SEARCH · Search USGS

Results for “Journal of Environmental Monitoring”

Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 289 records · Page 16Linked to original sources

USGS2008

Rainfall effects on rare annual plants

Variation in climate is predicted to increase over much of the planet this century. Forecasting species persistence with climate change thus requires understanding of how populations respond to climate variability, and the mechanisms underlying this response. Variable rainfall is well known to drive fluctuations in annual plant populations, yet the degree to which population response is driven by between-year variation in germination cueing, water limitation or competitive suppression is poorly understood. We used demographic monitoring and population models to examine how three seed banking, rare annual plants of the California Channel Islands respond to natural variation in precipitation and their competitive environments. Island plants are particularly threatened by climate change because their current ranges are unlikely to overlap regions that are climatically favourable in the future. Species showed 9 to 100-fold between-year variation in plant density over the 5–12 years of censusing, including a severe drought and a wet El Niño year. During the drought, population sizes were low for all species. However, even in non-drought years, population sizes and per capita growth rates showed considerable temporal variation, variation that was uncorrelated with total rainfall. These population fluctuations were instead correlated with the temperature after the first major storm event of the season, a germination cue for annual plants. Temporal variation in the density of the focal species was uncorrelated with the total vegetative cover in the surrounding community, suggesting that variation in competitive environments does not strongly determine population fluctuations. At the same time, the uncorrelated responses of the focal species and their competitors to environmental variation may favour persistence via the storage effect. Population growth rate analyses suggested differential endangerment of the focal annuals. Elasticity analyses and life table response experiments indicated that variation in germination has the same potential as the seeds produced per germinant to drive variation in population growth rates, but only the former was clearly related to rainfall. Synthesis . Our work suggests that future changes in the timing and temperatures associated with the first major rains, acting through germination, may more strongly affect population persistence than changes in season-long rainfall.

Journal of Ecology↗

USGS2023

Differential hypoxia tolerance of eastern oysters from the northern Gulf of Mexico at elevated temperature

Increasing prevalence of hypoxia in shallow waters of U.S. Gulf of Mexico (GoM) estuaries can pose a serious threat to eastern oysters ( Crassostrea virginica ). Their tolerance to hypoxia, however, is not well characterized, especially at elevated temperatures (>30 °C) typical of GoM estuaries in summer. Moreover, it is unknown whether differences in hypoxia tolerance exist between GoM oyster populations growing in estuaries differing in local environmental conditions. Wild oyster broodstocks were collected from four estuarine sites in Texas (Packery Channel, PC and Aransas Bay, AB) and Louisiana (Calcasieu Lake, CL and Vermilion Bay, VB) and their adult progenies (F1) were tested (Study 1) under continuous hypoxia (<2.0 mg O 2 L −1 ) at 32 °C. Significant differences in hypoxia tolerance were found between F1 populations with calculated median lethal time (LT 50 ) ranging from 3.9 to 12.5 days. PC and CL oysters were the most and least tolerant populations, respectively. The study was repeated twice more (Studies 2 and 3) using PC and CL oysters, and their responses at the organismic, cellular, and biochemical levels were investigated. Valve movement was monitored, and oysters were sampled to measure hemocyte density, plasma protein, calcium and glutathione concentrations, and digestive gland alanine and succinate concentrations after either 3–5 days (Study 2) or 1–3 days (Study 3) of hypoxia exposure. From the onset of hypoxia until their death, oysters stayed opened 13–32% of the time compared to 53–64% under normoxia, but no differences between populations were detected under hypoxia. PC oyster but not CL oyster plasma glutathione concentrations increased significantly in both studies. Under longer (3–5 days) hypoxia exposure, plasma calcium and glutathione concentrations of PC oysters were significantly higher than CL oysters. These results suggest PC oysters were better able to protect tissues against acidosis and oxidative damage during hypoxia and high temperature stress than CL oysters. Overall, our results indicate that oyster populations originating from the GoM vary in their response to hypoxia and high temperature stress and possess differential tolerance.

