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USGS2014

Aquifers of Arkansas: protection, management, and hydrologic and geochemical characteristics of groundwater resources in Arkansas

Sixteen aquifers in Arkansas that currently serve or have served as sources of water supply are described with respect to existing groundwater protection and management programs, geology, hydrologic characteristics, water use, water levels, deductive analysis, projections of hydrologic conditions, and water quality. State and Federal protection and management programs are described according to regulatory oversight, management strategies, and ambient groundwater-monitoring programs that currently (2013) are in place for assessing and protecting groundwater resources throughout the State. Physical attributes, groundwater geochemistry, and groundwater quality are described for each of the 16 aquifers of the State. Information in regard to the hydrology and geochemistry of each of the aquifers is summarized from about 550 historical and recent publications. Additionally, more than 8,000 sites with groundwater-quality data were obtained from the U.S. Geological Survey National Water Information System and the Arkansas Department of Environmental Quality databases and entered into a spatial database to investigate distribution and trends in chemical constituents for each of the aquifers. The 16 aquifers of the State were divided into two major physiographic regions of the State: the Coastal Plain Province (referred to as Coastal Plain) of eastern and southern Arkansas, which includes 11 of the 16 aquifers, and the Interior Highlands Division (referred to as Interior Highlands) of western Arkansas, which includes the remaining 5 aquifers. The 11 aquifers in the Coastal Plain consist of various geologic units that are Cenozoic in age and consist primarily of Cretaceous, Tertiary, and Quaternary sands, gravels, silts, and clays. Groundwater in the Coastal Plain represents one of the most valuable natural resources in the State, driving the economic engines of agriculture, while also supplying abundant water for commercial, industrial, and public-supply use. In terms of age from youngest to oldest, the aquifers of the Coastal Plain include Quaternary alluvial aquifers, including the Mississippi River Valley alluvial aquifer (the most important aquifer in Arkansas in terms of volume of use and economic benefits), the Jackson Group (a regional confining unit that served for decades as an important source of domestic supply), and the Cockfield, Sparta, Cane River, Carrizo, Wilcox, Nacatoch, Ozan, Tokio, and Trinity aquifers. The Mississippi River Valley alluvial aquifer accounts for approximately 94 percent of all groundwater used in the State, and the aquifer is used primarily for irrigation purposes. The Sparta aquifer is the second most important aquifer in terms of use, and the aquifer was used in the past dominantly as a source of public and industrial supply, although increasing irrigation use is occurring because of critically declining water levels in the Mississippi River Valley alluvial aquifer. Other aquifers of the Coastal Plain generally are used as important local sources of domestic, industrial, and public supply, in addition to other minor uses. Water quality generally is good for all aquifers of the Coastal Plain, except for elevated iron concentrations and localized areas of high salinity. The high salinity results from intrusion from underlying formations, evapotranspiration processes in areas of low recharge, and inadequate flushing in downgradient areas of residual salinity from deposition in marine environments. Trends in the spatial distribution of individual chemical constituents are related to position along the flow path for most aquifers of the Coastal Plain. These trends include elevated iron and nitrate concentrations with lower pH values and dissolved solids in groundwater from the outcrop areas, transitioning to lower iron and nitrate (related to changes in redox) and higher pH and dissolved solids (dominantly from the dissolution of carbonate minerals) in groundwater downgradient from outcrop areas. Groundwater generally trended from a calcium- to a sodium-bicarbonate water type with increasing cation exchange along the flow path. The Interior Highlands of western Arkansas has less reported groundwater use than other areas of the State, reflecting a combination of factors. These factors include prevalent and increasing use of surface water, less intensive agricultural uses, lower population and industry densities, lesser potential yield of the resource, and lack of detailed reporting. The overall low yields of aquifers of the Interior Highlands result in domestic supply as the dominant use, with minor industrial, public, and commercial-supply use. Where greater volumes are required for growth of population and industry, surface water is the greatest supplier of water needs in the Interior Highlands. The various aquifers of the Interior Highlands generally occur in shallow, fractured, well-indurated, structurally modified bedrock of this mountainous region of the State, as compared to the relatively flat-lying, unconsolidated sediments of the Coastal Plain. In terms of age from youngest to oldest, the aquifers of the Interior Highlands include: the Arkansas River Valley alluvial aquifer, the Ouachita Mountains aquifer, the Western Interior Plains confining system, the Springfield Plateau aquifer, and the Ozark aquifer. Spatial trends in groundwater geochemistry in the Interior Highlands differ greatly from trends noted for aquifers of the Coastal Plain. In the Coastal Plain, the prevalence of long regional flow paths results in regionally predictable and mappable geochemical changes along the flow paths. In the Interior Highlands, short, topographically controlled flow paths (from hilltops to valleys) within small watersheds represent the predominant groundwater-flow system. As such, dense data coverage from numerous wells would be required to effectively characterize these groundwater basins and define small-scale geochemical changes along any given flow path for aquifers of the Interior Highlands. Changes in geochemistry generally were related to rock type and residence time along individual flow paths. Dominant changes in geochemistry for the Ouachita Mountains aquifer and the Western Interior Plains confining system are attributed to rock/water interaction and changes in redox zonation along the flow path. In these areas, groundwater evolves along flow paths from a calcium- to a sodium-bicarbonate water type with increasing reducing conditions resulting in denitrification, elevated iron and manganese concentrations, and production of methane in the more geochemically evolved and strongest reducing conditions. In the Ozark and Springfield Plateau aquifers, rapid influx of surface-derived contaminants, especially nitrogen, coupled with few to no attenuation processes was attributed to the karst landscape developed on Mississippian- and Ordovician-age carbonate rocks of the Ozark Plateaus. Increasing nitrate concentrations are related to increasing agricultural land use, and areas of mature karst development result in higher nitrate concentrations than areas with less karst features.

