The Experts below are selected from a list of 204 Experts worldwide ranked by ideXlab platform

Lynn M Walter - One of the best experts on this subject based on the ideXlab platform.

  • mineral weathering rates in Glacial Drift soils sw michigan usa new constraints from seasonal sampling of waters and gases at soil monoliths
    Chemical Geology, 2008
    Co-Authors: Lixin Jin, Stephen K Hamilton, Lynn M Walter
    Abstract:

    Abstract Soil solutions and gases were sampled along 200 cm deep soil profiles from four instrumented soil monoliths in southwest Michigan, established on coarse-grained Glacial Drift deposits. Seasonal sampling enabled evaluation of thermodynamic versus kinetic controls on carbonate- and silicate-mineral weathering rates, allowing better integration with past field hydrogeochemical studies of Michigan soil and surface water systems. Silicate-weathering products dominate water chemistry in the upper soil zones. Carbonate minerals, comprised of subequal amounts of calcite and dolomite, are only present at depths below 150 cm. When present, carbonate dissolution is rapid and soil water Ca 2+ and Mg 2+ concentrations increase dramatically as observed in other natural soil study sites in southern Michigan. Soil water saturation states are near equilibrium with respect to calcite and slightly less saturated with respect to dolomite. The divalent cations of soil waters and soil CO 2 both show a seasonal trend, with concentration maxima occurring in September and minima in April, suggesting that soil water Ca 2+ and Mg 2+ concentrations are under equilibrium control with carbonate solubility limited by temperature-dependent pCO 2 rather than by direct effects of temperatures. Importantly, monolith soil water Mg 2+ /Ca 2+ and calcite and dolomite saturation states are lower than those of streams in the same watershed and also lower than those of soil waters in other Michigan watersheds. Because carbonate weight percentages and chemical compositions in these sites are similar, this difference likely reflects the short exposure path (thus short residence time) of soil waters to carbonate-rich horizons in the monoliths. The dissolution reactions of primary aluminosilicate minerals are incongruent with respect to Al and Si due to kaolinite formation. However, major cations (Ca 2+ , Mg 2+ , K + and Na + ) are stoichiometrically released from silicate dissolution. Na ⁎ (soil water Na + after correction for atmospheric input and derived primarily from plagioclase weathering) exhibits much less seasonality than divalent cations, with only slight elevations observed in the summer months. Soil water H 4 SiO 4 0 concentrations show seasonal variations similar to the divalent cations, but are determined by the balance between production (silicate-mineral dissolution) and consumption (kaolinite precipitation). Plagioclase and amphibole are below saturation, and these dissolution reactions must be kinetically controlled. Through a conservative tracer study, about 15% to 45% of applied Br passed out of the monolith profiles in 40–160 days and this long mineral–water contact time is especially important for slow reactions such as silicate dissolution. Based on water chemistry and discharge, bulk reaction rates of calcite, dolomite (Ca 0.5 Mg 0.5 CO 3 ), K-feldspar and plagioclase are calculated to be at 3400, 3100, 220, and 320 mol ha − 1 yr − 1 , respectively. Based on mass balance of soil composition, long-term plagioclase-weathering rates (over the past 12,500 years) are calculated at about 2400 mol ha − 1 yr − 1 , much higher than the current rates. This agrees with previous conclusions that weathering rates decrease with time, due to loss of reactive mineral surfaces. Furthermore, both long-term and short-term plagioclase dissolution rates in Michigan are relatively high compared to those in other watersheds with similar age, possibly due to fresh surfaces produced by glaciation, in combination with the high discharge and high plagioclase abundances.

  • silicate and carbonate mineral weathering in soil profiles developed on pleistocene Glacial Drift michigan usa mass balances based on soil water geochemistry
    Geochimica et Cosmochimica Acta, 2008
    Co-Authors: Erika L Williams, Kathryn Szramek, Lynn M Walter, Stephen K Hamilton
    Abstract:

    Abstract Geochemistry of soil, soil water, and soil gas was characterized in representative soil profiles of three Michigan watersheds. Because of differences in source regions, parent materials in the Upper Peninsula of Michigan (the Tahquamenon watershed) contain only silicates, while those in the Lower Peninsula (the Cheboygan and the Huron watersheds) have significant mixtures of silicate and carbonate minerals. These differences in soil mineralogy and climate conditions permit us to examine controls on carbonate and silicate mineral weathering rates and to better define the importance of silicate versus carbonate dissolution in the early stage of soil–water cation acquisition. Soil waters of the Tahquamenon watershed are the most dilute; solutes reflect amphibole and plagioclase dissolution along with significant contributions from atmospheric precipitation sources. Soil waters in the Cheboygan and the Huron watersheds begin their evolution as relatively dilute solutions dominated by silicate weathering in shallow carbonate-free soil horizons. Here, silicate dissolution is rapid and reaction rates dominantly are controlled by mineral abundances. In the deeper soil horizons, silicate dissolution slows down and soil–water chemistry is dominated by calcite and dolomite weathering, where solutions reach equilibrium with carbonate minerals within the soil profile. Thus, carbonate weathering intensities are dominantly controlled by annual precipitation, temperature and soil p CO 2 . Results of a conceptual model support these field observations, implying that dolomite and calcite are dissolving at a similar rate, and further dissolution of more soluble dolomite after calcite equilibrium produces higher dissolved inorganic carbon concentrations and a Mg 2+ /Ca 2+ ratio of 0.4. Mass balance calculations show that overall, silicate minerals and atmospheric inputs generally contribute 2+ and Mg 2+ in natural waters. Dolomite dissolution appears to be a major process, rivaling calcite dissolution as a control on divalent cation and inorganic carbon contents of soil waters. Furthermore, the fraction of Mg 2+ derived from silicate mineral weathering is much smaller than most of the values previously estimated from riverine chemistry.

