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• 561. [Article] Autogenous deformation and chemical shrinkage of high performance cementitious systems

  In the past ten years, renewed research interest has shown the benefits of internal curing by incorporating saturated lightweight fine aggregate (LWFA) in high performance concrete (HPC). As a result, ...

  Citation × Citation Citation Abstract Copy Title: Autogenous deformation and chemical shrinkage of high performance cementitious systems Author: Fu, Tengfei In the past ten years, renewed research interest has shown the benefits of internal curing by incorporating saturated lightweight fine aggregate (LWFA) in high performance concrete (HPC). As a result, the technology of internal curing has steadily progressed from laboratory studies to field applications. To determine the optimum LWFA content, information about the propensity for shrinkage in the cement paste, specifically the chemical shrinkage value, is needed. However, there is a lack of information on how to determine the ultimate chemical shrinkage value for HPC with supplementary cementitious materials (SCMs) and/or shrinkage reducing admixture (SRA). The purpose of this thesis was to identify a simple procedure to determine ultimate chemical shrinkage values for given concrete systems with SCMs and/or SRA. Modifications to the ASTM C1608 (Standard Test Method for Chemical Shrinkage of Hydraulic Cement Paste) were investigated up to a 14 day age. Neat paste (cement only), as well as binary and ternary systems, were measured to investigate the influence of SCMs and SRA on chemical shrinkage. Based on the observed data, an experimental prediction model was adopted and verified to estimate ultimate chemical shrinkage values for portland cement systems containing SCMs and/or SRA. The model agreed well with the obtained data and simplified the existing method of determining the ultimate chemical shrinkage value. Another purpose of this research was to investigate the effect of SCMs and SRA on autogenous deformation of HPC for which a buoyancy method was used. The findings provided insight into the mechanisms behind autogenous shrinkage and effective strategies to reduce autogenous shrinkage. Calcium aluminate cements (CACs) were also investigated as part of this research project as a rapid repair material for applications, such as high performance concrete bridge decks. Chemical shrinkage and autogenous deformation of CAC binders were tested in a similar manner to the OPC systems in this study. It was observed that GCX paste cured isothermally at 38 °C exhibited expansion with a particular shape of chemical shrinkage development curve. An X-ray diffraction suggested that the expansion might be related to the conversion process indicating that chemical shrinkage may be used as a predictor of conversion processes for CAC systems in isothermal condition. Title: Autogenous deformation and chemical shrinkage of high performance cementitious systems Author: Fu, Tengfei In the past ten years, renewed research interest has shown the benefits of internal curing by incorporating saturated lightweight fine aggregate (LWFA) in high performance concrete (HPC). As a result, the technology of internal curing has steadily progressed from laboratory studies to field applications. To determine the optimum LWFA content, information about the propensity for shrinkage in the cement paste, specifically the chemical shrinkage value, is needed. However, there is a lack of information on how to determine the ultimate chemical shrinkage value for HPC with supplementary cementitious materials (SCMs) and/or shrinkage reducing admixture (SRA). The purpose of this thesis was to identify a simple procedure to determine ultimate chemical shrinkage values for given concrete systems with SCMs and/or SRA. Modifications to the ASTM C1608 (Standard Test Method for Chemical Shrinkage of Hydraulic Cement Paste) were investigated up to a 14 day age. Neat paste (cement only), as well as binary and ternary systems, were measured to investigate the influence of SCMs and SRA on chemical shrinkage. Based on the observed data, an experimental prediction model was adopted and verified to estimate ultimate chemical shrinkage values for portland cement systems containing SCMs and/or SRA. The model agreed well with the obtained data and simplified the existing method of determining the ultimate chemical shrinkage value. Another purpose of this research was to investigate the effect of SCMs and SRA on autogenous deformation of HPC for which a buoyancy method was used. The findings provided insight into the mechanisms behind autogenous shrinkage and effective strategies to reduce autogenous shrinkage. Calcium aluminate cements (CACs) were also investigated as part of this research project as a rapid repair material for applications, such as high performance concrete bridge decks. Chemical shrinkage and autogenous deformation of CAC binders were tested in a similar manner to the OPC systems in this study. It was observed that GCX paste cured isothermally at 38 °C exhibited expansion with a particular shape of chemical shrinkage development curve. An X-ray diffraction suggested that the expansion might be related to the conversion process indicating that chemical shrinkage may be used as a predictor of conversion processes for CAC systems in isothermal condition. Close

• 562. [Article] Cation retention and solute transport related to porosity of pumiceous soils

  Previous studies of pumiceous soils in Oregon indicated that their physical and chemical properties were strongly related to the porous nature of the pumice matrix. Soils developed on air-fall pumice from ...

