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At least 739 records · Page 41Linked to original sources
USGS2009

Low-flow frequency and flow duration of selected South Carolina streams in the Pee Dee River basin through March 2007

Part of the mission of the South Carolina Department of Health and Environmental Control and the South Carolina Department of Natural Resources is to protect and preserve South Carolina's water resources. Doing so requires an ongoing understanding of streamflow characteristics of the rivers and streams in South Carolina. A particular need is information concerning the low-flow characteristics of streams; this information is especially important for effectively managing the State's water resources during critical flow periods such as the severe drought that occurred between 1998 and 2002 and the most recent drought that occurred between 2006 and 2009. In 2008, the U.S. Geological Survey, in cooperation with the South Carolina Department of Health and Environmental Control, initiated a study to update low-flow statistics at continuous-record streamgaging stations operated by the U.S. Geological Survey in South Carolina. Under this agreement, the low-flow characteristics at continuous-record streamgaging stations will be updated in a systematic manner during the monitoring and assessment of the eight major basins in South Carolina as defined and grouped according to the South Carolina Department of Health and Environmental Control's Watershed Water Quality Management Strategy. Depending on the length of record available at the continuous-record streamgaging stations, low-flow frequency characteristics are estimated for annual minimum 1-, 3-, 7-, 14-, 30-, 60-, and 90-day average flows with recurrence intervals of 2, 5, 10, 20, 30, and 50 years. Low-flow statistics are presented for 18 streamgaging stations in the Pee Dee River basin. In addition, daily flow durations for the 5-, 10-, 25-, 50-, 75-, 90-, and 95-percent probability of exceedance also are presented for the stations. The low-flow characteristics were computed from records available through March 31, 2007. The last systematic update of low-flow characteristics in South Carolina occurred more than 20 years ago and included data through March 1987. Of the 17 streamgaging stations included in this study, 15 had low-flow characteristics that were published in previous U.S. Geological Survey reports. A comparison of the low-flow characteristic for the minimum average flow for a 7-consecutive-day period with a 10-year recurrence interval from this study with the most recently published values indicated that 10 of the 15 streamgaging stations had values that were within ±25 percent of each other. Nine of the 15 streamgaging stations had negative percentage differences indicating the low-flow statistic had decreased since the previous study, 4 streamgaging stations had positive percent differences indicating that the low-flow statistic had increased since the previous study, and 2 streamgaging stations had a zero percent difference indicating no change since the previous study. The low-flow characteristics are influenced by length of record, hydrologic regime under which the record was collected, techniques used to do the analysis, and other changes that may have occurred in the watershed.

North Carolina, South Carolina↗
USGS2009

Predicting the natural flow regime: Models for assessing hydrological alteration in streams

Understanding the extent to which natural streamflow characteristics have been altered is an important consideration for ecological assessments of streams. Assessing hydrologic condition requires that we quantify the attributes of the flow regime that would be expected in the absence of anthropogenic modifications. The objective of this study was to evaluate whether selected streamflow characteristics could be predicted at regional and national scales using geospatial data. Long-term, gaged river basins distributed throughout the contiguous US that had streamflow characteristics representing least disturbed or near pristine conditions were identified. Thirteen metrics of the magnitude, frequency, duration, timing and rate of change of streamflow were calculated using a 20-50 year period of record for each site. We used random forests (RF), a robust statistical modelling approach, to develop models that predicted the value for each streamflow metric using natural watershed characteristics. We compared the performance (i.e. bias and precision) of national- and regional-scale predictive models to that of models based on landscape classifications, including major river basins, ecoregions and hydrologic landscape regions (HLR). For all hydrologic metrics, landscape stratification models produced estimates that were less biased and more precise than a null model that accounted for no natural variability. Predictive models at the national and regional scale performed equally well, and substantially improved predictions of all hydrologic metrics relative to landscape stratification models. Prediction error rates ranged from 15 to 40%, but were 25% for most metrics. We selected three gaged, non-reference sites to illustrate how predictive models could be used to assess hydrologic condition. These examples show how the models accurately estimate predisturbance conditions and are sensitive to changes in streamflow variability associated with long-term land-use change. We also demonstrate how the models can be applied to predict expected natural flow characteristics at ungaged sites. ?? 2009 John Wiley & Sons, Ltd.

River Research and Applications↗
USGS2008

Natural and Human Influences on Water Quality in a Shallow Regional Unconsolidated Aquifer, Northern Atlantic Coastal Plain