Arkasas↗
USGS2021

Estimating and forecasting time-varying groundwater recharge in fractured rock: A state-space formulation with preferential and diffuse flow to the water table

Rapid infiltration following precipitation may result in groundwater contamination from surface contaminants or pathogens. In fractured rock, contaminants can migrate rapidly to points of groundwater withdrawals. In contrast to the temporal availability of groundwater quality chemical indicators, meteorological and groundwater level observations are available in real-time to estimate time-varying recharge, which can act as a surrogate to identify periods of rapid infiltration that may indicate contamination susceptibility. Estimating recharge using methods, such as base-flow recession, unsaturated infiltration models, or Water-Table Fluctuations (WTF), cannot capitalize on currently available technologies and telecommunication infrastructure to conduct real-time recharge estimation at scales relevant to characterizing rapid infiltration. We present a linear, physics-based State-Space (SS) model of one-dimensional infiltration to estimate recharge, which includes preferential and diffuse-flow to the water table. The model can take advantage of real-time data for water-table altitude, precipitation, and evapotranspiration. Model parameters are calibrated over an observation period, and the Kalman Filter (KF) is subsequently applied to continuously update the observed (water-table altitude) and unobserved (groundwater recharge) system states and predict future states as new data become available. The SS/KF algorithm is demonstrated at the Masser Groundwater Recharge Site in Pennsylvania, USA and comparisons are made with recharge estimates from WTF methods. Model results indicate that the frequency of observations (daily versus sub-daily) dictates the allocation between preferential and diffuse flow. Additionally, because infiltration processes encompass many nonlinearities, model parameters estimated from observation periods need to be updated at least seasonally to account for changing recharge conditions.

