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At least 1,729 records · Page 96Linked to original sources
USGS2024

Factors contributing to pesticide contamination in riverine systems: The role of wastewater and landscape sources

Wastewater treatment plant (WWTP) discharges can be a source of organic contaminants, including pesticides, to rivers. An integrated model was developed for the Potomac River watershed (PRW) to determine the amount of accumulated wastewater percentage of streamflow (ACCWW) and calculate predicted environmental concentrations (PECs) for 14 pesticides in non-tidal National Hydrography Dataset Plus Version 2.1 stream segments. Predicted environmental concentrations were compared to measured environmental concentrations (MECs) from 32 stream sites that represented a range of ACCWW and land use to evaluate model performance and to assess possible non-WWTP loading sources. Statistical agreement between PECs and MECs was strongest for insecticides, followed by fungicides and herbicides. Principal component analysis utilizing optical fluorescence and ancillary water quality data identified wastewater and urban runoff sources. Pesticides that indicated relatively larger sources from WWTPs included dinotefuran, fipronil, carbendazim, thiabendazole, and prometon whereas imidacloprid, azoxystrobin, propiconazole, tebuconazole, and diuron were more related to urban runoff. In addition, PECs generally comprised a low proportion of MECs, which indicates possible dominant loading sources beyond WWTP discharges. Cumulative potential toxicity was higher for sites with greater ACCWW and/or located in developed areas. Imidacloprid, fipronil, and carbendazim accounted for the largest portion of predicted potential toxicity across sites. The chronic aquatic life toxicity benchmarks for freshwater invertebrates were exceeded for 82 % of the imidacloprid detections ( n = 28) and 47 % of the fipronil detections ( n = 19). These results highlight the ecological implications of pesticide contamination from WWTP discharges and also the potential legacy effects from accumulated soil and groundwater sources. Pesticide management strategies that mitigate both current and historical impacts may improve the health of aquatic ecosystems.

Potomac River watershed↗
USGS2012

Mapping plant species ranges in the Hawaiian Islands: developing a methodology and associated GIS layers

This report documents a methodology for projecting the geographic ranges of plant species in the Hawaiian Islands. The methodology consists primarily of the creation of several geographic information system (GIS) data layers depicting attributes related to the geographic ranges of plant species. The most important spatial-data layer generated here is an objectively defined classification of climate as it pertains to the distribution of plant species. By examining previous zonal-vegetation classifications in light of spatially detailed climate data, broad zones of climate relevant to contemporary concepts of vegetation in the Hawaiian Islands can be explicitly defined. Other spatial-data layers presented here include the following: substrate age, as large areas of the island of Hawai'i, in particular, are covered by very young lava flows inimical to the growth of many plant species; biogeographic regions of the larger islands that are composites of multiple volcanoes, as many of their species are restricted to a given topographically isolated mountain or a specified group of them; and human impact, which can reduce the range of many species relative to where they formerly were found. Other factors influencing the geographic ranges of species that are discussed here but not developed further, owing to limitations in rendering them spatially, include topography, soils, and disturbance. A method is described for analyzing these layers in a GIS, in conjunction with a database of species distributions, to project the ranges of plant species, which include both the potential range prior to human disturbance and the projected present range. Examples of range maps for several species are given as case studies that demonstrate different spatial characteristics of range. Several potential applications of species-range maps are discussed, including facilitating field surveys, informing restoration efforts, studying range size and rarity, studying biodiversity, managing invasive species, and planning of conservation efforts.

Hawai'i↗
USGS2020

An open source database for the synthesis of soil radiocarbon data: ISRaD version 1.0

Radiocarbon is a critical constraint on our estimates of the timescales of soil carbon cycling that can aid in identifying mechanisms of carbon stabilization and destabilization and improve the forecast of soil carbon response to management or environmental change. Despite the wealth of soil radiocarbon data that have been reported over the past 75 years, the ability to apply these data to global-scale questions is limited by our capacity to synthesize and compare measurements generated using a variety of methods. Here, we present the International Soil Radiocarbon Database (ISRaD; http://soilradiocarbon.org , last access: 16 December 2019), an open-source archive of soil data that include reported measurements from bulk soils, distinct soil carbon pools isolated in the laboratory by a variety of soil fractionation methods, samples of soil gas or water collected interstitially from within an intact soil profile, CO 2 gas isolated from laboratory soil incubations, and fluxes collected in situ from a soil profile. The core of ISRaD is a relational database structured around individual datasets (entries) and organized hierarchically to report soil radiocarbon data, measured at different physical and temporal scales as well as other soil or environmental properties that may also be measured and may assist with interpretation and context. Anyone may contribute their own data to the database by entering it into the ISRaD template and subjecting it to quality assurance protocols. ISRaD can be accessed through (1) a web-based interface, (2) an R package (ISRaD), or (3) direct access to code and data through the GitHub repository, which hosts both code and data. The design of ISRaD allows for participants to become directly involved in the management, design, and application of ISRaD data. The synthesized dataset is available in two forms: the original data as reported by the authors of the datasets and an enhanced dataset that includes ancillary geospatial data calculated within the ISRaD framework. ISRaD also provides data management tools in the ISRaD-R package that provide a starting point for data analysis; as an open-source project, the broader soil community is invited and encouraged to add data, tools, and ideas for improvement. As a whole, ISRaD provides resources to aid our evaluation of soil dynamics across a range of spatial and temporal scales. The ISRaD v1.0 dataset is archived and freely available at https://doi.org/10.5281/zenodo.2613911 (Lawrence et al., 2019).

