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USGS2012

A perspective on modern pesticides, pelagic fish declines, and unknown ecological resilience in highly managed ecosystems

Pesticides applied on land are commonly transported by runoff or spray drift to aquatic ecosystems, where they are potentially toxic to fishes and other nontarget organisms. Pesticides add to and interact with other stressors of ecosystem processes, including surface-water diversions, losses of spawning and rearing habitats, nonnative species, and harmful algal blooms. Assessing the cumulative effects of pesticides on species or ecological functions has been difficult for historical, legal, conceptual, and practical reasons. To explore these challenges, we examine current-use (modern) pesticides and their potential connections to the abundances of fishes in the San Francisco Estuary (California). Declines in delta smelt (Hypomesus transpacificus), Chinook salmon (Oncorhynchus tshawytscha), and other species have triggered mandatory and expensive management actions in the urbanizing estuary and agriculturally productive Central Valley. Our inferences are transferable to other situations in which toxics may drive changes in ecological status and trends.

California↗

USGS2007

Factors Affecting Spatial and Temporal Variability in Nutrient and Pesticide Concentrations in the Surficial Aquifer on the Delmarva Peninsula

Water quality in the unconfined, unconsolidated surficial aquifer on the Delmarva Peninsula is influenced by the availability of soluble ions from natural and human sources, and by geochemical factors that affect the mobility and fate of these ions within the aquifer. Ground-water samples were collected from 60 wells completed in the surficial aquifer of the peninsula in 2001 and analyzed for major ions, nutrients, and selected pesticides and degradation products. Analytical results were compared to similar data from a subset of sampled wells in 1988, as well as to land use, soils, geology, depth, and other potential explanatory variables to demonstrate the effects of natural and human factors on water quality in the unconfined surficial aquifer. This study was conducted as part of the National Water-Quality Assessment Program of the U.S. Geological Survey, which is designed (in part) to describe the status and trends in ground-water quality and to provide an understanding of natural and human factors that affect ground-water chemistry in different parts of the United States. Results of this study may be useful for water-resources managers tasked with addressing water-quality issues of local and regional importance because the surficial aquifer on the Delmarva Peninsula is a major source of water for domestic and public supply and provides the majority of flow in local streams. Human impacts are apparent in ground-water quality throughout the surficial aquifer. The surficial aquifer on the Delmarva Peninsula is generally sandy and very permeable with well-oxygenated ground water. Dissolved constituents found throughout various depths of the unconfined aquifer are likely derived from the predominantly agricultural practices on the peninsula, although effects of road salt, mineral dissolution, and other natural and human influences are also apparent in some areas. Nitrate occurred at concentrations exceeding natural levels in many areas, and commonly exceeded 10 milligrams per liter (as nitrogen). In addition to land use in the aquifer recharge area, concentrations of nitrate in ground water are related to regional patterns in soil drainage that affect underlying aquifer redox conditions. Over the peninsula, nitrate concentrations are not related to recharge date of the water, but are positively correlated with depth in shallow wells screened beneath agricultural areas. Nitrate concentrations increased in oxic areas (dissolved oxygen greater than 1 milligram per liter) of the deeper part of the surficial aquifer used for domestic supply by an average of about 2 milligrams per liter between 1988 and 2001, although no changes were apparent in shallower parts of the aquifer over that same period. Water in the surficial aquifer generally flows from land-surface recharge to surface-water discharge areas in less than 30 years. As a result, the entire flow system in the surficial aquifer has likely been affected by human activities on and near the land surface over the past several decades. Pesticide compounds occurred widely at low levels throughout the surficial aquifer. The most commonly used herbicides (metolachlor, alachlor, and atrazine) were the most commonly detected. These pesticides primarily occurred in ground water in the form of degradation products. The widespread occurrence of these and other pesticide compounds reflects their abundant use as well as chemical properties and aquifer characteristics that allow their movement into ground water. Mixtures of pesticides are common. Most samples contained at least 3 different compounds; several samples contained as many as 11. Pesticide concentrations in the surficial aquifer are relatively high beneath recharge areas with well-drained soils in the shallow part of the aquifer and in oxic environments throughout the surficial aquifer. Concentrations are generally below existing drinking-water standards, although standards are not available for all of the pesticide compound

Scientific Investigations Report↗

USGS2005

Simulated effects of irrigation on salinity in the Arkansas River Valley in Colorado

