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T.D. Bullen

Publications and source records attributed to T.D. Bullen.

35 records · Page 2Linked to original sources
USGS2003

Stable isotope fractionation of selenium by natural microbial consortia

The mobility and bioavailability of Se depend on its redox state, and reduction of Se oxyanions to less mobile, reduced species controls transport of this potentially toxic element in the environment. Stable isotope fractionation of Se is currently being developed as an indicator of Se immobilization through reduction. In this study, Se isotope fractionation resulting from reduction of Se(VI) and Se(IV) oxyanions by natural microbial consortia was measured in sediment slurry experiments under nearly natural conditions, with no substrate added. Experiments were conducted with a wide range of initial Se concentrations and with sediment and water from three locations with contrasting environmental settings. The products of Se(VI) and Se(IV) reduction were enriched in the lighter isotopes relative to the reactants. Shifts of -2.6 0 / 00 to -3.1 0 / 00 and -5.5 0 / 00 to -5.7 0 / 00 , respectively, were observed in the 80 Se/ 76 Se ratio. These isotopic fractionations did not depend significantly on initial Se concentrations, which were varied from 22 μg/l to 8 mg/l, or on geochemical differences among the sediments. These results provide estimates of Se isotope fractionation in organic-rich wetland environments but may not be appropriate for substrate-poor aquifers and marine sediments.

Chemical Geology↗
USGS2003

Possible roles of pH, temperature, and partial dissolution in determining boron concentration and isotopic composition in planktonic foraminifera

We present the first continuous records from 0 to 5 Ma (in 0.333 m.y. integrated time steps) of paired boron/calcium (B/Ca) ratios and boron isotopes (??11B) in the planktonic foraminifera Globogerinoides sacculifer (without sacc) from a site in the western equatorial Pacific Ocean (Ocean Drilling Program Site 806). These measurements, the first made in conjunction with calcification temperature (magnesium/calcium ratios) and average shell mass measurements, indicate that pH is not the sole environmental variable controlling B in planktonic foraminiferal calcite. Our data are consistent with calcification temperature exerting a primary control on B concentration and isotopic composition in planktonic foraminifera. If so, calcification temperature must be taken into account if pH for past oceans and atmospheric pCO2 are to be estimated from B isotope measurements in foraminiferal calcite. Doing so will substantially increase the uncertainty of PH estimates. Although this work was designed as a temporal study, its results define new aspects of calibrating the ??11B paleo-pH tracer. Copyright 2003 by the American Geophysical Union.

Paleoceanography↗
USGS2002

Use of ICP/MS with ultrasonic nebulizer for routine determination of uranium activity ratios in natural water

A method is described that allows precise determination of 234 U/ 238 U activity ratios (UAR) in most natural waters using commonly available inductively coupled plasma/mass spectrometry (ICP/MS) instrumentation and accessories. The precision achieved by this technique (±0.5% RSD, 1 sigma) is intermediate between thermal ionization mass spectrometry (±0.25% RSD, 1 sigma) and alpha particle spectrometry (±5% RSD, 1 sigma). It is precise and rapid enough to allow analysis of a large number of samples in a short period of time at low cost using standard, commercially available quadrupole instrumentation with ultrasonic nebulizer and desolvator accessories. UARs have been analyzed successfully in fresh to moderately saline waters with U concentrations of from less than 1 μg/L to nearly 100 μg/L. An example of the uses of these data is shown for a study of surface-water mixing in the North Platte River in western Nebraska. This rapid and easy technique should encourage the wider use of uranium isotopes in surface-water and groundwater investigations, both for qualitative (e.g. identifying sources of water) and quantitative (e.g. determining end-member mixing ratios purposes.

