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• 41. [Article] Spatial variability of African dust in soils in a montane tropical landscape in Puerto Rico

  Access to this item has been restricted by repository administrators at the request of the publisher, Elsevier, until July 23, 2017.

  Citation × Citation Citation Abstract Copy Title: Spatial variability of African dust in soils in a montane tropical landscape in Puerto Rico Author: McClintock, M. A., Porder, S., Brocard, G., Willenbring, J., Pett-Ridge, J. C., Tamayo, C. Access to this item has been restricted by repository administrators at the request of the publisher, Elsevier, until July 23, 2017. Title: Spatial variability of African dust in soils in a montane tropical landscape in Puerto Rico Author: McClintock, M. A., Porder, S., Brocard, G., Willenbring, J., Pett-Ridge, J. C., Tamayo, C. Access to this item has been restricted by repository administrators at the request of the publisher, Elsevier, until July 23, 2017. Close

• 42. [Article] A mathematical transformation of multi-angular remote sensing data for the study of vegetation change

  Vegetation change is an important factor affecting the global carbon cycle, land-atmosphere interaction, and terrestrial ecology. The study of vegetation change on a global scale can be used to evaluate ...

  Citation × Citation Citation Abstract Copy Title: A mathematical transformation of multi-angular remote sensing data for the study of vegetation change Author: Friedel, Robert G. Vegetation change is an important factor affecting the global carbon cycle, land-atmosphere interaction, and terrestrial ecology. The study of vegetation change on a global scale can be used to evaluate the impact of global climate change on terrestrial ecosystems. Satellite remote sensing can monitor vegetation change at the global scale, providing continuous samples of radiation reflected by vegetated surfaces with a temporal resolution of days. The MISR instrument offers the potential to sample the specular anisotropy of the Earth from up to 9 angles. Characterization of the specular anisotropy of vegetated surfaces on a global scale will provide information on the physical characteristics of vegetation affecting anisotropy not available from nadir-view only remote sensing. The objective of this study is to develop a Principal Components Analysis (PCA) transformation of multi-angular measurements of the Earth’s surface acquired by the MISR instrument, to examine the feasibility of quantifying the structural characteristics of different vegetation communities at a global scale. This transformation will be applied to a time-series analysis of the Kalmioposis Wilderness in the Siskiyou National Forest in Southwestern Oregon to better understand the changes in spectral and angular reflectance of a forest stand during re-growth after a stand-replacing disturbance. A sample encompassing a full phenologic cycle, of the red bands only from MISR cameras Ca – Cf, at scaled surface reflectance, provided the template on which PCA was performed. The sample of MISR data was created using imagery collected from 2001 – 2005 to provide a wide variety of vegetation and soils reflectance over a phenologic cycle. Sample data was rotated to the principal components as the new axes using the coefficients of rotation from an un-standardized PCA. Samples were evaluated at various latitudes, differing topography, and varying vegetation density and land cover to determine the properties of the scene controlling the range and magnitude of the principal components. Principal component 1 was found to have high negative correlation to NDVI. Principal component 2 was found to have high positive correlation to both the solar zenith angle and the relative azimuth angle between the MISR sensor and the path of incident radiation. Principal component 3 could not be correlated to any available metric, although evidence suggests that component 3 may carry useful information. The PCA transformation proved useful at relating the changes in vegetation after a fire at the Biscuit Complex. The changes in the BRDF as sampled by MISR were expressed through the principal components, but these changes could not be directly related to changing structural characteristics of the vegetation. The goal of assessing structural characteristics of vegetation through the PCA transformation to a single metric of vegetation structure was unsuccessful. The PCA transformation of the MISR sample successfully yielded a transformation where different classes of vegetation occupied distinct and unique