Alabama, Louisiana, Mississippi, Texas↗

USGS2001

After site selection and before data analysis: sampling, sorting, and laboratory procedures used in stream benthic macroinvertebrate monitoring programs by USA state agencies

A survey of methods used by US state agencies for collecting and processing benthic macroinvertebrate samples from streams was conducted by questionnaire; 90 responses were received and used to describe trends in methods. The responses represented an estimated 13,000-15,000 samples collected and processed per year. Kicknet devices were used in 64.5% of the methods; other sampling devices included fixed-area samplers (Surber and Hess), artificial substrates (Hester-Dendy and rock baskets), grabs, and dipnets. Regional differences existed, e.g., the 1-m kicknet was used more often in the eastern US than in the western US. Mesh sizes varied among programs but 80.2% of the methods used a mesh size between 500 and 600 (mu or u)m. Mesh size variations within US Environmental Protection Agency regions were large, with size differences ranging from 100 to 700 (mu or u)m. Most samples collected were composites; the mean area sampled was 1.7 m 2 . Samples rarely were collected using a random method (4.7%); most samples (70.6%) were collected using "expert opinion", which may make data obtained operator-specific. Only 26.3% of the methods sorted all the organisms from a sample; the remainder subsampled in the laboratory. The most common method of subsampling was to remove 100 organisms (range = 100-550). The magnification used for sorting ranged from 1 (sorting by eye) to 30x, which results in inconsistent separation of macroinvertebrates from detritus. In addition to subsampling, 53% of the methods sorted large/rare organisms from a sample. The taxonomic level used for identifying organisms varied among taxa; Ephemeroptera, Plecoptera, and Trichoptera were generally identified to a finer taxonomic resolution (genus and species) than other taxa. Because there currently exists a large range of field and laboratory methods used by state programs, calibration among all programs to increase data comparability would be exceptionally challenging. However, because many techniques are shared among methods, limited testing could be designed to evaluate whether procedural differences affect the ability to determine levels of environmental impairment using benthic macroinvertebrate communities.

Journal of the North American Benthological Societ↗

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↗

USGS2008

Land use and the structure of western US stream invertebrate assemblages: Predictive models and ecological traits

Inferences drawn from regional bioassessments could be strengthened by integrating data from different monitoring programs. We combined data from the US Geological Survey National Water-Quality Assessment (NAWQA) program and the US Environmental Protection Agency Wadeable Streams Assessment (WSA) to expand the scope of an existing River InVertebrate Prediction and Classification System (RIVPACS)-type predictive model and to assess the biological condition of streams across the western US in a variety of landuse classes. We used model-derived estimates of taxon-specific probabilities of capture and observed taxon occurrences to identify taxa that were absent from sites where they were predicted to occur (decreasers) and taxa that were present at sites where they were not predicted to occur (increasers). Integration of 87 NAWQA reference sites increased the scope of the existing WSA predictive model to include larger streams and later season sampling. Biological condition at 336 NAWQA test sites was significantly (p < 0.001) associated with basin land use and tended to be lower in basins with intensive landuse modification (e.g., mixed, urban, and agricultural basins) than in basins with relatively undisturbed land use (e.g., forested basins). Of the 437 taxa observed among reference and test sites, 180 (41%) were increasers or decreasers. In general, decreasers had a different set of ecological traits (functional traits or tolerance values) than did increasers. We could predict whether a taxon was a decreaser or an increaser based on just a few traits, e.g., desiccation resistance, timing of larval development, habit, and thermal preference, but we were unable to predict the type of basin land use from trait states present in invertebrate assemblages. Refined characterization of traits might be required before bioassessment data can be used routinely to aid in the diagnoses of the causes of biological impairment. ?? 2008 by The North American Benthological Society.

