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USGS2025

Deformation mechanisms in quartz veins and shear zones elucidate the origin of gold mineralization at Pogo, Alaska

Pogo is a quartz vein hosted, ca. 8 Moz gold deposit. Although it has similarities to orogenic and magmatic-hydrothermal deposits, its origin remains enigmatic. Observations from surface exposures, underground workings, and drill core provide new constraints on quartz vein origins with implications for mineralization. Abundant, largely barren metamorphic segregation quartz veins are found throughout interior Alaska and share characteristics with mineralized quartz veins at Pogo. Pogo quartz veins show crystal plastic deformation fabrics consistent with greenschist to amphibolite facies metamorphism and a lack of internal shear. In contrast, gold in Pogo quartz veins occurs in brittle microfaults and fractures with sulphides such as arsenopyrite and pyrrhotite. Major and minor cataclastic shear zones also exist at Pogo. Cataclastic shear zones commonly cut the mineralized quartz veins and porphyroclasts are dominated by quartz with the same plastic deformation fabrics found in the major Pogo quartz veins. The porphyroclasts, and the carbonaceous clay-rich matrix they sit in, also contain gold indicating that the shear zones postdate quartz and earliest gold deposition. These observations suggest that competency contrasts between the quartz veins and their phyllosilicate-rich host rocks controlled transient permeability formed by late, preferential brittle deformation events localizing sulphide ± gold deposition.

Alaska↗

USGS2024

Spatial differences in soil nutrients along a hydrographic gradient on floodplains in Dongting Lake

The spatial heterogeneity of soil nutrients is crucial for the water bird and whole floodplain wetland ecosystem in large lakes, and it is influenced by the dramatic water level changes and sedimentation progress in West Dongting Lake (WDL). Soil samples were collected at various soil depths along the Yuan River and Li River that feed into WDL. The concentrations of soil total organic carbon (TOC), total nitrogen (TN), total phosphorus (TP), and soil grain size were tested. The stoichiometric ratios of C, N, P, and the mean value of soil grain size ( Mz ) were calculated. The differences of soil TOC, TN, TP and the stoichiometric ratio at different sites and soil depths were compared. Linear regression was used to explore the relationships of Mz and nutrient concentrations, and relationships between TOC, TN, and TP. Redundancy analysis was used to explore the relationship between soil nutrients, heavy metal concentrations, and plant community diversity. The results showed that the distributions of soil TOC, TN, and TP concentrations differed across regions in west Dongting Lake along the Yuan and Li Rivers. Total organic carbon concentration differed at different sedimentation depths. Soil grain size showed negative effect with soil TOC, TN, and TP concentrations in this region. Plant community diversity correlated positively with soil TOC and negatively with Hg. West Dongting Lake was N limited despite the high wet deposition of N. It could potentially be attributed to the insufficient presence of aerobic environments for microbes during intermittent flooding of the floodplain, coupled with feeble mineralization. This study can provide valuable insights for the conservation of water bird habitats and wetland ecosystems.

West Dongting Lake↗

USGS2023

Cursed? Why one does not simply add new data sets to supervised geothermal machine learning models

Recent advances in machine learning (ML) identifying areas favorable to hydrothermal systems indicate that the resolution of feature data remains a subject of necessary improvement before ML can reliably produce better models. Herein, we consider the value of adding new features or replacing other, low-value features with new input features in existing ML pipelines. Our previous work identified stress and seismicity as having less value than the other feature types (i.e., heat flow, distance to faults, and distance to magmatic activity) for the 2008 USGS hydrothermal energy assessment; hence, a fundamental question regards if the addition of new but partially correlated features will improve resulting models for hydrothermal favorability. Therefore, we add new maps for shear strain rate and dilation strain rate to fit logistic regression and XGBoost models, resulting in new 7-feature models that are compared to the old 5-feature models. Because these new features share a degree of correlation with the original relatively uninformative stress and seismicity features, we also consider replacement of the two lower-value features with the two new features, creating new 5-feature models. Adding the new features improves the predictive skill of the new 7-feature model over that of the old 5-feature model; albeit, that improvement is not statistically significant because the new features are correlated with the old features and, consequently, the new features do not present considerable new information. However, the new 5-feature XGBoost model has a statistically significant increase in predictive skill for known positives over the old 5-feature model at p = 0.06. This improved performance is due to the lower-dimensional feature space of the former than that of the latter. In higher-dimensional feature space, relationships between features and the presence or absence of hydrothermal systems are harder to discern (i.e., the 7-feature model likely suffers from the “curse of dimensionality”).

