Besides well‐known effects of climate and parent material on silicate weathering the role of land... more Besides well‐known effects of climate and parent material on silicate weathering the role of land use change as a driver in the global silicon cycle is not well known. Changes in vegetation cover have altered reservoirs of silicon and carbon in plants and soils. This has potential consequences for plant‐Si availability, agricultural yields, and coastal eutrophication, as Si is a beneficial element for many crop plants and an essential nutrient for diatom growth. We here examined the role of sustained and intensive land use and human disturbance on silicon (Si) pool distribution in soils with similar climatological and bulk mineralogical characteristics. We show that land use impacts both biogenic and nonbiogenic Si pools. While biogenic Si strongly decreases along the land use change gradient (from forest to croplands), pedogenic silica fractions (e.g. pedogenic clays) increase in topsoils with a long duration of cultivation and soil disturbance. Our results suggest that nonbiogenic...
Wildfire is a natural disturbance, though elemental losses and changes that occur during combusti... more Wildfire is a natural disturbance, though elemental losses and changes that occur during combustion and post-fire erosion can have long-term impacts on soil properties, ecosystem productivity, and watershed condition. Here we evaluate the potential of forest residue-based materials to rehabilitate burned soils. We compare soil nutrient and water availability, and plant recovery after application of 37 t ha−1of wood mulch, 20 t ha−1of biochar, and the combination of the two amendments with untreated, burned soils. We also conducted a greenhouse trial to examine how biochar influenced soil nutrient and water content under two wetting regimes. The effects of wood mulch on plant-available soil N and water content were significant and seasonally consistent during the three-year field study. Biochar applied alone had few effects under field conditions, but significantly increased soil pH, Ca, P, and water in the greenhouse. The mulched biochar treatment had the greatest effects on soil N ...
Traditionally, soil scientists use shovels and augers to study soils and acquire infonnation on d... more Traditionally, soil scientists use shovels and augers to study soils and acquire infonnation on depth to bedrock. These tools are rather slow and tedious to operate, and the data collected are relatively expensive and therefore limited. In many areas, depth to bedrock is highly variable over short distances and extrapolations made from a limited number of widely spaced auger observations can be flawed. Commonly, a large number of borings is required to adequately characterize the distribution of bedrock depths within soil map units. Studies have shown that the depths to bedrock are underestimated with traditional soil survey tools (Doolittle et aI., 1988; Collins et aI., 1989). The probability of encountering a rock fragment often increases with increasing soil depth. Soil scientists frequently do not know whether bedrock or a large rock fragment restricted auger penetration and must make educated guesses about the depth to bedrock or map unit design. Limited by the tools nonnally used, soil scientists must infer the depth to bedrock from vegetative cover, exposures, and landscape position. These inferences are often based on associated or anticipated, rather than confinned, depths to bedrock. Alternative field methods are needed to complement traditional soil survey tools and to improve the characterization of bedrock depths within soil map units. Electromagnetic induction (EMI) and ground-penetrating radar (GPR) have been used extensively for these purposes. These tools can provide soil scientists with a better understanding of soil depth and variability. Ground-penetrating radar has proven to be highly effective in the coarse-and moderately coarse-textured soils of eastern United States. In semiarid and arid regions of the United States, soluble salts ofK, Na, and less soluble carbonates ofCa and Mg are more likely to accumulate in the upper parts of soils. These salts produce high attenuation rates that restrict the radar's penetration depths and severely diminish its results (Doolittle and Collins, 1995). Electromagnetic induction uses electromagnetic energy to measure the apparent conductivity of earthen materials. Apparent conductivity is a weighted, average conductivity measurement for a column of earthen materials to a specific depth (Greenhouse and Slaine, 1983). Variations in apparent conductivity are caused by changes in the electrical conductivity of earthen materials. The electrical conductivity of soils is influenced by the type and concentration of ions in solution, the amount and type of clays in the soil matrix, the volumetric water content, and the temperature and phase of the soil water (McNeill, 1980). The apparent conductivity of soils increases with increased soluble salts, water, and/or clay contents (Kachanoski et aI., 1988; Rhoades et aI., 1976). Interpretations of EM I data are based on the identification of spatial patterns within data sets. Though seldom diagnostic in themselves, lateral and vertical variations in apparent conductivity are used to infer changes in soils and soil properties.