Arizona, California, Colorado, Idaho, Montana, New↗

USGS2019

Let’s agree to disagree: Comparing auto-acoustic identification programs for northeastern bats

With the declines in abundance and changing distribution of white-nose syndrome–affected bat species, increased reliance on acoustic monitoring is now the new “normal.” As such, the ability to accurately identify individual bat species with acoustic identification programs has become increasingly important. We assessed rates of disagreement between the three U.S. Fish and Wildlife Service–approved acoustic identification software programs (Kaleidoscope Pro 4.2.0, Echoclass 3.1, and Bat Call Identification 2.7d) and manual visual identification using acoustic data collected during summers from 2003 to 2017 at Fort Drum, New York. We assessed the percentage of agreement between programs through pairwise comparisons on a total nightly count level, individual file level (e.g., individual echolocation pass call file), and grouped maximum likelihood estimate level (e.g., probability values that a species is misclassified as present when in fact it is absent) using preplanned contrasts, Akaike Information Criterion, and annual confusion matrices. Interprogram agreement on an individual file level was low, as measured by Cohen's Kappa (0.2–0.6). However, site-night level pairwise comparative analysis indicated that program agreement was higher (40–90%) using single season occupancy metrics. In comparing analytical outcomes of our different datasets (i.e., how comparable programs and visual identification are regarding the relationship between environmental conditions and bat activity), we determined high levels of congruency in the relative rankings of the model as well as the relative level of support for each individual model. This indicated that among individual software packages, when analyzing bat calls, there was consistent ecological inference beyond the file-by-file level at the scales used by managers. Depending on objectives, we believe our results can help users choose automated software and maximum likelihood estimate thresholds more appropriate for their needs and allow for better cross-comparison of studies using different automated acoustic software.

Journal of Fish and Wildlife Management↗

USGS2022

Using piecewise regression to identify biological phenomena in biotelemetry datasets

1. Technological advances in the field of animal tracking have greatly expanded the potential to remotely monitor animals, opening the door to exploring how animals shift their behavior over time or respond to external stimuli. A wide variety of animal-borne sensors can provide information on an animal’s location, movement characteristics, external environmental conditions, and internal physiological status. 2. Here, we demonstrate how piecewise regression can be used to identify the presence and timing of potential shifts in a variety of biological responses using GPS telemetry and other biologging data streams. Different biological latent states can be inferred by partitioning a time-series into multiple segments based on changes in modeled responses (e.g., their mean, variance, trend, degree of autocorrelation) and specifying a unique model structure for each interval. 3. We provide six example applications highlighting a variety of taxonomic species, data streams, timescales and biological phenomena. These examples include a short-term behavioural response (flee and return) by a trumpeter swan Cygnus buccinator following a GPS collar deployment; remote identification of parturition based on movements by a pregnant moose Alces alces ; a physiological response (spike in heart-rate) in a black bear Ursus americanus to a stressful stimulus(presence of a drone); a mortality event of a trumpeter swan signalled by changes in collar temperature and overall dynamic body acceleration; an unsupervised method for identifying the onset, return, duration and staging use of sandhill crane Antigone canadensis migration; and estimation of the transition between incubation and brood-rearing (i.e. hatching) for a breeding trumpeter swan. 4. We implement analyses using the MCP package in R, which provides functionality for specifying and fitting a wide variety of user-defined model structures in a Bayesian framework and methods for assessing and comparing models using information criteria and cross-validation measures.