Geothermal Resources Council Transactions↗

USGS1999

Streamflow, base flow, and ground-water recharge in the Housatonic River basin, western Massachusetts and parts of eastern New York and northwestern Connecticut

Streamflows for selected flow durations from 1 to 99 percent and the August median streamflows were estimated for 11 long-term streamflow-gaging stations in and near the study area. Estimates of streamflow and associated standard errors were determined for selected flow durations from 50 to 99 percent and the August median streamflows for 21 low-flow partial-record stations and for selected flow durations from 1 to 99 percent and the August median streamflows for two partial-record stations and seven short-term discontinued streamflow-gaging stations. Median streamflows per square mile for the 10-, 50-, and 90-percent flow durations and the August median streamflows were 3.90, 1.01, 0.185, and 0.248 cubic feet per second per square mile. Streamflows per square mile at selected flow-duration discharges between 1 and 99 percent at the 41 stations were related to basin characteristics to explain differences in streamflow characteristics. Basin characteristics included basin elevations, extent of stratified-drift deposits, land use, aspect, and underlying bedrock geology types. Most streamflow differences were positively correlated to basin elevation differences, most likely because precipitation increases with elevation, and to stratified-drift deposits, which allow more precipitation to recharge the ground water and to discharge later than do till and bedrock deposits. Mean base flow was computed from continuous records of daily mean discharge at 11 long-term streamflow-gaging stations in and near the study area. Mean annual base flow ranged from 13.4 to 24.5 inches per year. Minimum annual base flow ranged from 45 to 72 percent of mean annual rates at the 11 long-term stations, and the ratio of base flow to streamflow (base-flow index) ranged from 0.55 to 0.80. Base-flow durations between 1 and 99 percent were calculated from streamflow records at the 11 long-term streamflow-gaging stations. Base flow accounted for 45.5 to 85.0 percent of total annual streamflow at the 1- and 99-percent flow durations. Ground-water-recharge rates were computed from continuous records of daily mean discharge at 11 long-term streamflow-gaging stations in and near the study area. Mean annual ground-water-recharge rates ranged from 17.5 to 22.4 inches per year at 10 of the 11 long-term stations. Mean annual ground-water-recharge rates ranged from 2 to 7 inches per year higher than base flow. Minimum annual ground-water-recharge rates ranged from 48 to 72 percent of mean annual ground-water-recharge rates. Mean annual potential ground-water recharge was estimated from monthly climatological data collected at six climatological stations in and near the study area. Mean potential ground-water recharge ranged from about 17.9 to 28.9 inches per year, with a median value of 22.6 inches per year. This median value compares well to that calculated by use of streamflow records at the 11 streamflow-gaging stations (20.0 inches per year). Streamflows per square mile for the 10-, 50-, and 90-percent flow durations at stations in and near the study area were similar to those computed for other unregulated long-term continuous streamflow-gaging stations in central and eastern Massachusetts. Base-flow and ground-water-recharge rates in the study area compared closely to results from other studies in southeastern Massachusetts and Rhode Island, which were based on the same computational methods.

Connecticut, Massachusetts, New York↗

USGS2026

Bathymetric and velocimetric surveys at highway bridges crossing the Missouri River near Kansas City, Missouri, August 8–9, 2023