Agricultural irrigation has a substantial impact on water quantity and quality in the lower Arkansas River valley of southeastern Colorado. A two-dimensional flow and solute transport model was used to evaluate the potential effects of changes in irrigation on the quantity and quality of water in the alluvial aquifer and in the Arkansas River along an 17.7 km reach of the fiver. The model was calibrated to aquifer water level and dissolved solids concentration data collected throughout the 24 year study period (197195). Two categories of irrigation management were simulated with the calibrated model: (1) a decrease in ground water withdrawals for irrigation; and (2) cessation of all irrigation from ground water and surface water sources. In the modeled category of decreased irrigation from ground water pumping, there was a resulting 6.9% decrease in the average monthly ground water salinity, a 0.6% decrease in average monthly river salinity, and an 11.1% increase in ground water return flows to the river. In the modeled category of the cessation of all irrigation, average monthly ground water salinity decreased by 25%; average monthly river salinity decreased by 4.4%; and ground water return flows to the river decreased by an average of 64%. In all scenarios, simulated ground water salinity decreased relative to historical conditions for about 12 years before reaching a new dynamic equilibrium condition. Aquifer water levels were not sensitive to any of the modeled scenarios. These potential changes in salinity could result in improved water quality for irrigation purposes downstream from the affected area.

Ground Water↗

USGS1998

Shorebird use of managed wetlands in the Mississippi Alluvial Valley

We assessed shorebird densities on managed wetland habitats during fall and winter within the primarily agricultural landscape of the Mississippi Alluvial Valley. From November through March, shorebird densities were greater on soybean fields than on rice or moist-soil fields. Killdeer (Charadrius vociferus) and Common Snipe (Gallinago gallinago) were common throughout winter, whereas Yellowlegs (Tringa spp.) and ?peep? sandpipers (Calidris spp.) were present but less abundant. During fall, Dowitchers (Limnodromus spp.), Pectoral Sandpipers (Calidris melanotos), Killdeer, and peep sandpipers were the most abundant species on managed shorebird habitat units. Although shorebird densities were consistently greater on habitats managed by drawing down existing water, we were unable to detect a significant difference in densities from areas managed by flooding previously dry habitat.

American Midland Naturalist↗

USGS1994

Distribution and variability of nitrogen and phosphorus in the alluvial, High Plains, Rush Springs, and Blaine aquifers in western Oklahoma

Aquifers are the primary source of water for drinking and agricultural purposes in western Oklahoma. Health concerns about consuming nitrogen and an increased reliance on ground water for drinking necessitate a better understanding of the cause and effect of contamination from nutrients. The purpose of this project was to compile nutrients data from the National Water Information System data base for the alluvial aquifers west of longitude 98 degrees W. and from three bedrock aquifers, High Plains, Rush Springs, and Blaine, and provide this information in a report for future projects and for the facilitation of nutrient source management. The scope of the work consisted of (1) compiling ground-water quality data concerning nitrogen and phosphorus ions, (2) constructing boxplots illustrating data variability, (3) maps for each aquifer showing locations of wells when nitrogen and phosphorus ions were measured in ground water and where concentrations of nitrate and nitrite, reported as nitrogen, exceed the maximum contaminant level, and (4) calculating summary statistics. Nutrient data were obtained from the U.S. Geological Survey data base called the National Water Information System. Data were restricted to ground-water samples, but no restrictions were placed on well and water use or date and time of sampling. Compiled nutrient data consist of dissolved and total concentrations of the common nitrogen and phosphorus ions measured in ground water. For nitrogen these ions include nitrate, nitrite, ammonium, and nitrite plus nitrate. All concentrations are reported in milligrams per liter as nitrogen. Phosphorus in ground water is measured as the orthophosphate ion, and is reported in milligrams per liter as phosphorus. Nutrient variability is illustrated by a standard boxplot. The data are presented by aquifer or hydrologic subregion for alluvial aquifers, with one boxplot constructed for each nutrient compound if more than four analyses are present. Maps for each aquifer show where nitrogen and phosphorus have been measured in ground water and where the concentrations of nitrate and nitrite exceed the maximum contaminant level. A statistical summary for each aquifer and subregion show if censored data were present, number of samples in each data set, largest minimum reporting level for each nutrient compound, percentiles used to construct boxplots, and minimum and maximum values. Also given are the number of wells sampled in each aquifer and the number of wells exceeding the maximum contaminant level.

