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Peter Finke - One of the best experts on this subject based on the ideXlab platform.
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Evaluating sensitivity of silicate mineral dissolution rates to Physical Weathering using a soil evolution model (SoilGen2.25)
Biogeosciences, 2015Co-Authors: Emmanuel Opolot, Peter FinkeAbstract:Silicate mineral dissolution rates depend on the interaction of a number of factors categorized either as intrinsic (e.g. mineral surface area, mineral composition) or extrinsic (e.g. climate, hydrology, biological factors, Physical Weathering). Estimating the integrated effect of these factors on the silicate mineral dissolution rates therefore necessitates the use of fully mechanistic soil evolution models. This study applies a mechanistic soil evolution model (SoilGen) to explore the sensitivity of silicate mineral dissolution rates to the integrated effect of other soil-forming processes and factors. The SoilGen soil evolution model is a 1-D model developed to simulate the time-depth evolution of soil properties as a function of various soil-forming processes (e.g. water, heat and solute transport, chemical and Physical Weathering, clay migration, nutrient cycling, and bioturbation) driven by soil-forming factors (i.e., climate, organisms, relief, parent material). Results from this study show that although soil solution chemistry (pH) plays a dominant role in determining the silicate mineral dissolution rates, all processes that directly or indirectly influence the soil solution composition play an equally important role in driving silicate mineral dissolution rates. Model results demonstrated a decrease of silicate mineral dissolution rates with time, an obvious effect of texture and an indirect but substantial effect of Physical Weathering on silicate mineral dissolution rates. Results further indicated that clay migration and plant nutrient recycling processes influence the pH and thus the silicate mineral dissolution rates. Our silicate mineral dissolution rates results fall between field and laboratory rates but were rather high and more close to the laboratory rates possibly due to the assumption of far from equilibrium reaction used in our dissolution rate mechanism. There is therefore a need to include secondary mineral precipitation mechanism in our formulation. In addition, there is a need for a more detailed study that is specific to field sites with detailed measurements of silicate mineral dissolution rates, climate, hydrology, and mineralogy to enable the calibration and validation of the model. Nevertheless, this study is another important step to demonstrate the critical need to couple different soil-forming processes with chemical Weathering in order to explain differences observed between laboratory and field measured silicate mineral dissolution rates.
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Sensitivity of mineral dissolution rates to Physical Weathering : a modeling approach
The EGU General Assembly, 2015Co-Authors: Emmanuel Opolot, Peter FinkeAbstract:There is continued interest on accurate estimation of natural Weathering rates owing to their importance in soil formation, nutrient cycling, estimation of acidification in soils, rivers and lakes, and in understanding the role of silicate Weathering in carbon sequestration. At the same time a challenge does exist to reconcile discrepancies between laboratory-determined Weathering rates and natural Weathering rates. Studies have consistently reported laboratory rates to be in orders of magnitude faster than the natural Weathering rates (White, 2009). These discrepancies have mainly been attributed to (i) changes in fluid composition (ii) changes in primary mineral surfaces (reactive sites) and (iii) the formation of secondary phases; that could slow natural Weathering rates. It is indeed difficult to measure the interactive effect of the intrinsic factors (e.g. mineral composition, surface area) and extrinsic factors (e.g. solution composition, climate, bioturbation) occurring at the natural setting, in the laboratory experiments. A modeling approach could be useful in this case. A number of geochemical models (e.g. PHREEQC, EQ3/EQ6) already exist and are capable of estimating mineral dissolution / precipitation rates as a function of time and mineral mass. However most of these approaches assume a constant surface area in a given volume of water (White, 2009). This assumption may become invalid especially at long time scales. One of the widely used Weathering models is the PROFILE model (Sverdrup and Warfvinge, 1993). The PROFILE model takes into account the mineral composition, solution composition and surface area in determining dissolution / precipitation rates. However there is less coupling with other processes (e.g. Physical Weathering, clay migration, bioturbation) which could directly or indirectly influence dissolution / precipitation rates. We propose in this study a coupling between chemical Weathering mechanism (defined as a function of reactive area, solution composition, temperature, mineral composition) and the Physical Weathering module in the SoilGen