance to harbors, given the impact of wave action on vessel safety. Fishermen expressed interest in accurate representations of bathymetry, as well as in subsurface currents. Interface issues with the tool were also important. Fishermen stressed that simplicity and intuitive ease-of-use be balanced with richness of information. For example, fishermen expressed a preference for distance to be expressed in nautical miles rather than in the kilometers that are currently the default NVS setting. While they praised NVS for providing them with access to information on a wide variety of ocean conditions, the multiplicity of models available on NVS and the manner in which they were arranged could sometimes be confusing. Fishermen mentioned that they often use tools like NVS at sea, where the dynamic nature of the environment (i.e., on boat in constant motion) raises interface issues generally not present ashore. There was also concern about connectivity for an internet-based tool at sea, distant from internet or cellular connections. This research uncovered important details about the cooperative design process. Fishermen, in particular, expressed mixed feelings about cooperation with the scientific community, especially with respect to the perceived role scientists play in fisheries regulation. Fishermen also stated that the scientific community failed to value fishermen's knowledge. However, given the non-regulatory nature of this project, fishermen expressed cautious optimism. This research also uncovered practical considerations for cooperation between fishermen and scientists. For example, the best time for meetings and interviews with fishermen was October, November, and early December, during a lull in fishing activity that generally precedes the opening of the winter crab season. Early in the crab season, as well as late spring, were particularly bad times as the fishermen were generally busy. Fishermen's schedules may be irregular, dependent on fisheries regulations and on ocean conditions that may be highly uncertain. Scientists, by contrast, may have highly inflexible schedules, with numerous commitments booked months into the future. As a result, coordination between these two groups may prove challenging, and require creative thinking to maneuver around. Scientists expressed enthusiasm for using their ocean models to benefit the fishing community, as this demonstrated the applicability of their research to areas outside of academia. In the words of one participating scientist, "You want people to use the research that you’re doing." The idea of cooperation also met with a favorable response, but the value of middlemen who could intermediate between the communities was stressed. Lack of time was cited as a barrier to direct interaction, as was the perception that end-user interaction was a more appropriate job for social scientists, rather than oceanographers. The student software engineers who formed the tool's product development team also appreciated having a go-between to research the needs of the fishermen, "digest" the field data, and contribute findings to the design process. This freed the product development team to focus on its own strength (writing code), with the intermediary arranging occasional interactions with fishermen or scientists as necessary. However, the design team members did stress that as the new tool developed, direct interaction with fishermen would become more necessary. It may be that as the cooperative product development process continues the role of the intermediary may change. Those who study this in the future may find themselves facilitating and observing direct communication between participating fishermen, scientists, and development team members, rather than acting as the main channel of communication as has thus far been the case. This research has laid the groundwork for continuing development of a useful tool for Oregon's fishermen. It has also contributed to a mutually beneficial channel of communication between the fishing and scientific communities. Lessons learned about fishermen, scientists, and product designers can inform future iterations of the cooperative design process, as well as provide a basis for cooperation in other areas of research. However, these lessons and new channels of communication are only as valuable as the willingness to follow through with the cooperative development process. If the new tool never gets beyond the proof-of-concept stage, it may actually serve to worsen relations between the fishing and academic communities. According to one scientist, "If the project stops here, the fishermen will chalk this up to one more academic 'teaser' or failure." Fishermen, scientists, and development team members have all invested time, energy, and goodwill into this project. All three groups stand to realize that investment if the project succeeds, and to loose it if the project fails. True success in this project arguably means that the cooperative development process will be alive and benefiting the participants when this thesis is gathering dust on a shelf. Close

• 4190. [Article] Linkages among land use, riparian zones, and uptake and transformation of nitrate in stream ecosystems

  Land use alters the physical and biological structure of stream ecosystems and potentially alters their capacity to process nitrogen (N), an essential nutrient that has nearly doubled in abundance on the ...

