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Results for “Organic Geochemistry”

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USGS2007

A gel probe equilibrium sampler for measuring arsenic porewater profiles and sorption gradients in sediments: I. Laboratory development

A gel probe equilibrium sampler has been developed to study arsenic (As) geochemistry and sorption behavior in sediment porewater. The gels consist of a hydrated polyacrylamide polymer, which has a 92% water content. Two types of gels were used in this study. Undoped (clear) gels were used to measure concentrations of As and other elements in sediment porewater. The polyacrylamide gel was also doped with hydrous ferric oxide (HFO), an amorphous iron (Fe) oxyhydroxide. When deployed in the field, HFO-doped gels introduce a fresh sorbent into the subsurface thus allowing assessment of in situ sorption. In this study, clear and HFO-doped gels were tested under laboratory conditions to constrain the gel behavior prior to field deployment. Both types of gels were allowed to equilibrate with solutions of varying composition and re-equilibrated in acid for analysis. Clear gels accurately measured solution concentrations (??1%), and As was completely recovered from HFO-doped gels (??4%). Arsenic speciation was determined in clear gels through chromatographic separation of the re-equilibrated solution. For comparison to speciation in solution, mixtures of As(III) and As(V) adsorbed on HFO embedded in gel were measured in situ using X-ray absorption spectroscopy (XAS). Sorption densities for As(III) and As(V) on HFO embedded in gel were obtained from sorption isotherms at pH 7.1. When As and phosphate were simultaneously equilibrated (in up to 50-fold excess of As) with HFO-doped gels, phosphate inhibited As sorption by up to 85% and had a stronger inhibitory effect on As(V) than As(III). Natural organic matter (>200 ppm) decreased As adsorption by up to 50%, and had similar effects on As(V) and As(III). The laboratory results provide a basis for interpreting results obtained by deploying the gel probe in the field and elucidating the mechanisms controlling As partitioning between solid and dissolved phases in the environment. ?? 2008 American Chemical Society.

Environmental Science & Technology↗

USGS2019

Encylopedia of Caves

For many people, a visit to a cave is a wondrous event directing our minds to ponder the mysteries presented by these unique places and inspiring questions: How old is the cave? What was the role of water in forming the cave and where did the water come from? How is the cave connected to the surface environment? These are intriguing questions to ask, and karst scientists use isotope geochemistry to help solve these mysteries. Isotopes are atoms of the same chemical element that have the same number of protons but vary in their number of neutrons. As a result of their atomic mass difference, isotopes of a single element may exhibit slightly different chemical behavior. Radioisotopes are unstable and the nucleus of a parent isotope will spontaneously break apart (decay), releasing energy and changing into another element (daughter product) by loss or gain of protons, neutrons, or electrons. Stable isotopes, as implied by the name, are stable and do not spontaneously decay. These two types of isotopes are used widely by scientists to understand ancient and modern karst systems. Generally, radioisotopes are used for absolute dating karst water, cave sediments, cave formations (speleothems), and other material preserved in caves (such as bones). Stable isotopes can provide information about relative ages of cave water and speleothems. An absolute age provides a numeric date—such as 100,000 years old—whereas a relative age provides information that something is older or younger than something else—such as cave art is younger than a speleothem found in the same cave. Stable isotopes are used to study ancient karst systems because isotopic signals of past climate (paleoclimate) and environmental conditions (paleoenvironment) are preserved in speleothems and sediments. Stable isotopes are also used to understand modern systems, primarily through studies that distinguish sources of karst water, cave air, or contaminants, mixing of those sources, and biologic or chemical reactions that process compounds, such as breakdown of contaminants or organic matter. The variation in mass among isotopes is small, and isotope abundances are measured as a ratio of a common isotope to its less common isotopic counterparts (stable isotopes) or the abundance of a parent compared to daughter isotope (radioisotopes). As an example, hydrogen (H) has three naturally occurring isotopes. Most H comprises one proton (1H), but the rarer stable isotope (called deuterium) comprises one proton and one neutron (2H), and the radioisotope (called tritium) comprises one proton and two neutrons (3H). Because scientists use the minute differences in isotopes to test hypotheses, a scientist must understand the accuracy, precision, and error of the available methods, the assumptions about the chemical conditions of interest, and the limitations of the isotopic method being used. Many isotopic studies employ multiple isotopic tracers to better leverage the strengths and offset the limitations of using a single isotope. This article focuses on isotopes used to study the geology and hydrology of caves, but much additional isotopic work has been used to characterize the biology of caves.

Book chapter↗

USGS1997

Distribution of terminal electron-accepting processes in an aquifer having multiple contaminant sources

Concentrations of electron acceptors, electron donors, and H2 in groundwater were measured to determine the distribution of terminal electron-accepting processes (TEAPs) in an alluvial aquifer having multiple contaminant sources. Upgradient contaminant sources included two separate hydrocarbon point sources, one of which contained the fuel oxygenate methyl tertbutyl ether (MTBE). Infiltrating river water was a source of dissolved NO31 SO4 and organic carbon (DOC) to the downgradient part of the aquifer. Groundwater downgradient from the MTBE source had larger concentrations of electron acceptors (dissolved O2 and SO4) and smaller concentrations of TEAP end products (dissolved inorganic C, Fe2+ and CH4) than groundwater downgradient from the other hydrocarbon source, suggesting that MTBE was not as suitable for supporting TEAPs as the other hydrocarbons. Measurements of dissolved H2 indicated that SO4 reduction predominated in the aquifer during a period of high water levels in the aquifer and river. The predominant TEAP shifted to Fe3+ reduction in upgradient areas after water levels receded but remained SO4 reducing downgradient near the river. This distribution of TEAPs is the opposite of what is commonly observed in aquifers having a single contaminant point source and probably reflects the input of Dec and SO4 to the aquifer from the river. Results of this study indicate that the distribution of TEAPs in aquifers having multiple contaminant sources depends on the composition and location of the contaminants and on the availability of electron acceptors.

