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At least 559 records · Page 31Linked to original sources
USGS2004

Fish-habitat modeling for gap analysis to conserve the endangered Topeka shiner (Notropis topeka)

Decision support tools that predict fish distribution over broad spatial scales are needed to assist in planning watershed management and endangered species recovery. We developed a geographical information system model with multivariate logistic regression to rank valley segments for probable occurrence of the endangered Topeka shiner (Notropis topeka) using stream condition variables (stream size, groundwater potential, channel slope, streamflow, network position) and land-cover variables (percent pasture, percent trees) in streams characteristic of the North American Great Plains. The stream condition and land-cover models correctly classified 89% and 68% of outcomes (i.e., presence or absence), respectively. Field tests of maps of predicted species distribution resulted in more species occurrences than expected in valley segments classified as high potential for presence and less than expected in low-potential valley segments. Gaps between high-priority segments and protected land parcels were found in all basins. In 37 basins with Topeka shiners, protected land coverage was <1% in 17 basins, 1-5% in 10 basins, and 5-21.8% in 10 basins. Conservation activities in gaps are long-term conservation measures, but maps of predicted species distribution have many immediate applications.

Canadian Journal of Fisheries and Aquatic Sciences↗
USGS2022

Groundwater and surface-water data collection for the Walla Walla River Basin, Washington, 2018–22

The semi-arid Walla Walla River Basin (WWRB) spans 1777 square miles in the states of Washington and Oregon and supports a diverse agricultural region as well as cities and rural communities that are partially reliant on groundwater. Historically, surface water and groundwater data have been collected in the WWRB by several entities including federal, state, local, and tribal governments; irrigation districts; universities; and non-profits. This report describes the surface and groundwater data collection by the U.S. Geological Survey from February 2018 to April 2022 to provide the Washington State Department of Ecology and other stakeholders basic knowledge of existing water resources in the WWRB, Washington. Additionally, the data were collected to build a long-term groundwater dataset, with the intent to provide data for better understanding to assist in informed decisions about groundwater use, management, and conservation throughout the basin, and for future inclusion in a conceptual model of the groundwater-flow system (conceptual model). Data were collected and compiled for 237 sites—191 wells and 46 surface-water discharge sites. A small annual network of deep basalt wells was established in February 2018 to commence the data collection. In March 2020 and April 2021, additional field inventories were performed by locating and measuring groundwater wells in the WWRB. A subset of the inventoried wells were selected for an annual or a quarterly water level network to be measured until July 2024. In August 2020, field reconnaissance identified 46 surface-water sites to be measured for discharge, estimating gaining and losing reaches in streams for groundwater influences.

Oregon, Washington↗
USGS1985

Measurement of discharge using tracers

The development of fluorescent dyes and fluorometers that can measure these dyes at very low concentrations has made dye-dilution methods practical for measuring discharge. These methods are particularly useful for determining discharge under certain flow conditions that are unfavorable for current meter measurements. These include small streams, canals, and pipes where 1. Turbulence is excessive for current-meter measurement but conducive to good mixing. 2. Moving rocks and debris may damage instruments placed in the flow. 3. Cross-sectional areas or velocities are indeterminate or changing. 4. The flow is unsteady, such as the flow that exists with storm-runoff events on small streams and urban storm-sewer systems. 5. The flow is physically inaccessible or unsafe. From a practical standpoint, such methods are limited primarily to small streams, because of the excessively long channel-mixing lengths required for larger streams. Very good accuracy can be obtained provided that 1. Adequate mixing length and time are allowed. 2. Careful field and laboratory techniques are used. 3. Dye losses are not significant. This manual describes the slug-injection and constant-rate injection methods of performing tracer-dilution measurements. Emphasis is on the use of fluorescent dyes as tracers and the equipment, field methods, and laboratory procedures for performing such measurements. The tracer-velocity method is also briefly discussed.