Earth System Science Data↗
USGS2011

Self-potential investigations of a gravel bar in a restored river corridor

Self-potentials (SP) are sensitive to water fluxes and concentration gradients in both saturated and unsaturated geological media, but quantitative interpretations of SP field data may often be hindered by the superposition of different source contributions and time-varying electrode potentials. Self-potential mapping and close to two months of SP monitoring on a gravel bar were performed to investigate the origins of SP signals at a restored river section of the Thur River in northeastern Switzerland. The SP mapping and subsequent inversion of the data indicate that the SP sources are mainly located in the upper few meters in regions of soil cover rather than bare gravel. Wavelet analyses of the time-series indicate a strong, but non-linear influence of water table and water content variations, as well as rainfall intensity on the recorded SP signals. Modeling of the SP response with respect to an increase in the water table elevation and precipitation indicate that the distribution of soil properties in the vadose zone has a very strong influence. We conclude that the observed SP responses on the gravel bar are more complicated than previously proposed semi-empiric relationships between SP signals and hydraulic head or the thickness of the vadose zone. We suggest that future SP monitoring in restored river corridors should either focus on quantifying vadose zone processes by installing vertical profiles of closely spaced SP electrodes or by installing the electrodes within the river to avoid signals arising from vadose zone processes and time-varying electrochemical conditions in the vicinity of the electrodes.

Lake Constance, Neunforn, Thur catchment, Thur val↗
USGS2005

Determination of total mercury in biological and geological samples

The analytical chemist is faced with several challenges when determining mercury in biological and geological materials. These challenges include widespread mercury contamination, both in the laboratory and the environment, possible losses of mercury during sample preparation and digestion, the wide range of mercury values commonly observed, ranging from the low nanogram per gram or per liter for background areas to hundreds of milligrams per kilogram in contaminated or ore-bearing areas, great matrix diversity, and sample heterogeneity1. These factors can be naturally occurring or anthropogenic, but must be addressed to provide a precise and accurate analysis. Although there are many instrumental methods available for the successful determination of mercury, no one technique will address all problems or all samples all of the time. The approach for the determination of mercury used at the U.S. Geological Survey, Crustal Imaging and Characterization Team, Denver Laboratories, utilizes a suite of complementary instrumental methods when approaching a study requiring mercury analyses. Typically, a study could require the analysis of waters, leachates or selective digestions of solids, vegetation, and biological materials such as tissue, bone, or shell, soils, rocks, sediments, coals, sludges, and(or) ashes. No one digestion or sample preparation method will be suitable for all of these matrices. The digestions typically employed at our laboratories include: (i) a closed-vessel microwave method using nitric acid and hydrogen peroxide, followed by digestion/dilution with a nitric acid/sodium dichromate solution, (ii) a robotic open test-tube digestion with nitric acid and sodium dichromate, (iii) a sealed Teflon? vessel with nitric acid and sodium dichromate, (iv) a sealed glass bottle with nitric acid and sodium dichromate, or (v) open test tube digestion with nitric and sulfuric acids and vanadium pentoxide. The common factor in all these digestions is that they are very oxidative to ensure the conversion of all mercury forms into Hg (II). Each method of digestion has its advantages and limitations. The method of detection used in our laboratories involves a combination of an in-house, custom, classic continuous-flow cold-vapor atomic absorption spectrometry (CVAAS), a commercially available, automated, flow-injection and a continuous flow cold-vapor atomic fluorescence spectrometry (CV-AFS) systems, and a relatively new, automated and integrated approach where solid or liquid samples are thermally decomposed under an oxygen atmosphere (a nitrogen atmosphere is used for coals) and the released mercury vapor trapped onto a gold gauze and then thermally released into an AAS system. Other less frequently used instrumental methods available for the determination of mercury include inductively coupled plasma ? optical emission spectrometry (ICP-OES), inductively couple plasma ? mass spectrometry (ICP-MS) (both solution nebulization and laser ablation), and instrumental neutron activation analysis (INAA). Results from two case studies involving the determination of mercury in the challenging matrices of biological materials will be presented. These will include fillet, liver and stomach-content samples from grayling for a baseline/background study in Alaska, and samples of meat tissue and shell material from Tanner crabs from Glacier Bay, Alaska. These studies show that the method of digestion is more important than a very sensitive detection limit for mercury.