Data collected from more than 400 wells in the surficial unconfined aquifer in the Northern Atlantic Coastal Plain (New York through North Carolina) were compiled and analyzed to improve understanding of multiple natural and human influences on water quality in such shallow regional aquifers. Geochemical patterns were identified and described through principal components analysis on major ions, and correlation and logistic regression were used to relate observed concentrations of nitrate and selected pesticide compounds (atrazine, metolachlor, simazine, and deethylatrazine, an atrazine degradate) and volatile organic compounds (chloroform, 1,1,1-trichloroethane, tetrachlorethene, and methyl tert-butyl ether) to likely influences, such as observed geochemical patterns, land use, hydrogeology, and soils. Variability in major-ion concentrations is primarily related to ionic strength and redox condition. Concentrations of nitrate, pesticides, and volatile organic compounds are related to natural conditions, as well as the distribution of likely sources reflected in land use. Nitrate is most common in aerobic ground water and in relatively well-drained areas, for example; concentrations greater than 0.4 milligrams per liter may result from a variety of human activities, although concentrations greater than 3 milligrams per liter are more likely in agricultural areas. Atrazine, deethylatrazine, and metolachlor also are related to geochemical patterns, likely because ground-water geochemistry reflects hydrogeologic and soil conditions affecting pesticide transport to the water table. Results demonstrate the value of geochemical information along with the distribution of sources and other influences to understanding the regional occurrence of selected compounds in ground water. Such influences are not unique to the Northern Atlantic Coastal Plain, and thus observations and interpretations are relevant to broader areas.

Scientific Investigations Report↗
USGS2002

Hydrogeology and water quality of the Upper Three Runs aquifer in the vicinity of the Gibson Road Landfill, Fort Gordon, Georgia, June-November 1999

Fort Gordon military installation, a U.S. Department of the Army facility, is located in east-central Georgia southwest of Augusta. The military base operates a three-phase unlined landfill—Gibson Road Landfill— to store a variety of wastes. Phases I and II stored only household wastes, and these phases were discontinued during the mid–1990s. Fort Gordon currently (1999) operates Phase III of the landfill that stores only construction and demolition debris. Water-quality monitoring detected selected trace elements and organic compounds exceeding the maximum contaminant levels of the U.S. Environmental Protection Agency, National Primary Drinking Water Standards. The selected trace elements and organic compounds detected showed that contamination of ground water had occurred in the vicinity of the landfill. In 1999, the U.S. Geological Survey, in cooperation with the Environmental and Natural Resources Management Office of the U.S. Army Signal Center and Fort Gordon, Georgia, began an assessment of the hydrogeology and water quality in shallow ground water in the vicinity of the Gibson Road Landfill to delineate the extent of a ground-water contamination plume in the vicinity of the landfill. Hydrogeologic units in the Augusta area include the Upper Three Runs aquifer, the Gordon aquifer, the Millers Pond aquifer, and the Dublin aquifer. Only the shallowest aquifer, Upper Three Runs, was penetrated during this study. The Upper Three Runs aquifer is composed of sediments of the Barnwell Group. Mostly, these sediments are highly permeable fine to medium, well-sorted sand with lenses of clay. Ground-water flow is from northwest to southeast and generally was unaffected by seasonal variation during the period of study (June–November 1999). Water-table altitudes in the landfill area for the study period ranged from 394 feet (ft) to 445 ft above sea level. Ground-water samples analyzed for organic compounds and selected trace elements by a U. S. Environmental Protection Agency (USEPA) approved statistical test revealed that increases in contaminant concentrations above the detection limits had occurred during March and September 1999 in five wells—one of which is located upgradient. These organic compounds, respective increases in concentration, and the wells in which they were detected are: methylene chloride—wells 28AA29 (24 parts per billion [ppb] and 46 ppb), 28AA30 (86 ppb and 130 ppb), and 28AA31 (240 ppb and 140 ppb); 1,1-dichloroethene—well 28AA31 (10 ppb and 5.7 ppb); 1,1-dichloroethane— wells 28AA30 (81 ppb and 140 ppb) and 28AA31 (200 ppb and 130 ppb); and 1,1,1-trichloroethane—well 28AA31 (61 ppb and 37 ppb). Although in some wells the concentration decreased from March to September, the median concentrations were still higher in certain groups. Trace element compounds, their respective increases in concentration, and the wells in which they were detected are: chromium—well 28AA30 (1,190 ppb), vanadium—well 28AA30 (104 ppb); barium—wells 28AA27 (42.2 ppb) and 28AA32 (140 ppb), and beryllium—well 28AA30 (6.3 ppb). These increases occurred in September, with the exception of chromium in well 28AA30, which occurred in March. Although a statistical test indicated increases in contaminant concentrations had occurred, water from wells 28AA27, 28AA30, 28AA31, and 28AA32 had a decrease in contaminant concentrations from February 1998 to September 1999. U.S. Environmental Protection Agency, National Primary Drinking Water Regulations Maximum Contaminant Levels (PMCLs), formerly (MCLs) were exceeded in water from four wells for organic compounds and in five wells by selected trace elements during the February 1998, March 1999, and September 1999 sampling periods. The concentrations for the following organic compounds and the associated wells are: methylene chloride (PMCL is 5 ppb)—wells 28AA27 (February, 37 ppb; March, 24 ppb; and September, 9.6 ppb), 28AA29 (February, 20 ppb; March, 24 ppb; and September, 46 ppb), 28AA30 (February, 50 ppb; March, 86 ppb; and September, 130 ppb), and 28AA31 (February, 330 ppb; March 240 ppb; and September, 140 ppb); vinyl chloride (PMCL is 2 ppb)—well 28AA29 (March, 3.6 ppb; and September, 4.4 ppb); 1,1-dichloroethene (PMCL is 7 ppb)—wells 28AA30 (March 10 ppb; and September, 17 ppb) and 28AA31 (February, 13 ppb; and March, 10 ppb); and 1,1,2-trichloroethane (PMCL is 5 ppb)—well 28AA30 (March, 33 ppb). Contaminant concentrations decreased in well 28AA31 from March to September 1999; however, concentrations still exceeded the PMCL. The concentrations for the following selected trace elements exceeding PMCL and the associated wells during the sampling periods February 1998, March 1999, and September 1999 are: mercury (PMCL is 2 ppb)—well 28AA24 (September, 2.82 ppb), well 28AA25 (February, 3.1 ppb; March, 2.11 ppb; and September, 2.28 ppb), and well 28AA30 (September, 2.82 ppb); arsenic (PMCL is 50 ppb)—well 28AA30 (February, 90 ppb; and September, 114 ppb); thallium (PMCL is 2 ppb)—wells 28AA27 (March, 2.08 ppb) and 28AA29 (February, 2.56); barium (PMCL is 2,000 ppb)—well 28AA30 (March, 4,490 ppb); chromium (PMCL is 30 ppb)—well 28AA30 (February, 630 ppb; and March, 1,190 ppb); and beryllium (PMCL is 4 ppb)—well 28AA30 (September, 6.3 ppb). Water from seven wells, three of which are upgradient of the landfill, contained organic compounds and/or selected trace elements exceeding PMCLs during the period February 1998 to September 1999 according to private consultants. Contaminants present in upgradient wells most likely were caused by chemical dispersion, leachate migration, incorrectly defined landfill area, or natural ground-water flow beneath the landfill.