Techniques of Water-Resources Investigations↗
USGS2003

Simulation of ground-water flow and rainfall runoff with emphasis on the effects of land cover, Whittlesey Creek, Bayfield County, Wisconsin, 1999-2001

The effects of land cover on flooding and base-flow characteristics of Whittlesey Creek, Bayfield County, Wis., were examined in a study that involved ground-water-flow and rainfall-runoff modeling. Field data were collected during 1999-2001 for synoptic base flow, streambed head and temperature, precipitation, continuous streamflow and stream stage, and other physical characteristics. Well logs provided data for potentiometric-surface altitudes and stratigraphic descriptions. Geologic, soil, hydrography, altitude, and historical land-cover data were compiled into a geographic information system and used in two ground-water-flow models (GFLOW and MODFLOW) and a rainfall-runoff model (SWAT). A deep ground-water system intersects Whittlesey Creek near the confluence with the North Fork, producing a steady base flow of 17?18 cubic feet per second. Upstream from the confluence, the creek has little or no base flow; flow is from surface runoff and a small amount of perched ground water. Most of the base flow to Whittlesey Creek originates as recharge through the permeable sands in the center of the Bayfield Peninsula to the northwest of the surface-water-contributing basin. Based on simulations, model-wide changes in recharge caused a proportional change in simulated base flow for Whittlesey Creek. Changing the simulated amount of recharge by 25 to 50 percent in only the ground-water-contributing area results in relatively small changes in base flow to Whittlesey Creek (about 2?11 percent). Simulated changes in land cover within the Whittlesey Creek surface-water-contributing basin would have minimal effects on base flow and average annual runoff, but flood peaks (based on daily mean flows on peak-flow days) could be affected. Based on the simulations, changing the basin land cover to a reforested condition results in a reduction in flood peaks of about 12 to 14 percent for up to a 100-yr flood. Changing the basin land cover to 25 percent urban land or returning basin land cover to the intensive row-crop agriculture of the 1920s results in flood peaks increasing by as much as 18 percent. The SWAT model is limited to a daily time step, which is adequate for describing the surface-water/ground-water interaction and percentage changes. It may not, however, be adequate in describing peak flow because the instantaneous peak flow in Whittlesey Creek during a flood can be more than twice the magnitude of the daily mean flow during that same flood. In addition, the storage and infiltration capacities of wetlands in the basin are not fully understood and need further study.

Wisconsin↗
USGS2018

Estimating the effects of wetland conservation practices in croplands: Approaches for modeling in CEAP–Cropland Assessment

Quantifying the current and potential benefits of conservation practices can be a valuable tool for encouraging greater practice adoption on agricultural lands. A goal of the CEAP-Cropland Assessment is to estimate the environmental effects of conservation practices that reduce losses (exports) of soil, nutrients, and pesticides from farmlands to streams and rivers. The assessment approach combines empirical data on reported cropland practices with simulation modeling that compares field-level exports for scenarios “with practices” and “without practices.” Conserved, restored, and created wetlands collectively represent conservation practices that can influence sediment and nutrient exports from croplands. However, modeling the role of wetlands within croplands presents some challenges, including the potential for negative impacts of sediment and nutrient inputs on wetland functions. This Science Note outlines some preliminary solutions for incorporating wetlands and wetland practices into the CEAP-Cropland modeling framework. First, modeling the effects of wetland practices requires identifying wetland hydrogeomorphic type and accounting for the condition of both the wetland and an adjacent upland zone. Second, modeling is facilitated by classifying wetland-related practices into two functional categories (wetland and upland buffer). Third, simulating practice effects requires alternative field configurations to account for hydrological differences among wetland types. These ideas are illustrated for two contrasting wetland types (riparian and depressional).