Open-File Report↗
USGS2018

Quaternary sediment thickness and bedrock topography of the glaciated United States east of the Rocky Mountains

Beginning roughly 2.6 million years ago, global climate entered a cooling phase known as the Pleistocene Epoch. As snow in northern latitudes compacted into ice several kilometers thick, it flowed as glaciers southward across the North American continent. These glaciers extended across the northern United States, dramatically altering the landscape they covered. East of the Rocky Mountains, the ice coalesced into continental glaciers (called the Laurentide Ice Sheet) that at times blanketed much of the north-central and northeastern United States. To the west of the Laurentide Ice Sheet, glaciers formed in the mountains of western Canada and the United States and coalesced into the Cordilleran ice sheet; this relatively smaller ice mass extended into the conterminous United States in the northernmost areas of western Montana, Idaho, and Washington. Throughout the Pleistocene, landscape alteration occurred by (1) glacial erosion of the rocks and sediments; (2) redeposition of the eroded earth materials in a form substantially different from their source rocks, in terms of texture and overall character; and (3) disruption of preexisting drainage patterns by the newly deposited sediments. In many cases, pre-glacial drainage systems (including, for example, the Mississippi River) were rerouted because their older drainage courses became blocked with glacial sediment. The continental glaciers advanced and retreated many times across those areas. During each ice advance, or glaciation, erosion and deposition occurred, and the landscape was again altered. Through successive glaciations, the landscape and the bedrock surface gradually came to resemble their present configurations. As continental ice sheets receded and the Pleistocene ended, erosion and deposition of sediment (for example in stream valleys) continued to shape the landscape up to the present day (albeit to a lesser extent than during glaciation). The interval of time since the last recession of the glaciers is called the Holocene and, together with the Pleistocene, constitutes the Quaternary Period of geologic time; this publication characterizes the three-dimensional geometry of the Quaternary sediments and the bedrock surface that lies beneath. The pre-glacial landscape was underlain mostly by weathered bedrock generally similar in nature to that found in many areas of the non-glaciated United States. Glacial erosion and redeposition of earth materials produced a young, mineral-rich soil that formed the basis for the highly productive agricultural economy in the U.S. midcontinent. Extensive buried sands and gravels within the glacial deposits also provided a stimulus to other economic sectors by serving as high-quality aquifers supplying groundwater to the region’s industry and cities. An understanding of the three-dimensional distribution of these glacial sediments has direct utility for addressing various societal issues including groundwater quality and supply, and landscape and soil response to earthquake-induced shaking. The Quaternary sediment thickness map and bedrock topographic map shown here provide a regional overview and are intended to supplement the more detailed work on which they are based. Detailed mapping is particularly useful in populated areas for site-specific planning. In contrast, regional maps such as these serve to place local, detailed mapping in context; to permit the extrapolation of data into unmapped areas; and to depict large-scale regional geologic features and patterns that are beyond the scope of local, detailed mapping. They also can enhance the reader’s general understanding of the region’s landscape and geologic history and provide a source of information for regional decision making that could benefit by improved predictability of bedrock depth beneath the unconsolidated Quaternary sediments. To enable these maps to be analyzed in conjunction with other types of information, this publication also includes the map data in GIS compatible format.

