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At least 1,261 records · Page 70Linked to original sources
USGS2001

Processes of nickel and cobalt uptake by a manganese oxide forming sediment in Pinal Creek, Globe mining district, Arizona

A series of column experiments was conducted using manganese oxide coated sediments collected from the hyporheic zone in Pinal Creek (AZ), a metal-contaminated stream, to study the uptake and retention of Mn, Ni, and Co. Experimental variables included the absence (abiotic) and presence (biotic) of active Mn-oxidizing bacteria, the absence and presence of dissolved Mn, and sediment manganese oxide content. Uptake of Mn under biotic conditions was between 8 and 39% higher than under abiotic conditions. Continuous uptake of Mn due to biotic oxidation was evident from extraction of column sediments. Manganese uptake is hypothesized to initially occur as adsorption, which led to subsequent surface and/or microbial oxidation. Complete breakthrough of Ni within 100 pore volumes indicated no process of continuous uptake and was modeled as an equilibrium adsorption process. Nickel uptake in the presence of dissolved Mn was 67-100% reversible. Sediment extractions suggest that Ni uptake occurred through weak and strong adsorption. Continuous uptake of cobalt increased with sediment manganese oxide content, and Co uptake was up to 75% greater under biotic than abiotic conditions. Cobalt uptake was controlled by both existing and newly formed manganese oxides. Only a small amount of Co uptake was reversible (10-25%). XANES spectral analysis indicated that most Co(II) was oxidized to Co(III) and probably incorporated structurally into manganese oxides. Although manganese oxides were the primary phase controlling uptake and retention of Mn, Ni, and Co, the mechanisms varied among the metals.

Arizona↗
USGS2000

Modeling annual mallard production in the prairie-parkland region

Biologists have proposed several environmental factors that might influence production of mallards ( Anas platyrhynchos ) nesting in the prairie-parkland region of the United States and Canada. These factors include precipitation, cold spring temperatures, wetland abundance, and upland breeding habitat. I used long-term historical data sets of climate, wetland numbers, agricultural land use, and size of breeding mallard populations in multiple regression analyses to model annual indices of mallard production. Models were constructed at 2 scales: a continental scale that encompassed most of the mid-continental breeding range of mallards and a stratum-level scale that included 23 portions of that same breeding range. The production index at the continental scale was the estimated age ratio of mid-continental mallards in early fall; at the stratum scale my production index was the estimated number of broods of all duck species within an aerial survey stratum. Size of breeding mallard populations in May, and pond numbers in May and July, best modeled production at the continental scale. Variables that best modeled production at the stratum scale differed by region. Crop variables tended to appear more in models for western Canadian strata; pond variables predominated in models for United States strata; and spring temperature and pond variables dominated models for eastern Canadian strata. An index of cold spring temperatures appeared in 4 of 6 models for aspen parkland strata, and in only 1 of 11 models for strata dominated by prairie. Stratum-level models suggest that regional factors influencing mallard production are not evident at a larger scale. Testing these potential factors in a manipulative fashion would improve our understanding of mallard population dynamics, improving our ability to manage the mid-continental mallard population.

Alberta, Manitoba, Montana, North Dakota, Saskatch↗
USGS2014

Polychlorinated biphenyl congener distributions in burbot: evidence for a latitude effect

We compared the distributions of the congeners of polychlorinated biphenyls (PCBs) detected in whole-body samples of burbot ( Lota lota ) from Great Slave Lake and Lake Erie. Total PCB concentrations in Great Slave Lake burbot were about 1/60 of the concentrations in Lake Erie burbot. Burbot from Great Slave Lake contained a higher proportion of lower-chlorinated (2-6 chlorines) congeners than did burbot from Lake Erie; the reverse occurred for more highly chlorinated (7-9 chlorines) congeners. Hexachloro congeners, followed by pentachloro congeners, dominated the proportions of total PCB in burbot from both lakes. There were no differences between sexes in whole-body samples or between gonad and somatic tissues in the proportions of the 39 congeners and three sets of co-eluters detected in burbot from Great Slave Lake. In contrast, there were distinct sex differences in congener distributions for older burbot from Lake Erie. Our results generally supported a prediction of higher proportions of lower-chlorinated PCB homologs in organisms in remote polar areas. However, the latitudinal effect on PCB congener distribution may be more complex than that portrayed in previous studies.