  Citation × Citation Citation Abstract Copy Title: Linkages among land use, riparian zones, and uptake and transformation of nitrate in stream ecosystems Author: Sobota, Daniel J. Land use alters the physical and biological structure of stream ecosystems and potentially alters their capacity to process nitrogen (N), an essential nutrient that has nearly doubled in abundance on the biosphere during the past century from human activities. In this dissertation, I quantified uptake and transformation of nitrate (NO₃⁻) in small (≤ third-order) streams and related these dynamics to aquatic ecosystem processes, including primary production and organic matter decomposition, and attributes of riparian zone structure and vegetation composition. I also analyze patterns of stream NO₃⁻ processing among three classes of adjacent land use practices (forest, agriculture, and urban). In Chapter 2, ambient rates of NO₃⁻ uptake and transformation were measured with 24-hr releases of ¹⁵N-labeled NO₃⁻ in nine stream reaches in the Willamette River Basin of western Oregon during summer low flow (July – August). Three reaches each were surrounded by forested, agricultural or urban land use. After standardizing reaches to a 500-m length, I estimated that ≥ 20% of tracer ¹⁵NO₃⁻ was taken up by detrital and autotrophic biomass in eight of the reaches. In the remaining stream, which had the largest discharge (120 L s⁻¹) in this study, only 8% of the tracer was taken up in 500 m. Tracer labeling of detritus and autotrophic biomass and a positive correlation (rs=0.81) of uptake with gross primary production suggested that assimilation was the dominant uptake pathway in all streams. Denitrification, dissimilatory reduction of NO₃⁻ to N₂ and N₂O gases, composed 3 – 15% of ¹⁵N budgets over 500 m in two agricultural reaches and in one urban reach dominated by large slowly-turning over pools. However, denitrification was below detection limit at five of the remaining six reaches. This study showed that pathways of stream NO₃⁻ uptake and transformation differed among streams adjacent to three diverse land use practices. In Chapter 3, I quantified effects of substrate nutritional quality and inorganic N loading (as NO₃⁻) on wood breakdown in western Oregon streams. Short-term (< 2 month) breakdown rates of wood substrates of high nutritional quality (Alnus rubra; red alder) and low quality (Pseudotsuga menziesii; Douglas-fir) increased with dissolved inorganic N (11 to 111 mg N L⁻¹) across six streams (p = 0.04), but this relationship was confounded with concurrent increases in stream temperature. Across the six streams, breakdown rates of red alder were consistently double that of Douglas-fir. A longer-term study (313 d) in a coniferous forest Oregon Cascades stream suggested effects of increased NO₃⁻ availability on wood breakdown became evident after cellulose and lignin components of woody tissues began to decompose (> 4 months of incubation). Average breakdown rates substrates enriched with NO₃⁻ were higher than those incubated in low NO₃⁻ conditions, but this difference was not statistically significant. However, microbial biofilm respiration rates and activity of two enzymes involved in the breakdown of woody tissues (beta-glucosidase and phenol oxidase) on red alder had significantly greater responses to NO₃⁻ additions than on Douglas-fir after four months of incubation in the stream. Results suggest that increases in N loading to streams bordered by riparian forests with fast-growing deciduous species could increase wood breakdown rates. On the other hand, increases to N loading may have a smaller effect on wood breakdown in streams surrounded by long-lived coniferous species. In Chapter 4, I quantified patterns of stream channel and riparian zone attributes for 72 streams equally distributed among forests or grasslands, agriculture, and urban land use practices on from eight major North American regions. I also related these patterns to stream NO₃⁻ uptake determined from ¹⁵NO₃⁻ tracer releases. Agricultural and urban streams had a simplified channel structure (low width-to-depth ratio, low variation in stream depth, and high stream banks) relative to forest or grassland streams. Agricultural and urban streams also had a significantly smaller median sediment diameter (D₅₀) and fraction of benthic sediments composed by silt than in forest and grassland streams. Overstory canopy cover over the channel and in the riparian zone was lowest for agricultural streams but did not significantly differ between forest or grassland streams and urban streams. A multiple regression model showed that stream NO₃⁻ uptake decreased with increasing canopy cover, but also increased with abundance of silt in benthic sediments. This suggested NO₃⁻ uptake was strongly influenced by in-stream primary production and extent of anoxic environments (conducive for denitrification). A multiple regression model for fractional NO₃⁻ uptake by denitrification further supported the concept that extent of anoxic environments influenced overall NO₃⁻ uptake in streams. Through these studies, I demonstrated that attributes of riparian zone structure and vegetation composition can strongly influence NO₃⁻ uptake and transformation in stream ecosystems by controlling organic matter dynamics. I also have shown that riparian zone attributes vary significantly among three different land use types (forest or grassland, agriculture, and urban). Similarly, pathways of NO₃⁻ uptake and effects of NO₃⁻ on wood breakdown did or were expected to differ among different land use types / riparian zone characteristics. However, other factors besides riparian attributes, particularly level of nutrient loading, alteration of stream channel physical structure, and basin position of the stream, must be considered in concert when evaluating effects of land use on riparian zone and stream ecosystem