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USGS2026

Simulation of groundwater flow in the Silurian aquifer, eastern Iowa, 2020–45

The Silurian aquifer is an important water source for municipalities, industry, and rural households and communities in eastern Iowa, including Johnson County. Increasing demand for groundwater from the aquifer indicated that analytical tools may be beneficial to quantify groundwater resources and inform water-management decisions for the aquifer. The U.S. Geological Survey, in cooperation with the Johnson County Board of Supervisors, developed conceptual and numerical groundwater models to simulate water levels in the Silurian aquifer, determine groundwater budgets, and forecast changes in groundwater levels through 2045. A MODFLOW numerical model was constructed to match water levels for 2020 through 2022. Model performance was assessed by comparing simulated and observed water-level hydrographs at several pumping and monitoring wells. Hydrograph comparison indicates that the model simulates water levels accurately at monitoring wells that are not near areas of pumping and generally overpredicts water levels near pumping wells, while accurately simulating the drawdown trend over time at pumping wells. This transient model framework was then used to predict water levels through 2045 in a scenario of moderate drought and increased groundwater withdrawals. Results from the predictive model indicate as much as 13 meters of additional drawdown in 2045 from 2020 water levels in the area of pumping wells.

Iowa↗

USGS2025

Wet meadow regeneration through restoration of biophysical feedbacks

Wet meadows are globally significant ecosystems that provide critical hydrological, ecological, and biogeochemical functions, yet their extent has declined dramatically due to land use changes and hydrologic alteration. These sedge-dominated wetlands exist at the drier end of the wetland gradient, maintained by shallow groundwater and periodic inundation. This paper is a global synthesis of the ecological, geomorphic, and hydrological dynamics of wet meadows, with an emphasis on alluvial systems, to inform effective restoration strategies. We compare wet meadows to other wetlands, classify them into palustrine, lacustrine, and alluvial types, then focus on alluvial wet meadows and discuss how their formation and persistence depend on ground and surface water interactions, sediment deposition and flow obstructions, all mediated by biological processes. In particular, we highlight the role of hydric graminoids in resisting erosion and maintaining soil cohesion, how beaver promote meadow persistence, and the significance of wet meadows as carbon sinks. We also present stratigraphic evidence demonstrating that incision, often triggered by anthropogenic activity or changing climate, is the primary mechanism of alluvial wet meadow degradation, resulting in water table decline and shifts in vegetation composition. Restoration requires reversing these incisional processes through techniques that elevate water tables, disperse flow and retain sediment—methods traditionally associated with either soil conservation or stream restoration. These include nature-based solutions that create obstructions such as beaver dams and their analogues, rock and wood-based obstructions and incision trench or gully filling and grading. Given their multifunctional value—including but not limited to flood attenuation, biodiversity support, and carbon sequestration—wet meadows warrant a focused restoration framework. This review advocates for a valley-floor scale restoration paradigm that integrates hydrological reconnection, sediment retention, and biological reinforcement to ensure long-term resilience of these systems in the face of changing climate and land use pressures.

Frontiers in Environmental Science↗

USGS2024

Generalized potentiometric maps of the Fort Union, Hell Creek, and Fox Hills aquifers within the Standing Rock Reservation

Generalized potentiometric surfaces of the Fort Union, Hell Creek, and Fox Hills aquifers were constructed to assess the groundwater resources of the Standing Rock Reservation. Additionally, this information can provide water managers with tools and data to effectively manage water resources in the future. Previous studies that mapped the geology and hydrogeology of the area at differing scales were used to confirm in which aquifer the study wells were completed. Water-level data from wells are provided by the U.S. Geological Survey Groundwater System Inventory database, the South Dakota Department of Agriculture and Natural Resources, and the North Dakota Department of Water Resources. Hydrographs were constructed for five selected observation wells to evaluate historical water-level fluctuations and trends. Hydrographs for the Hell Creek aquifer showed a flat trend with a rise in 2020. Hydrographs for the deeper Fox Hills aquifer showed that water levels fluctuated in response to climatic conditions and demonstrated an increasing trend in water-level elevations starting in 2010. Hydrographs were not constructed for any wells completed in the Fort Union Formation because none of the wells had continuous long-term measurements. Generalized potentiometric surfaces, constructed from interpolating water-level elevations, gave insight into groundwater flow directions. Groundwater in the Fort Union aquifer likely flows radially outward from the northwest part of the study area to the northeast and south-southeast parts. Groundwater in the Hell Creek aquifer generally flows from higher elevations in the northwest towards lower areas, where surface-water tributaries have incised into the aquifer. Groundwater in the Fox Hills aquifer likely flows from higher elevations in the west, southwest, and central parts of the study area towards the valleys of the Grand River and Missouri River. Most wells used for constructing potentiometric maps had only one recorded water-level measurement from drillers at the time of well construction. These measurements are often subject to error because the well is still recovering and because of spatial limitations of data availability. Also, because single water-level measurements were recorded at different points in time, additional uncertainty is introduced by fluctuating climatic conditions effect on water levels. Potentiometric map interpretation limitations are a result of areas with sparse data. Limitations also arise from potentiometric surfaces generalizing a complex and dynamic hydrogeologic system; however, the generalized potentiometric surface maps can be used to assist water managers and can help prioritize locations for future monitoring in areas with high uncertainty from sparse existing data.