Water Resources Research↗
USGS1991

Capture myopathy in an endangered sandhill crane (Grus canadensis pulla)

Despite precautions to protect cranes, a 3-year-old endangered Mississippi sandhill crane ( Grus canadensis pulla ) was found caught in a leghold trap in Gautier, Mississippi, on 11 November 1987. The bird could have been in the trap for up to 16 hr and was standing and struggling to escape when it was discovered. Serum chemistries of the crane on 12 November revealed elevated lactic dehydrogenase (2,880 IU/L), alanine aminotransferase (ALT) (152 IU/L), and aspartate aminotransferase (AST) (>1,000 IU/L) values. Following surgical amputation of a fractured toe, the bird never attempted to stand and was unable to stand even when manually supported. Radiographic and physical examination of both legs did not reveal any anatomical abnormalities. Despite medical care, including supportive therapy, no improvement was observed in the bird's ability to stand and to support itself, and the bird died on 19 November. Serum chemistries and the postmortem and histopathologic findings were compatible with capture myopathy described in other species. Because of the possible susceptibility of long-legged birds such as the Mississippi sandhill crane to capture myopathy, special care must be taken when trapping, handling, chemically immobilizing, and transporting these species. In addition, precautions must be taken when conducting a predator-control program to ensure that nontarget wildlife are unlikely to encounter traps. Capture myopathy has only rarely been observed in wild birds, and this case represents the first report in a Mississippi sandhill crane.

Mississippi↗
USGS2012

Book review: Earthquakes and water

It is really nice to see assembled in one place a discussion of the documented and hypothesized hydrologic effects of earthquakes. The book is divided into chapters focusing on particular hydrologic phenomena including liquefaction, mud volcanism, stream discharge increases, groundwater level, temperature and chemical changes, and geyser period changes. These hydrologic effects are inherently fascinating, and the large number of relevant publications in the past decade makes this summary a useful milepost. The book also covers hydrologic precursors and earthquake triggering by pore pressure. A natural need to limit the topics covered resulted in the omission of tsunamis and the vast literature on the role of fluids and pore pressure in frictional strength of faults. Regardless of whether research on earthquake-triggered hydrologic effects ultimately provides insight into the physics of earthquakes, the text provides welcome common ground for interdisciplinary collaborations between hydrologists and seismologists. Such collaborations continue to be crucial for investigating hypotheses about the role of fluids in earthquakes and slow slip. Review info: Earthquakes and Water. By Wang, C.-Y. and Manga, M., 2010. ISBN: 9783642008092, 218 pp.

Geofluids↗
USGS1980

Chemical quality of water from community systems in New York, November 1970 to May 1975

Chemical analyses of 2,802 water samples from 784 of approximately 1,500 community water systems in the State of New York are presented. The data were collected from November 1970 to May 1975 and were originally released in a series of four U.S. Geological Survey open-file reports during the mid-1970's. The data were obtained and compiled by the Geological Survey and have been used by the State of New York in determining community system compliance with applicable drinking-water standards. The analyses include physical properties, major and minor constituents, pesticide residues, and radiochemical data. Some bottom-material analyses are included.

New York↗
USGS2006

Interactive effects of dissolved zinc and orthophosphate on phytoplankton from Coeur d'Alene Lake, Idaho

Within the longitudinal chemical-concentration gradient in Coeur d'Alene Lake, generated by inputs from the St. Joe and Coeur d'Alene Rivers, two dominant algal species, Chlorella minutissima and Asterionella formosa, were isolated and cultured in chemically defined media to examine growth response to a range of dissolved orthophosphate concentrations and zinc-ion activities representative of the region within- and up-gradient of the Coeur d'Alene River inlet to the lake. Although zinc is an essential micronutrient, the toxicity of algal species to elevated concentrations of uncomplexed zinc has been demonstrated, and affects the metabolism of phosphorus (Kuwabara, 1985a; Kuwabara and others, 1986), the limiting nutrient in the lake. This interaction between solutes could be of management interest. As an extension of field work conducted in August, 1999 (Kuwabara and others, 2003b), the water column and benthos of Coeur d'Alene Lake were sampled in August 2001, June 2004 and June 2005 (Fig. 1; Table 1) to provide the biological characterization in terms of phytoplankton community composition, benthic macroinvertebrate community composition and benthic chlorophyll concentrations, as well as chemical characterizations at six sites (three depths per site) within the lake. This work, in support of the Idaho Department of Environmental Quality and regional tribal organizations, provides the first phytoplankton response models in a format that may be incorporated into a process-interdependent water-quality model like CAEDYM (Fig. 2; Brookes and others, 2004; Centre for Water Research, 2006) as a management tool for the lake. This study provides information in support of developing process-interdependent solute-transport models for the watershed (that is, models integrating physical, geochemical and biological processes), and hence in support of subsequent evaluation of remediation or load-allocation strategies. The following two questions are posed: Are dissolved zinc and orthophosphate concentrations interactively associated with growth parameters of dominant phytoplankton species within the longitudinal concentration gradient of Coeur d'Alene Lake? If so, can these interactions be quantitatively incorporated into a water-quality model for the lake?

