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At least 37 records · Page 2Linked to original sources
USGS1979

Hydrology and water quality in the Nederlo Creek Basin, Wisconsin, before construction of two water-retention structures

The Nederlo Creek basin, in the "Driftless Area" of southwest Wisconsin, is geographically and hydrologically similar to other small basins in the area. Topography is rugged, with approximately 400 feet of relief between the boundary ridge tops and the valley floor. The water-retention structures (a dry floodwater- retention structure and a 43-acre reservoir) are to provide recreation and flood protection for the basin. Streamflow, springflow, precipitation, and groundwater levels were monitored at several sites to describe the hydrologic system. Streamflow is fairly constant at base flow, but rapid changes in discharge occur during periods of snowmelt or heavy rain; recession to base-flow discharge following these events is rapid. Surface runoff is a significant contributor to Streamflow only 10 percent of the time. The mean annual hydrologic budget for water years 1968-72 shows that of the 32.5 inches of precipitation on the basin, 6.4 inches left as runoff and 25.9 inches as evapotranspiration; ground-water storage increased an average of 0.2 inches per year. The water is a hard calcium magnesium bicarbonate type. Concentrations of major constituents in ground water and streams at base flow are similar, but concentrations in the stream generally decrease during periods when surface runoff contributes to Streamflow. Dissolved-oxygen concentrations in the stream are generally lowest during the summer; nighttime lows are generally between 7 and 8 milligrams per liter and daily maximums between 11 and 12.5 milligrams per liter. Diurnal water-temperature fluctuations of several degrees are common in streams during summer; daily maximum water temperatures as high as 26°C have been measured in some areas, but temperatures this high seldom persist for more than 2 hours. Estimates of mean annual total phosphorus and total nitrogen loads during 1967-74 fall within the ranges of 0.02 to 0.07 and 0.4 to 0.8 tons per square mile, respectively; 70 to 80 percent of the total phosphorus and 35 to 55 percent of the total nitrogen are transported during periods when surface runoff contributes to Streamflow. Mean annual suspended-sediment loads during 1968-74 range from 13 to 60 tons per square mile, with 74 to 86 percent of the total transported during periods when surface water contributes to streamflow. These sediment loads are at the low end of the range previously reported for streams in the "Driftless Area".

Wisconsin↗
USGS2011

Characterization of hydrology and salinity in the Dolores project area, McElmo Creek region, southwest Colorado, water years 1978-2006

Increasing salinity loading in the Colorado River has become a major concern for agricultural and municipal water supplies. The Colorado Salinity Control Act was implemented in 1974 to protect and enhance the quality of water in the Colorado River Basin. The U.S. Geological Survey, in cooperation with the Bureau of Reclamation and the Colorado River Salinity Control Forum, summarized salinity reductions in the McElmo Creek basin in southwest Colorado as a result of salinity-control modifications and flow-regime changes that result from the Dolores Project, which consists of the construction of McPhee reservoir on the Dolores River and salinity control modifications along the irrigation water delivery system. Flow-adjusted salinity trends using S-LOADEST estimations for a streamgage on McElmo Creek (site 1), that represents outflow from the basin, indicates a decrease in salinity load by 39,800 tons from water year 1978 through water year 2006, which is an average decrease of 1,370 tons per year for the 29-year period. Annual-load calculations for a streamgage on Mud Creek (site 6), that represents outflow from a tributary basin, indicate a decrease of 7,300 tons from water year 1982 through water year 2006, which is an average decrease of 292 tons per year for the 25-year period. The streamgage Dolores River at Dolores, CO (site 17) was chosen to represent a background site that is not affected by the Dolores Project. Annual load calculations for site 17 estimated a decrease of about 8,600 tons from water year 1978 through water year 2006, which is an average decrease of 297 tons per year for the 29-year period. The trend in salinity load at site 17 was considered to be representative of a natural trend in the region. Typically, salinity concentrations at outflow sites decreased from the pre-Dolores Project period (water years 1978—1984) to the post-Dolores Project period (water years 2000—2006). The median salinity concentration for site 1 (main basin outflow) decreased from 2,210 milligrams per liter per day in the preperiod to 2,110 milligrams per liter per day in the postperiod. The median salinity concentration for site 6 (tributary outflow) increased from 3,370 milligrams per liter per day in the preperiod to 3,710 milligrams per liter per day in the postperiod. Salinity concentrations typically increased at inflow sites from the preperiod to the postperiod. Salinity concentrations increased from 178 milligrams per liter per day during the preperiod at Main Canal #1 (site 16) to 227 milligrams per liter per day during the postperiod at the Dolores Tunnel Outlet near Dolores, CO (site 15). Calculation of the historical flow regime in McElmo Creek was done using a water-budget analysis of the basin. During water years 2000—2006, an estimated 845,000 acre-feet of water was consumed by crops and did not return to the creek as streamflow. The remaining 76,000 acre-feet, or 10,900 acre-feet per year for the 7-year postperiod, was assumed to represent a historical flow condition. The historical flow of 10,900 acre-feet per year is equivalent to 15.1 cubic feet per second. Average total dissolved solids concentrations for water in each type of sedimentary rock were used to estimate natural salinity loads. Most surface-water sites used to fit the criteria needed to achieve a natural TDS concentration were springs. An average spring TDS value for sandstones geology in the basin was 350 milligrams per liter, and the average value for Mancos Shale geology was 4,000 milligrams per liter. The natural salinity loads in McElmo Creek were estimated to be 29,100 tons per year, which is 43 percent of the salinity load that was calculated for the postperiod.

