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At least 217 records · Page 12Linked to original sources

USGS1986

Tests for injecting, storing, and recovering freshwater in a saline artesian aquifer, Lee County, Florida

An investigation was made of the suitability of a saline, artesian limestone aquifer for the injection, storage, and recovery of freshwater from the Caloosahatchee River. The tests were conducted on a well tapping a leaky artesian system that has a transmissivity of 800 square feet per day, a storage of 1 x 10-4, and a leakance of 0.01 per day. The specific capacity of the injection well was increased through acidizing and was decreased as a result of well clogging during injection. Three injection tests were made wherein the amounts of freshwater injected, the storage duration, and the quality of water injected varied. Analysis of the test data showed that freshwater recoverability ranged from 9.7 to 38.7 percent of the total injected. Differences were attributed principally to differences in the quality of water injected and storage duration. Repeated injection-recovery cycles probably would result in greater recoverability. Head buildup, nearly 200 feet in one test, was a prime problem related chiefly to clogging from suspended material in the injected water and to bacterial growth at the wellbore-limestone interface. Regular backflushing was required. Total head buildup decreased as a result of acidizing the injection well. No coliforms or fecal streptococcus were noted in the recovered water. Growth of anaerobic bacteria occurred. Changes in the quality of the recovered water included decreases in concentration of dissolved organic carbon by as much as 15 mg/L (milligrams per liter), organic nitrogen by as much as 0.80 mg/L, and nitrate by as much as 0.50 mg/L. Increases were noted in ammonia by 0.40 mg/L, and iron by as much as 0.60 mg/L. These changes are consistent with the presence of an anaerobic bacterial ecosystem.

Florida↗

USGS1988

Effects of two stormwater management methods on the quality of water in the upper Biscayne aquifer at two commercial areas in Dade County, Florida

This study is part of a continued effort to assess the effects of urban stormwater recharge on the water quality of the Biscayne aquifer in southeast Florida. In this report, the water-quality effects on shallow ground water resulting from stormwater disposal by exfiltration trench and grassy swale were investigated at two small commercial areas in Dade County, Florida. One study area (airport) was located near the Miami International Airport and had a drainage area of about 10 acres overlying a sandy soil; the other study area (free zone) was located at the Miami International Free Trade Zone and had a drainage area of about 20 acres overlying limestone. The monitoring design for each study area consisted of seven sites and included water-quality sampling of the stormwater in the catch basin of the exfiltration trench, ground water from two wells 1 foot from the trench (trench wells), two wells 20 feet from the trench, and ground water from two wells at the swale from April 1985 through May 1986. Eleven water-quality variables (target variables) commonly found in high levels in urban stormwater runoff were used as tracers to estimate possible changes in ground-water quality that may have been caused by stormwater recharge. Comparison of the distribution of target variables indicated that the concentrations tended to be greater in the stormwater in the exfiltration trench than in water from the two wells 1 foot from the trench at both study areas. The concentration difference for several target variables was statistically significant at the 5-percent level. Lead, for example, had median concentrations of 23 and 4 micrograms per liter, respectively, in stormwater and water from the two trench wells at the airport study area, and 38 and 2 micrograms per liter, respectively, in stormwater and groundwater at the free zone. Similar reductions in concentrations between stormwater and water from the two trench wells were indicated for zinc at both study areas and also for nitrogen, phosphorus, and organic content at the free zone. This trend suggested that the exfiltration trench at both study areas may function as a partial trap for some chemical substances present in stormwater. A comparison of the distribution of the 11 target variables and major ionic composition in water from the two trench wells and the two wells 20 feet from the trench did not indicate a notable horizontal stratification at either study area. A vertical difference between 10 and 15 feet, however, was indicated at the free zone with major ions in greater concentrations at 15 feet. The vertical variability in groundwater near the trench at the free zone may have been the result of stormwater dilution in the upper (10-foot) zone. The ground-water quality at the swale was quite dissimilar to that near the exfiltration trench at both the airport and free zone study areas. Data indicated that the groundwater environment at both sales was anaerobic as evidenced by abundant ammonia nitrogen and iron and trace levels of sulfate. Anaerobic conditions at the swale may have been the result of poor drainage and high organic content of soils. Significant biochemical cycling in the ground water at the swales precluded any assessment of quality effects that may result from storm-water infiltration.