Lake Erie;Great Slave Lake↗
USGS1983

The environmental history and present condition of Saudi Arabia's northern sand seas

Saudi Arabia's northern sand seas are composed dominantly of stable dune systems, even though the modern climate is arid. The stable dunes are large and support a sparse semidesert vegetation. Active dunes are small and commonly confined to the crests of stable dunes; they comprise less than 5 percent of the dunes in the sand seas. Both the stability of the major dune systems and the small percentage of active dunes in the modern environment indicate a significant decrease in the average velocity and frequency of sand-moving winds since the time of stable-dune deposition. Comparison of modern wind directions with dune trends indicates that southwesterly winds responsible for dune formation in the southern and western An Nafud sand sea and in Nafud Urayq are no longer prevailing winds. Lake deposits are locally interbedded with deposits of eolian sand and in the lee of stable dunes. Radiocarbon dating of calcareous lake deposits defines at least two episodes of moisture-effective climate and minimal eolianactivity: between about 32,000 and 24,000 B.P., just before the onset of the last worldwide glacial stade of the Pleistocene, and during the Holocene between about 8,500 and 5,000 B.P. One lake deposit is more than 38,000 years old and may have been deposited during an earlier pluvial episode about 85,000 to 70,000 B.P. Pollen extracted from these lake deposits indicates that vegetation during late Pleistocene and Holocene pluvial episodes was similar to the present semidesert vegetation; however, the density of shrubs and grasses on the dunes was greater. The main dune systems overlie the 32,000 to 24,000-yearold lake deposits, whereas the Holocene lakebeds are found in modern interdunal environments, usually at the base of stable dunes. The main dune systems probably formed between 24,000 and 8,500 B.P., during the last episode of worldwide cold temperatures. Increased windiness at this time is also recorded in the world's oceans and in both polar ice caps. Eolian sand below the older lake deposits was deposited before 32,000 B.P., and circumstantial evidence indicates that the sand seas may have begun to form as early as late Miocene. In the An Nafud, remnants of a middle Tertiary(?) surface suggest that the original sediment source for the An Nafud may have been the weathered sandstones that underlie this surface. After lacustrine deposition ceased in middle Holocene time, eolian activity increased slightly. Deflation on windward dune slopes has produced deflation scoops, which look like inverted deltas. The modern active dunes are composed of sand deflated from the stable dunes.

Open-File Report↗
USGS2019

Investigation of recent decadal-scale cyclical fluctuations in salinity in the lower Colorado river

Beginning in the late 1970s, 10- to 15-year cyclical oscillations in salinity were observed at lower Colorado River monitoring sites, moving upstream from the international border with Mexico, above Imperial Dam, below Hoover Dam, and at Lees Ferry. The cause of these cyclical trends in salinity was unknown. These salinity cycles complicate the U.S. Bureau of Reclamation's (Reclamation) responsibility for managing salinity in the river for delivery of water to Mexico to meet treaty obligations. This study develops a conceptual model of the salinity cycles from time-series water quality, streamflow, and precipitation data in both the lower and upper Colorado River Basins in order to provide Reclamation the ability to understand, anticipate, and manage future salinity cycles in the lower river. Compared with the Lees Ferry record, both maximum and minimum salinity levels increase downstream by about 25% at Hoover Dam, by about 49% at Imperial Dam, and by about 69% at the northern international boundary with Mexico. In the upper basin, cyclical salinity trends are evident at the outflow of three major tributaries, where salinity is also noted to be inversely related to streamflow. Time series trends in precipitation within the catchments of the three upper basin tributaries indicate cyclical periods with above normal precipitation and periods with below normal precipitation. Periods of greater than normal precipitation in the contributing areas correspond with declines in salinity at the catchment monitoring sites and periods of less than normal precipitation correspond with rising salinity at the sites. Based on the conceptual model developed in this investigation, a multiple linear regression model was developed using a stepwise variable selection procedure to simulate salinity in Lake Powell inflow. Important variables in the explanation of salinity entering Lake Powell include flow from the three upper basin tributaries, seasonality, and mean precipitation in the upper basin, among others. The root mean square error of prediction for the MLR model was 31.48 mg/L (5.7%).