  • relative weathering intensity of calcite versus dolomite in carbonate bearing temperate zone watersheds carbonate geochemistry and fluxes from catchments within the st lawrence and danube river basins
    Geochemistry Geophysics Geosystems, 2007
    Co-Authors: Erika L Williams, Kathryn Szramek, Jennifer C Mcintosh, Tjasa Kanduc, Nives Ogrinc, Lynn M Walter
    Abstract:

    [1] Calcite and dolomite solubilities in open weathering environments are proportional to pCO2 and inversely proportional to temperature, and dolomite solubility is progressively greater than calcite below 25°C. The continent-scale weathering budget reveals the significance of the Northern Hemisphere (NH) to globally integrated riverine fluxes of Ca2+, Mg2+, and HCO3−. The NH contributes 70% of the global HCO3− flux while only 54% of the riverine discharge. We present results of a comparative hydrogeochemical study of carbonate mineral equilibria and weathering fluxes in two NH carbonate-rich river basins. Surface water geochemistry and discharge were determined for headwater streams in Michigan and Slovenia within the St. Lawrence and Danube river basins. Michigan watersheds are established atop carbonate-bearing Glacial Drift deposits derived from erosion of Paleozoic strata with thick soil horizons (100–300 cm). Slovenia watersheds drain Mesozoic bedrock carbonates in alpine and dinaric karst environments with thin soil horizons (0–70 cm). Carbonate weathering intensity is a parameter that normalizes river runoff and HCO3− concentration to catchment area (meq HCO3− km−2 s−1), summing calcite and dolomite contributions, and is used to gauge the effects of climate, land use, and soil thickness on organic-inorganic carbon processing rates. Importantly, Michigan riverine discharge is one-tenth of Slovenian rivers, providing the opportunity to evaluate the kinetics of carbonate mineral equilibration. The study rivers are HCO3− − Ca2+ − Mg2+ waters, supersaturated for calcite at pCO2 values in excess of the atmosphere. As discharge varies, HCO3− concentrations differ by less than 20% for any location, and Mg2+/Ca2+ remains relatively fixed for Michigan (0.5) and Slovenia streams (0.4), requiring that dolomite dissolution exceed calcite on a mole basis. The ability of calcite and dolomite dissolution to keep pace with increased discharge indicates carbonate weathering is limited only by water flux and temperature-dependent solubility in these watersheds. Carbonate weathering intensity in Michigan and Slovenia exceeds the world average by factors between 2 and 20, and dolomite weathering intensity, estimated from riverine Mg2+ fluxes, exceeds the world average by factors between 2 and 15. Thus global fluxes of carbonate-related weathering products appear heavily skewed toward carbonate-bearing environments at higher latitudes with relatively low mean annual temperatures and high discharge.

  • paleowaters in silurian devonian carbonate aquifers geochemical evolution of groundwater in the great lakes region since the late pleistocene
    Geochimica et Cosmochimica Acta, 2006
    Co-Authors: Jennifer C Mcintosh, Lynn M Walter
    Abstract:

    Abstract Changes in the climatic conditions during the Late Quaternary and Holocene greatly impacted the hydrology and geochemical evolution of groundwaters in the Great Lakes region. Increased hydraulic gradients from melting of kilometer-thick Pleistocene ice sheets reorganized regional-scale groundwater flow in Paleozoic aquifers in underlying intracratonic basins. Here, we present new elemental and isotopic analyses of 134 groundwaters from Silurian-Devonian carbonate and overlying Glacial Drift aquifers, along the margins of the Illinois and Michigan basins, to evaluate the paleohydrology, age distribution, and geochemical evolution of confined aquifer systems. This study significantly extends the spatial coverage of previously published groundwaters in carbonate and Drift aquifers across the Midcontinent region, and extends into deeper portions of the Illinois and Michigan basins, focused on the freshwater–saline water mixing zones. In addition, the hydrogeochemical data from Silurian-Devonian aquifers were integrated with deeper basinal fluids, and brines in Upper Devonian black shales and underlying Cambrian-Ordovician aquifers to reveal a regionally extensive recharge system of Pleistocene-age waters in glaciated sedimentary basins. Elemental and isotope geochemistry of confined groundwaters in Silurian-Devonian carbonate and Glacial Drift aquifers show that they have been extensively altered by incongruent dissolution of carbonate minerals, dissolution of halite and anhydrite, cation exchange, microbial processes, and mixing with basinal brines. Carbon isotope values of dissolved inorganic carbon (DIC) range from −10 to −2‰, 87Sr/86Sr ratios range from 0.7080 to 0.7090, and δ 34 S – SO 4 values range from +10 to 30‰. A few waters have elevated δ13CDIC values (>15‰) from microbial methanogenesis in adjacent organic-rich Upper Devonian shales. Radiocarbon ages and δ18O and δD values of confined groundwaters indicate they originated as subGlacial recharge beneath the Laurentide Ice Sheet (14–50 ka BP, −15 to −13‰ δ18O). These paleowaters are isolated from shallow flow systems in overlying Glacial Drift aquifers by lake-bed clays and/or shales. The presence of isotopically depleted waters in Paleozoic aquifers at relatively shallow depths illustrates the importance of continental glaciation on regional-scale groundwater flow. Modern groundwater flow in the Great Lakes region is primarily restricted to shallow unconfined Glacial Drift aquifers. Recharge waters in Silurian-Devonian and unconfined Drift aquifers have δ18O values within the range of Holocene precipitation: −11 to −8‰ and −7 to −4.5‰ for northern Michigan and northern Indiana/Ohio, respectively. Carbon and Sr isotope systematics indicate shallow groundwaters evolved through congruent dissolution of carbonate minerals under open and closed system conditions (δ13CDIC = −14.7 to−11.1‰ and 87Sr/86Sr = 0.7080–0.7103). The distinct elemental and isotope geochemistry of Pleistocene- versus Holocene-age waters further confirms that surficial flow systems are out of contact with the deeper basinal-scale flow systems. These results provide improved understanding of the effects of past climate change on groundwater flow and geochemical processes, which are important for determining the sustainability of present-day water resources and stability of saline fluids in sedimentary basins.

  • carbonate and plagioclase weathering rates in pleistocene Glacial Drift deposits solute fluxes from soils to shallow groundwater systems
    GeCAS, 2005
    Co-Authors: L Jin, Erika L Williams, Lynn M Walter, Stephen K Hamilton, W K Kellogg, S I Dworkin, Hogg Creek, South Bosque River, Lake Waco
    Abstract:

    ,Thick Pleistocene Glacial Drift deposits mantle large portions of the upper Midwestern U.S.A.. In lower Michigan, high permeability of soils and underlying Glacial Drift produce unusually close chemical linkages among soil, ground and surface waters. This region also provides an ideal natural laboratory with abundant organic matter and freshly eroded, reactive minerals in which to determine sequence and mass balances of carbonate and silicate mineral weathering and the

Kathryn Szramek - One of the best experts on this subject based on the ideXlab platform.

  • silicate and carbonate mineral weathering in soil profiles developed on pleistocene Glacial Drift michigan usa mass balances based on soil water geochemistry
    Geochimica et Cosmochimica Acta, 2008
    Co-Authors: Erika L Williams, Kathryn Szramek, Lynn M Walter, Stephen K Hamilton
    Abstract:

    Abstract Geochemistry of soil, soil water, and soil gas was characterized in representative soil profiles of three Michigan watersheds. Because of differences in source regions, parent materials in the Upper Peninsula of Michigan (the Tahquamenon watershed) contain only silicates, while those in the Lower Peninsula (the Cheboygan and the Huron watersheds) have significant mixtures of silicate and carbonate minerals. These differences in soil mineralogy and climate conditions permit us to examine controls on carbonate and silicate mineral weathering rates and to better define the importance of silicate versus carbonate dissolution in the early stage of soil–water cation acquisition. Soil waters of the Tahquamenon watershed are the most dilute; solutes reflect amphibole and plagioclase dissolution along with significant contributions from atmospheric precipitation sources. Soil waters in the Cheboygan and the Huron watersheds begin their evolution as relatively dilute solutions dominated by silicate weathering in shallow carbonate-free soil horizons. Here, silicate dissolution is rapid and reaction rates dominantly are controlled by mineral abundances. In the deeper soil horizons, silicate dissolution slows down and soil–water chemistry is dominated by calcite and dolomite weathering, where solutions reach equilibrium with carbonate minerals within the soil profile. Thus, carbonate weathering intensities are dominantly controlled by annual precipitation, temperature and soil p CO 2 . Results of a conceptual model support these field observations, implying that dolomite and calcite are dissolving at a similar rate, and further dissolution of more soluble dolomite after calcite equilibrium produces higher dissolved inorganic carbon concentrations and a Mg 2+ /Ca 2+ ratio of 0.4. Mass balance calculations show that overall, silicate minerals and atmospheric inputs generally contribute 2+ and Mg 2+ in natural waters. Dolomite dissolution appears to be a major process, rivaling calcite dissolution as a control on divalent cation and inorganic carbon contents of soil waters. Furthermore, the fraction of Mg 2+ derived from silicate mineral weathering is much smaller than most of the values previously estimated from riverine chemistry.