Florida↗

USGS1993

Hydrology, vegetation, and soils of four north Florida River flood plains with an evaluation of state and federal wetland determinations

A study of hydrologic conditions, vegetation, and soils was made in wetland forests of four north Florida streams from 1987 to 1990. The study was conducted by the U.S. Geological Survey in cooperation with the Florida Department of Environmental Regulation to support State and Federal efforts to improve wetland delineation methodology in flood plains. Plant communities and soils were described and related to topographic position and long-term hydrologic conditions at 10 study plots located on 4 streams. Detailed appendixes give average duration, frequency, and depth of flooding; canopy, subcanopy, and ground-cover vegetation; and taxonomic classification, series, and profile descriptions of soils for each plot. Topographic relief, range in stage, and depth of flooding were greatest on the alluvial flood plain of the Ochlockonee River, the largest of the four streams. Soils were silty in the lower elevations of the flood plain, and tree communities were distinctly different in each topographic zone. The Aucilla River flood plain was dominated by levees and terraces with very few depressions or low backwater areas. Oaks dominated the canopy of both lower and upper terraces of the Aucilla flood plain. Telogia Creek is a blackwater stream that is a major tributary of the Ochlockonee River. Its low, wet flood plain was dominated by Wyssa ogeche (Ogeechee tupelo) trees, had soils with mucky horizons, and was inundated by frequent floods of very short duration. The St. Marks River, a spring-fed stream with high base flow, had the least topographic relief and lowest range in stage of the four streams. St. Marks soils had a higher clay content than the other streams, and limestone bedrock was relatively close to the surface. Wetland determinations of the study plots based on State and Federal regulatory criteria were evaluated. Most State and Federal wetland determinations are based primarily on vegetation and soil characteristics because hydrologic records are usually not available. In this study, plots were located near long-term gaging stations, thus wetland determinations based on plant and soil characteristics could be evaluated at sites where long-term hydrologic conditions were known. Inconsistencies among hydrology, vegetation, and soil determinations were greatest on levee communities of the Ochlockonee and Aucilla River flood plains. Duration of average annual longest flood was almost 2 weeks for both plots. The wetland species list currently used (1991) by the State lacks many ground-cover species common to forested flood plains of north Florida rivers. There were 102 ground-cover species considered upland plants by the State that were present on the nine annually flooded plots of this study. Among them were 34 species that grew in areas continuously flooded for an average of 5 weeks or more each year. Common flood-plain species considered upland plants by the State were: Hypoxis leptocarpa (yellow star-grass), and two woody vines, Brunnichia ovata (ladies' eardrops) and Campsis radican s (trumpet-creeper), which were common in areas flooded continuously for 6 to 9 weeks a year; Sebastiania fruticosa (Sebastian-bush), Chasmanthium laxum (spikegrass), and Panicum dichotomum (panic grass), which typically grew in areas flooded an average of 2 to 3 weeks or more per year; Vitis rotundifolia (muscadine) and Toxicodendron radicans (poison-ivy), usually occurring in areas flooded an average of 1 to 2 weeks a year; and Quercus virginiana (live oak) present most often in areas flooded approximately 1 week a year. Federal wetland regulations (1989) limited wetland jurisdiction to only those areas that are inundated or saturated during the growing season. However, year-round hydrologic records were chosen in this report to describe the influence of hydrology on vegetation, because saturation, inundation, or flowing water can have a variety of both beneficial and adverse effects on flood-plain vegetation at any time of the year. These effects can occur because: (1) Soil temperatures in north Florida are probably high enough in winter for anaerobic conditions to develop in saturated soils. (2) Many plants in the flood plains of north Florida are active in the nongrowing season and might be adapted to anaerobic conditions in winter. (3) Other effects of standing water, such as decreased light penetration, prevention of seed germination, and protection of seeds from herbivores; and effects of flowing water, such as scouring and deposition of sediments, seed dispersal, and mechanical injury, can occur any time of year.

Florida↗

USGS1996

Geochemical and isotopic composition of ground water with emphasis on sources of sulfate in the upper Floridan Aquifer in parts of Marion, Sumter, and Citrus counties, Florida