Scientific Investigations Map↗
USGS2022

Virginia Bridge Scour Pilot Study—Hydrological Tools

Hydrologic and geophysical components interact to produce streambed scour. This study investigates methods for improving the utility of estimates of hydrologic flow in streams and rivers used when evaluating potential pier scour over the design-life of highway bridges in Virginia. Recent studies of streambed composition identify potential bridge design cost savings when attributes of cohesive soil and weathered rock unique to certain streambeds are considered within the bridge planning design. To achieve potential cost savings, however, attributes and effects of scour forces caused by water movement across the streambed surface must be accurately described and estimated. This study explores the potential for improving estimates of the hydrologic component, namely hydrologic flow, afforded by empirically based deterministic, probabilistic, and statistical modeling of flows using streamgage data from 10 selected sites in Virginia. Methods are described and tools are provided that may assist with estimating hydrological components of flow duration and potential cumulative stream power for bridge designs in specific settings, and calculation of comprehensive projections of anticipated individual bridge pier scour rates. Examples of hydrologic properties needed to determine the rates of streambed scour are described for sites spanning a range of basin sizes and locations in Virginia. Deterministic, probabilistic, and statistical modeling methods are demonstrated for estimating hydrological components of streambed scour over a bridge design lifespan. Eight tools provide examples of streamflow analysis using daily and instantaneous streamflow data collected at 10 study sites in Virginia. Tool 1 provides a generalized system dynamics model of streamflow and sediment motion that may be used to estimate hydrologic flow over time. Tool 2 illustrates at-a-station hydraulic geometry using methods pioneered by Leopold and others. Tool 3 provides a system dynamics model developed to test the use of Monte-Carlo sampling of instantaneous streamflow measurements to augment and increase precision of site-specific period-of-record daily-flow values useful for driving stream-power and streambed scour estimates. Tool 4 integrates deterministic modeling, maximum likelihood logistic regression, and Monte-Carlo sampling to identify probable hydrologic flows. Tool 5 provides instantaneous flow hydrologic envelope profiles, using measured instantaneous flow data integrated with measured daily-flow value data. Tool 6 provides precise estimates of hydrologic flow over entire data time-series suitable for driving scour simulation models. Tool 7 provides a threshold of flow and probability of time-under-load interactive calculator that allows selection of a desired bridge design lifespan, ranging from 1 to 250 years, and identification of a flow interval of interest. Tool 8 provides a flow-random sampling interactive tool, developed to facilitate easy access to large datasets of randomly sampled flow data measurements from unique locations for purposes of computing and testing future models of bridge pier scour.

Virginia↗
USGS2000

An assessment of irrigation needs and crop yield for the United States under potential climate changes

Past assessments of climate change on U.S. agriculture have mostly focused on changes in crop yield. Few studies have included the entire conterminous U.S., and few studies have assessed changing irrigation requirements. None have included the effects of changing soil moisture characteristics as determined by changing climatic forcing. This study assesses changes in irrigation requirements and crop yields for five crops in the areas of the U.S. where they have traditionally been grown. Physiologically-based crop models are used to incorporate inputs of climate, soils, agricultural management, and drought stress tolerance. Soil moisture values from a macroscale hydrologic model run under a future climate scenario are used to initialize soil moisture content at the beginning of each growing season. Historical crop yield data is used to calibrate model parameters and determine locally acceptable drought stress as a management parameter. Changes in irrigation demand and crop yield are assessed for both means and extremes by comparing results for atmospheric forcing close to the present climate with those for a future climate scenario. Assessments using the Canadian Center for Climate Modeling and Analysis General Circulation Model (CGCM1) indicate greater irrigation demands in the southern U.S. and decreased irrigation demands in the northern and western U.S. Crop yields typically increase except for winter wheat in the southern U.S. and corn. Variability in both irrigation demands and crop yields increases in most cases. Assessment results for the CGCM1 climate scenario are compared to those for the Hadley Centre for Climate Prediction and Research GCM (HadCM2) scenario for southwestern Georgia. The comparison shows significant differences in irrigation and yield trends, both in magnitude and direction. The differences reflect the high forecast uncertainty of current GCMs. Nonetheless, both GCMs indicate higher variability in future climatic forcing and, consequently, in the response of agricultural systems.

Open-File Report↗
USGS2021

Precipitation-driven flood-inundation mapping of the Little Blue River at Grandview, Missouri

The U.S. Geological Survey (USGS), in cooperation with the City of Grandview, Missouri, assessed flooding of the Little Blue River at Grandview resulting from varying precipitation magnitudes and durations and expected land-cover changes. The precipitation scenarios were used to develop a library of flood-inundation maps that included a 3.5-mile reach of the Little Blue River and tributaries within and adjacent to the city. A hydrologic model of the upper Little Blue River Basin and a hydraulic model of a selected study reach of the Little Blue River and tributaries were constructed to assess streamflow magnitudes associated with simulated precipitation amounts and the resulting flood-inundation conditions. The U.S. Army Corps of Engineers Hydrologic Engineering Center-Hydrologic Modeling System (HEC–HMS; version 4.4.1) was used to simulate the amount of streamflow produced from a range of rain events. The Hydrologic Engineering Center-River Analysis System (HEC–RAS; version 5.0.7) was then used to construct a steady-state hydraulic model to map resulting areas of flood inundation. Both models were calibrated to the May 28, 2020, high-flow event that produced a peak streamflow approximating a 10-percent annual exceedance probability (10-year flood-frequency recurrence interval) at the Little Blue River at Grandview streamgage (USGS station 06893750). The calibrated HEC–HMS model was used to simulate streamflows from design rainfall events of 1- to 8-hour durations and ranging from a 100- to 0.2-percent annual exceedance probability. Flood-inundation maps were produced for USGS streamflow stages of 17.0 feet (ft), or near bankfull, to 23.0 ft, or a stage exceeding the 0.2-percent annual exceedance interval flood, using the HEC–RAS model. The consequence of each precipitation duration-frequency value was represented by a 1-ft increment inundation map based on the generated peak streamflow from that rainfall event and the corresponding stage at the reference USGS streamgage. Four scenarios were developed with the HEC–HMS hydrologic model: (1) current (2016) land cover, normal antecedent soil-moisture conditions; (2) current land cover, wet antecedent soil-moisture conditions; (3) future land cover, normal antecedent soil-moisture conditions; and (4) future land cover, wet antecedent soil-moisture conditions. The future land-cover condition was estimated based on anticipated development in the basin. All precipitation scenarios were input into each of the four land-cover antecedent moisture conditions and then assigned to a resulting flood-inundation map based on the generated peak flow and corresponding stage at the reference streamgage.