  Citation × Citation Citation Abstract Copy Title: Cation retention and solute transport related to porosity of pumiceous soils Author: Doak, William Herman, 1941- Previous studies of pumiceous soils in Oregon indicated that their physical and chemical properties were strongly related to the porous nature of the pumice matrix. Soils developed on air-fall pumice from the eruption of Mt. Mazama (Crater Lake, Oregon) had low thermal conductivities and low volumetric heat capacities. Values for cation exchange capacities were considered to be high. It was thought that values reflected index solution trapping in pores rather than electrostatic exchange capacity. The presence of 2:1 phyllosilicates in pumice soils was at variance with data on volcanic soils from Japan. Effective retention of soil solution in pumice pores was suggested as a mechanism by which products of silicate hydrolysis might attain concentrations required for 2:1 phyllosilicate synthesis in weakly developed pumice soils. Since the porous nature of a pumice soil is so important to its physical and chemical properties, this study attempted to quantify some of the relationships. Porosity in Newberry and Mazama pumice was related to cation exchange capacity, ionic diffusion through pumice particles, mass transport of solutes by displacement and equilibration between internal pores and external solutions. An index ion depletion technique was developed to determine electrostatic cation exchange capacities of pumice soils. This technique was successful in separating electrostatic exchange from the previously reported phenomenon of index solution trapping. CEC values for all pumice samples ranged between 0.31 and 4.56 meq/ 100 g. The values increased slightly with particle size and with degree of weathering. The younger (2000 B. P. ) Newberry pumice had lower CEC values than the older (6600 B. P.) Mazama pumice. Porous system diffusion coefficients were determined through pumice particles and related to internal porosity. Observed porous system diffusion coefficients were smaller than the bulk solution coefficients. When the porous system diffusion coefficients were corrected for volumetric moisture content, the resulting effective diffusivities were in the range of those for the bulk solutions. Miscible displacement methods were used to correlate the location of breakthrough curves with particle size and internal pore volume for pumice from different sources. Increased translation of solute breakthrough curves toward smaller effluent volumes was observed with increased particle size. This volumetric translation was not highly correlated with measurements of internal pore volume. The leftward translations were strongly correlated (r = 0. 93) with the midrange diameter of particles in the columns and appeared to be a function of increased mixing between the resident and displacing solutions. Under saturated conditions involving a hydraulic gradient, pumice soils should be considered as highly leached. Static equilibration studies demonstrated that the amount of solute retained by pumice samples after equilibration is controlled by the degree of moisture saturation prior to introduction into the index solution. Air trapped in internal pores by capillary rise was only slowly replaced by index solution. Partial and complete drying after solution equilibration reduced the rate and total recovery of index ion. Air entered the pumice blocking access to index solution in the internal pores. A drying treatment following solution saturation was the only way salt trapping could be induced. From a management perspective, the behavior of solutes during a wetting and drying cycle could be quite important. The annual precipitation pattern would result in saturated conditions with intense leaching during the winter and unsaturated conditions with salt trapping during the summer. Management practices for the coarse pumice soils of central Oregon should reflect these soil chemical and physical properties . Title: Cation retention and solute transport related to porosity of pumiceous soils Author: Doak, William Herman, 1941- Previous studies of pumiceous soils in Oregon indicated that their physical and chemical properties were strongly related to the porous nature of the pumice matrix. Soils developed on air-fall pumice from the eruption of Mt. Mazama (Crater Lake, Oregon) had low thermal conductivities and low volumetric heat capacities. Values for cation exchange capacities were considered to be high. It was thought that values reflected index solution trapping in pores rather than electrostatic exchange capacity. The presence of 2:1 phyllosilicates in pumice soils was at variance with data on volcanic soils from Japan. Effective retention of soil solution in pumice pores was suggested as a mechanism by which products of silicate hydrolysis might attain concentrations required for 2:1 phyllosilicate synthesis in weakly developed pumice soils. Since the porous nature of a pumice soil is so important to its physical and chemical properties, this study attempted to quantify some of the relationships. Porosity in Newberry and Mazama pumice was related to cation exchange capacity, ionic diffusion through pumice particles, mass transport of solutes by displacement and equilibration between internal pores and external solutions. An index ion depletion technique was developed to determine electrostatic cation exchange capacities of pumice soils. This technique was successful in separating electrostatic exchange from the previously reported phenomenon of index solution trapping. CEC values for all pumice samples ranged between 0.31 and 4.56 meq/ 100 g. The values increased slightly with particle size and with degree of weathering. The younger (2000 B. P. ) Newberry pumice had lower CEC values than the older (6600 B. P.) Mazama pumice. Porous system diffusion coefficients were determined through pumice particles and related to internal porosity. Observed porous system diffusion coefficients were smaller than the bulk solution coefficients. When the porous system diffusion coefficients were corrected for volumetric moisture content, the resulting effective diffusivities were in the range of those for the bulk solutions. Miscible displacement methods were used to correlate the location of breakthrough curves with particle size and internal pore volume for pumice from different sources. Increased translation of solute breakthrough curves toward smaller effluent volumes was observed with increased particle size. This volumetric translation was not highly correlated with measurements of internal pore volume. The leftward translations were strongly correlated (r = 0. 93) with the midrange diameter of particles in the columns and appeared to be a function of increased mixing between the resident and displacing solutions. Under saturated conditions involving a hydraulic gradient, pumice soils should be considered as highly leached. Static equilibration studies demonstrated that the amount of solute retained by pumice samples after equilibration is controlled by the degree of moisture saturation prior to introduction into the index solution. Air trapped in internal pores by capillary rise was only slowly replaced by index solution. Partial and complete drying after solution equilibration reduced the rate and total recovery of index ion. Air entered the pumice blocking access to index solution in the internal pores. A drying treatment following solution saturation was the only way salt trapping could be induced. From a management perspective, the behavior of solutes during a wetting and drying cycle could be quite important. The annual precipitation pattern would result in saturated conditions with intense leaching during the winter and unsaturated conditions with salt trapping during the summer. Management practices for the coarse pumice soils of central Oregon should reflect these soil chemical and physical properties . Close

• 563. [Article] Integrating fleets, markets and ocean dynamics : a bioeconomic analysis of the Oregon ocean shrimp fishery

  Questions relating to economic performance, biological conservation and variation in resource abundance and harvest of ocean shrimp have led to increasing pressure for management action. Developing effective ...