CEAP-Wetlands Science Note↗
USGS2009

Water Budgets of the Walker River Basin and Walker Lake, California and Nevada

The Walker River is the main source of inflow to Walker Lake, a closed-basin lake in west-central Nevada. The only outflow from Walker Lake is evaporation from the lake surface. Between 1882 and 2008, upstream agricultural diversions resulted in a lake-level decline of more than 150 feet and storage loss of 7,400,000 acre-feet. Evaporative concentration increased dissolved solids from 2,500 to 17,000 milligrams per liter. The increase in salinity threatens the survival of the Lahontan cutthroat trout, a native species listed as threatened under the Endangered Species Act. This report describes streamflow in the Walker River basin and an updated water budget of Walker Lake with emphasis on the lower Walker River basin downstream from Wabuska, Nevada. Water budgets are based on average annual flows for a 30-year period (1971-2000). Total surface-water inflow to the upper Walker River basin upstream from Wabuska was estimated to be 387,000 acre-feet per year (acre-ft/yr). About 223,000 acre-ft/yr (58 percent) is from the West Fork of the Walker River; 145,000 acre-ft/yr (37 percent) is from the East Fork of the Walker River; 17,000 acre-ft/yr (4 percent) is from the Sweetwater Range; and 2,000 acre-ft/yr (less than 1 percent) is from the Bodie Mountains, Pine Grove Hills, and western Wassuk Range. Outflow from the upper Walker River basin is 138,000 acre-ft/yr at Wabuska. About 249,000 acre-ft/yr (64 percent) of inflow is diverted for irrigation, transpired by riparian vegetation, evaporates from lakes and reservoirs, and recharges alluvial aquifers. Stream losses in Antelope, Smith, and Bridgeport Valleys are due to evaporation from reservoirs and agricultural diversions with negligible stream infiltration or riparian evapotranspiration. Diversion rates in Antelope and Smith Valleys were estimated to be 3.0 feet per year (ft/yr) in each valley. Irrigated fields receive an additional 0.8 ft of precipitation, groundwater pumpage, or both for a total applied-water rate of 3.8 ft/yr. The average corrected total evapotranspiration rate for alfalfa is 3.2 ft/yr so about 0.6 ft/yr (15 percent) flushes salts from the soil. The diversion rate in Bridgeport Valley was estimated to be 1.1 ft/yr and precipitation is 1.3 ft/yr. The total applied-water rate of 2.4 ft/yr is used to irrigate pasture grass. The total applied water rate in the East Fork of the Walker River and Mason Valley was estimated to be 4.8 ft/yr in each valley. The higher rate likely is due to appreciable infiltration, riparian evapotranspiration, or both. Assuming a diversion rate of 3.0 ft/yr, stream loss due to infiltration and riparian evapotranspiration is about 3,000 acre-ft/yr along the East Fork of the Walker River and 14,000 acre-ft/yr in Mason Valley. In the lower Walker River basin, overall and groundwater budgets were calculated for Wabuska to Schurz, Nev., and Schurz to Walker Lake. An overall water budget was calculated for the combined reaches. Imbalances in the water budgets range from 1 to 7 percent, which are insignificant statistically, so the water budgets balance. Total inflow to the Wabuska-Walker Lake reach from the river and others sources is 140,000 acre-ft/yr. Stream and subsurface discharge into the northern end of Walker Lake totals 110,000 acre-ft/yr. About 30,000 acre-ft/yr is lost on the Walker River Indian Reservation from agricultural evapotranspiration, evapotranspiration by native and invasive vegetation, domestic pumpage, and subsurface outflow from the basin through Double Spring and the Wabuska lineament. Alfalfa fields in the upper Walker River basin are lush and have an average corrected total evapotranspiration rate of 3.2 ft/yr. Alfalfa fields on the Walker River Indian Reservation are not as lush and have a total corrected evapotranspiration rate of 1.6-2.1 ft/yr, which partly could be due to alkaline soils that were submerged by Pleistocene Lake Lahontan. The total applied-water rate is 7.0 ft/yr, almost twice the

Scientific Investigations Report↗
USGS2008

Isotopic variations of dissolved copper and zinc in stream waters affected by historical mining