Georgia↗
USGS2004

Methods of analysis by the U.S. Geological Survey National Water Quality Laboratory-Determination of organochlorine pesticides and polychlorinated biphenyls in bottom and suspended sediment by gas chromatography with electron-capture detection

A method applicable for the determination of 19 organochlorine (OC) pesticides, including total toxaphene as a complex mixture, and 3 polychlorinated biphenyl (PCB) mixtures as Aroclor equivalents--Aroclor 1016/1242, 1254, and 1260--in soil, aquatic bottom sediment, and suspended sediment is described. Method performance data are presented. The solvent system is designed to extract simultaneously selected OC pesticides and PCBs from the same sample matrix. The compounds are extracted by conventional Soxhlet extraction with dichloromethane, followed by partial isolation using gel permeation chromatography (GPC) to remove inorganic sulfur and large naturally present molecules from the sediment extract. The aliquot of extract collected from the GPC for OCs (OC pesticides and PCBs) is split into two sample fractions by alumina/silica combined-column chromatography, followed by Florisil adsorption chromatography to remove interfering compounds in the second fraction. The OC fractions are analyzed by dual capillary-column gas chromatography with electron-capture detection (GC/ECD). This report is limited to the determination of selected OC pesticides and PCBs by GC/ECD using this method. Interim reporting levels (IRLs) have been set at 0.400 to 3.12 micrograms per kilogram for 18 individual OC pesticides, 200 micrograms per kilogram for toxaphene, and 4.04 to 4.68 micrograms per kilogram for the PCBs, based on a sample size of 25-gram equivalent dry weight. These reporting levels may change following additional determinations of method detection limits.

Water-Resources Investigations Report↗
USGS1956

Saline waters in New York State, Long Island, Staten Island and Manhattan, and upstate New York

In connection with studies of the practicability of conversion of saline water to fresh water, the U. S. Geological Survey assembled data on the occurrence, distribution, quantity, and chemical quality of saline waters as of 1955 for a report entitled, "Preliminary survey of the saline water resources of the United States" to be released when completed as a U. S. Geological Survey Water Supply Paper 1374. This report comprises data for New York State. Saline water is defined herein as any mixture of fresh and salt water having more than 1,000 parts per million (ppm) of dissolved solids. In the Nation as a whole there are, of course, all gradations of salinity from 1,000 ppm up to the 30,000 to 35,000 ppm characteristic of sea water, and the even higher salinities of certain natural brines. Sea water, and other water of comparable salinity, will be referred to here as "sea water" or "high-chloride water". This report contains two parts: one for Long Island, Staten Island, and Manhattan, N. Y., and the other for Upstate New York. Figure 1 shows the locations of the places named and important occurrences of saline water in and near Long Island. Tables 1 and 2 list, respectively, well data and chemical analyses for selected wells in Long Island, Staten Island, and Manhattan, N. Y.; tables 3 and 4 list, respectively, well data and chemical analyses for selected wells in Upstate New York. For many samples, only the chloride concentration and not the total dissolved solids has been determined. However, it is safe to assume that the total dissolved solids in natural water are substantially in excess of 1,000 ppm where the chloride is at or nearly at this concentration.