  Citation × Citation Citation Abstract Copy Title: Integrating fleets, markets and ocean dynamics : a bioeconomic analysis of the Oregon ocean shrimp fishery Author: Gallagher, Charmaine Marie Questions relating to economic performance, biological conservation and variation in resource abundance and harvest of ocean shrimp have led to increasing pressure for management action. Developing effective management policies for this highly variable resource requires a comprehensive understanding of the fishery and marine processes. Important factors in understanding the fishery include oceanographic influences on shrimp distribution, abundance, and fishery and market dynamics. Fishery regulations for Oregon ocean shrimp, Pandalus jordani, are designed to protect age one shrimp from overharvest and sustain long-term fishery benefits. The research presented in this dissertation describes the development and analysis of analytical models ranging from classical, biological based yield-per-recruit management approaches to optimization models that incorporate economic variables and environmental recruitment relationships. This research is composed of three separate but complimentary papers regarding management of the ocean shrimp fishery. In the first paper, a yield-per-recruit analysis found that high natural mortality rates lead to yield maximization by selecting relatively young shrimp. The revenue-per-recruit analysis found that by delaying the season opening date, shrimp revenue would generate higher total revenues, while decreasing total fishing mortality and harvest. The second paper utilized a nonlinear optimization model with cost and market information to compare harvest strategies on fishery yield, gross revenue and discounted net present value (NPV). A key extension modeled a vertically integrated fishery from harvest through processing and compared harvest strategies based on wholesale prices, shrimp quality and processing yields. The optimization model that generated high yields exhibited high levels of effort and landings but low profits and NPV. The revenue policy maximization resulted in allocation of seasonal effort that produced high value older shrimp. NPV maximization generated high value shrimp landings with lower seasonal effort. Variability in shrimp recruitment and the impact on fishery utilization, income and efficiency was analyzed in the third paper. The optimization model that incorporated a stock recruit relationship and effects of environmental variables indicated an optimal harvest strategy that protects the spawning stock within a season and closes the fishery in years of poor recruitment. The results of this research highlight the complexity of management decisions when environmental forces and economic factors are jointly considered. Title: Integrating fleets, markets and ocean dynamics : a bioeconomic analysis of the Oregon ocean shrimp fishery Author: Gallagher, Charmaine Marie Questions relating to economic performance, biological conservation and variation in resource abundance and harvest of ocean shrimp have led to increasing pressure for management action. Developing effective management policies for this highly variable resource requires a comprehensive understanding of the fishery and marine processes. Important factors in understanding the fishery include oceanographic influences on shrimp distribution, abundance, and fishery and market dynamics. Fishery regulations for Oregon ocean shrimp, Pandalus jordani, are designed to protect age one shrimp from overharvest and sustain long-term fishery benefits. The research presented in this dissertation describes the development and analysis of analytical models ranging from classical, biological based yield-per-recruit management approaches to optimization models that incorporate economic variables and environmental recruitment relationships. This research is composed of three separate but complimentary papers regarding management of the ocean shrimp fishery. In the first paper, a yield-per-recruit analysis found that high natural mortality rates lead to yield maximization by selecting relatively young shrimp. The revenue-per-recruit analysis found that by delaying the season opening date, shrimp revenue would generate higher total revenues, while decreasing total fishing mortality and harvest. The second paper utilized a nonlinear optimization model with cost and market information to compare harvest strategies on fishery yield, gross revenue and discounted net present value (NPV). A key extension modeled a vertically integrated fishery from harvest through processing and compared harvest strategies based on wholesale prices, shrimp quality and processing yields. The optimization model that generated high yields exhibited high levels of effort and landings but low profits and NPV. The revenue policy maximization resulted in allocation of seasonal effort that produced high value older shrimp. NPV maximization generated high value shrimp landings with lower seasonal effort. Variability in shrimp recruitment and the impact on fishery utilization, income and efficiency was analyzed in the third paper. The optimization model that incorporated a stock recruit relationship and effects of environmental variables indicated an optimal harvest strategy that protects the spawning stock within a season and closes the fishery in years of poor recruitment. The results of this research highlight the complexity of management decisions when environmental forces and economic factors are jointly considered. Close

• 564. [Article] Water management effects on birdsfoot trefoil seed production

  There is no information available on water management of birdsfoot trefoil grown for seed. Information is also not available describing how to minimize seed losses due to shattering in order to obtain ...

  Citation × Citation Citation Abstract Copy Title: Water management effects on birdsfoot trefoil seed production Author: García-Díaz, Carlos Alberto There is no information available on water management of birdsfoot trefoil grown for seed. Information is also not available describing how to minimize seed losses due to shattering in order to obtain consistently high birdsfoot trefoil seed yields. The objectives of this research are to: (i) quantify crop water use, effects of soil-water availability and optimal water management conditions for birdsfoot trefoil grown for seed, (ii) determine the effects of irrigation timing and amount on flower production, seed yield, and yield components, and (iii) quantify the effects of soil-water availability on seed shattering and determine optimal harvest time to reduce seed yield losses due to shattering. Five supplemental irrigations treatments and a non-irrigated control were applied in 1994 and 1995; in 1996, only treatments low stress and non irrigated control were investigated, near Corvallis, OR on a Woodburn silt loam soil (fine-silty, mixed, mesic Aquultic Argixeroll). Increasing amounts of applied water increased seasonal ET[subscript c] with low stressed plants having the greatest ET[subscript c] and non-irrigated control plants the least. The fraction of available soil-water used was primarily dependent upon the irrigation depletion percentage and secondarily dependent upon irrigation replacement amount. Soil-water conditions favorable for vegetative development and seed yield water use efficiency are opposite. Birdsfoot trefoil grown for seed requires minimal or no supplemental irrigation. For non-irrigated conditions, the crop water requirement ranges from 240 to 255 mm. In the first year of production, plants under low-stress conditions sustained flowering longer than with limited or no irrigation applications. Flowering was not affected by irrigation in subsequent years of production. Total above-ground phytomass production was correlated with the amount of applied irrigation water (r=0.92). Umbel density and number of seeds per pod are the primary determinants of total seed yield (r=0.77 and 0.92, respectively). Manipulation of the reproductive development pattern by different water application times and amounts does not affect peak seed shattering events. Crop-water stress status affects the percentage of total shattered seeds shattered at harvest time (r=-0.76). Increasing amounts of applied water increase the percentage of potential shatter losses that will shatter by harvest time (r=0.65). Seed shatter losses fluctuate during the reproductive development period but are not influenced by the water application treatments. Climatic variables as measured in this experiment cannot be used to predict the time of peak seed shatter events. A total of 109 heat units are needed from the time from initial pod dehiscence until rapid shattering occurs. Title: Water management effects on birdsfoot trefoil seed production Author: García-Díaz, Carlos Alberto There is no information available on water management of birdsfoot trefoil grown for seed. Information is also not available describing how to minimize seed losses due to shattering in order to obtain consistently high birdsfoot trefoil seed yields. The objectives of this research are to: (i) quantify crop water use, effects of soil-water availability and optimal water management conditions for birdsfoot trefoil grown for seed, (ii) determine the effects of irrigation timing and amount on flower production, seed yield, and yield components, and (iii) quantify the effects of soil-water availability on seed shattering and determine optimal harvest time to reduce seed yield losses due to shattering. Five supplemental irrigations treatments and a non-irrigated control were applied in 1994 and 1995; in 1996, only treatments low stress and non irrigated control were investigated, near Corvallis, OR on a Woodburn silt loam soil (fine-silty, mixed, mesic Aquultic Argixeroll). Increasing amounts of applied water increased seasonal ET[subscript c] with low stressed plants having the greatest ET[subscript c] and non-irrigated control plants the least. The fraction of available soil-water used was primarily dependent upon the irrigation depletion percentage and secondarily dependent upon irrigation replacement amount. Soil-water conditions favorable for vegetative development and seed yield water use efficiency are opposite. Birdsfoot trefoil grown for seed requires minimal or no supplemental irrigation. For non-irrigated conditions, the crop water requirement ranges from 240 to 255 mm. In the first year of production, plants under low-stress conditions sustained flowering longer than with limited or no irrigation applications. Flowering was not affected by irrigation in subsequent years of production. Total above-ground phytomass production was correlated with the amount of applied irrigation water (r=0.92). Umbel density and number of seeds per pod are the primary determinants of total seed yield (r=0.77 and 0.92, respectively). Manipulation of the reproductive development pattern by different water application times and amounts does not affect peak seed shattering events. Crop-water stress status affects the percentage of total shattered seeds shattered at harvest time (r=-0.76). Increasing amounts of applied water increase the percentage of potential shatter losses that will shatter by harvest time (r=0.65). Seed shatter losses fluctuate during the reproductive development period but are not influenced by the water application treatments. Climatic variables as measured in this experiment cannot be used to predict the time of peak seed shatter events. A total of 109 heat units are needed from the time from initial pod dehiscence until rapid shattering occurs. Close

• 565. [Article] The response of beans to fluorodifen as affected by light and other factors

  Studies with fluorodifen were conducted to gain more information about its field performance and the influence of light quantity, quality and timing of exposure on its phytotoxic properties. Uptake and ...