Journal of Animal Ecology↗

USGS2024

Great Lakes mallard population dynamics

Breeding mallard ( Anas platyrhynchos ) populations in the Great Lakes region (Michigan, Minnesota, Wisconsin, USA) declined by >40% between 2000–2022 based on abundance data collected during spring aerial surveys. Mallards are an important waterfowl species in this region, where an estimated 60–80% of the mallard harvest is composed of locally banded birds. Extensive population monitoring datasets are available for mallards, presenting an opportunity to address complex questions such as estimating productivity at large spatial and temporal scales, identifying the effects of harvest on mallard demography, quantifying mechanisms for harvest compensation, and integrating multiple datasets to quantify the demographic drivers of population change. Our objective was to simultaneously examine factors affecting demographic parameters and their relative contribution to Great Lakes mallard population dynamics. We used 32 years of banding, band recovery, and aerial survey data collected for mallards from Michigan and Wisconsin to develop an integrated population model (IPM). We used age ratios at banding to estimate productivity, band recoveries from hunter-harvested birds to estimate annual survival and cause-specific mortality (i.e., harvest or non-hunting), and modeled abundance using aerial survey and demographic parameter estimates from 1991–2022. The IPM results indicated the decline in Great Lakes mallard abundance was caused by increased non-hunting mortality and a decline in productivity. Productivity varied spatially but temporally declined with the loss of Conservation Reserve Program area. Moreover, our productivity assessment provided evidence of density dependence in reproduction. Non-hunting mortality was 3.5–6.7 times and 1.3–4.2 times greater than harvest mortality for adult and juvenile female mallards, respectively, indicating environmental factors during spring and summer, not harvest, most greatly influenced annual mortality for female mallards. Our IPM reduced uncertainty in the factors affecting Great Lakes mallard population dynamics and indicated management actions that address non-hunting mortality and productivity would be most effective in increasing Great Lakes mallard abundance.

Michigan, Wisconsin↗

USGS2023

Predicting methane emissions and developing reduction strategies for a Central Appalachian Basin, USA, longwall mine through analysis and modeling of geology and degasification system performance

Coal mine methane is a safety concern in active mines due to explosion risk and an environmental concern due to the greenhouse gas (GHG) properties of methane emissions to the atmosphere. Depending on the mine design and operation, structural and stratigraphic characteristics of the geology, and the properties of coal beds affected by mining, a significant amount of methane can be released during coal extraction. These emissions may be low and uniform, but they also can be high and abrupt, if not captured by using pre- and post-mining methods of degasification or not controlled by ventilation during mining. Therefore, emissions should be monitored and predicted accurately for underground safety and GHG reduction. Ventilation and degasification systems should be designed accordingly by taking into account the mine geological properties and the degasification system's performance. This paper presents a comprehensive study to predict emissions and proposes alternatives to reduce emissions in a longwall mine extracting metallurgical coal from the Pocahontas No. 3 coal bed in Virginia (Central Appalachian Basin), USA. The work focused on mining activity in four adjacent panels through analysis and modeling of geology and evaluation of the performance of the methane control system. Results showed that the mine geology contained a significant amount of gas within and around the panel areas, which was controlled by utilizing different degasification methods besides ventilation during mining. The study showed that after pre-mining degasification using fractured vertical wells and in-seam horizontal wells, each panel potentially contained ∼19 MMscf and ∼ 2 MMscf of gas remaining to be handled by the gob gas ventholes (GGVs) and the ventilation, respectively, per acre of mining. It was shown that extending the pre-mining degasification duration of vertical wells by as much as 4 years or drilling more horizontal wells with closer spacing could significantly reduce ventilation and gob emissions during the mining of coal.

Kentucky, Virginia, West Virginia↗

USGS2018

Prediction uncertainty and data worth assessment for groundwater transport times in an agricultural catchment

Uncertainties about the age of base-flow discharge can have serious implications for the management of degraded environmental systems where subsurface pathways, and the ongoing release of pollutants that accumulated in the subsurface during past decades, dominate the water quality signal. Numerical groundwater models may be used to estimate groundwater return times and base-flow ages and thus predict the time required for stakeholders to see the results of improved agricultural management practices. However, the uncertainty inherent in the relationship between (i) the observations of atmospherically-derived tracers that are required to calibrate such models and (ii) the predictions of system age that the observations inform have not been investigated. For example, few if any studies have assessed the uncertainty of numerically-simulated system ages or evaluated the uncertainty reductions that may result from the expense of collecting additional subsurface tracer data. In this study we combine numerical flow and transport modeling of atmospherically-derived tracers with prediction uncertainty methods to accomplish four objectives. First, we show the relative importance of head, discharge, and tracer information for characterizing response times in a uniquely data rich catchment that includes 266 age-tracer measurements (SF 6 , CFCs, and 3 H) in addition to long term monitoring of water levels and stream discharge. Second, we calculate uncertainty intervals for model-simulated base-flow ages using both linear and non-linear methods, and find that the prediction sensitivity vector used by linear first-order second-moment methods results in much larger uncertainties than non-linear Monte Carlo methods operating on the same parameter uncertainty. Third, by combining prediction uncertainty analysis with multiple models of the system, we show that data-worth calculations and monitoring network design are sensitive to variations in the amount of water leaving the system via stream discharge and irrigation withdrawals. Finally, we demonstrate a novel model-averaged computation of potential data worth that can account for these uncertainties in model structure.