In inland areas of northwest central Florida, sulfate concentrations in the Upper Floridan aquifer are extremely variable and sometimes exceed drinking water standards (250 milligrams per liter). This is unusual because the aquifer is unconfined and near the surface, allowing for active recharge. The sources of sulfate and geochemical processes controlling ground-water composition were evaluated in this area. Water was sampled from thirty-three wells in parts of Marion, Sumter, and Citrus Counties, within the Southwest Florida Water Management District; these included at least a shallow and a deep well at fifteen separate locations. Ground water was analyzed for major ions, selected trace constituents, dissolved organic carbon, and stable isotopes (sulfur-34 of sulfate and sulfide, carbon-13 of inorganic carbon, deuterium, and oxygen-18). Sulfate concentrations ranged from less than 0.2 to 1,400 milligrams per liter, with higher sulfate concentrations usually in water from deeper wells. The samples can be categorized into a low sulfate group (less than 30 milligrams per liter) and a high sulfate group (greater than 30 milligrams per liter). For the high sulfate waters, concentrations of calcium and magnesium increased concurrently with sulfate. Chemical and isotopic data and mass-balance modeling indicate that the composition of high sulfate waters is controlled by dedolomitization reactions (dolomite dissolution and calcite precipitation, driven by dissolution of gypsum). Gypsum occurs deeper in the aquifer than open intervals of sampled wells. Upward flow has been documented in deeper parts of the aquifer in the study area, which may be driven by localized discharge areas or rapid flow in shallow parts of the aquifer. Mixing between shallow ground water and sulfate-rich water that dissolved gypsum at the base of the aquifer is probably responsible for the range of concentrations observed in the study area. Other solutes that increased with sulfate apparently originate from the gypsum itself, from other mineral assemblages found deeper in the aquifer in association with gypsum, and from residual seawater from less-flushed, deeper parts of the aquifer. These ions are subsequently transported with sulfate to shallower parts of the aquifer where gypsum is not present. The composition of low sulfate ground water is controlled by differences in the extent of microbially mediated reactions, which produce carbon dioxide. This, in turn, influences the extent of calcite dissolution. Ground waters which underwent limited microbial reactions contained dissolved oxygen and were usually in ridge areas where recharge typically is rapid. Anaerobic waters were in lower lying areas of Sumter County, where soils are poorly drained and aquifer recharge is slow. Anaerobic waters had higher concentrations of calcium, bicarbonate, sulfide, dissolved organic carbon, iron, manganese, and silica, and had lower concentrations of nitrate than aerobic ground waters. For low sulfate waters, sulfate generally originates from meteoric sources (atmospheric precipitation), with variable amounts of oxidation of reduced sulfur and sulfate reduction. Sulfide is sometimes removed from solution, probably by precipitation of a sulfide minerals such as pyrite. In areas where deep ground water has low sulfate concentrations, the shallow flow system is apparently deeper than where high sulfate concentrations occur, and upwelling of sulfate-rich water is negligible. The range of sulfate concentrations observed in the study area and differences in sulfate concentrations with depth indicate a complex interaction between shallow and deep ground-water flow systems.

Florida↗

USGS1996

Assessment of intrinsic bioremediation of gasoline contamination in the shallow aquifer, Laurel Bay Exchange, Marine Corps Air Station Beaufort, South Carolina

Laboratory, field, and digital solute-transport- modeling studies demonstrate that microorganisms indigenous to the shallow ground-water system at Laurel Bay Exchange, Marine Corps Air Station Beaufort, South Carolina, can degrade petroleum hydrocarbons in gasoline released at the site. Microorganisms in aquifer sediments incubated in the laboratory under aerobic and anaerobic conditions mineralized radiolabeled carbon 14-toluene to 14 C-carbon dioxide with first-order rate constants of K bio = -0.640 per day and K bio = -0.003 per day, respectively. Digital solute- transport modeling using the numerical code SUTRA revealed that anaerobic biodegradation of benzene occurs with a first-order rate constant near K bio = -0.00025 per day. Sandy aquifer material beneath Laurel Bay Exchange is characterized by relatively high hydraulic conductivities (K aq = 8.9 to 17.3 feet per day), average ground-water flow rate of about 60 feet per year, and a relatively uniform hydraulic gradient of 0.004 feet per foot. The sandy aquifer material also has low adsorptive potentials for toluene and benzene (both about K ad = 2.0 x 10 -9 cubic feet per milligram), because of the lack of natural organic matter in the aquifer. The combination of this ground-water-flow rate and absence of significant adsorptive capacity in the aquifer permits toluene and benzene concentrations to be detected downgradient from the source area in monitoring wells, even though biodegradation of these compounds has been demonstrated. Solute-transport simulations, however, indicate that toluene and benzene will not reach the Broad River, the nearest point of contact with wildlife or human populations, about 3,600 feet west of the site boundary. These simulations also show that contamination will not be transported to the nearest Marine Corps property line about 2,400 feet south of the site. This is primarily because the source of contaminants has essentially been removed, and the low adsorptive capacity of the aquifer sediments has prevented the occurrence of an adsorbed, continuous source of petroleum hydrocarbons. Therefore, digital simulations of toluene and benzene transport at Laurel Bay Exchange indicate that intrinsic bioremediation could be a successful remediation alternative for prohibiting transport of dissolved toluene and benzene to the Broad River.