  Citation × Citation Citation Abstract Copy Title: The response of beans to fluorodifen as affected by light and other factors Author: Pollak, Tomas Studies with fluorodifen were conducted to gain more information about its field performance and the influence of light quantity, quality and timing of exposure on its phytotoxic properties. Uptake and trans location in three plant species were also investigated. These studies were aimed at evaluating the usefulness of this chemical as a selective herbicide for controlling weeds in beans (Phaseolus vulgaris L.) in Oregon. Field data compiled for a period of three consecutive years indicated that the highest yields of green beans were obtained when fluorodifen was applied at a rate of 6 lb/A preemergence. At higher rates, crop injury was noticeable in the form of shortening of midrib and necrotic lesions on hypocotyls and other plant tissues such as cotyledons that came into contact with the herbicide. Occasionally these symptoms were observed at rates as low as 1 lb/A under an unspecified set of conditions occurring in the field. A combination of fluorodifen applied preemergence and cultivation two weeks after emergence of the crop provided the best weed controls Shading the crop at different stages of development did not provide an explanation for the cause of stem lesion development, but when shade was provided from application until the first true leaf, phytotoxicity was noticeable. Three soil types and two watering regimes did not provide significant, consistent phytotoxicity or stem burning. By the use of neutral density filters, different intensities of light with the same spectral emission were obtained in growth chambers. Bean and soybean plants were more sensitive to fluorodifen at low levels of light. The percentage dry weight reduction decreased as the light intensity increased from 1,000 to 2,000 ft/c. In determining the critical period in which light enhances fluorodifen injury to beans and soybeans, it was found that plants exposed to light on the second to third day after planting were most severely injured. When filters were used to evaluate the influence of light quality on fluorodifen toxicity to beans and soybeans, these plants were more sensitive to fluorodifen when exposed to yellow and red light than when exposed to blue or white light. Phytotoxic symptoms were observed especially under yellow light. Exposure to light at the time of crop emergence resulted in the greatest phytotoxicity. Autoradiography and radioassay results indicated that ¹⁴C-fluorodifen was absorbed mostly within six hours after application. The distribution pattern remained fairly constant in beans and soybeans with the largest percentage of activity remaining in the treated portion at all times. Greater mobility of the label was observed in cucumber plants with some acropetal and basipetal movement recorded from the treated leaves 12 hours after applications. Covering the treated leaf did not alter the uptake of fluorodifen in any of the three plant species. Following applications to stem and roots, a similar pattern was observed, rapid uptake but little or no mobility. The unicellular algae Chlorella was used to assess the effect of fluorodifen on photosynthesis and respiration of green plant tissues. It was found that the growth of Chlorella was severely affected by low concentrations of fluorodifen in the light. The same herbicide concentrations had no effect in the dark. Under the conditions of this study, fluorodifen caused just a slight increase in the respiration of Chlorella, while photosynthesis was severely inhibited at concentrations of 1 ppm of fluorodifen. In a separate study, the persistence of fluorodifen in soil subjected to different environmental conditions was evaluated by gas chromatography. Fluorodifen was degraded more readily under high temperatures, provided that the soil was dry. Title: The response of beans to fluorodifen as affected by light and other factors Author: Pollak, Tomas Studies with fluorodifen were conducted to gain more information about its field performance and the influence of light quantity, quality and timing of exposure on its phytotoxic properties. Uptake and trans location in three plant species were also investigated. These studies were aimed at evaluating the usefulness of this chemical as a selective herbicide for controlling weeds in beans (Phaseolus vulgaris L.) in Oregon. Field data compiled for a period of three consecutive years indicated that the highest yields of green beans were obtained when fluorodifen was applied at a rate of 6 lb/A preemergence. At higher rates, crop injury was noticeable in the form of shortening of midrib and necrotic lesions on hypocotyls and other plant tissues such as cotyledons that came into contact with the herbicide. Occasionally these symptoms were observed at rates as low as 1 lb/A under an unspecified set of conditions occurring in the field. A combination of fluorodifen applied preemergence and cultivation two weeks after emergence of the crop provided the best weed controls Shading the crop at different stages of development did not provide an explanation for the cause of stem lesion development, but when shade was provided from application until the first true leaf, phytotoxicity was noticeable. Three soil types and two watering regimes did not provide significant, consistent phytotoxicity or stem burning. By the use of neutral density filters, different intensities of light with the same spectral emission were obtained in growth chambers. Bean and soybean plants were more sensitive to fluorodifen at low levels of light. The percentage dry weight reduction decreased as the light intensity increased from 1,000 to 2,000 ft/c. In determining the critical period in which light enhances fluorodifen injury to beans and soybeans, it was found that plants exposed to light on the second to third day after planting were most severely injured. When filters were used to evaluate the influence of light quality on fluorodifen toxicity to beans and soybeans, these plants were more sensitive to fluorodifen when exposed to yellow and red light than when exposed to blue or white light. Phytotoxic symptoms were observed especially under yellow light. Exposure to light at the time of crop emergence resulted in the greatest phytotoxicity. Autoradiography and radioassay results indicated that ¹⁴C-fluorodifen was absorbed mostly within six hours after application. The distribution pattern remained fairly constant in beans and soybeans with the largest percentage of activity remaining in the treated portion at all times. Greater mobility of the label was observed in cucumber plants with some acropetal and basipetal movement recorded from the treated leaves 12 hours after applications. Covering the treated leaf did not alter the uptake of fluorodifen in any of the three plant species. Following applications to stem and roots, a similar pattern was observed, rapid uptake but little or no mobility. The unicellular algae Chlorella was used to assess the effect of fluorodifen on photosynthesis and respiration of green plant tissues. It was found that the growth of Chlorella was severely affected by low concentrations of fluorodifen in the light. The same herbicide concentrations had no effect in the dark. Under the conditions of this study, fluorodifen caused just a slight increase in the respiration of Chlorella, while photosynthesis was severely inhibited at concentrations of 1 ppm of fluorodifen. In a separate study, the persistence of fluorodifen in soil subjected to different environmental conditions was evaluated by gas chromatography. Fluorodifen was degraded more readily under high temperatures, provided that the soil was dry. Close

• 566. [Article] Soil temperature suppression on growth and yield of potato (Solanum tuberosum L.) in warm climates of Sri Lanka

  Potato (Solanum tuberosum L.) is one of the most productive and nutritious food crops. Due to its adaptability to cool climates, production in Sri Lanka has been restricted to erosion-prone highlands. ...