Arizona, Colorado, Nevada, New Mexico, Utah, Wyomi↗
USGS2021

Pervasive changes in stream intermittency across the United States

Non-perennial streams are widespread, critical to ecosystems and society, and the subject of ongoing policy debate. Prior large-scale research on stream intermittency has been based on long-term averages, generally using annually aggregated data to characterize a highly variable process. As a result, it is not well understood if, how, or why the hydrology of non-perennial streams is changing. Here, we investigate trends and drivers of three intermittency signatures that describe the duration, timing, and dry-down period of stream intermittency across the continental United States (CONUS). Half of gages exhibited a significant trend through time in at least one of the three intermittency signatures, and changes in no-flow duration were most pervasive (41% of gages). Changes in intermittency were substantial for many streams, and 7% of gages exhibited changes in annual no-flow duration exceeding 100 days during the study period. Distinct regional patterns of change were evident, with widespread drying in southern CONUS and wetting in northern CONUS. These patterns are correlated with changes in aridity, though drivers of spatiotemporal variability were diverse across the three intermittency signatures. While the no-flow timing and duration were strongly related to climate, dry-down period was most strongly related to watershed land use and physiography. Our results indicate that non-perennial conditions are increasing in prevalence over much of CONUS and binary classifications of 'perennial' and 'non-perennial' are not an accurate reflection of this change. Water management and policy should reflect the changing nature and diverse drivers of changing intermittency both today and in the future.

Environmental Research Letters↗
USGS2006

Comparison of selenium bioaccumulation in the clams Corbicula fluminea and Potamocorbula amurensis: A bioenergetic modeling approach

Selenium uptake from food (assimilation efficiency) and dissolved phase (influx rate) as well as loss kinetics (efflux rate) were compared between two bivalves, Corbicula fluminea and Potamocorbula amurensis. The effects of salinity and temperature on these kinetic parameters for both clam species also were evaluated. The Asiatic clam, C. fluminea, more efficiently assimilated Se associated with algae (66-87%) than Se associated with oxic sediments (20-37%). However, no consistent difference was found between Se assimilation efficiencies from both food types (19-60%) for P. amurensis. The temperature and salinity had a minor influence on the Se assimilation from ingested food. However, the effects of temperature and salinity were more evident in the uptake from dissolved sources. The influx rate of Se(IV) increased by threefold with the increase of temperature from 5 to 21??C for C. fluminea. The increase of salinity from 4 to 20 psu decreased the uptake rate constant (ku) of Se in P. amurensis from 0.011 to 0.005 L/g/h, whereas salinity change (0-8 psu) had a negligible effect on the Se influx rate of C. fluminea. The Se influx rate of P. amurensis decreased by half with the 3.5-fold increase in tissue dry weight. The rate constant of loss was greater for P. amurensis (0.029/d at 8 psu) than for C. fluminea (0.014/d at 0 psu and 0.01/d at 8 psu). A bioenergetic model suggests that dietary uptake is the dominant pathway for Se bioaccumulation in the two clams in San Francisco Bay and that interspecies differences in Se bioaccumulation can be explained by differences in food ingestion rates. ?? 2006 SETAC.

Environmental Toxicology and Chemistry↗
USGS2022

Sensitivity of headwater streamflow to thawing permafrost and vegetation change in a warming Arctic

Climate change has the potential to impact headwater streams in the Arctic by thawing permafrost and subsequently altering hydrologic regimes and vegetation distribution, physiognomy and productivity. Permafrost thaw and increased subsurface flow have been inferred from the chemistry of large rivers, but there is limited empirical evidence of the impacts to headwater streams. Here we demonstrate how changing vegetation cover and soil thaw may alter headwater catchment hydrology using water budgets, stream discharge trends, and chemistry across a gradient of ground temperature in northwestern Alaska. Colder, tundra-dominated catchments shed precipitation through stream discharge, whereas in warmer catchments with greater forest extent, evapotranspiration and infiltration are substantial fluxes. Forest soils thaw earlier, remain thawed longer, and display seasonal water content declines, consistent with greater evapotranspiration and infiltration. Streambed infiltration and water chemistry indicate that even minor warming can lead to increased infiltration and subsurface flow. Additional warming, permafrost loss, and vegetation shifts in the Arctic will deliver water back to the atmosphere and to subsurface aquifers in many regions, with the potential to substantially reduce discharge in headwater streams, if not compensated by increasing precipitation. Decreasing discharge in headwater streamflow will have important implications for aquatic and riparian ecosystems.