  • relative weathering intensity of calcite versus dolomite in carbonate bearing temperate zone watersheds carbonate geochemistry and fluxes from catchments within the st lawrence and danube river basins
    Geochemistry Geophysics Geosystems, 2007
    Co-Authors: Erika L Williams, Kathryn Szramek, Jennifer C Mcintosh, Tjasa Kanduc, Nives Ogrinc, Lynn M Walter
    Abstract:

    [1] Calcite and dolomite solubilities in open weathering environments are proportional to pCO2 and inversely proportional to temperature, and dolomite solubility is progressively greater than calcite below 25°C. The continent-scale weathering budget reveals the significance of the Northern Hemisphere (NH) to globally integrated riverine fluxes of Ca2+, Mg2+, and HCO3−. The NH contributes 70% of the global HCO3− flux while only 54% of the riverine discharge. We present results of a comparative hydrogeochemical study of carbonate mineral equilibria and weathering fluxes in two NH carbonate-rich river basins. Surface water geochemistry and discharge were determined for headwater streams in Michigan and Slovenia within the St. Lawrence and Danube river basins. Michigan watersheds are established atop carbonate-bearing Glacial Drift deposits derived from erosion of Paleozoic strata with thick soil horizons (100–300 cm). Slovenia watersheds drain Mesozoic bedrock carbonates in alpine and dinaric karst environments with thin soil horizons (0–70 cm). Carbonate weathering intensity is a parameter that normalizes river runoff and HCO3− concentration to catchment area (meq HCO3− km−2 s−1), summing calcite and dolomite contributions, and is used to gauge the effects of climate, land use, and soil thickness on organic-inorganic carbon processing rates. Importantly, Michigan riverine discharge is one-tenth of Slovenian rivers, providing the opportunity to evaluate the kinetics of carbonate mineral equilibration. The study rivers are HCO3− − Ca2+ − Mg2+ waters, supersaturated for calcite at pCO2 values in excess of the atmosphere. As discharge varies, HCO3− concentrations differ by less than 20% for any location, and Mg2+/Ca2+ remains relatively fixed for Michigan (0.5) and Slovenia streams (0.4), requiring that dolomite dissolution exceed calcite on a mole basis. The ability of calcite and dolomite dissolution to keep pace with increased discharge indicates carbonate weathering is limited only by water flux and temperature-dependent solubility in these watersheds. Carbonate weathering intensity in Michigan and Slovenia exceeds the world average by factors between 2 and 20, and dolomite weathering intensity, estimated from riverine Mg2+ fluxes, exceeds the world average by factors between 2 and 15. Thus global fluxes of carbonate-related weathering products appear heavily skewed toward carbonate-bearing environments at higher latitudes with relatively low mean annual temperatures and high discharge.

  • arsenic mobility in groundwater surface water systems in carbonate rich pleistocene Glacial Drift aquifers michigan
    Applied Geochemistry, 2004
    Co-Authors: Kathryn Szramek, Lynn M Walter, Patti Mccall
    Abstract:

    Abstract Within the Lower Peninsula of Michigan, groundwaters from the Marshall Formation (Mississippian) contain As derived from As-rich pyrites, often exceeding the World Heath Organization drinking water limit of 10 μg/L. Many Michigan watersheds, established on top of Pleistocene Glacial Drift derived from erosion of the underlying Marshall Formation, also have waters with elevated As. The Huron River watershed in southeastern Lower Michigan is a well characterized hydrogeochemical system of Glacial Drift deposits, proximate to the Marshall Fm. subcrop, which hosts carbonate-rich groundwaters, streams, and wetlands (fens), and well-developed soil profiles. Aqueous and solid phase geochemistry was determined for soils, soil waters, surface waters (streams and fens) and groundwaters from Glacial Drift aquifers to better understand the hydrogeologic and chemical controls on As mobility. Soil profiles established on the Glacial Drift exhibit enrichment in both Fe and As in the oxyhydroxide-rich zone of accumulation. The amounts of Fe and As present as oxyhydroxides are comparable to those reported from bulk Marshall Fm. core samples by previous workers. However, the As host in core samples is largely unaltered pyrite and arsenopyrite. This suggests that the transformation of Fe sulfides to Fe oxyhydroxides largely retains As and Fe at the oxidative weathering site. Groundwaters have the highest As values of all the waters sampled, and many were at or above the World Health limit. Most groundwaters are anaerobic, within the zones of Fe3+ and As(V) reduction. Although reduction of Fe(III) oxyhydroxides is the probable source of As, there is no correlation between As and Fe concentrations. The As/Fe mole ratios in Drift groundwaters are about an order of magnitude greater than those in soil profiles, suggesting that As is more mobile than Fe. This is consistent with the dominance of As(III) in these groundwaters and with the partitioning of Fe2+ into carbonate cements. Soil waters have very low As and Fe contents, consistent with the stability of oxyhydroxides under oxidizing vadose conditions. When CO2 charged groundwaters discharge in streams and fens, dissolved As is effectively removed by adsorption onto Fe-oxides or carbonate marls. Although Fe does not display conservative behavior with As in groundwaters, a strong positive correlation exists between As and Sr concentrations. As water–rock interactions proceed, the As/Fe and Sr/Ca ratios would be expected to increase because both As and Sr behave as incompatible elements. Comparisons with groundwater chemistries from other Drift-hosted aquifers proximate to the Marshall sandstone are consistent with these relations. Thus, the Sr content of carbonate-rich groundwaters may provide useful constraints on the occurrence, origin and evolution of dissolved As in such systems.