Idaho↗
USGS2014

Desert wetlands in the geologic record

Desert wetlands support flora and fauna in a variety of hydrologic settings, including seeps, springs, marshes, wet meadows, ponds, and spring pools. Over time, eolian, alluvial, and fluvial sediments become trapped in these settings by a combination of wet ground conditions and dense plant cover. The result is a unique combination of clastic sediments, chemical precipitates, and organic matter that is preserved in the geologic record as ground-water discharge (GWD) deposits. GWD deposits contain information on the timing and magnitude of past changes in water-table levels and, therefore, are a potential source of paleohydrologic and paleoclimatic information. In addition, they can be important archeological and paleontological archives because desert wetlands provide reliable sources of fresh water, and thus act as focal points for human and faunal activities, in some of the world's harshest and driest lands. Here, we review some of the physical, sedimentological, and geochemical characteristics common to GWD deposits, and provide a contextual framework that researchers can use to identify and interpret geologic deposits associated with desert wetlands. We discuss several lines of evidence used to differentiate GWD deposits from lake deposits (they are commonly confused), and examine how various types of microbiota and depositional facies aid in reconstructing past environmental and hydrologic conditions. We also review how late Quaternary GWD deposits are dated, as well as methods used to investigate desert wetlands deeper in geologic time. We end by evaluating the strengths and limitations of hydrologic and climatic records derived from GWD deposits, and suggest several avenues of potential future research to further develop and utilize these unique and complex systems.

Earth-Science Reviews↗
USGS2005

CO2 dynamics in the Amargosa Desert: Fluxes and isotopic speciation in a deep unsaturated zone

Natural unsaturated-zone gas profiles at the U.S. Geological Survey's Amargosa Desert Research Site, near Beatty, Nevada, reveal the presence of two physically and isotopically distinct CO 2 sources, one shallow and one deep. The shallow source derives from seasonally variable autotrophic and heterotrophic respiration in the root zone. Scanning electron micrograph results indicate that at least part of the deep CO 2 source is associated with calcite precipitation at the 110-m-deep water table. We use a geochemical gas-diffusion model to explore processes of CO 2 production and behavior in the unsaturated zone. The individual isotopic species 12 CO 2 , 13 CO 2 , and 14 CO 2 are treated as separate chemical components that diffuse and react independently. Steady state model solutions, constrained by the measured δ 13 C (in CO 2 ), and δ 14 C (in CO 2 ) profiles, indicate that the shallow CO 2 source from root and microbial respiration composes ∼97% of the annual average total CO 2 production at this arid site. Despite the small contribution from deep CO 2 production amounting to ∼0.1 mol m −2 yr −1 , upward diffusion from depth strongly influences the distribution of CO 2 and carbon isotopes in the deep unsaturated zone. In addition to diffusion from deep CO 2 production, 14 C exchange with a sorbed CO 2 phase is indicated by the modeled δ 14 C profiles, confirming previous work. The new model of carbon-isotopic profiles provides a quantitative approach for evaluating fluxes of carbon under natural conditions in deep unsaturated zones.