Environmental Science & Technology↗
USGS2002

Strontium isotopic signatures of the streams and lakes of Taylor Valley, Southern Victoria Land, Antarctica: Chemical weathering in a polar climate

We have collected and analyzed a series of water samples from three closed-basin lakes (Lakes Bonney, Fryxell, and Hoare) in Taylor Valley, Antarctica, and the streams that flow into them. In all three lakes, the hypolimnetic waters have different 87Sr/86Sr ratios than the surface waters, with the deep water of Lakes Fryxell and Hoare being less radiogenic than the surface waters. The opposite occurs in Lake Bonney. The Lake Fryxell isotopic ratios are lower than modern-day ocean water and most of the whole-rock ratios of the surrounding geologic materials. A conceivable source of Sr to the system could be either the Cenozoic volcanic rocks that make up a small portion of the till deposited in the valley during the Last Glacial Maximum or from marble derived from the local basement rocks. The more radiogenic ratios from Lake Bonney originate from ancient salt deposits that flow into the lake from Taylor Glacier and the weathering of minerals with more radiogenic Sr isotopic ratios within the tills. The Sr isotopic data from the streams and lakes of Taylor Valley strongly support the notion documented by previous investigators that chemical weathering has been, and is currently, a major process in determining the overall aquatic chemistry of these lakes in this polar desert environment.

Aquatic Geochemistry↗
USGS2001

Differential rates of feldspar weathering in granitic regoliths

Differential rates of plagioclase and K-feldspar weathering commonly observed in bedrock and soil environments are examined in terms of chemical kinetic and solubility controls and hydrologic permeability. For the Panola regolith, in the Georgia Piedmont Province of southeastern United States, petrographic observations, coupled with elemental balances and 87Sr/86Sr ratios, indicate that plagioclase is being converted to kaolinite at depths > 6 m in the granitic bedrock. K-feldspar remains pristine in the bedrock but subsequently weathers to kaolinite at the overlying saprolite. In contrast, both plagioclase and K-feldspar remain stable in granitic bedrocks elsewhere in Piedmont Province, such as Davis Run, Virginia, where feldspars weather concurrently in an overlying thick saprolite sequence. Kinetic rate constants, mineral surface areas, and secondary hydraulic conductivities are fitted to feldspar losses with depth in the Panola and Davis Run regoliths using a time-depth computer spreadsheet model. The primary hydraulic conductivities, describing the rates of meteoric water penetration into the pristine granites, are assumed to be equal to the propagation rates of weathering fronts, which, based on cosmogenic isotope dating, are 7 m/106 yr for the Panola regolith and 4 m/106 yr for the Davis Run regolith. Best fits in the calculations indicate that the kinetic rate constants for plagioclase in both regoliths are factors of two to three times faster than K-feldspar, which is in agreement with experimental findings. However, the range for plagioclase and K-feldspar rates (kr = 1.5 x 10-17 to 2.8 x 10-16 mol m-2 s-1) is three to four orders of magnitude lower than for that for experimental feldspar dissolution rates and are among the slowest yet recorded for natural feldspar weathering. Such slow rates are attributed to the relatively old geomorphic ages of the Panola and Davis Run regoliths, implying that mineral surface reactivity decreases significantly with time. Differential feldspar weathering in the low-permeability Panola bedrock environment is more dependent on relative feldspar solubilities than on differences in kinetic reaction rates. Such weathering is very sensitive to primary and secondary hydraulic conductivities (qp and qs), which control both the fluid volumes passing through the regolith and the thermodynamic saturation of the feldspars. Bedrock permeability is primarily intragranular and is created by internal weathering of networks of interconnected plagioclase phenocrysts. Saprolite permeability is principally intergranular and is the result of dissolution of silicate phases during isovolumetric weathering. A secondary to primary hydraulic conductivity ratio of qs/qp = 150 in the Panola bedrock results in kinetically controlled plagioclase dissolution but thermodynamically inhibited K-feldspar reaction. This result is in accord with calculated chemical saturation states for groundwater sampled in the Panola Granite. In contrast, greater secondary conductivities in the Davis Run saprolite, qs/qp = 800, produces both kinetically controlled plagioclase and K-feldspar dissolution. Faster plagioclase reaction, leading to bedrock weathering in the Panola Granite but not at Davis Run, is attributed to a higher anorthite component of the plagioclase and a wetter and warmer climate. In addition, the Panola Granite has an abnormally high content of disseminated calcite, the dissolution of which precedes the plagioclase weathering front, thus creating additional secondary permeability. Copyright ?? 2001 Elsevier Science Ltd.