New York↗
USGS2006

Effects of structural complexity enhancement on eastern red-backed salamander (Plethodon cinereus) populations in northern hardwood forests

Managing for stand structural complexity in northern hardwood forests has been proposed as a method for promoting microhabitat characteristics important to eastern red-backed salamanders (Plethodon cinereus). We evaluated the effects of alternate, structure-based silvicultural systems on red-backed salamander populations at two research sites in northwestern Vermont. Treatments included two uneven-aged approaches (single-tree selection and group-selection) and one unconventional approach, termed "structural complexity enhancement" (SCE), that promotes development of late-successional structure, including elevated levels of coarse woody debris (CWD). Treatments were applied to 2 ha units and were replicated two to four times depending on treatment. We surveyed red-backed salamanders with a natural cover search method of transects nested within vegetation plots 1 year after logging. Abundance estimates corrected for detection probability were calculated from survey data with a binomial mixture model. Abundance estimates differed between study areas and were influenced by forest structural characteristics. Model selection was conducted using Akaike Information Criteria, corrected for over-dispersed data and small sample size (QAICc). We found no difference in abundance as a response to treatment as a whole, suggesting that all of the uneven-aged silvicultural systems evaluated can maintain salamander populations after harvest. However, abundance was tied to specific structural habitat attributes associated with study plots within treatments. The most parsimonious model of habitat covariates included site, relative density of overstory trees, and density of more-decayed and less-decayed downed CWD. Abundance responded positively to the density of downed, well-decayed CWD and negatively to the density of poorly decayed CWD and to overstory relative density. CWD volume was not a strong predictor of salamander abundance. We conclude that structural complexity enhancement and the two uneven-aged approaches maintained important microhabitat characteristics for red-backed salamander populations in the short term. Over the long-term, given decay processes as a determinant of biological availability, forestry practices such as SCE that enhance CWD availability and recruitment may result in associated population responses. ?? 2006 Elsevier B.V. All rights reserved.

Forest Ecology and Management↗
USGS2009

Passive seismic monitoring of natural and induced earthquakes: Case studies, future directions and socio-economic relevance

An important discovery in crustal mechanics has been that the Earth’s crust is commonly stressed close to failure, even in tectonically quiet areas. As a result, small natural or man-made perturbations to the local stress field may trigger earthquakes. To understand these processes, Passive Seismic Monitoring (PSM) with seismometer arrays is a widely used technique that has been successfully applied to study seismicity at different magnitude levels ranging from acoustic emissions generated in the laboratory under controlled conditions, to seismicity induced by hydraulic stimulations in geological reservoirs, and up to great earthquakes occurring along plate boundaries. In all these environments the appropriate deployment of seismic sensors, i.e., directly on the rock sample, at the earth’s surface or in boreholes close to the seismic sources allows for the detection and location of brittle failure processes at sufficiently low magnitude-detection threshold and with adequate spatial resolution for further analysis. One principal aim is to develop an improved understanding of the physical processes occurring at the seismic source and their relationship to the host geologic environment. In this paper we review selected case studies and future directions of PSM efforts across a wide range of scales and environments. These include induced failure within small rock samples, hydrocarbon reservoirs, and natural seismicity at convergent and transform plate boundaries. Each example represents a milestone with regard to bridging the gap between laboratory-scale experiments under controlled boundary conditions and large-scale field studies. The common motivation for all studies is to refine the understanding of how earthquakes nucleate, how they proceed and how they interact in space and time. This is of special relevance at the larger end of the magnitude scale, i.e., for large devastating earthquakes due to their severe socio-economic impact.

Book chapter↗
USGS1981

The partitioning of copper among selected phases of geologic media of two porphyry copper districts, Puerto Rico

In experiments designed to determine the manner in which copper is partitioned among selected phases that constitute geologic media, we have applied the five-step sequential extraction procedure of Chao and Theobald to the analysis of drill core, soils, and stream sediments of the Rio Vivi and Rio Tanama porphyry copper districts of Puerto Rico. The extraction procedure affords a convenient means of determining the trace-metal content of the following fractions: (1) Mn oxides and “reactive” Fe oxides; (2) “amorphous” Fe oxides; (3) “crystalline” Fe oxides; (4) sulfides and magnetite; and (5) silicates. An additional extraction between steps (1) and (2) was performed to determine organic-related copper in stream sediments. The experimental results indicate that apportionment of copper among phases constituting geologic media is a function of geochemical environment. Distinctive partitioning patterns were derived from the analysis of drill core from each of three geochemical zones: (a) the supergene zone of oxidation; (b) the supergene zone of enrichment; and (c) the hypogene zone; and similarly, from the analysis of; (d) soils on a weakly leached capping; (e) soils on a strongly leached capping; and (f) active stream sediment. The experimental results also show that geochemical contrasts (anomaly-to-background ratios) vary widely among the five fractions of each sampling medium investigated, and that at least one fraction of each medium provides substantially stronger contrast than does the bulk medium. Fraction (1) provides optimal contrast for stream sediments of the district; fraction (2) provides optimal contrast for soils on a weakly leached capping; fraction (3) provides optimal contrast for soils on a strongly leached capping. Selective extraction procedures appear to have important applications to the orientation and interpretive stages of geochemical exploration. Further investigation and testing of a similar nature are recommended.