model which calculates the evolution of particle size (used for surface area calculation) as influenced by temperature gradients. The solution composition in the SoilGen model is also influenced by other processes such as atmospheric inputs, organic matter decomposition, cation exchange, secondary mineral formation and leaching. We then apply this coupled mechanism on a case study involving 3 loess soil profiles to analyze the sensitivity of mineral Weathering rates to Physical Weathering. Initial results show some sensitivity but not that dramatic. The less sensitivity was attributed to dominance of resistant primary minerals (> 70% quartz). Scenarios with different sets of mineralogy will be tested and sensitivity results in terms of silicate mineral dissolution rates and CO2-consumption will be presented in the conference. References Sverdrup H and Warfvinge P., 1993. Calculating field Weathering rates using a mechanistic geochemical model PROFILE. Applied Geochemistry, 8:273-283. White, A.F., 2009. Natural Weathering rates of silicate minerals. In: Drever, J.I. (Ed.), Surface and Ground Water, Weathering and Soils. In: Holland, H.D., Turekian, K.K. (Eds.), Treatise on Geochemistry. vol. 5. Elsevier-Pergamon, Oxford, pp. 133–168.
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Towards an improved modeling of chemical Weathering in the SoilGen soil evolution model
The EGU General Assembly, 2014Co-Authors: Emmanuel Opolot, Peter FinkeAbstract:As the need for soil information particularly in the fields of agriculture, land evaluation, hydrology, biogeochemistry and climate change keeps increasing, models for soil evolution are increasingly becoming valuable tools to provide such soil information. Although still limited, such models are progressively being developed. The SoilGen model is one of such models with capabilities to provide soil information such as soil texture, pH, base saturation, organic carbon, CEC, etc over multi-millennia time scale. SoilGen is a mechanistic water flow driven pedogenetic model describing soil forming processes such as carbon cycling, clay migration, decalcification, bioturbation, Physical Weathering and chemical Weathering. The model has been calibrated and confronted with field measurements in a number of case studies, giving plausible results. Discrepancies between measured and simulated soil properties as concluded from case studies have been mainly attributed to (i) the simple chemical Weathering system (ii) poor estimates of initial data inputs such as bulk density and element fluxes, and (iii) incorrect values of variables that describe boundary conditions such as precipitation and potential evapotranspiration. This study focuses on extending the chemical Weathering system, such that it can deal with a more heterogeneous composition of primary minerals and includes more elements such as Fe and Si. We propose and discuss here an extended description of chemical Weathering in the model that is based on more primary minerals, taking into account the role of the specific area of these minerals, and the effect of Physical Weathering on these specific areas over time. In the initial stage, the proposed chemical Weathering mechanism is also implemented in PHREEQC (a widely applied geochemical code with capabilities to simulate equilibrium reactions involving water and minerals, surface complexes and ion exchangers, etc.) to facilitate comparison with the model results. Results of both modeling approaches are comparable. There is however need to confront such test results with measurements.
Byong Kwon Park - One of the best experts on this subject based on the ideXlab platform.
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chemical and Physical Weathering in south patagonian rivers a combined sr u be isotope approach
Geochimica et Cosmochimica Acta, 2013Co-Authors: Borom Lee, Yeongcheol Han, Youngsook Huh, Craig C. Lundstrom, Lionel Siame, Jong Ik Lee, Byong Kwon ParkAbstract:Abstract We investigated Physical and chemical Weathering in south Patagonia, encompassing both the tectonically active Andes with alpine glaciers and the quiescent seaboard plain with arid climate. Chemical denudation rates determined from riverine dissolved major elements were (0.07–5) × 10 5 tons year −1 , and the long-term rates of CO 2 consumption by alkaline earth silicates were (0.03–0.5) × 10 5 mol km −2 year −1 , commensurate with the average global CO 2 consumption rate (0.25 × 10 5 mol km −2 year −1 ). Unradiogenic strontium isotope ratios indicated that the source of silicate Weathering was volcanic sedimentary cover. Basin average total denudation rates based on 10 Be measured in active streambed sediments ranged from 0.009 to 0.6 mm year −1 . Uranium series disequilibria suggested that there is significant redistribution of nuclides between the dissolved and suspended material. When applying the simultaneous gain and loss model to the U-series data of the suspended load, sediment residence times of 10–150 ky were obtained. Comparison of the dissolved load-based chemical denudation rate and 10 Be-based total denudation rate revealed that some basins are dominated by chemical and some by Physical denudation.