  Citation × Citation Citation Abstract Copy Title: Soil temperature suppression on growth and yield of potato (Solanum tuberosum L.) in warm climates of Sri Lanka Author: Tharmarajah, S. K. Potato (Solanum tuberosum L.) is one of the most productive and nutritious food crops. Due to its adaptability to cool climates, production in Sri Lanka has been restricted to erosion-prone highlands. Vast potential exists for expansion of potato cultivation in the lowlands while production areas in the highlands are limited by crop saturation. High soil temperatures characteristic of lowland tropical areas strongly limit potato cultivation during warmer months. Previous research, however, revealed that soil temperature can be reduced by various techniques. Although soil temperature manipulation has been tried successfully, the effect of these techniques on potato growth, dry matter partitioning, and tuber yield has not been studied. Experiment addressing these questions was conducted in two consecutive cropping seasons from July to October of 1991 (Yala season) and December to March of 1991-1992 (Maha season) at the Regional Agricultural Research Center at Bandarawela (6° 5l'N latitude, 80° 59' longitude, and 1300 m a.s.l.), Sri Lanka. The Yala season is warmer while the Maha season is cooler. Treatments included various soil temperature suppression systems such as rice straw mulching, interplanting, and hilling. Rice straw mulch suppressed soil temperature by 1-6°C during the day. This system hastened emergence and canopy development and increased potato plant height, leaf area index (LAI), crop growth rate (CGR), and net assimilation rate (NAR) in both seasons. LAI and CGR showed a quadratic relationship with time under rice straw mulch system. Interplanting soybean (Glycine max L.), sweet potato (Ipomoea batatas L.) or double rows of potato resulted in no appreciable effect on soil temperature suppression, or plant growth in either season, except for emergence which improved under potato-soybean. Dry matter partitioning to tubers was highest and showed a linear relationship with time under rice straw mulch and rice straw-bridge systems while interplanting and hilling treatments did not influence these factors substantially. Further, straw mulch improved total dry matter (TDM) production, which showed a linear relationship with time. Tuber yield, individual tuber weight, harvest index, and percentage of large tubers were improved under rice straw mulching systems compared with interplanting and hilling. Title: Soil temperature suppression on growth and yield of potato (Solanum tuberosum L.) in warm climates of Sri Lanka Author: Tharmarajah, S. K. Potato (Solanum tuberosum L.) is one of the most productive and nutritious food crops. Due to its adaptability to cool climates, production in Sri Lanka has been restricted to erosion-prone highlands. Vast potential exists for expansion of potato cultivation in the lowlands while production areas in the highlands are limited by crop saturation. High soil temperatures characteristic of lowland tropical areas strongly limit potato cultivation during warmer months. Previous research, however, revealed that soil temperature can be reduced by various techniques. Although soil temperature manipulation has been tried successfully, the effect of these techniques on potato growth, dry matter partitioning, and tuber yield has not been studied. Experiment addressing these questions was conducted in two consecutive cropping seasons from July to October of 1991 (Yala season) and December to March of 1991-1992 (Maha season) at the Regional Agricultural Research Center at Bandarawela (6° 5l'N latitude, 80° 59' longitude, and 1300 m a.s.l.), Sri Lanka. The Yala season is warmer while the Maha season is cooler. Treatments included various soil temperature suppression systems such as rice straw mulching, interplanting, and hilling. Rice straw mulch suppressed soil temperature by 1-6°C during the day. This system hastened emergence and canopy development and increased potato plant height, leaf area index (LAI), crop growth rate (CGR), and net assimilation rate (NAR) in both seasons. LAI and CGR showed a quadratic relationship with time under rice straw mulch system. Interplanting soybean (Glycine max L.), sweet potato (Ipomoea batatas L.) or double rows of potato resulted in no appreciable effect on soil temperature suppression, or plant growth in either season, except for emergence which improved under potato-soybean. Dry matter partitioning to tubers was highest and showed a linear relationship with time under rice straw mulch and rice straw-bridge systems while interplanting and hilling treatments did not influence these factors substantially. Further, straw mulch improved total dry matter (TDM) production, which showed a linear relationship with time. Tuber yield, individual tuber weight, harvest index, and percentage of large tubers were improved under rice straw mulching systems compared with interplanting and hilling. Close

• 567. [Article] Exploiting Hordeum vulgare subsp. spontaneum genetic resources : diversity analysis and germplasm development

  Wild barley (Hordeum vulgare subsp. spontaneum) could be a source of useful genes for improving cultivated barley. The useful genes present in Hordeum vulgare subsp. spontaneum may be new alleles at described ...