Geochimica et Cosmochimica Acta↗
USGS2000

Fractionation of selenium isotopes during bacterial respiratory reduction of selenium oxyanions

Reduction of selenium oxyanions by microorganisms is an important process in the biogeochemical cycling of selenium. Numerous bacteria can reduce Se oxyanions, which are used as electron acceptors during the oxidation of organic matter in anoxic environments. In this study, we used a double spike ( 82 Se and 74 Se) thermal ionization mass spectrometry technique to quantify the isotopic fractionation achieved by three different species of anaerobic bacteria capable of accomplishing growth by respiratory reduction of selenate [SeO 4 2− or Se(VI)] or selenite [SeO 3 2− or Se(IV)] to Se(IV) or elemental selenium [Se(0)] coupled with the oxidation of lactate. Isotopic discrimination in these closed system experiments was evaluated by Rayleigh fractionation equations and numerical models. Growing cultures of Bacillus selenitireducens , a haloalkaliphile capable of growth using Se(IV) as an electron acceptor, induced a 80 Se/ 76 Se fractionation of −8.0 ± 0.4‰ (instantaneous ϵ value) during reduction of Se(IV) to Se(0). With Bacillus arsenicoselenatis , a haloalkaliphile capable of growth using Se(VI) as an electron acceptor, fractionations of −5.0 ± 0.5‰ and −6.0 ± 1.0‰ were observed for reduction of Se(VI) to Se(IV) and reduction of Se(IV) to Se(0), respectively. In growing cultures of Sulfurospirillum barnesii , a freshwater species capable of growth using Se(VI), fractionation was small initially, but near the end of the log growth phase, it increased to −4.0 ± 1.0‰ and −8.4 ± 0.4‰ for reduction of Se(VI) to Se(IV) and reduction of Se(IV) to Se(0), respectively. Washed cell suspensions of S. barnesii induced fractionations of −1.1 ± 0.4‰ during Se(VI) reduction, and −9.1 ± 0.5% for Se(IV) reduction, with some evidence for smaller values (e.g., −1.7‰) in the earliest-formed Se(0) results. These results demonstrate that dissimilatory reduction of selenate or selenite induces significant isotopic fractionation, and suggest that significant Se isotope ratio variation will be found in nature.

Geochimica et Cosmochimica Acta↗
USGS1999

The role of disseminated calcite in the chemical weathering of granitoid rocks

Accessory calcite, present at concentrations between 300 and 3000 mg kg-1, occurs in fresh granitoid rocks sampled from the Merced watershed in Yosemite National Park, CA, USA; Loch Vale in Rocky Mountain National Park CO USA; the Panola watershed, GA USA; and the Rio Icacos, Puerto Rico. Calcite occurs as fillings in microfractures, as disseminated grains within the silicate matrix, and as replacement of calcic cores in plagioclase. Flow-through column experiments, using de-ionized water saturated with 0.05 atm. CO2, produced effluents from the fresh granitoid rocks that were dominated by Ca and bicarbonate and thermodynamically saturated with calcite. During reactions up to 1.7 yr, calcite dissolution progressively decreased and was superceded by steady state dissolution of silicates, principally biotite. Mass balance calculations indicate that most calcite had been removed during this time and accounted for 57-98% of the total Ca released from these rocks. Experimental effluents from surfically weathered granitoids from the same watersheds were consistently dominated by silicate dissolution. The lack of excess Ca and alkalinity indicated that calcite had been previously removed by natural weathering. The extent of Ca enrichment in watershed discharge fluxes corresponds to the amounts of calcite exposed in granitoid rocks. High Ca/Na ratios relative to plagioclase stoichiometries indicate excess Ca in the Yosemite, Loch Vale, and other alpine watersheds in the Sierra Nevada and Rocky Mountains of the western United States. This Ca enrichment correlates with strong preferential weathering of calcite relative to plagioclase in exfoliated granitoids in glaciated terrains. In contrast, Ca/Na flux ratios are comparable to or less than the Ca/Na ratios for plagioclase in the subtropical Panola and tropical Rio Icacos watersheds, in which deeply weathered regoliths exhibit concurrent losses of calcite and much larger masses of plagioclase during transport-limited weathering. These results indicate that the weathering of accessory calcite may strongly influence Ca and alkalinity fluxes from silicate rocks during and following periods of glaciation and tectonism but is much less important for older stable geomorphic surfaces.