Maryland↗

USGS2026

Evolution of arsenic speciation during thermal treatment simulating wildfire heating in arsenic-rich sediments

Understanding arsenic transformations during wildfires can help better constrain the environmental impacts of increased wildfire intensity, frequency, and burned area. Previous studies have monitored the evolution of metal(loid) speciation at specific time/temperature endpoints, hampering the comprehension of the dynamic transformations of metal(loid)s during wildfires. Here, a novel approach, namely in situ time-resolved X-ray absorption near edge structure (TR-XANES) spectroscopy, was used for the first time to monitor the heat-induced redox transformations of arsenic (As) in two As-rich sediments with different characteristics. No arsenic transformations were observed in either sediment at room temperature or when the sediments were heated to a maximum temperature of 400 ºC. When heated to a maximum temperature of 600 or 700 ºC, As underwent complex, dynamic, and partially reversible redox transformations, the extent of which varied with sediment properties, initial As speciation, and heating temperature and duration. In the case of sediments initially containing As(V) and a low sulfide/sulfate ratio, the As(V) was reduced to As(III) over a short period of time, followed by immediate reoxidation of As(III) to As(V). The extent of the transient As reduction increased with increasing maximum temperature. The final As speciation at the end of the heating experiment was not substantially different from that at the beginning of the experiment. In contrast, in sediments that were best described by a more complex combination of reference compounds (As(V) coprecipitated with or adsorbed on iron oxide, arseniosiderite, arsenopyrite) with a high sulfide/sulfate ratio, As(V) phases were reduced to As(III) and As(III) was further reduced to As(-I) (at 700 ºC, only), followed by delayed reoxidation of As(-I) to As(III) (at 700 ºC, only) and reoxidation of As(III) to As(V). Approximately 9% and 26% of all As remained as As(III) ( i.e., was not reoxidized to As(V)) at the end of the experiment when heated to a maximum temperature of 600 and 700 ºC, respectively, which is higher than the relative abundance of As(III) in the native sediment. These fire-induced As transformations can potentially enhance As mobilization to surface water and groundwater, posing risks to environmental and human health.

California↗

USGS2016

Potential utility of environmental DNA for early detection of Eurasian watermilfoil ( Myriophyllum spicatum )

Considering the harmful and irreversible consequences of many biological invasions, early detection of an invasive species is an important step toward protecting ecosystems (Sepulveda et al. 2012). Early detection increases the probability that suppression or eradication efforts will be successful because invasive populations are small and localized (Vander Zanden et al. 2010). However, most invasive species are not detected early because current tools have low detection probabilities when target species are rare and the sampling effort required to achieve acceptable detection capabilities with current tools is seldom tractable (Jerde et al. 2011). As a result, many invasive species go undetected until they are abundant and suppression efforts become costly. Novel DNA-based surveillance tools have recently revolutionized early detection abilities using environmental DNA (eDNA) present in the water (Darling and Mahon 2011, Bohmann et al. 2014). In brief, eDNA monitoring enables the identification of organisms from DNA present and collected in water samples. Aquatic and semiaquatic organisms release DNA contained in sloughed, damaged, or partially decomposed tissue and waste products into the water and molecular techniques allow this eDNA in the water column to be identified from simple and easy-tocollect water samples (Darling and Mahon 2011). Despite limited understanding of the production, persistence, and spread of DNA in water (Barnes et al. 2014), eDNA monitoring has been applied not only to invasive species (Jerde et al. 2011), but also to species that are rare, endangered, or highly elusive (Spear et al. 2014). However, most eDNA research and monitoring has focused on detection of invertebrates and vertebrates and less attentionhas been given to developing eDNA techniques for detecting aquatic invasive plants. Eurasian watermilfoil (EWM; Myriophyllum spicatum L.) is an invasive species for which improved early detection would be particularly helpful. Advanced EWM invasions have negative impacts on native biodiversity, recreational boating, fishing, and other types of aquatic tourism (e.g., Eiswerth et al. 2000). On a broader scale, EWM can also be harmful to man-made aquatic infrastructure, such as hydroelectric dams. If an EWM invasion can be detected in an early stage where eradication is still a possibility, many of these negative consequences can be limited or prevented altogether (e.g., Madsen et al. 2002). The purpose of this research was to develop and validate a traditional polymerase chain reaction (PCR) assay for the detection of pure and hybridized EWM DNA using both laboratory and field experiments. We performed a pilot experiment in outdoor tanks to determine the basic functionality and sensitivity of the assay. Following this initial test, we collected field samples from Michigan and Montana lakes with and without known EWM populations. Taken together, our findings suggest that eDNA techniques have potential to be a useful strategy for the early detection of EWM.