  Citation × Citation Citation Abstract Copy Title: Exploiting Hordeum vulgare subsp. spontaneum genetic resources : diversity analysis and germplasm development Author: Matus, Iván Ariel Wild barley (Hordeum vulgare subsp. spontaneum) could be a source of useful genes for improving cultivated barley. The useful genes present in Hordeum vulgare subsp. spontaneum may be new alleles at described loci, or these may be entirely new genes in the sense that there is limited allelic variation at these loci in the cultivated germplasm pool. This research was directed at gene discovery in wild barley and involved two steps: (i) characterization of diversity using genetic markers and (ii) development and characterization of novel germplasm for gene discovery. Simple Sequence Repeats (SSRs) of known map location were used to survey three representative groups of barley germplasm: a sample of crop progenitor (Hordeum vulgare subsp. spontaneum) accessions, a group of mapping population parents, and a group of varieties and elite breeding lines. The objectives were to determine the informativeness and utility of SSRs in differentiating and classifying the three sets of barley germplasm. Crop progenitors had the highest number of alleles per SSR locus, followed by mapping population parents and elite breeding lines. The cluster analysis indicated a high level of diversity within the crop progenitor accessions and within the mapping population parents. It revealed a much lower level of diversity within the elite breeding germplasm. A set of Recombinant Chromosome Substitution Lines (RCSLs) representing introgressions of Hordeum vulgare subsp. spontaneum genome in to a cultivated barley background were developed using the Advanced Backcross strategy. An accession of Hordeum vulgare subsp. spontaneum was the donor parent and the variety "Harrington" was the recurrent parent. The RCSLs were developed via two backcrosses to the recurrent parent followed by six generations of selfing. The genomic architecture of the RCSLs was determined by molecular marker fingerprinting with SSRs. The consequences of introgressions of Hordeum vulgare subsp. spontaneum genome segments into the recurrent parent were assessed in terms of inflorescence yield components, malting quality traits, and domestication-related traits. Hordeum spontaneum subsp. spontaneum, despite its overall inferior phenotype, contributed favorable alleles for some characters of agronomic performance. In other cases, the introgressions caused a disruption of the Harrington phenotype, a "reverse genetics" approach to gene discovery. Title: Exploiting Hordeum vulgare subsp. spontaneum genetic resources : diversity analysis and germplasm development Author: Matus, Iván Ariel Wild barley (Hordeum vulgare subsp. spontaneum) could be a source of useful genes for improving cultivated barley. The useful genes present in Hordeum vulgare subsp. spontaneum may be new alleles at described loci, or these may be entirely new genes in the sense that there is limited allelic variation at these loci in the cultivated germplasm pool. This research was directed at gene discovery in wild barley and involved two steps: (i) characterization of diversity using genetic markers and (ii) development and characterization of novel germplasm for gene discovery. Simple Sequence Repeats (SSRs) of known map location were used to survey three representative groups of barley germplasm: a sample of crop progenitor (Hordeum vulgare subsp. spontaneum) accessions, a group of mapping population parents, and a group of varieties and elite breeding lines. The objectives were to determine the informativeness and utility of SSRs in differentiating and classifying the three sets of barley germplasm. Crop progenitors had the highest number of alleles per SSR locus, followed by mapping population parents and elite breeding lines. The cluster analysis indicated a high level of diversity within the crop progenitor accessions and within the mapping population parents. It revealed a much lower level of diversity within the elite breeding germplasm. A set of Recombinant Chromosome Substitution Lines (RCSLs) representing introgressions of Hordeum vulgare subsp. spontaneum genome in to a cultivated barley background were developed using the Advanced Backcross strategy. An accession of Hordeum vulgare subsp. spontaneum was the donor parent and the variety "Harrington" was the recurrent parent. The RCSLs were developed via two backcrosses to the recurrent parent followed by six generations of selfing. The genomic architecture of the RCSLs was determined by molecular marker fingerprinting with SSRs. The consequences of introgressions of Hordeum vulgare subsp. spontaneum genome segments into the recurrent parent were assessed in terms of inflorescence yield components, malting quality traits, and domestication-related traits. Hordeum spontaneum subsp. spontaneum, despite its overall inferior phenotype, contributed favorable alleles for some characters of agronomic performance. In other cases, the introgressions caused a disruption of the Harrington phenotype, a "reverse genetics" approach to gene discovery. Close

• 568. [Article] The agronomic, environmental, and economic implications of the introduction of terbacil for weed control in Oregon commercial peppermint operations

  The use of terbacil for weed control was adapted by a high percentage of Oregon peppermint growers soon after its introduction in 1967. To help clarify some of the implications of terbacil usage, three ...

  Citation × Citation Citation Abstract Copy Title: The agronomic, environmental, and economic implications of the introduction of terbacil for weed control in Oregon commercial peppermint operations Author: Harris, James O. The use of terbacil for weed control was adapted by a high percentage of Oregon peppermint growers soon after its introduction in 1967. To help clarify some of the implications of terbacil usage, three studies were undertaken to collect information concerning (a) the movement and build-up of terbacil in various soils, (b) possible contamination of "waste" and ground irrigation water, and (c) the economic and cultural practice changes which resulted from terbacil usage. Using soil samples taken from commercial fields, depth of terbacil penetration into the soil profile was greater in lighter soils than in heavier soils. Residues seemed to accumulate near the surface of the ridge in rill irrigated fields. No evidence of continued build-up of the chemical with repeated applications was seen in the soils tested. Analysis of water samples taken from the waste ditch of a rill irrigated field showed only a low concentration of terbacil, and this decreased with each irrigation. No residues were found in water samples taken from two shallow wells located in treated fields. Analysis of cash weed control costs of growers in the Willamette Valley and Jefferson County showed sizeable savings with the use of terbacil in the majority of cases. There was a corresponding savings in time spent on mint operations. This savings in time and money may have contributed to the increase in peppermint acreage noted among those growers who participated in the study. Because of fear of spreading Verticillium wilt (Verticillium albo-atrum or V. dahliae), many growers had quit annual plowing of their mint before terbacil was introduced, and many had experienced problems with weeds under this scheme. When terbacil was introduced, it appeared to solve this problem by giving very good weed control on most of the weeds. However, problems developed because most perennial weeds and a few annuals were not controlled. At present this is a major concern. Terbacil has a long residual life in the soil which can be an important advantage for control of weeds in peppermint since peppermint is a perennial crop and quite tolerant of terbacil. However, few other crops are tolerant. Over half of the growers interviewed who had taken a treated field out of production had experienced trouble in following with other crops. Unfortunately, there seems to be no pattern or set of circumstances which can help the grower predict whether or not he will have difficulty. Title: The agronomic, environmental, and economic implications of the introduction of terbacil for weed control in Oregon commercial peppermint operations Author: Harris, James O. The use of terbacil for weed control was adapted by a high percentage of Oregon peppermint growers soon after its introduction in 1967. To help clarify some of the implications of terbacil usage, three studies were undertaken to collect information concerning (a) the movement and build-up of terbacil in various soils, (b) possible contamination of "waste" and ground irrigation water, and (c) the economic and cultural practice changes which resulted from terbacil usage. Using soil samples taken from commercial fields, depth of terbacil penetration into the soil profile was greater in lighter soils than in heavier soils. Residues seemed to accumulate near the surface of the ridge in rill irrigated fields. No evidence of continued build-up of the chemical with repeated applications was seen in the soils tested. Analysis of water samples taken from the waste ditch of a rill irrigated field showed only a low concentration of terbacil, and this decreased with each irrigation. No residues were found in water samples taken from two shallow wells located in treated fields. Analysis of cash weed control costs of growers in the Willamette Valley and Jefferson County showed sizeable savings with the use of terbacil in the majority of cases. There was a corresponding savings in time spent on mint operations. This savings in time and money may have contributed to the increase in peppermint acreage noted among those growers who participated in the study. Because of fear of spreading Verticillium wilt (Verticillium albo-atrum or V. dahliae), many growers had quit annual plowing of their mint before terbacil was introduced, and many had experienced problems with weeds under this scheme. When terbacil was introduced, it appeared to solve this problem by giving very good weed control on most of the weeds. However, problems developed because most perennial weeds and a few annuals were not controlled. At present this is a major concern. Terbacil has a long residual life in the soil which can be an important advantage for control of weeds in peppermint since peppermint is a perennial crop and quite tolerant of terbacil. However, few other crops are tolerant. Over half of the growers interviewed who had taken a treated field out of production had experienced trouble in following with other crops. Unfortunately, there seems to be no pattern or set of circumstances which can help the grower predict whether or not he will have difficulty. Close