Alaska↗
USGS2011

Functional ecology of saltglands in shorebirds: Flexible responses to variable environmental conditions

1. Birds of marine environments have specialized glands to excrete salt, the saltglands. Located on the skull between the eyes, the size of these organs is expected to reflect their demand, which will vary with water turnover rates as a function of environmental (heat load, salinity of prey and drinking water) and organismal (energy demand, physiological state) factors. On the basis of inter- and intraspecific comparisons of saltgland mass (msg) in 29 species of shorebird (suborder Charadrii) from saline, fresh and mixed water habitats, we assessed the relative roles of organism and environment in determining measured msg species. 2. The allometric exponent, scaling dry msg to shorebird total body mass (mb), was significantly higher for coastal marine species (0Æ88, N = 19) than for nonmarine species (0Æ43, N = 14). Within the marine species, those ingesting bivalves intact had significantly higher msg than species eating soft-bodied invertebrates, indicating that seawater contained within the shells added to the salt load. 3. In red knots (Calidris canutus), dry msg varied with monthly averaged ambient temperature in a U-shaped way, with the lowest mass at 12Æ5 C. This probably reflects increased energy demand for thermoregulation at low temperatures and elevated respiratory water loss at high temperatures. In fuelling bar-tailed godwits (Limosa lapponica), dry msg was positively correlated with intestine mass, an indicator of relative food intake rates. These findings suggest once more that saltgland masses vary within species (and presumably individuals) in relation to salt load, that is a function of energy turnover (thermoregulation and fuelling) and evaporative water needs. 4. Our results support the notion that msg is strongly influenced by habitat salinity, and also by factors influencing salt load and demand for osmotically free water including ambient temperature, prey type and energy intake rates. Saltglands are evidently highly flexible organs. The small size of saltglands when demands are low suggests that any time costs of adjustment are lower than the costs of maintaining a larger size in this small but essential piece of metabolic machinery.

Functional Ecology↗
USGS2012

Microgravity methods for characterization of groundwater-storage changes and aquifer properties in the karstic Madison aquifer in the Black Hills of South Dakota, 2009-12

A study of groundwater storage in the karstic Madison aquifer in the Black Hills of South Dakota using microgravity methods was conducted by the U.S. Geological Survey in cooperation with West Dakota Water Development District, South Dakota Department of Environment and Natural Resources, and Lawrence County. Microgravity measurements from 2009 to 2012 were used to investigate groundwater-storage changes and effective porosity in unconfined areas of the Madison aquifer. Time-lapse microgravity surveys that use portable high-sensitivity absolute and relative gravimeters indicated temporal-gravity changes as a result of changing groundwater mass. These extremely precise measurements of gravity required characterization and removal of internal instrumental and external environmental effects on gravity from the raw data. The corrected data allowed groundwater-storage volume to be quantified with an accuracy of about plus or minus 0.5 foot of water per unit area of aquifer. Quantification of groundwater-storage change, coupled with water-level data from observation wells located near the focus areas, also was used to calculate the effective porosity at specific altitudes directly beneath gravity stations. Gravity stations were established on bedrock outcrops in three separate focus areas for this study. The first area, the Spring Canyon focus area, is located to the south of Rapid City with one gravity station on the rim of Spring Canyon near the area where Spring Creek sinks into the Madison aquifer. The second area, the Doty focus area, is located on outcrops of the Madison Limestone and Minnelusa Formation to the northwest of Rapid City, and consists of nine gravity stations. The third area, the Limestone Plateau focus area, consists of a single gravity station in the northwestern Black Hills located on an outcrop of the Madison Limestone. An absolute-gravity station, used to tie relative-gravity survey data together, was established on a relatively impermeable bedrock outcrop to minimize groundwater-storage change at the reference location. Data from the three focus areas allow for interpretation of groundwater-storage characteristics using microgravity measurements. Gravity measurements, together with water-level data from an observation well located 2 miles from the Spring Canyon focus area and measured streamflow in Spring Creek, provided evidence that rapid groundwater-storage change, responding to changes in sinking streamflow over the recharge area of the aquifer, occurred in the Madison aquifer directly beneath the gravity station at Spring Canyon. This phenomenon likely was a result of groundwater movement through caverns, conduits, and fractures, which are common in karst aquifers. Spatially and temporally separated microgravity data for the Doty focus area indicated horizontal and vertical heterogeneity of effective porosity for the Madison aquifer. One such example of this was indicated by water-level measurements at an observation well and gravity measurements at four gravity stations in the southeastern part of the Doty area, which were used to estimate effective porosity values ranging from greater than 0 to 0.18. A decrease in groundwater storage determined by microgravity measurements during the spring recharge period for five upgradient stations in the Doty focus area indicated the possibility of rapid release and downgradient cascading of perched groundwater. Evidence for similar phenomena was documented for Wind Cave and Brooks Cave in the Black Hills. Absolute-gravity measurements at the Limestone Plateau focus area confirmed the relation between water levels in an observation well and changes in groundwater storage. Comparison of these gravity measurements with water levels in a nearby observation well resulted in an effective porosity estimate of 0.02 for the Madison aquifer beneath the gravity station.

