Geology topics

Anthony J. Tesoriero

Publications and source records attributed to Anthony J. Tesoriero.

28 records · Page 2Linked to original sources

USGS2014

Nitrogen speciation and trends, and prediction of denitrification extent, in shallow US groundwater

Uncertainties surrounding nitrogen cycling complicate assessments of the environmental effects of nitrogen use and our understanding of the global carbon–nitrogen cycle. In this paper, we synthesize data from 877 ambient-monitoring wells across the US to frame broad patterns of nitrogen speciation and trends. At these sites, groundwater frequently contains substantial co-occurring NO 3 − and XSN 2 (N 2 from denitrification), reflecting active/ongoing denitrification and/or a mixture of undenitrified and denitrified groundwater. NO 3 − and NH 4 + essentially do not co-occur, indicating that the dominant source of NH 4 + at these sites likely is not dissimilatory reduction of NO 3 − to NH 4 + . Positive correlations of NH 4 + with apparent age, CH 4 , dissolved organic carbon, and indicators of reduced conditions are consistent with NH 4 + mobilization from degradation of aquifer organic matter and contraindicate an anthropogenic source of NH 4 + for most sites. Glacial aquifers and eastern sand and gravel aquifers generally have lower proportions of NO 3 − and greater proportions of XSN 2 than do fractured rock and karst aquifers and western sand and gravel aquifers. NO 3 − dominates in the youngest groundwater, but XSN 2 increases as residence time increases. Temporal patterns of nitrogen speciation and concentration reflect (1) changing NO 3 − loads over time, (2) groundwater residence-time controls on NH 4 + mobilization from solid phases, and (3) groundwater residence-time controls on denitrification. A simple classification tree using readily available variables (a national coverage of soil water depth, generalized geology) or variables reasonably estimated in many aquifers (residence time) identifies categorical denitrification extent (<10%, 10–50%, and >50%) with 79% accuracy in an independent testing set, demonstrating a predictive application based on the interconnected effects of redox, geology, and residence time.

Journal of Hydrology↗

USGS2013

Vulnerability of streams to legacy nitrate sources

The influence of hydrogeologic setting on the susceptibility of streams to legacy nitrate was examined at seven study sites having a wide range of base flow index (BFI) values. BFI is the ratio of base flow to total streamflow volume. The portion of annual stream nitrate loads from base flow was strongly correlated with BFI. Furthermore, dissolved oxygen concentrations in streambed pore water were significantly higher in high BFI watersheds than in low BFI watersheds suggesting that geochemical conditions favor nitrate transport through the bed when BFI is high. Results from a groundwater-surface water interaction study at a high BFI watershed indicate that decades old nitrate-laden water is discharging to this stream. These findings indicate that high nitrate levels in this stream may be sustained for decades to come regardless of current practices. It is hypothesized that a first approximation of stream vulnerability to legacy nutrients may be made by geospatial analysis of watersheds with high nitrogen inputs and a strong connection to groundwater (e.g., high BFI).

Indiana;Maryl;Nebraska;North Carolina;Washington;W↗

USGS2012

Redox reaction rates in shallow aquifers: Implications for nitrate transport in groundwater and streams

Groundwater age and water chemistry data along flow paths from recharge areas to streams were used to evaluate the trends and transformations of agricultural chemicals. Results from this analysis indicate that median nitrate recharge concentrations in these agricultural areas have increased markedly over the last 50 years from 4 mg N/L in samples collected prior to 1983 to 7.5 mg N/L in samples collected since 1983. The effect that nitrate accumulation in shallow aquifers will have on drinking water quality and stream ecosystems is dependent on the rate of redox reactions along flow paths and on the age distribution of nitrate discharging to supply wells and streams.

Conference Paper↗

USGS2011

O2 reduction and denitrification rates in shallow aquifers

O 2 reduction and denitrification rates were determined in shallow aquifers of 12 study areas representing a wide range in sedimentary environments and climatic conditions. Zero‐ and first‐order rates were determined by relating reactant or product concentrations to apparent groundwater age. O 2 reduction rates varied widely within and between sites, with zero‐order rates ranging from <3 μmol L −1 yr −1 to more than 140 μmol L −1 yr −1 and first‐order rates ranging from 0.02 to 0.27 yr −1 . Moderate denitrification rates (10–100 μmol N L −1 yr −1 ; 0.06–0.30 yr −1 ) were observed in most areas with O 2 concentrations below 60 μmol L −1 , while higher rates (>100 μmol N L −1 yr −1 ; >0.36 yr −1 ) occur when changes in lithology result in a sharp increase in the supply of electron donors. Denitrification lag times (i.e., groundwater travel times prior to the onset of denitrification) ranged from <20 yr to >80 yr. The availability of electron donors is indicated as the primary factor affecting O 2 reduction rates. Concentrations of dissolved organic carbon (DOC) and/or sulfate (an indicator of sulfide oxidation) were positively correlated with groundwater age at sites with high O 2 reduction rates and negatively correlated at sites with lower rates. Furthermore, electron donors from recharging DOC are not sufficient to account for appreciable O 2 and nitrate reduction. These relations suggest that lithologic sources of DOC and sulfides are important sources of electrons at these sites but surface‐derived sources of DOC are not. A review of published rates suggests that denitrification tends to occur more quickly when linked with sulfide oxidation than with carbon oxidation.