Open-File Report↗

USGS2005

Sediment-transport investigations of the upper Yellowstone River, Montana, 1999 through 2001: Data collection, analysis, and simulation of sediment transport

The upper Yellowstone River in Montana is an important State and national water resource, providing recreational, agricultural, and commercial benefits. Floods in 1996 and 1997, with recorded peak discharges having recurrence intervals close to 100 years, caused substantial streambank erosion and hill- slope mass wasting. Large quantities of sand-, gravel-, and cobble-sized material entrained by the flood flows became flood-bar deposits, creating a source of sediment available for transport during future floods. The flood damage and resulting sedimentation raised concerns about potential streambank-stabilization projects and how the river and riparian corridor might be managed in the future. The U.S. Geological Survey, in cooperation with the Park Conservation District, the Montana Department of Transportation, and the U.S. Army Corps of Engineers, investigated sediment transport in the upper Yellowstone River near Livingston from 1999 through 2001 as part of a cumulative effects study to provide a scientific basis for future river management decisions. The purpose of this report is to present the results of data collection, analysis, and simulation of sediment transport for the upper Yellowstone River. The study area included a 13.5-mile study reach of the upper Yellowstone River where substantial sediment transport occurred in 1996 and 1997. In this study area, the upper Yellowstone River is a high gradient, coarse-bed stream having a slope of about 0.0028 foot per foot or more than 14 feet per mile. The study area drains about 3,551 square miles, and runoff results primarily from snowmelt during the spring and summer months. As part of sediment-transport investigations, the U.S. Geological Survey surveyed river cross sections, characterized streambed-material particle size using particle counts and sieve analyses, and collected bedload- and suspended-sediment data during three runoff seasons (1999-2001). Data were collected for stream discharges that ranged from 2,220 cubic feet per second (typical of pre- and post-runoff discharge) to 25,100 cubic feet per second (about 125 percent of bankfull discharge). The distribution of streambed-material particle size was determined, and sediment-transport curves for bedload discharge, suspended-sediment discharge, and total-sediment discharge were developed. The threshold values of streamflow and average stream velocity needed for initiation of bedload transport for selected sediment-size classes showed that little to no bedload was transported for an average stream velocity below about 3 feet per second, and the only particle size transported as bedload at that velocity was sand. Over the range of stream discharges sampled and with silt- and finer-sized particles excluded, bedload discharge averaged about 18 percent of the total-sediment discharge, equal to bedload discharge plus suspended-sediment discharge. At the lowest and highest stream discharges sampled, bedload was, respectively, less than about 2 percent and about 30 percent of the total-sediment discharge. Over the range of stream discharges sampled, the sand-sized part of the total suspended-sediment discharge averaged about 48 percent, where the total suspended-sediment discharge included sand-, silt- and finer-sized particles. At the lowest and highest stream discharges sampled, the sand-sized part of the total suspended-sediment discharge was, respectively, less than about 16 percent and about 50 percent of the total suspended-sediment discharge. The sediment-transport curves were compared to curves for selected sites in the western United States having drainage areas ranging from 21 square miles to over 20,000 square miles. Daily sediment loads transported at bankfull discharge were calculated for each site and results were plotted in relation to drainage area. Results based on the 1999-2001 data-collection period indicate that the estimated daily bedload transported at bankfull discharge in the upper Yellowstone River exceeded the envelope line that bounds the upper end of the data for other selected sites in the Northern Rocky Mountains and is similar in magnitude to that for selected sites in Alaska having braided channels and glacial and snowmelt runoff. Similar comparisons for suspended sediment indicate that daily suspended-sediment load at bankfull discharge is relatively high in the upper Yellowstone River, plotting slightly above the envelope line that bounds the upper end of the data for other selected sites in the Northern Rocky Mountains. Sediment data were used to develop individual transport equations for seven size classes of sediment ranging from small cobbles to very fine sand. A step-wise regression procedure relating sediment discharge to important hydraulic variables showed that average stream velocity was the only significant variable at the 95-percent confidence level. Bedload and suspended-sediment data and equations indicate that more sand is transported for a given velocity than any other particle size, and very little sand-size sediment load is transported below an average stream velocity of about 2.5 feet per second. Transport of coarser-sized sediment (limited to bedload) becomes very little for an average velocity less than about 3.5 feet per second. Results for the 1999-2001 data-collection period indicate that sediment transport in the upper Yellowstone River tends to be limited more by the transport capacity of the stream (capacity or transport limited), than to the availability of sediment in the watershed (supply limited). Sediment data collected and analyzed were used to simulate sediment transport in the study reach using the BRIdge Stream Tube model for Alluvial River Simulation, or BRI-STARS computer model. The model was calibrated and verified using selected data from historical runoff periods. Simulated total-sediment loads, on a reach-averaged basis, were in good agreement with the total-sediment loads determined from the transport curve for the 2-year flood hydrograph but were considerably smaller for the total-sediment loads determined from the transport curve for the 50-, 100-, and 500-year flood hydrographs. The differences probably were largely due to the inability of the model to simulate streambank erosion, hillslope mass-wasting, and other channel-widening processes, which had supplied substantial quantities of sediment to the channel during the 1996 and 1997 floods, and probably continued to contribute to the sediment load in the subsequent years (1999-2001) when the data were collected. Furthermore, the transport curve was applied beyond the measured data for the highest discharges, and may thus be unreliable. Also, the transport curve derived from only limited data may not apply over the full duration of the hydrograph and sediment might be transported over only a portion of the hydrograph, especially for rivers like the upper Yellowstone where snowmelt runoff predominates. The true sediment discharge is, therefore, unknown and might be closer to the simulated values than to the values calculated from the transport curve.