South Carolina↗

USGS1996

Distribution of petroleum hydrocarbons and toluene biodegradation, Knox Street fire pits, Fort Bragg, North Carolina

An investigation was conducted at the Knox Street fire pits, Fort Bragg, North Carolina, to monitor the distribution of toluene, ethylbenzene, and xylene (TEX) in soil vapor, ground water, and ground-water/vapor to evaluate if total concentrations of TEX at the site are decreasing with time, and to quantify biodegradation rates of toluene in the unsaturated and saturated zones. Soil-vapor and ground-water samples were collected around the fire pits and ground-water/vapor samples were collected along the ground-water discharge zone, Beaver Creek, on a monthly basis from June 1994 through June 1995. Concentrations of TEX compounds in these samples were determined with a field gas chro- matograph. Laboratory experiments were performed on aquifer sediment samples to measure rates of toluene biodegradation by in situ micro- organisms. Based on field gas chromatographic analytical results, contamination levels of TEX compounds in both soil vapor and ground water appear to decrease downgradient of the fire-pit source area. During the 1-year study period, the observed temporal and spatial trends in soil vapor TEX concentrations appear to reflect differences in the distribution of TEX among solid, aqueous, and gaseous phases within fuel-contaminated soils in the unsaturated zone. Soil temperature and soil moisture are two important factors which influence the distribution of TEX com- pounds among the different phases. Because of the short period of data collection, it was not possible to distinguish between seasonal fluc- tuations in soil vapor TEX concentrations and an overall net decrease in TEX concentrations at the study site. No seasonal trend was observed in total TEX concentrations for ground- water samples collected at the study site. Although the analytical results could not be used to determine if ground-water TEX concen- trations decreased during the study at a specific location, the data were used to examine rate constants of toluene biodegradation. Based on ground-water toluene concentration data, a maximum rate constant for anaerobic biodegradation of toluene in the saturated zone was estimated to be as low as 0.002 d-1 or as high as 0.026 d-1. Based on analyses of ground-water/vapor samples, toluene was the prin- cipal TEX compound identified in ground water discharging to Beaver Creek. Observed decreases in ground-water/vapor toluene concentrations during the study period may reflect a decrease in source inputs, an increase in dilution caused by higher ground-water flow, and(or) removal by biological or other physical processes. Rate constants of toluene anaerobic biodegradation determined by laboratory measurements illustrate a typical acclimation response of micro-organisms to hydrocarbon contamination in sediments collected from the site. Toluene biodegradation rate constants derived from laboratory microcosm studies ranged from 0.001 to 0.027 d-1, which is similar to the range of 0.002 to 0.026 d-1 for toluene biodegradation rate constants derived from ground-water analytical data. The close agreement of toluene biodegradation rate constants reported using both approaches offer strong evidence that toluene can be degraded at environmentally significant rates at the study site.

Water-Resources Investigations Report↗

USGS1999

Iron in the aquifer system of Suffolk County, New York, 1990-98

High concentrations of dissolved iron in ground water contribute to the biofouling of public-supply wells, and the treatment and remediation of biofouling are costly. Water companies on Long Island, N.Y., spend several million dollars annually to recondition, redevelop, and replace supply wells and distribution lines; treat dissolved iron with sequestering agents or by filtration; and respond to iron-related complaints by customers. This report summarizes the results of studies done by the U.S. Geological Survey, in cooperation with the Suffolk County Water Authority, to characterize the geochemistry and microbiology of iron in the aquifer system of Suffolk County. This information should be helpful for the siting and operation of supply wells. Concentrations of dissolved iron in Long Island's ground water, and the frequency of iron biofouling of wells, are highest in ground-water-discharge zones, particularly near the south shore. Ground water along a deep north-south flowpath of the Magothy aquifer in southwestern Suffolk County becomes anaerobic (oxygen deficient) and Fe(III) reducing at a distance of 8 to 10 kilometers south of the ground-water divide, and this change coincides with the downgradient increase in dissolved iron concentrations. The distribution of organic carbon, and the distribution and local variations in reactivity of Fe(III), in Magothy aquifer sediments have resulted in localized differences in redox microenvironments. For example, Fe(III)-reducing zones are associated with anaerobic conditions, where relatively large amounts of Fe(III) oxyhydroxide grain coatings are present, whereas sulfate-reducing zones are associated with lignite-rich lenses of silt and clay and appear to have developed in response to the depletion of available Fe(III) oxyhydroxides. The sulfate-reducing zones are characterized by relatively low concentrations of dissolved iron (resulting from iron-disulfide precipitation) and may be large enough to warrant water-supply development. Specific-capacity and water-quality data from wells screened in the Magothy aquifer indicate that water from biofouled wells contains higher median concentrations of total and dissolved iron and manganese, total phosphate, and dissolved sulfate, and lower median concentrations of dissolved oxygen and alkalinity, and lower pH, than does water from unaffected wells. Corresponding data from wells screened in the upper glacial aquifer indicate that water from biofouled wells contains higher median concentrations of total and dissolved manganese and dissolved sulfate, and lower pH, than does water from unaffected wells. Filamentous bacteria were detected in 31 (or 72 percent) of the 43 biofilm samples obtained from biofouled wells during reconditioning. The predominant filamentous organism was Gallionella ferruginea, a major biofouling agent in the upper glacial and Magothy aquifers throughout Suffolk County. Mineral-saturation indices indicate that most of the well-encrusting material is deposited when the wells are shut down. Furthermore, the use of treated water (which has a high pH and sometimes high concentrations of dissolved iron) for pump prelubrication when wells are shut down could greatly increase the rate of iron oxidation.