Understanding how bison behaved in the past can provide key insights for today's managers, ecolog... more Understanding how bison behaved in the past can provide key insights for today's managers, ecologists, and anthropologists. However, the direct application of both historic documentation and modern field observations may not provide the necessary insights for understanding bison behaviors in archeological and paleontological contexts. In order to develop a better understanding of possible behavior within these contexts, we have developed individual foraging histories for 22 Bison bison from the Glenrock Buffalo Jump assemblage of the Plains Late Prehistoric period in Wyoming and four Pleistocene B. priscus from the Ukraine. Incremental stable carbon isotopic values of dental enamel were used to determine foraging histories. The progressive development of enamel allows for samples to be selected that represent distinct periods of an individual's life. Comparison of these dietary patterns among members of a herd can demonstrate foraging behaviors of 25 26
urated soils (Patrick and Jugsujinda, 1992). The reduc- tion of Mn oxides before Fe oxides is con... more urated soils (Patrick and Jugsujinda, 1992). The reduc- tion of Mn oxides before Fe oxides is consistent with Manganese solubility has become a primary concern in the soils the theoretical redox potentials under which Mn oxides and water supplies in the Alamosa River basin, Colorado due to both crop toxicity problems and concentrations that exceed water quality vs. Fe oxides
Humans colonized Hawaii about 1200 years ago and have progressively modified vegetation, particul... more Humans colonized Hawaii about 1200 years ago and have progressively modified vegetation, particularly in mesic to dry tropical forests. We use δ 13 C to evaluate the contribution of C 3 and C 4 plants to deep soil organic matter to reconstruct pre-human contact vegetation patterns along a wet to dry climate transect on Kohala Mountain, Hawaii Island. Precontact vegetation assemblages fall into three distinct zones: a wet C 3 dominated closed canopy forest where annual rainfall is N 2000 mm, a dry C 4 dominated grassland with annual rainfall b 500 mm, and a broad transition zone between these communities characterized by either C 3 trees with higher water-use efficiency than the rainforest trees or C 3 trees with a small amount of C 4 grasses intermixed. The likelihood of C 4 grass understory decreases with increasing rainfall. We show that the total concentration of rock-derived nutrients in the b 2-mm soil fraction differs in each of these vegetation zones. Nutrient losses are driven by leaching at high rainfall and by plant cycling and wind erosion at low rainfall. By contrast, nutrients are best preserved in surface soils of the intermediate rainfall zone, where rainfall supports abundant plant growth but does not contribute large amounts of water in excess of evapotranspiration. Polynesian farmers exploited these naturally enriched soils as they intensified their upland agricultural systems during the last three centuries before European contact.
Silicon stable isotopes can be used to trace the biogeochemical pathways of Si as it moves from i... more Silicon stable isotopes can be used to trace the biogeochemical pathways of Si as it moves from its continental sources to its sink in ocean sediments. Along the way, Si is incorporated into clay minerals, taken up by plants where it forms plant opal, and leached into rivers, the major land-to-ocean conduit. Compared to igneous rocks, the waters that drain
Oxygen isotope ratios of pedogenic carbonates were analyzed along a climatic gradient in the Palo... more Oxygen isotope ratios of pedogenic carbonates were analyzed along a climatic gradient in the Palouse region of eastern Washington State to evaluate changes in their isotopic composition with changing climate. A modern analog approach was used to assess the relationship between the istotope ratios in the pedogenic carbonates with those in soil water (measured in June when we anticipated carbonate formation might occur because of low soil water content), and meteoric water from two National Atmospheric Deposition Program (NADP) sites adjacent to our sequence. Mean annual meteoric water δ18O values (wrt VSMOW) from the two NADP sites varied slightly with elevation, —13.9‰ at the Starkey site (elevation 1253 m) and —13.0‰ at the Palouse site, (elevation 766 m) but showed distinct seasonal trends with weighted means ranging from —11.9‰ during autumn to —15.0‰ during the winter. Carbonate δ18O (wrt VPDB) varied significantly with MAP, ranging from —14.1‰ at the most arid site to —11.4‰ at...
