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At least 883 records · Page 49Linked to original sources
USGS2014

Remote sensing analysis of riparian vegetation response to desert marsh restoration in the Mexican Highlands

Desert marshes, or cienegas, are extremely biodiverse habitats imperiled by anthropogenic demands for water and changing climates. Given their widespread loss and increased recognition, remarkably little is known about restoration techniques. In this study, we examine the effects of gabions (wire baskets filled with rocks used as dams) on vegetation in the Cienega San Bernardino, in the Arizona, Sonora portion of the US-Mexico border, using a remote-sensing analysis coupled with field data. The Normalized Difference Vegetation Index (NDVI), used here as a proxy for plant biomass, is compared at gabion and control sites over a 27-year period during the driest months (May/June). Over this period, green-up occurred at most sites where there were gabions and at a few of the control sites where gabions had not been constructed. When we statistically controlled for differences among sites in source area, stream order, elevation, and interannual winter rainfall, as well as comparisons of before and after the initiation of gabion construction, vegetation increased around gabions yet did not change (or decreased) where there were no gabions. We found that NDVI does not vary with precipitation inputs prior to construction of gabions but demonstrates a strong response to precipitation after the gabions are built. Field data describing plant cover, species richness, and species composition document increases from 2000 to 2012 and corroborate reestablished biomass at gabions. Our findings validate that gabions can be used to restore riparian vegetation and potentially ameliorate drought conditions in a desert cienega.

Ecological Engineering↗
USGS2021

The local responses of aquatic ecosystems to adjacent grassland conservation: Can streams of dreams exist in a degraded riverscape?

Landscape homogenization and the removal of riparian areas have altered stream ecosystems worldwide. Numerous conservation programmes attempt to improve water quality and increase instream habitat heterogeneity to elicit desired biological responses. However, the effectiveness of many conservation efforts on isolated stream fragments remains unknown, especially in grassland regions. The effects of grassland conservation practices and the re-establishment of riparian corridors in the James River basin, South Dakota (USA) on stream water quality, habitat availability and aquatic macroinvertebrate and fish assemblages were studied in an agriculturally dominated prairie landscape. Grassland conservation efforts may have repaired riparian condition, reduced turbidity and created more diverse instream habitat complexes at conservation sites based on comparisons with paired reference reaches. Reference sites were relatively homogeneous, with prevalent siltation, bank erosion and disturbances to the riparian vegetation. Owing to significant riparian vegetation development, overhanging and aquatic vegetation, benthic detritus and woody materials were significantly more common at conservation reaches. Restoration efforts that assume ‘if you (re-)build it, they will come’ (i.e. the ‘field of dreams’ hypothesis) underestimate other important barriers to biodiversity restoration in dynamic, grassland riverscapes. Although aquatic organisms in grassland ecosystems are adapted to rapidly inhabit available habitats, the development of niche space at conservation reaches did not directly result in colonization by aquatic life. Grassland management actions did not address stream connectivity issues or overcome land use influences elsewhere in the riverscape that may govern the responses of aquatic macroinvertebrates and fish. Stream fragmentation and continuing, damaging land use patterns seemed to exceed the positive effects of restoring isolated stream reaches in these heavily degraded catchments. Catchment-scale management strategies that combine reach-level restoration actions with efforts to improve connectivity are likely to be more successful in degraded riverscapes.

South Dakota↗
USGS1983

Hydrology of the Price River basin, Utah, with emphasis on selected coal-field areas