Bathymetric and velocimetric data were collected by the U.S. Geological Survey, in cooperation with the Missouri Department of Transportation, near 8 bridge crossings of the Missouri River near Kansas City, Missouri, on August 8–9, 2023. A multibeam echosounder mapping system was used to obtain channel-bed elevations for river reaches that extended about 1,550 to 1,640 feet longitudinally and generally extended laterally across the active channel from bank to bank during low floodflow to nonflood conditions. These surveys provided the channel geometry and hydraulic conditions of the river at the time of the surveys and provided characteristics of scour holes, which may be useful in developing or verifying predictive guidelines or equations for computing potential scour depth. The data collected from the surveys may also be useful to the Missouri Department of Transportation as a record of low floodflow conditions in regards to the stability and integrity of the bridges with respect to bridge scour. Bathymetric data were collected around every in-channel pier. Scour holes were at most piers where bathymetry could be obtained, except for those piers on banks or surrounded by riprap. All the bridge sites in this study were surveyed and documented in previous studies. The average difference between the bathymetric surfaces ranged from 0.07 to 4.16 feet higher in 2023 than 2019, which indicates overall deposition between the survey dates, as might be expected based purely on streamflow at the time of the survey. However, the average difference between the bathymetric surfaces ranged from 1.44 feet higher to 1.88 feet lower in 2023 than 2015, which indicates a dynamic equilibrium of scour and deposition overall between those surveys, despite the lower flow conditions in 2023. Similarly, the average difference between the bathymetric surfaces ranged from 3.18 feet higher to 5.19 feet lower in 2023 than 2011, which indicates a relative equilibrium between scour and deposition overall, albeit the trend was toward scour as might be expected because of the substantial flood event in 2011. Riprap blankets and alignment to flow had a substantial effect on the size of the scour hole for a given pier. Piers that were partially or fully surrounded by riprap blankets had scour holes that were substantially smaller (to nonexistent) compared to piers with no rock or riprap and effectively mitigated the scour holes historically observed at these piers. Several of the structures had piers that were skewed to primary approach flow. At most of the structures, the scour hole was deeper and longer on the side of the pier with impinging flow than the leeward side, with some amount of deposition on the leeward side, as typically observed at piers skewed to approach flow.

Kansas, Missouri↗

USGS2026

Teach me how to pycap: A high-capacity well decision support tool using analytical solutions in Python

Regulatory agencies in humid temperate environments rely on timely evaluations of streamflow depletion and drawdown to protect aquatic ecosystems and existing water users. Numerical models offer detailed insights, but their complexity and time demands often preclude their practical use in rapid decision-making. We present pycap-dss, an open-source Python package that implements a suite of analytical solutions for estimating streamflow depletion and drawdown. The tool supports superposition of multiple wells and time-varying pumping, enabling cumulative impact assessments in situations with multiple wells and streams. The software is modular and extensible, allowing users to interchange solutions or add new analytical methods. A YAML-based configuration supports batch processing of multiple wells, and an optional AnalysisProject class facilitates integration with regulatory workflows. Rigorous unit and regression testing ensures computational reliability, and continuous integration supports ongoing development. We demonstrate deterministic examples of drawdown where multiple solutions are readily compared and streamflow depletion with multiple wells in the Central Sands region of Wisconsin. We also show the value of Monte Carlo analyses of streamflow depletion in the same Central Sands example, leveraging computational efficiency to evaluate the uncertainty of individual and cumulative streamflow depletion calculations from over 200 high-capacity wells.

Wisconsin↗

USGS1999

Environmental setting and water-quality issues in the lower Tennessee River basin

The goals of the National Water-Quality Assessment Program are to describe current water-quality conditions for a large part of the Nation's water resources, identify water-quality changes over time, and identify the primary natural and human factors that affect water quality. The lower Tennessee River Basin is one of 59 river basins selected for study. The water-quality assessment of the lower Tennessee River Basin study unit began in 1997. The lower Tennessee River Basin study unit encompasses an area of about 19,500 square miles and extends from Chattanooga, Tennessee, to Paducah, Kentucky. The study unit had a population of about 1.5 million people in 1995. The study unit was subdivided into subunits with relatively homogeneous geology and physiography. Subdivision of the study unit creates a framework to assess the effects of natural and cultural settings on water quality. Nine subunits were delineated in the study unit; their boundaries generally coincide with level III and level IV ecoregion boundaries. The nine subunits are the Coastal Plain, Transition, Western Highland Rim, Outer Nashville Basin, Inner Nashville Basin, Eastern Highland Rim, Plateau Escarpment and Valleys, Cumberland Plateau, and Valley and Ridge.The lower Tennessee River Basin consists of predominantly forest (51 percent) and agricultural land (40 percent). Activities related to agricultural land use, therefore, are the primary cultural factors likely to have a widespread effect on surface- and ground-water quality in the study unit. Inputs of total nitrogen and phosphorus from agricultural activities in 1992 were about 161,000 and 37,900 tons, respectively. About 3.7 million pounds (active ingredient) of pesticides was applied to crops in the lower Tennessee River Basin in 1992. State water-quality agencies identified nutrient enrichment and pathogens as water-quality issues affecting both surface and ground water in the lower Tennessee River Basin. Water-quality data collected by State and Federal agencies between 1980 and 1996 were summarized to characterize surface- and ground-water quality of the subunits with respect to these issues. Median concentrations of nitrogen species generally were less than 1 milligram per liter in surface and ground water in all subunits, and were highest throughout the subunits that had the largest percentages of agricultural land use. Median phosphorus concentrations also were less than 1 milligram per liter in all subunits. Phosphatic limestones present in two subunits had a larger effect on phosphorus concentrations in surface and ground water than did the amount of agricultural land use in these subunits. Median counts of fecal coliform were higher in surface water than in ground water in all subunits. The highest median counts in surface water were in the Valley and Ridge (7,500 colonies per 100 milliliters) and the Outer Nashville Basin subunits (5,000 colonies per 100 milliliters). Highest median counts in ground water were in the Inner and Outer Nashville Basin subunit. Natural setting likely has an important effect with respect to fecal contamination of surface and ground water in the lower Tennessee River Basin.