Journal of Aquatic Plant Management↗

USGS2026

The impacts of cover crop biomass on satellite-based detectability of cover crops in Maryland

Cover crop adoption in the U.S. has increased over the past decades, increasing the need to quantify their performance and environmental benefits. While remote sensing (RS)-based approaches for detecting cover crop presence have been developed, there has been limited research on how cover crops with varied biomass and management practices influence detectability. Using unique field-level cover crop presence and biomass datasets in Maryland, U.S., we investigated how RS-based detectability changes for cover crops with varied aboveground biomass, planting, and termination dates. Specifically, we proposed a time-integrated satellite-based greenness feature from Harmonized Landsat-8 and Sentinel-2 (HLS) time series from 2017 to 2021 to estimate biomass of cover crops and evaluated their detectability using a phenology-based cover crop detection framework. The impacts of cover crop planting and termination dates on cover crop biomass were also analyzed. Our results demonstrated that Normalized Difference Vegetation Index (NDVI) estimated biomass with higher accuracy compared to other vegetation indices, and the time-integrated model estimated biomass with higher accuracy than the single-date “snapshot” linear model (R2 from 0.53 to 0.66 and RMSE from 922 kg/ha to 747 kg/ha). While the snapshot models were species sensitive, the time-integrated models showed strong robustness across different species. Detectability increased with cover crop biomass, as detected cover crops averaged 963.3 ±719.5 kg/ha compared to 297.2 ± 209.0 kg/ha for non-detected cover crops. Detection accuracy reached 96.1% for fields exceeding 500 kg/ha, compared with an overall accuracy of 62.7%. Earlier planting and later termination increased biomass and detectability, with biomass rising by 4.14 kg/ha/day (p < 0.01). This study demonstrates how management practices affect cover crop biomass and detectability via satellite time series and provides insights that can inform management of cover crops and monitoring of their effects on agroecosystems.

Maryland↗

USGS2015

Synergistic and singular effects of river discharge and lunar illumination on dam passage of upstream migrant yellow-phase American eels

Monitoring of dam passage can be useful for management and conservation assessments of American eel, particularly if passage counts can be examined over multiple years. During a 7-year study (2007–2013) of upstream migration of American eels within the lower Shenandoah River (Potomac River drainage), we counted and measured American eels at the Millville Dam eel pass, where annual study periods were determined by the timing of the eel pass installation during spring or summer and removal during fall. Daily American eel counts were analysed with negative binomial regression models, with and without a year (YR) effect, and with the following time-varying environmental covariates: river discharge of the Shenandoah River at Millville (RDM) and of the Potomac River at Point of Rocks, lunar illumination (LI), water temperature, and cloud cover. A total of 17 161 yellow-phase American eels used the pass during the seven annual periods, and length measurements were obtained from 9213 individuals (mean = 294 mm TL, s.e. = 0.49, range 183–594 mm). Data on passage counts of American eels supported an additive-effects model (YR + LI + RDM) where parameter estimates were positive for river discharge (β = 7.3, s.e. = 0.01) and negative for LI (β = −1.9, s.e. = 0.34). Interestingly, RDM and LI acted synergistically and singularly as correlates of upstream migration of American eels, but the highest daily counts and multiple-day passage events were associated with increased RDM. Annual installation of the eel pass during late spring or summer prevented an early spring assessment, a period with higher RDM relative to those values obtained during sampling periods. Because increases in river discharge are climatically controlled events, upstream migration events of American eels within the Potomac River drainage are likely linked to the influence of climate variability on flow regime.