Montana↗

USGS2024

Temporal analysis of water chemistry and smallmouth bass (Micropterus dolomieu) health at two sites with divergent land use in the Susquehanna River watershed, Pennsylvania, USA

Monitoring wild fish health and exposure effects in impacted rivers and streams with differing land use has become a valuable research tool. Smallmouth bass ( Micropterus dolomieu ) are a sensitive, indicator species that exhibit signs of immunosuppression and endocrine disruption in response to water quality changes and contaminant exposure. To determine the impact of agriculture and development on smallmouth bass health, two sites (a developed/agriculture site and a forested site) in the Susquehanna River watershed, Pennsylvania were selected where bass and water chemistry were sampled from 2015 to 2019. Smallmouth bass were sampled for histopathology to assess parasite and macrophage aggregate density in the liver and spleen, condition factor (Ktl), hepatic gene transcript abundance, hepatosomatic index (HSI), and a health assessment index (HAI). Land use at the developed/agriculture site included greater pesticide application rates and phytoestrogen crop cover and more detections and higher concentrations of pesticides, wastewater-associated contaminants, hormones, phytoestrogens, and mycotoxins than at the forested site. Additionally, at the developed/agriculture site, indicators of molecular changes, including oxidative stress, immune/inflammation, and lipid metabolism-related hepatic gene transcripts, were associated with more contaminants and land use variables. At both sites, there were multiple associations of contaminants with liver and/or spleen macrophage aggregate density, indicating that changes at the molecular level seemed to be a better indicator of exposures unique to each site. The findings illustrate the importance of timing for land management practices, the complex mixtures aquatic animals are exposed to, and the temporal changes in contaminant concentration. Agricultural practices that affect hepatic gene transcripts associated with immune function and disease resistance were demonstrated which could negatively affect smallmouth bass populations.

Pennsylvania↗

USGS2006

Global synthesis of groundwater recharge in semiarid and arid regions

Global synthesis of the findings from ∼140 recharge study areas in semiarid and arid regions provides important information on recharge rates, controls, and processes, which are critical for sustainable water development. Water resource evaluation, dryland salinity assessment (Australia), and radioactive waste disposal (US) are among the primary goals of many of these recharge studies. The chloride mass balance (CMB) technique is widely used to estimate recharge. Average recharge rates estimated over large areas (40–374 000 km 2 ) range from 0·2 to 35 mm year −1 , representing 0·1–5% of long-term average annual precipitation. Extreme local variability in recharge, with rates up to ∼720 m year −1 , results from focussed recharge beneath ephemeral streams and lakes and preferential flow mostly in fractured systems. System response to climate variability and land use/land cover (LU/LC) changes is archived in unsaturated zone tracer profiles and in groundwater level fluctuations. Inter-annual climate variability related to El Niño Southern Oscillation (ENSO) results in up to three times higher recharge in regions within the SW US during periods of frequent El Niños (1977–1998) relative to periods dominated by La Niñas (1941–1957). Enhanced recharge related to ENSO is also documented in Argentina. Climate variability at decadal to century scales recorded in chloride profiles in Africa results in recharge rates of 30 mm year −1 during the Sahel drought (1970–1986) to 150 mm year −1 during non-drought periods. Variations in climate at millennial scales in the SW US changed systems from recharge during the Pleistocene glacial period (≥10 000 years ago) to discharge during the Holocene semiarid period. LU/LC changes such as deforestation in Australia increased recharge up to about 2 orders of magnitude. Changes from natural grassland and shrublands to dryland (rain-fed) agriculture altered systems from discharge (evapotranspiration, ET) to recharge in the SW US. The impact of LU change was much greater than climate variability in Niger (Africa), where replacement of savanna by crops increased recharge by about an order of magnitude even during severe droughts. Sensitivity of recharge to LU/LC changes suggests that recharge may be controlled through management of LU. In irrigated areas, recharge varies from 10 to 485 mm year −1 , representing 1–25% of irrigation plus precipitation. However, irrigation pumpage in groundwater-fed irrigated areas greatly exceeds recharge rates, resulting in groundwater mining. Increased recharge related to cultivation has mobilized salts that accumulated in the unsaturated zone over millennia, resulting in widespread groundwater and surface water contamination, particularly in Australia. The synthesis of recharge rates provided in this study contains valuable information for developing sustainable groundwater resource programmes within the context of climate variability and LU/LC change.