Puerto Rico↗
USGS2018

Evidence for major input of riverine organic matter into the ocean

The changes in the structure of XAD-8 isolated dissolved organic matter (DOM) samples along a river (Penobscot River) to estuary (Penobscot Bay) to ocean (across the Gulf of Maine) transect and from the Pacific Ocean were investigated using selective and two dimensional (2D) nuclear magnetic resonance (NMR) spectroscopy coupled with elemental and carbon isotope analysis. The results provide important insights into the nature of relatively stable structures in the river-to-ocean continuum and the enigma of the fate of terrestrial DOM in the marine system. First, lignin and carboxyl-rich alicyclic molecules (CRAMs), which are indistinguishable from mass spectrometry, were clearly differentiated with NMR spectroscopy. NMR unambiguously showed that CRAMs persisted along the river-to-ocean transect and in the Pacific Ocean, while lignin residues dramatically decreased in abundance from the river to the coastal ocean and the Pacific Ocean. The results challenge a previous conclusion that lignin-derived compounds are refractory and can accumulate in the coastal ocean. The loss of terrestrial plant-derived aromatic compounds such as lignin and tannin residues throughout the sequence of riverine, coastal, and open ocean DOM extracts could also partially explain the decreasing organic carbon recovery by XAD-8 isolation and the change in carbon stable isotope composition from riverine DOM (δ 13 C −27.6‰) to ocean DOM (δ 13 C −23.0‰) extracts. The observation, from advanced NMR, of similar CRAM molecules in XAD-8 isolated DOM samples from the Penobscot River to the Penobscot Bay and from the ocean refutes a previous conclusion that XAD-isolated DOM samples from seawater and river are distinctly different. The alicyclic structural features of CRAMs and their presence as the major structural units in DOM extracts from the Penobscot River to Gulf of Maine transect, together with the deduced old 14 C age of CRAMs in the ocean, imply that terrestrial CRAMs may persist on timescales long enough to be transported into the ocean.

Organic Geochemistry↗
USGS2014

Groundwater geochemical and selected volatile organic compound data, Operable Unit 1, Naval Undersea Warfare Center, Division Keyport, Washington, July 2013

Previous investigations indicate that concentrations of chlorinated volatile organic compounds (CVOCs) are substantial in groundwater beneath the 9-acre former landfill at Operable Unit 1, Naval Undersea Warfare Center, Division Keyport, Washington. The U.S. Geological Survey has continued to monitor groundwater geochemistry to ensure that conditions remain favorable for contaminant biodegradation as specified in the Record of Decision for the site. This report presents groundwater geochemical and selected CVOC data collected at Operable Unit 1 by the U.S. Geological Survey during July 9–18, 2013, in support of longterm monitoring for natural attenuation. Groundwater samples were collected from 13 wells and 9 piezometers, as well as from 10 shallow groundwater passive-diffusion sampling sites in the nearby marsh. Samples from all wells and piezometers were analyzed for oxidation-reduction (redox) sensitive constituents and dissolved gases. Samples from all piezometers and four wells also were analyzed for CVOCs, as were all samples from the passive-diffusion sampling sites. In 2013, concentrations of redox-sensitive constituents measured at all wells and piezometers were consistent with those measured in previous years, with dissolved oxygen concentrations at all except an upgradient well 0.2 milligrams per liter or less; little to no detectable nitrate; abundant dissolved manganese, iron, and methane; and commonly detected sulfide. In the upper aquifer of the northern plantation in 2013, CVOC concentrations at all piezometers were similar to those measured in previous years, and concentrations of the reductive dechlorination byproducts ethane and ethene were slightly lower or the same as concentrations measured in 2012. In the upper aquifer of the southern plantation, CVOC concentrations measured in piezometers during 2013 continued to be variable as in previous years, and often very high, and reductive dechlorination byproducts were detected in two of the three wells and in all but one piezometer. Beneath the marsh adjacent to the southern plantation, chloroethene concentrations measured in 2013 continued to vary spatially and temporaly, and also were very high. Total CVOC concentrations, at what have been historically the most contaminated passive-diffusion sampler sites (S-4, S-4B, S-5, and S-5B) remained elevated. For the intermediate aquifer in 2013, concentrations of reductive dechlorination byproducts ethane and ethene and CVOCs were consistent with those measured in previous years.