Alabama, Georgia, Kentucky, Mississippi, Tennessee↗

USGS2025

AAPG Energy and Minerals Division Tight Oil and Gas Committee Activities and Commodity Report for 2021-2022: Tuscaloosa Marine Shale, Gulf Coast basin, Louisiana and Mississippi

The Upper Cretaceous Tuscaloosa marine shale (TMS) potential production area encompasses 20.4 million acres across central Louisiana (LA), southern Mississippi (MS), southwestern Alabama (AL), and a small southwestern section of the Florida panhandle (Hackley et al., 2018). It remains a minor and largely undeveloped unconventional shale oil play with production from the TMS confined along the east-west LA-MS State boundary (Fig. 1). The mean undiscovered, technically recoverable resources in the TMS are estimated at 1.5 billion barrels of oil and 4.6 trillion cubic feet of gas (Hackley et al., 2018). Geochemical analyses of source rock solvent extracts and oil samples indicate that, in the play area, the TMS is the primary source of shale oil produced from the TMS as well as of accumulated oils in the underlying conventional reservoirs of the lower Tuscaloosa (Hackley et al., 2020). The API gravity of TMS oils ranges from approximately 34 to 46 degrees (Hackley et al., 2020; Croke et al., 2020).

AAPG Wiki↗

USGS2024

Insights on gas hydrate formation and growth within an interbedded sand reservoir from well logging at the Qiongdongnan Basin, South China Sea

Although variable well log resolution and its control on saturation estimation has been studied, it has not been directly applied to a specific location to explore the nature of gas hydrate within a sand reservoir. We applied in-situ measurements of resistivities, neutron porosity, and gamma ray at two sites in the Qiongdongnan Basin, South China Sea (QDN-W05–2021 and QDN-W08–2021) to investigate the reservoir parameters of a hydrate-bearing sand reservoir. Our results show that gas hydrate is distributed in 5 zones with a total thickness of 10.7 m and an average saturation of 69% at the QDN-W05–2021 site, while they are distributed in 2 zones with a total thickness of 4.3 m and an average saturation of 49% at the QDN-W08–2021 site. We found that variances in saturations estimated from lateral-extra deep button (RX), phase shift (P40H-P40L), and attenuation (A40H-A40L) resistivities within the laterally mapped continuous sand body were affected by the nature of gas hydrate occurrences. Results indicate gas hydrate forms and accumulates at the center of the sand layer and tends to be less or not present toward the top and base. Integrated with seismic data, the in-situ measurements provide insights in the evolution of a mushroom-shaped, hydrate-gas reservoir system. In the system, free gas is likely horizontally transported from the top-center of the gas chimney to the surrounding areas in the early stage dominated by a warm-gas environment, whereas hydrate forms in the opposite pathway starting from the surrounding areas in the following stage with temperature reducing. Our study suggests that high-resolution in-situ measurements not only are a tool to identify the physical properties, but also can be used to help explain the physical process of hydrate growth and accumulation.