South Dakota↗
USGS2004

A Complex Systems Model Approach to Quantified Mineral Resource Appraisal

For federal and state land management agencies, mineral resource appraisal has evolved from value-based to outcome-based procedures wherein the consequences of resource development are compared with those of other management options. Complex systems modeling is proposed as a general framework in which to build models that can evaluate outcomes. Three frequently used methods of mineral resource appraisal (subjective probabilistic estimates, weights of evidence modeling, and fuzzy logic modeling) are discussed to obtain insight into methods of incorporating complexity into mineral resource appraisal models. Fuzzy logic and weights of evidence are most easily utilized in complex systems models. A fundamental product of new appraisals is the production of reusable, accessible databases and methodologies so that appraisals can easily be repeated with new or refined data. The data are representations of complex systems and must be so regarded if all of their information content is to be utilized. The proposed generalized model framework is applicable to mineral assessment and other geoscience problems. We begin with a (fuzzy) cognitive map using (+1,0,-1) values for the links and evaluate the map for various scenarios to obtain a ranking of the importance of various links. Fieldwork and modeling studies identify important links and help identify unanticipated links. Next, the links are given membership functions in accordance with the data. Finally, processes are associated with the links; ideally, the controlling physical and chemical events and equations are found for each link. After calibration and testing, this complex systems model is used for predictions under various scenarios.

Environmental Management↗
USGS2000

Distribution, movement, and fate of nitrate in the surficial aquifer beneath citrus groves, Indian River, Martin, and St. Lucie Counties, Florida

The surficial aquifer system beneath citrus groves in Indian River, Martin, and St. Lucie Counties, Florida, was studied to determine the effects of citrus agriculture on ground-water quality. The surficial aquifer is the primary drinking-water source for Martin and St. Lucie Counties and furnishes about 33 percent of the drinking-water for Indian River County. Water-quality samples and water-level data were collected from December 1996 through October 1998. Nitrate concentrations in ground water exceeded 10 milligrams per liter (mg/L), the U.S. Environmental Protection Agency's maximum contaminant level for nitrate reported as nitrogen, in 5 percent of the samples from citrus groves. These exceedances occurred in samples from wells with depths of 10 feet or less at citrus groves, and mostly in samples collected during or immediately following fertilizer applications. Samples from wells with depths of 20-25 feet contained little or no nitrate. The decreased nitrate concentrations in ground water with depth was not consistent with chloride and dissolved-solids concentrations, two other common indicators of agricultural activity. Chloride and dissolved-solids concentrations remained elevated in ground-water samples from all depths at citrus groves; median chloride and dissolved-solids concentrations in samples from citrus sites were 125 and 779 mg/L, respectively. In comparison, samples from the reference site had maximum chloride and dissolved-solids concentrations of 61 and 366 mg/L, respectively. Based on the age of ground water at 20-25 foot depths (3-50 years, measured with tritium and helium-3 concentration ratios), nitrate concentrations also should have remained elevated with depth because fertilizers have been used for at least 20-30 years at these citrus groves. Nitrate concentrations decreased with depth as a result of denitrification. This could have occurred because favorable conditions for denitrification existed in the aquifer, including high concentrations of dissolved organic carbon and iron (median concentrations of 25.5 and 1.75 mg/L, respectively at citrus sites) and low concentrations of dissolved oxygen (median concentration of 0.9 mg/L at citrus sites), which indicates that reducing conditions were present. Evidence that denitrification occurred included the enrichment of ground water with depth in the heavier isotope of nitrogen, nitrogen-15 ( 15 N). Ground water from wells screened 10-15 feet below land surface had a median d 15 N value of 24.6 per mil, whereas ground water from wells screened 5-10 feet below land surface had a median d 15 N value of 9.4 per mil. Fertilizer samples had a median d 15 N value of 3.0 per mil. Increased d 15 N values coincident with decreased nitrate concentrations with depth indicates that fractionation occurred during denitrification reactions. Finally, excess nitrogen gas, a byproduct of denitrification reactions, was detected at concentrations ranging from 0-8 mg/L in samples from wells screened 10-25 feet below land surface.