Data obtained during a hydrologic study of the Price River basin, Utah, are used to describe seasonal variations of flow of springs, relation between ground water and surface water, hydraulic properties of the ground-water reservoir, ground-water recharge and discharge, flood characteristics of streams, mineralogic composition and depositional rates of sediments, nutrient and inorganic loading in streams and Scofield Reservoir, and water budgets for selected basins. Additional study and monitoring are needed to detect possible hydrologic changes caused by coal mining. Much of the ground-water discharge from the Star Point Sandstone in the Mesaverde Group in the Wasatch Plateau occurs along faults. In the Book Cliffs, where faulting is less extensive, most of the ground-water discharge is from the Flagstaff Limestone. The Flagstaff Limestone is greatly diffusive, has a small storage coefficient, and contains water which is perched. Springs issuing from the Star Point Sandstone in the Mud Creek drainage (Wasatch Plateau) had recession indexes greater than 365 days per log cycle. Springs issuing at higher altitudes from the Colton Formation and the Flagstaff Limestone in the Soldier Creek area (Book Cliffs) have great seasonal variability, with recession indexes ranging from 24 to 115 days per log cycle. Estimated transmissivities in the Soldier Creek area ranged from 0.003 foot squared per day in the lower part of the Castlegate Sandstone to 0.07 foot squared per day in the Price River Formation. Seepage from the Star Point Sandstone is the major contributor to base flow of the stream in Eccles Canyon (Wasatch Plateau). Gains of as much as 230 gallons per minute occurred near a fault zone which crosses Eccles Canyon at the junction with South Fork Canyon. The potentiometric surface of water in the Blackhawk Formation in the Wasatch Plateau (Mud Creek drainage) and the Book Cliffs (Soldier Creek area) generally is above the coal zones, and dewatering will be necessary in most places during mining. The total reported mine discharge during 1980 was about 2,800 acre-feet. During the 1980 water year, ground-water discharge from the Flagstaff Limestone contributed about 4,400 acre-feet, or 41 percent of the combined streamflow of Coal, Soldier, and Dugout Creeks. Discharge from the Blackhawk and other formations contributed about 2,200 acre-feet, or 21 percent of the streamflow. The recharge to a 4,020-acre outcrop of the Flagstaff Limestone in the Soldier Creek area was determined from measurements of the discharge of springs and seepage gains in streams. The estimated recharge was 2 inches per year, or 12 percent of the April 1 snowpack, or 9 percent of the precipitation during 1980. Benthic-diversity indexes at streams in the Book Cliffs and Wasatch Plateau are related to the size of the bed material. The Shannon-Weiner diversity index for five sites in the Mud Creek drainage ranged from 1.57 to 4.20 during four sampling periods in 1979-80. In the Soldier Creek drainage, the diversity index for four sampling sites ranged from 0.8 to 2.3 during three sampling periods in 1979-80. Sediment deposition in Scofield Reservoir during 1943-79 was estimated to be 3,000 acre-feet but most of the coal deposition in the reservoir occurred prior to about 1950. An anaerobic zone develops in the reservoir during the summer, but the water in the reservoir completely mixes during late summer or early fall.

Utah↗
USGS1986

Hydrology of the Price River basin, Utah, with emphasis on selected coal-field areas