North Dakota, South Dakota↗

USGS2025

Status of water-level altitudes and long-term and short-term water-level changes in the Chicot and Evangeline (undifferentiated) and Jasper aquifers, greater Houston area, Texas, 2024

Since the early 1900s, groundwater withdrawn from the primary aquifers that compose the Gulf Coast aquifer system—the Chicot, Evangeline, and Jasper aquifers—has been an important source of water in the greater Houston area, Texas. This report, prepared by the U.S. Geological Survey in cooperation with the Harris-Galveston Subsidence District, City of Houston, Fort Bend Subsidence District, Lone Star Groundwater Conservation District, and Brazoria County Groundwater Conservation District, is one in an annual series of reports depicting the status of water-level altitudes and water-level changes in these aquifers in the greater Houston area. In this report, the Chicot and Evangeline aquifers are treated as a single aquifer for the purposes of providing annual assessments of regional-scale water-level altitudes and water-level changes over time. In 2024, shaded depictions of estimated water-level altitudes for the Chicot and Evangeline aquifers (undifferentiated) ranged from about 301 feet (ft) below the North American Vertical Datum of 1988 (NAVD 88) to about 184 ft above NAVD 88. The largest decline in water-level altitudes depicted by the 1977–2024 long-term water-level-change map was in south-central Montgomery County. In comparison, the 1990–2024 long-term water-level-change map depicts the largest declines in water-level altitudes in an area northwest of The Woodlands and in an area of northern Waller County. The largest rise in water-level altitudes for 1977–2024 is depicted in an area of east-central Harris County, whereas the largest rise in water-level altitudes for 1990–2024 is depicted in an area of central Harris County. The 5-year short-term water-level-change map depicts the largest declines in several parts of the study area, but these declines are concentrated primarily in northern Fort Bend County, southwestern Harris County, and south-central Montgomery County. The largest rise for 2019–24 is depicted at a well in northern Fort Bend County. The 1-year short-term water-level-change map depicts the largest declines at a well in northern Fort Bend County and a well in west-central Harris County. The largest rise for 2023–24 is depicted at a well in east-central Fort Bend County. In 2024, shaded depictions of estimated water-level altitudes for the Jasper aquifer ranged from about 255 ft below NAVD 88 to about 321 ft above NAVD 88. The 2000–24 long-term water-level-change map depicts the largest water-level decline in an area of central San Jacinto County; the largest rise is depicted in an area of central Grimes County. The 5-year short-term water-level-change map depicts the largest declines across parts of central and southern Montgomery County and at one well in north-central Harris County. The largest rise for 2019–24 is depicted at a well centered on the Montgomery-Grimes County line. The 1-year short-term water-level-change map depicts the largest declines at two wells in south-central Montgomery County and one well in northwestern Montgomery County on the west side of Lake Conroe. The largest rises during 2023–24 are depicted at one well in northwestern Montgomery County and one well in south-central Montgomery County.

Texas↗

USGS2025

Assessment of channel morphology, hydraulics, and bedload transport along the Siletz River, western Oregon