Water Resources Research↗
USGS1968

Hydrology of Crater, East and Davis Lakes, Oregon; with section on Chemistry of the Lakes

Crater, East, and Davis Lakes are small bodies of fresh water that occupy topographically closed basins in Holocene volcanic terrane. Because the annual water supply exceeds annual evaporation, water must be lost by seepage from each lake. The seepage rates vary widely both in volume and in percentage of the total water supply. Crater Lake loses about 89 cfs (cubic feet per second), equivalent to about 72 percent of its average annual supply. East Lake loses about 2.3 cfs, or about 44 percent of its estimated supply. Davis Lake seepage varies greatly with lake level, but the average loss is about 150 cfs, more than 90 percent of its total supply. The destination of the seepage loss is not definitely known for any of the lakes. An approximate water budget was computed for stationary level for each lake, by using estimates 'by the writer to supplement the hydrologic data available. The three lake waters are dilute. Crater Lake contains about 80 ppm, (parts per million) of dissolved solids---mostly silica, sodium, and bicarbonate, and lesser amounts of calcium, sulfate, and chloride. Much of the dissolved-solids content of Crater Lake---especially the sulfate and chloride---may be related to fumarole and thermal-spring activity that presumably followed the collapse of Mount Mazama. Although Grater Lake loses an estimated 7,000 tons of its 1.5million-ton salt content each year by leakage, the chemical character of the lake did not change appreciably between 1912 and 1964. East Lake contains 200 ppm of dissolved solids, which includes major proportions of calcium, sodium, bicarbonate, and sulfate, but almost no chloride. The lake apparently receives much of its dissolved solids from subsurface thermal springs. Annual solute loss from East Lake by leakage is about 450 tons, or 3 percent of the lake's 15,000-ton estimated solute content. Davis Lake contains only 48 ppm of dissolved solids, much of which is silica and bicarbonate; chloride is almost completely absent. Approximate physical and hydrologic data for the lakes are summarized in the following table. [Table]

Water Supply Paper↗
USGS1997

Bibliography of selected references on the hydrogeologic and chemical properties of the Galena-Platteville bedrock unit in Illinois and Wisconsin, 1877-1997

This report presents selected references concerning the Galena-Platteville deposits in Illinois and Wisconsin published from 1877 to 1997. Sources of the bibliographic information are the Universities of Illinois and Wisconsin Library Computer Systems; Illinet Online; the Illinois and Wisconsin District Libraries of the U.S. Geological Survey; U.S. Geological Survey Selected Water Resources Abstracts; U.S. Environmental Protection Agency reports; and Federal, State, and local agencies, corporations, and consultants. The bibliography is arranged alphabetically, by county, in Illinois and Wisconsin. The references available for each county are arranged alphabetically by author. In addition, one or more selected hydrogeologic key words describing the content of the reference follow each listing. These key words are geophysical properties, hydraulic properties, inorganic geochemistry, lithology, organic geochemistry, physical properties, and water use. Included in the bibliography are 186 references obtained for 15 counties in Illinois and 21 counties in Wisconsin.

Water-Resources Investigations Report↗
USGS2012

Factors controlling nitrate fluxes in groundwater in agricultural areas

The impact of agricultural chemicals on groundwater quality depends on the interactions of biogeochemical and hydrologic factors. To identify key processes affecting distribution of agricultural nitrate in groundwater, a parsimonious transport model was applied at 14 sites across the U.S. Simulated vertical profiles of NO 3 - , N 2 from denitrification, O 2 , Cl - , and environmental tracers of groundwater age were matched to observations by adjusting the parameters for recharge rate, unsaturated zone travel time, fractions of N and Cl - inputs leached to groundwater, O 2 reduction rate, O 2 threshold for denitrification, and denitrification rate. Model results revealed important interactions among biogeochemical and physical factors. Chloride fluxes decreased between the land surface and water table possibly because of Cl - exports in harvested crops (averaging 22% of land-surface Cl - inputs). Modeled zero-order rates of O 2 reduction and denitrification were correlated. Denitrification rates at depth commonly exceeded overlying O 2 reduction rates, likely because shallow geologic sources of reactive electron donors had been depleted. Projections indicated continued downward migration of NO 3 - fronts at sites with denitrification rates <0.25 mg-N L -1 yr -1 . The steady state depth of NO 3 - depended to a similar degree on application rate, leaching fraction, recharge, and NO 3 - and O 2 reaction rates. Steady state total mass in each aquifer depended primarily on the N application rate. In addition to managing application rates at land surface, efficient water use may reduce the depth and mass of N in groundwater because lower recharge was associated with lower N fraction leached. Management actions to reduce N leaching could be targeted over aquifers with high-recharge and low-denitrification rates.