Geochimica et Cosmochimica Acta↗
USGS1999

The effect of temperature on experimental and natural chemical weathering rates of granitoid rocks

The effects of climatic temperature variations (5-35??C) on chemical weathering are investigated both experimentally using flow-through columns containing fresh and weathered granitoid rocks and for natural granitoid weathering in watersheds based on annual solute discharge. Although experimental Na and Si effluent concentrations are significantly higher in the fresh relative to the weathered granitoids, the proportional increases in concentration with increasing temperature are similar. Si and Na exhibit comparable average apparent activation energies (E(a)) of 56 and 61 kJ/mol, respectively, which are similar to those reported for experimental feldspar dissolution measured over larger temperature ranges. A coupled temperature-precipitation model, using an expanded database for solute discharge fluxes from a global distribution of 86 granitoid watersheds, produces an apparent activation energy for Si (51 kJ/mol), which is also comparable to those derived from the experimental study. This correlation reinforces evidence that temperature does significantly impact natural silicate weathering rates. Effluent K concentrations in the column study are elevated with respect to other cations compared to watershed discharge due to the rapid oxidation/dissolution of biotite. K concentrations are less sensitive to temperature, resulting in a lower average E(a) value (27 kJ/mol) indicative of K loss from lower energy interlayer sites in biotite. At lower temperatures, initial cation release from biotite is significantly faster than cation release from plagioclase. This agrees with reported higher K/Na ratios in cold glacial watersheds relative to warmer temperate environments. Increased release of less radiogenic Sr from plagioclase relative to biotite at increasing temperature produces corresponding decreases in 87Sr/86Sr ratios in the column effluents. A simple mixing calculation using effluent K/Na ratios, Sr concentrations and 87Sr/86Sr ratios for biotite and plagioclase approximates stoichiometric cation ratios from biotite/plagioclase dissolution at warmer temperatures (35??C), but progressively overestimates the relative proportion of biotite with decreasing temperature. Ca, Mg, and Sr concentrations closely correlate, exhibit no consistent trends with temperature, and are controlled by trace amounts of calcite or exchange within weathered biotite. The inability of the watershed model to differentiate a climate signal for such species correlates with the lower temperature dependence observed in the experimental studies.

Geochimica et Cosmochimica Acta↗
USGS1999

Selenium isotope ratios as indicators of selenium sources and oxyanion reduction

Selenium stable isotope ratio measurements should serve as indicators of sources and biogeochemical transformations of Se. We report measurements of Se isotope fractionation during selenate reduction, selenite sorption, oxidation of reduced Se in soils, and Se volatilization by algae and soil samples. These results, combined with previous work with Se isotopes, indicate that reduction of soluble oxyanions is the dominant cause of Se isotope fractionation. Accordingly, Se isotope ratios should be useful as indicators of oxyanion reduction, which can transform mobile species to forms that are less mobile and less bioavailable. Additional investigations of Se isotope fractionation are needed to confirm this preliminary assessment. We have developed a new method for measurement of natural Se isotope ratio variation which requires less than 500 ng Se per analysis and yields ±0.2‰ precision on 80 Se/ 76 Se. A double isotope spike technique corrects for isotopic fractionation during sample preparation and mass spectrometry. The small minimum sample size is important, as Se concentrations are often below 1 ppm in solids and 1 μg/L in fluids. The Se purification process is rapid and compatible with various sample matrices, including acidic rock or sediment digests.