regions of PCA space. The first two principal components were successfully correlated to measurable and definable metrics of vegetation and solar illumination. The third principal component, for which a correlation could not be found, was suggestive of carrying unique information and merits further investigation. The transformation of multi-angular red band reflectance as presented in this study may prove to be a valuable method of estimating biomass at a global scale. With principal components correlated to measures of biomass in NDVI and to the shadowing of the ground through the angle of solar illumination, the PCA relates characteristics of vegetated scenes in a minimum of bands. Title: A mathematical transformation of multi-angular remote sensing data for the study of vegetation change Author: Friedel, Robert G. Vegetation change is an important factor affecting the global carbon cycle, land-atmosphere interaction, and terrestrial ecology. The study of vegetation change on a global scale can be used to evaluate the impact of global climate change on terrestrial ecosystems. Satellite remote sensing can monitor vegetation change at the global scale, providing continuous samples of radiation reflected by vegetated surfaces with a temporal resolution of days. The MISR instrument offers the potential to sample the specular anisotropy of the Earth from up to 9 angles. Characterization of the specular anisotropy of vegetated surfaces on a global scale will provide information on the physical characteristics of vegetation affecting anisotropy not available from nadir-view only remote sensing. The objective of this study is to develop a Principal Components Analysis (PCA) transformation of multi-angular measurements of the Earth’s surface acquired by the MISR instrument, to examine the feasibility of quantifying the structural characteristics of different vegetation communities at a global scale. This transformation will be applied to a time-series analysis of the Kalmioposis Wilderness in the Siskiyou National Forest in Southwestern Oregon to better understand the changes in spectral and angular reflectance of a forest stand during re-growth after a stand-replacing disturbance. A sample encompassing a full phenologic cycle, of the red bands only from MISR cameras Ca – Cf, at scaled surface reflectance, provided the template on which PCA was performed. The sample of MISR data was created using imagery collected from 2001 – 2005 to provide a wide variety of vegetation and soils reflectance over a phenologic cycle. Sample data was rotated to the principal components as the new axes using the coefficients of rotation from an un-standardized PCA. Samples were evaluated at various latitudes, differing topography, and varying vegetation density and land cover to determine the properties of the scene controlling the range and magnitude of the principal components. Principal component 1 was found to have high negative correlation to NDVI. Principal component 2 was found to have high positive correlation to both the solar zenith angle and the relative azimuth angle between the MISR sensor and the path of incident radiation. Principal component 3 could not be correlated to any available metric, although evidence suggests that component 3 may carry useful information. The PCA transformation proved useful at relating the changes in vegetation after a fire at the Biscuit Complex. The changes in the BRDF as sampled by MISR were expressed through the principal components, but these changes could not be directly related to changing structural characteristics of the vegetation. The goal of assessing structural characteristics of vegetation through the PCA transformation to a single metric of vegetation structure was unsuccessful. The PCA transformation of the MISR sample successfully yielded a transformation where different classes of vegetation occupied distinct and unique regions of PCA space. The first two principal components were successfully correlated to measurable and definable metrics of vegetation and solar illumination. The third principal component, for which a correlation could not be found, was suggestive of carrying unique information and merits further investigation. The transformation of multi-angular red band reflectance as presented in this study may prove to be a valuable method of estimating biomass at a global scale. With principal components correlated to measures of biomass in NDVI and to the shadowing of the ground through the angle of solar illumination, the PCA relates characteristics of vegetated scenes in a minimum of bands. Close