Missouri↗
USGS2016

Urban base flow with low impact development

A novel form of urbanization, low impact development (LID), aims to engineer systems that replicate natural hydrologic functioning, in part by infiltrating stormwater close to the impervious surfaces that generate it. We sought to statistically evaluate changes in a base flow regime because of urbanization with LID, specifically changes in base flow magnitude, seasonality, and rate of change. We used a case study watershed in Clarksburg, Maryland, in which streamflow was monitored during whole-watershed urbanization from forest and agricultural to suburban residential development using LID. The 1.11-km 2 watershed contains 73 infiltration-focused stormwater facilities, including bioretention facilities, dry wells, and dry swales. We examined annual and monthly flow during and after urbanization (2004–2014) and compared alterations to nearby forested and urban control watersheds. We show that total streamflow and base flow increased in the LID watershed during urbanization as compared with control watersheds. The LID watershed had more gradual storm recessions after urbanization and attenuated seasonality in base flow. These flow regime changes may be because of a reduction in evapotranspiration because of the overall decrease in vegetative cover with urbanization and the increase in point sources of recharge. Precipitation that may once have infiltrated soil, been stored in soil moisture to be eventually transpired in a forested landscape, may now be recharged and become base flow. The transfer of evapotranspiration to base flow is an unintended consequence to the water balance of LID.

Hydrological Processes↗
USGS2005

Heat as a tracer to estimate dissolved organic carbon flux from a restored wetland

Heat was used as a natural tracer to characterize shallow ground water flow beneath a complex wetland system. Hydrogeologic data were combined with measured vertical temperature profiles to constrain a series of two‐dimensional, transient simulations of ground water flow and heat transport using the model code SUTRA ( Voss 1990 ). The measured seasonal temperature signal reached depths of 2.7 m beneath the pond. Hydraulic conductivity was varied in each of the layers in the model in a systematic manual calibration of the two‐dimensional model to obtain the best fit to the measured temperature and hydraulic head. Results of a series of representative best‐fit simulations represent a range in hydraulic conductivity values that had the best agreement between simulated and observed temperatures and that resulted in simulated pond seepage values within 1 order of magnitude of pond seepage estimated from the water budget. Resulting estimates of ground water discharge to an adjacent agricultural drainage ditch were used to estimate potential dissolved organic carbon (DOC) loads resulting from the restored wetland. Estimated DOC loads ranged from 45 to 1340 g C/(m 2 year), which is higher than estimated DOC loads from surface water. In spite of the complexity in characterizing ground water flow in peat soils, using heat as a tracer provided a constrained estimate of subsurface flow from the pond to the agricultural drainage ditch.

Ground Water↗
USGS2009

Database of the geologic map of North America— Adapted from the map by J.C. Reed, Jr. and others (2005)

Introduction The Geological Society of America's (GSA) Geologic Map of North America (Reed and others, 2005a; 1:5,000,000) shows the geology of a significantly large area of the Earth, centered on North and Central America and including the submarine geology of parts of the Atlantic and Pacific Oceans. This map is now converted to a Geographic Information System (GIS) database that contains all geologic and base-map information shown on the two printed map sheets and the accompanying explanation sheet. We anticipate this map database will be revised at some unspecified time in the future, likely through the actions of a steering committee managed by the GSA and staffed by scientists from agencies including those responsible for the original map compilation. Regarding the use of this product, as noted by the map's compilers: “The Geologic Map of North America is an essential educational tool for teaching the geology of North America to university students and for the continuing education of professional geologists in North America and elsewhere. In addition, simplified maps derived from the Geologic Map of North America are useful for enlightening younger students and the general public about the geology of the continent.” With publication of this database, the preparation of any type of simplified map is made significantly easier. More important perhaps, the database provides a more accessible means to explore the map information and to compare and analyze it in conjunction with other types of information (for example, land use, soils, biology) to better understand the complex interrelations among factors that affect Earth resources, hazards, ecosystems, and climate.