Water Resources Research↗

USGS2010

The influence of nutrients and physical habitat in regulating algal biomass in agricultural streams

This study examined the relative influence of nutrients (nitrogen and phosphorus) and habitat on algal biomass in five agricultural regions of the United States. Sites were selected to capture a range of nutrient conditions, with 136 sites distributed over five study areas. Samples were collected in either 2003 or 2004, and analyzed for nutrients (nitrogen and phosphorous) and algal biomass (chlorophyll a ). Chlorophyll a was measured in three types of samples, fine-grained benthic material (CHL FG ), coarse-grained stable substrate as in rock or wood (CHL CG ), and water column (CHL S ). Stream and riparian habitat were characterized at each site. TP ranged from 0.004–2.69 mg/l and TN from 0.15–21.5 mg/l, with TN concentrations highest in Nebraska and Indiana streams and TP highest in Nebraska. Benthic algal biomass ranged from 0.47–615 mg/m 2 , with higher values generally associated with coarse-grained substrate. Seston chlorophyll ranged from 0.2–73.1 μg/l, with highest concentrations in Nebraska. Regression models were developed to predict algal biomass as a function of TP and/or TN. Seven models were statistically significant, six for TP and one for TN; r 2 values ranged from 0.03 to 0.44. No significant regression models could be developed for the two study areas in the Midwest. Model performance increased when stream habitat variables were incorporated, with 12 significant models and an increase in the r 2 values (0.16–0.54). Water temperature and percent riparian canopy cover were the most important physical variables in the models. While models that predict algal chlorophyll a as a function of nutrients can be useful, model strength is commonly low due to the overriding influence of stream habitat. Results from our study are presented in context of a nutrient-algal biomass conceptual model.

Environmental Management↗

USGS2005

Nitrogen transport and transformations in a coastal plain watershed: Influence of geomorphology on flow paths and residence times

Nitrogen transport and groundwater‐surface water interactions were examined in a coastal plain watershed in the southeastern United States. Groundwater age dates, calculated using chlorofluorocarbon and tritium concentrations, along with concentrations of nitrogen species and other redox‐active constituents, were used to evaluate the fate and transport of nitrate. Nitrate is stable only in recently recharged (<10 years) water found in the upper few meters of saturated thickness in the upland portion of a surficial aquifer. Groundwater with a residence time between 10 and 30 years typically has low nitrate and elevated excess N 2 concentrations, indications that denitrification has reduced nitrate concentrations. Groundwater older than 30 years also has low nitrate concentrations but contains little or no excess N 2 , suggesting that this water did not contain elevated concentrations of nitrate along its flow path. Nitrate transport to streams varies between first‐ and third‐order streams. Hydrologic, lithologic, and chemical data suggest that the surficial aquifer is the dominant source of flow and nitrate to a first‐order stream. Iron‐reducing conditions occur in groundwater samples from the bed and banks of the first‐order stream, suggesting that direct groundwater discharge is denitrified prior to entering the stream. However, nitrogen from the surficial aquifer is transported directly to the stream via a tile drain that bypasses these reduced zones. In the alluvial valley of a third‐order stream the erosion of a confining layer creates a much thicker unconfined alluvial aquifer with larger zones of nitrate stability. Age dating and chemical information (SiO 2 , Na/K ratios) suggest that water in the alluvial aquifer is derived from short flow paths through the riparian zone and/or from adjacent streams during high‐discharge periods.