We are happy to welcome readers to the spring 2020 issue of the APA Newsletter on Teaching Philos... more We are happy to welcome readers to the spring 2020 issue of the APA Newsletter on Teaching Philosophy. This issue features one article on teaching, a review essay on C.D.C. Reeve's new translation of Aristotle's De Anima, poems by two philosophers, and a list of recently published books that will be of interest to philosophy instructors.
This study investigates the carbon isotope systematics of benzene, toluene, ethylbenzene, and xyl... more This study investigates the carbon isotope systematics of benzene, toluene, ethylbenzene, and xylene monoaromatic hydrocarbons (BTEX) with regard to an improved understanding of the behavior of these compounds in the subsurface, particularly during remediation processes. We found that fractionation eects due to vaporization are small and positive for all compounds studied (D 13 C vapor±liquid Q+0.2-), and that fractionation eects due to soil adsorption are also likely to be small ( 13 C-labeled compounds cannot be resolved from unlabeled compounds by HPLC). We also evaluated use of the isotopic composition of contaminants as tracers of source and migration in the subsurface by performing a survey of the bulk isotopic composition of commercially available sources of BTEX. The results indicate that a wide range of d 13 C values exist (e.g., benzene, À23.87-to À29.40-). Our work suggests that stable C isotope analysis has great potential for qualifying, and possibly quantifying, the subsurface processes aecting contaminant concentrations. In particular, stable isotope analysis may be especially bene®cial for monitoring the ecacy of abiological and biological remediation eorts. #
Carbon is sequestered in soils,by accumulation of recalcitrant organic matter and by bicarbonate ... more Carbon is sequestered in soils,by accumulation of recalcitrant organic matter and by bicarbonate weathering of silicate minerals. Carbon fixation by ecosystems helps drive Weathering processes in soii$ and that in turn diverts carbon from annuai photosynthesis-soii respiration cycling into the (ong-term geological oarbon cycle. To quantify rates of carbon transfer during soil development in moist temperate grassland and desert scrubland ecosystems, we measured organic and inorganic residues derived from the interaction of soii biota and siiicate minerai weathering for twenty-two soil profiles in arkosic sediments of differing ages. in moist temperate grasslands, net annual removal of carbon from the atmosphere by organic carbon accumulation and silicate weathering ranges from about 8.5 g m-z yrl for young soils to 0.7 g m-z yrl for old soils. in desert scrublands, net annual carbon removal is about 0.2 g m-z yr-1 for young soils and 0.01 g m-z yr-1 for old soils. in soils of both ecosystems, organic carbon accumulation exceeds C02 removal by weathering. However, as soils age, rates of C02 consumption by weathering accounts for greater amounts of carbon sequestration, increasing from 2% to 8% in the grassland soils and from 29f0 to 40%'o in the scrubland soils. in soils of desert scrublands, carbonate accumulation far outstrips organic carbon accumulation, but about 909'oof this mass is derived from aerosolic sources that do not contribute to iong-term sequestration of atmospheric carbon dioxide.