Erika L Williams - One of the best experts on this subject based on the ideXlab platform.

  • silicate and carbonate mineral weathering in soil profiles developed on pleistocene Glacial Drift michigan usa mass balances based on soil water geochemistry
    Geochimica et Cosmochimica Acta, 2008
    Co-Authors: Erika L Williams, Kathryn Szramek, Lynn M Walter, Stephen K Hamilton
    Abstract:

    Abstract Geochemistry of soil, soil water, and soil gas was characterized in representative soil profiles of three Michigan watersheds. Because of differences in source regions, parent materials in the Upper Peninsula of Michigan (the Tahquamenon watershed) contain only silicates, while those in the Lower Peninsula (the Cheboygan and the Huron watersheds) have significant mixtures of silicate and carbonate minerals. These differences in soil mineralogy and climate conditions permit us to examine controls on carbonate and silicate mineral weathering rates and to better define the importance of silicate versus carbonate dissolution in the early stage of soil–water cation acquisition. Soil waters of the Tahquamenon watershed are the most dilute; solutes reflect amphibole and plagioclase dissolution along with significant contributions from atmospheric precipitation sources. Soil waters in the Cheboygan and the Huron watersheds begin their evolution as relatively dilute solutions dominated by silicate weathering in shallow carbonate-free soil horizons. Here, silicate dissolution is rapid and reaction rates dominantly are controlled by mineral abundances. In the deeper soil horizons, silicate dissolution slows down and soil–water chemistry is dominated by calcite and dolomite weathering, where solutions reach equilibrium with carbonate minerals within the soil profile. Thus, carbonate weathering intensities are dominantly controlled by annual precipitation, temperature and soil p CO 2 . Results of a conceptual model support these field observations, implying that dolomite and calcite are dissolving at a similar rate, and further dissolution of more soluble dolomite after calcite equilibrium produces higher dissolved inorganic carbon concentrations and a Mg 2+ /Ca 2+ ratio of 0.4. Mass balance calculations show that overall, silicate minerals and atmospheric inputs generally contribute 2+ and Mg 2+ in natural waters. Dolomite dissolution appears to be a major process, rivaling calcite dissolution as a control on divalent cation and inorganic carbon contents of soil waters. Furthermore, the fraction of Mg 2+ derived from silicate mineral weathering is much smaller than most of the values previously estimated from riverine chemistry.

  • relative weathering intensity of calcite versus dolomite in carbonate bearing temperate zone watersheds carbonate geochemistry and fluxes from catchments within the st lawrence and danube river basins
    Geochemistry Geophysics Geosystems, 2007
    Co-Authors: Erika L Williams, Kathryn Szramek, Jennifer C Mcintosh, Tjasa Kanduc, Nives Ogrinc, Lynn M Walter
    Abstract:

    [1] Calcite and dolomite solubilities in open weathering environments are proportional to pCO2 and inversely proportional to temperature, and dolomite solubility is progressively greater than calcite below 25°C. The continent-scale weathering budget reveals the significance of the Northern Hemisphere (NH) to globally integrated riverine fluxes of Ca2+, Mg2+, and HCO3−. The NH contributes 70% of the global HCO3− flux while only 54% of the riverine discharge. We present results of a comparative hydrogeochemical study of carbonate mineral equilibria and weathering fluxes in two NH carbonate-rich river basins. Surface water geochemistry and discharge were determined for headwater streams in Michigan and Slovenia within the St. Lawrence and Danube river basins. Michigan watersheds are established atop carbonate-bearing Glacial Drift deposits derived from erosion of Paleozoic strata with thick soil horizons (100–300 cm). Slovenia watersheds drain Mesozoic bedrock carbonates in alpine and dinaric karst environments with thin soil horizons (0–70 cm). Carbonate weathering intensity is a parameter that normalizes river runoff and HCO3− concentration to catchment area (meq HCO3− km−2 s−1), summing calcite and dolomite contributions, and is used to gauge the effects of climate, land use, and soil thickness on organic-inorganic carbon processing rates. Importantly, Michigan riverine discharge is one-tenth of Slovenian rivers, providing the opportunity to evaluate the kinetics of carbonate mineral equilibration. The study rivers are HCO3− − Ca2+ − Mg2+ waters, supersaturated for calcite at pCO2 values in excess of the atmosphere. As discharge varies, HCO3− concentrations differ by less than 20% for any location, and Mg2+/Ca2+ remains relatively fixed for Michigan (0.5) and Slovenia streams (0.4), requiring that dolomite dissolution exceed calcite on a mole basis. The ability of calcite and dolomite dissolution to keep pace with increased discharge indicates carbonate weathering is limited only by water flux and temperature-dependent solubility in these watersheds. Carbonate weathering intensity in Michigan and Slovenia exceeds the world average by factors between 2 and 20, and dolomite weathering intensity, estimated from riverine Mg2+ fluxes, exceeds the world average by factors between 2 and 15. Thus global fluxes of carbonate-related weathering products appear heavily skewed toward carbonate-bearing environments at higher latitudes with relatively low mean annual temperatures and high discharge.