• 569. [Article] Assessment of ground water recharge and quality under agricultural production in Lane County, Oregon

  Assessment of the environmental impacts of an agricultural production system requires information on both soil water quality and solute flux. Passive Capillary Samplers (PCAPS), which sample water from ...

  Citation × Citation Citation Abstract Copy Title: Assessment of ground water recharge and quality under agricultural production in Lane County, Oregon Author: Shelby, Patrick M. Assessment of the environmental impacts of an agricultural production system requires information on both soil water quality and solute flux. Passive Capillary Samplers (PCAPS), which sample water from the vadose zone using fiber glass wicks, have shown potential to provide both flux and solute concentration in unsaturated zone sampling but have not been tested under long-term, natural, rainfall conditions. The objectives of this study are to (1) evaluate PCAPS operation under non-steady, natural rain and irrigation fed conditions, (2) determine the samplers ability to estimate recharge, and (3) estimate the loss of nutrients resulting from agricultural production. 32 PCAPS and 78 suction cup samplers were installed below the root zone at 16 commercial fields in Lane County, Oregon. PCAPS' were installed in positions using ground penetrating radar such that PCAPS' were placed in homogeneous or concave profile locations. Two PCAPS and six suction cups were installed at each site. Rain gages and TDR probes were installed at eight of the 16 sites. These data were used to develop a mass balance for each of the eight special study sites. Comparison to mass balance data indicates that the PCAPS flux measurements were within 10% of the mass balance estimated recharge. Surface runoff of potential drainage water during periods of high rainfall was a point of concern for estimated recharge discrepancies because runoff was not measured. The saturated hydraulic conductivity was shown to be the most influential design parameter for matching wick and soil types. On the other hand, the incident flux, rather than conductivity, determined the ultimate ground water recharge. PCAPS collection was found to be significantly correlated (average R²=0.75) to the mass balance monthly estimated recharge. To estimate the mean monthly recharge at each site with a 30% bound on the mean and 95% confidence level, 20 PCAPS would be required at each site. PCAPS were found to be superior to suction cup samplers for estimating ground water recharge concentrations because PCAPS were able to sample both flux and resident concentrations. Mint and row crop, organic and inorganic, production systems contributed to the largest adverse environmental impacts with average recharge concentrations for mint and row crop of 24 mg L⁻¹ and 28 mg L⁻¹, respectively. Orchard and blueberry production systems had little impact with their seasonal concentrations averaging below the EPA water quality standard. Amounts of percolation were key in determining which management systems were inefficiently operated. Over-irrigation during the summer lead to increased losses of nitrogen for the mint production systems in the summer as well as the winter. Over-fertilization was important for creating significant differences in seasonal mass losses of nitrogen from row crop production systems. Overall, the PCAPS estimated nitrogen loss was 12% lower than that calculated using a simplified nitrogen mass balance approach. Best management practice suggestions concerning irrigation, fertilization and cover cropping were provided as a direct result of the findings of the project. With technical support and increase in concern over nitrate contamination, farmers should be able to control leaching losses without the use of quotas or allotments. Title: Assessment of ground water recharge and quality under agricultural production in Lane County, Oregon Author: Shelby, Patrick M. Assessment of the environmental impacts of an agricultural production system requires information on both soil water quality and solute flux. Passive Capillary Samplers (PCAPS), which sample water from the vadose zone using fiber glass wicks, have shown potential to provide both flux and solute concentration in unsaturated zone sampling but have not been tested under long-term, natural, rainfall conditions. The objectives of this study are to (1) evaluate PCAPS operation under non-steady, natural rain and irrigation fed conditions, (2) determine the samplers ability to estimate recharge, and (3) estimate the loss of nutrients resulting from agricultural production. 32 PCAPS and 78 suction cup samplers were installed below the root zone at 16 commercial fields in Lane County, Oregon. PCAPS' were installed in positions using ground penetrating radar such that PCAPS' were placed in homogeneous or concave profile locations. Two PCAPS and six suction cups were installed at each site. Rain gages and TDR probes were installed at eight of the 16 sites. These data were used to develop a mass balance for each of the eight special study sites. Comparison to mass balance data indicates that the PCAPS flux measurements were within 10% of the mass balance estimated recharge. Surface runoff of potential drainage water during periods of high rainfall was a point of concern for estimated recharge discrepancies because runoff was not measured. The saturated hydraulic conductivity was shown to be the most influential design parameter for matching wick and soil types. On the other hand, the incident flux, rather than conductivity, determined the ultimate ground water recharge. PCAPS collection was found to be significantly correlated (average R²=0.75) to the mass balance monthly estimated recharge. To estimate the mean monthly recharge at each site with a 30% bound on the mean and 95% confidence level, 20 PCAPS would be required at each site. PCAPS were found to be superior to suction cup samplers for estimating ground water recharge concentrations because PCAPS were able to sample both flux and resident concentrations. Mint and row crop, organic and inorganic, production systems contributed to the largest adverse environmental impacts with average recharge concentrations for mint and row crop of 24 mg L⁻¹ and 28 mg L⁻¹, respectively. Orchard and blueberry production systems had little impact with their seasonal concentrations averaging below the EPA water quality standard. Amounts of percolation were key in determining which management systems were inefficiently operated. Over-irrigation during the summer lead to increased losses of nitrogen for the mint production systems in the summer as well as the winter. Over-fertilization was important for creating significant differences in seasonal mass losses of nitrogen from row crop production systems. Overall, the PCAPS estimated nitrogen loss was 12% lower than that calculated using a simplified nitrogen mass balance approach. Best management practice suggestions concerning irrigation, fertilization and cover cropping were provided as a direct result of the findings of the project. With technical support and increase in concern over nitrate contamination, farmers should be able to control leaching losses without the use of quotas or allotments. Close

• 570. [Article] Effects of light, nutrients, and grazing on periphyton communities in streams

  Relative effects of light, nutrients, and grazing on primary production were investigated in streams in the Cascade Mountains of Oregon and in laboratory streams. Relative magnitudes of primary production ...