ABSTRACT Background/Question/Methods The contemporary landscapes of the short-grass steppe ecosys... more ABSTRACT Background/Question/Methods The contemporary landscapes of the short-grass steppe ecosystem possess a remarkably diverse soil mantle. While spatial heterogeneity does indeed exist among soils in the short-grass steppe, the combined effects of vegetation and climate have created a uniquely spatial homogenous soil-landscape mosaic when compared to soil of other ecosystems. We identified dominate soil conditioning variables (state factors, Jenny1940) by combining Soil Survey Geographic data with geologic, geomorphic, and elevation data in northeastern Colorado, therefore isolating geographic areas where contributions of single state factor outrank the combined contribution of other factors. In water limited systems areas such as the short-grass steppe, three broad phases of soil development can be identified according to landscape age that we believe to be ecologically and biogeochemically significant. Results/Conclusions In a similar fashion to Vitousek et al (2008) we identified and characterized functional pedologic phases within water limited SGS ecosystems in which soils are either 1) Aggrading or Building with regard to soil development, 2) are in an Intermediate or Equilibrium stage of soil development, and 3) Degrading or Declining in terms of soil development. This geographic approach to modeling pedologic and ecohydrologic dynamics identify regions where soil capacity to store water and nutrients at a relative maximum and are used as the basis for assessing ecosystem vulnerability.
Page 1. http://bul.sagepub.com/ NASSP Bulletin http://bul.sagepub.com/content/74/ 523/103.citatio... more Page 1. http://bul.sagepub.com/ NASSP Bulletin http://bul.sagepub.com/content/74/ 523/103.citation The online version of this article can be found at: DOI: 10.1177/019263659007452316 1990 74: 103 NASSP Bulletin Eugene ...
Isotopic analysis of soil water requires complete extraction of water from the soil matrix to ens... more Isotopic analysis of soil water requires complete extraction of water from the soil matrix to ensure against isotopic fractionation. A variant of the standard CO2–water equilibration technique avoids distillation of soil water that can cause isotopic fractionation. Reproducibility of direct equilibration is between 0.3‰ and 0.4‰. Longer equilibration times are necessary for soil with a fine particle size distribution and/or low water content than for standard CO2–water equilibrations. Differences in the δ18O value between unsterilized and sterilized (by γ-radiation) sample pairs suggests that respiration can contribute to changing the δ18O value of soil water. Measured δ18O values of samples prepared by adding water with a known δ18O value to dry soil increase with increasing water content and are always more negative than the δ18O value of the added water, especially at low water contents. The combination of contamination by residual water, heterogeneities due to difficulty with physical mixing of the sample, possible kinetic fractionations when small amounts of water are added to dry soil, contribute to these trends. These tests suggest that direct equilibration is a quick and relatively easy approach for measuring the δ18O value of soil water.
This paper is centered on the specific effects of plants on the soil weathering environment; we a... more This paper is centered on the specific effects of plants on the soil weathering environment; we attempt to address how to quantify this component of the ecosystem and assess feedbacks between plants and weathering processes that influence the degree and rates of mineral weathering. The basic processes whereby plants directly influence the soil chemical environment is through the generation of weathering agents, biocycling of cations, and the production of biogenic minerals. Plants may indirectly influence soil processes through the ...
Abstract Terrestrial silicate weathering rates and processes are important for studies of modern ... more Abstract Terrestrial silicate weathering rates and processes are important for studies of modern and paleo-climate. Recently, Si isotope geochemistry has shed light on Si cycling in marine systems, which is directly linked to the terrestrial Si cycle as nearly 80% of the Si is supplied by continental run-off water. Understanding the terrestrial Si-isotope geochemistry is crucial for a more comprehensive understanding of the global Si cycle. Weathering of primary minerals in the pedosphere releases Si that can be incorporated into secondary ...
Abstract Over geologic timescales, biologically mediated weathering processes influence atmospher... more Abstract Over geologic timescales, biologically mediated weathering processes influence atmospheric CO2 content and global climate because the net effect of silicate weathering is the transfer of atmospheric CO2 to HCO-3 These weathering processes further influence atmospheric CO2 due to a net transfer of dissolved silica to the oceans which promotes diatom production and sedimentation there by adding carbon to the oceanic reservoir. There is a substantial body of evidence that suggests that plants may transform silica into more ...