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Chemical and Physical Weathering in south Patagonian rivers: A combined Sr–U–Be isotope approach
Geochimica et Cosmochimica Acta, 2013Co-Authors: Borom Lee, Yeongcheol Han, Youngsook Huh, Craig C. Lundstrom, Lionel Siame, Jong Ik Lee, Byong Kwon ParkAbstract:Abstract We investigated Physical and chemical Weathering in south Patagonia, encompassing both the tectonically active Andes with alpine glaciers and the quiescent seaboard plain with arid climate. Chemical denudation rates determined from riverine dissolved major elements were (0.07–5) × 10 5 tons year −1 , and the long-term rates of CO 2 consumption by alkaline earth silicates were (0.03–0.5) × 10 5 mol km −2 year −1 , commensurate with the average global CO 2 consumption rate (0.25 × 10 5 mol km −2 year −1 ). Unradiogenic strontium isotope ratios indicated that the source of silicate Weathering was volcanic sedimentary cover. Basin average total denudation rates based on 10 Be measured in active streambed sediments ranged from 0.009 to 0.6 mm year −1 . Uranium series disequilibria suggested that there is significant redistribution of nuclides between the dissolved and suspended material. When applying the simultaneous gain and loss model to the U-series data of the suspended load, sediment residence times of 10–150 ky were obtained. Comparison of the dissolved load-based chemical denudation rate and 10 Be-based total denudation rate revealed that some basins are dominated by chemical and some by Physical denudation.
Emmanuel Opolot - One of the best experts on this subject based on the ideXlab platform.
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Evaluating sensitivity of silicate mineral dissolution rates to Physical Weathering using a soil evolution model (SoilGen2.25)
Biogeosciences, 2015Co-Authors: Emmanuel Opolot, Peter FinkeAbstract:Silicate mineral dissolution rates depend on the interaction of a number of factors categorized either as intrinsic (e.g. mineral surface area, mineral composition) or extrinsic (e.g. climate, hydrology, biological factors, Physical Weathering). Estimating the integrated effect of these factors on the silicate mineral dissolution rates therefore necessitates the use of fully mechanistic soil evolution models. This study applies a mechanistic soil evolution model (SoilGen) to explore the sensitivity of silicate mineral dissolution rates to the integrated effect of other soil-forming processes and factors. The SoilGen soil evolution model is a 1-D model developed to simulate the time-depth evolution of soil properties as a function of various soil-forming processes (e.g. water, heat and solute transport, chemical and Physical Weathering, clay migration, nutrient cycling, and bioturbation) driven by soil-forming factors (i.e., climate, organisms, relief, parent material). Results from this study show that although soil solution chemistry (pH) plays a dominant role in determining the silicate mineral dissolution rates, all processes that directly or indirectly influence the soil solution composition play an equally important role in driving silicate mineral dissolution rates. Model results demonstrated a decrease of silicate mineral dissolution rates with time, an obvious effect of texture and an indirect but substantial effect of Physical Weathering on silicate mineral dissolution rates. Results further indicated that clay migration and plant nutrient recycling processes influence the pH and thus the silicate mineral dissolution rates. Our silicate mineral dissolution rates results fall between field and laboratory rates but were rather high and more close to the laboratory rates possibly due to the assumption of far from equilibrium reaction used in our dissolution rate mechanism. There is therefore a need to include secondary mineral precipitation mechanism in our formulation. In addition, there is a need for a more detailed study that is specific to field sites with detailed measurements of silicate mineral dissolution rates, climate, hydrology, and mineralogy to enable the calibration and validation of the model. Nevertheless, this study is another important step to demonstrate the critical need to couple different soil-forming processes with chemical Weathering in order to explain differences observed between laboratory and field measured silicate mineral dissolution rates.