Significant Findings Chinook salmon ( Oncorhynchus tshawytscha ) and Pacific lamprey ( Entosphenus tridentatus ) are native, anadromous fish species in the Siletz River Basin, western Oregon, that face many threats to their survival in freshwater and the ocean. The Confederated Tribes of Siletz Indians of Oregon seek to mitigate freshwater threats to Chinook salmon and Pacific lamprey, where possible, with habitat conservation and restoration efforts. This study was conducted to assist the Confederated Tribes of Siletz Indians of Oregon in documenting and understanding the hydrogeomorphic processes shaping present-day habitat conditions and assessing future habitat implications for Chinook salmon and Pacific lamprey along the main-stem Siletz River. As such, this study focused on understanding geomorphic processes and patterns of channel change, including lateral and vertical adjustments in channel position and changes in bed-material sediment (sands, gravels, and cobbles that mantle the channel bed), which collectively determine overall patterns of channel morphology and fluvial habitats. Objective One was to evaluate lateral changes in channel position, vertical changes in bed elevation, and longitudinal patterns in bed-material particle size along the Siletz River using detailed channel maps developed from aerial photographs collected from 1939 to 2016, long-term records of stage and discharge collected by the U.S. Geological Survey (USGS) near the City of Siletz, and sediment particle size data. Objective Two was to assess hydraulic conditions using one- and two-dimensional hydraulic models and transport capacity of bed-material sediment using bedload transport models and sediment particle size data for a range of discharge conditions. Objective Three was to identify potential burrowing habitat for lamprey larvae (PBH) along the Siletz River network and provide insights in local factors influencing PBH along the main-stem Siletz River. The overall findings are synthesized to describe habitat implications for Chinook salmon and Pacific lamprey under present-day and future conditions. Results of Objective One, an evaluation of changes in channel position and bed elevations and longitudinal patterns in bed-material particle size along the Siletz River, include the following From 1939 to 2016, channel planform and the mapped area of gravel bars did not change considerably along the 97.2-kilometers (km) of Siletz River between Elk Creek and Millport Slough, except for in short sections generally less than 1 km long. This inherent lateral channel stability results from the resistant bedrock and terraces that bound most of the channel and limit lateral changes in channel position. Intermittent sections along the study reach where the active channel widened at channel bends displayed noticeable planform changes and increases in mapped bar area. From water year (WY; a 12-month period from October 1 through September 30 and named for the year in which it ends) 1906 to 2021, changes in the stage-discharge relation interpreted as rising and lowering channel bed levels were observed at the USGS streamgage 14305500 (Siletz River at Siletz, OR) in response to floods (such as high flows in February 1996 and January 2002 that exceeded 0.1 and 0.667 annual exceedance probabilities [AEP] events, respectively). However, the rating curve representing the stage-discharge relation did not change in response to high-magnitude floods between 2007 and 2021. Along the approximately 54-km of the Siletz River between Moonshine Park and the Bulls Bag area, surficial particle distributions varied considerably between sampling sites in response to changes in channel width and gradient, sediment inputs from tributaries, and basin geology. Despite this variability, median particle sizes tended to decrease in size in the downstream direction over the 54 km. Results of Objective Two, an evaluation of hydraulic and bedload transport conditions along the Siletz River, include the following The most substantial increases in maximum and mean water velocity and bedload sediment transport capacity occurred at events between the 0.995 and 0.50 AEPs. Events of these magnitudes occur approximately every 1–2 years. Smaller events (0.995 AEP) are generally contained by the banks of the main channel, whereas larger events (0.50 AEP) generally spill over the banks and inundate high-elevation bar and low-elevation floodplain surfaces. Multiple smaller floods within a WY that exceed the 0.995 and 0.50 AEPs (such as in WY 1996) can transport as much or more bed-material sediment than a single, higher magnitude event (such as the maximum event recorded in WY 2000 with an estimated AEP of around 0.002). Bedload transport capacity generally exceeds sediment supply (greater than 2 millimeters [mm]) for most of the study area from Wildcat Creek to the City of Siletz as evidenced by substantial in-channel bedrock. Despite overall conditions of limited sediment supply, transport capacity still varies considerably within and between years with discharge magnitude and spatially in relation to local hydraulics imposed by bedrock, channel morphology, and human infrastructure (such as bridges). Results of Objective Three, an analysis of PBH for lamprey larvae, include the following About 28 percent of the Siletz River network meets the mean annual suspended sediment loads and channel slope criteria for PBH. Along the main-stem Siletz River, in-channel bedrock outcrops and high transport capacity are expected to further constrain PBH. Together, these results suggest that most of the Siletz River between Wildcat Creek and the City of Siletz has had only modest vertical and lateral change between the 1930s and 2010s because of the bedrock in and along the main channel and the river’s relatively high transport capacity relative to bed-material sediment supply. However, localized sections of the Siletz River where the active channel widens, particularly at channel bends, exhibited some change in channel planform and the locations and area of gravel bars. In the future, moderate increases in autumn-winter discharge may not result in substantial changes in coarse gravel bars along the Siletz River but may result in selective transport of finer bed-material sediment (gravel, sands, and silts) that provide spawning habitats for Chinook salmon and Pacific lamprey and burrowing habitats for lamprey larvae. Assuming no substantial changes in bed-material sediment supply, increased bedload transport capacity may cause frequent entrainment of lamprey larvae that are burrowed in coarse sand deposits, suspension and downstream transport of salmon eggs incubating in gravels, and reductions in the areas of spawning gravels for Chinook salmon and Pacific lamprey. Exact implications of current and future discharge conditions for these species along the Siletz River depends on many factors, including sediment supply, local hydraulics, and the timing of flood events relative to fish life stages.

Oregon↗

USGS2025

Relationship of atmospheric nitrogen deposition to soil nitrogen cycling along an elevation gradient in the Colorado Front Range

Microbial processing of atmospheric nitrogen (N) deposition regulates the retention and mobilization of N in soils, with important implications for water quality. Understanding the links between N deposition, microbial communities, N transformations, and water quality is critical as N deposition shifts toward reduced N and remains persistently high in many regions. Here, we investigated these connections along an elevation transect in the Colorado Front Range. Although rates of N deposition and pools of extractable N increased down the elevation transect, soil microbial communities and N transformation rates did not follow clear elevational patterns. The subalpine microbial community was distinct, corresponding to a high C:N ratio and low pH, while the microbial communities at the lower elevation sites were all very similar. Net nitrification, mineralization, and nitrification potential rates were highest at the Plains (1,700 m) and Montane (2,527 m) sites, suggesting that these ecosystems mobilize N. In contrast, the net immobilization of N observed at the Foothills (1,978 m) and Subalpine (3,015 m) sites suggests that these ecosystems retain N deposition. The contrast in N transformation rates between the plains and foothills, both of which receive elevated N deposition, may be due to spatial heterogeneity not captured in this study and warrants further investigation. Stream N concentrations from the subalpine to the foothills were consistently low, indicating that these soils are currently able to process and retain N deposition, but this may be disrupted if drought, wildfire, or land-use change alter the ability of the soils to retain N.

Colorado↗

USGS2026

Creation of aerial camera system boresight installations in Bangor, Maine; Monroe, Louisiana; and Bassville Park, Florida

Aerial camera systems rely on boresights for defining internal and external metrics. The U.S. Fish and Wildlife Service’s Migratory Bird Surveys Branch required boresights to calibrate their camera systems for creating georeferenced imagery that can then be used in geographic information systems. The U.S. Geological Survey created high-accuracy boresight installations in Bangor, Maine, in July 2024; Monroe, Louisiana, in September 2024; and Bassville Park, Florida, in January 2025 to provide this metric-defining capacity to the U.S. Fish and Wildlife Service. This U.S. Geological Survey Data Report details the methods and results of the boresight installation process and provides camera operators with the data needed to use each of the installations.