Besides well‐known effects of climate and parent material on silicate weathering the role of land... more Besides well‐known effects of climate and parent material on silicate weathering the role of land use change as a driver in the global silicon cycle is not well known. Changes in vegetation cover have altered reservoirs of silicon and carbon in plants and soils. This has potential consequences for plant‐Si availability, agricultural yields, and coastal eutrophication, as Si is a beneficial element for many crop plants and an essential nutrient for diatom growth. We here examined the role of sustained and intensive land use and human disturbance on silicon (Si) pool distribution in soils with similar climatological and bulk mineralogical characteristics. We show that land use impacts both biogenic and nonbiogenic Si pools. While biogenic Si strongly decreases along the land use change gradient (from forest to croplands), pedogenic silica fractions (e.g. pedogenic clays) increase in topsoils with a long duration of cultivation and soil disturbance. Our results suggest that nonbiogenic...
Wildfire is a natural disturbance, though elemental losses and changes that occur during combusti... more Wildfire is a natural disturbance, though elemental losses and changes that occur during combustion and post-fire erosion can have long-term impacts on soil properties, ecosystem productivity, and watershed condition. Here we evaluate the potential of forest residue-based materials to rehabilitate burned soils. We compare soil nutrient and water availability, and plant recovery after application of 37 t ha−1of wood mulch, 20 t ha−1of biochar, and the combination of the two amendments with untreated, burned soils. We also conducted a greenhouse trial to examine how biochar influenced soil nutrient and water content under two wetting regimes. The effects of wood mulch on plant-available soil N and water content were significant and seasonally consistent during the three-year field study. Biochar applied alone had few effects under field conditions, but significantly increased soil pH, Ca, P, and water in the greenhouse. The mulched biochar treatment had the greatest effects on soil N ...
Traditionally, soil scientists use shovels and augers to study soils and acquire infonnation on d... more Traditionally, soil scientists use shovels and augers to study soils and acquire infonnation on depth to bedrock. These tools are rather slow and tedious to operate, and the data collected are relatively expensive and therefore limited. In many areas, depth to bedrock is highly variable over short distances and extrapolations made from a limited number of widely spaced auger observations can be flawed. Commonly, a large number of borings is required to adequately characterize the distribution of bedrock depths within soil map units. Studies have shown that the depths to bedrock are underestimated with traditional soil survey tools (Doolittle et aI., 1988; Collins et aI., 1989). The probability of encountering a rock fragment often increases with increasing soil depth. Soil scientists frequently do not know whether bedrock or a large rock fragment restricted auger penetration and must make educated guesses about the depth to bedrock or map unit design. Limited by the tools nonnally used, soil scientists must infer the depth to bedrock from vegetative cover, exposures, and landscape position. These inferences are often based on associated or anticipated, rather than confinned, depths to bedrock. Alternative field methods are needed to complement traditional soil survey tools and to improve the characterization of bedrock depths within soil map units. Electromagnetic induction (EMI) and ground-penetrating radar (GPR) have been used extensively for these purposes. These tools can provide soil scientists with a better understanding of soil depth and variability. Ground-penetrating radar has proven to be highly effective in the coarse-and moderately coarse-textured soils of eastern United States. In semiarid and arid regions of the United States, soluble salts ofK, Na, and less soluble carbonates ofCa and Mg are more likely to accumulate in the upper parts of soils. These salts produce high attenuation rates that restrict the radar's penetration depths and severely diminish its results (Doolittle and Collins, 1995). Electromagnetic induction uses electromagnetic energy to measure the apparent conductivity of earthen materials. Apparent conductivity is a weighted, average conductivity measurement for a column of earthen materials to a specific depth (Greenhouse and Slaine, 1983). Variations in apparent conductivity are caused by changes in the electrical conductivity of earthen materials. The electrical conductivity of soils is influenced by the type and concentration of ions in solution, the amount and type of clays in the soil matrix, the volumetric water content, and the temperature and phase of the soil water (McNeill, 1980). The apparent conductivity of soils increases with increased soluble salts, water, and/or clay contents (Kachanoski et aI., 1988; Rhoades et aI., 1976). Interpretations of EM I data are based on the identification of spatial patterns within data sets. Though seldom diagnostic in themselves, lateral and vertical variations in apparent conductivity are used to infer changes in soils and soil properties.