Water Resources Research↗
USGS1985

Degradation of carbohydrates and lignins in buried woods

Spruce, alder, and oak woods deposited in coastal sediments were characterized versus their modern counterparts by quantification of individual neutral sugars and lignin-derived phenols as well as by scanning electron microscopy, 13 C NMR, and elemental analysis. The buried spruce wood from a 2500 yr old deposit was unaltered whereas an alder wood from the same horizon and an oak wood from an open ocean sediment were profoundly degraded. Individual sugar and lignin phenol analyses indicate that at least 90 and 98 wt% of the initial total polysaccharides in the buried alder and oak woods, respectively, have been degraded along with 15–25 wt% of the lignin. At least 75% of the degraded biopolymer has been physically lost from these samples. This evidence is supported by the SEM, 13 C NMR and elemental analyses, all of which indicate selective loss of the carbohydrate moiety. The following order of stability was observed for the major biochemical constituents of both buried hardwoods: vanillyl and p- hydroxyl "> p-hydroxyl lignin structural units > syringyl and lignin structural units > pectin > α-cellulose > hemicellulose. This sequence can be explained by selective preservation of the compound middle lamella regions of the wood cell walls. The magnitude and selectivity of the indicated diagenetic reactions are sufficient to cause major changes in the chemical compositions of wood-rich sedimentary organic mixtures and to provide a potentially large in situ nutrient source.

Geochimica et Cosmochimica Acta↗
USGS1974

Distribution of copper in biotite and biotite alteration products in intrusive rocks near two Arizona porphyry copper deposits

Biotite and its alteration products (primarily chlorite) from igneous rocks around the Ray and Esperanza (Esperanza-Sierrita) porphyry copper deposits, Arizona, were analyzed for copper by electron microprobe. The copper occurs in amounts >90 p/m (limit of detection) in most of the chlorites analyzed, is concentrated at the optical and chemical boundary of chlorite and biotite, and is not associated with sulfur. Most unaltered igneous and hydrothermal biotites analyzed contain <90 p/m Cu, and except for one sample, all copper that was detected can be explained as contamination by copper from chlorite grains. The paucity of detectable copper in igneous and hydrothermal biotite and its presence in daughter chlorite suggest that the positive association noted by some workers between the proximity of an ore deposit and the copper content of biotite might be partly the result: of increased amounts of chloritization of biotite near a deposit coupled with difficulty in physically cleaning the biotite separates. Additionally, previous speculations that (1) part of the copper in a deposit may come from altered biotite, and (2) copper in biotite indicates how copper behaves in a differentiating magma, are of doubtful value if based on data derived from analyses of bulk mineral separates.

Arizona↗
USGS1996

Phytoplankton bloom dynamics in coastal ecosystems: A review with some general lessons from sustained investigation of San Francisco Bay, California