Florida, Louisiana, Maine↗

USGS2024

Methodology for inclusion of produced and stored carbon dioxide in the U.S. Geological Survey Federal lands greenhouse gas inventory

The U.S. Geological Survey (USGS) has developed two new carbon dioxide (CO2) emissions and sequestration accounting methods for use in future reports. The first method is a Federal lease-produced CO2 emissions calculation for an update of the report, “Federal Lands Greenhouse Gas Emissions and Sequestration in the United States.” The methodology to incorporate Federal lease CO2 production emissions into the updated report relies on CO2 sales royalty data from the Office of Natural Resources Revenue (ONRR). The end usage points for the gas include enhanced oil recovery with CO2 (CO2-EOR), food and beverage, and chemical production. CO2-EOR is the main end point for natural CO2 production in the United States; it accounted for 94% of usage in 2022 [1]. Federal lands emissions from this sector are estimated at 460 metric tons of CO2 in 2022, a very small amount relative to most other Federal lands emissions sector estimates. The second new method, planned for a separate report, is a calculation of the geologic storage of CO2 on Federal lands. The second method estimates the CO2 stored under Federal surface lands and documents Federal climate change mitigation efforts. Currently, there is no storage of CO2 at an industrial level on Federal lands, however multiple proposals and projects are planned. This method was developed on non-Federal lands datasets in an effort to prepare for when these activities on Federal lands will require accounting. National estimates for CO2 geologic storage using this method, but without a Federal lands filtering step, totaled 8.0 million metric tons (Mt) in 2022. The two methods described here are new benchmark methods in a collection of accounting procedures to document the current state of greenhouse gas emissions and their storage on Federal lands. These benchmarks can then be used to measure any subsequent changes in emissions from or carbon storage beneath Federal lands. While the magnitude of the values is currently non-existent to small, emissions mitigation goals established by decision makers indicate that these values will grow, and their documentation will take on greater value and use.

continental United States↗

USGS2024

A journey to the center of the USGS National Strong-motion Project processing and beyond

The United States Geological Survey (USGS) National Strong Motion Project (NSMP) has the primary U.S. government responsibility to acquire, process, and disseminate significant strong-motion earthquake ground motion records measured at surficial free-field stations, structures (buildings, dams, and bridges, and geotechnical arrays to the earthquake engineering community. As a result of the deployment of modern seismic instrumentation and growth of tools such as web-services, earthquake data from U.S. and international seismic networks are more accessible than ever. Our mission is to provide raw and processed strong-motion waveforms with PGA values greater than 0.1%g for M3.0 earthquakes and larger in California and M4.0 and larger within the conterminous US, Hawaii, Puerto Rico, and Alaska. Datasets of interest to the engineering and geophysics communities, such as event sequences in areas of induced seismicity and significant global events, are also processed and posted at the Center for Engineering Strong Motion Data (CESMD) at strongmotioncenter.org when available through collaboration with the international strong-motion data community. Here we outline (1) the NSMP’s current workflow to acquire, process, and distribute data at CESMD; (2) our new endeavours and collaborations focusing on comparison and integration of waveform processing software, development of techniques for metadata quality checks before and after earthquakes, and construction of a dynamic site characterization repository; and (3) our topics for possible collaboration topics across the global strong-motion community.

Conference Paper↗

USGS2000

Regional evaluation of evapotranspiration in the Everglades

Nine sites in the Florida Everglades were selected and instrumented for collection of data necessary for evapotranspiration-determination using the Bowen-ratio energy-budget method. The sites were selected to represent the sawgrass or cattail marshes, wet prairie, and open-water areas that constitute most of the natural Everglades system. At each site, measurements necessary for evapotranspiration (ET) calculation and modeling were automatically made and stored on-site at 15- or 30-minute intervals. Data collected included air temperature and humidity at two heights, wind speed and direction, incoming solar radiation, net solar radiation, water level and temperature, soil moisture content, soil temperature, soil heat flux, and rainfall. Data summarized in this report were collected from January 1996 through December 1997, and the development of site-specific and regional models of ET for this period is described. Latent heat flux is the energy flux density equivalent of the ET rate. Modified Priestley-Taylor models of latent heat flux as a function of selected independent variables were developed at each site. These models were used to fill in periods of missing latent heat flux measurement, and to develop regional models of the entire Everglades region. The regional models may be used to estimate ET in wet prairie, sawgrass or cattail marsh, and open-water portions of the natural Everglades system. The models are not applicable to forested areas or to the brackish areas adjacent to Florida Bay. Two types of regional models were developed. One type of model uses measurements of available energy at a site, together with incoming solar energy and water depth, to estimate hourly ET. This available-energy model requires site data for net radiation, water heat storage, and soil heat flux, as well as data for incoming solar radiation and water depth. The other type of model requires only incoming solar energy, air temperature, and water depth data to provide estimates of hourly ET. The second model thus uses data that are more readily available than the data required for the available-energy model. Computed ET mean annual totals for all nine sites for the 1996-97 period ranged from 42.4 inches per year at a site where the water level is below land surface for several months each year to 57.4 inches per year at an open-water site with no emergent vegetation. Although the density of photosynthetically-active plant leaves has been shown to relate directly to ET in some studies, it does not appear to relate directly to ET in the Everglades, based on comparison of annual ET data with leaf-area index, defined as the Normalized Difference Vegetation Index (NDVI), data from satellite imagery. NDVI and ET appear to be inversely related in the Everglades. The greatest ET rates occurred at open-water sites where the NDVI data indicated the lowest leaf-area index. Among the remaining vegetated sites, there is no clear relation between ET and NDVI, though the highest ET rate corresponded to the lowest NDVI and one of the lowest ET rates corresponded to the highest NDVI value. The variation in ET follows a seasonal pattern, with lowest monthly ET totals occurring in December through February, and highest ET occurring in May through August. The greatest range in monthly ET among all nine sites for the 2-year period occurred at site 3: from 1.81 inches in December 1997 to 6.84 inches in July 1996. A study to compare the Bowen-ratio/energy balance method of ET measurement with the eddy-correlation method was done at one site from June 22, 1998, through September 28, 1998. This comparison indicated that both methods gave comparable values of the Bowen ratio, but there was a considerable difference in available energy measured by the two methods. The mean of all 30-minute measured turbulent heat fluxes from the eddy-correlation apparatus for June 22 through September 29, 1998, was 137.4 watts per square meter, and the mean of the corresponding measured energy was 163.6 watts per square meter, or about 20 percent greater. The disagreement in mean energy fluxes measured by the two methods is problematical and is not fully understood. Although the difference seems to be related to friction velocity, and is practically non-existent at values of friction velocity greater than 0.3 meter per second, the "correctness" of either method cannot be determined with the data available.

