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Richard L. Smith

Publications and source records attributed to Richard L. Smith.

33 records · Page 2Linked to original sources
USGS2007

Isotopic analysis of N and O in nitrite and nitrate by sequential selective bacterial reduction to N2O

Nitrite is an important intermediate species in the biogeochemical cycling of nitrogen, but its role in natural aquatic systems is poorly understood. Isotopic data can be used to study the sources and transformations of NO 2 - in the environment, but methods for independent isotopic analyses of NO 2 - in the presence of other N species are still new and evolving. This study demonstrates that isotopic analyses of N and O in NO 2 - can be done by treating whole freshwater or saltwater samples with the denitrifying bacterium Stenotrophomonas nitritireducens , which selectively reduces NO 2 - to N 2 O for isotope ratio mass spectrometry. When calibrated with solutions containing NO 2 - with known isotopic compositions determined independently, reproducible δ 15 N and δ 18 O values were obtained at both natural-abundance levels (±0.2−0.5‰ for δ 15 N and ±0.4−1.0‰ for δ 18 O) and moderately enriched 15 N tracer levels (±20−50‰ for δ 15 N near 5000‰) for 5−20 nmol of NO 2 - (1−20 μmol/L in 1−5 mL aliquots). This method is highly selective for NO 2 - and was used for mixed samples containing both NO 2 - and NO 3 - with little or no measurable cross-contamination. In addition, mixed samples that were analyzed with S. nitritireducens were treated subsequently with Pseudomonas aureofaciens to reduce the NO 3 - in the absence of NO 2 - , providing isotopic analyses of NO 2 - and NO 3 - separately in the same aliquot. Sequential bacterial reduction methods like this one should be useful for a variety of isotopic studies aimed at understanding nitrogen cycling in aquatic environments. A test of these methods in an agricultural watershed in Indiana provides isotopic evidence for both nitrification and denitrification as sources of NO 2 - in a small stream.

Indiana↗
USGS2006

Ammonium transport and reaction in contaminated groundwater: Application of isotope tracers and isotope fractionation studies

Ammonium (NH 4 + ) is a major constituent of many contaminated groundwaters, but its movement through aquifers is complex and poorly documented. In this study, processes affecting NH 4 + movement in a treated wastewater plume were studied by a combination of techniques including large‐scale monitoring of NH 4 + distribution; isotopic analyses of coexisting aqueous NH 4 + , NO 3 − , N 2 , and sorbed NH 4 + ; and in situ natural gradient 15 NH 4 + tracer tests with numerical simulations of 15 NH 4 + , 15 NO 3 − , and 15 N 2 breakthrough data. Combined results indicate that the main mass of NH 4 + was moving downgradient at a rate about 0.25 times the groundwater velocity. Retardation factors and groundwater ages indicate that much of the NH 4 + in the plume was recharged early in the history of the wastewater disposal. NO 3 − and excess N 2 gas, which were related to each other by denitrification near the plume source, were moving downgradient more rapidly and were largely unrelated to coexisting NH 4 + . The δ 15 N data indicate areas of the plume affected by nitrification (substantial isotope fractionation) and sorption (no isotope fractionation). There was no conclusive evidence for NH 4 + ‐consuming reactions (nitrification or anammox) in the anoxic core of the plume. Nitrification occurred along the upper boundary of the plume but was limited by a low rate of transverse dispersive mixing of wastewater NH 4 + and O 2 from overlying uncontaminated groundwater. Without induced vertical mixing or displacement of plume water with oxic groundwater from upgradient sources, the main mass of NH 4 + could reach a discharge area without substantial reaction long after the more mobile wastewater constituents are gone. Multiple approaches including in situ isotopic tracers and fractionation studies provided critical information about processes affecting NH 4 + movement and N speciation.