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Evaluating sensitivity of silicate mineral dissolution rates to Physical Weathering using a soil evolution model (SoilGen2.25)
Biogeosciences Discussions, 2015Co-Authors: Emmanuel Opolot, P. A. FinkeAbstract:Abstract. Silicate mineral dissolution rates depend on the interaction of a number of factors categorized either as intrinsic (e.g. mineral surface area, mineral composition) or extrinsic (e.g. climate, hydrology, biological factors, Physical Weathering). Estimating the integrated effect of these factors on the silicate mineral dissolution rates therefore necessitates the use of fully mechanistic soil evolution models. This study applies a mechanistic soil evolution model (SoilGen) to explore the sensitivity of silicate mineral dissolution rates to the integrated effect of other soil forming processes and factors. The SoilGen soil evolution model is a 1-D model developed to simulate the time-depth evolution of soil properties as a function of various soil forming processes (e.g. water, heat and solute transport, chemical and Physical Weathering, clay migration, nutrient cycling and bioturbation) driven by soil forming factors (i.e., climate, organisms, relief, parent material). Results from this study show that although soil solution chemistry (pH) plays a dominant role in determining the silicate mineral dissolution rates, all processes that directly or indirectly influence the soil solution composition equally play an important role in driving silicate mineral dissolution rates. Model results demonstrated a decrease of silicate mineral dissolution rates with time, an obvious effect of texture and an indirect but substantial effect of Physical Weathering on silicate mineral dissolution rates. Results further indicated that clay migration and plant nutrient recycling processes influence the pH and thus the silicate mineral dissolution rates. Our silicate mineral dissolution rates results fall between field and laboratory rates but were rather high and more close to the laboratory rates owing to the assumption of far from equilibrium reaction used in our dissolution rate mechanism. There is therefore need to include secondary mineral precipitation mechanism in our formulation. In addition, there is need for a more detailed study that is specific to field sites with detailed measurements of silicate mineral dissolution rates, climate, hydrology and mineralogy to enable the calibration and validation of the model. Nevertheless, this study is another important step to demonstrate the critical need to couple different soil forming processes with chemical Weathering in order to explain differences observed between laboratory and field measured silicate mineral dissolution rates.
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Sensitivity of mineral dissolution rates to Physical Weathering : a modeling approach
The EGU General Assembly, 2015Co-Authors: Emmanuel Opolot, Peter FinkeAbstract:There is continued interest on accurate estimation of natural Weathering rates owing to their importance in soil formation, nutrient cycling, estimation of acidification in soils, rivers and lakes, and in understanding the role of silicate Weathering in carbon sequestration. At the same time a challenge does exist to reconcile discrepancies between laboratory-determined Weathering rates and natural Weathering rates. Studies have consistently reported laboratory rates to be in orders of magnitude faster than the natural Weathering rates (White, 2009). These discrepancies have mainly been attributed to (i) changes in fluid composition (ii) changes in primary mineral surfaces (reactive sites) and (iii) the formation of secondary phases; that could slow natural Weathering rates. It is indeed difficult to measure the interactive effect of the intrinsic factors (e.g. mineral composition, surface area) and extrinsic factors (e.g. solution composition, climate, bioturbation) occurring at the natural setting, in the laboratory experiments. A modeling approach could be useful in this case. A number of geochemical models (e.g. PHREEQC, EQ3/EQ6) already exist and are capable of estimating mineral dissolution / precipitation rates as a function of time and mineral mass. However most of these approaches assume a constant surface area in a given volume of water (White, 2009). This