Colorado↗
USGS1996

Hydrogeology of the surficial aquifer system in Southwest Florida

Restoration and management of the south Florida ecosystem will be guided by hydrologic models that simulate water flowing through the wetlands and shallow subsurface aquifers beneath them. The restoration of the ecosystem is, essentially, the restoration of the natural hydrologic system. As surface water is re-diverted from manmade canals to its more natural state as overland flow, several changes are predicted to occur. First, because water flowing over land moves more slowly than in canals, overland flow should remain in the wetland ecosystem for a longer period each year. Second, as the flowing water spreads out over the wetlands, recharge to the shallow aquifers should increase as more of that water infiltrates into the ground. The U.S. Corps of Engineers and the South Florida Water Management District (SFWMD) will use hydrologic models to anticipate the consequences of these proposed restoration plans. This research program is designed to provide essential subsurface data to improve hydrologic models for land and water managers in southwest Florida where subsurface information is lacking. Obtaining hydrogeological data requires core drilling, corehole testing, and rock and sediment analysis.

Florida↗
USGS1977

A brief investigation of the surface-water hydrology of Yemen Arab Republic

Yemen, near the southwest tip of the Arabian Peninsula, is a mountainous country bordered by a desert on the east and a coastal plain on the west. Rainfall is low and seasonal; consequently, most streams (wadis) are ephemeral. The natural flow regimens of many of the smaller wadis are modified by terracing for agriculture. The only streamflow data available in Yemen are short records on four large wadis. A brief field investigation and application of reconnaissance techniques are the bases for the largely qualitative description of the hydrology, and for the proposal to collect streamflow data needed for orderly development of the expanding economy. (Woodard-USGS)

Open-File Report↗
USGS1996

Evaluation of the streamflow-gaging network of Alaska in providing regional streamflow information