Marine Geology↗

USGS2023

Hidden system identification: Basin modeling as a tool for examining sedimentary geothermal resource potential

Three-dimensional (3D) geologic and temperature models have been developed for the onshore U.S. Gulf Coast. The results from these models identify areas of moderate- to high-temperature (90°-150°C and >150°C; respectively) geothermal resources at depths <6 km. This modeling study addresses the fundamental challenge of predicting where opportune temperature and lithology coincide. Unlike traditional geothermal systems with surface expressions of hydrothermal circulation (e.g., hot springs, fumaroles, sinter), sedimentary geothermal systems (SGS) are generally hidden. Historically, simplified efforts to predict subsurface temperatures in sedimentary basins have focused on linear temperature extrapolation that does not consider the variable thermal properties of different lithologies or lithologic changes with depth (e.g., compaction, lithification). Therefore, the need to understand basin architecture and predict temperatures in 3D within SGS is paramount to identifying geothermal resources and determining economic feasibility. Basin modeling software has long been used to characterize the subsurface conditions of sedimentary basins, including temperature, in the pursuit of finding hydrocarbons. This tool can also be adapted to evaluate the potential of geothermal resources in a sedimentary basin by predicting the confluence of desirable temperatures and reservoir lithologies. In this work, PetroMod basin modeling software was used to create a regional geologic model of the onshore U.S. Gulf Coast, covering over 500,000 km 2 calibrated to temperature data from wells. Inputs include structural surfaces from commercial databases, lithology information derived from published literature, and corrected bottom-hole temperatures (BHT) from over 6,000 wells. The resulting 3D geologic model can be used to predict temperatures throughout the basin. Maps were exported showing the depth, depositional unit, and reservoir lithology at which temperatures of 90°C and 150°C were reached, revealing over 400,000 km 2 of moderate- to high-temperature resources at depths <6 km. These maps function as a first-order screening tool to identify areas where low-, moderate-, or high-grade resource potential may exist, based on temperature and if optimal reservoir lithologies or depositional units of interest are present. Depending on the success criteria of a project, the same maps can be exported for any isotherm or incorporate other 1407 Gardner and Birdwell subsurface properties. The methodology employed in this work can be applied in any sedimentary basin with available subsurface data. Further calibration incorporating other data, including pressure and porosity, can expand the utility of basin modeling for geothermal evaluations. Basin modeling is a powerful but underutilized tool for identifying prospective geothermal resources in sedimentary basins.

Conference Paper↗

USGS2025

An empirical Green’s function approach for isolating directivity effects in earthquake ground-motion amplitudes

In this study, we apply an empirical Green’s function (eGf) method within a ground‐motion modeling framework to mitigate trade‐offs between source, path, and site effects. Many physical processes contribute to spatial variations in observed ground motions, including earthquake radiation pattern, directivity, variable path attenuation, and site effects. Current nonergodic ground‐motion models use spatially varying coefficients for path and site effects, but they do not address trade‐offs with complex earthquake source effects. To quantify the influence of directivity on ground‐motion amplitudes, we use records from multiple smaller earthquakes with epicenters near that of a larger event. We use these small magnitude events as eGfs and estimate repeatable path and site effects at individual stations, assuming that the average adjustments are not controlled by directivity. We adjust residuals from the larger earthquake using the eGf terms, isolating effects related to the rupture. This method clearly enhances the observed broadband directivity observed in the 2022 M 5.1 and 2007 M 5.4 Alum Rock earthquake ground motions, reinforcing the conclusion that their ruptures were unilateral. For the 2004 M 6.0 Parkfield earthquake, we find a bilateral rupture model better fits the data because variations in rupture velocity, slip rate, and slip distribution seem to have a stronger effect on the ground motions than rupture direction alone. Applying eGf adjustments reduces the standard deviation of the rupture models over the three earthquakes by 32% on average and by up to 57% for the 2022 Alum Rock earthquake, confirming we have effectively removed repeatable effects related to the wave propagation path and site response. We propose a novel measure of the frequency‐dependent directivity amplification strength as the reduction in ground‐motion residual variability gained by fitting a directivity model; for the three earthquakes considered, this parameter varies between 25% and 75%, indicating that directivity can strongly influence ground motions and should be considered in ground‐motion modeling.