Florida↗

USGS2025

Refining the earthquake history of south-central Alaska through lake records

The Alaska–Aleutian subduction zone (AASZ) is one of the world's most seismically active plate boundaries and the source of the 1964 M w 9.2 Great Alaska earthquake–the second largest instrumentally recorded earthquake in the world. Understanding the nature and frequency of such earthquakes is necessary for seismic and tsunami hazard assessment, but instrumental and historical records that span less than 150 years are too short to allow a statistically reliable analysis of earthquake recurrence times. This calls for studies of evidence of past earthquakes, extending the earthquake catalog further back in time. Subduction-zone paleoseismology in south-central Alaska is predominantly based on coastal evidence of land-level changes and tsunamis generated by megathrust earthquakes and preserved in the geological record. A complementary approach is lacustrine paleoseismology, which is still a relatively young discipline in Alaska. However, globally, lake basins are well-established high-resolution and continuous recorders of paleoseismic activity along subduction zones, relying on the identification of underwater landslide deposits and turbidites generated by seismic shaking. As a result, lake basins not only register ground shaking from megathrust earthquakes, but also from intraslab and crustal earthquakes, which are typically not accompanied by significant land-level changes. In this review paper, we combine coastal and lacustrine paleoseismology approaches to refine the south-central Alaskan earthquake history by comparing the paleoseismic records from two lakes (i.e., Eklutna Lake, located in the Chugach Mountain Range, and Skilak Lake, situated on the Kenai Peninsula) with the coastal and crustal earthquake catalog in Alaska. The resulting age ranges of all known megathrust earthquakes involving the Alaskan megathrust between the Kodiak and Prince William Sound (PWS) sections are more precise and accurate for the last 1.3 kyrs BP than the previously published age ranges from coastal records. As a result, this study supports the following key conclusions: (1) The 1964 CE earthquake was an exceptionally strong and unique event in the last 2000 years, rupturing the PWS, Kenai, Barren Islands, and Kodiak sections simultaneously. (2) The high-resolution and seasonal markings of the varved lake records now disentangle for the first time closely timed earthquakes, which was not possible based on the coastal evidence alone. (3) No persistent megathrust rupture boundaries exist. So, the possibility of a full rupture of the entire eastern AASZ, from PWS to Semidi cannot be excluded. (4) The rupture pattern in the eastern AASZ reveals superimposed cycles of multi-asperity ruptures (1964 earthquake) and clustered complementary partial ruptures, or rupture cascades. (5) The PWS section hosts the largest asperity in the eastern AASZ. (6) The shaking record of megathrust earthquakes indicates a time-dependent (quasiperiodic) behavior for the study area, but the observation of complementary clusters means that the hazards will not drop to zero but instead may even increase for a neighboring section. (7) The time-independent behavior of intraplate earthquakes implies that the intraslab hazard did not decrease following the 2016 and 2018 earthquakes. This study utilizes an integrated approach for subduction zone paleoseismology as a solution for unraveling recurrence and rupture patterns in Alaska, which can be applied worldwide.