Hydrological Processes↗

USGS2022

Assessment of cropland inundation due to the operation of the Reelfoot Lake spillway in West Tennessee

Running Reelfoot Bayou (RRB) is the outlet canal of Reelfoot Lake, the largest natural lake in Tennessee. RRB is not able to contain discharge from Reelfoot Lake greater than the bankfull discharge of 28 m 3 /s (1000 ft 3 /s), which typically occurs at the beginning of the growing season (April–June). Historically, the planting of crops has been delayed until flooding subsides and cropland has drained. The objective of this study is a preliminary quantification of cropland inundation to determine its spatial distribution in the RRB floodplain. Inundated croplands in the RRB floodplain were delineated over a range of spillway discharges from 2 to 57 m 3 /s (70–2000 ft 3 /s), using one-dimensional–two-dimensional hydrodynamic modeling and multispectral satellite images (Landsat 8 and Sentinel-2). The composite maps made by combining the simulated and image-derived flood maps were overlaid on the United States Department of Agriculture CropScape layer to determine the inundation of individual summer crops during the growing season. About 25% of the inundated croplands are flooded at discharges of RRB less than 28 m 3 /s, implying wetland hydrology. The results of this analysis can be used to inform operational management of the Reelfoot Lake spillway.

Tennessee↗

USGS2011

Temporal trends in algae, benthic invertebrate, and fish assemblages in streams and rivers draining basins of varying land use in the south-central United States, 1993-2007

Site-specific temporal trends in algae, benthic invertebrate, and fish assemblages were investigated in 15 streams and rivers draining basins of varying land use in the south-central United States from 1993–2007. A multivariate approach was used to identify sites with statistically significant trends in aquatic assemblages which were then tested for correlations with assemblage metrics and abiotic environmental variables (climate, water quality, streamflow, and physical habitat). Significant temporal trends in one or more of the aquatic assemblages were identified at more than half (eight of 15) of the streams in the study. Assemblage metrics and abiotic environmental variables found to be significantly correlated with aquatic assemblages differed between land use categories. For example, algal assemblages at undeveloped sites were associated with physical habitat, while algal assemblages at more anthropogenically altered sites (agricultural and urban) were associated with nutrient and streamflow metrics. In urban stream sites results indicate that streamflow metrics may act as important controls on water quality conditions, as represented by aquatic assemblage metrics. The site-specific identification of biotic trends and abiotic–biotic relations presented here will provide valuable information that can inform interpretation of continued monitoring data and the design of future studies. In addition, the subsets of abiotic variables identified as potentially important drivers of change in aquatic assemblages provide policy makers and resource managers with information that will assist in the design and implementation of monitoring programs aimed at the protection of aquatic resources.

Arkansas, Colorado, Kansas, Kentucky, Louisiana, M↗

USGS2023

Estimating groundwater pumping for irrigation: A method comparison

Effective groundwater management is critical to future environmental, ecological, and social sustainability and requires accurate estimates of groundwater withdrawals. Unfortunately, these estimates are not readily available in most areas due to physical, regulatory, and social challenges. Here, we compare four different approaches for estimating groundwater withdrawals for agricultural irrigation. We apply these methods in a groundwater-irrigated region in the state of Kansas, USA, where high-quality groundwater withdrawal data are available for evaluation. The four methods represent a broad spectrum of approaches: (1) the hydrologically-based Water Table Fluctuation method (WTFM); (2) the demand-based SALUS crop model; (3) estimates based on satellite-derived evapotranspiration (ET) data from OpenET; and (4) a landscape hydrology model which integrates hydrologic- and demand-based approaches. The applicability of each approach varies based on data availability, spatial and temporal resolution, and accuracy of predictions. In general, our results indicate that all approaches reasonably estimate groundwater withdrawals in our region, however, the type and amount of data required for accurate estimates and the computational requirements vary among approaches. For example, WTFM requires accurate groundwater levels, specific yield, and recharge data, whereas the SALUS crop model requires adequate information about crop type, land use, and weather. This variability highlights the difficulty in identifying what data, and how much, are necessary for a reasonable groundwater withdrawal estimate, and suggests that data availability should drive the choice of approach. Overall, our findings will help practitioners evaluate the strengths and weaknesses of different approaches and select the appropriate approach for their application.