Data Series↗
USGS2015

Monitoring ground-surface heating during expansion of the Casa Diablo production well field at Mammoth Lakes, California

The Long Valley hydrothermal system supports geothermal power production from 3 binary plants (Casa Diablo) near the town of Mammoth Lakes, California. Development and growth of thermal ground at sites west of Casa Diablo have created concerns over planned expansion of a new well field and the associated increases in geothermal fluid production. To ensure that all areas of ground heating are identified prior to new geothermal development, we obtained high-resolution aerial thermal infrared imagery across the region. The imagery covers the existing and proposed well fields and part of the town of Mammoth Lakes. Imagery results from a predawn flight on Oct. 9, 2014 readily identified the Shady Rest thermal area (SRST), one of two large areas of ground heating west of Casa Diablo, as well as other known thermal areas smaller in size. Maximum surface temperatures at 3 thermal areas were 26–28 °C. Numerous small areas with ground temperatures >16 °C were also identified and slated for field investigations in summer 2015. Some thermal anomalies in the town of Mammoth Lakes clearly reflect human activity.Previously established projects to monitor impacts from geothermal power production include yearly surveys of soil temperatures and diffuse CO2 emissions at SRST, and less regular surveys to collect samples from fumaroles and gas vents across the region. Soil temperatures at 20 cm depth at SRST are well correlated with diffuse CO2 flux, and both parameters show little variation during the 2011–14 field surveys. Maximum temperatures were between 55–67 °C and associated CO2 discharge was around 12–18 tonnes per day. The carbon isotope composition of CO2 is fairly uniform across the area ranging between –3.7 to –4.4 ‰. The gas composition of the Shady Rest fumarole however has varied with time, and H2S concentrations in the gas have been increasing since 2009.

California↗
USGS2011

Erosion, storage, and transport of sediment in two subbasins of the Rio Puerco, New Mexico

Arroyos in the American Southwest proceed through cut-and-fill cycles that operate at centennial to millennial time scales. The geomorphic community has put much effort into understanding the causes of arroyo cutting in the late Quaternary and in the modern record (late 1800s), while little effort has gone into understanding how arroyos fill and the sources of this fill. Here, we successfully develop a geographic information system (GIS)-modeled sediment budget that is based on detailed field measurements of hillslope and channel erosion and deposition. Field measurements were made in two arroyo basins draining different lithologies and undergoing different land disturbance (Volcano Hill Wash, 9.30 km 2 ; Arroyo Chavez, 2.11 km 2 ) over a 3 yr period. Both basins have incised channels that formed in response to the late nineteenth-century incision of the Rio Puerco. Large volumes of sediment were generated during arroyo incision, equal to more than 100 yr of the current annual total sediment load (bed load + suspended load) in each basin. Downstream reaches in both arroyos are presently aggrading, and the main source of the sediment is from channel erosion in upstream reaches and first- and second-order tributaries. The sediment budget shows that channel erosion is the largest source of sediment in the current stage of the arroyo cycle: 98% and 80% of the sediment exported out of Volcano Hill Wash and Arroyo Chavez, respectively. The geomorphic surface most affected by arroyo incision and one of the most important sediment sources is the valley alluvium, where channel erosion, gullying, soil piping, and grazing all occur. Erosion rates calculated for the entire Volcano Hill Wash (-0.26 mm/yr) and Arroyo Chavez (-0.53 mm/yr) basins are higher than the modeled upland erosion rates in each basin, reflecting the large contributions from channel erosion. Erosion rates in each basin are affected by a combination of land disturbance (grazing) and lithology--erodible sandstones and shales in Arroyo Chavez compared with basalt for Volcano Hill Wash. Despite these differences, hillslope sediment yields are similar to long-term denudation rates. As the arroyo fills over time from mouth to headwaters, hillslope sediment becomes a more significant sediment source.