Zinc and Cu play important roles in the biogeochemistry of natural systems, and it is likely that these interactions result in mass-dependent fractionations of their stable isotopes. In this study, we examine the relative abundances of dissolved Zn and Cu isotopes in a variety of stream waters draining six historical mining districts located in the United States and Europe. Our goals were to (1) determine whether streams from different geologic settings have unique or similar Zn and Cu isotopic signatures and (2) to determine whether Zn and Cu isotopic signatures change in response to changes in dissolved metal concentrations over well-defined diel (24-h) cycles. Average δ 66 Zn and δ 65 Cu values for streams varied from +0.02‰ to +0.46‰ and −0.7‰ to +1.4‰, respectively, demonstrating that Zn and Cu isotopes are heterogeneous among the measured streams. Zinc or Cu isotopic changes were not detected within the resolution of our measurements over diel cycles for most streams. However, diel changes in Zn isotopes were recorded in one stream where the fluctuations of dissolved Zn were the largest. We calculate an apparent separation factor of ∼0.3‰ ( 66/64 Zn) between the dissolved and solid Zn reservoirs in this stream with the solid taking up the lighter Zn isotope. The preference of the lighter isotope in the solid reservoir may reflect metabolic uptake of Zn by microorganisms. Additional field investigations must evaluate the contributions of soils, rocks, minerals, and anthropogenic components to Cu and Zn isotopic fluxes in natural waters. Moreover, rigorous experimental work is necessary to quantify fractionation factors for the biogeochemical reactions that are likely to impact Cu and Zn isotopes in hydrologic systems. This initial investigation of Cu and Zn isotopes in stream waters suggests that these isotopes may be powerful tools for probing biogeochemical processes in surface waters on a variety of temporal and spatial scales.

Geochimica et Cosmochimica Acta↗
USGS1997

Computation of selected hydraulic variables for the lower Yampa River in northwestern Colorado

Computation of selected hydraulic variables was done for three reaches on the lower Yampa River that were identified as having natural or manmadebarriers that might impede the migration of endangered Colorado squawfish. The three reaches included the Patrick Sweeney and the MaybellCanal diversion structures and Cross Mountain Canyon. Minimum stream depths and maximum stream velocities for a range of streamflows werecomputed using the Water-Surface PROfile computation program for cross sections in each of the three reaches. Cross-section information used asinput to the computation program was determined from field surveys or from existing detailed topographic information. Output options in theprogram were used to generate tables of hydraulic variables for streamflows ranging from 50 to 400 cubic feet per second, including minimum depths and maximum velocities for 20 stream tubes in each of the cross sections selected for study.

Open-File Report↗
USGS2005

Quality of nutrient data from streams and ground water sampled during water years 1992-2001

Proper interpretation of water-quality data requires consideration of the effects that bias and variability might have on measured constituent concentrations. In this report, methods are described to estimate the bias due to contamination of samples in the field or laboratory and the variability due to sample collection, processing, shipment, and analysis. Contamination can adversely affect interpretation of measured concentrations in comparison to standards or criteria. Variability can affect interpretation of small differences between individual measurements or mean concentrations. Contamination and variability are determined for nutrient data from quality-control samples (field blanks and replicates) collected as part of the National Water-Quality Assessment (NAWQA) Program during water years 1992-2001. Statistical methods are used to estimate the likelihood of contamination and variability in all samples. Results are presented for five nutrient analytes from stream samples and four nutrient analytes from ground-water samples. Ammonia contamination can add at least 0.04 milligram per liter in up to 5 percent of all samples. This could account for more than 22 percent of measured concentrations at the low range of aquatic-life criteria (0.18 milligram per liter). Orthophosphate contamination, at least 0.019 milligram per liter in up to 5 percent of all samples, could account for more than 38 percent of measured concentrations at the limit to avoid eutrophication (0.05 milligram per liter). Nitrite-plus-nitrate and Kjeldahl nitrogen contamination is less than 0.4 milligram per liter in 99 percent of all samples; thus there is no significant effect on measured concentrations of environmental significance. Sampling variability has little or no effect on reported concentrations of ammonia, nitrite-plus-nitrate, orthophosphate, or total phosphorus sampled after 1998. The potential errors due to sampling variability are greater for the Kjeldahl nitrogen analytes and for total phosphorus sampled before 1999. The uncertainty in a mean of 10 concentrations caused by sampling variability is within a small range (1 to 7 percent) for all nutrients. These results can be applied to interpretation of environmental data collected during water years 1992-2001 in 52 NAWQA study units.