Potomac River drainage, Shenandoah River↗

USGS2008

Limited occurrence of denitrification in four shallow aquifers in agricultural areas of the United States

The ability of natural attenuation to mitigate agricultural nitrate contamination in recharging aquifers was investigated in four important agricultural settings in the United States. The study used laboratory analyses, field measurements, and flow and transport modeling for monitoring well transects (0.5 to 2.5 km in length) in the San Joaquin watershed, California, the Elkhorn watershed, Nebraska, the Yakima watershed, Washington, and the Chester watershed, Maryland. Ground water analyses included major ion chemistry, dissolved gases, nitrogen and oxygen stable isotopes, and estimates of recharge date. Sediment analyses included potential electron donors and stable nitrogen and carbon isotopes. Within each site and among aquifer-based medians, dissolved oxygen decreases with ground water age, and excess N 2 from denitrification increases with age. Stable isotopes and excess N 2 imply minimal denitrifying activity at the Maryland and Washington sites, partial denitrification at the California site, and total denitrification across portions of the Nebraska site. At all sites, recharging electron donor concentrations are not sufficient to account for the losses of dissolved oxygen and nitrate, implying that relict, solid phase electron donors drive redox reactions. Zero-order rates of denitrification range from 0 to 0.14 μmol N L −1 d −1 , comparable to observations of other studies using the same methods. Many values reported in the literature are, however, orders of magnitude higher, which is attributed to a combination of method limitations and bias for selection of sites with rapid denitrification. In the shallow aquifers below these agricultural fields, denitrification is limited in extent and will require residence times of decades or longer to mitigate modern nitrate contamination.

Journal of Environmental Quality↗

USGS2016

Environmental factors influence lesser scaup migration chronology and population monitoring

Identifying environmental metrics specific to lesser scaup ( Aythya affinis ; scaup) spring migration chronology may help inform development of conservation, management and population monitoring. Our objective was to determine how environmental conditions influence spring migration of lesser scaup to assess the effectiveness of the Waterfowl Breeding Population and Habitat Survey in accurately estimating scaup populations. We first compared peak timing of mallard ( Anas platyrhynchos ) and scaup migration from weekly ground surveys in North Dakota, USA because the Waterfowl Breeding Population and Habitat Survey is designed to capture annual mallard migration. As predicted, we detected that peak timing of scaup and mallard migrations differed in 25 of 36 years investigated (1980–2010). We marked scaup with satellite transmitters ( n = 78; 7,403 locations) at Long Point, Lake Erie, Ontario, Canada; Pool 19 of the Mississippi River, Iowa and Illinois, USA; and Presque Isle Bay, Lake Erie, Pennsylvania, USA. We tested the assumption that our marked scaup were representative of the continental population using the traditional survey area by comparing timing of migration of marked birds and scaup counted in the North Dakota Game and Fish Department survey. We detected a strong positive correlation between marked scaup and the survey data, which indicated that marked scaup were representative of the population. We subsequently used our validated sample of marked scaup to investigate the effects of annual variation in temperature, precipitation, and ice cover on spring migration chronology in the traditional and eastern survey areas of the Waterfowl Breeding Population and Habitat Survey, 2005–2010. We evaluated competing environmental models to explain variation in timing and rate of scaup migration at large-scale and local levels. Spring migration of scaup occurred earlier and faster during springs with warmer temperatures and greater precipitation, variables known to influence energy budgets and wetland availability. Our results suggest that surveys designed to index abundance of breeding mallards is imprecise for estimating scaup abundance, and inaccurate at estimating breeding population size by survey stratum.