Kansas↗

USGS1994

Potentiometric surface of the upper Floridan Aquifer in the St. Johns River Water Management District and vicinity, Florida, May 1994

This map depicts the potentiometric surface of the Upper Floridan aquifer in the St. Johns River Water Management District and vicinity for May 1994. The map is based on water-level measurements made at approximately 1,000 wells and several springs. Data on the map were contoured using 5-foot contour intervals in most areas. The potentiometric surface of this karstic aquifer generally reflects land surface topography. Potentiometric surface highs often correspond to topographic highs, which are areas of surficial recharge to the Upper Floridan aquifer. Springs within topographic lows along with areas of more diffuse upward leakage are natural zones of discharge. Municipal, agricultural, and industrial withdrawals have lowered the potentiometric surface in some areas. The potentiometric surface ranged from 125 feet above sea level in Polk County to 32 feet below sea level in Nassau County. Water levels in May 1994 generally were 0 to 3 feet lower than those measured in May 1993. Water levels in May 1994 in northeast Florida generally were 0 to 3 feet higher than in September 1993, except in the lower St. Johns River basin, where water levels were 0 to 4 feet lower than in September 1993. In the rest of the mapped area, water levels in May 1994 generally were 0 to 4 feet lower than those measured in September 1993.

Open-File Report↗

USGS2015

Summary of hydrologic modeling for the Delaware River Basin using the Water Availability Tool for Environmental Resources (WATER)

The Water Availability Tool for Environmental Resources (WATER) is a decision support system for the nontidal part of the Delaware River Basin that provides a consistent and objective method of simulating streamflow under historical, forecasted, and managed conditions. In order to quantify the uncertainty associated with these simulations, however, streamflow and the associated hydroclimatic variables of potential evapotranspiration, actual evapotranspiration, and snow accumulation and snowmelt must be simulated and compared to long-term, daily observations from sites. This report details model development and optimization, statistical evaluation of simulations for 57 basins ranging from 2 to 930 km 2 and 11.0 to 99.5 percent forested cover, and how this statistical evaluation of daily streamflow relates to simulating environmental changes and management decisions that are best examined at monthly time steps normalized over multiple decades. The decision support system provides a database of historical spatial and climatic data for simulating streamflow for 2001–11, in addition to land-cover and general circulation model forecasts that focus on 2030 and 2060. WATER integrates geospatial sampling of landscape characteristics, including topographic and soil properties, with a regionally calibrated hillslope-hydrology model, an impervious-surface model, and hydroclimatic models that were parameterized by using three hydrologic response units: forested, agricultural, and developed land cover. This integration enables the regional hydrologic modeling approach used in WATER without requiring site-specific optimization or those stationary conditions inferred when using a statistical model.

Delaware, Maryland, New Jersey, New York, Pennsylv↗

USGS2024

Riparian methylmercury production increases riverine mercury flux and food web concentrations

The production and uptake of toxic methylmercury (MeHg) impacts aquatic ecosystems globally. Rivers can be dynamic and difficult systems to study for MeHg production and bioaccumulation, hence identifying sources of MeHg to these systems is both challenging and important for resource management within rivers and main-stem reservoirs. Riparian zones, which are known biogeochemical hotspots for MeHg production, are understudied as potential sources of MeHg to rivers. Here, we present a comprehensive quantification of the hydrologic and biogeochemical processes governing MeHg concentrations, loads, and bioaccumulation at 16 locations along 164 km of the agriculturally intensive Snake River (Idaho, Oregon USA) during summer baseflow conditions, with emphasis on riparian production of MeHg. Approximately one-third of the MeHg load of the Snake River could not be attributed to inflowing waters (upgradient, tributaries, or irrigation drains). Across the study reach, increases in MeHg loads in surface waters were significantly correlated with MeHg concentrations in riparian porewaters, suggesting riparian zones were likely an important source of MeHg to the Snake River. Across all locations, MeHg concentrations in surface waters positively correlated with MeHg concentrations in benthic snails and clams, supporting that riparian produced MeHg was assimilated into local aquatic food webs. This study contributes new insights into riparian MeHg production within rivers which can inform mitigation efforts to reduce MeHg bioaccumulation in fish.