Scientific Investigations Report↗
USGS2025

Stratigraphy, structure, and geomorphology of the central Appalachians across the North Mountain fault zone near Harrisonburg, Virginia, USA

This field trip focuses on the geology of the central Appalachian Valley and Ridge province near Harrisonburg, Virginia, USA. Recent geologic mapping utilizing 1-m resolution lidar data has revealed new insights into the Paleozoic stratigraphy, structural geology, and Neogene landscape evolution of the region. The detailed mapping reveals the presence of the Big Spring Station Member and multiple thrombolite zones in the Cambrian Conococheague Formation extending as far south as the Briery Branch 7.5 min quadrangle, providing insights into Late Cambrian sea-level fluctuations. Multiple outcrop exposures in the study area of this guidebook confirm recent work in Pennsylvania, USA, showing that the Ordovician Reedsville Shale overlies the Martinsburg Formation and that the two are distinct and mappable as separate formations rather than laterally equivalent units as previously interpreted. Our work extends the Silurian Williamsport Sandstone into Shenandoah County, Virginia, and describes its facies relationships with the Bloomsburg Formation along strike and across the Adams Run anticline. Mapping within the thick Devonian siliciclastic sequence reveals the presence of the Mahantango Formation on the western limb of Supin Lick syncline and illustrates its complex facies relationship with the Millboro Shale. In addition, we highlight new mapping criteria for the Brallier and Foreknobs Formations and demonstrate how the specific changes to the placement of the contact between them addresses previous challenges in their differentiation. We present cosmogenic burial ages of broad alluvial fan sediments in the Shenandoah Valley near Timberville and Briery Branch, Virginia, and erosion rates estimated for the Briery Branch stream basin. Both analyses provide new constraints on the timing of landscape evolution and karst development since the middle Pliocene. This field guide also highlights some significant structural features within the North Mountain fault zone, such as evidence of imbricated thrust sheets cut by cross-strike faults that have been exploited by Eocene igneous intrusions. Map-scale horses of Silurian and Ordovician rocks hold up ridges that are oblique to the regional strike. Deformation internal to one of these horse blocks is shown to be non-coaxial with respect to the main regional northwest directed transport.

Virginia↗
USGS1983

Reconnaissance of surface-water resources in the Kobuk River basin, Alaska, 1979-80

Surface water data were collected at selected sites in the Kobuk River Basin in northwest Alaska in August 1979 and April 1980. In August 1979, frequent heavy rains caused abnormally high flows in the basin; unit runoff values, computed from discharge measurements at 25 sites, ranged from 0.08 to 12.2 cu ft/sec/sq mi. Mean unit runoff for August computed from 13 years of record at a stream gaging station on the Kobuk River ranged from 1 to 3 cu ft/sec/sq mi. Unit runoff computed from discharge measurements made at eight sites in April 1980 ranged from 0 to 0.30 cubic feet per second per square mile. These values are in reasonable agreement with those derived from the record at the gaging station. High-water marks of maximum evident floods and evidence of ice-affected flooding were found at near bankfull stages at 17 sites on the Kobuk River and its tributaries. Computed unit runoff for the maximum evident floods generally decreases with increasing drainage area. Unit runoff ranges from about 50 to 75 cu ft/sec/sq mi for drainage areas < 1,000 sq mi to < 25 cu ft/sec/sq mi for larger areas. Field determinations were made of water temperature, pH, alkalinity, dissolved-oxygen concentration, and specific conductance, and discharge was measured at about 40 stream sites and one spring. Water samples for laboratory analysis of dissolved inorganic constituents and biological samples were collected in August 1979. Water quality data indicate that the surface waters would be acceptable for most uses; they are a calcium bicarbonate type having dissolved-solids concentrations between 50 and 140 milligm/liter. The pristine nature of the waters is also indicated by the overall diversity and composition of its benthic invertebrate community. A more highly mineralized (about 550 milligm/liter dissolved solids) sodium bicarbonate water flows from Reed River Hot Spring. (USGS)