Journal of Wildlife Management↗

USGS2018

Imidacloprid sorption and transport in cropland, grass buffer and riparian buffer soils

An understanding of neonicotinoid sorption and transport in soil is critical for determining and mitigating environmental risk associated with the most widely used class of insecticides. The objective of this study was to evaluate mobility and transport of the neonicotinoid imidacloprid (ICD) in soils collected from cropland, grass vegetative buffer strip (VBS), and riparian VBS soils. Soils were collected at six randomly chosen sites within grids that encompassed all three land uses. Single-point equilibrium batch sorption experiments were conducted using radio-labeled ( 14 C) ICD to determine solid–solution partition coefficients ( K d ). Column experiments were conducted using soils collected from the three vegetation treatments at one site by packing soil into glass columns. Water flow was characterized by applying Br − as a nonreactive tracer. A single pulse of 14 C-ICD was then applied, and ICD leaching was monitored for up to 45 d. Bromide and ICD breakthrough curves for each column were simulated using CXTFIT and HYDRUS-1D models. Sorption results indicated that ICD sorbs more strongly to riparian VBS ( K d = 22.6 L kg −1 ) than crop ( K d = 11.3 L kg −1 ) soils. Soil organic C was the strongest predictor of ICD sorption ( p < 0.0001). The column transport study found mean peak concentrations of ICD at 5.83, 10.84, and 23.8 pore volumes for crop, grass VBS, and riparian VBS soils, respectively. HYDRUS-1D results indicated that the two-site, one-rate linear reversible model best described results of the breakthrough curves, indicating the complexity of ICD sorption and demonstrating its mobility in soil. Greater sorption and longer retention by the grass and riparian VBS soils than the cropland soil suggests that VBS may be a viable means to mitigate ICD loss from agroecosystems, thereby preventing ICD transport into surface water, groundwater, or drinking water resources.

Vadose Zone Journal↗

USGS2017

Comparison of American Fisheries Society (AFS) standard fish sampling techniques and environmental DNA for characterizing fish communities in a large reservoir

Recently, methods involving examination of environmental DNA (eDNA) have shown promise for characterizing fish species presence and distribution in waterbodies. We evaluated the use of eDNA for standard fish monitoring surveys in a large reservoir. Specifically, we compared the presence, relative abundance, biomass, and relative percent composition of Largemouth Bass Micropterus salmoides and Gizzard Shad Dorosoma cepedianum measured through eDNA methods and established American Fisheries Society standard sampling methods for Theodore Roosevelt Lake, Arizona. Catches at electrofishing and gillnetting sites were compared with eDNA water samples at sites, within spatial strata, and over the entire reservoir. Gizzard Shad were detected at a higher percentage of sites with eDNA methods than with boat electrofishing in both spring and fall. In contrast, spring and fall gillnetting detected Gizzard Shad at more sites than eDNA. Boat electrofishing and gillnetting detected Largemouth Bass at more sites than eDNA; the exception was fall gillnetting, for which the number of sites of Largemouth Bass detection was equal to that for eDNA. We observed no relationship between relative abundance and biomass of Largemouth Bass and Gizzard Shad measured by established methods and eDNA copies at individual sites or lake sections. Reservoirwide catch composition for Largemouth Bass and Gizzard Shad (numbers and total weight [g] of fish) as determined through a combination of gear types (boat electrofishing plus gillnetting) was similar to the proportion of total eDNA copies from each species in spring and fall field sampling. However, no similarity existed between proportions of fish caught via spring and fall boat electrofishing and the proportion of total eDNA copies from each species. Our study suggests that eDNA field sampling protocols, filtration, DNA extraction, primer design, and DNA sequencing methods need further refinement and testing before incorporation into standard fish sampling surveys.

Arizona↗