Understanding how bison behaved in the past can provide key insights for today's managers, ecolog... more Understanding how bison behaved in the past can provide key insights for today's managers, ecologists, and anthropologists. However, the direct application of both historic documentation and modern field observations may not provide the necessary insights for understanding bison behaviors in archeological and paleontological contexts. In order to develop a better understanding of possible behavior within these contexts, we have developed individual foraging histories for 22 Bison bison from the Glenrock Buffalo Jump assemblage of the Plains Late Prehistoric period in Wyoming and four Pleistocene B. priscus from the Ukraine. Incremental stable carbon isotopic values of dental enamel were used to determine foraging histories. The progressive development of enamel allows for samples to be selected that represent distinct periods of an individual's life. Comparison of these dietary patterns among members of a herd can demonstrate foraging behaviors of 25 26
urated soils (Patrick and Jugsujinda, 1992). The reduc- tion of Mn oxides before Fe oxides is con... more urated soils (Patrick and Jugsujinda, 1992). The reduc- tion of Mn oxides before Fe oxides is consistent with Manganese solubility has become a primary concern in the soils the theoretical redox potentials under which Mn oxides and water supplies in the Alamosa River basin, Colorado due to both crop toxicity problems and concentrations that exceed water quality vs. Fe oxides
Humans colonized Hawaii about 1200 years ago and have progressively modified vegetation, particul... more Humans colonized Hawaii about 1200 years ago and have progressively modified vegetation, particularly in mesic to dry tropical forests. We use δ 13 C to evaluate the contribution of C 3 and C 4 plants to deep soil organic matter to reconstruct pre-human contact vegetation patterns along a wet to dry climate transect on Kohala Mountain, Hawaii Island. Precontact vegetation assemblages fall into three distinct zones: a wet C 3 dominated closed canopy forest where annual rainfall is N 2000 mm, a dry C 4 dominated grassland with annual rainfall b 500 mm, and a broad transition zone between these communities characterized by either C 3 trees with higher water-use efficiency than the rainforest trees or C 3 trees with a small amount of C 4 grasses intermixed. The likelihood of C 4 grass understory decreases with increasing rainfall. We show that the total concentration of rock-derived nutrients in the b 2-mm soil fraction differs in each of these vegetation zones. Nutrient losses are driven by leaching at high rainfall and by plant cycling and wind erosion at low rainfall. By contrast, nutrients are best preserved in surface soils of the intermediate rainfall zone, where rainfall supports abundant plant growth but does not contribute large amounts of water in excess of evapotranspiration. Polynesian farmers exploited these naturally enriched soils as they intensified their upland agricultural systems during the last three centuries before European contact.
Silicon stable isotopes can be used to trace the biogeochemical pathways of Si as it moves from i... more Silicon stable isotopes can be used to trace the biogeochemical pathways of Si as it moves from its continental sources to its sink in ocean sediments. Along the way, Si is incorporated into clay minerals, taken up by plants where it forms plant opal, and leached into rivers, the major land-to-ocean conduit. Compared to igneous rocks, the waters that drain
Oxygen isotope ratios of pedogenic carbonates were analyzed along a climatic gradient in the Palo... more Oxygen isotope ratios of pedogenic carbonates were analyzed along a climatic gradient in the Palouse region of eastern Washington State to evaluate changes in their isotopic composition with changing climate. A modern analog approach was used to assess the relationship between the istotope ratios in the pedogenic carbonates with those in soil water (measured in June when we anticipated carbonate formation might occur because of low soil water content), and meteoric water from two National Atmospheric Deposition Program (NADP) sites adjacent to our sequence. Mean annual meteoric water δ18O values (wrt VSMOW) from the two NADP sites varied slightly with elevation, —13.9‰ at the Starkey site (elevation 1253 m) and —13.0‰ at the Palouse site, (elevation 766 m) but showed distinct seasonal trends with weighted means ranging from —11.9‰ during autumn to —15.0‰ during the winter. Carbonate δ18O (wrt VPDB) varied significantly with MAP, ranging from —14.1‰ at the most arid site to —11.4‰ at...