Data obtained during a hydrologic study of the Price River basin, Utah, are used to describe seasonal variations off low of springs, relation between ground water and surface water, hydraulic properties of the ground-water reservoir, ground-water recharge and discharge, flood characteristics of streams, mineralogic composition and depositional rates of sediments, nutrient and inorganic loading in streams and Scofield Reservoir, and water budgets for selected basins. Additional study and monitoring are needed to detect possible hydrologic changes caused by coal mining. Much of the ground-water discharge from the Star Point Sandstone in the Mesaverde Group in the Wasatch Plateau occurs along faults. In the Book Cliffs, where faulting is less extensive, most of the ground-water discharge is from the Flagstaff Limestone. The Flagstaff Limestone is greatly diffusive, has a small storage coefficient, and contains water which is perched. Springs issuing from the Star Point Sandstone in the Mud Creek drainage (Wasatch Plateau) had recession indexes greater than 365 days per log cycle. Springs issuing at higher altitudes from the Colton Formation and the Flagstaff Limestone in the Soldier Creek area (Book Cliffs) have great seasonal variability, with recession indexes ranging from 24 to 115 days per log cycle. Estimated transmissivities in the Soldier Creek area ranged from 0.003 foot squared per day in the lower part of the Castlegate Sandstone to 0.07 foot squared per day in the Price River Formation. Seepage from the Star Point Sandstone is the major contributor to base flow of the stream in Eccles Canyon (Wasatch Plateau). Gains of as much as 230 gallons per minute occurred near a fault zone which crosses Eccles Canyon at the junction with South Fork Canyon. The potentiometric surface of water in the Blackhawk Formation in the Wasatch Plateau (Mud Creek drainage) and the Book Cliffs (Soldier Creek area) generally is above the coal zones, and dewatering will be necessary in most places during mining. The total reported mine discharge during 1980 was about 2,800 acre-feet. During the 1980 water year, ground-water discharge from the Flagstaff Limestone contributed about 4,400 acre-feet, or 41 percent of the combined streamflow of Coal, Soldier, and Dugout Creeks. Discharge from the Blackhawk and other formations contributed about 2,200 acrefeet, or 21 percent of the streamflow. The recharge to a 4,020-acre outcrop of the Flagstaff Limestone in the Soldier Creek area was determined from measurements of the discharge of springs and seepage gains in streams. The estimated recharge was 2 inches per year, or 12 percent of the April 1 snowpack, or 9 percent of the precipitation during 1980. Benthic-diversity indexes at streams in the Book Cliffs and Wasatch Plateau are related to the size of the bed material. The Shannon-Weiner diversity index for five sites in the Mud Creek drainage ranged from 1.57 to 4.'20 during four sampling periods in 1979-80. In the Soldier Creek drainage, the diversity index for four sampling sites ranged from 0.8 to 2.3 during three sampling periods in 1979-80. Sediment deposition in Scofield Reservoir during 1943-79 was estimated to be 3,000 acre-feet but most of the coal deposition in the reservoir occurred prior to about 1950. An anaerobic zone develops in the reservoir during the summer, but water in the reservoir completely mixes during late summer or early fall.

Utah↗
USGS2018

Habitat mosaics and path analysis can improve biological conservation of aquatic biodiversity in ecosystems with low-head dams

Conserving native biodiversity depends on restoring functional habitats in the face of human-induced disturbances. Low-head dams are a ubiquitous human impact that degrades aquatic ecosystems worldwide. To improve our understanding of how low-head dams impact habitat and associated biodiversity, our research examined complex interactions among three spheres of the total environment. i.e., how low-head dams ( anthroposphere ) affect aquatic habitat ( hydrosphere ), and native biodiversity ( biosphere ) in streams and rivers. Creation of lake-like habitats upstream of low-head dams is a well-documented major impact of dams. Alterations downstream of low head dams also have important consequences, but these downstream dam effects are more challenging to detect. In a multidisciplinary field study at five dammed and five undammed sites within the Neosho River basin, KS, we tested hypotheses about two types of habitat sampling (transect and mosaic) and two types of statistical analyses (analysis of covariance and path analysis). We used fish as our example of biodiversity alteration. Our research provided three insights that can aid environmental professionals who seek to conserve and restore fish biodiversity in aquatic ecosystems threatened by human modifications. First, a mosaic approach identified habitat alterations below low-head dams (e.g. increased proportion of riffles) that were not detected using the more commonly-used transect sampling approach. Second, the habitat mosaic approach illustrated how low-head dams reduced natural variation in stream habitat. Third, path analysis, a statistical approach that tests indirect effects, showed how dams, habitat, and fish biodiversity interact. Specifically, path analysis revealed that low-head dams increased the proportion of riffle habitat below dams, and, as a result, indirectly increased fish species richness . Furthermore, the pool habitat that was created above low-head dams dramatically decreased fish species richness. As we show here, mosaic habitat sampling and path analysis can help conservation practitioners improve science-based management plans for disturbed aquatic systems worldwide.