  Citation × Citation Citation Abstract Copy Title: Effects of light, nutrients, and grazing on periphyton communities in streams Author: Gregory, Stanley Vincent Relative effects of light, nutrients, and grazing on primary production were investigated in streams in the Cascade Mountains of Oregon and in laboratory streams. Relative magnitudes of primary production and associated processes were examined for one year in a stream that flowed through a clearcut and an old-growth forest in the Cascade Mountains. Diel patterns of nutrients in four streams of different size indicated greater demand for inorganic nitrogen than phosphorus and suggested that uptake by aquatic primary producers was responsible for diel fluctuations of nutrient concentrations. Atomic ratios of N/P supported the conclusion that primary producers were most probably nitrogen limited. In an experiment of light and nitrate addition to a stream in an old-growth forest, primary producer processes were enhanced by addition of light (11000 lux) and by addition of both light and nitrate. There was no effect of nitrate addition on accumulation of algae, gross primary production, net community primary production, community respiration, P/R ratios, or community structure of diatoms at low ambient light levels (1100 lux). Addition of light resulted in greater colonization of algae, gross primary production, net community primary production, community respiration, P/R ratios and altered community structure of diatoms. The watershed was clearcut one year later and the experiment was essentially repeated with artificial shading instead of artificial lighting. Responses of colonization and primary production to light and nitrate in the clearcut were similar to those observed in the previous experiment in the old-growth forest. Interactions between primary producers and grazers in lotic systems were examined in laboratory streams. Different densities of snails were established in laboratory channels; primary production in these channels was compared to production in a channel without grazers. Heavy and intermediate grazing resulted in decreases in standing crop of chlorophyll a, biomass/chlorophyll ratios, biomass of periphyton, gross primary production, and net community primary production. Low grazing densities did not significantly alter the above factors. Gross primary production increased with increasing standing crop of chlorophyll a but assimilation number was much greater at low standing crops; therefore, there was a partial compensatory mechanism for adjustment to grazing pressure. Total primary production was approximately equal at both high and intermediate densities of grazers and was greater at low densities of grazers and no grazing. Taxonomic structure of periphyton was altered by heavy and intermediate grazing but not changed at low grazing pressures. Snail growth increased with increasing biomass of periphyton. Responses of aquatic primary producers to canopy removal were examined in a clearcut and old-growth forest section of a stream in the Cascade Mountains of Oregon. Standing crop of chlorophyll a, biomass of periphyton, community respiration, assimilation number, and respiration per unit weight of periphyton were all significantly greater in the clearcut than in the old-growth forested section. Gross primary production was approximately 2.5 times greater in the open section than in the shaded section. Turnover times of periphyton were shorter in the clearcut than in the old-growth forest site. Photosynthetic efficiency was greater in the shaded site than in the open section. Processes of primary production were generally enhanced in the clearcut section of Mack Creek as compared to the old-growth forested section. Shifts of food bases in streams from allochthonous material to autochthonous primary production may have major effects on structure and function of stream ecosystems. Succession of energy bases is best viewed in terms of overall watershed succession. Aquatic primary producers are an integral component of stream ecosystems and a major determinant of the nature and dynamics of higher trophic levels in streams. Title: Effects of light, nutrients, and grazing on periphyton communities in streams Author: Gregory, Stanley Vincent Relative effects of light, nutrients, and grazing on primary production were investigated in streams in the Cascade Mountains of Oregon and in laboratory streams. Relative magnitudes of primary production and associated processes were examined for one year in a stream that flowed through a clearcut and an old-growth forest in the Cascade Mountains. Diel patterns of nutrients in four streams of different size indicated greater demand for inorganic nitrogen than phosphorus and suggested that uptake by aquatic primary producers was responsible for diel fluctuations of nutrient concentrations. Atomic ratios of N/P supported the conclusion that primary producers were most probably nitrogen limited. In an experiment of light and nitrate addition to a stream in an old-growth forest, primary producer processes were enhanced by addition of light (11000 lux) and by addition of both light and nitrate. There was no effect of nitrate addition on accumulation of algae, gross primary production, net community primary production, community respiration, P/R ratios, or community structure of diatoms at low ambient light levels (1100 lux). Addition of light resulted in greater colonization of algae, gross primary production, net community primary production, community respiration, P/R ratios and altered community structure of diatoms. The watershed was clearcut one year later and the experiment was essentially repeated with artificial shading instead of artificial lighting. Responses of colonization and primary production to light and nitrate in the clearcut were similar to those observed in the previous experiment in the old-growth forest. Interactions between primary producers and grazers in lotic systems were examined in laboratory streams. Different densities of snails were established in laboratory channels; primary production in these channels was compared to production in a channel without grazers. Heavy and intermediate grazing resulted in decreases in standing crop of chlorophyll a, biomass/chlorophyll ratios, biomass of periphyton, gross primary production, and net community primary production. Low grazing densities did not significantly alter the above factors. Gross primary production increased with increasing standing crop of chlorophyll a but assimilation number was much greater at low standing crops; therefore, there was a partial compensatory mechanism for adjustment to grazing pressure. Total primary production was approximately equal at both high and intermediate densities of grazers and was greater at low densities of grazers and no grazing. Taxonomic structure of periphyton was altered by heavy and intermediate grazing but not changed at low grazing pressures. Snail growth increased with increasing biomass of periphyton. Responses of aquatic primary producers to canopy removal were examined in a clearcut and old-growth forest section of a stream in the Cascade Mountains of Oregon. Standing crop of chlorophyll a, biomass of periphyton, community respiration, assimilation number, and respiration per unit weight of periphyton were all significantly greater in the clearcut than in the old-growth forested section. Gross primary production was approximately 2.5 times greater in the open section than in the shaded section. Turnover times of periphyton were shorter in the clearcut than in the old-growth forest site. Photosynthetic efficiency was greater in the shaded site than in the open section. Processes of primary production were generally enhanced in the clearcut section of Mack Creek as compared to the old-growth forested section. Shifts of food bases in streams from allochthonous material to autochthonous primary production may have major effects on structure and function of stream ecosystems. Succession of energy bases is best viewed in terms of overall watershed succession. Aquatic primary producers are an integral component of stream ecosystems and a major determinant of the nature and dynamics of higher trophic levels in streams. Close