• 43. [Article] Effects of wildfire on growth and demographics of coastal cutthroat trout in headwater streams

  Wildfire is a largely terrestrial perturbation broadly recognized as an agent of disturbance and ecological change in forested biomes. Effects of post-fire conditions on biotic components of aquatic systems ...

  Citation × Citation Citation Abstract Copy Title: Effects of wildfire on growth and demographics of coastal cutthroat trout in headwater streams Author: Heck, Michael P. Wildfire is a largely terrestrial perturbation broadly recognized as an agent of disturbance and ecological change in forested biomes. Effects of post-fire conditions on biotic components of aquatic systems have been less well-documented, although hypothetically, the two are strongly connected. In fact, the influence of wildfire may be most profound in headwater streams because of the tight linkage between aquatic and terrestrial ecosystems. We sought to understand the influence of post-fire conditions on fish in headwater streams by observing growth and demographics of coastal cutthroat trout (Oncorhynchus clarkii clarkii) following wildfire. During the summer of 2002, wildfire burned portions of three headwater watersheds in the North Umpqua basin of western Oregon. Burn severities ranged from moderate to severe. A reference stream was selected from a nearby fourth watershed. All fish-bearing portions of the stream network in the four watersheds were surveyed for 3 years following the wildfire, and 1,295 scale samples were collected from coastal cutthroat trout for age and growth analysis. Stream temperatures in the burned watersheds changed significantly following the wildfire (p < 0.016), with increases of up to 23% in the most severely burned watershed. During summer electrofishing surveys in the burned watersheds, both young-of-the-year and fish ≥ age 1 were captured; in the unburned watershed, the vast majority of fish captured were ≥ age 1. Age-frequency analyses revealed that fish in older age classes (age ≥ 3) were more prevalent in the unburned watershed than in the burned watersheds. Relative growth rates and length at last annulus formation of coastal cutthroat trout were positively related to the number of degree days during the growing season, and Pearson correlation coefficients ranged from 0.60 (p < 0.07) to 0.90 (p < 0.01). Growth rates and size of fish were not significantly correlated with relative density of fish (p ≥ 0.14). Contrary to the commonly held assumption that wildfire is detrimental to biota in aquatic systems, these results suggest that in the short term (≤ 3 years), fish in the study streams adjusted to environmental change caused by wildfire. Title: Effects of wildfire on growth and demographics of coastal cutthroat trout in headwater streams Author: Heck, Michael P. Wildfire is a largely terrestrial perturbation broadly recognized as an agent of disturbance and ecological change in forested biomes. Effects of post-fire conditions on biotic components of aquatic systems have been less well-documented, although hypothetically, the two are strongly connected. In fact, the influence of wildfire may be most profound in headwater streams because of the tight linkage between aquatic and terrestrial ecosystems. We sought to understand the influence of post-fire conditions on fish in headwater streams by observing growth and demographics of coastal cutthroat trout (Oncorhynchus clarkii clarkii) following wildfire. During the summer of 2002, wildfire burned portions of three headwater watersheds in the North Umpqua basin of western Oregon. Burn severities ranged from moderate to severe. A reference stream was selected from a nearby fourth watershed. All fish-bearing portions of the stream network in the four watersheds were surveyed for 3 years following the wildfire, and 1,295 scale samples were collected from coastal cutthroat trout for age and growth analysis. Stream temperatures in the burned watersheds changed significantly following the wildfire (p < 0.016), with increases of up to 23% in the most severely burned watershed. During summer electrofishing surveys in the burned watersheds, both young-of-the-year and fish ≥ age 1 were captured; in the unburned watershed, the vast majority of fish captured were ≥ age 1. Age-frequency analyses revealed that fish in older age classes (age ≥ 3) were more prevalent in the unburned watershed than in the burned watersheds. Relative growth rates and length at last annulus formation of coastal cutthroat trout were positively related to the number of degree days during the growing season, and Pearson correlation coefficients ranged from 0.60 (p < 0.07) to 0.90 (p < 0.01). Growth rates and size of fish were not significantly correlated with relative density of fish (p ≥ 0.14). Contrary to the commonly held assumption that wildfire is detrimental to biota in aquatic systems, these results suggest that in the short term (≤ 3 years), fish in the study streams adjusted to environmental change caused by wildfire. Close

• 44. [Article] Regional Contingencies in the Relationship between Aboveground Biomass and Litter in the World’s Grasslands

  To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work. This is the publisher’s final pdf. The published article is copyrighted by Public ...

  Citation × Citation Citation Abstract Copy Title: Regional Contingencies in the Relationship between Aboveground Biomass and Litter in the World’s Grasslands Author: Cleland, Elsa E., Orrock, John L., Morgan, John W., Davies, Kendi F., Li, Wei, Stevens, Carly J., Firn, Jennifer, Melbourne, Brett A., Harpole, W. Stan, Hagenah, Nicole, Hobbie, Sarah, Borer, Elizabeth T., McCulley, Rebecca L., Chu, Chengjin, Knops, Johannes M. H., DeCrappeo, Nicole M., Seabloom, Eric W., O’Halloran, Lydia R., Prober, Suzanne M., MacDougall, Andrew S., Bakker, Jonathan D., Du, Guozhen, Hofmockel, Kirsten S. To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work. This is the publisher’s final pdf. The published article is copyrighted by Public Library of Science and can be found at: http://www.plos.org/. Title: Regional Contingencies in the Relationship between Aboveground Biomass and Litter in the World’s Grasslands Author: Cleland, Elsa E., Orrock, John L., Morgan, John W., Davies, Kendi F., Li, Wei, Stevens, Carly J., Firn, Jennifer, Melbourne, Brett A., Harpole, W. Stan, Hagenah, Nicole, Hobbie, Sarah, Borer, Elizabeth T., McCulley, Rebecca L., Chu, Chengjin, Knops, Johannes M. H., DeCrappeo, Nicole M., Seabloom, Eric W., O’Halloran, Lydia R., Prober, Suzanne M., MacDougall, Andrew S., Bakker, Jonathan D., Du, Guozhen, Hofmockel, Kirsten S. To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work. This is the publisher’s final pdf. The published article is copyrighted by Public Library of Science and can be found at: http://www.plos.org/. Close

• 45. [Article] A model-data comparison of gross primary productivity: Results from the North American Carbon Program site synthesis

  This is the publisher’s final pdf. The published article is copyrighted by the American Geophysical Union and can be found at: http://www.agu.org/journals/jgr/. To the best of our knowledge, one or more ...