Kansas↗
USGS2021

Evaluating the impact of watershed development and climate change on stream ecosystems: A Bayesian network modeling approach

A continuous-variable Bayesian network (cBN) model is used to link watershed development and climate change to stream ecosystem indicators. A graphical model, reflecting our understanding of the connections between climate change, weather condition, loss of natural land cover, stream flow characteristics , and stream ecosystem indicators is used as the basis for selecting flow metrics for predicting macroinvertebrate-based indicators. Selected flow metrics were then linked to variables representing watershed development and climate change. We fit the model to data from two river basins in southeast US and the resulting model was used to simulate future stream ecological conditions using projected future climate and development scenarios. The three climate models predicted varying ecological condition trajectories, but similar worst-case ecological conditions. The established modeling approach couples mechanistic understanding with field data to develop predictions of management-relevant variables across a heterogeneous landscape. We discussed the transferability of the modeling approach.

North Carolina, South Carolina, Virginia↗
USGS2015

Life-stage-specific physiology defines invasion extent of a riverine fish

Many ecologists have called for mechanism-based investigations to identify the underlying controls on species distributions. Understanding these controls can be especially useful to construct robust predictions of how a species range may change in response to climate change or the extent to which a non-native species may spread in novel environments. Here, we link spatially intensive observations with mechanistic models to illustrate how physiology determines the upstream extent of the aquatic ectotherm smallmouth bass ( Micropterus dolomieu ) in two headwater rivers. Our results demonstrate that as temperatures become increasingly cold across a downstream to upstream gradient, food consumption in age 0 bass becomes increasingly constrained, and as a result, these fish become growth limited. Sufficient first summer growth of age 0 bass is essential for overwinter survival because young bass must persist from energy reserves accumulated during the summer, and those reserves are determined by body size. Our field data reveal the upstream extent of adult bass reproduction corresponds to a point in the downstream/upstream gradient where cold temperatures impair growth opportunities in young bass. This pattern was repeated in both study streams and explained why bass positioned nests twice as far upstream in the warm compared to the cold stream in the same basin. Placement of spawning nests by adult bass is likely subject to strong evolutionary selection in temperate systems: if bass spawn too far upstream, their young are unlikely to grow large enough to survive the winter. Consumption and growth in older bass (age 3–4) was far less sensitive to temperature. Based on these data, we suggest that temperature-sensitive age 0 bass constrain the upstream distribution limits of bass within temperate streams. In this study, we investigated how temperature-dependent physiology changed through the life history of a species and, in doing so, identified a climate-sensitive life-history stage that likely sets the distributional limits of all other life-history stages. We anticipate the framework developed here could be employed to identify how similar stage-specific environmental sensitivity determines distribution in many other ectothermic species.

Oregon↗
USGS2005

Comparison of instream methods for measuring hydraulic conductivity in sandy streambeds

Streambed hydraulic conductivity (K) values were determined at seven stream transects in the Platte River Basin in Nebraska using different instream measurement techniques. Values were compared to determine the most appropriate technique(s) for use in sandy streambeds. Values of K determined from field falling‐ and constant‐head permeameter tests analyzed using the Darcy equation decreased as permeameter diameter increased. Seepage meters coupled with hydraulic gradient measurements failed to yield K values in 40% of the trials. Consequently, Darcy permeameter and seepage meter tests were not preferred approaches. In the upper 0.25 m of the streambed, field falling‐ and constant‐head permeameter tests analyzed with the Hvorslev solution generally had similar K values that were significantly greater than those determined using the Hazen grain‐size, Bouwer and Rice slug test for anisotropic and isotropic conditions, and Alyamani and Sen grain‐size methods; median differences between these tests and the Hvorslev falling‐head 60 cm diameter permeameter were about 8, 9, 17, and 35 m/day, respectively. The Hvorslev falling‐head permeameter test is considered the most robust method for measuring K of the upper 0.25 m of the streambed because of the inherent limitations of the empirical grain‐size methods and less sediment disturbance for permeameter than slug tests. However, lateral variability in K along transects on the Platte, North Platte, and Wood Rivers was greater than variability in K between valid permeameter, grain‐size, or slug tests, indicating that the method used may matter less than making enough measurements to characterize spatial variability adequately. At the Platte River tributary sites, the upper 0.3 m of the streambed typically had greater K than sediment located 0.3 to 2.5 m below the streambed surface, indicating that deposits below the streambed may limit ground water/surface water fluxes. The Hvorslev permeameter tests are not a practical measurement approach for these greater depths. Thus, selection of a method for measuring streambed K needs to consider the vertical location of the sediments that are most likely to limit the rate of ground water/surface water interaction.