Florida↗
USGS2004

EXAFS study of mercury(II) sorption to Fe- and Al-(hydr)oxides - II. Effects of chloride and sulfate

Common complexing ligands such as chloride and sulfate can significantly impact the sorption of Hg(II) to particle surfaces in aqueous environmental systems. To examine the effects of these ligands on Hg(II) sorption to mineral sorbents, macroscopic Hg(II) uptake measurements were conducted at pH 6 and [Hg]i=0.5 mM on goethite (??-FeOOH), ??-alumina (??-Al2O3), and bayerite (??-Al(OH)3) in the presence of chloride or sulfate, and the sorption products were characterized by extended X-ray absorption fine structure (EXAFS) spectroscopy. The presence of chloride resulted in reduced uptake of Hg(II) on all three substrates over the Cl- concentration ([Cl-]) range 10-5 to 10-2 M, lowering Hg surface coverages on goethite, ??-alumina, and bayerite from 0.42 to 0.07 ??mol/m2, 0.06 to 0.006 ??mol/m2, and 0.55 to 0.39 ??mol/m2 ([Cl -]=10-5 to 10-3 M only), respectively. This reduction in Hg(II) uptake is primarily a result of the formation of stable, nonsorbing aqueous HgCl2 complexes in solution, limiting the amount of free Hg(II) available to sorb. At higher [Cl-] beam reduction of Hg(II) to Hg(I) was observed, resulting in the possible formation of aqueous Hg2Cl2 species and the precipitation of calomel, Hg 2Cl2(s). The presence of sulfate caused enhanced Hg(II) uptake over the sulfate concentration ([SO42-]) range 10-5 to 0.9 M, increasing Hg surface coverages on goethite, ??-alumina, and bayerite from 0.39 to 0.45 ??mol/m2, 0.11 to 0.38 ??mol/m2, and 0.36 to 3.33 ??mol/m2, respectively. This effect is likely due to the direct sorption or accumulation of sulfate ions at the substrate interface, effectively reducing the positive surface charge that electrostatically inhibits Hg(II) sorption. Spectroscopic evidence for ternary surface complexation was observed in isolated cases, specifically in the Hg-goethite-sulfate system at high [SO42-] and in the Hg-goethite-chloride system. ?? 2003 Elsevier Inc. All rights reserved.

Journal of Colloid and Interface Science↗
USGS2007

Geochemical and geophysical examination of submarine groundwater discharge and associated nutrient loading estimates into Lynch Cove, Hood Canal, WA