New York↗

USGS2004

Tropical Archaea: Diversity associated with the surface microlayer of corals

Recent 16S rDNA studies have focused on detecting uncultivated bacteria associated with Caribbean reef corals in an effort to address the ecological roles of coral-associated microbes. Reports of Archaea associated with fishes and marine invertebrates raised the question of whether Archaea might also be part of the coral-associated microbial community. DNA analysis of mucus from 3 reef-building species of Caribbean corals, Montastraea annularis complex, Diploria strigosa and D. labyrinthiformis in the US Virgin Islands yielded 34 groups of archaeal 16S ribotypes (defined at the level of 97% similarity). The majority (75%) was most closely matched by BLAST searches to sequences derived from marine water column samples, whereas the remaining ribotypes were most similar to sequences isolated from anoxic environments (15%) and hydrothermal vents (9%). Unlike previous 16S studies of coral-associated Bacteria, the results do not suggest specific associations between particular archaeal sequences and individual coral species. Marine Archaea (Groups I, II and III) in addition to Thermoplasma -like, methanogen, and marine benthic crenarchaeote phylotypes, were detected in the mucus of tropical corals. The finding of sequences from coral-associated Archaea that are closely related to strict and facultative anaerobes, as well as to uncultivated Archaea from other types of anoxic environments, suggests that anaerobic micro-niches may exist in coral mucus layers. Archaea, with their unique biogeochemical capabilities, broaden the scope of possible interactions between corals and their associated microbial communities.

Marine Ecology Progress Series↗

USGS2026

Diverging mineral chemistry of iron and nickel throughout Earth’s changing redox conditions reveals foundation for their evolution as protein cofactors

Iron (Fe) and nickel (Ni) were both foundational to early metabolism, yet their biological trajectories diverged as Earth’s surface redox state changed. Here, we integrate mineral chemistry network analysis, protein metal-site coordination-sphere analysis, and curated redox comparisons to test how geochemistry and metalloprotein architecture co-evolved. Mineral network analyses show broader electronegativity variation and network diversity for Fe-bearing minerals through time relative to Ni-bearing minerals. In structural analyses of protein metal centers in a combined Fe/Ni protein structure set, it is shown that Fe- and Ni-associated environments differ in amino-acid composition, hydropathy structure, and cysteine representation. The greater chemical diversity and electronegativity variation in Fe minerals mirror the higher redox and structural versatility of Fe-binding proteins. The presence of Fe in a broader range of mineral and protein environments demonstrates the chemical adaptability of the metal, from the anoxic Archean to oxidative Earth surface conditions following the Great Oxidation Event. Iron, with its broad redox potential range in Fe-oxidoreductases, has a central role in both anaerobic and aerobic metabolisms. Nickel, by contrast, is less widespread in biology. Today, Ni is predominantly employed in deeply branching anaerobic pathways and by proteins with narrower redox potential ranges. Our results show that evolutionary processes, constrained by metal chemistry, habitually utilize Fe as a redox generalist while retaining Ni in specialized roles. The divergent paths of Ni and Fe, from rocks to proteins, demonstrate the intimate relationship between planetary geochemistry and metabolic origins on Earth and suggest that Fe/Ni geochemistry may inform habitability assessments in extraterrestrial environments when interpreted within specific planetary environmental contexts.