In 1906, the U.S. Geological Survey (USGS) began operating a network of streamflow-gaging stations in Alaska. The primary purpose of the streamflow- gaging network has been to provide peak flow, average flow, and low-flow characteristics to a variety of users. In 1993, the USGS began a study to evaluate the current network of 78 stations. The objectives of this study were to determine the adequacy of the existing network in predicting selected regional flow characteristics and to determine if providing additional streamflow-gaging stations could improve the network's ability to predict these characteristics. Alaska was divided into six distinct hydrologic regions: Arctic, Northwest, Southcentral, Southeast, Southwest, and Yukon. For each region, historical and current streamflow data were compiled. In Arctic, Northwest, and Southwest Alaska, insufficient data were available to develop regional regression equations. In these areas, proposed locations of streamflow-gaging stations were selected by using clustering techniques to define similar areas within a region and by spatial visual analysis using the precipitation, physiographic, and hydrologic unit maps of Alaska. Sufficient data existed in Southcentral and Southeast Alaska to use generalized least squares (GLS) procedures to develop regional regression equations to estimate the 50-year peak flow, annual average flow, and a low-flow statistic. GLS procedures were also used for Yukon Alaska but the results should be used with caution because the data do not have an adequate spatial distribution. Network analysis procedures were used for the Southcentral, Southeast, and Yukon regions. Network analysis indicates the reduction in the sampling error of the regional regression equation that can be obtained given different scenarios. For Alaska, a 10-year planning period was used. One scenario showed the results of continuing the current network with no additional gaging stations and another scenario showed the results of adding gaging stations to the network. With the exception of the annual average discharge equation for Southeast Alaska, by adding gaging stations in all three regions, the sampling error was reduced to a greater extent than by not adding gaging stations. The proposed streamflow-gaging network for Alaska consists of 308 gaging stations, of which 32 are designated as index stations. If the proposed network can not be implemented in its entirety, then a lesser cost alternative would be to establish the index stations and to implement the network for a particular region.

Water-Resources Investigations Report↗
USGS2026

Satellite time series analysis to quantify changing climax ciénegas using a state and transition model approach

Ciénegas are rare wetlands in arid landscapes of the North American Southwest, historically providing critical ecological and hydrological functions but increasingly threatened by changing climate and land use pressures. This study quantifies changes in ciénega condition and floodplain dynamics using a state-and-transition model (STM) informed by expert knowledge and remote sensing. Key factors include woody plant encroachment, water availability, and soil aggradation. We mapped 31 ciénegas with high-resolution imagery and analyzed Landsat data (1985–2023) to assess vegetation health and moisture using the Normalized Difference Vegetation Index (NDVI) and Normalized Difference Infrared Index (NDII). Results show substantial interannual variability in phenology, water stress, and soil moisture, with regional drying and elevation strongly influencing ciénega resilience. We classified ciénegas into three functional states—healthy, desiccated, and dormant—and mapped their 2023 condition. Trend analyses indicate most ciénegas exhibit greening despite drought, though localized variability underscores the need for site-specific management. None are in a stable climax (reference) state; rather, they transition among states in response to external drivers. Increasing woody plant cover and surface drying, likely linked to declining regional water tables, favor deep-rooted species over wetland grasses—a pattern mirrored in adjacent control plots. Spatially explicit analysis revealed intra-ciénega variability often masked by aggregated data, highlighting the importance of high-resolution monitoring. Seasonal and long-term trends provide context for understanding ciénega dynamics, including degradation and restoration pathways. This study emphasizes the importance of groundwater conservation and demonstrates how remote sensing supports long-term monitoring. The STM framework offers a practical tool for adaptive management to sustain freshwater resources in arid environments.

Arizona, New Mexico↗
USGS2014

Anuran site occupancy and species richness as tools for evaluating restoration of a hydrologically-modified landscape

A fundamental goal of wetland restoration is to reinstate pre-disturbance hydrological conditions to degraded landscapes, facilitating recolonization by native species and the production of resilient, functional ecosystems. To evaluate restoration success, baseline conditions need to be determined and a reference target needs to be established that will serve as an ecological blueprint in the restoration process. During the summer wet seasons of 2010 and 2011, we used automated recording units to monitor a community of calling anuran amphibians in the Picayune Strand State Forest of Southwest Florida, USA. This area is undergoing hydrological restoration as part of the Comprehensive Everglades Restoration Plan. We compared occurrence of anurans at sites in the restoration area, to nearby locations in relatively undisturbed habitat (reference sites). We assessed the utility of the latter as restoration targets, using a hierarchical model of community species occupancy to estimate the probability of occurrence of anurans in restoration and reference locations. We detected 14 species, 13 of which were significantly more likely to occur in reference areas. All 14 species were estimated by our model to occur at these sites but, across both years, only 8–13 species were estimated to occur at restoration sites. The composition and structure of these habitats within and adjacent to the Picayune Strand State Forest indicate that they are suitable targets for habitat restoration, as measured by amphibian occurrence and species richness. These areas are important sources for recolonization of anuran amphibians as the hydrologically degraded Picayune Strand undergoes restoration to mitigate the effects of overdrainage and habitat loss.