Ground Water↗
USGS1999

Effectiveness of an electrical barrier in blocking a sea lamprey spawning migration on the Jordan River, Michigan

Mark-recapture studies indicated that a pulsed-DC electrical barrier set to a 2-ms pulse width and 10 pulses/s completely blocked the spawning migration of sea lampreys Petromyzon marinus in the Jordan River, Michigan. Capture efficiency of fyke nets averaged 24% for four groups, about 300 tagged sea lampreys each, released upstream of the barrier; no unmarked sea lampreys and none of the 1,194 sea lampreys tagged and released downstream of the barrier were captured in the fyke nets while the barrier was energized. At a lower pulsator setting (1-ms pulse width; 10 pulses/s), 1 of 900 sea lampreys released below the barrier was recaptured in the nets. Sea lampreys from downstream were captured in the fyke nets after the barrier was de-energized, indicating that the barrier should remain in operation later than mid-July. Both sea lampreys and teleosts exposed to the electrical field were stunned but exhibited no apparent damage at either barrier setting. The pulsed-DC electrical barrier should help reduce the use of chemical lampricides for controlling sea lampreys in some Great Lakes streams and would be particularly suited for streams where even the smallest low-head barrier would create an unacceptably large impoundment.

Michigan↗
USGS1966

Appraisal of near-surface subsidence on the Panoche Creek fan, Fresno County, California

Near-surface subsidence results chiefly from the compaction of deposits by an overburden load as the clay bond supporting the deposits is weakened by water percolating through the deposits for the first time since burial. About 100 square miles of alluvial-fan deposits in western Fresno County, California, have been affected by manmade near-surface subsidence within the past few decades. Subsidence of 3-5 feet is common and 10-15 feet of subsidence has occurred within small areas. Oren cracks form between areas undergoing different amounts of settlement, and are a characteristic feature of compaction due to wetting. Differential settlement occurring within short distances has destroyed or damaged ditches, canals, roads, pipelines, electric-transmission towers, and buildings, and has made the irrigation of crops difficult. The areas of known near-surface subsidence along the alinement of the San Luis Canal-California Aqueduct were compacted by ponding before construction of the canal. The 11 miles of canal alinement that cross the fan of Panoche Creek were not ponded before construction. ,Although a few reports of local residents to the California Department of Water Resources indicated that some very small areas of settlement had occurred after irrigation, it was generally considered that the fan would not be susceptible to widespread near-surface subsidence. The irrigated fields did not show the pronounced hummocky relief and subsidence hollows that were typical of the areas of known near-surface subsidence. Nit as strong was the evidence from core holes that showed that the deposits, even in areas that had never been irrigated, were roughly at field capacity instead of being moisture deficient. This seemed logical because Panoche Creek had been observed to flow for 1-5 months during years of heavy rainfall, in contrast to the ephemeral flow of streams on the Moreno Gulch fan to the northwest and on the Tumey Gulch fan to the south. It was assumed that if similar flows had occurred in the past, the deposits would have been wetted thoroughly from the land surface to the water table with each major period of flow and deposition.