Applied Geochemistry↗

USGS2010

Geochemical evolution processes and water-quality observations based on results of the National Water-Quality Assessment Program in the San Antonio segment of the Edwards aquifer, Texas, 1996-2006

As part of the National Water-Quality Assessment Program, the U.S. Geological Survey collected and analyzed groundwater samples during 1996-2006 from the San Antonio segment of the Edwards aquifer of central Texas, a productive karst aquifer developed in Cretaceous-age carbonate rocks. These National Water-Quality Assessment Program studies provide an extensive dataset of groundwater geochemistry and water quality, consisting of 249 groundwater samples collected from 136 sites (wells and springs), including (1) wells completed in the shallow, unconfined, and urbanized part of the aquifer in the vicinity of San Antonio (shallow/urban unconfined category), (2) wells completed in the unconfined (outcrop area) part of the regional aquifer (unconfined category), and (3) wells completed in and springs discharging from the confined part of the regional aquifer (confined category). This report evaluates these data to assess geochemical evolution processes, including local- and regional-scale processes controlling groundwater geochemistry, and to make water-quality observations pertaining to sources and distribution of natural constituents and anthropogenic contaminants, the relation between geochemistry and hydrologic conditions, and groundwater age tracers and travel time. Implications for monitoring water-quality trends in karst are also discussed. Geochemical and isotopic data are useful tracers of recharge, groundwater flow, fluid mixing, and water-rock interaction processes that affect water quality. Sources of dissolved constituents to Edwards aquifer groundwater include dissolution of and geochemical interaction with overlying soils and calcite and dolomite minerals that compose the aquifer. Geochemical tracers such as magnesium to calcium and strontium to calcium ratios and strontium isotope compositions are used to evaluate and constrain progressive fluid-evolution processes. Molar ratios of magnesium to calcium and strontium to calcium in groundwater typically increase along flow paths; results for samples of Edwards aquifer groundwater show an increase from shallow/urban unconfined, to unconfined, to confined groundwater categories. These differences are consistent with longer residence times and greater extents of water-rock interaction controlling fluid compositions as groundwater evolves from shallow unconfined groundwater to deeper confined groundwater. Results for stable isotopes of hydrogen and oxygen indicate specific geochemical processes affect some groundwater samples, including mixing with downdip saline water, mixing with recent recharge associated with tropical cyclonic storms, or mixing with recharge water than has undergone evaporation. The composition of surface water recharging the aquifer, as well as mixing with downdip water from the Trinity aquifer or the saline zone, also might affect water quality. A time-series record (1938-2006) of discharge at Comal Springs, one of the major aquifer discharge points, indicates an upward trend for nitrate and chloride concentrations, which likely reflects anthropogenic activities. A small number of organic contaminants were routinely or frequently detected in Edwards aquifer groundwater samples. These were the pesticides atrazine, its degradate deethylatrazine, and simazine; the drinking-water disinfection byproduct chloroform; and the solvent tetrachloroethene. Detection of these contaminants was most frequent in samples of the shallow/urban unconfined groundwater category and least frequent in samples of the unconfined groundwater category. Results indicate that the shallow/urban unconfined part of the aquifer is most affected by anthropogenic contaminants and the unconfined part of the aquifer is the least affected. The high frequency of detection for these anthropogenic contaminants aquifer-wide and in samples of deep, confined groundwater indicates that the entire aquifer is susceptible to water-quality changes as a result of anthropogenic activities. L

Texas↗

USGS1993

Radionuclides in ground water of the Carson River Basin, western Nevada and eastern California, U.S.A.

Ground water is the main source of domestic and public supply in the Carson River Basin. Ground water originates as precipitation primarily in the Sierra Nevada in the western part of Carson and Eagle Valleys, and flows down gradient in the direction of the Carson River through Dayton and Churchill Valleys to a terminal sink in the Carson Desert. Because radionuclides dissolved in ground water can pose a threat to human health, the distribution and sources of several naturally occurring radionuclides that contribute to gross-alpha and gross-beta activities in the study area were investigated. Generally, alpha and beta activities and U concentration increase from the up-gradient to down-gradient hydrographic areas of the Carson River Basin, whereas 222 Rn concentration decreases. Both 226 Ra and 228 Ra concentrations are similar throughout the study area. Alpha and beta activities and U concentration commonly exceed 100 pCi/l in the Carson Desert at the distal end of the flow system. Radon-222 commonly exceeds 2,000 pCi/l in the western part of Carson and Eagle Valleys adjacent to the Sierra Nevada. Radium-226 and 228 Ra concentrations are <5pCi/l. Four ground water samples were analyzed for 210 Po and one sample contained a high concentration of 21 pCi/l. Seven samples were analyzed for 210 Pb; six contained <3pCi/l and one contained 12 pCi/l. Thorium-230 was detected at concentrations of 0.15 and 0.20 pCi/l in two of four samples. Alpha-emitting radionuclides in the ground water originated from the dissolution of U-rich granitic rocks in the Sierra Nevada by CO 2 , oxygenated water. Dissolution of primary minerals, mainly titanite (sphene) in the granitic rocks, releases U to the water. Dissolved U is probably removed from the water by adsorption on Fe- and Mn-oxide coatings on fracture surfaces and fine-grained sediment, by adsorption on organic matter, and by coprecipitation with Fe and Mn oxides. These coated sediments are transported throughout the basin by fluvial processes. Thus, U is transported as dissolved and adsorbed species. A rise in the water table in the Carson Desert because of irrigation has resulted in the oxidation of U-rich organic matter and dissolution of U-bearing coatings on sediments, producing unusually high U concentration in the ground water. Alpha activity in the ground water is almost entirely from the decay of U dissolved in the water. Beta activity in ground water samples is primarily from the decay of 40 K dissolved in the water and ingrowth of 238 U progeny in the sample before analysis. Approximately one-half of the measured beta activity may not be present in ground water in the aquifer, but instead is produced in the sample after collection and before analysis. Potassium-40 is primarily from the dissolution of K-containing minerals, probably K-feldspar and biotite. Radon-222 is primarily from the decay of 226 Ra in the aquifer materials. Radium in the ground water is thought to be mainly from alpha recoil associated with the decay of Th in the aquifer material. Some Ra may be from dissolution (or desorption) or Ra-rich coatings on sediments.