Florida↗
USGS2012

Thermal and hydrological observations near Twelvemile Lake in discontinuous permafrost, Yukon Flats, interior Alaska, September 2010-August 2011

A series of ground-based observations were made between September 2010 and August 2011 near Twelvemile Lake, 19 kilometers southwest of Fort Yukon, Alaska, for use in ongoing hydrological analyses of watersheds in this region of discontinuous permafrost. Measurements include depth to ground ice, depth to water table, soil texture, soil moisture, soil temperature, and water pressure above the permafrost table. In the drained basin of subsiding Twelvemile Lake, we generally find an absence of newly formed permafrost and an undetectable slope of the water table; however, a sloping water table was observed in the low-lying channels extending into and away from the lake watershed. Datasets for these observations are summarized in this report and can be accessed by clicking on the links in each section or from the Downloads folder of the report Web page.

Alaska↗
USGS2003

Simulation of ground-water flow in the Cedar River alluvium, northwest Black Hawk County and southwest Bremer County, Iowa

Flooding and high ground-water levels after large or frequent rainstorms have occurred in an area of about 30 square miles along the eastern bank of the Cedar River from Cedar Falls in northwest Black Hawk County to Janesville in southwest Bremer County, Iowa. The U.S. Geological Survey, in cooperation with Black Hawk County, conducted a hydrologic study of the Cedar River alluvium in the northwest Black Hawk and southwest Bremer Counties, to improve understanding of the ground-water flow system and evaluate the effects of hypothetical variations in recharge and discharge conditions. A steady-state ground-water flow model was constructed for the area using November 2001 hydrologic conditions. The model was discretized into an 83-row by 47-column grid of cells measuring approximately 500 feet by 500 feet. Two model layers, one for the alluvium and one for the underlying bedrock units, were used to represent flow in the area. Precipitation during 2001 was similar to historical normals. Precipitation during 1999, especially during the summer when flooding occurred, was well above the historical normals. Borings in the unconsolidated deposits in the study area confirmed the presence of a bedrock valley dipping to the south in the central part of the study area. Water-level measurements in 2001 indicate that ground-water flow in much of the alluvial aquifer parallels the direction of flow in the Cedar River toward the south rather than following shorter flow paths to the west toward the Cedar River. Under steady-state conditions and 2001 pumpage, primary sources of inflow to the ground-water flow system are the Cedar River (65.5 percent), recharge through infiltration of precipitation and upland runoff (31.4 percent), and subsurface flow across the lateral boundaries (3.1 percent). The primary components of outflow from the ground-water flow system are intermittent streams (56.0 percent) and the Cedar River (43.7 percent). Two hypothetical scenarios were used to assess the potential effects of higher river levels and increased recharge compared to the steadystate conditions. For one scenario, river levels were set to bankfull conditions, and a recharge of 1.2 times the steady-state rate was applied. This simulation was used to evaluate the effects of wet conditions. This scenario led to increased water levels, in general, and large areas of shallow (0 to 10 feet) depths to water along the eastern part of the model area near Highway 218. For the second scenario, conditions were the same as for the first scenario, but streambed conductance of intermittent streams modeled as drains was increased to 10 times the steady-state value to simulate increased flow of water from the shallow groundwater flow system. The area with depth to water of 0 to 10 feet along the eastern part of the model area was substantially smaller than that of the first scenario. In general, once high ground-water levels occur, either because of high Cedar River water Abstract levels or above normal local precipitation or both, ground-water in the central part of the study area along Highway 218 flows toward the south rather than following shorter flow paths to the Cedar River. Intermittent streams in the study area discharge substantial amounts of water from the ground-water flow system.