Water-Resources Investigations Report↗
USGS2021

Workflow for using unmanned aircraft systems and traditional geospatial data to delineate agricultural drainage tiles at edge-of-field sites

Managing nutrient and sediment runoff from fields that drain to the Great Lakes is key to mitigating harmful algal blooms. Implementation of best management practices on agricultural land is considered a critical step to improving water quality in these streams, however the effect of these best management practices is difficult to quantify. The purpose of this study was to use a suite of high-resolution imagery acquired with unmanned aircraft systems (including a combination of visible, multispectral, and thermal cameras) to better characterize edge-of-field (EOF) sites in Michigan and Wisconsin that are monitored in cooperation with the Great Lakes Restoration Initiative. This high-resolution imagery (2.5–12-centimeter ground resolution) was used to delineate artificial subsurface drainage (tile-drain) networks and surface water flow paths that indicate contributing areas (that is, all area that drains to a monitored point) at these EOF sites, providing better characterization of each study site. Contributing areas for these sites ranged from 2.86 to 5.07 hectares and, among the sites, tile drains were identified as those that followed soil properties and those that were more densely patterned networks. These surveys also indicated that the contributing area monitored at the EOF sites may cross field boundaries and is not always coincident with the area underlain by subsurface drainage.

Indiana, Michigan, Ohio, Wisconsin↗
USGS2022

Remote sensing of visible dye concentrations during a tracer experiment on a large, turbid river

Understanding dispersion in rivers is critical for numerous applications, such as characterizing larval drift for endangered fish species and responding to spills of hazardous materials. Injecting a visible dye into the river can yield insight on dispersion processes, but conventional field instrumentation yields limited data on variations in dye concentration over time at a few, fixed points. Remote sensing can provide more detailed, spatially distributed information on the dye's motion, but this approach has only been tested in clear-flowing streams. The purpose of this study was to assess the potential of remote sensing to facilitate tracer studies in more turbid rivers. To pursue this objective, we injected Rhodamine WT dye into the Missouri River and collected field spectra from a boat, videos from a small unoccupied aircraft system (sUAS), and orthophotos from an airplane. Applying an optimal band ratio analysis (OBRA) algorithm to the field spectra revealed strong correlations ( R 2 = 0.936) between a spectrally based quantity and in situ concentration measurements. OBRA also performed well for broadband RGB (red, green, blue) images extracted from the sUAS-based videos; the resulting concentration maps were used to produce animations that captured movement of the dye pulse. Spectral mixture analysis of repeat orthophoto coverage yielded relative concentration estimates that provided a synoptic perspective on dispersion of the dye throughout the entire 13.8 km reach over the full 2.5-hr duration of the experiment. The results of this study demonstrate the potential to remotely sense tracer dye concentrations in large, highly turbid rivers.

Missouri↗
USGS1999

Pesticides in stream sediment and aquatic biota: distribution, trends, and governing factors

More than 20 years after the ban of DDT and other organochlorine pesticides, pesticides continue to be detected in air, rain, soil, surface water, bed sediment, and aquatic and terrestrial biota throughout the world. Recent research suggests that low levels of some of these pesticides may have the potential to affect the development, reproduction, and behavior of fish and wildlife, and possibly humans. Pesticides in Stream Sediment and Aquatic Biota: Distribution, Trends, and Governing Factors assesses the occurrence and behavior of pesticides in bed sediment and aquatic biota-the two major compartments of the hydrologic system where organochlorine pesticides are most likely to accumulate. This book collects, for the first time, results from several hundred monitoring studies and field experiments, ranging in scope from individual sites to the entire nation. Comprehensive tables provide concise summaries of study locations, pesticides analyzed, and study outcomes. Comprehensive and extensively illustrated, Pesticides in Stream Sediment and Aquatic Biota: Distribution, Trends, and Governing Factors evaluates the sources, environmental fate, geographic distribution, and long-term trends of pesticides in bed sediment and aquatic biota. The book focuses on organochlorine pesticides, but also assesses the potential for currently used pesticides to be found in bed sediment and aquatic biota. Topics covered in depth include the effect of land use on pesticide occurrence, mechanisms of pesticide uptake and accumulation by aquatic biota, and the environmental significance of observed levels of pesticides in stream sediment and aquatic biota.