Idaho, Oregon↗

USGS2017

Geologic map of the Beacon Rock quadrangle, Skamania County, Washington

The Beacon Rock 7.5′ quadrangle is located approximately 50 km east of Portland, Oregon, on the north side of the Columbia River Gorge, a scenic canyon carved through the axis of the Cascade Range by the Columbia River. Although approximately 75,000 people live within the gorge, much of the region remains little developed and is encompassed by the 292,500-acre Columbia River Gorge National Scenic Area, managed by a consortium of government agencies “to protect and provide for the enhancement of the scenic, cultural, recreational and natural resources of the Gorge and to protect and support the economy of the Columbia River Gorge area.” As the only low-elevation corridor through the Cascade Range, the gorge is a critical regional transportation and utilities corridor (Wang and Chaker, 2004). Major state and national highways and rail lines run along both shores of the Columbia River, which also provides important water access to ports in the agricultural interior of the Pacific Northwest. Transmission lines carry power from hydroelectric facilities in the gorge and farther east to the growing urban areas of western Oregon and Washington, and natural-gas pipelines transect the corridor (Wang and Chaker, 2004). These lifelines are highly vulnerable to disruption by earthquakes, landslides, and floods. A major purpose of the work described here is to identify and map geologic hazards, such as faults and landslide-prone areas, to provide more accurate assessments of the risks associated with these features. The steep canyon walls of the map area reveal extensive outcrops of Miocene flood-basalt flows of the Columbia River Basalt Group capped by fluvial deposits of the ancestral Columbia River, Pliocene lavas erupted from the axis of the Cascade arc to the east, and volcanic rocks erupted from numerous local vents. The Columbia River Basalt Group unconformably rests on a sequence of late Oligocene and early Miocene rocks of the ancestral Cascade volcanic arc, which underlies most of the map area. The resistant flood-basalt flows form some of the famous landforms in the map area, such as Hamilton Mountain. Extensive landslide complexes have developed where the basalt flows were emplaced on weak volcaniclastic rocks.

Washington↗

USGS1999

Hydrogeology, water use, and simulation of flow in the High Plains aquifer in northwestern Oklahoma, southeastern Colorado, southwestern Kansas, northeastern New Mexico, and northwestern Texas

The U.S. Geological Survey, in cooperation with the Oklahoma Water Resources Board, began a three-year study of the High Plains aquifer in northwestern Oklahoma in 1996. The primary purpose of this study was to develop a ground-water flow model to provide the Water Board with the information it needs to manage the quantity of water withdrawn from the aquifer. The study area consists of about 7,100 square miles in Oklahoma and about 20,800 square miles in adjacent states to provide appropriate hydrologic boundaries for the flow model. The High Plains aquifer includes all sediments from the base of the Ogallala Formation to the potentiometric surface. The saturated thickness in Oklahoma ranges from more than 400 feet to less than 50 feet. Natural recharge to the aquifer from precipitation occurs throughout the area but is extremely variable. Dryland agricultural practices appear to enhance recharge from precipitation, and part of the water pumped for irrigation also recharges the aquifer. Natural discharge occurs as discharge to streams, evapotranspiration where the depth to water is shallow, and diffuse ground-water flow across the eastern boundary. Artificial discharge occurs as discharge to wells. Irrigation accounted for 96 percent of all use of water from the High Plains aquifer in the Oklahoma portion of the study area in 1992 and 93 percent in 1997. Total estimated water use in 1992 for the Oklahoma portion of the study area was 396,000 acre-feet and was about 3.2 million acre-feet for the entire study area. Since development of the aquifer, water levels have declined more than 100 feet in small areas of Texas County, Oklahoma, and more than 50 feet in areas of Cimarron County. Only a small area of Beaver County had declines of more than 10 feet, and Ellis County had rises of more than 10 feet. A flow model constructed using the MODFLOW computer code had 21,073 active cells in one layer and had a 6,000- foot grid in both the north-south and east-west directions. The model was used to simulate the period before major development of the aquifer and the period of development. The model was calibrated using observed conditions available as of 1998. The predevelopment-period model integrated data or estimates on the base of aquifer, hydraulic conductivity, streambed and drain conductances, and recharge from precipitation to calculate the predevelopment altitude of the water table, discharge to the rivers and streams, and other discharges. Hydraulic conductivity, recharge, and streambed conductance were varied during calibration so that the model produced a reasonable representation of the observed water table altitude and the estimated discharge to streams. Hydraulic conductivity was reduced in the area of salt dissolution in underlying Permianage rocks. Recharge from precipitation was estimated to be 4.0 percent of precipitation in greater recharge zones and 0.37 percent in lesser recharge zones. Within Oklahoma, the mean difference between water levels simulated by the model and measured water levels at 86 observation points is -2.8 feet, the mean absolute difference is 44.1 feet, and the root mean square difference is 52.0 feet. The simulated discharge is much larger than the estimated discharge for the Beaver River, is somewhat larger for Cimarron River and Wolf Creek, and is about the same for Crooked Creek. The development-period model added specific yield, pumpage, and recharge due to irrigation and dryland cultivation to simulate the period 1946 through 1997. During calibration, estimated specific yield was reduced by 15 percent in Oklahoma east of the Cimarron-Texas County line. Simulated recharge due to irrigation ranges from 24 percent for the 1940s and 1950s to 2 percent for the 1990s. Estimated recharge due to dryland cultivation is about 3.9 percent of precipitation. The mean difference between the simulated and observed waterlevel changes from predevelopment to 1998 at 162 observation points in Oklahoma is less than 0.01 foot, the mean absolute difference is 13.1 feet, and the root mean square difference is 17.9 feet. The model simulates 7.8 cubic feet per second discharge to the Beaver River above Optima Reservoir at the end of 1997, whereas the river was actually dry to this point by this time. The model simulates a decrease in discharge to the Cimarron River and Wolf Creek that appears to be reasonable. The sensitivity of the predevelopment-period model to changes in recharge and hydraulic conductivity was tested. Simulated water levels are sensitive to changes in both recharge and hydraulic conductivity. Simulated discharge to streams is sensitive to recharge but is insensitive to hydraulic conductivity. Recharge and hydraulic conductivity are closely related with respect to water levels but are not related with respect to discharge to streams. The sensitivity of the development-period model to changes in specific yield and recharge due to dryland cultivation was tested. The model appears more sensitive to specific yield, but the two inputs were not varied over the same range in percent change. The calibrated development-period model was used to simulate water-level changes from 1998 to 2020 using mean 1996-97 pumpage. The largest simulated water-level changes in Oklahoma occur in Texas County where water levels are simulated to decline 25 to 50 additional feet over a large area. Water levels also are simulated to decline 10 to 25 additional feet in two large areas of Cimarron County, two areas in Beaver County, and one area in Ellis County, all in Oklahoma. Water levels are simulated to decline more than 100 additional feet in several areas in Kansas and were simulated to decline 50 to 100 additional feet in several areas in Texas.