California, Nevada↗

USGS2008

Mineralogy and geochemistry of boehmite-rich coals: New insights from the Haerwusu Surface Mine, Jungar Coalfield, Inner Mongolia, China

Boehmite-rich coal of Pennsylvanian age was discovered earlier at the Heidaigou Surface Mine, Jungar Coalfield, Inner Mongolia, China. This paper reports new results on 29 bench samples of the no. 6 coal from a drill core from the adjacent Haerwusu Surface Mine, and provides new insights into the origin of the minerals and elements present. The results show that the proportion of inertinite in the no. 6 coal is higher than in other Late Paleozoic coals in northern China. Based on mineral proportions (boehmite to kaolinite ratio) and major element concentrations in the coal benches of the drill core, the no. 6 coal may be divided into five sections (I to V). Major minerals in Sections I and V are kaolinite. Sections II and IV are mainly kaolinite with a trace of boehmite, and Section III is high in boehmite. The boehmite is derived from bauxite in the weathered surface (Benxi Formation) in the sediment-source region. The no. 6 coal is rich in Al2O3 (8.89%), TiO2 (0.47%), Li (116????g/g), F (286????g/g), Ga (18????g/g), Se (6.1????g/g), Sr (350????g/g), Zr (268????g/g), REEs (172????g/g), Pb (30????g/g), and Th (17????g/g). The elements are classified into five associations by cluster analysis, i.e. Groups A, B, C, D, and E. Group A (ash-SiO2-Al2O3-Na2O-Li) and Group B (REE-Sc-In-Y-K2O-Rb-Zr-Hf-Cs-U-P2O5-Sr-Ba-Ge) are strongly correlated with ash yield and mainly have an inorganic affinity. The elements that are negatively or less strongly correlated with ash yield (with exceptions of Fe2O3, Be, V, and Ni) are grouped in the remaining three associations: Group C, Se-Pb-Hg-Th-TiO2-Bi-Nb-Ta-Cd-Sn; Group D, Co-Mo-Tl-Be-Ni-Sb-MgO-Re-Ga-W-Zn-V-Cr-F-Cu; and Group E, S-As-CaO-MnO-Fe2O3. Aluminum is mainly distributed in boehmite, followed by kaolinite. The high correlation coefficients of the Li-ash, Li-Al2O3, and Li-SiO2 pairs indicate that Li is related to the aluminosilicates in the coal. The boehmite-rich coal is high in gallium and F, which occur in boehmite and the organic matter. Selenium and Pb are mainly in epigenetic clausthalite fillings in fractures. The abundant rare earth elements in the coal benches were supplied from two sources: the bauxite on the weathered surface of the Benxi Formation and from adjacent partings by groundwater leaching during diagenesis. The light rare earth elements (LREEs) are more easily leached from the partings and incorporated into the organic matter than the heavy REEs, leading to a higher ratio of LREEs to HREEs in the coal benches than in the overlying partings. ?? 2008 Elsevier B.V. All rights reserved.

International Journal of Coal Geology↗

USGS2015

Priority pollutants and associated constituents in untreated and treated discharges from coal mining or processing facilities in Pennsylvania, USA

Clean sampling and analysis procedures were used to quantify more than 70 inorganic constituents, including 35 potentially toxic or hazardous constituents, organic carbon, and other characteristics of untreated (influent) and treated (effluent) coal-mine discharges (CMD) at 38 permitted coal-mining or coal-processing facilities in the bituminous coalfield and 4 facilities in the anthracite coalfield of Pennsylvania. Of the 42 facilities sampled during 2011, 26 were surface mines, 11 were underground mines, and 5 were coal refuse disposal operations. Treatment of CMD with caustic soda (NaOH), lime (CaO or Ca(OH) 2 ), flocculent, or limestone was ongoing at 21%, 40%, 6%, and 4% of the facilities, respectively; no chemicals were added at the remaining facilities. All facilities with CMD treatment incorporated structures for active or passive aeration and settling of metal-rich precipitate. The untreated influent samples had wide ranges of pH (2.8–7.6), hot acidity (−600 to 8000 mg/L as CaCO 3 ), specific conductance (SC; 253–13,000 μS/cm), total dissolved solids (TDS; 168–18,100 mg/L), and associated dissolved (<0.45-μm pore-size filter) constituents, including SO 4 (14.7–10,700 mg/L), Fe (<0.01 to 4100 mg/L), Mn (0.02–136 mg/L), Al (<0.01 to 128 mg/L), and Zn (<0.003 to 18.8 mg/L). Concentrations of Ag (<1 μg/L), Hg (<1 μg/L), Sn (<0.5 μg/L), and CN (<0.01 mg/L) were below detection limits. Only one influent sample met permitted mine effluent (PME) limits plus dissolved-constituent criteria maximum concentration (CMC) thresholds for the protection of freshwater aquatic organisms. The pH of the treated effluent samples ranged from 5.5 to 11.9 and was greater than or equal to the pH of the corresponding influent at all sites. All the effluent samples met CMC levels for dissolved concentrations of Ag, As, Ba, Cd, Cl, Cr, Pb, Ni, Sb, Se, Tl, V, NH 3 , NO 2 , NO 3 , and CN; however, nine violated one or more of the PME limits for pH (<6, n = 1), net acidity (>0, n = 3), Fe (>7 mg/L, n = 1), or Mn (>5 mg/L, n = 8), plus one or more exceeded CMC levels for Al (>0.75 mg/L, n = 2), Co (>95 μg/L, n = 5), Zn (>307 μg/L, n = 1), Cu (>7.4 μg/L, n = 1), or Se (>12.8 μg/L, n = 3). Although CMC exceedances for Co and Zn were attributed to samples also violating the PME limit for pH or Mn, the samples that exceeded the CMC for Al, Cu, or Se met applicable PME limits for pH, Fe, and Mn. Furthermore, many of the pH-compliant effluents did not meet reference criteria for SO 4 and related measures of ionic strength, including TDS, SC, and osmotic pressure. The Wilcoxon matched-pair signed-ranks statistic was used to test if the overall difference between the effluent and influent pairs was equal to zero. Constituents that statistically were the same for effluent and influent ( p > 0.05) included flow rate, SC, osmotic pressure, hardness, alkalinity, total organic carbon (TOC), K, Cl, NO 3 , PO 4 , Sb, Sr, Br, Se, Mo, and V. Although temperature, dissolved oxygen, pH, Ca, and Na were greater in the effluent than the influent, most constituents decreased as a result of treatment, including TDS, acidity, SO 4 , Al, Fe, Mn, Mg, As, Ba, Be, Cd, Cr, Co, Cu, F, Pb, Ni, NH 3 , Tl, Ti, U, Zn, Zr, total phenols, total inorganic carbon (TIC), biological oxygen demand (BOD), and chemical oxygen demand (COD). Nevertheless, some constituents that decreased, such as SO 4 , still did not meet reference criteria. Findings from this study suggest that typical chemical or aerobic treatment of CMD to pH > 6 with removal of Fe to <7 mg/L and Mn to <5 mg/L may provide a reasonable measure of protection for aquatic life from priority pollutant metals and other toxic or hazardous constituents in effluent but may not be effective for achieving permissible or background levels for TDS, SC, osmotic pressure, or concentrations of SO 4 and some other pollutants, including Se, Br, and Cl, if present.