Geochimica et Cosmochimica Acta↗
USGS1999

Oxygen and iron isotope studies of magnetite produced by magnetotactic bacteria

A series of carefully controlled laboratory studies was carried out to investigate oxygen and iron isotope fractionation during the intracellular production of magnetite (Fe3O4) by two different species of magnetotactic bacteria at temperatures between 4??and 35??C under microaerobic and anaerobic conditions. No detectable fractionation of iron isotopes in the bacterial magnetites was observed. However, oxygen isotope measurements indicated a temperature-dependent fractionation for Fe3O4 and water that is consistent with that observed for Fe3O4 produced extracellularly by thermophilic Fe3+-reducing bacteria. These results contrast with established fractionation curves estimated from either high-temperature experiments or theoretical calculations. With the fractionation curve established in this report, oxygen-18 isotope values of bacterial Fe3O4 may be useful in paleoenvironmental studies for determining the oxygen-18 isotope values of formation waters and for inferring paleotemperatures.

Science↗
USGS1999

Factors controlling elevated lead concentrations in water samples from aquifer systems in Florida

Concentrations of total lead (Pb) and dissolved Pb exceeded the U.S. Environmental Protection Agency action level of 15 micrograms per liter (mg/L) in approximately 19 percent and 1.3 percent, respectively, of ground-water samples collected during 1991-96 from a statewide network of monitoring wells designed to delineate background water quality of Florida's major aquifer systems. Differences in total Pb concentrations among aquifer systems reflect the combined influence of anthropogenic sources and chemical conditions in each system. A highly significant (p<0.001) difference in median total Pb concentrations was found for water samples from wells with water-level recording devices that contain Pb-counterweights (14 mg/L) compared to non-recorder wells (2 mg/L). Differences between total Pb concentrations for recorder and non-recorder wells are even more pronounced when compared for each aquifer system. The largest differences for recorder status are found for the surficial aquifer system, where median total Pb concentrations are 44 and 2.4 mg/L for recorder wells and non-recorder wells, respectively. Leaching of Pb from metal casing materials is another potential source of Pb in ground water samples. Median total Pb concentrations in water samples from the surficial, intermediate, and Floridan aquifer systems are higher from recorder wells cased with black iron than for recorder wells with steel and PVC casing material. S Stable isotopes of Pb were used in this study to distinguish between anthropogenic and natural sources of Pb in ground water, as Pb retains the isotopic signature of the source from which it is derived. Based on similarities between slopes and intercepts of trend lines for various sample types (plots of 206Pb/204Pb versus 208Pb/204Pb and 207Pb/204Pb versus 208Pb/204Pb) the predominant source of total Pb in water samples from the surficial aquifer system is corrosion of Pb counterweights. It is likely that only ground-water samples, not the aquifer, were contaminated with elevated Pb concentrations. Pb-isotopic ratios of water from the Floridan aquifer system plot between trend lines connecting the isotopic composition of Pb counterweights and the composition of acid leachates of material from the Floridan aquifer system, indicating that Pb in these waters most likely is a mixture of Pb derived from aquifer material and corrosion of Pb counterweights.