Life↗

USGS2021

Restoration of mangrove forest

Mangrove forests occur worldwide along tropical coasts in inundated soils where primary production and anaerobic conditions contribute to the building of soil organic matter (Also see Mangroves Hot-spot, Volume 2). Note that peat may accumulate in certain coastal mangrove (Middleton and McKee, 2001). The actual amount of soil organic matter stored in these wetlands depends on the balance between primary production and decomposition processes (Middleton and McKee, 2001; Kolka et al., 2018; Middleton, 2020). The restoration of mangroves can increase carbon stocks both in soil and aboveground biomass (Wickland et al., 2013; Chimner et al., 2017; Friess et al., 2019). While tropical inland peatland forests may have higher carbon sequestration rates than mangrove swamps, methane (CH4) emissions are generally lower in mangrove swamp, so that these wetlands have greater carbon sequestration potential (Kolka et al., 2018; Al-Haj and Fulweiler, 2020). Mangroves and forested boreal and temperate peatlands tend to store more carbon than non-forested peatlands (Kolka et al., 2018).

Book chapter↗

USGS2014

Adaptations of indigenous bacteria to fuel contamination in karst aquifers in south-central Kentucky

The karst aquifer systems in southern Kentucky can be dynamic and quick to change. Microorganisms that live in these unpredictable aquifers are constantly faced with environmental changes. Their survival depends upon adaptations to changes in water chemistry, taking advantage of positive stimuli and avoiding negative environmental conditions. The U.S. Geological Survey conducted a study in 2001 to determine the capability of bacteria to adapt in two distinct regions of water quality in a karst aquifer, an area of clean, oxygenated groundwater and an area where the groundwater was oxygen depleted and contaminated by jet fuel. Water samples containing bacteria were collected from one clean well and two jet fuel contaminated wells in a conduit-dominated karst aquifer. Bacterial concentrations, enumerated through direct count, ranged from 500,000 to 2.7 million bacteria per mL in the clean portion of the aquifer, and 200,000 to 3.2 million bacteria per mL in the contaminated portion of the aquifer over a twelve month period. Bacteria from the clean well ranged in size from 0.2 to 2.5 mm, whereas bacteria from one fuel-contaminated well were generally larger, ranging in size from 0.2 to 3.9 mm. Also, bacteria collected from the clean well had a higher density and, consequently, were more inclined to sink than bacteria collected from contaminated wells. Bacteria collected from the clean portion of the karst aquifer were predominantly (,95%) Gram-negative and more likely to have flagella present than bacteria collected from the contaminated wells, which included a substantial fraction (,30%) of Gram-positive varieties. The ability of the bacteria from the clean portion of the karst aquifer to biodegrade benzene and toluene was studied under aerobic and anaerobic conditions in laboratory microcosms. The rate of fuel biodegradation in laboratory studies was approximately 50 times faster under aerobic conditions as compared to anaerobic, sulfur-reducing conditions. The optimum pH for fuel biodegradation ranged from 6 to 7. These findings suggest that bacteria have adapted to water-saturated karst systems with a variety of active and passive transport mechanisms.

Kentucky↗

USGS2003

Big Soda Lake (Nevada). 1. Pelagic bacterial heterotrophy and biomass

Bacterial activities and abundance were measured seasonally in the water column of meromictic Big Soda Lake which is divided into three chemically distinct zones: aerobic mixolimnion, anaerobic mixolimnion, and anaerobic monimolimnion. Bacterial abundance ranged between 5 and 52 x 10 6 cells ml −1 , with highest biomass at the interfaces between these zones: 2–4 mg C liter −1 in the photosynthetic bacterial layer (oxycline) and 0.8–2.0 mg C liter −1 in the chemocline. Bacterial cell size and morphology also varied with depth: small coccoid cells were dominant in the aerobic mixolimnion, whereas the monimolimnion had a more diverse population that included cocci, rods, and large filaments. Heterotrophic activity was measured by [methyl- 3 H]thymidine incorporation and [ 14 C]glutamate uptake. Highest uptake rates were at or just below the photosynthetic bacterial layer and were attributable to small (<1 µ m) heterotrophs rather than the larger photosynthetic bacteria. These high rates of heterotrophic uptake were apparently linked with fermentation; rates of other mineralization processes (e.g. sulfate reduction, methanogenesis, denitrification) in the anoxic mixolimnion were insignificant. Heterotrophic activity in the highly reduced monimolimnion was generally much lower than elsewhere in the water column. Therefore, although the monimolimnion contained most of the bacterial abundance and biomass (&sim;60%), most of the cells there were inactive.