Pennsylvania↗

USGS1998

Factors controlling As and U in shallow ground water, southern Carson Desert, Nevada

Unusually high As and U concentrations (> 100 ??g/L) are widespread in shallow ground water beneath the southern Carson Desert. The high concentrations, which locally exceed 1000 ??g/L, are of concern from a human health standpoint because the shallow ground water is used for domestic supply. Possible affects on wildlife are also of concern because the ground water flows into shallow lakes and marshes within wildlife refuges. Arsenic and U concentrations in ground water of the southern Carson Desert appear to be affected by evaporative concentration, redox reactions, and adsorption. The relation of these elements with Cl suggest that most of the high concentrations can be attributed to evaporative concentration of Carson River water, the primary source of recharge. Some ground water contains higher As and U concentrations that cannot be explained by evaporative concentration alone. Oxidation-reduction reactions, involving metal oxides and sedimentary-organic matter, appear to contribute As, U, inorganic C, Fe and Mn to the ground water. Arsenic in Fe-oxide was confirmed by chemical extraction and is consistent with laboratory adsorption studies. Uranium in both sedimentary-organic C and Fe-oxide coatings has been confirmed by fission tracks and petrographic examination. Arsenic concentrations in the ground water and chemical extracts of aquifer sediments are broadly consistent with adsorption as a control on some dissolved As concentrations. An apparent loss of As from some ground water as evaporative concentration proceeds is consistent with adsorption as a control on As. However, evidence for adsorption should be viewed with caution, because the adsorption model used values for the adsorbent that have not been shown to be valid for the aquifer sediments throughout the southern Carson Desert. Hydrologic and geochemical conditions in the Carson Desert are similar to other areas with high As and U concentrations in ground water, including the Salton Sea basin and southern San Joaquin Valley of California. Hydrologic and geochemical conditions that produced some sandstone-tyPe U-ore deposits, including those in the non-marine, closed-basin sediments of the Morrison Formation near Grants, New Mexico, suggest that the Carson Desert may be a modern analog for those systems.

Applied Geochemistry↗

USGS2015

The fate of cyanide in leach wastes at gold mines: an environmental perspective

This paper reviews the basic chemistry of cyanide, methods by which cyanide can be analyzed, and aspects of cyanide behavior that are most relevant to environmental considerations at mineral processing operations associated with gold mines. The emphasis is on research results reported since 1999 and on data gathered for a series of U.S. Geological Survey studies that began in the late 1990s. Cyanide is added to process solutions as the CN − anion, but ore leaching produces numerous other cyanide-containing and cyanide-related species in addition to the desired cyanocomplex of gold. These can include hydrogen cyanide (HCN); cyanometallic complexes of iron, copper, zinc, nickel, and many other metals; cyanate (CNO − ); and thiocyanate (SCN − ). The fate of these species in solid wastes and residual process solutions that remain once gold recovery activities are terminated and in any water that moves beyond the ore processing facility dictates the degree to which cyanide poses a risk to aquatic organisms and aquatic-dependent organisms in the local environment. Cyanide-containing and cyanide-related species are subject to attenuation mechanisms that lead to dispersal to the atmosphere, chemical transformation to other carbon and nitrogen species, or sequestration as cyanometallic precipitates or adsorbed species on mineral surfaces. Dispersal to the atmosphere and chemical transformation amount to permanent elimination of cyanide, whereas sequestration amounts to storage of cyanide in locations from which it can potentially be remobilized by infiltrating waters if conditions change. From an environmental perspective, the most significant cyanide releases from gold leach operations involve catastrophic spills of process solutions or leakage of effluent to the unsaturated or saturated zones. These release pathways are unfavorable for two important cyanide attenuation mechanisms that tend to occur naturally: dispersal of free cyanide to the atmosphere and sunlight-catalyzed dissociation of strong cyanometallic complexes, which produces free cyanide that can then disperse to the atmosphere. The widest margins of environmental safety will be achieved where mineral processing operations are designed so that time for offgassing, aeration, and sunlight exposure are maximized in the event that cyanide-bearing solutions are released inadvertently.