Florida↗
USGS1997

Comagmatic A-type granophyre and rhyolite from the Alid volcanic center, eritrea, northeast Africa

Granophyric blocks within late-Pleistocene pyroclastic flow ejecta from the Alid volcanic center, northeast Africa, are the rapidly crystallized, intrusive equivalent of pumice from the pyroclastic flow. Phenocryst compositions and geochemical characteristics of the pumice and granophyre are virtually identical. Silicate melt inclusions and other geochemical and geological constraints reveal those processes leading to development of the granophyric texture. Rhyolitic (A-type) magma with ∼2.6 wt % dissolved H 2 O and a temperature near 870°C was intruded to within 2–4 km of the surface, causing deformation and structural doming of shallow marine and subaerial strata. Eruptions of crystal-poor rhyolite from this shallow magma chamber caused degassing, which forced undercooling and consequent granophyric crystallization of some of the magma remaining in the intrusion. The most recent eruption from Alid excavated the crystallized granitic wall of the magma chamber, bringing the granophyric clasts to the surface.

Journal of Petrology↗
USGS1997

Sulfate-water isotope geothermometry and lead isotope data for the regional geothermal system in the Twin Falls area, south-central Idaho

Sulfate-water isotope geothermometry for the geothermal system at Twin Falls, Idaho indicates aquifer-temperatures of 90?? to 106 ??C; most sites are between 90?? and 93 ??C. 206Pb/204pb and 280Pb/204Pb of individual thermal waters are principally a function of how much lead has been dissolved from the carbonate and silicate fractions of the Paleozoic limestone collected west of Grand View Peak. Although most thermal waters are recovered from Tertiary rhyolite, very little of the dissolved lead is from the rhyolite. Recharge to this system occurs in northern Nevada and the fluid moves northward in the Paleozoic limestones. The occurrence of thermal fluid in the Idavada Volcanics near and south of Twin Falls, Idaho is the result of upward movement of this fluid from the Paleozoic limestone.

Conference Paper↗
USGS1997

The variable role of slab-derived fluids in the generation of a suite of primitive calc-alkaline lavas from the Southernmost Cascades, California

The compositional continuum observed in primitive calc-alkaline lavas erupted from small volcanoes across the southernmost Cascade arc is produced by the introduction of a variable proportion of slab-derived fluid into the superjacent peridotite layer of the mantle wedge. Magmas derived from fluid-rich sources are erupted primarily in the forearc and are characterized by Sr and Pb enrichment (primitive mantle-normalized Sr/P > 5.5), depletions of Ta and Nb, low incompatible-element abundances, and MORB-like Sr and Pb isotopic ratios. Magmas derived from fluid-poor sources are erupted primarily in the arc axis and behind the arc, and are characterized by weak enrichment in Sr [1.0 < (Sr/P)N < 1.3], weak depletions in Ta and Nb, higher incompatible-element abundances, and OIB-like Sr, Nd, and Pb isotopic ratios. Fluxing the mantle wedge above the subducting slab with H2O-rich fluid stabilizes amphibole and enriches the wedge peridotites in incompatible elements, particularly unradiogenic Sr and Pb. The hydrated amphibole-bearing portion of the mantle wedge is downdragged beneath the forearc, where its solidus is exceeded, yielding melts that are enriched in Sr and Pb, and depleted in Ta and Nb (reflecting both high Sr and Pb relative to Ta and Nb in the fluid, and the greater compatibility of Ta and Nb in amphibole compared to other silicate phases in the wedge). A steady decrease of the fluid-contributed geochemical signature away from the trench is produced by the progressive dehydration of the downdragged portion of the mantle wedge with depth, resulting from melt extraction and increased temperature at the slab-wedge interface. Inverse correlation between incompatible-element abundances and the size of the fluid-contributed geochemical signature is generated by melting of more depleted peridotites, rather than by significant differences in the degree of melting. High-(Sr/P)N lavas of the forearc are generated by melting of a MORB-source-like peridotite that has been fluxed with a greater proportion of slab-derived fluid, and low (Sr/P)N lavas of the arc axis are produced by melting of an OIB-source-like peridotite in the presence of a smaller proportion of slab-derived fluid. This study documents the control that a slab-derived fluid can have on incompatible element and isotopic systematics of arc magmas by 1) the addition of incompatible elements to the wedge, 2) the stabilization of hydrous phases in the wedge, and 3) the lowering of peridotite solidi.