  Citation × Citation Citation Abstract Copy Title: A model-data comparison of gross primary productivity: Results from the North American Carbon Program site synthesis Author: Hilton, Timothy W., Hollinger, David Y., Ricciuto, Dan, Dragoni, Danilo, Chen, Jiquan, Peng, Changhui, Richardson, Andrew D., Verbeeck, Hans, Gu, Lianhong, Roulet, Nigel, Williams, Chris, Oechel, Walter, Law, Beverly, Sahoo, Alok, Anderson, Ryan, Chen, Jing M., Tonitto, Christina, Grant, Robert F., Barr, Alan, Jain, Atul, Vargas, Rodrigo, McCaughey, J. Harry, Black, T. Andrew, Arain, M. Altaf, Tian, Hanqin, Torn, Margaret, Desai, Ankur R., Bolstad, Paul, Munger, J. William, Monson, Russ, Raczka, Brett M., Dietze, Michael, Zhou, Xiaolu, Schwalm, Christopher R., Humphreys, Elyn, Margolis, Hank A., Kucharik, Chris, Poulter, Benjamin, Lokipitiya, Erandathie, Schaefer, Kevin, Price, David T., Dimitrov, Dimitre, Curtis, Peter S., Baker, Ian, Davis, Kenneth J., Liu, Shuguang, Riley, William J., Matamala, Roser, Thornton, Peter, Weng, Ensheng, Gough, Christopher This is the publisher’s final pdf. The published article is copyrighted by the American Geophysical Union and can be found at: http://www.agu.org/journals/jgr/. To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work. Title: A model-data comparison of gross primary productivity: Results from the North American Carbon Program site synthesis Author: Hilton, Timothy W., Hollinger, David Y., Ricciuto, Dan, Dragoni, Danilo, Chen, Jiquan, Peng, Changhui, Richardson, Andrew D., Verbeeck, Hans, Gu, Lianhong, Roulet, Nigel, Williams, Chris, Oechel, Walter, Law, Beverly, Sahoo, Alok, Anderson, Ryan, Chen, Jing M., Tonitto, Christina, Grant, Robert F., Barr, Alan, Jain, Atul, Vargas, Rodrigo, McCaughey, J. Harry, Black, T. Andrew, Arain, M. Altaf, Tian, Hanqin, Torn, Margaret, Desai, Ankur R., Bolstad, Paul, Munger, J. William, Monson, Russ, Raczka, Brett M., Dietze, Michael, Zhou, Xiaolu, Schwalm, Christopher R., Humphreys, Elyn, Margolis, Hank A., Kucharik, Chris, Poulter, Benjamin, Lokipitiya, Erandathie, Schaefer, Kevin, Price, David T., Dimitrov, Dimitre, Curtis, Peter S., Baker, Ian, Davis, Kenneth J., Liu, Shuguang, Riley, William J., Matamala, Roser, Thornton, Peter, Weng, Ensheng, Gough, Christopher This is the publisher’s final pdf. The published article is copyrighted by the American Geophysical Union and can be found at: http://www.agu.org/journals/jgr/. To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work. Close

• 46. [Article] Distinguishing biological and physical controls on soil respiration

  Soil respiration, or the combined CO₂ emissions from roots and soil microorganisms, constitutes one of the largest losses of carbon (C) from terrestrial ecosystems. The major drivers of soil respiration, ...