Applied Geochemistry↗

USGS2008

Hydrogeology, Chemical Characteristics, and Transport Processes in the Zone of Contribution of a Public-Supply Well in York, Nebraska

In 2001, the U.S. Geological Survey, as part of the National Water Quality Assessment (NAWQA) Program, initiated a topical study of Transport of Anthropogenic and Natural Contaminants (TANC) to PSW (public-supply wells). Local-scale and regional-scale TANC study areas were delineated within selected NAWQA study units for intensive study of processes effecting transport of contaminants to PSWs. This report describes results from a local-scale TANC study area at York, Nebraska, within the High Plains aquifer, including the hydrogeology and geochemistry of a 108-square-kilometer study area that contains the zone of contribution to a PSW selected for study (study PSW), and describes factors controlling the transport of selected anthropogenic and natural contaminants to PSWs. Within the local-scale TANC study area, the High Plains aquifer is approximately 75 m (meter) thick, and includes an unconfined aquifer, an upper confining unit, an upper confined aquifer, and a lower confining unit with lower confined sand lenses (units below the upper confining unit are referred to as confined aquifers) in unconsolidated alluvial and glacial deposits overlain by loess and underlain by Cretaceous shale. From northwest to southeast, land use in the local-scale TANC study area changes from predominantly irrigated agricultural land to residential and commercial land in the small community of York (population approximately 8,100). For the purposes of comparing water chemistry, wells were classified by degree of aquifer confinement (unconfined and confined), depth in the unconfined aquifer (shallow and deep), land use (urban and agricultural), and extent of mixing in wells in the confined aquifer with water from the unconfined aquifer (mixed and unmixed). Oxygen (delta 18O) and hydrogen (delta D) stable isotopic values indicated a clear isotopic contrast between shallow wells in the unconfined aquifer (hereinafter, unconfined shallow wells) and most monitoring wells in the confined aquifers (hereinafter, confined unmixed wells). Delta 18O and delta D values for a minority of wells in the confined aquifers were intermediate between those for the unconfined shallow wells and those for the confined unmixed wells. These intermediate values were consistent with mixing of water from unconfined and confined aquifers (hereinafter, confined mixed wells). Oxidation-reduction conditions were primarily oxic in the unconfined aquifer and variably reducing in the confined aquifers. Trace amounts of volatile organic compounds (VOC), particularly tetrachloroethylene (PCE) and trichloroethylene (TCE), were widely detected in unconfined shallow urban wells and indicated the presence of young urban recharge waters in most confined mixed wells. The presence of degradation products of agricultural pesticides (acetochlor and alachlor) in some confined mixed wells suggests that some fraction of the water in these wells also was the result of recharge in agricultural areas. In the unconfined aquifer, age-tracer data (chlorofluorocarbon and sulfur hexafluoride data, and tritium to helium-3 ratios) fit a piston-flow model, with apparent recharge ages ranging from 7 to 48 years and generally increasing with depth. Age-tracer data for the confined aquifers were consistent with mixing of 'old' water, not containing modern tracers recharged in the last 60 years, and exponentially-mixed 'young' water with modern tracers. Confined unmixed wells contained less than (<) 3 percent (%) young water mixed with a much larger fraction greater than or equal to (>=) 97% of old water. Confined mixed wells contained >30% young water and mean ages ranged from 12 to 14 years. Median concentrations of nitrate (as nitrogen, hereinafter, nitrate-N) were 17.3 and 16.0 mg/L (milligram per liter) in unconfined shallow urban and agricultural wells, respectively, indicating a range of likely nitrate sources. Septic systems are most numerous near the edge of the urban area and appear to be

Scientific Investigations Report↗

USGS2004

Suwannee river basin and estuary integrated science workshop: September 22-24, 2004 Cedar Key, Florida

In response to the growing number of environmental concerns in the mostly pristine Suwannee River Basin and the Suwannee River Estuary system, the States of Florida and Georgia, the Federal government, and other local organizations have identified the Suwannee River as an ecosystem in need of protection because of its unique biota and important water resources. Organizations with vested interests in the region formed a coalition, the Suwannee Basin Interagency Alliance (SBIA), whose goals are to promote coordination in the identification, management, and scientific knowledge of the natural resources in the basin and estuary. To date, an integrated assessment of the physical, biological, and water resources has not been completed. A holistic, multi-disciplinary approach is being pursued to address the research needs in the basin and estuary and to provide supportive data for meeting management objectives of the entire ecosystem. The USGS is well situated to focus on the larger concerns of the basin and estuary by addressing specific research questions linking water supply and quality to ecosystem function and health across county and state boundaries. A strategic plan is being prepared in cooperation with Federal, State, and local agencies to identify and implement studies to address the most compelling research issues and management questions, and to conduct fundamental environmental monitoring studies. The USGS, Suwannee River Water Management District and the Florida Marine Research Institute are co-sponsoring this scientific workshop on the Suwannee River Basin and Estuary to: Discuss current and past research findings, Identify information gaps and research priorities, and Develop an action plan for coordinated and relevant research activities in the future. This workshop builds on the highly successful basin-wide conference sponsored by the Suwannee Basin Interagency Alliance that was held three years ago in Live Oak, Florida. This years workshop will focus on identifying information needs and priorities and developing partnerships. The USGS is seeking to define the role of the USGS Florida Integrated Science Center (FISC) in conducting integrated research in the Suwannee River Basin, and to establish a cooperative program with other agencies. Participants interested in river, floodplain, springs, estuary, or basin-wide issues are encouraged to attend. Topics for this years workshop include: Water quality and geochemistry: nutrient enrichment, reduction of nutrient loading to ground water, contaminants, and land use, Hydrogeology: interactions among ground water, surface water and ecosystem, modeling, and baseline mapping, Ecosystem dynamics: structure, process, species, and habitats (estuarine, riverine, floodplain, and wetland), and Information management: data sharing, database development, geographic information system (GIS), and basin-wide models.