Iowa↗
USGS2011

Millennial precipitation reconstruction for the Jemez Mountains, New Mexico, reveals changing drought signal

Drought is a recurring phenomenon in the American Southwest. Since the frequency and severity of hydrologic droughts and other hydroclimatic events are of critical importance to the ecology and rapidly growing human population of this region, knowledge of long-term natural hydroclimatic variability is valuable for resource managers and policy-makers. An October–June precipitation reconstruction for the period AD 824–2007 was developed from multi-century tree-ring records of Pseudotsuga menziesii (Douglas-fir), Pinus strobiformis (Southwestern white pine) and Pinus ponderosa (Ponderosa pine) for the Jemez Mountains in Northern New Mexico. Calibration and verification statistics for the period 1896–2007 show a high level of skill, and account for a significant portion of the observed variance (>50%) irrespective of which period is used to develop or verify the regression model. Split-sample validation supports our use of a reconstruction model based on the full period of reliable observational data (1896–2007). A recent segment of the reconstruction (2000–2006) emerges as the driest 7-year period sensed by the trees in the entire record. That this period was only moderately dry in precipitation anomaly likely indicates accentuated stress from other factors, such as warmer temperatures. Correlation field maps of actual and reconstructed October–June total precipitation, sea surface temperatures and 500-mb geopotential heights show characteristics that are similar to those indicative of El Niño–Southern Oscillation patterns, particularly with regard to ocean and atmospheric conditions in the equatorial and north Pacific. Our 1184-year reconstruction of hydroclimatic variability provides long-term perspective on current and 20th century wet and dry events in Northern New Mexico, is useful to guide expectations of future variability, aids sustainable water management, provides scenarios for drought planning and as inputs for hydrologic models under a broader range of conditions than those provided by historical climate records.

New Mexico↗
USGS2004

Review of Knowledge on the Occurrence, Chemical Composition, and Potential Use for Desalination of Saline Ground Water in Arizona, New Mexico, and Texas with a Discussion of Potential Future Study Needs

Increasing demand on the limited supplies of freshwater in the desert Southwest, as well as other parts of the United States, has increased the level of interest in saline-water resources. Saline ground water has long been recognized as a potentially important contributor to water supply in the Southwest, as demonstrated by the number of hydrologic, geologic, and engineering studies on the distribution of saline water and the feasibility of desalination. Potential future study needs include investigating and documenting the three-dimensional distribution of salinity and chemical composition of saline-water resources and the hydraulic properties of aquifers containing these saline-water resources, assessing the chemical suitability of saline water for use with existing and anticipated desalination technologies, simulating the effect of withdrawal of saline ground water on water levels and water composition in saline and adjoining or overlying freshwater aquifers, and determining the suitability of target geologic formations for injection of desalination-generated waste.

Open-File Report↗
USGS2023

So goes the snow: Alaska snowpack changes and impacts on pacific salmon in a warming climate

In Alaska’s watersheds, climate change is altering the nature and role of the snowpack, defined as snow accumulation that melts in spring. Generally, the amount of precipitation that falls as snow and the length of the snow-cover season both decrease as temperatures exceed 0°C (32°F) more frequently. The impacts of climate change on snowpack vary among watersheds. In southern, coastal parts of Alaska, large decreases in spring snowpack are expected by the mid-21st century, even with more winter precipitation because temperatures warm to above freezing, causing a shift from snow to rain or more melt during the winter. In contrast, modest early spring increases in the snowpack are expected in watersheds where temperatures remain below freezing. In these locations temperatures warm but remain cold enough for the extra winter precipitation to fall as snow, even though the snowpack will begin accumulating later in the fall and melt earlier in the spring as temperatures rise during those warmer seasons. Because potential impacts on hydrological and ecological systems will vary among watersheds, it is difficult to generalize the resulting ecological impacts at broad spatial scales. Here, we explore likely impacts on hydrology in critical anadromous fish habitat in southwest Alaska.