  Citation × Citation Citation Abstract Copy Title: Distinguishing biological and physical controls on soil respiration Author: Phillips, Claire L. Soil respiration, or the combined CO₂ emissions from roots and soil microorganisms, constitutes one of the largest losses of carbon (C) from terrestrial ecosystems. The major drivers of soil respiration, which include soil moisture, temperature, and substrate quality, have been known for some time. Nevertheless, correlations between these drivers and soil respiration vary substantially by site, and there is a lack of mechanistic principles that would allow prediction of soil respiration rates across sites and through time. Here I present three studies that attempted to characterize and differentiate biological and physical mechanisms controlling soil respiration. The purpose of the first study was to quantify the proportion of soil respiration derived from ectomycorrhizal (EcM) fungal mats, which can form dense aggregations of hyphae near the surface of forest soils. By comparing respiration rates on mats with neighboring non-mat soils, I estimated that approximately 10% of soil respiration was derived from EcM mats in an old-growth Douglas fir forest site. Seasonally, mat contributions correlated with soil moisture, which may be due to a physiological response of EcM fungi, but it also likely related to moisture impacts on CO₂ flux contributions in deep soil below where EcM mats tend to colonize. In the second study I examined diel patterns of soil respiration, and used a gas diffusion model to develop a theoretical basis for why respiration is often lagged several hours from soil temperature. This study demonstrated that soil heat and gas transport can cause complex diel patterns in soil respiration, which must be accounted for to correctly interpret the impacts of temperature and other forcing factors on soil respiration. Finally, the third study examined the carbon isotopic composition of soil respiration (δ¹³CO₂), and whether δ¹³CO₂ is influenced by recent plant photosynthates, as has been suggested previously, or instead by microbial or gas-transport effects. I ruled out microbial effects as a possible influence on moisture-related δ¹³CO₂ dynamics, but showed that gas transport likely influenced measurements of δ¹³CO₂ at high and low-moisture. Collectively, an important conclusion from these studies is that analysis of soil gradients, including gradients in environmental conditions, biological activity, and soil physical properties across the soil profile, helps to explain the dynamics of CO₂ fluxes from the soil surface. By examining respiration as a product of processes occurring across soil profiles, in contrast to treating soil as a flat surface or a homogenous medium, more mechanistic and universal relationships become apparent. Title: Distinguishing biological and physical controls on soil respiration Author: Phillips, Claire L. Soil respiration, or the combined CO₂ emissions from roots and soil microorganisms, constitutes one of the largest losses of carbon (C) from terrestrial ecosystems. The major drivers of soil respiration, which include soil moisture, temperature, and substrate quality, have been known for some time. Nevertheless, correlations between these drivers and soil respiration vary substantially by site, and there is a lack of mechanistic principles that would allow prediction of soil respiration rates across sites and through time. Here I present three studies that attempted to characterize and differentiate biological and physical mechanisms controlling soil respiration. The purpose of the first study was to quantify the proportion of soil respiration derived from ectomycorrhizal (EcM) fungal mats, which can form dense aggregations of hyphae near the surface of forest soils. By comparing respiration rates on mats with neighboring non-mat soils, I estimated that approximately 10% of soil respiration was derived from EcM mats in an old-growth Douglas fir forest site. Seasonally, mat contributions correlated with soil moisture, which may be due to a physiological response of EcM fungi, but it also likely related to moisture impacts on CO₂ flux contributions in deep soil below where EcM mats tend to colonize. In the second study I examined diel patterns of soil respiration, and used a gas diffusion model to develop a theoretical basis for why respiration is often lagged several hours from soil temperature. This study demonstrated that soil heat and gas transport can cause complex diel patterns in soil respiration, which must be accounted for to correctly interpret the impacts of temperature and other forcing factors on soil respiration. Finally, the third study examined the carbon isotopic composition of soil respiration (δ¹³CO₂), and whether δ¹³CO₂ is influenced by recent plant photosynthates, as has been suggested previously, or instead by microbial or gas-transport effects. I ruled out microbial effects as a possible influence on moisture-related δ¹³CO₂ dynamics, but showed that gas transport likely influenced measurements of δ¹³CO₂ at high and low-moisture. Collectively, an important conclusion from these studies is that analysis of soil gradients, including gradients in environmental conditions, biological activity, and soil physical properties across the soil profile, helps to explain the dynamics of CO₂ fluxes from the soil surface. By examining respiration as a product of processes occurring across soil profiles, in contrast to treating soil as a flat surface or a homogenous medium, more mechanistic and universal relationships become apparent. Close

• 47. [Article] Effects of ungulate herbivory on aspen, cottonwood, and willow development under forest fuels treatment regimes

  This is the publisher’s final pdf. The published article is copyrighted by Elsevier and can be found at: http://www.journals.elsevier.com/forest-ecology-and-management/. To the best of our knowledge, one ...