Water Resources Research↗

USGS2000

Fate and origin of 1,2-dichloropropane in an unconfined shallow aquifer

A shallow aquifer with different redox zones overlain by intensive agricultural activity was monitored for the occurrence of 1,2-dichloropropane (DCP) to assess the fate and origin of this pollutant. DCP was detected more frequently in groundwater samples collected in aerobic and nitrate-reducing zones than those collected from iron-reducing zones. Simulated DCP concentrations for groundwater entering an iron-reducing zone were calculated from a fate and transport model that included dispersion, sorption, and hydrolysis but not degradation. Simulated concentrations were well in excess of measured values, suggesting that microbial degradation occurred in the iron-reducing zone. Microcosm experiments were conducted using aquifer samples collected from iron-reducing and aerobic zones to evaluate the potential for microbial degradation of DCP and to explain field observations. Hydrogenolysis of DCP and production of monochlorinated propanes in microcosm experiments occurred only with aquifer materials collected from the iron-reducing zone, and no dechlorination was observed in microcosms established with aquifer materials collected from the aerobic zones. Careful analyses of the DCP/1,2,2-trichloropropane ratios in groundwater indicated that older fumigant formulations were responsible for the high levels of DCP present in this aquifer.A shallow aquifer with different redox zones overlain by intensive agricultural activity was monitored for the occurrence of 1,2-dichloropropane (DCP) to assess the fate and origin of this pollutant. DCP was detected more frequently in groundwater samples collected in aerobic and nitrate-reducing zones than those collected from iron-reducing zones. Simulated DCP concentrations for groundwater entering an iron-reducing zone were calculated from a fate and transport model that included dispersion, sorption, and hydrolysis but not degradation. Simulated concentrations were well in excess of measured values, suggesting that microbial degradation occurred in the iron-reducing zone. Microcosm experiments were conducted using aquifer samples collected from iron-reducing and aerobic zones to evaluate the potential for microbial degradation of DCP and to explain field observations. Hydrogenolysis of DCP and production of monochlorinated propanes in microcosm experiments occurred only with aquifer materials collected from the iron-reducing zone, and no dechlorination was observed in microcosms established with aquifer materials collected from the aerobic zones. Careful analyses of the DCP/1,2,2-trichloropropane ratios in groundwater indicated that older fumigant formulations were responsible for the high levels of DCP present in this aquifer.

Washington↗

USGS2000

Mechanism and rate of denitrification in an agricultural watershed: Electron and mass balance along groundwater flow paths

The rate and mechanism of nitrate removal along and between groundwater flow paths were investigated using a series of well nests screened in an unconfined sand and gravel aquifer. Intensive agricultural activity in this area has resulted in nitrate concentrations in groundwater often exceeding drinking water standards. Both the extent and rate of denitrification varied depending on the groundwater flow path. While little or no denitrification occurred in much of the upland portions of the aquifer, a gradual redox gradient is observed as aerobic upland groundwater moves deeper in the aquifer. In contrast, a sharp shallow redox gradient is observed adjacent to a third‐order stream as aerobic groundwater enters reduced sediments. An essentially complete loss of nitrate concurrent with increases in excess N 2 provide evidence that denitrification occurs as groundwater enters this zone. Electron and mass balance calculations suggest that iron sulfide (e.g., pyrite) oxidation is the primary source of electrons for denitrification. Denitrification rate estimates were based on mass balance calculations using nitrate and excess N 2 coupled with groundwater travel times. Travel times were determined using a groundwater flow model and were constrained by chlorofluorocarbon‐based age dates. Denitrification rates were found to vary considerably between the two areas where denitrification occurs. Denitrification rates in the deep, upland portions of the aquifer were found to range from <0.01 to 0.14 m M of N per year; rates at the redoxcline along the shallow flow path range from 1.0 to 2.7 m M of N per year. Potential denitrification rates in groundwater adjacent to the stream may be much faster, with rates up to 140 m M per year based on an in situ experiment conducted in this zone.

Water Resources Research↗

USGS2000

Water quality in the Puget Sound basin, Washington and British Columbia, 1996-98

Puget Sound basin streams during 1995-98 met most guidelines and criteria. Seventy-four manmade compounds were detected and different mixtures linked to land use. Urban expansion into forested areas is changing stream habitats--urban and agricultural streams are warmer and support less diverse insect populations than streams in forested areas. Elevated nitrate concentrations and the presence of manmade organic compounds indicated shallow ground water in urban and agricultural settings is vulnerable to contamination.

Circular↗

USGS1998

Assessing groundwater vulnerability using logistic regression

Determining the likelihood that groundwater contains elevated concentrations of contaminants can help water resource managers protect drinking water supplies. For example, this information is useful for selecting new sites for drinking water sources and designing more cost-effective monitoring strategies for existing sources. Groundwater vulnerability has typically been assessed using largely qualitative methods and expressed as relative measures of risk. In this study, a statistical approach was used to quantify the likelihood that a well contains an elevated concentration of nitrate or a detectable concentration of atrazine. The occurrence of elevated nitrate concentrations or detectable concentrations of atrazine in groundwater was related to both natural and anthropogenic variables using logistic regression. The variables that best explain the occurrence of elevated nitrate concentrations were well depth, surficial geology, and the percentages of urban and agricultural land within a radius of 3.2 kilometers of a well. Well depth and roadside application of atrazine best explained the occurrence of detectable concentrations of atrazine. From these relations, multiple logistic regression models were developed which predict the probability that a well has an elevated nitrate concentration or a detectable concentration of atrazine.

Conference Paper↗