California↗

USGS2025

Remote single-station seismic monitoring of the July–October 2022 earthquake swarm at Tau volcano, American Samoa

From July to October 2022, a non-eruptive volcanic earthquake swarm occurred within ~15 km of Taʻū Island, located in eastern American Samoa. Felt reports from local residents were the only available information about the swarm when it started, as American Samoa lacked a seismic monitoring network. We developed a consistent single-station catalog for the entire swarm, using seismic data from the nearest station IU.AFI, ~250 km away. We applied the EQTransformer deep-learning model (Mousavi et al., 2020), automatically picking Pn and Sn arrivals on IU.AFI continuous data. We retained only events with Sn-Pn times of 22.5–25 seconds, consistent with the expected locations based on felt reports, then detected smaller swarm events with subsequent template-matching. This single-station catalog characterized the swarm’s onset and escalation to peak activity before a multi-agency field response team installed a local seismic network in mid-August 2022. This permanent seismic network captured the swarm’s decline. EQTransformer identified short S-P times on the first two locally deployed seismometers, both Raspberry Shake sensors, to constrain the swarm’s distance from Taʻū Island. Modern seismological processing methods, combined with basic observations such as felt reports, can quickly contribute useful information during an earthquake response in a poorly monitored region.

American Somoa↗

USGS1991

Wetland sedimentation and vegetation patterns near selected highway crossings in West Tennessee

Wetland sedimentation and vegetation patterns at 11 highway crossings in West Tennessee were studied from 1987 to 1989. The purpose of the study was to investigate potential adverse effects of highway crossings on wetlands. Sedimentation rates, determined from root-burial depths, were highly variable. Average rates offine-grained deposition ranged from 0.005 to 0.033 foot per year for stations in locally ponded areas and from -0.002 to 0.039 foot per year for stations in drained areas. Sedimentation rates upstream from highway crossings were not significantly different from downstream rates at 8 of the 11 study sites. Three study sites had significantly greater sedimentation rates downstream. Sand splays were observed downstream from bridges at most study sites. Vegetation patterns and tree growth appear most strongly related to hydropetiod, defined as the average length of time an area is covered by water each year. The influence of sedimentation on tree growth is difficult to separate from the influence of hydroperiod because areas with high sedimentation rates typically have long hydroperiods. Estimated hydroperiod increased no more than 1 percent because of backwater from the highway crossings at the 11 study sites, while the estimated average depth of flood-plain inundation increased by an average of 6 percent.

Tennessee↗

USGS2025

Groundwater budget for the surficial aquifer surrounding Lake Nokomis, Minneapolis, Minnesota

During prolonged periods of above-average precipitation, rising groundwater levels have the potential to cause damage to and interfere with underground infrastructure and building foundations. To understand the relations between precipitation and groundwater in the vicinity of Lake Nokomis, the U.S. Geological Survey, in collaboration with the University of Minnesota, quantified five components of the groundwater budget: groundwater recharge, change in surficial aquifer storage, surficial aquifer groundwater discharge to Lake Nokomis, groundwater evapotranspiration, and groundwater discharge to underlying bedrock aquifers. Field data, geologic records, and empirical calculation methods were used to quantify groundwater budget components for April 2023 through April 2024. Lake water budget data indicate that Lake Nokomis is a flowthrough system during periods with no outflow through the weir, with groundwater inputs equal to outputs. Roughly 40 percent of precipitation that fell in the study area was added to the surficial aquifer as recharge. Uncertainty in the vertical hydraulic conductivity resulted in wide-ranging estimates (spanning three orders of magnitude) of water discharging from the surficial aquifer to the underlying bedrock aquifer. Drought conditions persisted for the duration of this study and were not representative of the conditions that motivated this study. This study is a start towards understanding relations between precipitation, Lake Nokomis levels, and groundwater levels that could affect local underground infrastructure.