Alaska↗
USGS2024

Hydrologic and hydraulic analyses of Silver Creek and selected tributaries associated with Scott Air Force Base, Illinois, 2022–24

A hydrologic model of the Silver Creek Basin in southwest Illinois, and a hydraulic model of a selected reach of Silver Creek and local tributaries on and near Scott Air Force Base, Illinois, were developed to assess the effects of temporal land-use development in the Silver Creek Basin, the potential effects of projected changes based on future precipitation, and the effects of added detention storage in selected tributaries near Scott Air Force Base. The hydrologic model consists of a total of 52 scenarios—24 scenarios for an assessment of basin-wide changes in hydrology, and 28 scenarios for the hydraulic analysis of a focus area of Silver Creek and tributaries on and near Scott Air Force Base. Scenarios were run for precipitation events of 2-year through 500-year recurrence intervals (50-percent through 0.2-percent annual exceedance probability) and 24-hour durations. The effects of detention structures added to Silver Creek tributaries throughout Scott Air Force Base were greater on water-level profiles (about 1 to 3 feet) than the effects of projected (2050) changes in precipitation (about 1 foot or less) in these basins. The results indicated that despite the increases in water-surface elevations resulting from projected increases in precipitation, the detention structures could provide a net reduction in water-surface elevations in the flood-prone western tributaries on the base. The effects of detention structures and projected precipitation also were assessed using the mapped extent of inundation for the simulated probabilistic precipitation scenarios. As an example, limited inundation of a residential area along Ash Creek was evident in the 5-year recurrence interval event for the scenarios without detention storage, whereas the first indications of flooding in the residential area from the scenario with detention storage were in the 50-year recurrence interval event. Changes in hydrologic conditions followed a spatial pattern similar to that of the changes in land-cover development, with the greatest changes in the downstream one-half of the Silver Creek Basin and most pronounced in subbasins on and surrounding Scott Air Force Base. There was up to an estimated 54.6-percent increase in peak streamflows in subbasins on or near Scott Air Force Base from historical (1992) to current (2019) conditions, but changes in peak streamflows of as much as 144 percent are anticipated under the planned (to about 2050) land cover plus projected (2050) precipitation. The changes in the timing of peak streamflows were towards earlier peaks, with cumulative changes between historical and projected conditions approaching 0.75 hour (45 minutes) for a 2-year recurrence interval event. Results of the percentage change in cumulative event volume were similar to those of percentage change in peak streamflows in terms of magnitude of change and temporal and spatial distribution of changes. The greatest magnitude of percentage change in the assessed hydrologic properties was associated with the 2-year recurrence interval event, and the magnitude of the percentage change decreased with increasing probabilistic event recurrence interval. Subbasins with a substantial change in runoff yield between historical and current conditions were primarily in the downstream one-half of the Silver Creek Basin and most were within or adjacent to Scott Air Force Base. The magnitude of runoff yield changes increased with recurrence interval, and maximum changes were associated with subbasins on base and with the changes between the historical and current conditions.

Illinois↗
USGS1984

Description and evaluation of the information transfer workshop series "Coal hydrology in Virginia"

A series of workshops was conducted in September, 1982, by staff of the Virginia Office, Mid-Atlantic District of the U.S.-Geological Survey for the benefit of coal operators, consultants, and resource managers in the coal-producing area of southwest Virginia. The purpose of the workshop series was to present hydrologic information and data by the U.S. Geological Survey collected during four years of study of the. coal hydrology of Virginia. The workshop series was held one day a week for three weeks at two locations within southwest Virginia in order to reduce travel time and overnight travel costs for participants. Results of an independently conducted questionnaire indicate the series was a success. The report summarizes the workshop preparation, organization, and presentation, and gives general conclusions and suggestions for those interested in conducting workshops.

Open-File Report↗
USGS1985

Effects of sanitary sewers on ground-water levels and streams in Nassau and Suffolk Counties, New York; part 2: Development and application of southwest Suffolk County model

By 1990, sanitary sewers in Nassau County Sewage Disposal Districts 2 and 3 and Suffolk County Southwest Sewer District will discharge to the ocean 140 cu ft of water/sec that would otherwise be returned to the groundwater system through septic tanks and similar systems. To evaluate the effects of this loss on groundwater levels and streamflow, the U.S. Geological Survey developed a groundwater flow model that couples a fine-scale subregional model to a regional model of larger scale. The regional model generates flux boundary conditions for the subregional model, and the subregional model provides detail in the area of concern. Results indicate that the water table will decline by as much as 8 ft along the Suffolk-Nassau county line, with effects decreasing eastward. Base flow is predicted to decrease by as much as 73% in a stream along the county line, but this effect will decrease to zero just east of the sewered area. This report is one of a series describing the predicted hydrologic effects of sewers in southern Nassau and southwest Suffolk Counties. (USGS)