Water Resources Research↗
USGS2006

Ground-water-quality data for a treated-wastewater plume undergoing natural restoration, Ashumet Valley, Cape Cod, Massachusetts

A plume of contaminated ground water extends from former disposal beds at the Massachusetts Military Reservation wastewater-treatment plant toward Ashumet Pond, and farther southward toward coastal ponds and Vineyard Sound, Cape Cod, Massachusetts. Treated sewage-derived wastewater was discharged to the rapid-infiltration beds for nearly 60 years before the disposal site was moved to a different location in December 1995. Water-quality samples were collected periodically from monitoring wells and multilevel samplers during and after the disposal period to characterize the nature and extent of the contaminated ground water and to observe the water-quality changes after the wastewater disposal ceased. Data are presented here for water samples collected from 1994 through 2004 from 16 wells (at 2 locations) and 14 multilevel samplers (at 9 locations) along a longitudinal transect that extends through one of the disposal beds. Data collected from the treated-wastewater plume are presented in tabular format. These data include field parameters; concentrations of cations, anions, nitrate, ammonium, and organic and inorganic carbon species; and ultraviolet/visible absorbance. The natural restoration of the sand and gravel aquifer after removal of the nearly 60-year-long treated-wastewater source, along with interpretations of the water quality in the treated-wastewater plume on Cape Cod, have been documented in several published reports that are listed in the references.

Massachusetts↗
USGS2005

Water-quality data from two agricultural drainage basins in northwestern Indiana and northeastern Illinois: I. Lagrangian and synoptic data, 1999-2002

Methods of data collection and results of analyses are presented for Lagrangian and synoptic water-quality data collected from two agricultural drainages, the Iroquois River in northwestern Indiana and Sugar Creek in northwestern Indiana and northeastern Illinois. During six separate sampling trips, in April, June and September 1999, May 2000, September 2001 and April 2002, 152 discrete water samples were collected to characterize the water chemistry over the course of 2 to 4 days on each of these drainages. Data were collected for nutrients, major inorganic constituents, dissolved organic carbon, trace elements, dissolved gases, total bacterial cell counts, chlorophyll- a concentrations, and suspended sediment concentrations. In addition, field measurements of streamflow, pH, specific conductance, water temperature, and dissolved oxygen concentration were made during all trips except April 1999.

Indiana, Illinois↗
USGS2004

Changes in ground-water quality near two granular-iron permeable reactive barriers in a sand and gravel aquifer, Cape Cod, Massachusetts, 1997-2000

Two experimental permeable reactive barriers (PRBs) of granular zero-valent iron were emplaced in the path of a tetrachloroethene plume (the Chemical Spill-10 plume) at the Massachusetts Military Reservation, Cape Cod, Massachusetts, in June 1998. The goal of the field experiment was to achieve emplacement of a granular-iron PRB deeper than attempted before. The PRBs were expected to create a reducing environment and degrade the tetrachloroethene by reductive dechlorination. The goal of the work presented in this report was to observe temporary and sustained changes to the ground-water chemistry downgradient from the PRBs. A hydraulic-fracturing method involving injection of the granular iron with a guar-biopolymer and enzyme slurry was used to install the parallel 30- to 33-foot-wide wall-shaped barriers at a depth of 82 to 113 feet below land surface. An acetic acid and enzyme mixture was subsequently injected in wells near the barriers to degrade the guar biopolymer. Prior to the emplacement, tetrachloroethene concentrations in the Chemical Spill-10 plume at the study area were as high as 250 micrograms per liter. Other water properties in the plume generally were similar to the properties of uncontaminated ground water in the area, which typically has dissolved oxygen concentrations of 250 to 375 micromoles per liter, pH of 5.5 to 6.0, and specific conductance of 60 to 90 microsiemens per centimeter. Water-quality samples were collected periodically from monitoring wells near the PRBs to determine how the emplacement of the granular-iron walls altered the ground-water quality. In addition, an automated well-sampling device measured temperature, specific conductance, pH, and dissolved oxygen every 1–4 days for 16 months in a well downgradient from the two parallel PRBs. Temporary increases (lasting about 5 to 6 months) in specific conductance were observed downgradient from the PRBs as a result of the sodium chloride, potassium carbonate, and other salts included in the slurry and the acetic acid and enzyme mixture that was subsequently injected to degrade the guar biopolymer. Temporary increases in the concentrations of major cations (sodium, potassium, magnesium, and calcium) were observed downgradient from the PRBs, as were temporary but substantial increases in the dissolved and total organic carbon concentrations. Methane was detected, sulfate concentrations decreased temporarily, and concentrations of dissolved inorganic carbon increased in samples from wells downgradient from the PRBs. A sustained (longer than 12 months) reducing environment, in which dissolved oxygen concentrations decreased to zero, the pH increased to about 6.8, and dissolved iron concentrations increased substantially, developed as a result of the oxidation (corrosion) of the granular iron; this zone persisted at least 65 feet downgradient from the PRBs. The pH and dissolved iron concentrations increased with distance from the granular-iron walls. Concentrations of arsenic, cobalt, manganese, and phosphorus increased, and nitrate concentrations were reduced to below the detection limit downgradient from the walls. A sustained decrease of tetrachloroethene concentrations was not observed; however, reductive dechlorination products were observed at wells downgradient from the PRBs during several rounds of sampling. The emplacement of zero-valent iron in the aquifer to remove tetrachloroethene from the ground water caused changes in the water chemistry that persisted farther downgradient from the PRBs than has been observed at other sites because of the low chemical reactivity of the quartz-dominated aquifer sediments and the low ambient dissolved chemical concentrations in the ground water. The small transverse dispersion in the aquifer and the probable long-term persistence of the iron indicate that the chemically altered zone probably will extend a substantial distance downgradient from the PRBs for a substantial period of time (years); further investigation would be needed to determine this distance.