  Citation × Citation Citation Abstract Copy Title: Effects of ungulate herbivory on aspen, cottonwood, and willow development under forest fuels treatment regimes Author: Dick, Brian L., Endress, Bryan A., Boyd, Jennifer M., Parks, Catherine G., Wisdom, Michael J., Vavra, Martin, Naylor, Bridgett J. This is the publisher’s final pdf. The published article is copyrighted by Elsevier and can be found at: http://www.journals.elsevier.com/forest-ecology-and-management/. To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work. Title: Effects of ungulate herbivory on aspen, cottonwood, and willow development under forest fuels treatment regimes Author: Dick, Brian L., Endress, Bryan A., Boyd, Jennifer M., Parks, Catherine G., Wisdom, Michael J., Vavra, Martin, Naylor, Bridgett J. This is the publisher’s final pdf. The published article is copyrighted by Elsevier and can be found at: http://www.journals.elsevier.com/forest-ecology-and-management/. To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work. Close

• 48. [Article] Surface complexation of protons and sulfate by kaolinite

  The emission of sulfur oxides from anthropogenic sources represents a potential threat to terrestrial ecosystems. Sulfate, the most highly oxidized form of sulfur, is the most common form of inorganic ...

  Citation × Citation Citation Abstract Copy Title: Surface complexation of protons and sulfate by kaolinite Author: Wildensee, Frank The emission of sulfur oxides from anthropogenic sources represents a potential threat to terrestrial ecosystems. Sulfate, the most highly oxidized form of sulfur, is the most common form of inorganic sulfur in most soil environments. The sorption of sulfate may influence the alkalinity of the soil solution and as a consequence the pH of surface waters. Batch experiments were performed to determine the influence of pH, total sulfate concentration and solubility of the adsorbent on the sorption of sulfate by kaolinite. Proton surface charge density for kaolinite was determined over a solution pH range from 3.5 to 11.0 in the absence and presence of sulfate (10.99 to 526.3 μM) in 0.1 M NaCl0₄ at 298 K. Total aluminum (Al[subscript TS]) and silica (Si[subscript TS]) concentrations were measured as a function of pH after varying reaction times (2 to 60 h). The dissolution of kaolinite was incongruent (Al[subscript TS]/Si[subscript TS] ≠ 1) over the entire pH range. Proton adsorption by edge surface functional groups of kaolinite, corrected for proton consuming dissolution reactions, showed no influence of the reaction time. Titration data were modeled by the nonlinear least squares fitting routine FITEQL to obtain intrinsic proton complexation constants. Aluminol, aquo and silanol groups were found to undergo complexation reactions. Average values over all reaction times and total sulfate concentrations for log K₋ (int) and log K₊ (int) were -9.3 and 7.3 for aluminol and aquo groups, and -5.2 and 4.9 for silanol groups, respectively. The total concentration of surface sites was 1.74 cmol kg⁻¹. This higher value, in comparison to the theoretically determined concentration, could be explained by differences in the particle size of kaolinite. Kinetics of sulfate sorption by kaolinite KGa-1, determined in a stirred batch reaction in 0.1 M NaCl0₄ for a suspension density of 33.33 g L⁻¹ at pH 4.5 and 6.5 were rapid. No sorption reaction could be observed after 1 min reaction time. Sulfate sorption was independent of pH and increased linearly with the free sulfate concentration. Linear regressions resulted in an overall partition coefficient for sulfate of 7.8 L kg⁻¹ (R² - 0.99) between solid and solution. A multiple regression model showed that pH was not a significant variable in determining the amount of sulfate sorbed. Specific adsorption by edge surface