Alaska↗

USGS2024

A comparative analysis of OpenET for evaluating evapotranspiration in California almond orchards

The almond industry in California faces water management challenges that are being exacerbated by droughts, climate change, and groundwater sustainability legislation. The Tree-crop Remote sensing of Evapotranspiration eXperiment (T-REX) aims to explore opportunities to improve precision irrigation management for woody perennial cropping systems. Almond orchards in the California Central Valley were equipped with eddy covariance flux measurements to evaluate satellite remote sensing-based evapotranspiration (RSET) models. OpenET provides high-resolution (30-m spatial and daily temporal) RSET data, synthesizing decades of research for practical water management. This study provides an evaluation of OpenET performance at six almond sites covering a large range in soils, age, and variety. It also compares OpenET ensemble evapotranspiration (ET) data with applied irrigation and precipitation records over an additional 148 almond orchards located in the Central Valley of California. Results show OpenET models, including the ensemble ET value, produced reasonable and actionable ET values, with overall coefficient of determination (R 2 ) and mean absolute error values of 0.73- and 0.95-mm d −1 at the daily time step, respectively. However, given the temporal sampling of Landsat (8-day revisit) and the interpolation methods used, the assessed ET models had difficulty in capturing short-term variability in almond ET; for example, the rapid decline in measured ET observed as a response to lack of irrigation preceding and during almond harvest. The study also drew attention to the spatial complexity in scenarios where irrigated orchards are surrounded by hot/dry areas, causing discrepancies between measured and modeled ET values. In comparison with irrigation records, OpenET ensemble ET was capable of quantifying water input (applied irrigation + precipitation) in almond orchards to within 13 % when evaluating monthly data. Initial results presented here reinforce the idea that RSET models, such as in OpenET, are powerful tools, yet their application requires nuanced understanding and careful consideration of local conditions.

California↗

USGS2024

Hydrologic investigations and a preliminary conceptual model of the groundwater system at North Penn Area 1 Superfund Site, Souderton, Montgomery County, Pennsylvania

The U.S. Geological Survey (USGS) conducted hydrogeologic investigations, reviewed existing data, and developed a preliminary conceptual model of the groundwater system as part of technical support of the U.S. Environmental Protection Agency (EPA) at the North Penn Area 1 Superfund Site (hereafter, the NP1 Site) located within the Borough of Souderton in Montgomery County, Pennsylvania. Field work and monitoring took place during 2012–18. The area is underlain by sedimentary formations that form a fractured-rock aquifer used for drinking water and industrial supply. The EPA placed the Site on the National Priorities List in 1989, identifying tetrachloroethylene (PCE) and trichloroethylene (TCE) as contaminants of concern. During 2012–18, the USGS conducted field activities that included drilling an 82-foot (ft)-deep monitoring well (MG 2220) in 2016, reconstructing a 208-ft-deep former industrial production well (MG 668 [Granite Knitting Mill]), and collecting borehole geophysical and video logs and water levels from those and five additional wells, which ranged in depth from about 50 to 200 ft below land surface. Continuous water levels were collected during 2014–17, and a synoptic set of water levels were measured in April 2018 in the seven wells. The borehole geophysical logs (caliper, acoustic televiewer, natural gamma, single-point resistance, vertical flow, and fluid temperature and resistivity) and borehole video logs in the seven wells were evaluated to assess potential for lithologic correlation and to identify and describe water-bearing features, which included both low- and high-angle fractures and other openings oriented along dipping bedding planes, joints, or possible faults. Borehole geophysical logs collected by USGS in 1992 in a 300-ft-deep former production well near the Site were also evaluated. Few to no distinctive features were identified on geophysical logs (natural gamma and single-point resistance) that could be used for correlation, thus limiting this approach to determining local geologic structure. Extensive fracturing in the upper 62 ft of monitoring well MG 2220 indicates that the well was likely drilled through a zone of faulting, and other evidence of faulting is present in the area near the Site. Assessment of continuous water levels showed hydraulic connections among some wells as indicated by rising or falling water levels in response to changes in pumping rates at nearby wells. A map of water levels measured in April 2018 indicates potential for groundwater flow generally toward the stream to the south and southwest of the Site, but the limited water-level data are insufficient to describe vertical groundwater gradients or lateral gradients in any detail. Review of 1999–2022 volatile organic compound (VOC) monitoring data collected by the Pennsylvania Department of Environmental Protection for five monitoring wells indicates that the highest groundwater concentrations of PCE and TCE were found in samples from extraction well MG 2201 (S-1) downgradient from, and nearest to, the previously identified Site contaminant source area, and these concentrations fluctuated through time. PCE concentrations were higher than TCE concentrations in samples from all five monitoring wells and were much higher than TCE concentrations in samples from extraction well MG 2201 (S-1). Temporally variable recharge is a possible factor affecting observed fluctuations in PCE concentrations in groundwater samples from well extraction MG 2201 (S-1), as indicated by a general inverse relation between PCE concentrations and water levels in a nearby long-term observation well. The PCE concentration of 1,830 micrograms per liter (μg/L) in a May 2018 water sample from monitoring well MG 2220 was more than four times the PCE concentration of 444 μg/L in a December 2017 sample from the nearby extraction well MG 2201 (S-1), which is open to fewer fractures. Low concentrations of VOCs were measured in surface water at two stream sites downgradient from wells with the highest groundwater VOC concentrations at the Site, indicating that discharge of contaminated groundwater to the stream is likely. Development of a conceptual model of the groundwater system was constrained by limited data. In areas with no pumping, groundwater-flow directions generally are thought to be controlled by topography and geologic structure (bedding orientation) and likely to the south and southwest of the Site, with local flow directions affected by orientations of fractures, joints, and local faults. Additional investigations that could help improve the conceptual model of the groundwater system and help delineate the extent of groundwater contamination and its transport are discussed.