  • carbonate and plagioclase weathering rates in pleistocene Glacial Drift deposits solute fluxes from soils to shallow groundwater systems
    GeCAS, 2005
    Co-Authors: L Jin, Erika L Williams, Lynn M Walter, Stephen K Hamilton, W K Kellogg, S I Dworkin, Hogg Creek, South Bosque River, Lake Waco
    Abstract:

    ,Thick Pleistocene Glacial Drift deposits mantle large portions of the upper Midwestern U.S.A.. In lower Michigan, high permeability of soils and underlying Glacial Drift produce unusually close chemical linkages among soil, ground and surface waters. This region also provides an ideal natural laboratory with abundant organic matter and freshly eroded, reactive minerals in which to determine sequence and mass balances of carbonate and silicate mineral weathering and the

Jennifer C Mcintosh - One of the best experts on this subject based on the ideXlab platform.

  • relative weathering intensity of calcite versus dolomite in carbonate bearing temperate zone watersheds carbonate geochemistry and fluxes from catchments within the st lawrence and danube river basins
    Geochemistry Geophysics Geosystems, 2007
    Co-Authors: Erika L Williams, Kathryn Szramek, Jennifer C Mcintosh, Tjasa Kanduc, Nives Ogrinc, Lynn M Walter
    Abstract:

    [1] Calcite and dolomite solubilities in open weathering environments are proportional to pCO2 and inversely proportional to temperature, and dolomite solubility is progressively greater than calcite below 25°C. The continent-scale weathering budget reveals the significance of the Northern Hemisphere (NH) to globally integrated riverine fluxes of Ca2+, Mg2+, and HCO3−. The NH contributes 70% of the global HCO3− flux while only 54% of the riverine discharge. We present results of a comparative hydrogeochemical study of carbonate mineral equilibria and weathering fluxes in two NH carbonate-rich river basins. Surface water geochemistry and discharge were determined for headwater streams in Michigan and Slovenia within the St. Lawrence and Danube river basins. Michigan watersheds are established atop carbonate-bearing Glacial Drift deposits derived from erosion of Paleozoic strata with thick soil horizons (100–300 cm). Slovenia watersheds drain Mesozoic bedrock carbonates in alpine and dinaric karst environments with thin soil horizons (0–70 cm). Carbonate weathering intensity is a parameter that normalizes river runoff and HCO3− concentration to catchment area (meq HCO3− km−2 s−1), summing calcite and dolomite contributions, and is used to gauge the effects of climate, land use, and soil thickness on organic-inorganic carbon processing rates. Importantly, Michigan riverine discharge is one-tenth of Slovenian rivers, providing the opportunity to evaluate the kinetics of carbonate mineral equilibration. The study rivers are HCO3− − Ca2+ − Mg2+ waters, supersaturated for calcite at pCO2 values in excess of the atmosphere. As discharge varies, HCO3− concentrations differ by less than 20% for any location, and Mg2+/Ca2+ remains relatively fixed for Michigan (0.5) and Slovenia streams (0.4), requiring that dolomite dissolution exceed calcite on a mole basis. The ability of calcite and dolomite dissolution to keep pace with increased discharge indicates carbonate weathering is limited only by water flux and temperature-dependent solubility in these watersheds. Carbonate weathering intensity in Michigan and Slovenia exceeds the world average by factors between 2 and 20, and dolomite weathering intensity, estimated from riverine Mg2+ fluxes, exceeds the world average by factors between 2 and 15. Thus global fluxes of carbonate-related weathering products appear heavily skewed toward carbonate-bearing environments at higher latitudes with relatively low mean annual temperatures and high discharge.

  • paleowaters in silurian devonian carbonate aquifers geochemical evolution of groundwater in the great lakes region since the late pleistocene
    Geochimica et Cosmochimica Acta, 2006
    Co-Authors: Jennifer C Mcintosh, Lynn M Walter
    Abstract:

    Abstract Changes in the climatic conditions during the Late Quaternary and Holocene greatly impacted the hydrology and geochemical evolution of groundwaters in the Great Lakes region. Increased hydraulic gradients from melting of kilometer-thick Pleistocene ice sheets reorganized regional-scale groundwater flow in Paleozoic aquifers in underlying intracratonic basins. Here, we present new elemental and isotopic analyses of 134 groundwaters from Silurian-Devonian carbonate and overlying Glacial Drift aquifers, along the margins of the Illinois and Michigan basins, to evaluate the paleohydrology, age distribution, and geochemical evolution of confined aquifer systems. This study significantly extends the spatial coverage of previously published groundwaters in carbonate and Drift aquifers across the Midcontinent region, and extends into deeper portions of the Illinois and Michigan basins, focused on the freshwater–saline water mixing zones. In addition, the hydrogeochemical data from Silurian-Devonian aquifers were integrated with deeper basinal fluids, and brines in Upper Devonian black shales and underlying Cambrian-Ordovician aquifers to reveal a regionally extensive recharge system of Pleistocene-age waters in glaciated sedimentary basins. Elemental and isotope geochemistry of confined groundwaters in Silurian-Devonian carbonate and Glacial Drift aquifers show that they have been extensively altered by incongruent dissolution of carbonate minerals, dissolution of halite and anhydrite, cation exchange, microbial processes, and mixing with basinal brines. Carbon isotope values of dissolved inorganic carbon (DIC) range from −10 to −2‰, 87Sr/86Sr ratios range from 0.7080 to 0.7090, and δ 34 S – SO 4 values range from +10 to 30‰. A few waters have elevated δ13CDIC values (>15‰) from microbial methanogenesis in adjacent organic-rich Upper Devonian shales. Radiocarbon ages and δ18O and δD values of confined groundwaters indicate they originated as subGlacial recharge beneath the Laurentide Ice Sheet (14–50 ka BP, −15 to −13‰ δ18O). These paleowaters are isolated from shallow flow systems in overlying Glacial Drift aquifers by lake-bed clays and/or shales. The presence of isotopically depleted waters in Paleozoic aquifers at relatively shallow depths illustrates the importance of continental glaciation on regional-scale groundwater flow. Modern groundwater flow in the Great Lakes region is primarily restricted to shallow unconfined Glacial Drift aquifers. Recharge waters in Silurian-Devonian and unconfined Drift aquifers have δ18O values within the range of Holocene precipitation: −11 to −8‰ and −7 to −4.5‰ for northern Michigan and northern Indiana/Ohio, respectively. Carbon and Sr isotope systematics indicate shallow groundwaters evolved through congruent dissolution of carbonate minerals under open and closed system conditions (δ13CDIC = −14.7 to−11.1‰ and 87Sr/86Sr = 0.7080–0.7103). The distinct elemental and isotope geochemistry of Pleistocene- versus Holocene-age waters further confirms that surficial flow systems are out of contact with the deeper basinal-scale flow systems. These results provide improved understanding of the effects of past climate change on groundwater flow and geochemical processes, which are important for determining the sustainability of present-day water resources and stability of saline fluids in sedimentary basins.

Alan E. Kehew - One of the best experts on this subject based on the ideXlab platform.

  • use of nitrogen isotopes and other geochemical tools to evaluate the source of ammonium in a confined Glacial Drift aquifer ottawa county michigan usa
    Applied Geochemistry, 2017
    Co-Authors: Derrick A Lingle, Alan E. Kehew, R V Krishnamurthy
    Abstract:

    Abstract This study utilized several isotopic tracers and geochemical parameters to characterize the source and hydrogeochemical setting of elevated ammonium (NH 4 + ) concentrations (>2 mg/L) in a confined Glacial Drift aquifer in Ottawa County, Michigan. Results from this investigation indicate that NH 4 + is attributed to degrading in situ organic matter and not from surficial anthropogenic sources. Tritium, δ 18 O, and δ 2 H values suggest that primary recharge in the confined aquifer occurred during the middle to late Holocene and before the mid-1900's. Geochemical constituents, including redox parameters and a suite of common ions, demonstrate a compositional difference between the confined and unconfined aquifers in the study area and therefore further support the isolation of the confined aquifer from a significant amount of recent recharge (post 1950's). Insignificant δ 15 N- NH 4 + fractionation (+0.81‰ to +1.38‰) implies that NH 4 + in the confined aquifer originated from degrading in situ organic matter. A complete Rotosonic Glacial sediment core, collected to characterize the physical setting of the NH 4 + -rich aquifer, confirmed the presence of in situ organic matter in the confined aquifer. A limited set of δ 15 N-NO 3 and δ 18 O-NO 3 values suggest that the application of manure to row crops may be contributing nitrate (up to 10 mg/L) to nearby shallow residential wells. As implemented in this study, the use of multiple geochemical and isotopic parameters, including δ 15 N-NH 4 , can be applied to evaluate the potential source of NH 4 + in an aquifer.

  • redox evolution in Glacial Drift aquifers role of diamicton units in reduction of fe iii
    Environmental Earth Sciences, 2011
    Co-Authors: Nathaniel A Barnes, Alan E. Kehew, R V Krishnamurthy, Carla M Koretsky
    Abstract:

    High iron concentrations create water quality problems for municipal use in Glacial Drift aquifer units. The chemical evolution of oxic groundwater in shallow aquifer units to anoxic groundwater in deeper aquifer units, in which soluble Fe(II) is stable, is attributed to coupled reduction of Fe(III) on aquifer solids with oxidation of organic carbon. The objective of this study was to characterize the distribution of organic carbon in aquifer and aquitard sediments to determine the availability of potential electron donors to drive these reactions. To do this, four complete rotasonic cores in a Glacial aquifer/aquitard system were sampled at close intervals for analyses of grain-size distribution and organic carbon content. The results indicate significantly higher organic carbon concentrations in diamicton (till) units that function as aquitards, relative to coarse-grained aquifer units. In addition, readily reducible iron content in the diamicton units and lower aquifer unit materials is sufficient to produce far more dissolved iron than is present in the aquifer. Groundwater evolves to the level of iron reduction as a terminal electron-accepting process as it moves downward through aquitard units along flow paths from upland recharge areas to downgradient discharge areas. Deeper aquifer units are therefore unlikely to contain groundwater with low iron concentration.