California↗
USGS1965

The operation and maintenance of a crest-stage gaging station

The purpose of this manual is to familiarize field personnel with the procedures involved in operating crest-stage gaging stations. Crest-stage gages are used to determine the elevation of a peak stage occurring at a specific location in a stream. A crest-stage gage consists of a length of 14-inch diameter pipe installed in a vertical position in the stream channel (figure 1). The pipe is vented and equipped with an intake system that allows water to enter and leave the pipe as the stream rises and recedes. An equal length of aluminum "T" channel (staff) is inserted in the pipe and made to rest on a positive stop called a datum pin. When granulated cork is placed in the gage, the cork will float on the rising stage, then adhere to the staff after the stage recedes. The peak stage is then determined by removing the staff and measuring the distance between the cork line and the lower end of the staff. The primary purpose of a crest-stage gaging station is to collect hydrologic data for flood-frequency analyses. Collection of data for such analyses involves operating a network of stations for a period of years until sufficient peak flow data are obtained to accurately define flood-frequency curves. Because carelessness in collecting data at the gage site might result in the loss of an entire year's flood event, the importance of proper operation and maintenance of these gages can not be overemphasized. Peak discharges are related to the basin characteristics and major changes in these characteristics must be evaluated. For€st fires, timber harvest, or a new road location that alters the natural drainage of the basin, may effect the intensity and timing of the runoff of the basin. Rigid datum controls must be maintained at the gage site throughout the period of record. Physical changes of the site resulting from flood flows or manmade alterations must be evaluated. If a drainage structure such as a culvert is part of the site features, free-flow conditions must be maintained or obstructions carefully documented.

Open-File Report↗
USGS1981

Flood of May 5 and 6, 1981, Mobile, Alabama

Heavy and intense rainfall in the late evening and early morning hours, May 5 and 6, 1981, caused widespread flooding along streams and low-lying areas in the port city of Mobile, Ala. More than 12 inches of rain fell between 6 p.m. May 5, and 3 a.m. May 6. Damage caused by flooding was estimated by the Mobile Department of Public Works to be millions of dollars. Maximum water surface elevations on streams in the area were 2 to 3 feet higher than those that occurred during a similar flood in April 1980. The approximate extent of flooding delineated on maps using flood profiles obtained by field surveys will provide a basis for formulating effective flood plain zoning that could minimize existing and future flood problems. (USGS)

Open-File Report↗
USGS1994

Operational Procedures for Collecting Water-Quality Samples at Monitoring Sites on Maple Creek Near Nickerson and the Platte River at Louisville, Eastern Nebraska

Prototype stream-monitoring sites were operated during part of 1992 in the Central Nebraska Basins (CNBR) and three other study areas of the National Water-Quality Assessment (NAWQ) Program of the U.S. Geological Survey. Results from the prototype project provide information needed to operate a net- work of intensive fixed station stream-monitoring sites. This report evaluates operating procedures for two NAWQA prototype sites at Maple Creek near Nickerson and the Platte River at Louisville, eastern Nebraska. Each site was sampled intensively in the spring and late summer 1992, with less intensive sampling in midsummer. In addition, multiple samples were collected during two high- flow periods at the Maple Creek site--one early and the other late in the growing season. Water-samples analyses included determination of pesticides, nutrients, major ions, suspended sediment, and measurements of physical properties. Equipment and protocols for the water-quality sampling procedures were evaluated. Operation of the prototype stream- monitoring sites included development and comparison of onsite and laboratory sample-processing proce- dures. Onsite processing was labor intensive but allowed for immediate preservation of all sampled constituents. Laboratory processing required less field labor and decreased the risk of contamination, but allowed for no immediate preservation of the samples.

Open-File Report↗
USGS2009

Estimated bankfull discharge for selected Michigan rivers and regional hydraulic geometry curves for estimating bankfull characteristics in southern Michigan rivers