Pennsylvania↗

USGS2025

Leveraging wildfire to augment forest management and amplify forest resilience

Successive catastrophic wildfire seasons in western North America have escalated the urgency around reducing fire risk to communities and ecosystems. In historically frequent-fire forests, fuel buildup as a result of fire exclusion is contributing to increased fire severity. The probability of high-severity fire can be reduced by active forest management that reduces fuels, prompting federal and state agencies to commit significant resources to increase the pace and scale of fuel reduction treatments. However, lower severity areas of wildfires also have the potential to act as “treatments,” and even catastrophic fires with large areas of high severity can still have substantial areas of lower severity fire that may be improving forest conditions locally. We quantified active management and wildfire severity across yellow pine and mixed conifer (YPMC) forests in the Sierra Nevada of California over a 22-year period (2001–2022). We did not detect increases in the area treated through time, but the area of beneficial wildfire (low to moderate severity) increased substantially, exceeding active treatment area in 8 of 22 years. Overall, beneficial wildfire treated ~17% more area than all treatments combined, and roughly four times more area than fire-related treatments alone. We then used disturbance history to evaluate resistance to high-severity wildfire and forest loss across the YPMC range. Of the 2.3 million ha YPMC of forests in 2001, 20% lost mature forests due to high-severity fire by 2022, which is nearly half of all YPMC area burned. Most of the landscape (47%) remains at risk of high-severity fire because it had no restorative disturbances, but 33% of the study area has some level of resistance to high-severity wildfire. In these areas, resistance will need to be enhanced and maintained over time via active management or managed wildfire, but these treatment needs will likely outpace capacity even under optimistic implementation scenarios. Given limited resources for implementing active management and the likelihood of a more fiery future, incorporating beneficial wildfire into landscape-level treatment planning has the potential to amplify the impact of active management treatments.

California, Nevada↗

USGS2025

Sources of water and salts for the Zuni Salt Lake in west-central New Mexico

The Zuni Salt Lake is located in a maar in west-central New Mexico and contains hypersaline water that has long been used by Native Americans for religious purposes and the collection of salt. There have been several investigations suggesting different sources for the water and salt to the lake. Springs, seeps, and ephemeral streamflow have all been observed to contribute freshwater to the lake, and brackish to hypersaline seeps have been documented along the banks of the lake. This report summarizes the findings of a study that characterizes the lake’s hydrology, its water and salinity sources, and the hydrogeologic conceptual model. Regional groundwater levels indicate that each of the aquifers in the area have the potential to discharge groundwater to the lake. There is also evidence of vertical groundwater flow pathways at the maar that were likely created by the igneous intrusion that fractured the intersecting aquifers. A detailed water budget was constructed from continuous lake stage, precipitation, and evaporation data to estimate the groundwater inflow to the Zuni Salt Lake. It was determined that groundwater inflow to the lake is 441 ±94 acre-feet per year, which composes as much as 77 percent of the total inflows. The high sodium and chloride concentrations measured in two hypersaline samples collected near the lake indicate that the majority of the dissolved solids entering the lake are from a hypersaline groundwater source. The geochemical and isotopic compositions measured in the lake and surrounding features support the interpretation that hypersaline groundwater is the primary source of salts to the lake, which is likely sourced from the older (and deeper) Permian units. The hypersaline groundwater samples collected during this investigation have a unique aqueous chemistry relative to each of the mapped aquifers, and variability in groundwater compositions is interpreted to result from differences in minerology and residence time.

New Mexico↗

USGS2026

Spatial variation in effectiveness and costs of sagebrush restoration treatments across the western United States

Natural resource managers strive to improve restoration efficiency across the vast network of public lands of the United States, seeking the best return on investment through innovation, geographic prioritization, and adaptive management. This challenge is exemplified by ecosystems dominated by sagebrush ( Artemisia spp.), which occur across the western United States and have been degraded by increasing wildfire frequency driven by invasive plant spread, among other factors. However, both costs and effectiveness of sagebrush restoration can vary spatially due to management practices in addition to biotic and abiotic factors, and characterizing this variation could inform broad-scale planning. We leveraged published models of sagebrush recovery and treatment costs to predict and evaluate cost-effectiveness of aerial and drill seeding Artemisia spp. across 429 718 km 2 that overlapped 12 US states. Compared to natural recovery, effectiveness for both methods was generally low, yet effectiveness was often greater, and costs were always greater, for drill than aerial seeding, resulting in slightly higher cost-effectiveness on average for drill seeding. Cost-effectiveness for both treatments increased near major roads and in areas with more repeated burns. Cost-effectiveness also increased with predisturbance cover of sagebrush but decreased with herbaceous cover. However, we also identified areas where aerial seeding was more cost-effective than drill seeding, particularly with greater slope. Our results provide spatially explicit estimates and potential mechanisms of cost-effectiveness for two common seeding methods for sagebrush, which can help prioritize limited resources, guide land use, and improve restoration efficiency and effectiveness across public rangelands of the western United States.

western United States↗

USGS2026

A temporal look at the influence of topographic amplification on earthquake-triggered landslides in 3D seismic simulations