Washington↗
USGS2007

Nutrient and Suspended-Sediment Trends in the Missouri River Basin, 1993-2003

Trends in streamflow and concentration of total nitrogen, nitrite plus nitrate, ammonia, total phosphorus, orthophosphorus, and suspended sediment were determined for the period from 1993 to 2003 at selected stream sites in the Missouri River Basin. Flow-adjusted trends in concentration (the trends that would have occurred in the absence of natural changes in streamflow) and non-flow-adjusted trends in concentration (the overall trends resulting from natural and human factors) were determined. In the analysis of flow-adjusted trends, the removal of streamflow as a variable affecting concentration allowed trends caused by other factors such as implementation of best management practices to be identified. In the analysis of non-flow-adjusted trends, the inclusion of any and all factors affecting concentration allowed trends affecting aquatic ecosystems and the status of streams relative to water-quality standards to be identified. Relations between the flow-adjusted and non-flow-adjusted trends and changes in streamflow, nutrient sources, ground-water inputs, and implementation of management practices also were examined to determine the major factors affecting the trends. From 1993 to 2003, widespread downward trends in streamflow indicated that drought conditions from about 2000 to 2003 led to decreasing streamflow throughout much of the Missouri River Basin. Flow-adjusted trends in nitrite plus nitrate and ammonia concentrations were split nearly equally between nonsignificant and downward; at about one-half of the sites, management practices likely were contributing to measurable decreases in concentrations of nitrite plus nitrate and ammonia. Management practices had less of an effect on concentrations of total nitrogen; downward flow-adjusted trends in total nitrogen concentrations occurred at only 2 of 19 sites. The pattern of non-flow-adjusted trends in nitrite plus nitrate concentrations was similar to the pattern of flow-adjusted trends; non-flow-adjusted trends were split nearly equally between nonsignificant and downward. A substantial source of nitrite plus nitrate to these streams likely was ground water; because of the time required for ground water to travel to streams, there may have been a lag time between the implementation of some pollution-control strategies and improvement in stream quality, contributing to the nonsignificant trends in nitrite plus nitrate. There were more sites with downward non-flow-adjusted trends than flow-adjusted trends in both ammonia and total nitrogen concentrations, possibly a result of decreased surface runoff from nonpoint sources associated with the downward trends in streamflow. No strong relations between any of the nitrogen trends and changes in nutrient sources or landscape characteristics were identified. Although there were very few upward trends in nitrogen from 1993 to 2003, there were upward flow-adjusted trends in total phosphorus concentrations at nearly one-half of the sites. At these sites, not only were pollution-control strategies not contributing to measurable decreases in total phosphorus concentrations, there was likely an increase in phosphorus loading on the land surface. There were fewer upward non-flow-adjusted than flow-adjusted trends in total phosphorus concentrations; at the majority of sites, overall total phosphorus concentrations did not change significantly during this period. The preponderance of upward flow-adjusted trends and nonsignificant non-flow-adjusted trends indicates that in some areas of the Missouri River Basin, overall concentrations of total phosphorus would have been higher without the decrease in streamflow and the associated decrease in surface runoff during the study period. During the study period, phosphorus loads from fertilizer generally increased at over one-half of the sites in the basin. Upward flow-adjusted trends were related to increasing fertilizer use in the upstream drainage area, particularly in the 10 percent

Scientific Investigations Report↗
USGS2009

Nutrient Trends in Streams and Rivers of the United States, 1993-2003

Trends in streamflow and concentrations and loads of total phosphorus, total nitrogen, and nitrate were determined for the period from 1993 to 2003 in selected streams and ricers of the United States. Flow-adjusted trends in concentration (the trends that would have occurred in the absence of natural chances in streamflow), non-flow-adjusted trends in concentration (the trends resulting from both natural and human factors), and trends in load (trends in the nutrient mass transported downstream) were determined, and the results were examined spatially to determine whether a consistent pattern of trends occurred across groups of sites at multiple locations. Relations between the trends and changes in nutrient sources and streamflow are examined. See document for complete abstract.

Scientific Investigations Report↗
USGS2010

Occurrence and distribution of organic chemicals and nutrients and comparison of water-quality data from public drinking-water supplies in the Columbia aquifer in Delaware, 2000-08