Massachusetts↗
USGS2003

Big Soda Lake (Nevada). 2. Pelagic sulfate reduction

The epilimnion of hypersaline, alkaline, meromictic Big Soda Lake contains an average 58 mmol sulfate liter −1 and 0.4 µ mol dissolved iron liter −1 . The monimolimnion, which is permanently anoxic, has a sulfide concentration ranging seasonally from 4 to 7 mmol liter −1 . Depth profiles of sulfate reduction in the monimolimnion, assayed with a 35 S tracer technique and in situ incubations, demonstrated that sulfate reduction occurs within the water column of this extreme environment. The average rate of reduction in the monimolimnion was 3 µ mol sulfate liter −1 d −1 in May compared to 0.9 in October. These values are comparable to rates of sulfate reduction reported for anoxic waters of more moderate environments. Sulfate reduction also occurred in the anoxic zone of the mixolimnion, though at significantly lower rates (0.025–0.090 µ mol liter −1 d −1 at 25 m). Additions of FeS (1.0 mmol liter −1 ) doubled the endogenous rate of sulfate reduction in the monimolimnion, while MnS and kaolinite had no effect. These results suggest that sulfate reduction in Big Soda Lake is iron limited and controlled by seasonal variables other than temperature. Estimates of the organic carbon mineralized by sulfate reduction exceed measured fluxes of particulate organic carbon sinking from the mixolimnion. Thus, additional sources of electron donors (other than those derived from the sinking of pelagic autotrophs) may also fuel monimolimnetic sulfate reduction in the lake.

Nevada↗
USGS2003

Phosphorus in a ground-water contaminant plume discharging to Ashumet Pond, Cape Cod, Massachusetts, 1999

The discharge of a plume of sewagecontaminated ground water emanating from the Massachusetts Military Reservation to Ashumet Pond on Cape Cod, Massachusetts, has caused concern about excessive loading of nutrients, particularly phosphorus, to the pond. The U.S. Air Force is considering remedial actions to mitigate potentially adverse effects on the ecological characteristics of the pond from continued phosphorus loading. Concentrations as great as 3 milligrams per liter of dissolved phosphorus (as P) are in ground water near the pond's shoreline; concentrations greater than 5 milligrams per liter of phosphorus are in ground water farther upgradient. Temporary drive-point wells were used to collect water samples from 2 feet below the pond bottom to delineate concentration distributions in the pore waters of the pond-bottom sediments. Measurements in the field of specific conductance and colorimetrically determined orthophosphate concentrations provided real-time data to guide the sampling. The contaminant plume discharges to the Fishermans Cove area of Ashumet Pond as evidenced by elevated levels of specific conductance and boron, which are chemically conservative indicators of the sewage-contaminated ground water. Concentrations of nonconservative species, such as dissolved phosphorus, manganese, nitrate, and ammonium, also were elevated above background levels in ground water discharging to the pond, but in spatially complex distributions that reflect their distributions in ground water upgradient of the pond. Phosphorus concentrations exceeded background levels (greater than 0.10 milligram per liter) in the pond-bottom pore water along 875 feet of shoreline. Greatest concentrations (greater than 2 milligrams per liter) occurred within 30 feet of the shore in an area about 225 feet long. Calculations of phosphorus flux in the aquifer upgradient of Ashumet Pond, as determined from water-flux estimates from a steady-state ground-water-flow model and phosphorus concentrations (in 1999) from multilevel samplers about 75 feet upgradient of the pond, indicate that dissolved phosphorus moves towards the pond and discharges to it with the inflowing ground water at a rate as high as about 316 kilograms per year.