Earthquakes are a primary trigger for landslides, often leading to catastrophic consequences. While numerous studies have explored the spatial distribution of earthquake-triggered landslides, understanding the interaction between seismic waves and topography remains a critical challenge. Topographic irregularities can cause seismic wave amplification, altering ground shaking, and can trigger landslides that are challenging for predictive models to anticipate. This study investigates the spatial and temporal evolution of topographically amplified landslides, focusing on coseismic landslides triggered by the Mw 7.5 mainshock of the 2018 Papua New Guinea earthquake and post-seismic landslides associated with its four aftershocks, each exceeding Mw 6.0. We employ low-frequency, three-dimensional numerical ground shaking simulations and data-driven multivariate analyses to examine how landslides evolved from the coseismic to post-seismic periods. Our findings reveal a spatial shift in landslide distribution, in which the mainshock triggered slope failures predominantly on steep hillslopes, and the aftershocks triggered landslides on gentler slopes, often near geologic boundaries. We attribute this transition partly to the earthquake legacy effect of the mainshock, where the mainshock caused weakening of these hillslopes, making them more prone to failure when aftershocks occur. Additionally, the concentration of failures along geologic contacts in the post-seismic phase suggests that site amplification, stemming from contrasts in subsurface materials, exerts a key influence on landslide occurrence. Although not explicitly captured in our current numerical simulations, this mechanism warrants further investigation for more accurate hazard modeling.

JGR Solid Earth↗

USGS2024

Simulation of groundwater flow in the Long Island, New York regional aquifer system for pumping and recharge conditions from 1900 to 2019

The U.S. Geological Survey has developed a transient, groundwater-flow model that simulates hydrologic conditions in the Long Island aquifer system as part of an ongoing (since 2016) multiyear, cooperative investigation with the New York State Department of Environmental Conservation. The goals of this investigation are to assist stakeholders and resource managers to evaluate the response of the hydrologic system to changes in future hydraulic stresses. Responses in the hydrologic system include changes in water levels in the hydrogeologic units; discharge to streams, coastal waters, and subsurface infrastructure; and the extent of saline groundwater in the aquifers. Hydraulic stresses include future water-supply management and changes in land use and infrastructure. The numerical model synthesizes a diverse set of physiographic, geologic, climatic, land-use, and historical population, water use, and infrastructure data to physically represent the Long Island aquifer system from land surface to bedrock and to simulate annual hydrologic conditions between 1900 and 2019. A three-dimensional hydrogeologic framework was developed from existing and recently collected borehole geologic and geophysical data collected as part of a companion drilling program. Water-transmitting properties of the principal aquifer sediments were defined in three dimensions from new and existing lithologic logs. The distribution of recharge from precipitation was estimated from landscape characteristics and climate data. Anthropogenic recharge from wastewater, leaky infrastructure, and storm runoff were estimated from population, infrastructure, and pumping data. Water-use data, including well locations, depths, and pumping rates, were obtained from historical sources and records and used to estimate pumping stresses continuously in time and space, at an annual average time scale. The data were incorporated into a three-dimensional numerical model using the U.S. Geological Survey finite difference modeling code MODFLOW 6; the model encompassed all of Long Island and surrounding surface waters and simulated historical hydrologic conditions from 1900 to 2019. The calibration process involved trial and error adjustments using prior knowledge to improve general fit to observations followed by an inverse calibration to update and optimize input parameters, using an iterative ensemble smoother algorithm implemented in PEST++ version 5.0. This resulted in a model that generally was in good agreement with observed, dynamically varying hydrologic conditions from 1900 to 2019. The calibrated model was used to develop two base-case models for scenario testing of future, hypothetical conditions where one represented average-annual conditions, and one represented average-seasonal conditions from 2010 to 2019. The model representing average-annual conditions was modified further to represent an alternate sea-level position of 6 feet above the North American Vertical Datum of 1988, and the model representing average-seasonal conditions was modified to represent the average seasonal effects of a 5-year drought imposed upon current hydrologic conditions. Recharge is the sole source of water to the aquifer system; groundwater discharges to coastal water and streams and is withdrawn by pumped wells. Model-estimated annual recharge ranged from about 11 inches in 1965 to 41 inches in 1983. On average, from 2010 to 2019, about 23 percent of water was pumped from wells, and about 47 and 27 percent discharged to coastal waters and streams, respectively; the remaining 4 percent was water that moved into storage in the aquifer matrix. Water levels on Long Island vary naturally during time in response to changes in recharge; the amount of variation is largest in the interior of the island, in areas with highest water table altitudes near groundwater divides and lowest near streams and the coastal waters. The total range of water table altitudes on Long Island between 1900 and 2019 ranged from near 0 to more than 70 feet in western parts of Long Island. The largest range in altitudes is in New York City and is associated with areas of large historical withdrawals between the 1920s and the late 1980s. Water table altitudes generally varied by less than 10 feet in eastern Suffolk County, where the aquifer is under more natural conditions. Saltwater intrusion is of great concern on Long Island, particularly in western Long Island where both the unconfined and confined parts of the aquifer system have been intruded in response to large-scale groundwater withdrawals; however, the volume of freshwater in the islandwide aquifer system only has changed by about 5 percent between 1900 and 2019. The decadal change in the freshwater volume was largest during the early and mid-20th century, corresponding to the largest historical pumping, but that volume change did not exceed 1 percent. The negligible change in freshwater volume suggests that saltwater intrusion as of 2019 was limited at an islandwide scale but continues to occur in local areas of Queens and Nassau Counties, adversely affecting current water supplies and limiting future water supplies for affected communities. The regional groundwater model developed for this investigation is a tool that can be used to help determine the viability of current and future water supplies at a regional scale and can be used to support development of additional models at finer scale to support more focused assessments of groundwater sustainability.

New York↗