assumption may become invalid especially at long time scales. One of the widely used Weathering models is the PROFILE model (Sverdrup and Warfvinge, 1993). The PROFILE model takes into account the mineral composition, solution composition and surface area in determining dissolution / precipitation rates. However there is less coupling with other processes (e.g. Physical Weathering, clay migration, bioturbation) which could directly or indirectly influence dissolution / precipitation rates. We propose in this study a coupling between chemical Weathering mechanism (defined as a function of reactive area, solution composition, temperature, mineral composition) and the Physical Weathering module in the SoilGen model which calculates the evolution of particle size (used for surface area calculation) as influenced by temperature gradients. The solution composition in the SoilGen model is also influenced by other processes such as atmospheric inputs, organic matter decomposition, cation exchange, secondary mineral formation and leaching. We then apply this coupled mechanism on a case study involving 3 loess soil profiles to analyze the sensitivity of mineral Weathering rates to Physical Weathering. Initial results show some sensitivity but not that dramatic. The less sensitivity was attributed to dominance of resistant primary minerals (> 70% quartz). Scenarios with different sets of mineralogy will be tested and sensitivity results in terms of silicate mineral dissolution rates and CO2-consumption will be presented in the conference. References Sverdrup H and Warfvinge P., 1993. Calculating field Weathering rates using a mechanistic geochemical model PROFILE. Applied Geochemistry, 8:273-283. White, A.F., 2009. Natural Weathering rates of silicate minerals. In: Drever, J.I. (Ed.), Surface and Ground Water, Weathering and Soils. In: Holland, H.D., Turekian, K.K. (Eds.), Treatise on Geochemistry. vol. 5. Elsevier-Pergamon, Oxford, pp. 133–168.
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Towards an improved modeling of chemical Weathering in the SoilGen soil evolution model
The EGU General Assembly, 2014Co-Authors: Emmanuel Opolot, Peter FinkeAbstract:As the need for soil information particularly in the fields of agriculture, land evaluation, hydrology, biogeochemistry and climate change keeps increasing, models for soil evolution are increasingly becoming valuable tools to provide such soil information. Although still limited, such models are progressively being developed. The SoilGen model is one of such models with capabilities to provide soil information such as soil texture, pH, base saturation, organic carbon, CEC, etc over multi-millennia time scale. SoilGen is a mechanistic water flow driven pedogenetic model describing soil forming processes such as carbon cycling, clay migration, decalcification, bioturbation, Physical Weathering and chemical Weathering. The model has been calibrated and confronted with field measurements in a number of case studies, giving plausible results. Discrepancies between measured and simulated soil properties as concluded from case studies have been mainly attributed to (i) the simple chemical Weathering system (ii) poor estimates of initial data inputs such as bulk density and element fluxes, and (iii) incorrect values of variables that describe boundary conditions such as precipitation and potential evapotranspiration. This study focuses on extending the chemical Weathering system, such that it can deal with a more heterogeneous composition of primary minerals and includes more elements such as Fe and Si. We propose and discuss here an extended description of chemical Weathering in the model that is based on more primary minerals, taking into account the role of the specific area of these minerals, and the effect of Physical Weathering on these specific areas over time. In the initial stage, the proposed chemical Weathering mechanism is also implemented in PHREEQC (a widely applied geochemical code with capabilities to simulate equilibrium reactions involving water and minerals, surface complexes and ion exchangers, etc.) to facilitate comparison with the model results. Results of both modeling approaches are comparable. There is however need to confront such test results with measurements.
Cornelia Rumpel - One of the best experts on this subject based on the ideXlab platform.