Colorado, Kansas, New Mexico, Oklahoma, Texas↗

USGS2018

Combining nutrient, productivity, and landscape-based regressions improves predictions of lake nutrients and provides insight into nutrient coupling at macroscales

Empirical nutrient models that describe lake nutrient, productivity, and water clarity relationships among lakes play a prominent role in limnology. Landscape-based regressions are also used to understand macroscale variability of lake nutrients, clarity, and productivity (hereafter referred to as nutrient-productivity). Predictions from both models are used to inform eutrophication management globally. To date, these two classes of models are generally conducted separately, which ignores the known dependencies among nutrient-productivity variables. We present a statistical model that integrates nutrient-productivity and landscape-based regressions—where lake nutrients, productivity, and clarity variables are modeled jointly. We fitted a joint nutrient-productivity model to over 7000 lakes with three nutrients (total phosphorus, total nitrogen, nitrate concentrations), chlorophyll a concentrations, and Secchi disk depth as response variables and landscape features as predictor variables. Because lakes in different regions respond to landscape features differently, we focused our analysis on two subregions with different dominant land uses, the agricultural Midwest and the forested Northeast U.S. Predictive performance was enhanced by modeling nutrient-productivity variables jointly. We also found strong evidence that nutrient-productivity variables were coupled, and that only nitrate may be decoupled from other nutrient-productivity variables in the forested region. We speculate that these regional differences may be related to differences in the strength of biogeochemical cycles and stoichiometric controls between these regions. Jointly modeling nutrient-productivity variables in lakes effectively integrates the two dominant approaches for studying lakes nutrient-productivity relationships and provides novel insight into macroscale patterns of the coupling of nutrients, chlorophyll, and water clarity in lakes.

Limnology and Oceanography↗

USGS2025

Greenhouse gas emissions from ditches in oil palm plantations on tropical peatlands in Malaysia

Tropical peatlands, which store 20% of global peat carbon, are increasingly threatened by conversion to alternative land-uses such as oil palm plantations, pulp wood plantations, crop growth or other economic activities. This transformation involves peatland drainage, which lowers water tables, exposes peat to oxygen, and alters greenhouse gas (GHG) emissions: increasing carbon dioxide (CO 2 ) and nitrous oxide (N 2 O) fluxes while reducing methane (CH 4 ) emissions from soils. However, drainage ditches created in the process may become significant sources of CH 4 due to anoxic conditions. This study quantified GHG fluxes from drainage ditches in Sarawak, Malaysia, through spatial sampling conducted during the daytime in the transitional period between the drier and wetter seasons using portable trace gas analyzers. Median fluxes were 0.19 g CH 4 m −2 d −1 , 17.1 g CO 2 m −2 d −1 , and − 0.12 mg N 2 O m −2 d −1 . Physical water parameters such as pH, oxygen concentration, temperature, and oxidation–reduction potential were found to be significant drivers of GHG fluxes. The median emissions from ditches in one hectare of land were 5.84 kg CO 2 ha −1 d −1 , 2.78 kg CH 4 as CO 2 eq ha −1 d −1 , and − 0.001 kg N 2 O as CO 2 eq ha −1 d −1 . These findings underscore the role of drainage ditches as CH 4 sources in tropical peatland agriculture, highlighting the need for further research into GHG management in these modified landscapes.

Scientific Reports↗