groups via ligand exchange could be excluded, mainly due to the complete lack of a pH influence on sulfate sorption. Precipitation of a sparingly soluble aluminum sulfate mineral was considered a possible mechanism controlling sulfate concentration in solution. The solubility of several aluminum and aluminum sulfate minerals was computed using the solution speciation program MICROQL. Precipitation of basaluminite, a basic aluminum sulfate mineral present in acid sulfate soils, was found to be possible within the pH range from 5.0 to 6.0. However, no conclusive evidence can be presented for precipitation being the mechanism of sulfate sorption in presence of kaolinite. Title: Surface complexation of protons and sulfate by kaolinite Author: Wildensee, Frank The emission of sulfur oxides from anthropogenic sources represents a potential threat to terrestrial ecosystems. Sulfate, the most highly oxidized form of sulfur, is the most common form of inorganic sulfur in most soil environments. The sorption of sulfate may influence the alkalinity of the soil solution and as a consequence the pH of surface waters. Batch experiments were performed to determine the influence of pH, total sulfate concentration and solubility of the adsorbent on the sorption of sulfate by kaolinite. Proton surface charge density for kaolinite was determined over a solution pH range from 3.5 to 11.0 in the absence and presence of sulfate (10.99 to 526.3 μM) in 0.1 M NaCl0₄ at 298 K. Total aluminum (Al[subscript TS]) and silica (Si[subscript TS]) concentrations were measured as a function of pH after varying reaction times (2 to 60 h). The dissolution of kaolinite was incongruent (Al[subscript TS]/Si[subscript TS] ≠ 1) over the entire pH range. Proton adsorption by edge surface functional groups of kaolinite, corrected for proton consuming dissolution reactions, showed no influence of the reaction time. Titration data were modeled by the nonlinear least squares fitting routine FITEQL to obtain intrinsic proton complexation constants. Aluminol, aquo and silanol groups were found to undergo complexation reactions. Average values over all reaction times and total sulfate concentrations for log K₋ (int) and log K₊ (int) were -9.3 and 7.3 for aluminol and aquo groups, and -5.2 and 4.9 for silanol groups, respectively. The total concentration of surface sites was 1.74 cmol kg⁻¹. This higher value, in comparison to the theoretically determined concentration, could be explained by differences in the particle size of kaolinite. Kinetics of sulfate sorption by kaolinite KGa-1, determined in a stirred batch reaction in 0.1 M NaCl0₄ for a suspension density of 33.33 g L⁻¹ at pH 4.5 and 6.5 were rapid. No sorption reaction could be observed after 1 min reaction time. Sulfate sorption was independent of pH and increased linearly with the free sulfate concentration. Linear regressions resulted in an overall partition coefficient for sulfate of 7.8 L kg⁻¹ (R² - 0.99) between solid and solution. A multiple regression model showed that pH was not a significant variable in determining the amount of sulfate sorbed. Specific adsorption by edge surface groups via ligand exchange could be excluded, mainly due to the complete lack of a pH influence on sulfate sorption. Precipitation of a sparingly soluble aluminum sulfate mineral was considered a possible mechanism controlling sulfate concentration in solution. The solubility of several aluminum and aluminum sulfate minerals was computed using the solution speciation program MICROQL. Precipitation of basaluminite, a basic aluminum sulfate mineral present in acid sulfate soils, was found to be possible within the pH range from 5.0 to 6.0. However, no conclusive evidence can be presented for precipitation being the mechanism of sulfate sorption in presence of kaolinite. Close