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Effect of Physical Weathering on the carbon sequestration potential of biochars and hydrochars in soil
Global Change Biology - Bioenergy, 2015Co-Authors: Christophe Naisse, Cyril Girardin, Romain Lefevre, Alessandro Pozzi, Robert Maas, Arne Stark, Cornelia RumpelAbstract:Physical Weathering can modify the stability of biochar after field exposure. The aim of our study was to determine the potential carbon sequestration of the two chars at different timescales. We investigated the modification in composition and stability resulting from Physical Weathering of two different chars produced (i) at low temperature (250 degrees C) by hydrothermal carbonization (HTC); and (ii) at high temperature (1200 degrees C) by gasification (GS) using contrasting feedstocks. Physical Weathering of HTC and GS placed on a water permeable canvas was performed through successive wetting/drying and freezing/thawing cycles. Carbon loss was assessed by mass balance. Chemical stability of the remaining material was evaluated as resistance to acid dichromate oxidation, and biological stability was assessed during laboratory incubation. Moreover, we assessed modification in potential priming effects due to Physical Weathering. Physical Weathering induced a carbon loss ranging between 10 and 40% of the total C mass depending on the feedstock. This C loss is most probably related to leaching of small particulate and dissolved compounds. GS produced from maize silage showed the highest C loss. The chemical stability of HTC and GS was unaffected by Physical Weathering. In contrast, Physical Weathering strongly increased the biological stability of HTC and GS char produced from maize silage. After Physical Weathering, the half-life (t(1/2)) of GS was doubled but only slight increase was noted for those of HTC. During the first weeks of incubation, HTC addition to soil stimulated native soil organic matter (SOM) mineralization (positive priming effect), while the GS addition led to protection of the native SOM against biologic degradation (negative priming effect). Physical Weathering led to reduction in these priming effects. Model extrapolations based on our data showed that decadal C sequestration potential of GS and HTC is globally equivalent when all losses including those due to priming and Physical Weathering were taken into account. However, at century scale only GS may have the potential to increase soil C storage.
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Effect of Physical Weathering on the carbon sequestration potential of biochars and hydrochars in soil.
GCB Bioenergy, 2014Co-Authors: Christophe Naisse, Cyril Girardin, Romain Lefevre, Alessandro Pozzi, Robert Maas, Arne Stark, Cornelia RumpelAbstract:Physical Weathering can modify the stability of biochar after field exposure. The aim of our study was to determine the potential carbon sequestration of the two chars at different timescales. We investigated the modification in composition and stability resulting from Physical Weathering of two different chars produced (i) at low temperature (250 °C) by hydrothermal carbonization (HTC); and (ii) at high temperature (1200 °C) by gasification (GS) using contrasting feedstocks. Physical Weathering of HTC and GS placed on a water permeable canvas was performed through successive wetting/drying and freezing/thawing cycles. Carbon loss was assessed by mass balance. Chemical stability of the remaining material was evaluated as resistance to acid dichromate oxidation, and biological stability was assessed during laboratory incubation. Moreover, we assessed modification in potential priming effects due to Physical Weathering. Physical Weathering induced a carbon loss ranging between 10 and 40% of the total C mass depending on the feedstock. This C loss is most probably related to leaching of small particulate and dissolved compounds. GS produced from maize silage showed the highest C loss. The chemical stability of HTC and GS was unaffected by Physical Weathering. In contrast, Physical Weathering strongly increased the biological stability of HTC and GS char produced from maize silage. After Physical Weathering, the half-life (t1/2) of GS was doubled but only slight increase was noted for those of HTC. During the first weeks of incubation, HTC addition to soil stimulated native soil organic matter (SOM) mineralization (positive priming effect), while the GS addition led to protection of the native SOM against biologic degradation (negative priming effect). Physical Weathering led to reduction in these priming effects. Model extrapolations based on our data showed that decadal C sequestration potential of GS and HTC is globally equivalent when all losses including those due to priming and Physical Weathering were taken into account. However, at century scale only GS may have the potential to increase soil C storage.
Candace E. Martin - One of the best experts on this subject based on the ideXlab platform.