Massachusetts↗
USGS1998

Using transport model interpretations of tracer tests to study microbial processes in groundwater

It has long been known that microorganisms affect the geochemistry of groundwater. But despite this recognition, little detailed information is available regarding the rates and the factors controlling microbial processes in groundwater. Part of the reason stems from the relatively inaccessible nature of most groundwater and the difficulties encountered in obtaining representative samples of groundwater and subsurface sediments. At the same time, most groundwater systems are nutrient poor or oligotrophic environments in which the resident microorganisms are severely stressed and often nearly inactive. These populations are functioning so slowly that many types of activity measurements designed to assess microbial processes in more productive environments are ineffective for groundwater. However, because groundwater is by far the largest reservoir of freshwater in the world ( Freeze and Cherry 1979 ), our lack of knowledge about groundwater microorganisms and their processes represents a significant void in the study of microbial ecology and in our ability to predict the outcome when these reserves are compromised by contamination.

Book chapter↗
USGS1994

Autotrophic, hydrogen-oxidizing, denitrifying bacteria in groundwater, potential agents for bioremediation of nitrate contamination

Addition of hydrogen or formate significantly enhanced the rate of consumption of nitrate in slurried core samples obtained from an active zone of denitrification in a nitrate-contaminated sand and gravel aquifer (Cape Cod, Mass.). Hydrogen uptake by the core material was immediate and rapid, with an apparent K m of 0.45 to 0.60 μM and a V max of 18.7 nmol cm -3 h -1 at 30°C. Nine strains of hydrogen-oxidizing denitrifying bacteria were subsequently isolated from the aquifer. Eight of the strains grew autotrophically on hydrogen with either oxygen or nitrate as the electron acceptor. One strain grew mixotrophically. All of the isolates were capable of heterotrophic growth, but none were similar to Paracoccus denitrificans , a well-characterized hydrogen-oxidizing denitrifier. The kinetics for hydrogen uptake during denitrification were determined for each isolate with substrate depletion progress curves; the K m s ranged from 0.30 to 3.32 μM, with V max s of 1.85 to 13.29 fmol cell -1 h -1 . Because these organisms appear to be common constituents of the in situ population of the aquifer, produce innocuous end products, and could be manipulated to sequentially consume oxygen and then nitrate when both were present, these results suggest that these organisms may have significant potential for in situ bioremediation of nitrate contamination in groundwater.

Massachusetts↗
USGS1993

Aspects of the biogeochemistry of methane in Mono Lake and the Mono Basin of California

Above-ambient levels of methane and higher hydrocarbons were detected in the atmosphere of the Mono Basin. These gases emanated from several different sources, including natural gas seeps (thermogenic and biogenic), and methanogenic activity in sediments. Seeps were distributed over nearly 33% of the lake bottom and were also present in the exposed former lakebed. They originated from one or more natural gas deposits that underlie the basin. Seeps associated with hot springs had a thermogenic character, whereas the others had the characteristics of bacterially formed gases. The radiocarbon content of methane in all seep gases was low (5-11% modern carbon), indicating an age of greater than about 20,000 years. Dissolved methane increased with depth in the sediments, ultimately reaching saturation levels (1-3 mM). The outward diffusive flux of methane into the anoxic bottom waters elevated concentrations to 60 µM during the 1984-1988 meromictic interval. The radiocarbon content of hypolimnion methane was equivalent to that of the dissolved inorganic carbon (~80% modern carbon), indicating derivation from current methanogenic activity. Oxidation by anaerobic bacteria was the major sink for this methane. Methane that escaped oxidation transited to the epilimnion where it attained supersaturation (0.1-3.0 µM) relative to the atmosphere. Measured outward fluxes over a 2-year period were highly variable, ranging from 0.01 to 4.82 mmoles CH 4 m -2 d -1 . Bacterial activity was detected in the sediments of the hypolimnion High rates of sulfate reduction (~200 µmoles L -1 d -1 ) were measured in the upper 5-cm interval but decreased > 10-fold with depth. The highest rate of methanogenic activity was ~1 µmole L -1 d -1 , as measured by reduction of 14 CO 2 . Bacteria metabolized dimethylsulfide, trimethylamine, acetate, and glucose to primarily CO 2 and some CH 4 . Turnovers of glucose (k = 0.16 d -1 ) and trimethylamine (k = 0.09 d -1 ) were highest in the upper 2.5-cm interval and decreased as much as 10-fold with depth. These results confirm that a low rate of methanogenic activity occurs in this extreme environment and is the source of methane to the hypolimnion.