• 49. [Article] Dynamics of water-soluble carbon in forest soils of contrasting fertility

  Most soil organic C is in a stable form, associated with clay minerals in the upper soil profile. Upon environmental and land-use changes, stable soil C is subject to losses, which influence the global ...

  Citation × Citation Citation Abstract Copy Title: Dynamics of water-soluble carbon in forest soils of contrasting fertility Author: Wagai, Rota Most soil organic C is in a stable form, associated with clay minerals in the upper soil profile. Upon environmental and land-use changes, stable soil C is subject to losses, which influence the global C cycle and the productivity of terrestrial ecosystems. However, mechanisms controlling soil C destabilization are not well understood. Microbial respiration and leaching are the two major fates of destabilized C. I hypothesized that water-soluble C plays an important role in soil C turnover and studied the susceptibility of water-soluble C both to leaching and to microbial degradation. Furthermore, I studied factors influencing the amount of water-soluble C and its biodegradability using five soils from a wide fertility gradient. First, soil columns (20 cm of top soil) with and without Douglas-fir seedlings were leached every 2 weeks for 20 weeks and the soils were extracted with water before and after the 20-week study period. Extracts contained 8 to 17 times more dissolved organic C (DOC) than did leachates. Similarly, biodegradable DOC (BDOC) in extracts was 4 to 96 times that in leachates. The leachable C pool was constant over the 20 weeks regardless of the presence of tree seedlings in soil leaching columns, while the extractable C pooi declined by 31 to 40% over time. A soil C destabilization model was proposed based on the changes in measured C pools (particulate, water-extractable, and leachable C) and the estimates of soil respiration and microbial biomass from a previous work. Microbial respiration accounted for 86 to 92% of the C destabilized. Leached C accounted for the remaining 8 to 14%, indicating its minor role in C mobilization in the system studied. However, the model didn't rule out the possibility that extractable C accounts for a significant portion of microbial respiration. Second, the hypothesis that water-extractable C is a major energy source for microbes was tested using Douglas-fir forest soils from two sites (Cascade Head and Wind River) and with and without red-alder influence. Despite a large range of soil fertility (C:N ratio of 13 to 31), C extracted before and after the 2-month soil incubation showed a strong correlation with the C respired during the incubation period (r2 = 0.71 and 0.92), suggesting the efficacy of extractable C pools to predict the availability of C to soil microbes. Furthermore, DOC and BDOC pool were relatively constant during the 2- month incubation, indicating the possibility that a rapid regeneration and degradation of extractable C explain the measured microbial respiration during the study period. No clear correlation was found between DOC and dissolved organic N. Across all stands, soil C:N ratio showed a strong correlation with the relative amount of BDOC in the DOC incubation (r2 = 0.72) and with the relative amount of C respired from bulk soil (per g C basis) at the end of incubation period (r2 = 0.72), suggesting a strong influence of soil C:N on the overall C availability to soil microbes both in solution and solid phase. Water-extractable C deserves continued attention as a strong predictor of available C for soil microbes and as a potentially significant energy source for microbial respiration. More information is needed to estimate the regeneration rate of labile extractable C and to identify factors controlling soil C degradation. Title: Dynamics of water-soluble carbon in forest soils of contrasting fertility Author: Wagai, Rota Most soil organic C is in a stable form, associated with clay minerals in the upper soil profile. Upon environmental and land-use changes, stable soil C is subject to losses, which influence the global C cycle and the productivity of terrestrial ecosystems. However, mechanisms controlling soil C destabilization are not well understood. Microbial respiration and leaching are the two major fates of destabilized C. I hypothesized that water-soluble C plays an important role in soil C turnover and studied the susceptibility of water-soluble C both to leaching and to microbial degradation. Furthermore, I studied factors influencing the amount of water-soluble C and its biodegradability using five soils from a wide fertility gradient. First, soil columns (20 cm of top soil) with and without Douglas-fir seedlings were leached every 2 weeks for 20 weeks and the soils were extracted with water before and after the 20-week study period. Extracts contained 8 to 17 times more dissolved organic C (DOC) than did leachates. Similarly, biodegradable DOC (BDOC) in extracts was 4 to 96 times that in leachates. The leachable C pool was constant over the 20 weeks regardless of the presence of tree seedlings in soil leaching columns, while the extractable C pooi declined by 31 to 40% over time. A soil C destabilization model was proposed based on the changes in measured C pools (particulate, water-extractable, and leachable C) and the estimates of soil respiration and microbial biomass from a previous work. Microbial respiration accounted for 86 to 92% of the C destabilized. Leached C accounted for the remaining 8 to 14%, indicating its minor role in C mobilization in the system studied. However, the model didn't rule out the possibility that extractable C accounts for a significant portion of microbial respiration. Second, the hypothesis that water-extractable C is a major energy source for microbes was tested using Douglas-fir forest soils from two sites (Cascade Head and Wind River) and with and without red-alder influence. Despite a large range of soil fertility (C:N ratio of 13 to 31), C extracted before and after the 2-month soil incubation showed a strong correlation with the C respired during the incubation period (r2 = 0.71 and 0.92), suggesting the efficacy of extractable C pools to predict the availability of C to soil microbes. Furthermore, DOC and BDOC pool were relatively constant during the 2- month incubation, indicating the possibility that a rapid regeneration and degradation of extractable C explain the measured microbial respiration during the study period. No clear correlation was found between DOC and dissolved organic N. Across all stands, soil C:N ratio showed a strong correlation with the relative amount of BDOC in the DOC incubation (r2 = 0.72) and with the relative amount of C respired from bulk soil (per g C basis) at the end of incubation period (r2 = 0.72), suggesting a strong influence of soil C:N on the overall C availability to soil microbes both in solution and solid phase. Water-extractable C deserves continued attention as a strong predictor of available C for soil microbes and as a potentially significant energy source for microbial respiration. More information is needed to estimate the regeneration rate of labile extractable C and to identify factors controlling soil C degradation. Close

• 50. [Article] Performance of Linear and Nonlinear Two-Leaf Light Use Efficiency Models at Different Temporal Scales

  To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work. This is the publisher’s final pdf. The published article is copyrighted by MDPI and ...

  Citation × Citation Citation Abstract Copy Title: Performance of Linear and Nonlinear Two-Leaf Light Use Efficiency Models at Different Temporal Scales Author: Law, Beverly E., Wu, Xiaocui, Ju, Weimin, et al., Zhou, Yanlian To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work. This is the publisher’s final pdf. The published article is copyrighted by MDPI and can be found at: http://www.mdpi.com/journal/remotesensing Title: Performance of Linear and Nonlinear Two-Leaf Light Use Efficiency Models at Different Temporal Scales Author: Law, Beverly E., Wu, Xiaocui, Ju, Weimin, et al., Zhou, Yanlian To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work. This is the publisher’s final pdf. The published article is copyrighted by MDPI and can be found at: http://www.mdpi.com/journal/remotesensing Close