structure and function. Title: Linkages among land use, riparian zones, and uptake and transformation of nitrate in stream ecosystems Author: Sobota, Daniel J. Land use alters the physical and biological structure of stream ecosystems and potentially alters their capacity to process nitrogen (N), an essential nutrient that has nearly doubled in abundance on the biosphere during the past century from human activities. In this dissertation, I quantified uptake and transformation of nitrate (NO₃⁻) in small (≤ third-order) streams and related these dynamics to aquatic ecosystem processes, including primary production and organic matter decomposition, and attributes of riparian zone structure and vegetation composition. I also analyze patterns of stream NO₃⁻ processing among three classes of adjacent land use practices (forest, agriculture, and urban). In Chapter 2, ambient rates of NO₃⁻ uptake and transformation were measured with 24-hr releases of ¹⁵N-labeled NO₃⁻ in nine stream reaches in the Willamette River Basin of western Oregon during summer low flow (July – August). Three reaches each were surrounded by forested, agricultural or urban land use. After standardizing reaches to a 500-m length, I estimated that ≥ 20% of tracer ¹⁵NO₃⁻ was taken up by detrital and autotrophic biomass in eight of the reaches. In the remaining stream, which had the largest discharge (120 L s⁻¹) in this study, only 8% of the tracer was taken up in 500 m. Tracer labeling of detritus and autotrophic biomass and a positive correlation (rs=0.81) of uptake with gross primary production suggested that assimilation was the dominant uptake pathway in all streams. Denitrification, dissimilatory reduction of NO₃⁻ to N₂ and N₂O gases, composed 3 – 15% of ¹⁵N budgets over 500 m in two agricultural reaches and in one urban reach dominated by large slowly-turning over pools. However, denitrification was below detection limit at five of the remaining six reaches. This study showed that pathways of stream NO₃⁻ uptake and transformation differed among streams adjacent to three diverse land use practices. In Chapter 3, I quantified effects of substrate nutritional quality and inorganic N loading (as NO₃⁻) on wood breakdown in western Oregon streams. Short-term (< 2 month) breakdown rates of wood substrates of high nutritional quality (Alnus rubra; red alder) and low quality (Pseudotsuga menziesii; Douglas-fir) increased with dissolved inorganic N (11 to 111 mg N L⁻¹) across six streams (p = 0.04), but this relationship was confounded with concurrent increases in stream temperature. Across the six streams, breakdown rates of red alder were consistently double that of Douglas-fir. A longer-term study (313 d) in a coniferous forest Oregon Cascades stream suggested effects of increased NO₃⁻ availability on wood breakdown became evident after cellulose and lignin components of woody tissues began to decompose (> 4 months of incubation). Average breakdown rates substrates enriched with NO₃⁻ were higher than those incubated in low NO₃⁻ conditions, but this difference was not statistically significant. However, microbial biofilm respiration rates and activity of two enzymes involved in the breakdown of woody tissues (beta-glucosidase and phenol oxidase) on red alder had significantly greater responses to NO₃⁻ additions than on Douglas-fir after four months of incubation in the stream. Results suggest that increases in N loading to streams bordered by riparian forests with fast-growing deciduous species could increase wood breakdown rates. On the other hand, increases to N loading may have a smaller effect on wood breakdown in streams surrounded by long-lived coniferous species. In Chapter 4, I quantified patterns of stream channel and riparian zone attributes for 72 streams equally distributed among forests or grasslands, agriculture, and urban land use practices on from eight major North American regions. I also related these patterns to stream NO₃⁻ uptake determined from ¹⁵NO₃⁻ tracer releases. Agricultural and urban streams had a simplified channel structure (low width-to-depth ratio, low variation in stream depth, and high stream banks) relative to forest or grassland streams. Agricultural and urban streams also had a significantly smaller median sediment diameter (D₅₀) and fraction of benthic sediments composed by silt than in forest and grassland streams. Overstory canopy cover over the channel and in the riparian zone was lowest for agricultural streams but did not significantly differ between forest or grassland streams and urban streams. A multiple regression model showed that stream NO₃⁻ uptake decreased with increasing canopy cover, but also increased with abundance of silt in benthic sediments. This suggested NO₃⁻ uptake was strongly influenced by in-stream primary production and extent of anoxic environments (conducive for denitrification). A multiple regression model for fractional NO₃⁻ uptake by denitrification further supported the concept that extent of anoxic environments influenced overall NO₃⁻ uptake in streams. Through these studies, I demonstrated that attributes of riparian zone structure and vegetation composition can strongly influence NO₃⁻ uptake and transformation in stream ecosystems by controlling organic matter dynamics. I also have shown that riparian zone attributes vary significantly among three different land use types (forest or grassland, agriculture, and urban). Similarly, pathways of NO₃⁻ uptake and effects of NO₃⁻ on wood breakdown did or were expected to differ among different land use types / riparian zone characteristics. However, other factors besides riparian attributes, particularly level of nutrient loading, alteration of stream channel physical structure, and basin position of the stream, must be considered in concert when evaluating effects of land use on riparian zone and stream ecosystem structure and function. Close