California↗
USGS1984

Denitrification in San Francisco Bay intertidal sediments

The acetylene block technique was employed to study denitrification in intertidal estuarine sediments. Addition of nitrate to sediment slurries stimulated denitrification. During the dry season, sediment-slurry denitrification rates displayed Michaelis-Menten kinetics, and ambient NO 3 − + NO 2 − concentrations (≤26 μM) were below the apparent K m (50 μM) for nitrate. During the rainy season, when ambient NO 3 − + NO 2 − concentrations were higher (37 to 89 μM), an accurate estimate of the K m could not be obtained. Endogenous denitrification activity was confined to the upper 3 cm of the sediment column. However, the addition of nitrate to deeper sediments demonstrated immediate N 2 O production, and potential activity existed at all depths sampled (the deepest was 15 cm). Loss of N 2 O in the presence of C 2 H 2 was sometimes observed during these short-term sediment incubations. Experiments with sediment slurries and washed cell suspensions of a marine pseudomonad confirmed that this N 2 O loss was caused by incomplete blockage of N 2 O reductase by C 2 H 2 at low nitrate concentrations. Areal estimates of denitrification (in the absence of added nitrate) ranged from 0.8 to 1.2 μmol of N 2 m −2 h −1 (for undisturbed sediments) to 17 to 280 μmol of N 2 m −2 h −1 (for shaken sediment slurries).

California↗
USGS1983

Anaerobic oxalate degradation: Widespread natural occurrence in aquatic sediments

Significant concentrations of oxalate (dissolved plus particulate) were present in sediments taken from a diversity of aquatic environments, ranging from 0.1 to 0.7 mmol/liter of sediment. These included pelagic and littoral sediments from two freshwater lakes (Searsville Lake, Calif., and Lake Tahoe, Calif.), a hypersaline, meromictic, alkaline lake (Big Soda Lake, Nev.), and a South San Francisco Bay mud flat and salt marsh. The oxalate concentration of several plant species which are potential detrital inputs to these aquatic sediments ranged from 0.1 to 5.0% (wt/wt). In experiments with litter bags, the oxalate content of Myriophyllum sp. samples buried in freshwater littoral sediments decreased to 7% of the original value in 175 days. This suggests that plant detritus is a potential source of the oxalate within these sediments. [ 14 C]oxalic acid was anaerobically degraded to 14 CO 2 in all sediment types tested, with higher rates evident in littoral sediments than in the pelagic sediments of the lakes studied. The turnover time of the added [ 14 C]oxalate was less than 1 day in Searsville Lake littoral sediments. The total sediment oxalate concentration did not vary significantly between littoral and pelagic sediments and therefore did not appear to be controlling the rate of oxalate degradation. However, depth profiles of [ 14 C]oxalate mineralization and dissolved oxalate concentration were closely correlated in freshwater littoral sediments; both were greatest in the surface sediments (0 to 5 cm) and decreased with depth. The dissolved oxalate concentration (9.1 μmol/liter of sediment) was only 3% of the total extractable oxalate (277 μmol/liter of sediment) at the sediment surface. These results suggest that anaerobic oxalate degradation is a widespread phenomenon in aquatic sediments and may be limited by the dissolved oxalate concentration within these sediments.

California, Nevada↗