We are happy to welcome readers to the spring 2020 issue of the APA Newsletter on Teaching Philos... more We are happy to welcome readers to the spring 2020 issue of the APA Newsletter on Teaching Philosophy. This issue features one article on teaching, a review essay on C.D.C. Reeve's new translation of Aristotle's De Anima, poems by two philosophers, and a list of recently published books that will be of interest to philosophy instructors.
This study investigates the carbon isotope systematics of benzene, toluene, ethylbenzene, and xyl... more This study investigates the carbon isotope systematics of benzene, toluene, ethylbenzene, and xylene monoaromatic hydrocarbons (BTEX) with regard to an improved understanding of the behavior of these compounds in the subsurface, particularly during remediation processes. We found that fractionation eects due to vaporization are small and positive for all compounds studied (D 13 C vapor±liquid Q+0.2-), and that fractionation eects due to soil adsorption are also likely to be small ( 13 C-labeled compounds cannot be resolved from unlabeled compounds by HPLC). We also evaluated use of the isotopic composition of contaminants as tracers of source and migration in the subsurface by performing a survey of the bulk isotopic composition of commercially available sources of BTEX. The results indicate that a wide range of d 13 C values exist (e.g., benzene, À23.87-to À29.40-). Our work suggests that stable C isotope analysis has great potential for qualifying, and possibly quantifying, the subsurface processes aecting contaminant concentrations. In particular, stable isotope analysis may be especially bene®cial for monitoring the ecacy of abiological and biological remediation eorts. #
Carbon is sequestered in soils,by accumulation of recalcitrant organic matter and by bicarbonate ... more Carbon is sequestered in soils,by accumulation of recalcitrant organic matter and by bicarbonate weathering of silicate minerals. Carbon fixation by ecosystems helps drive Weathering processes in soii$ and that in turn diverts carbon from annuai photosynthesis-soii respiration cycling into the (ong-term geological oarbon cycle. To quantify rates of carbon transfer during soil development in moist temperate grassland and desert scrubland ecosystems, we measured organic and inorganic residues derived from the interaction of soii biota and siiicate minerai weathering for twenty-two soil profiles in arkosic sediments of differing ages. in moist temperate grasslands, net annual removal of carbon from the atmosphere by organic carbon accumulation and silicate weathering ranges from about 8.5 g m-z yrl for young soils to 0.7 g m-z yrl for old soils. in desert scrublands, net annual carbon removal is about 0.2 g m-z yr-1 for young soils and 0.01 g m-z yr-1 for old soils. in soils of both ecosystems, organic carbon accumulation exceeds C02 removal by weathering. However, as soils age, rates of C02 consumption by weathering accounts for greater amounts of carbon sequestration, increasing from 2% to 8% in the grassland soils and from 29f0 to 40%'o in the scrubland soils. in soils of desert scrublands, carbonate accumulation far outstrips organic carbon accumulation, but about 909'oof this mass is derived from aerosolic sources that do not contribute to iong-term sequestration of atmospheric carbon dioxide.