Phytoplankton blooms are prominent features of biological variability in shallow coastal ecosystems such as estuaries, lagoons, bays, and tidal rivers. Long-term observation and research in San Francisco Bay illustrates some patterns of phytoplankton spatial and temporal variability and the underlying mechanisms of this variability. Blooms are events of rapid production and accumulation of phytoplankton biomass that are usually responses to changing physical forcings originating in the coastal ocean (e.g., tides), the atmosphere (wind), or on the land surface (precipitation and river runoff). These physical forcings have different timescales of variability, so algal blooms can be short-term episodic events, recurrent seasonal phenomena, or rare events associated with exceptional climatic or hydrologic conditions. The biogeochemical role of phytoplankton primary production is to transform and incorporate reactive inorganic elements into organic forms, and these transformations are rapid and lead to measurable geochemical change during blooms. Examples include the depletion of inorganic nutrients (N, P, Si), supersaturation of oxygen and removal of carbon dioxide, shifts in the isotopic composition of reactive elements (C, N), production of climatically active trace gases (methyl bromide, dimethylsulfide), changes in the chemical form and toxicity of trace metals (As, Cd, Ni, Zn), changes in the biochemical composition and reactivity of the suspended particulate matter, and synthesis of organic matter required for the reproduction and growth of heterotrophs, including bacteria, zooplankton, and benthic consumer animals. Some classes of phytoplankton play special roles in the cycling of elements or synthesis of specific organic molecules, but we have only rudimentary understanding of the forces that select for and promote blooms of these species. Mounting evidence suggests that the natural cycles of bloom variability are being altered on a global scale by human activities including the input of toxic contaminants and nutrients, manipulation of river flows, and translocation of species. This hypothesis will be a key component of our effort to understand global change at the land-sea interface. Pursuit of this hypothesis will require creative approaches for distinguishing natural and anthropogenic sources of phytoplankton population variability, as well as recognition that the modes of human disturbance of coastal bloom cycles operate interactively and cannot be studied as isolated processes.

California↗
USGS2008

Assessing sulfate reduction and methane cycling in a high salinity pore water system in the northern Gulf of Mexico

Pore waters extracted from 18 piston cores obtained on and near a salt-cored bathymetric high in Keathley Canyon lease block 151 in the northern Gulf of Mexico contain elevated concentrations of chloride (up to 838 mM) and have pore water chemical concentration profiles that exhibit extensive departures (concavity) from steady-state (linear) diffusive equilibrium with depth. Minimum ??13C dissolved inorganic carbon (DIC) values of -55.9??? to -64.8??? at the sulfate-methane transition (SMT) strongly suggest active anaerobic oxidation of methane (AOM) throughout the study region. However, the nonlinear pore water chemistry-depth profiles make it impossible to determine the vertical extent of active AOM or the potential role of alternate sulfate reduction pathways. Here we utilize the conservative (non-reactive) nature of dissolved chloride to differentiate the effects of biogeochemical activity (e.g., AOM and/or organoclastic sulfate reduction) relative to physical mixing in high salinity Keathley Canyon sediments. In most cases, the DIC and sulfate concentrations in pore waters are consistent with a conservative mixing model that uses chloride concentrations at the seafloor and the SMT as endmembers. Conservative mixing of pore water constituents implies that an undetermined physical process is primarily responsible for the nonlinearity of the pore water-depth profiles. In limited cases where the sulfate and DIC concentrations deviated from conservative mixing between the seafloor and SMT, the ??13C-DIC mixing diagrams suggest that the excess DIC is produced from a 13C-depleted source that could only be accounted for by microbial methane, the dominant form of methane identified during this study. We conclude that AOM is the most prevalent sink for sulfate and that it occurs primarily at the SMT at this Keathley Canyon site.

Marine and Petroleum Geology↗
USGS1993

Sharpness of upper-mantle discontinuities determined from high-frequency reflections

AN understanding of the nature of seismic discontinuities in the Earth's upper mantle is important for understanding mantle processes: in particular, the amplitude and sharpness of these discontinuities are critical for assessing models of upper-mantle phase changes and chemical layering. So far, seismic studies aimed at determining the thickness and lateral variability of upper-mantle discontinuities have yielded equivocal results, particularly for the discontinuity at 410km depth1,2. Here we present short-period (0.8-2.0 s) recordings of upper-mantle precursors to the seismic phase P???P??? (PKPPKP) from two South American earthquakes recorded by the ???700-station short-period array in California. Our results show that the 410- and 660-km discontinuities beneath the Indian Ocean are locally simple and sharp, corresponding to transition zones of 4 km or less. These observations pose problems for mineral physics models3-5, which predict a transitional thickness greater than 6 km for the peridotite to ??-spinel phase transition. In contrast to the results of long-period studies6,7, we observe no short-period arrivals from near 520 km depth.