Book↗
USGS2020

Magnetic field variations in Alaska: Recording space weather events on seismic stations in Alaska

Seismometers are highly sensitive instruments to not only ground motion but also many other nonseismic noise sources (e.g., temperature, pressure, and magnetic field variations). We show that the Alaska component of the Transportable Array is particularly susceptible to recording magnetic storms and other space weather events because the sensors used in this network are unshielded and magnetic flux variations are stronger at higher latitudes. We also show that vertical‐component seismic records across Alaska are directly recording magnetic field variations between 40 and 800 s period as opposed to actual ground motion during geomagnetic events with sensitivities ranging from 0.004 to 0.48 &#x2009;&#x2009; ( m / s 2 ) / T "> 0.48 ( m / s 2 ) / T 0.48 (m/s2)/T ⁠ . These sensitivities were found on a day where the root mean square variation in the magnetic field was 225 nT. Using a method developed by Forbriger (2007 , his section 3.1), we show that improving vertical seismic resolution of an unshielded sensor by as much as 10 dB in the 100–400 s period band using magnetic data from a collocated three‐component magnetometer is possible. However, due to large spatial variations in Earth’s magnetic field, this methodology becomes increasingly ineffective as the distance between the seismometer and magnetometer increases (no more than 200 km separation). A potential solution to this issue may be to incorporate relatively low‐cost magnetometers as an additional environmental data stream at high‐latitude seismic stations. We demonstrate that the Bartington Mag‐690 sensors currently deployed at Global Seismographic Network sites are not only acceptable for performing corrections to seismic data, but are also capable of recording many magnetic field signals with similar signal‐to‐noise ratios, in the 20–1000 s period band, as the observatory grade magnetometers operated by the U.S. Geological Survey Geomagnetism Program. This approach would densify magnetic field observations and could also contribute to space weather monitoring by supplementing highly calibrated magnetometers with additional sensors.

Alaska↗
USGS2007

Ground water stratification and delivery of nitrate to an incised stream under varying flow conditions

Ground water processes affecting seasonal variations of surface water nitrate concentrations were investigated in an incised first-order stream in an agricultural watershed with a riparian forest in the coastal plain of Maryland. Aquifer characteristics including sediment stratigraphy, geochemistry, and hydraulic properties were examined in combination with chemical and isotopic analyses of ground water, macropore discharge, and stream water. The ground water flow system exhibits vertical stratification of hydraulic properties and redox conditions, with sub-horizontal boundaries that extend beneath the field and adjacent riparian forest. Below the minimum water table position, ground water age gradients indicate low recharge rates (2-5 cm yr-1) and long residence times (years to decades), whereas the transient ground water wedge between the maximum and minimum water table positions has a relatively short residence time (months to years), partly because of an upward increase in hydraulic conductivity. Oxygen reduction and denitrification in recharging ground waters are coupled with pyrite oxidation near the minimum water table elevation in a mottled weathering zone in Tertiary marine glauconitic sediments. The incised stream had high nitrate concentrations during high flow conditions when much of the ground water was transmitted rapidly across the riparian zone in a shallow oxic aquifer wedge with abundant outflow macropores, and low nitrate concentrations during low flow conditions when the oxic wedge was smaller and stream discharge was dominated by upwelling from the deeper denitrified parts of the aquifer. Results from this and similar studies illustrate the importance of near-stream geomorphology and subsurface geology as controls of riparian zone function and delivery of nitrate to streams in agricultural watersheds.

Maryland↗