ABSTRACT Background/Question/Methods The contemporary landscapes of the short-grass steppe ecosys... more ABSTRACT Background/Question/Methods The contemporary landscapes of the short-grass steppe ecosystem possess a remarkably diverse soil mantle. While spatial heterogeneity does indeed exist among soils in the short-grass steppe, the combined effects of vegetation and climate have created a uniquely spatial homogenous soil-landscape mosaic when compared to soil of other ecosystems. We identified dominate soil conditioning variables (state factors, Jenny1940) by combining Soil Survey Geographic data with geologic, geomorphic, and elevation data in northeastern Colorado, therefore isolating geographic areas where contributions of single state factor outrank the combined contribution of other factors. In water limited systems areas such as the short-grass steppe, three broad phases of soil development can be identified according to landscape age that we believe to be ecologically and biogeochemically significant. Results/Conclusions In a similar fashion to Vitousek et al (2008) we identified and characterized functional pedologic phases within water limited SGS ecosystems in which soils are either 1) Aggrading or Building with regard to soil development, 2) are in an Intermediate or Equilibrium stage of soil development, and 3) Degrading or Declining in terms of soil development. This geographic approach to modeling pedologic and ecohydrologic dynamics identify regions where soil capacity to store water and nutrients at a relative maximum and are used as the basis for assessing ecosystem vulnerability.
Page 1. http://bul.sagepub.com/ NASSP Bulletin http://bul.sagepub.com/content/74/ 523/103.citatio... more Page 1. http://bul.sagepub.com/ NASSP Bulletin http://bul.sagepub.com/content/74/ 523/103.citation The online version of this article can be found at: DOI: 10.1177/019263659007452316 1990 74: 103 NASSP Bulletin Eugene ...
Isotopic analysis of soil water requires complete extraction of water from the soil matrix to ens... more Isotopic analysis of soil water requires complete extraction of water from the soil matrix to ensure against isotopic fractionation. A variant of the standard CO2–water equilibration technique avoids distillation of soil water that can cause isotopic fractionation. Reproducibility of direct equilibration is between 0.3‰ and 0.4‰. Longer equilibration times are necessary for soil with a fine particle size distribution and/or low water content than for standard CO2–water equilibrations. Differences in the δ18O value between unsterilized and sterilized (by γ-radiation) sample pairs suggests that respiration can contribute to changing the δ18O value of soil water. Measured δ18O values of samples prepared by adding water with a known δ18O value to dry soil increase with increasing water content and are always more negative than the δ18O value of the added water, especially at low water contents. The combination of contamination by residual water, heterogeneities due to difficulty with physical mixing of the sample, possible kinetic fractionations when small amounts of water are added to dry soil, contribute to these trends. These tests suggest that direct equilibration is a quick and relatively easy approach for measuring the δ18O value of soil water.
This paper is centered on the specific effects of plants on the soil weathering environment; we a... more This paper is centered on the specific effects of plants on the soil weathering environment; we attempt to address how to quantify this component of the ecosystem and assess feedbacks between plants and weathering processes that influence the degree and rates of mineral weathering. The basic processes whereby plants directly influence the soil chemical environment is through the generation of weathering agents, biocycling of cations, and the production of biogenic minerals. Plants may indirectly influence soil processes through the ...
Abstract Terrestrial silicate weathering rates and processes are important for studies of modern ... more Abstract Terrestrial silicate weathering rates and processes are important for studies of modern and paleo-climate. Recently, Si isotope geochemistry has shed light on Si cycling in marine systems, which is directly linked to the terrestrial Si cycle as nearly 80% of the Si is supplied by continental run-off water. Understanding the terrestrial Si-isotope geochemistry is crucial for a more comprehensive understanding of the global Si cycle. Weathering of primary minerals in the pedosphere releases Si that can be incorporated into secondary ...
Abstract Over geologic timescales, biologically mediated weathering processes influence atmospher... more Abstract Over geologic timescales, biologically mediated weathering processes influence atmospheric CO2 content and global climate because the net effect of silicate weathering is the transfer of atmospheric CO2 to HCO-3 These weathering processes further influence atmospheric CO2 due to a net transfer of dissolved silica to the oceans which promotes diatom production and sedimentation there by adding carbon to the oceanic reservoir. There is a substantial body of evidence that suggests that plants may transform silica into more ...
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