Nature↗
USGS2025

Pesticide concentrations in multiple physical and biological stream matrices are impacted by a bioenergy production facility receiving pesticide coated corn seeds

Insecticide and fungicide seed coatings have become prevalent in conventional agriculture in recent decades. From 2015 to 2021, the AltEn bioenergy plant (Mead, Nebraska, USA) generated ethanol from almost 100% unused/expired treated corn seeds. This use of these seeds for ethanol production resulted in the accumulation of large amounts of contaminated wastewater and solid residue, a portion of which was applied to surrounding farmland. To better understand the potential long-term environmental effects from the processing of treated seeds at this facility, five nearby stream sites were sampled in 2022 after the closure of the plant; these included two sites directly impacted by AltEn, one upstream, and two downstream of the impacted sites. Water and sediment were collected in March through July, and algae and fish samples were collected in July for chemical analysis. Overall, 60 pesticide compounds (parents and transformation products) were detected in one or more matrices, including 23 fungicides, 20 insecticides, 16 herbicides, and 1 bacterial growth inhibitor. Pesticide results (maximum detection frequency, maximum concentration) varied substantially by environmental compartment: water (100% multiple pesticides; 4,600 ng L −1 thiamethoxam transformation product (NOA-407475)), algae (100% multiple pesticides, 190 ng g −1 atrazine), sediment (60% dithiopyr, 2.3 ng g −1 acetochlor) and fish (20% pyraclostrobin, 2.2 ng g −1 atrazine). Pesticides associated with treated corn seeds (e.g., insecticides clothianidin, thiamethoxam; fungicides fluoxastrobin, thiabendazole) were detected at significantly higher concentrations ( p < 0.05) in stream water from sites impacted by the AltEn facility compared to non-impacted sites. Study results indicate that pesticides associated with the AltEn facility continue to be a source of contaminants to aquatic systems after the plant’s closure in 2021.

Environmental Toxicology and Chemistry↗
USGS1998

Seasonal uranium distributions in the coastal waters off the Amazon and Mississippi Rivers

The chemical reactivity of uranium was investigated across estuarine gradients from two of the world’s largest river systems: the Amazon and Mississippi. Concentrations of dissolved (<0.45 μm) uranium (U) were measured in surface waters of the Amazon shelf during rising (March 1990), flood (June 1990) and low (November 1991) discharge regimes. The dissolved U content was also examined in surface waters collected across estuarine gradients of the Mississippi outflow region during April 1992, August 1993, and November (1993). All water samples were analyzed for U by isotope dilution inductively coupled plasma mass spectrometry (ICP-MS). In Amazon shelf surface waters uranium increased nonconservatively from about 0.01 μg I −1 at the river’s mouth to over 3 μg I −1 at the distal site, irrespective of river discharge stage. Observed large-scale U removal at salinities generally less than 15 implies a) that riverine dissolved U was extensively adsorbed by freshly-precipitated hydrous metal oxides (e.g., FeOOH, MnO 2 ) as a result of flocculation and aggregation, and b) that energetic resuspension and reworking of shelf sediments and fluid muds on the Amazon shelf released a chemically reactive particle/colloid to the water column which can further scavenge dissolved U across much of the estuarine gradient. In contrast, the estuarine chemistry of U is inconclusive within surface waters of the Mississippi shelf-break region. U behavior is most likely controlled less by traditional sorption and/or desorption reactions involving metal oxides or colloids than by the river’s variable discharge regime (e.g., water parcel residence time during estuarine mixing, nature of particulates, sediment storage and resuspension in, the confined lower river), and plume dispersal. Mixing of the thin freshwater lens into ambient seawater is largely defined by wind-driven rather than physical processes. As a consequence, in the Mississippi outflow region uranium predominantly displays conservative behavior; removal is evident only during anomalous river discharge regimes. ‘Products-approach’ mixing experiments conducted during the Flood of 1993 suggest the importance of small particles and/or colloids in defining a depleted U versus salinity distribution.

Louisiana↗