New Mexico↗
USGS2004

Characterization of Ground-Water Quality, Upper Republican Natural Resources District, Nebraska, 1998-2001

Nearly all rural inhabitants and livestock in the Upper Republican Natural Resources District (URNRD) in southwestern Nebraska use ground water that can be affected by elevated nitrate concentrations. The development of ground-water irrigation in this area has increased the vulnerability of ground water to the introduction of fertilizers and other agricultural chemicals. In 1998, the U.S. Geological Survey, in cooperation with the Upper Republican Natural Resources District, began a study to characterize the quality of ground water in the Upper Republican Natural Resources District area with respect to physical properties and concentrations of major ions, coliform bacteria, nitrate, and pesticides, and to assess the presence of nitrogen concentrations in the unsaturated zone. At selected well sites, the ground-water characterization also included tritium and nitrogen-isotope analyses to provide information about the approximate age of the ground water and potential sources of nitrogen detected in ground-water samples, respectively. In 1998, ground-water samples were collected from 101 randomly selected domestic-well sites. Of the 101 samples collected, 26 tested positive for total coliform bacteria, exceeding the U.S. Environmental Protection Agency's Maximum Contaminant Level (MCL) of zero colonies. In 1999, ground-water samples were collected from 31 of the 101 well sites, and 16 tested positive for coliform bacteria. Nitrates were detected in ground water from all domestic-well samples and from all but four of the irrigation-well samples collected from 1998 to 2001. Eight percent of the domestic-well samples and 3 percent of the irrigation-well samples had nitrate concentrations exceeding the U.S. Environmental Protection Agency's MCL for drinking water of 10 milligrams per liter. Areas with nitrate concentrations exceeding 6 milligrams per liter, the URNRD's ground-water management-plan action level, were found predominantly in north-central Chase, western and south-central Dundy, and south-central Perkins Counties. Generally, these concentrations were detected in samples from wells located in upland areas with permeable soils and a high percentage of cropland. In 1999, 31 of the ground-water samples collected from irrigation wells were analyzed for pesticides, and 14 samples (45 percent) had detectable concentrations of at least one pesticide compound. In 2000, all of the 23 irrigation-well samples analyzed had one or more pesticides present at detectable concentrations. In 2001, 12 of 26 domestic-well samples (46 percent) had detectable concentrations. Although the analytical method used during the study was changed to increase the number of pesticides included in the analyses, the pesticides detected in the ground-water samples from domestic and irrigation wells were limited to the commonly used herbicide compounds acetochlor, alachlor, atrazine, metolachlor, prometon, propachlor, propazine, trifluralin, and the atrazine degradation product deethylatrazine. Of the compounds detected, only atrazine (3.0 micrograms per liter) and alachlor (2.0 micrograms per liter) have MCLs established by the U.S. Environmental Protection Agency. None of the ground-water samples from the URNRD study area had concentrations that exceeded either MCL. Tritium age-dating analyses indicate water from about one-third of the sites entered the ground-water system prior to 1952. Because the increase in agricultural practices occurred during the 1950s and 1960s, it can be assumed that this water was not influenced by agricultural practices. Nitrogen-isotope speciation analyses for samples from three irrigation wells indicated that the source of nitrates in the ground water probably is synthetic fertilizer; however, the source at most irrigation wells probably is either naturally occurring or a mixture of water from various anthropogenic sources (such as synthetic fertilizer and animal waste).

Scientific Investigations Report↗
USGS2002

Dust coatings on basaltic rocks and implications for thermal infrared spectroscopy of Mars

Thin coatings of atmospherically deposited dust can mask the spectral characteristics of underlying surfaces on Mars from the visible to thermal infrared wavelengths, making identification of substrate and coating mineralogy difficult from lander and orbiter spectrometer data. To study the spectral effects of dust coatings, we acquired thermal emission and hemispherical reflectance spectra (5–25 μm; 2000–400 cm −1 ) of basaltic andesite coated with different thicknesses of air fall‐deposited palagonitic soils, fine‐grained ceramic clay powders, and terrestrial loess. The results show that thin coatings (10–20 μm) reduce the spectral contrast of the rock substrate substantially, consistent with previous work. This contrast reduction continues linearly with increasing coating thickness until a “saturation thickness” is reached, after which little further change is observed. The saturation thickness of the spectrally flat palagonite coatings is ∼100–120 μm, whereas that for coatings with higher spectral contrast is only ∼50–75 μm. Spectral differences among coated and uncoated samples correlate with measured coating thicknesses in a quadratic manner, whereas correlations with estimated surface area coverage are better fit by linear functions. Linear mixture modeling of coated samples using the rock substrate and coating materials as end‐members is also consistent with their measured coating thicknesses and areal coverage. A comparison of ratios of Thermal Emission Spectrometer (TES) spectra of dark and bright intracrater and windstreak deposits associated with Radau crater suggests that the dark windstreak material may be coated with as much as 90% areal coverage of palagonitic dust. The data presented here also will help improve interpretations of upcoming mini‐TES and Thermal Emission Imaging System (THEMIS) observations of coated Mars surface materials.