The U.S. Geological Survey, in cooperation with the Delaware Department of Natural Resources and Environmental Control and the Delaware Geological Survey, conducted a groundwater-quality investigation to (a) describe the occurrence and distribution of selected contaminants, and (b) document any changes in groundwater quality in the Columbia aquifer public water-supply wells in the Coastal Plain in Delaware between 2000 and 2008. Thirty public water-supply wells located throughout the Columbia aquifer of the Delaware Coastal Plain were sampled from August through November of 2008. Twenty-two of the wells in the sampling network for this project were previously sampled in 2000. Eight new wells were selected to replace wells no longer in use. Groundwater collected from the wells was analyzed for the occurrence and distribution of selected pesticides, pesticide degradates, volatile organic compounds, nutrients, and major inorganic ions. Nine of the wells were analyzed for radioactive elements (radium-226, radium-228, and radon). Groundwater-quality data were compared for sites sampled in both 2000 and 2008 to document any changes in water quality. One or more pesticides were detected in samples from 29 of the 30 wells. There were no significant differences in pesticide and pesticide degradate concentrations and similar compounds were detected when comparing sampling results from 2000 and 2008. Pesticide and pesticide degradate concentrations were generally less than 1 microgram per liter. Twenty-four compounds, 14 pesticides, and 10 pesticide degradates were detected in at least one sample; the pesticide degradates, metolachlor ethanesulfonic acid, deethylatrazine, and alachlor ethanesulfonic acid were the most frequently detected compounds, each found in more than 50 percent of samples. Almost 80 percent of the detected pesticides were agricultural herbicides, which reflects the prevalence and wide distribution of agriculture in sampled areas, as well the dominance of agricultural pesticides among the target analytes for this study. No concentration of a pesticide or pesticide degradate exceeded any regulatory standard. Dieldrin, an insecticide that has been banned for several decades, was detected at a concentration that exceeded a non-regulatory health-based screening level of 0.002 micrograms per liter at nine sites. Volatile organic compounds (VOCs) were generally detected at concentrations of less than 1 microgram per liter, although 7 of the 31 detected VOCs had concentrations greater than 1 microgram per liter. There were no significant differences in VOC concentrations from 2000 to 2008; however, among the resampled wells, the mean number of VOCs detected per well was significantly different over the 8-year period. The number of VOCs detected per well decreased in 73 percent of the resampled wells; the decrease ranged from one to eight fewer detections in 2008 than in 2000. Chloroform and methyl tert-butyl ether were the most frequently detected VOCs, at 90 percent and 63 percent, respectively, among the 30 wells. Solvents were the most frequently detected class of VOCs. All measured concentrations of VOCs in groundwater were below established standards for drinking water and below other health-based guidelines. There were no significant differences in nutrient or major-ion concentrations between 2000 and 2008, however, the medians of two field measurements, pH and dissolved oxygen, were significantly higher in 2008 than in 2000 in the resampled wells. Although pH and dissolved oxygen were higher, water was still acidic and predominantly oxic. Nitrate was the predominant nutrient species in the Columbia aquifer, with a 90-percent detection frequency. The median nitrate concentration in groundwater was 4.88 milligrams per liter, which was slightly lower than, but not significantly different from, the median of 5.23 milligrams per liter for the 2000 samples. Concentrations of nitrate exceeded the U.S. Environmental Protection Agency's Maximum Contaminant Level or Federal drinking-water standard of 10 milligrams per liter as nitrogen in samples from two wells. Eight of the 30 wells sampled had iron or manganese concentrations that exceeded the U.S. Environmental Protection Agency's Secondary Maximum Contaminant Level; nine samples exceeded the Health Advisory Limit set by the Delaware Division of Public Health of 20 milligrams per liter for sodium in drinking water. Two radiochemical isotopes, radium-226 and radon-222, were detected in all nine groundwater samples analyzed; five samples had detectable levels of radium-228 activity. None of the samples exceeded the U.S Environmental Protection Agency's Maximum Contaminant Level for radium or radon in drinking water. Although radioactive elements were more frequently detected in 2008 than in 2000, this increased detection frequency is more likely due to lower detection levels in 2008 than 2000. The average age of groundwater entering the screens of the production wells sampled in 2008 ranged from 6 to 35 years, with a median groundwater age of 22 years. Groundwater age was positively correlated with well depth and negatively correlated with dissolved oxygen. Data from the 22 resampled wells indicate a significant positive difference in the average modeled groundwater-sample-age results. The average groundwater age from samples collected in 2008 was generally 7 years older than the average groundwater age from samples collected in 2000.

Delaware↗
USGS2018

Revised groundwater-flow model of the glacial aquifer system north of Aberdeen, South Dakota, through water year 2015