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chemical and Physical Weathering in new zealand s southern alps monitored by bedload sediment major element composition
Applied Geochemistry, 2007Co-Authors: Christopher Q. Kautz, Candace E. MartinAbstract:Abstract The Haast and Clutha rivers drain opposing flanks of New Zealand’s Southern Alps. Major element analyses of grain size fractions (2–1 mm, 1 mm–355 μm, 355–63 μm, and 2 O 5 concentrations in all river sediment suggests that most CaO is bound in a combination of phosphate-bearing minerals such as apatite along with other heavy mineral phases with similar hydrodynamic properties (e.g. epidote). Chemical index of alteration (CIA) values for grain size fractions from both rivers are similar (Haast: 54–63, Clutha: 49–61) and do not systematically vary with grain size or sample location. Al 2 O 3 –CaO ∗ + Na 2 O–K 2 O (A–CN–K) relationships suggest that CIA values are controlled by albite–muscovite mixing rather than feldspar Weathering. Both A–CN–K relationships and modal mineralogical calculations from Clutha river samples indicate progressive downstream attrition of muscovite from coarser to finer grain size fractions. In contrast, Haast river sediments display less variable normative muscovite concentrations and no downstream enrichment/depletion trends. The Haast and Clutha watersheds have drastically different sediment yields, but the similarity of sediments from both rivers indicates that there is minimal climatic control on the Weathering intensity of fluvial sediments. Rather, bedload geochemistry is controlled primarily by mechanical breakdown of lithic fragments and subsequent preferential attrition of muscovite > albite > quartz. The geochemical signature of mechanical attrition and hydrodynamic winnowing is more developed in Clutha river samples because of longer sediment residence time within its fluvial system. These findings suggest that high standing island (HSI) fluvial sedimentary evolution is characterized by the dominance of Physical Weathering processes and the absence of silicate chemical Weathering signatures.
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Chemical and Physical Weathering in New Zealand's Southern Alps monitored by bedload sediment major element composition
2007Co-Authors: Christopher Q. Kautz, Candace E. MartinAbstract:The Haast and Clutha rivers drain opposing flanks of New Zealand's Southern Alps. Major element analyses of grain size fractions (2-1 mm, 1 mm-355 μm, 355-63 μm, and albite > quartz. The geochemical signature of mechanical attrition and hydrodynamic winnowing is more developed in Clutha river samples because of longer sediment residence time within its fluvial system. These findings suggest that high standing island (HSI) fluvial sedimentary evolution is characterized by the dominance of Physical Weathering processes and the absence of silicate chemical Weathering signatures.
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Chemical and Physical Weathering in New Zealand’s Southern Alps monitored by bedload sediment major element composition
Applied Geochemistry, 2007Co-Authors: Christopher Q. Kautz, Candace E. MartinAbstract:Abstract The Haast and Clutha rivers drain opposing flanks of New Zealand’s Southern Alps. Major element analyses of grain size fractions (2–1 mm, 1 mm–355 μm, 355–63 μm, and 2 O 5 concentrations in all river sediment suggests that most CaO is bound in a combination of phosphate-bearing minerals such as apatite along with other heavy mineral phases with similar hydrodynamic properties (e.g. epidote). Chemical index of alteration (CIA) values for grain size fractions from both rivers are similar (Haast: 54–63, Clutha: 49–61) and do not systematically vary with grain size or sample location. Al 2 O 3 –CaO ∗ + Na 2 O–K 2 O (A–CN–K) relationships suggest that CIA values are controlled by albite–muscovite mixing rather than feldspar Weathering. Both A–CN–K relationships and modal mineralogical calculations from Clutha river samples indicate progressive downstream attrition of muscovite from coarser to finer grain size fractions. In contrast, Haast river sediments display less variable normative muscovite concentrations and no downstream enrichment/depletion trends. The Haast and Clutha watersheds have drastically different sediment yields, but the similarity of sediments from both rivers indicates that there is minimal climatic control on the Weathering intensity of fluvial sediments. Rather, bedload geochemistry is controlled primarily by mechanical breakdown of lithic fragments and subsequent preferential attrition of muscovite > albite > quartz. The geochemical signature of mechanical attrition and hydrodynamic winnowing is more developed in Clutha river samples because of longer sediment residence time within its fluvial system. These findings suggest that high standing island (HSI) fluvial sedimentary evolution is characterized by the dominance of Physical Weathering processes and the absence of silicate chemical Weathering signatures.