Open-File Report↗

USGS2019

Quantifying changes to infaunal communities associated with several deep-sea coral habitats in the Gulf of Mexico and their potential recovery from the DWH oil spill

Extensive information is available about infaunal soft-sediment communities in the Gulf of Mexico (Gulf) (Pequegnat et al. 1990, Rowe and Kennicutt II 2009, Wei et al. 2010), particularly from the large-scale sampling effort of the Deep Gulf of Mexico Benthos (DGOMB) project in the early 2000s (Rowe and Kennicutt II 2009). Infaunal soft-sediment communities in the northern Gulf differ by geographic location and depth (Rowe and Kennicutt II 2009, Wei et al. 2010). Density decreases with depth, while taxa diversity exhibits a mid-depth (1,100-1,300 m) maximum (Rowe and Kennicutt II 2009). Community composition is influenced by both geographic location and depth, with zones (as defined by Wei et al. 2010) encompassing specific depth ranges, ranging from 635 to 3,314 m, and separated into east and west components. These zones were correlated to detrital particulate organic carbon (POC) export flux, primarily from the Mississippi River (Wei et al. 2010), where POC flux decreases with depth (Biggs et al. 2008). The flux of POC has also been found to be higher in the northeast Gulf than the northwest (Biggs et al. 2008), and consequently, biomass of infaunal communities is positively correlated with sedimentorganic carbon content (Morse and Beazley 2008). Most of the deep Gulf is composed of soft-sediment environments, but the relative flat seafloor is punctuated in areas with other heterogeneous habitats, including chemosynthetic environments and deepsea coral habitats. Deep-sea corals create a complex three-dimensional structure that enhances local biodiversity, supporting diverse and abundant fish and invertebrate communities (Mortensen et al. 1995, Costello et al. 2005, Henry and Roberts 2007, Ross and Quattrini 2007, Buhl-Mortensen et al. 2010). In recent years, knowledge of the sphere of influence of deep-sea corals has expanded, with evidence that coral habitats also influence surrounding sediments (Mienis et al. 2012, Demopoulos et al. 2014, Fisher et al. 2014, Demopoulos et al. 2016, Bourque and Demopoulos 2018). Deep-sea corals are capable of altering their associated biotic and abiotic environment, thus serving as ecosystem engineers (e.g., Jones et al. 1994). The depositional environment and associated hydrodynamic regime around coral habitats differ from the extensive expanses of soft-sediments that dominate the sea floor (e.g., Mienis et al. 2009a. 2009a, Mienis et al. 2009b, Mienis et al. 2012), with the three-dimensional structure of the coral causing turbulent flows that enhance sediment accumulation adjacent to coral structures. In the northern Gulf, deep-sea corals generally occur on mounds of authigenic carbonate (Schroeder 2002) where elevation above the benthic boundary layer into higher velocity laminar flows allows for increased availability of food resources (Buhl-Mortensen and Mortensen 2005). The different hydrodynamics around corals likely affects the sediment geochemistry and in turn infaunal community structure and function (Demopoulos et al. 2014). Ecosystem-based research on Gulf infaunal communities has primarily focused on soft-sediment environments. Initial research on deep-sea coral-associated infaunal communities focused on Lophelia pertusa (e.g., Demopoulos et al. 2014), and more recent studies focused on octocorals (Fisher et al. 2014, Demopoulos et al. 2016, Bourque and Demopoulos 2018) and comparisons among coral habitat types (Bourque and Demopoulos 2018). Coral-adjacent sediment communities are distinctly different from nearby background soft-sediment (Demopoulos et al. 2014, Bourque and Demopoulos 2018), with a sphere of influence estimated to be between 14 and 100 m (Demopoulos et al. 2014, Bourque and Demopoulos 2018). The coral type (e.g., L. pertusa, Madrepora oculata, octocorals) also influences sediment communities, with L. pertusa habitats distinct from both M. oculata and octocoral habitats (Bourque and Demopoulos 2018). Differences among coral communities are influenced by depth,

Gulf of Mexico↗

USGS2014

Spectroscopy from Space

This chapter reviews detection of materials on solid and liquid (lakes and ocean) surfaces in the solar system using ultraviolet to infrared spectroscopy from space, or near space (high altitude aircraft on the Earth), or in the case of remote objects, earth-based and earth-orbiting telescopes. Point spectrometers and imaging spectrometers have been probing the surfaces of our solar system for decades. Spacecraft carrying imaging spectrometers are currently in orbit around Mercury, Venus, Earth, Mars, and Saturn, and systems have recently visited Jupiter, comets, asteroids, and one spectrometer-carrying spacecraft is on its way to Pluto. Together these systems are providing a wealth of data that will enable a better understanding of the composition of condensed matter bodies in the solar system. Minerals, ices, liquids, and other materials have been detected and mapped on the Earth and all planets and/or their satellites where the surface can be observed from space, with the exception of Venus whose thick atmosphere limits surface observation. Basaltic minerals (e.g., pyroxene and olivine) have been detected with spectroscopy on the Earth, Moon, Mars and some asteroids. The greatest mineralogic diversity seen from space is observed on the Earth and Mars. The Earth, with oceans, active tectonic and hydrologic cycles, and biological processes, displays the greatest material diversity including the detection of amorphous and crystalline inorganic materials, organic compounds, water and water ice. Water ice is a very common mineral throughout the Solar System and has been unambiguously detected or inferred in every planet and/or their moon(s) where good spectroscopic data has been obtained. In addition to water ice, other molecular solids have been observed in the solar system using spectroscopic methods. Solid carbon dioxide is found on all systems beyond the Earth except Pluto, although CO 2 sometimes appears to be trapped in other solids rather than as an ice on some objects. The largest deposits of carbon dioxide ice are found on Mars. Sulfur dioxide ice is found in the Jupiter system. Nitrogen and methane ices are common beyond the Uranian system. Saturn’s moon Titan probably has the most complex active extra-terrestrial surface chemistry involving organic compounds. Some of the observed or inferred compounds include ices of benzene (C 6 H 6 ), cyanoacetylene (HC 3 N), toluene (C 7 H 8 ), cyanogen (C 2 N 2 ), acetonitrile (CH 3 CN), water (H 2 O), carbon dioxide (CO 2 ), and ammonia (NH 3 ). Confirming compounds on Titan is hampered by its thick smoggy atmosphere, where in relative terms the atmospheric interferences that hamper surface characterization lie between that of Venus and Earth. In this chapter we exclude discussion of the planets Jupiter, Saturn, Uranus, and Neptune because their thick atmospheres preclude observing the surface, even if surfaces exist. However, we do discuss spectroscopic observations on a number of the extra-terrestrial satellite bodies. Ammonia was predicted on many icy moons but is notably absent among the definitively detected ices with possible exceptions on Charon and possible trace amounts on some of the Saturnian satellites. Comets, storehouses of many compounds that could exist as ices in their nuclei, have only had small amounts of water ice definitively detected on their surfaces from spectroscopy. Only two asteroids have had a direct detection of surface water ice, although its presence can be inferred in others.