New York↗
USGS1992

U-Pb dating of uranium deposits in collapse breccia pipes of the Grand Canyon region

Two major periods of uranium mineralization are indicated by U-Pb isotope dating of uranium ores from collapse breeeia pipes in the Grand Canyon region, northern Arizona. The Hack 2 and 3, Kanab North, and EZ 1 and 2 orebodies apparently formed in the interval of 200 + or - 20 Ma, similar to ages inferred for strata-bound, Late Triassic-hosted uranium deposits in southern Utah and northern Arizona. Samples from the Grand Canyon and Pine Nut pipes, however, indicate a distinctly older age of about 260 Ma. The Pigeon, Orphan, and Arizona-1 deposits were apparently mineralized before 220, 186, and 169 Ma, respectively, but no useful upper age limits can be inferred. There is no evidence in the U-Pb isotope data for uranium mineralization related to Laramide tectonism, mid-Tertiary volcanism, or late Tertiary uplift. The clustering in ages for a variety of uranium deposits at about (or slightly younger than) the age of the lower part of the Chinle Formation (Late Triassic) suggests that uranium in these deposits may have been derived by leaching from volcanic ash in the Chinle and mobilized by ground-water movement resulting from changing hydrologic gradients caused by regional uplift to the southwest. Pb isotope ratios of galenas in mineralized pipes are more radiogenic than those of sulfides from either uranium-poor pipes or occurrences away from pipes. This isotopic contrast suggests that fluids which passed through the pipes had interacted with the Proterozoic basement, possibly through the vertical fractures which influenced the location and evolution of the pipes themselves. Regardless of the source of the common Pb in the uranium-bearing pipes, the generally distinct Pb isotope composition of their galenas (compared to those of barren pipes and nonpipe sulfides in the region) may provide a useful exploration guide.

Economic Geology↗
USGS2022

Water-level fluctuations and water temperature effects on young-of-year Largemouth Bass in a southwest irrigation reservoir

The effects of a warming climate will alter the hydrological cycles of arid southwestern U.S. reservoirs which primarily support agricultural needs, provide flood control, and generate hydroelectric power while secondarily supporting fish communities and sport fishing opportunities. The success of littoral spawning fishes depends on the timing and variability of water levels. The onset of drought between 2017 and 2018 provided an opportunity to evaluate the timing of hatch dates and relative abundance of young-of-year Largemouth Bass Micropterus salmoides across two water years of varying water temperatures and water levels in a southwestern U.S. reservoir. A retrospective analysis of otoliths in young-of-year Largemouth Bass revealed similar hatch dates in 2017 (14 April–29 May) and 2018 (13 April–28 May) despite differences in water temperature and water level rate of change. Median water temperature during hatch dates was greater in 2017 (median 19.0°C, range 14.3–24.4°C) than 2018 (17.6°C, range 13.5–21.7°C). Water level rate of change during hatch dates in 2017 was positive (+3.1 to +13.1 cm/d), which reflected reservoir filling. In contrast, water level rate of change during hatch dates in 2018 was negative (−8.5 to −0.6 cm/d), which reflected reservoir receding. Relative abundance of young-of-year fish was greater in 2017 (21.7 fish/h) when the reservoir was filling compared with relative abundance in 2018 (6.8 fish/h) when the reservoir was receding. The median growth rate was greater in 2017 (1.02 mm/d) when the reservoir was filling than in 2018 (0.82 mm/d) when the reservoir was receding. Despite differences in water temperature and contrasting reservoir levels between the two water years, the Largemouth Bass population in a southwest U.S. reservoir exhibited similar hatch dates reported for the species in southeastern and northeastern U.S. reservoirs. While water demand in the 21st century may exceed availability, the opportunity exists to collaborate with water managers to benefit Largemouth Bass populations in southwestern reservoirs.

New Mexico↗