Nevada↗

USGS1999

Phytoremediation of trichloroethene (TCE) using cottonwood trees

Phytoremediation uses the natural ability of plants to degrade contaminants in ground water. A field demonstration designed to remediate aerobic shallow ground water that contains trichloroethene began in April 1996 with the planting of cottonwood trees over an approximately 0.2-hectare area at the Naval Air Station, Fort Worth, Tx. Ground water was sampled in July 1997, November 1997, February 1998, and June 1998. Analyses from samples indicate that tree roots have the potential to create anaerobic conditions in the ground water that will facilitate degradation of trichloroethene by microbially mediated reductive dichlorination. Dissolved oxygen concentrations, which varied across the site, were smallest near a mature cottonwood tree (about-20 years old) 60 meters southwest of the cottonwood plantings. Reduction of dissolved oxygen is the primary microbially mediated reaction occurring in the ground water beneath the planted trees, whereas near the mature cottonwood tree, data indicate that methanogenesis is the most probable reaction occurring. Reductive dichlorination either is not occurring or is not a primary process away from the mature tree. On the basis of isotopic analyses of carbon-13 at locations away from the mature tree, trichloroethene concentration is controlled by volatilization. Phytoremediation uses the natural ability of plants to degrade contaminants in ground water. A field demonstration designed to remediate aerobic shallow ground water that contains trichloroethene began in April 1996 with the planting of cottonwood trees over an approximately 0.2-hectare area at the Naval Air Station, Fort Worth, Tx. Ground water was sampled in July 1997, November 1997, February 1998, and June 1998. Analyses from samples indicate that tree roots have the potential to create anaerobic conditions in the ground water that will facilitate degradation of trichloroethene by microbially mediated reductive dichlorination. Dissolved oxygen concentrations, which varied across the site, were smallest near a mature cottonwood tree (about-20 years old) 60 meters southwest of the cottonwood plantings. Reduction of dissolved oxygen is the primary microbially mediated reaction occurring in the ground water beneath the planted trees, whereas near the mature cottonwood tree, data indicate that methanogenesis is the most probable reaction occurring. Reductive dichlorination either is not occurring or is not a primary process away from the mature tree. On the basis of isotopic analyses of carbon-13 at locations away from the mature tree, trichloroethene concentration is controlled by volatilization.

Conference Paper↗

USGS2002

Microbial ecology of a crude oil contaminated aquifer

Detailed microbial analyses of a glacial outwash aquifer contaminated by crude oil provide insights into the pattern of microbial succession from iron reducing to methanogenic in the anaerobic portion of the contaminant plume. We analysed sediments from this area for populations of aerobes, iron reducers, fermenters and methanogens, using the most probable number method. On the basis of the microbial data the anaerobic area can be divided into distinct physiological zones dominated by either iron-reducers or a consortium of fermenters and methanogens. Chemistry and permeability data show that methanogenic conditions develop first in areas of high hydrocarbon flux. Thus, we find methanogens both in high permeability horizons and also where separate-phase crude oil is present in either the saturated or unsaturated zone. Microbial numbers peak at the top of the separate-phase oil suggesting that growth is most rapid in locations with access to both hydrocarbons and nutrients infiltrating from the surface.

IAHS-AISH Publication↗

USGS2005

Physiological characterization of a broad spectrum reductively dechlorinating consortium

A wetland sediment-derived microbial consortium (WBC-2) was developed by the US Geological Survey and propagated in vitro to large quantities by SiREM Laboratory for potential use in bioaugmentation applications. On the basis of bench-scale tests, the consortium could completely dechlorinate 1,1,2,2-tetrachloroethylene, tetrachloroethylene, trichloroethylene, 1,1,2-trichloroethane, cis- and trans-1,2-dichoroethylene, 1,1-dichloroethylene, 1,2-dichloroethane, and vinyl chloride in culture medium. Batch microcosms were carried out under anaerobic conditions in culture medium with neutral pH and with pH adjusted from acidic (pH 4, 5, and 6) to alkaline (pH 8 and 9). To evaluate oxygen sensitivity of WBC-2, an aliquot was removed from an anaerobic culture vessel and poured into smaller containers on the bench top where a series of oxygen exposures were applied to the culture by bubbling ambient air through the culture at a rate of ??? 100 mL/min. Chlorinated methanes tended to inhibit activity of a wide range of microorganisms. Although toxicity effects from CT addition were observed with WBC-2 in liquid culture at 3 mg/L concentration, WBC-2 in the columns could maintain degradation of CT and chloroform (CF) and of the chlorinated ethanes and ethylenes at CT and CF concentrations of 10 and 20 mg/L, respectively. This is an abstract of a paper presented at the Proceedings of the 8th International In Situ and On-Site Bioremediation Symposium (Baltimore, MD 6/6-9/2005).

