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Water quality and pollution contamination depend strongly on geochemical processes involving reactions with mineral surfaces and substrates. Such processes include weathering reactions that contribute dissolved chemicals, sorption that removes aqueous species, and electron transfer mechanisms that establish redox conditions. Although extensive research has been conducted on the aqueous chemistry, minimal information exists on the corresponding solid phases and their effects on chemical transport. Objectives of this project are to: investigate the composition and structure of common mineral surfaces and determine the extent of heterogeneity between specific surfaces and the bulk mineral phase; determine the mechanism...
Stream-bed sediment for the size fraction less than 150 μm, examined in 14,000 samples collected mostly from minor tributaries to the major rivers throughout the Mississippi River drainage system, is composed of 5 mineral fractions identified by factor analysis—Al-silicate minerals, quartz, calcite and dolomite, heavy minerals, and an Fe–Mn fraction. The Al-silicate fraction parallels its distribution in the regolith, emphasizing the local sediment source as a primary control to its distribution. Quartz and the heavy-mineral fraction, and associated trace elements, exhibit a complementary distribution to that of the Al-silicate fraction, with a level of enrichment in the bed sediment that is achieved through winnowing...
A number of studies have shown that dust delivers essential nutrients that sustain terrestrial productivity over millennia. Dust, however, contains a range of elements ranging from base cations, N and P, to heavy metals. Some of these elements will stimulate primary productivity over the time scale of soil development while others, such as metals, could inhibit biological activity. As dust accumulates, it also influences water flux and availability by altering soil texture. We are examining the ecological impacts of dust accumulation in Canyonlands National Park in Utah. Using magnetic susceptibility as a proxy for far-traveled dust, we have established transects in sandy surficial deposits (50-90% sand) in which...
The Rio Icacos basin, in Puerto Rico, is the site of the highest measured chemical solute fluxes for a catchment on granodiorite; this is partly attributable to high annual rainfall (4300 mm), high average temperature (23 °C), and moderate relief. The bulk of these fluxes is contributed by dissolution of plagioclase and amphiboles in zones of partially weathered rock (0.5–1.5 m thick) underlying saprolite. These zones are characterized by systems of onion-skin “rindlets” (each 3–10 cm thick) in which porosity development is dominated by weathering of plagioclase to kaolinite. Fe-bearing aluminosilicate minerals hornblende, augite, and biotite persist in the weathered rock after plagioclase has weathered to completion,...
Categories: Publication; Types: Citation; Tags: Bedrock, Solute flux, weathering
The goal of our research is to understand how climate and land use change will alter soil function including nutrient, carbon and water cycling.
Water quality and pollution contamination depend strongly on geochemical processes involving reactions with mineral surfaces and substrates. Such processes include weathering reactions that contribute dissolved chemicals, sorption that removes aqueous species, and electron transfer mechanisms that establish redox conditions. Although extensive research has been conducted on the aqueous chemistry, minimal information exists on the corresponding solid phases and their effects on chemical transport. Objectives of this project are to: investigate the composition and structure of common mineral surfaces and determine the extent of heterogeneity between specific surfaces and the bulk mineral phase; determine the mechanism...
The project focuses on the use of analytical techniques that we have developed to support a wide range of studies in water-rock interaction, integrating solid phase mineralogy and elemental chemistry and clay mineralogy into hydrologic and contaminant studies.
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This 1:50,000-scale geologic map represents a compilation of the most recent geologic studies of the upper Arkansas River valley, between Leadville and Salida, Colorado. The valley is structurally controlled by an extensional fault system that forms part of the prominent northern Rio Grande rift, an intra-continental region of crustal extension. This work also incorporates new detailed geologic mapping of poorly understood areas within the map area and reinterprets previously studied areas, aided by lidar data that covers 59 percent of the map area. The mapped region extends into the Proterozoic metamorphic and intrusive rocks in the Sawatch Range west of the valley and the Mosquito Range to the east. Paleozoic...
Categories: Data; Tags: 207Pb/206Pb zircon age, 40Ar/39Ar age, Arkansas River, Balltown, Balltown placer gold mining areas, All tags...
Soil denitrification is an ecologically important nitrogen removal mechanism that releases to the atmosphere the greenhouse gas N2O, an intermediate product from the reduction of NO3 − to N2. In this study we evaluate the relationship between soil carbon and denitrification potential in watersheds with bedrock acting as a nonpoint source of nitrogen, testing the hypothesis that nitrate leaching to stream water is in part regulated by denitrification. Two sites, one in a Mediterranean climate and the other in an arid climate, were investigated to understand the interplay between carbon and denitrification potential. Both sites included carbonaceous bedrock with relatively high nitrogen concentrations (>1,000 mg N...
Categories: Publication; Types: Citation; Tags: carbon, denitrification, soil, weathering
Climate is a major control on geomorphology, yet the effects of aspect-related differences in microclimate have been little studied. We examined several 60–100-m-deep canyons in semiarid northeastern Arizona, where rock type and structure are essentially constant, but where field data and a high-resolution digital elevation model reveal consistent morphologic and microclimatic differences between asymmetric north- and south-facing sideslopes. Cliffs account for 29% of the vertical relief of south-facing slopes but only 2.5% of north-facing slopes. Excluding cliffs, south-facing slopes are 1–3° steeper than north-facing slopes and have significantly less weathered bedrock. We monitored air, surface and subsurface...
Soil denitrification is an ecologically important nitrogen removal mechanism that releases to the atmosphere the greenhouse gas N2O, an intermediate product from the reduction of NO3 ? to N2. In this study we evaluate the relationship between soil carbon and denitrification potential in watersheds with bedrock acting as a nonpoint source of nitrogen, testing the hypothesis that nitrate leaching to stream water is in part regulated by denitrification. Two sites, one in a Mediterranean climate and the other in an arid climate, were investigated to understand the interplay between carbon and denitrification potential. Both sites included carbonaceous bedrock with relatively high nitrogen concentrations (>1,000 mg N...
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Sr isotope ratios in carbonate-rich lacustrine strata provide highly resolved and geographically specific records of past changes in weathering and regional drainage patterns. The Eocene Green River Formation is perhaps the best documented pre-Quaternary lacustrine unit in the world; therefore, these strata are ideally suited for studying the behavior of Sr. The 87Sr/86Sr ratios measured for primary carbonate in lake expansion- contraction cycles of the Laney Member are directly linked to changing lake facies. Four distinct cycles are preserved in a 6.4 m interval of the Arco Washakie Basin No. 1 core, each represented by a vertical succession of transgressive stromatolite facies containing dolomicritic intraclasts,...


    map background search result map search result map Strontium isotope record of paleohydrology and continental weathering, Eocene Green River Formation, Wyoming Data release for the geologic map of the upper Arkansas River valley region, north-central Colorado Data release for the geologic map of the upper Arkansas River valley region, north-central Colorado Strontium isotope record of paleohydrology and continental weathering, Eocene Green River Formation, Wyoming