Minnesota↗

USGS2025

Multidecadal change in pesticide concentrations relative to human health benchmarks in the Nation’s groundwater

Groundwater-quality trend assessments identify aquifers that are responding to changes in pesticide use and the compounds that may pose a threat to water availability. The U.S. Geological Survey has been monitoring pesticide concentrations in groundwater for 25 principal aquifers across the conterminous United States since 1993. The groundwater well locations represent a range of soils, climate, and landforms. The wells are used to monitor groundwater underlying selected agricultural and urban settings and groundwater used for domestic supply. This study examined changes in relative concentrations, defined here as the percentage of wells with pesticide concentrations exceeding a human health benchmark (HHB). HHBs used in this report are legally enforceable drinking-water standards and nonenforceable drinking water levels. Relative pesticide concentration increases may lead to decreased water availability, as restrictions may be put in place for groundwater used as a drinking-water source. This study focused on concentration changes in 22 pesticides that were included in laboratory analysis from 1993 to 2023. The analysis and interpretation of these pesticide concentrations in groundwater have been separated into approximate decadal intervals (decade 1 (1993–2001), decade 2 (2002–12), and decade 3 (2013–22). For one pesticide, 1,2-dibromo-3-chloropropane (DBCP), concentration data were also collected in decade 4 (2023–onward). Atrazine, deethylatrazine, alachlor, prometon, and simazine were 5 pesticides detected at moderate concentrations (greater than 10 percent of the HHB but less than or equal to the HHB). The percentage of wells that had groundwater pesticide concentrations in the moderate concentration category decreased from 7 percent in decade 1 to 2 percent in decade 3. The agricultural networks had the highest percentages of wells with moderate concentrations, and these percentages decreased from 13 percent in decade 1 to 4 percent in decade 3. Moderate concentrations in the urban networks decreased between decades 1 and 2 from 4 percent to 0 percent. No moderate concentrations occurred in the urban networks in decade 3. The percentage of wells with moderate concentrations in the domestic supply networks (1 percent) was the lowest of all the network types and did not change across the three decades. Moderate atrazine or deethylatrazine concentrations occurred across all three decades in aggregated ecoregions representing similar soils, climate, and landforms in the Semiarid West, Midcontinent, and Northeastern United States. Moderate concentrations of prometon, alachlor, and simazine also occurred in the Midcontinent, Arid West, Northeast, South Atlantic Gulf, and Semiarid West regions, but the moderate concentrations did not persist across all three decades. DBCP was the only pesticide that exceeded its respective HHB, and the exceedances occurred across all four decades. In this report, the DBCP analysis was limited to one well network in the Central Valley, California. Agricultural use of DBCP was suspended in 1977. Forty-five years after being banned, DBCP concentrations were greater than the maximum contaminant level of 2 micrograms per liter (μg/L), but the number of exceedances decreased from 50 percent to 15 percent of the samples between 1993 and 2023. This assessment of decadal groundwater pesticide concentrations provides a characterization of changes in water availability because of pesticide contamination in areas where groundwater is used as a drinking-water source. The results highlight the importance of continued long-term monitoring and assessment of groundwater pesticides to identify locations and specific compounds that may pose a potential risk to human health.

continental United States↗

USGS2026

Seasonal migrations and other movements

In the past 25 years new information has been obtained on the migrations and movements of mountain sheep (bighorn [Ovis canadensis], thinhorn [Ovis dalli]). This chapter provides a comprehensive overview of mountain sheep migration and other movements across their broad distribution in western North America. Across the range of mountain sheep, migrations and other seasonal movements define a complex movement portfolio that relates to and supports all aspects of mountain sheep ecology. Bighorn and thinhorn species have examples of migratory behaviors that span the continuum between annual residents and long-distance migrants. Migratory behaviors can be characterized as low- or high-elevation residents; elevational migrations and other variants; and geographic migrants. Native populations that have been extant on the landscape without notable human intervention have greater migratory propensity and more diverse migratory portfolios due to the maintenance of migration through cultural learning and social transmission. Restored and augmented populations, where the population-level knowledge of migration has been lost or greatly reduced, are largely nonmigratory, although translocations show some ability to restore short-distance elevational migrations. Seasonal spring and fall migrations are less common in desert bighorn sheep (O. canadensis spp.) or bighorn sheep living in canyon or prairie breaks landscapes. Mineral lick visitation is important and common across the range of mountain sheep. Managing for migratory diversity can help to sustain migratory behavior in the face of climate change and other anthropogenic pressures, which can limit landscape connectivity between seasonal ranges or alter the spatiotemporal dynamics of regional phenology with cascading effects to other biotic and abiotic interactions such as the need to balance forage and predation risk or the spatial refugia with increased temperatures.