Geochemical tracer data (i.e., 222 Rn and four naturally occurring Ra isotopes), electromagnetic (EM) seepage meter results, and high-resolution, stationary electrical resistivity images were used to examine the bi-directional (i.e., submarine groundwater discharge and recharge) exchange of a coastal aquifer with seawater. Our study site for these experiments was Lynch Cove, the terminus of Hood Canal, WA, where fjord-like conditions dramatically limit water column circulation that can lead to recurring summer-time hypoxic events. In such a system a precise nutrient budget may be particularly sensitive to groundwater-derived nutrient loading. Shore-perpendicular time-series subsurface resistivity profiles show clear, decimeter-scale tidal modulation of the coastal aquifer in response to large, regional hydraulic gradients, hydrologically transmissive glacial terrain, and large (4-5 m) tidal amplitudes. A 5-day 222 Rn time-series shows a strong inverse covariance between 222 Rn activities (0.5−29 dpm L -1 ) and water level fluctuations, and provides compelling evidence for tidally modulated exchange of groundwater across the sediment/water interface. Mean Rn-derived submarine groundwater discharge (SGD) rates of 85 ± 84 cm d -1 agree closely in the timing and magnitude with EM seepage meter results that showed discharge during low tide and recharge during high tide events. To evaluate the importance of fresh versus saline SGD, Rn-derived SGD rates (as a proxy of total SGD) were compared to excess 226Ra-derived SGD rates (as a proxy for the saline contribution of SGD). The calculated SGD rates, which include a significant (>80%) component of recycled seawater, are used to estimate associated nutrient (NH 4+ , Si, PO 4 3- , NO 3 + NO 2 , TDN) loads to Lynch Cove. The dissolved inorganic nitrogen (DIN = NH 4 + NO 2 + NO 3 ) SGD loading estimate of 5.9 × 10 4 mol d -1 is 1−2 orders of magnitude larger than similar estimates derived from atmospheric deposition and surface water runoff, respectively.

Washington↗
USGS2018

Evidence of repeated long-distance movements by lake charr Salvelinus namaycush in Lake Huron

Movements and dispersal distances of acoustically-tagged adult lake charr Salvelinus namaycush were estimated based on detections at acoustic receivers in Lake Huron during 2010–2014. Most lake charr were detected only at receivers proximate to their release location or were not detected at all, but 3–9% of tagged lake charr were detected at receivers located over 100 km from their release location. Several fish made extensive repeated migrations within the lake, some at the scale of the entire main basin. Our observations show that some lake charr individuals repeat a similar pattern each year of moving long distances, and some fish were observed to show annual fidelity to presumed foraging sites in the spring at a spatial scale of approximately 200 km. Our telemetry-based estimates were minimum estimates of dispersal, as the placement of receivers within Lake Huron was not optimal for detection of lake charr and did not cover the majority of the lake. Further study of long-distance movement in lake charr is necessary to fully understand the implications of this behavior to lake charr ecology, population dynamics, and management in the Great Lakes.

Lake Huron↗
USGS1997

Water-quality assessment of the Rio Grande Valley, Colorado, New Mexico and Texas: Fish communities at selected sites, 1993-95

Fish communities at 10 sites in the Rio Grande Basin were sampled during low-flow periods between 1993 and 1995 as part of the U.S. Geological Survey National Water-Quality Assessment Program. The ecology of fish communities is one of several lines of evidence used to characterize water-quality conditions. This report describes the fish communities at selected sites in the Rio Grande Basin and relates the structure of these fish communities to the physical and chemical characteristics of the streams. Twenty-nine species of fish representing 10 families were identified in 25 samples collected during this study. Species richness ranged from 1 to 13. Cluster analysis of the 25 samples collected during this study delineated four groups of sites that were based on the similarity of the fish communities. The first two groups were individual sites with low species richness. The third group contained the most samples, and the fourth group consisted of samples from the Rio Grande at Isleta, New Mexico, and the Rio Grande at El Paso, Texas. The shift in community structure of samples from group 3 to group 4 reflects changes from predominantly coldwater fishes to warmwater fishes. Four metrics of biotic integrity (percentages of introduced individuals, omnivores, tolerant individuals, and anomalies) were used in this study to provide a broad overview of the community structure. The relative percentages of introduced species at the Rio Grande near Del Norte, Colorado; Saguache Creek near Saguache, Colorado; Rio Grande below Taos Junction Bridge, near Taos, New Mexico; and Rio Grande at Isleta are indicative of biological stress on the communities at these sites. The dominance of omnivores in samples from the Rio Grande below Taos Junction Bridge, near Taos; Rio Chama near Chamita, New Mexico; Rio Grande at Isleta; and Rio Grande at El Paso is an indication of environmental stress at these sites. In 1995, tolerant species accounted for the entire fish community at the Rio Grande at Isleta. In all samples the occurrence of anomalies was less than 2 percent of the individuals, with the exception of the sample from the Rio Grande at Isleta. On the basis of the relative percentages of introduced individuals, omnivores, tolerant individuals, and anomalies, the biotic integrity at the Rio Grande at Isleta appears to be the most impaired of all sites and shows indications of potential chemical and physical perturbations. Fish communities from three reaches at the Santa Fe River above Cochiti Lake, New Mexico, and the Rio Grande at Isleta were sampled in 1995 to assess small-scale spatial patterns in the structure of fish communities. The spatial pattern at these sites might be associated with natural variability of the fish communities or with the presence of habitat features such as pools. The total number of individuals and relative abundance in a sample varied at sites sampled yearly during this study. All sites, with the exception of the Rio Grande near Del Norte, had a decline in total number of individuals in a sample. The temporal decline in the total number of individuals at these site might be associated with the natural variability within the fish communities.