Reviews in Mineralogy and Geochemistry↗

USGS1994

Ground-water quality and geochemistry in Dayton, Stagecoach, and Churchill Valleys, western Nevada

The U.S. Geological Survey investigated the quality of ground water in the Dayton, Stagecoach, and Churchill Valleys as part of the Carson River Basin National Water-Quality Assessment (NAWQA) pilot study. Four aquifer systems have been de- lineated in the study area. Principal aquifers are unconsolidated deposits at altitudes of less than 4,900 feet above sea level and more than 50 feet below land surface. Shallow aquifers are at altitudes of less than 4,900 feet and less than 50 feet below land surface. Upland aquifers are above 4,900 feet and provide recharge to the principal aquifers. Thermal aquifers, defined as those having a water temperature greater than 30 degrees Celsius, are also present. Ground water used in Dayton, Stagecoach, and Churchill Valleys is pumped from principal aquifers in unconsolidated basin-fill deposits. Ground water in these aquifers originates as precipitation in the adjacent mountains and is recharged by the Carson River and by underflow from adjacent upstream valleys. Ground-water flow is generally parallel to the direction of surface-water flow in the Carson River. Ground water is discharged by pumping, evapo- transpiration, and underflow into the Carson River. The results of geochemical modeling indicate that as ground water moves from upland aquifers in mountainous recharge areas to principal aquifers in basin-fill deposits, the following processes probably occur: (1) plagioclase feldspar, sodium chloride, gypsum (or pyrite), potassium feldspar, and biotite dissolve; (2) calcite precipitates; (3) kaolinite forms; (4) small amounts of calcium and magnesium in the water exchange for potassium on aquifer minerals; and (5) carbon dioxide is gained or lost. The geochemical models are consistent with (1) phases identified in basin- fill sediments; (2) chemical activity of major cations and silica; (3) saturation indices of calcite and amorphous silica; (4) phase relations for aluminosilicate minerals indicated by activity diagrams; and (5) results of optical, X-ray diffraction, and scanning-electron microscopy examination of mineral grains in the aquifer sediments. Sulfur-isotopic composition of ground- water samples also supports the models. In general, the quality of ground water in the study area meets Nevada State drinking-water standards and is acceptable for most uses. In addition to analysis for major ions, samples were analyzed for 22 inorganic trace elements, 3 nutrients, and 4 radionuclides. Selenium in 1 sample is the only constituent that exceeded Nevada State primary drinking-water standards. Nevada State secondary- drinking water standards were exceeded for fluoride in 1 sample, for iron in 7 samples, and for manganese in 19 samples. Minor constituent con- centrations are generally the result of local redox conditions, and are primarily from minerals in volcanic and marine metasedimentary rocks, metal- oxide coatings on mineral grains, and organic matter.

Open-File Report↗

USGS2008

Influence of groundwater recharge and well characteristics on dissolved arsenic concentrations in southeastern Michigan groundwater

Arsenic concentrations exceeding 10 ??g/l, the United States maximum contaminant level and the World Health Organization guideline value, are frequently reported in groundwater from bedrock and unconsolidated aquifers of southeastern Michigan. Although arsenic-bearing minerals (including arsenian pyrite and oxide/hydroxide phases) have been identified in Marshall Sandstone bedrock of the Mississippian aquifer system and in tills of the unconsolidated aquifer system, mechanisms responsible for arsenic mobilization and subsequent transport in groundwater are equivocal. Recent evidence has begun to suggest that groundwater recharge and characteristics of well construction may affect arsenic mobilization and transport. Therefore, we investigated the relationship between dissolved arsenic concentrations, reported groundwater recharge rates, well construction characteristics, and geology in unconsolidated and bedrock aquifers. Results of multiple linear regression analyses indicate that arsenic contamination is more prevalent in bedrock wells that are cased in proximity to the bedrock-unconsolidated interface; no other factors were associated with arsenic contamination in water drawn from bedrock or unconsolidated aquifers. Conditions appropriate for arsenic mobilization may be found along the bedrock-unconsolidated interface, including changes in reduction/oxidation potential and enhanced biogeochemical activity because of differences between geologic strata. These results are valuable for understanding arsenic mobilization and guiding well construction practices in southeastern Michigan, and may also provide insights for other regions faced with groundwater arsenic contamination. ?? Springer-Verlag 2008.