Conference Paper↗

USGS1997

Natural attenuation of chlorinated hydrocarbons in a freshwater wetland

Natural attenuation of chlorinated volatile organic compounds (VOC's) occurs as ground water discharges from a sand aquifer to a freshwater wetland at Aberdeen Proving Ground, Md. Field and laboratory results indicate that biotransformation in the anaerobic wetland sediments is an important attenuation process. Relatively high concentrations of the parent compounds trichloroethylene (TCE) and 1,1,2,2-tetrachloroethane (PCA) and low or undetectable concentrations of daughter products were measured in the aquifer. In contrast, relatively high concentrations of the daughter products cis- and trans-1,2-dichloroethylene (12DCE); vinyl chloride (VC); 1,1,2-trichloroethane (112TCA); and 1,2-dichloroethane (12DCA) were measured in ground water in the wetland sediments, although total VOC concentrations decreased upward from about 1 mu mol/L (micromoles per liter) at the base of the wetland sediments to less than 0.2 near the surface. Microcosm experiments showed that 12DCE and VC are produced from anaerobic degradation of both TCE and PCA; PCA degradation also produced 112TCA and 12DCA.

Maryland↗

USGS1978

Reconnaissance for microbial activity in the Magothy aquifer, Bay Park, New York, four years after artificial recharge

Tertiary-treated sewage effluent was injected into the Magothy aquifer at Bay Park, Long Island, N.Y., between 1968 and 1973. In 1977, the microbial flora in water samples from the injection well and from three nearby wells were surveyed. Differences in the composition of the microbial flora among the four wells were found. A bacterial community dominated by facultative and obligate anaerobes, including two Clostridium species and methanogenic bacteria, was found at a well 6.1 m from the injection well. By contrast, except for isolation of Clostridium sphenoides from a well 30 m away, only obligate aerobes and facultative anaerobes were found in water from the injection well and the 30 m well. Only a small number of obligate aerobes were found in samples from a well 61 m away. These results suggest that nutrients in the recharge water formed an organically enriched zone to at least a distance of 6.1 m from the point of injection but not as far as 61 m. Extensive pumping at the end of the injection program apparently removed exogeneous nutrients near the injection well.

New York↗

USGS1998

Ground-water age and atmospheric tracers: Simulation studies and analysis of field data from the Mirror Lake site, New Hampshire

The use of environmental tracers in characterization of ground-water systems is investigated through mathematical modeling of ground-water age and atmospheric tracer transport, and by a field study at the Mirror Lake site, New Hampshire. Theory is presented for modeling ground-water age using the advective-dispersive transport equation. The transport equation includes a zero-order source of unit strength, corresponding to the rate of aging, and can accommodate matrix diffusion and other exchange processes. The effect of temperature fluctuations and layered soils on transport of atmospheric gases to the water table is investigated using a one-dimensional numerical model of chlorofluorocarbon (CFC-11) transport. The nonlinear relation between temperature and Henry's Law coefficient (reflecting air/water phase partitioning) can cause the apparent recharge temperature to be elevated above the annual mean temperature where the water table is shallow. In addition, fine-grained soils can isolate the air phase in the unsaturated zone from the atmosphere. At the USGS' Mirror Lake, New Hampshire fractured-rock research site CFC concentrations near the water table are depleted where dissolved oxygen is low. CFC-11 and CFC-113 are completely absent under anaerobic conditions, while CFC-12 is as low as one-third of modern concentrations. Anaerobic biodegradation apparently consumes CFC's near the water table at this site. One area of active degradation appears to be associated with streamflow loss to ground water. Soil gas concentrations are generally close to atmospheric levels, although some spatial correlation is observed between depleted concentrations of CFC-11 and CFC-113 in soil gas and water-table samples. Results of unsaturated-zone monitoring indicate that recharge occurs throughout the year in the watershed, even during summer evapotranspiration periods, and that seasonal temperature fluctuations occur as much as 5 meters below land surface. Application of ground-water age and CFC-11 transport models to the large-scale ground-water system at Mirror Lake illustrates the similarities between age and chemical transport. Generally, bedrock porosities required to match observed apparent ages from CFC concentrations are high relative to porosities measured on cores. Although matrix diffusion has no effect on steady-state age, it can significantly reduce CFC concentrations in fractured rock in which the effective porosity is low.

New Hampshire↗