Colorado, New Mexico, Texas↗
USGS2022

Nitrogen enrichment during soil organic matter burning and molecular evidence of maillard reactions

Wildfires in forested watersheds dramatically alter stored and labile soil organic matter (SOM) pools and the export of dissolved organic matter (DOM). Ecosystem recovery after wildfires depends on soil microbial communities and revegetation and therefore is limited by the availability of nutrients, such as nitrogen-containing and labile, water-soluble compounds. However, SOM byproducts produced at different wildfire intensities are poorly understood, leading to difficulties in assessing wildfire severity and predicting ecosystem recovery. In this work, water-extractable organic matter (WEOM) from laboratory microcosms of soil burned at discrete temperatures was characterized by ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry to study the impacts of fire temperature on SOM and DOM composition. The molecular composition derived from different burn temperatures indicated that nitrogen-containing byproducts were enriched with heating and composed of a wide range of aromatic features and oxidation states. Mass difference-based analysis also suggested that products formed during heating could be modeled using transformations along the Maillard reaction pathway. The enrichment of N-containing SOM and DOM at different soil burning intensities has important implications for ecosystem recovery and downstream water quality.

Environmental Science and Technology↗
USGS2026

Linking distribution and return-on-investment models to optimize woody management for prairie grouse in Nebraska

Grasslands in Nebraska, USA, face threats from agricultural conversion, urban development, and woody encroachment, all of which negatively affect prairie grouse ( Tympanuchus spp.) populations. To optimize conservation planning, Nebraska wildlife agencies developed probabilistic area-based surveys for greater prairie-chicken ( T. cupido ) and sharp-tailed grouse ( T. phasianellus ) to sample landscapes across a range of environmental conditions. This design improves historical surveys and enables the development of distribution models that quantitatively define habitat associations and support scenario-based conservation planning. Using survey data collected during 2020–2022, we modeled prairie grouse occurrence and abundance as functions of land cover, topography, and climate using Bayesian logistic and zero-inflated negative binomial models with regularized horseshoe priors. We then conducted a maximum potential return-on-investment analysis of woody cover treatments, assuming sustained treatment success, relative to projected impacts of woody encroachment on prairie grouse populations by 2050. Among modeled associations were a positive association with grasslands having low woody cover and a negative association with grasslands having high woody cover. Across the 3-year period, median estimated annual populations were 142,380 for greater prairie-chicken (range of 95% CIs across years = 68,821–277,615) and 64,154 for sharp-tailed grouse (range of 95% CIs across years = 27,550–146,559). Under projected woody encroachment, mean predicted population declines were 10% for greater prairie-chicken (range of 95% CIs = 7–14%) and 6% for sharp-tailed grouse (range of 95% CIs = 5–7%). Areas with high prairie grouse density and low treatment costs in 2021, and high projected woody encroachment and population loss by 2050, offered the greatest return on investment for woody management. Return on investment was greatest in the northwestern Shortgrass Prairie ecoregion (northwestern Nebraska) for sharp-tailed grouse and the eastern Sandhills ecoregion (central Nebraska) for both species. These models underscore the value of evidence-based, quantitative approaches for prioritizing conservation actions on working lands. Scenario-based modeling could be extended to guide other treatments, such as optimizing restoration (e.g., Conservation Reserve Program) or incentivizing grassland persistence in areas with predicted climate resilience.

Nebraska↗