Journal of Geophysical Research E: Planets↗
USGS2015

Global patterns and environmental controls of perchlorate and nitrate co-occurrence in arid and semi-arid environments

Natural perchlorate (ClO 4 − ) is of increasing interest due to its wide-spread occurrence on Earth and Mars, yet little information exists on the relative abundance of ClO 4 − compared to other major anions, its stability, or long-term variations in production that may impact the observed distributions. Our objectives were to evaluate the occurrence and fate of ClO 4 − in groundwater and soils/caliche in arid and semi-arid environments (southwestern United States, southern Africa, United Arab Emirates, China, Antarctica, and Chile) and the relationship of ClO 4 − to the more well-studied atmospherically deposited anions NO 3 − and Cl − as a means to understand the prevalent processes that affect the accumulation of these species over various time scales. ClO 4 − is globally distributed in soil and groundwater in arid and semi-arid regions on Earth at concentrations ranging from 10 −1 to 10 6 μg/kg. Generally, the ClO 4 − concentration in these regions increases with aridity index, but also depends on the duration of arid conditions. In many arid and semi-arid areas, NO 3 − and ClO 4 − co-occur at molar ratios (NO 3 − /ClO 4 − ) that vary between ∼10 4 and 10 5 . We hypothesize that atmospheric deposition ratios are largely preserved in hyper-arid areas that support little or no biological activity (e.g. plants or bacteria), but can be altered in areas with more active biological processes including N 2 fixation, N mineralization, nitrification, denitrification, and microbial ClO 4 − reduction, as indicated in part by NO 3 − isotope data. In contrast, much larger ranges of Cl − /ClO 4 − and Cl − /NO 3 − ratios indicate Cl − varies independently from both ClO 4 − and NO 3 − . The general lack of correlation between Cl − and ClO 4 − or NO 3 − implies that Cl − is not a good indicator of co-deposition and should be used with care when interpreting oxyanion cycling in arid systems. The Atacama Desert appears to be unique compared to all other terrestrial locations having a NO 3 − /ClO 4 − molar ratio ∼10 3 . The relative enrichment in ClO 4 − compared to Cl − or NO 3 − and unique isotopic composition of Atacama ClO 4 − may reflect either additional in-situ production mechanism(s) or higher relative atmospheric production rates in that specific region or in the geological past. Elevated concentrations of ClO 4 − reported on the surface of Mars, and its enrichment with respect to Cl − and NO 3 − , could reveal important clues regarding the climatic, hydrologic, and potentially biologic evolution of that planet. Given the highly conserved ratio of NO 3 − /ClO 4 − in non-biologically active areas on Earth, it may be possible to use alterations of this ratio as a biomarker on Mars and for interpreting major anion cycles and processes on both Mars and Earth, particularly with respect to the less-conserved NO 3 − pool terrestrially.

Geochimica et Cosmochimica Acta↗
USGS2011

Historical trends of hypoxia in Changjiang River estuary: Applications of chemical biomarkers and microfossils

Over the past two decades China has become the largest global consumer of fertilizers, which has enhanced river nutrient fluxes and caused eutrophication and hypoxia in the Yangtze (Changjiang) large river delta-front estuary (LDE). In this study, we utilized plant pigments, lignin-phenols, stable isotopes (δ 13 C and δ 15 N) and foraminiferal microfossils in 210 Pb dated cores to examine the history of hypoxia in the Changjiang LDE. Two sediment cores were collected onboard R/V Dong Fang Hong 2 using a stainless-steel box-corer; one at a water depth of 24.7 m on Jun. 15, 2006 and the other at 52 m on Nov. 20, 2007, both in the hypoxic region off the Changjiang LDE. There has been a significant increase in the abundance of plant pigments after 1979 that are indicators of enhanced diatom and cyanobacterial abundance, which agrees with post-1980 record of increasing nutrient loads in the Changjiang River. The increased inputs of terrestrially derived materials to the LDE are largely woody plant sources and most likely due to deforestation that began in the early 1950s. However, post-1960 lignin data did not reflect enhanced loading of woody materials despite continued deforestation possibly due to increased trapping from greater dam construction, a reduction of deforestation in the drainage basin since the last 1990s, and soil conservation practices. The lack of linkages between bulk indices (stable isotopes, % OC, molar C/N ratios) and microfossil/chemical biomarkers may reflect relative differences in the amount of carbon tracked by these different proxies. Although NO3− is likely responsible for most of the changes in phytoplankton production (post 1970s), historical changes in N loading from the watershed and hypoxia on the LDE shelf may not be as well linked in East China Sea (ECS) sediments due to possible denitrification/ammonification processes; finally, increases in low-oxygen tolerant foraminiferal microfossils indicate there has been an increase in the number of hypoxic bottom water events on the Changjiang LDE over the past 60 years.

Changjiang River↗