Regional hydraulic geometry curves are power-function equations that relate riffle dimensions and bankfull discharge to drainage-basin size. They are defined by data collected through surveys conducted at stable stream reaches and can be used to aid watershed managers, design engineers, and others involved in determination of the best course of action for an unstable stream. Hydraulic geometry curves provide a mechanism through which comparisons can be made between riffle dimensions collected at an unstable stream to those collected at stable streams within the same region. In 2005, a study was initiated to delineate regional hydraulic geometry curves for Michigan. After in-office review of 343 U.S. Geological Survey streamgaging stations and an extensive field reconnaissance effort, 44 stable reaches were selected for this study. Detailed surveys that included cross-sectional and longitudinal profiles and pebble counts were conducted at selected streamgages, which were distributed throughout Michigan. By use of survey data from riffle cross sections and water-surface slope, bankfull discharge was estimated and compared to flood-recurrence intervals using regional flood equations. This comparison shows that bankfull discharges in Michigan recur more frequently than every 2 years. Regional hydraulic geometry curves were developed rather than statewide curves owing to large differences in factors that control channel geometry across the State. However, after the data were subdivided according to ecoregions, it was determined that there were enough data to delineate regional hydraulic geometry curves only for the Southern Lower Michigan Ecoregion. For this ecoregion, geometry curve equations and their coefficients of determination are: Width = 8.19 x DA 0.44 ; R 2 = 0.69, Depth = 0.67 x DA 0.27 ; R 2 = 0.28, Area = 4.38 x DA 0.74 ; R 2 = 0.59, where DA is the drainage area and R 2 is the coefficient of determination. By use of discharge estimates for the Southern Lower Michigan Ecoregion, a bankfull discharge curve was delineated. The corresponding equation and its coefficient of determination are: Discharge = 4.05 x DA 0.95 ; R 2 = 0.60.

Michigan↗
USGS2026

Arsenic and isotope concentrations in the lower Platte River valley of eastern Nebraska, early 1970s to 2023

The City of Lincoln, Nebraska, has been monitoring concentrations of arsenic in their source water and evaluating their options for treatment and removal since at least 2002. In 2022, the City of Lincoln, Nebr., with funding assistance from the Nebraska Water Sustainability Fund, began cooperating with the U.S. Geological Survey to examine arsenic concentrations in surface water and groundwater in the lower Platte River valley and the area around City of Lincoln Water System (LWS) well field. Arsenic data collected from the Platte River since 1974 were examined using the “weighted regression on time, discharge, and season” model, which compared the streamflow (also referred to as “discharge”), time of year, and season to estimate concentrations of arsenic. Annual mean arsenic concentrations modeled for more than 49 years at the Platte River at Louisville, Nebr., U.S. Geological Survey streamgage (station 06805500), indicated a significant increasing trend. Arsenic concentrations in the Platte River were seasonal, with the highest concentrations being observed during mid- to late summer. When seasonal patterns and streamflow were combined with arsenic concentrations in the Platte River during low streamflow conditions, groundwater contributions, which can have higher arsenic concentrations, make up a larger portion of the streamflow. Arsenic samples were collected from upstream rivers in 2022 and 2023 and were paired to analyze the arsenic contributions at the U.S. Geological Survey streamgage on the Platte River near Ashland, Nebr. (station 06801000), near the City of Lincoln well field. The arsenic concentrations from the streamgage on the Platte River near Ashland, Nebr., location, were higher than the U.S. Geological Survey streamgage on the Elkhorn River at Waterloo, Nebr. (station 06800500), and significantly lower than at the U.S. Geological Survey streamgage on the Platte River near Leshara, Nebr.(station 06796500), indicating that the Platte River usually contributes a higher concentration of arsenic than does the Elkhorn River as they join near Ashland, Nebr. During 1991–2023, six groundwater monitoring wells were analyzed to identify trends in arsenic concentrations. Two of the six wells had a positive trend during the 33-year period. One monitoring well did not reveal a long-term trend during this period but showed a trend during 2019–23, correlating to a period when the island in the middle of the Platte River was connected to the east bank of the river when manganese reducing conditions were present and groundwater levels were declining in the well. Across all wells the oxidation and reduction (redox) condition during the time of sampling was assessed. Mixed anoxic and (or) oxic redox condition was the most common redox process and the highest sampled arsenic concentrations in monitoring wells were observed in anoxic conditions driven by manganese reduction. Groundwater arsenic concentrations had seasonal variation around the City of Lincoln well field, with higher arsenic concentrations tending to be further south in comparison to samples collected further north. Isotope samples were collected and analyzed in surface water and groundwater around the LWS well field. The samples indicate that the proportion of surface water present in the LWS production wells can be higher in the spring and lower in the summer. With higher arsenic concentrations observed in the stream water during the summer period, the LWS source water can be affected by these elevated arsenic concentrations even though the proportion of surface water is lower.

Nebraska↗