Canadian Mineralogist↗
USGS1996

Kinetic and mineralogic controls on the evolution of groundwater chemistry and 87Sr/86Sr in a sandy silicate aquifer, northern Wisconsin, USA

Substantial flowpath-related variability of 87Sr/86Sr is observed in groundwaters collected from the Trout Lake watershed of northern Wisconsin. In the extensive shallow aquifer composed of sandy glacial outwash, groundwater is recharged either by seepage from lakes or by precipitation that infiltrates the inter-lake uplands. 87Sr/86Sr of groundwater derived mainly as seepage from a precipitation-dominated lake near the head of the watershed decreases with progressive water chemical evolution along its flowpath due primarily to enhanced dissolution of relatively unradiogenic plagioclase. In contrast, 87Sr/86Sr of groundwater derived mainly from precipitation that infiltrates upland areas is substantially greater than that of precipitation collected from the watershed, due to suppression of plagioclase dissolution together with preferential leaching of Sr from radiogenic phases such as K-feldspar and biotite. The results of a column experiment that simulated the effects of changing residence time of water in the aquifer sand indicate that mobile waters obtain relatively unradiogenic Sr, whereas stagnant waters obtain relatively radiogenic Sr. Nearly the entire range of strontium-isotope composition observed in groundwaters from the watershed was measured in the experimental product waters. The constant mobility of water along groundwater recharge flowpaths emanating from the lakes promotes the dissolution of relatively unradiogenic plagioclase, perhaps due to effective dispersal of clay mineral nuclei resulting from dissolution reactions. In contrast, episodic stagnation in the unsaturated zone along the upland recharge flowpaths suppresses plagioclase dissolution, perhaps due to accumulation of clay mineral nuclei on its reactive surfaces. Differences in redox conditions along these contrasting flowpaths probably enhance the observed differences in strontium isotope behavior. This study demonstrates that factors other than the calculated state of mineral saturation must be considered when attempting to simulate chemical evolution along flowpaths, and that reaction models must be able to incorporate changing contributions from reacting minerals in the calculations.

Geochimica et Cosmochimica Acta↗
USGS1993

Water, energy, and biogeochemical budgets investigation at Panola Mountain research watershed, Stockbridge, Georgia; A research plan

The Panola Mountain Research Watershed (PMRW), located in the Panola Mountain State Conservation Park near Stockbridge, Georgia has been selected as a core research watershed under the Water, Energy and Biogeochemical Budgets (WEBB) research initiative of the U.S. Geological Survey (USGS) Global Climate Change Program. This research plan describes ongoing and planned research activities at PMRW from 1984 to 1994. Since 1984, PMRW has been studied as a geochemical process research site under the U.S. Acid Precipitation Thrust Program. Research conducted under this Thrust Program focused on the estimation of dry atmospheric deposition, short-term temporal variability of streamwater chemistry, sulfate adsorption characteristics of the soils, groundwater chemistry, throughfall chemistry, and streamwater quality. The Acid Precipitation Thrust Program continues (1993) to support data collection and a water-quality laboratory. Proposed research to be supported by the WEBB program is organized in 3 interrelated categories: streamflow generation and water-quality evolution, weathering and geochemical evolution, and regulation of soil-water chemistry. Proposed research on streamflow generation and water-quality evolution will focus on subsurface water movement, its influence in streamflow generation, and the associated chemical changes of the water that take place along its flowpath. Proposed research on weathering and geochemical evolution will identify the sources of cations observed in the streamwater at Panola Mountain and quantify the changes in cation source during storms. Proposed research on regulation of soil-water chemistry will focus on the poorly understood processes that regulate soil-water and groundwater chemistry. (USGS)

Georgia↗