Book chapter↗

USGS2025

Groundwater flowpath characteristics drive variability in per- and polyfluoroalkyl substances (PFAS) loading across a stream-wetland system

Groundwater-dependent ecosystems in areas with industrial land use are at risk of exposure to a PFAS chemicals. We investigated one such system with several known PFAS source areas, where high and low permeability sediments (glacial) coupled with groundwater-lake and groundwater/surface-water interactions created complex ‘source to seep’ dynamics. Using heat-tracing and chemical methods, numerous preferential groundwater discharge zones were identified and sampled across the upper Quashnet River stream-wetland system in Mashpee, MA, USA, downgradient of Joint Base Cape Cod (JBCC). Surface-water and groundwater samples were analyzed for 40 PFAS compounds between March and October 2022. Samples were collected from groundwater seeps identified as preferential discharge points (PDPs), wells upgradient of the stream-wetland system, contributing flow-through kettle lakes, and along Quashnet River surface-waters. PFAS from sampled waters contained perfluorinated carboxylates (PFPea, PFHxA, PFNA), perfluorinated sulfonates (PFBS, PFPeS, PFHxS, PFOS), fluorotelomer sulfonates (6:2, 8:2 FtS), and perfluoroalkyl sulfonamides (PFOSA). Samples from PDPs and wells had measured PFAS concentrations ranging from non-detect to 4677 ng/L ng/L (mean = 418 ng/L, std. = 709 ng/L), and a range of deuterium excess values (3.2 to 15.9 per mil) indicative of varying degrees of groundwater-lake interaction prior to groundwater flowpath emergence at PDPs. Correlations ( p < 0.01) between deuterium excess, %PFAS precursors, and terminal PFAS compounds highlighted potential precursor transformations associated with lake-groundwater exchange along flowpaths sourcing PDPs. However, some seepages had higher total PFAS concentrations (>1000 ng/L) than upgradient kettle lakes despite showing lake (evaporative) isotopic signatures, indicating the potential for groundwater flowpath convergence at wetland discharge zones and the influence of lakebed PFAS precursor reactions. Results from these synoptic surveys address gaps in the existing PFAS literature by demonstrating the importance of subsurface fate and transport on PFAS compound concentrations and mass loading in preferential groundwater discharge zones.

Massachusetts↗

USGS2025

Hydrogeology, water budget, and simulated groundwater availability in the Salt Fork Arkansas River and Chikaskia River alluvial aquifers, northern Oklahoma, 1980–2020

The 1973 Oklahoma Groundwater Law (Oklahoma Statute §82–1020.5) requires that the Oklahoma Water Resources Board conduct hydrologic investigations of the State’s aquifers to determine the maximum annual yield for each groundwater basin. The U.S. Geological Survey, in cooperation with the Oklahoma Water Resources Board, conducted an updated hydrologic investigation of the Salt Fork Arkansas River and Chikaskia River alluvial aquifers in northern Oklahoma for the study period spanning 1980–2020 and evaluated the simulated effects of potential groundwater withdrawals on groundwater flow and availability in the Salt Fork Arkansas River alluvial aquifer. A hydrogeologic framework and conceptual model were developed to guide the development of a numerical model. Three groundwater-availability scenarios were evaluated by using the calibrated numerical model, which was focused on the Salt Fork Arkansas River alluvial aquifer. These scenarios were used to (1) estimate equal-proportionate-share groundwater withdrawal rates, (2) quantify the potential effects of projected well withdrawals on groundwater storage over a 50-year period, and (3) simulate the potential effects of a hypothetical 10-year drought. The 20-, 40-, and 50-year equal-proportionate-share groundwater withdrawal rates for the Salt Fork Arkansas River alluvial aquifer under normal recharge conditions were about 0.63, 0.58, and 0.57 acre-foot per acre per year, respectively. Projected 50-year groundwater withdrawal scenarios were used to simulate the effects of modified well withdrawal rates. Because well withdrawals were less than 2 percent of the calibrated numerical-model water budget, changes to the well groundwater withdrawal rates had little effect on simulated Salt Fork Arkansas River base flows and groundwater storage in the Salt Fork Arkansas River alluvial aquifer. A hypothetical 10-year drought scenario was used to simulate the potential effects of a prolonged period of reduced recharge on groundwater storage. Groundwater storage at the end of the hypothetical drought period was 14.5 percent less than the groundwater storage of the calibrated numerical model without the simulated drought.

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