  • spatial and temporal distribution of herbicides and herbicide degradates in a shallow Glacial Drift aquifer surface water system south central michigan
    Ground Water Monitoring and Remediation, 2005
    Co-Authors: Gerald A Unterreiner, Alan E. Kehew
    Abstract:

    Herbicide and herbicide degradate compounds were measured in tile drains, monitoring wells, domestic wells, and in the receiving stream at a farm in south-central Michigan, in which corn, soybeans, and livestock are the major products. Immunoassay screens of two herbicide groups (triazines and alachlor) in 2000 showed a decrease in the number of detections from June to September, after the well-known spring flush, of 48% to 26% for alachlor and 62% to 22% for the triazines. Gas chromatography/mass spectrometry and liquid chromatography/mass spectrometry analyses of 2001 samples documented a fall flush as well, mobilizing relatively high levels of both parent and degradate compounds to the tile drain system. The compounds included both metolachlor and atrazine, which were applied on the farm earlier that year, as well as the degradates of alachlor, which had not been applied on the farm for several years. In four tile drain samples, metolachlor was detected at concentrations ranging from 18 to 25 μg/L, whereas atrazine ranged from nondetect to 2.25 μg/L. Contrary to previous studies, metolachlor concentrations were higher than metolachlor ethane sulfonic acid, by a factor of 3 to 7. The high soil permeability, high water table, and shallow screened intervals of monitoring wells directly below the point of application may explain the lesser degree of breakdown at the point of sampling. Although most detections were below maximum contaminant level or health advisory levels, the unknown effects of degradates and the aggregate levels of compounds measured in many samples may pose higher health risks than for individual compounds.

  • hydrogeochemical interaction between a wetland and an unconfined Glacial Drift aquifer southwestern michigan
    Ground Water, 1998
    Co-Authors: Alan E. Kehew, Richard N Passero, R V Krishnamurthya, Cole K Lovett, Marilyn A Bettsc, Brent A Dayharsh
    Abstract:

    In the Glacial topography of southwestern Michigan, the water table does not always conform exactly to the land surface and flow-through wetlands, those with both ground water recharge and discharge, are common. The W-l wetland in Cass County, Michigan, a flow-through system, shows a distinct contrast between upgradient and downgradient ground water quality. Ground water discharging into the wetland is oxic, has up to 40 mg/L NO3-N derived from fertilizer and hog manure application to corn fields, and has major ion concentrations typical of the shallow unconfined aquifer in the area. In contrast, shallow ground water that originates as recharge from the wetland forms a plume extending downgradient that can be identified by isotopic enrichment in 18O and deuterium resulting from evaporation in the wetland prior to recharge and by distinct chemical characteristics similar to the wetland surface water (low conductivity and alkalinity, low concentrations of sulfate, nitrate and dissolved oxygen and high concentrations of ammonia, and DOC). As the wetland surface water infiltrates into the unconfined aquifer, conductivity and alkalinity increase due to carbonate mineral dissolution and iron concentrations increase as ferric iron in the aquifer solids serves as an electron acceptor in microbially mediated reactions. The other chemical characteristics, including the lack of nitrate, persist in the flow system for significant distances downgradient from the wetland. The chemical and isotopic composition of shallow ground water around wetlands can be used to spatially delineate areas of ground-water discharge to the wetland and ground water recharge from the wetland, thereby providing a supplemental method to the use of sometimes inconclusive hydraulic head data in the determination of wetland recharge-discharge function. In this study, the chemical and isotopic data confirm that the water table does not replicate surface topography around closed depressions in the landscape.

  • Groundwater quality variations in Glacial Drift and bedrock aquifers, Barry County, Michigan, U.S.A.
    Environmental Geology and Water Sciences, 1992
    Co-Authors: Alan E. Kehew, Margene K. Brewer
    Abstract:

    Groundwater samples from 288 domestic wells in Barry County, Michigan, were analyzed for 33 inorganic chemical parameters. Variations in chemical composition were investigated by considering the possible effects of human impact, aquifer type (bedrock vs Glacial Drift), chemical evolution along groundwater flow paths, and Glacial landform type (moraine vs outwash). Approximately 25 percent of the Glacial Drift wells were classified as degraded by human impact and were excluded from further analysis of chemical variation. Two-sample tests comparing individual concentrations from Drift and bedrock aquifers suggest that groundwater in the Marshall Sandstone aquifer is derived from local recharge through the Glacial Drift. This conclusion is supported by generalized groundwater flow patterns recognized for the two aquifers.