Environmental Geochemistry and Health↗

USGS2001

Geochemistry and origins of mineralized waters in the Floridan aquifer system, northeastern Florida

Increases in chloride concentration have been observed in water from numerous wells tapping the Floridan aquifer system in northeastern Florida. Although most increases have been in the eastern part of Duval County, Florida, no spatial pattern in elevated chloride concentrations is discernible. Possible sources of the mineralized water include modern seawater intrusion; unflushed Miocene-to-Pleistocene-age seawater or connate water in aquifer sediments; or mineralized water from deeper zones of the aquifer system or from formations beneath the Floridan aquifer system. The purpose of this study was to document the chemical and isotopic characteristics of water samples from various aquifer zones, and from geochemical and hydrogeologic data, to infer the source of the increased mineralization. Water samples were collected from 53 wells in northeastern Florida during 1997-1999. Wells tapped various zones of the aquifer including: the Fernandina permeable zone (FPZ), the upper zone of the Lower Floridan aquifer (UZLF), the Upper Floridan aquifer (UFA), and both the UFA and the UZLF. Water samples were analyzed for major ions and trace constituents and for isotopes of carbon, oxygen, hydrogen, sulfur, strontium, chlorine, and boron. Samples of rock from the aquifer were analyzed for isotopes of oxygen, carbon, and strontium. In general, water from various aquifer zones cannot be differentiated based on chemistry, except for water from FPZ wells. Major-ion concentrations vary as much within the upper zone of the Lower Floridan aquifer and the Upper Floridan aquifer as between these two zones. Simple models of mixing between fresh ground water and either modern seawater or water from the FPZ as a mineralized end member show that many water samples from the UZLF aquifer and the UFA are enriched in bicarbonate, calcium, magnesium, sulfate, fluoride, and silica and are depleted in sodium and potassium (as compared to concentrations predicted by simple mixing). Chemical mass-balance models of mixing and reactions between a hypothetical initial seawater and aquifer minerals cannot account for the observed water chemistry in a few wells, implying a source other than seawater, either ancient or modern, or the occurrence of other more complex rock-water reactions. Hydrogeologic and geochemical data from water and aquifer samples indicate that the most likely source of mineralized water in some wells yielding water with increasing chloride concentrations is water from the FPZ. In other wells, the flushing of Miocene-to-Pleistocene-age seawater can account for the observed chloride concentrations. The fact that most of the water samples collected are a mixture of less than one percent of mineralized water with more than 99 percent fresh or recharge water makes identifying the source of the mineralized water difficult. Differences in carbon-14 and sulfur-34 values probably reflect areal differences in aquifer mineralogy and distribution of organic carbon related to paleokarst features. Geochemical mass-balance models of seawater-rock interaction are unable to account for the chemical and isotopic composition of mineralized water from the FPZ, which implies another source of mineralized water, such as a brine, or the occurrence of more complex water-rock reactions.

Florida↗

USGS2008

Growing up green on serpentine soils: Biogeochemistry of serpentine vegetation in the Central Coast Range of California

Serpentine soils derived from the weathering of ultramafic rocks and their metamorphic derivatives (serpentinites) are chemically prohibitive for vegetative growth. Evaluating how serpentine vegetation is able to persist under these chemical conditions is difficult to ascertain due to the numerous factors (climate, relief, time, water availability, etc.) controlling and affecting plant growth. Here, the uptake, incorporation, and distribution of a wide variety of elements into the biomass of serpentine vegetation has been investigated relative to vegetation growing on an adjacent chert-derived soil. Soil pH, electrical conductivity, organic C, total N, soil extractable elements, total soil elemental compositions and plant digestions in conjunction with spider diagrams are utilized to determine the chemical relationships of these soil and plant systems. Plant available Mg and Ca in serpentine soils exceed values assessed in chert soils. Magnesium is nearly 3 times more abundant than Ca in the serpentine soils; however, the serpentine soils are not Ca deficient with Ca concentrations as high as 2235 mg kg-1. Calcium to Mg ratios (Ca:Mg) in both serpentine and chert vegetation are greater than one in both below and above ground tissues. Soil and plant chemistry analyses support that Ca is not a limiting factor for plant growth and that serpentine vegetation is actively moderating Mg uptake as well as tolerating elevated concentrations of bioavailable Mg. Additionally, results demonstrate that serpentine vegetation suppresses the uptake of Fe, Cr, Ni, Mn and Co into its biomass. The suppressed uptake of these metals mainly occurs in the plants' roots as evident by the comparatively lower metal concentrations present in above ground tissues (twigs, leaves and shoots). This research supports earlier studies that have suggested that ion uptake discrimination and ion suppression in the roots are major mechanisms for serpentine vegetation to tolerate the chemistry of serpentine soils. ?? 2008 Elsevier Ltd.

Applied Geochemistry↗

USGS2026

Using sediment chemical fractions and multivariate statistics on water to identify sources, mobility, and bioavailability of aluminum in the Florida River near Durango, Colorado

The Florida River in southwestern Colorado, USA, flows through the Southern Ute Reservation and is a cultural and water resource to Tribal and non-Tribal communities. High concentrations of total Al, up to 16 400 µg l –1 , have been detected in the Florida River. Elevated Al concentrations in water may affect aquatic organisms’ ability to regulate ions and inhibit respiratory functions. Water chemistry collected during three sampling events in 2022 from the Florida River and two of its tributaries are used here to better understand the spatial distribution, seasonality, and sources of Al concentrations in the Florida River. Streambed sediment and rock chemistry is also used to infer geologic sources of Al in the watershed. A five-stage sequential extraction was performed on streambed sediment and rock samples to help determine Al transport processes. We assessed relations between major and trace elements in water using a principal component analysis, finding that high Al concentrations in the Florida River (>3500 µg l –1 total Al) are caused by the erosion of Al-laden sediments. We used a stepwise multiple linear regression to investigate the relationship between land use and Al concentrations. Land use did not reliably predict Al concentration, though increased streamflow connected to reservoir releases – particularly in the Salt Creek tributary – were found to contribute Al to the Florida River during the irrigation season. In this study, we demonstrate that successful metal source appropriation may be achieved through limited field sampling when performed with sufficient water chemistry analysis, sequential chemical extraction of stream sediments, and statistical and land-use analysis.

Colorado↗