The city of Aberdeen, in northeastern South Dakota, requires an expanded and sustainable supply of water to meet current and future demands. Conceptual and numerical models of the glacial aquifer system in the area north of Aberdeen were developed by the U.S. Geological Survey in cooperation with the City of Aberdeen in 2012. The U.S. Geological Survey, in cooperation with the City of Aberdeen, completed a study to revise the original numerical groundwater-flow model using data through water year (WY) 2015 to aid the City of Aberdeen in their development of plans and strategies for a sustainable water supply and to increase understanding of the glacial aquifer system and groundwater-flow system near Aberdeen. The original model was revised to improve the fit between model-simulated values and observed (measured or estimated) data, provide greater insight into surface-water interactions, and improve the usefulness of the model for water-supply planning. The revised groundwater-flow model (hereafter referred to as the “revised model”) presented in this report supersedes the original model. The purpose of this report is to describe a revised groundwater-flow model including data collection, model calibration, and model results for the glacial aquifer system including the Elm, Middle James, and Deep James aquifers north of Aberdeen, South Dakota, using updated hydrologic data through WY 2015. The original numerical model was revised in several ways. The model was modified by adding four new layers, which included a surficial layer, two intervening confining layers, and a shale bedrock layer. The revised model provides an improved understanding of the groundwater-flow system in comparison to the original model. The principal aquifers of the model area include portions of the Elm, Middle James, and Deep James aquifers. The lithologic information used to define and describe the aquifers in the model area was unaltered; however, aquifer properties and boundary conditions were reviewed and updated using geological information reported by the South Dakota Department of Environmental and Natural Resources and information obtained from geophysical investigations for this study. The horizontal extent of the Elm, Middle James, and Deep James aquifers was unaltered from the original model. The thickness of the Deep James aquifer was modified based on interpretations from the geophysical investigations. In general, groundwater in the Elm aquifer flowed from northwest to southeast and locally towards rivers and streams. Similarly, in the Middle James and Deep James aquifers, groundwater also typically flowed southeast. The revisions made to the original model include use of the following MODFLOW stress packages: Recharge, Evapotranspiration, Time-Variant Specified Head, Wells, Drains, and Stream Flow Routing, all of which were updated from the original model except for the Stream Flow Routing Package, which replaced the River Package used in the original model. Model calibration is the process of estimating model parameters to minimize the differences, or residuals, between observed data and simulated values; therefore, Parameter ESTimation (PEST) software was used to optimize model input parameters by matching model-simulated values to observed data. Calibration parameters included horizontal hydraulic conductivity, vertical hydraulic conductivity, specific yield, specific storage, and vertical streambed conductance for stream and drain cells. Multipliers were used to calibrate the recharge and evapotranspiration stresses. Evapotranspiration extinction depth also was adjusted during model calibration. Comparisons to the original model are described to highlight the changes made in the revised model. In general, the revised model adequately simulates the natural system and compares favorably with observed hydrologic data. Simulated water levels were evaluated by comparing them to single water-level observations at selected well locations. The selected wells were the same wells used in the original model. The coefficient of determination value between simulated and observed water levels for the revised model was 0.89 and included simulated and observed values from October 1, 1974 (WY 1975), through September 30, 2015 (WY 2015). The coefficient of determination value for the original model was 0.94 and included simulated and observed values from October 1, 1974, through September 30, 2009. The difference may indicate that the original model could have been overfit to hydraulic head observations because base flow was not simulated. The additional data used in the revised model included some climatically wetter, more extreme periods, such as 2011, in which annual precipitation was 30.9 inches. Average annual precipitation for the original model timeframe, which included data from WYs 1975–2009, was 20.26 inches. Additional precipitation data for WYs 2010–15, included in the revised model timeframe, resulted in an average annual precipitation for WYs 1975–2015 in the model area of 20.6 inches. The larger variability in climate data coupled with the additional water-level data could explain the lower coefficient of determination for water levels in the revised model. The revised model was used to calculate various groundwater-budget components for steady-state and transient conditions for WYs 1975–2015. The time-variant specified-head cells in the revised model had the largest change when compared to the original steady-state model for inflows and outflows. Comparing the transient budget components between the original and the revised models indicated that inflow from recharge and time-variant specified-head cells had the greatest effect on groundwater inflows, and outflow from storage had the greatest effect on groundwater outflows. The simulated potentiometric contours from the revised model were compared with (1) the observed (interpreted) potentiometric surface (layer 2) and the hydraulic head values (layers 4 and 6) and (2) the simulated contours from the original model. The simulated hydraulic gradients and general direction of groundwater flow in the Elm aquifer in the revised model generally matched the observed potentiometric contours, the simulated potentiometric contours from the original model, and general flow directions interpreted to be perpendicular to the contours. Minor discrepancies between simulated potentiometric contours from the revised model and the observed potentiometric contours may be due to the lack of observed data in the model area. The revised model was designed to reduce the limitations of the original model. The revisions were validated by comparing the results of the original model with the revised model. A primary benefit of the revised model is the inclusion of the surficial deposits and the confining units as explicit layers in the model. The addition of the surficial layer was beneficial for three primary reasons: (1) more accurate representation of recharge from precipitation, (2) more accurate representation of groundwater evapotranspiration, and (3) more accurate representation of groundwater and surface-water interactions. The groundwater model is a numeric approximation of a complex physical hydrologic system, and the revised model data were interpolated in regions with sparse data. Additionally, model discretization included averaged and interpolated values for water use, withdrawal rates, and hydraulic conductivity. The revised model provides a useful estimate for hydraulic gradients, groundwater-flow directions, and aquifer response to groundwater withdrawals.

South Dakota↗
USGS1990

Potentiometric surface of the Edwards-Trinity aquifer system and contiguous hydraulically connected units, west-central Texas, winter, 1974-75

The potentiometric surface of the Edwards-Trinity aquifer system and contiguous hydraulically connected units (from December 1974 through February 1975) was mapped as part of the Edwards-Trinity Regional Aquifer-System Analysis (RASA) project. A major goal of the Edwards-Trinity RASA project is to understand and describe the regional flow system (Bush, 1986). The development of a digital ground-water flow model of the aquifer system is a key part of the project. This potentiometric map will be used in the calibration of the ground-water flow model and in understanding ground-water movement in the aquifer system. The map depicts the potentiometric surface of the major aquifers of the Edwards-Trinity aquifer system and contiguous units that form a continuous hydraulically connected regional aquifer within the study area in west-central Texas (fig. 1). The potentiometric surface of an aquifer is an imaginary surface defined by contouring locations of equal static head (the altitude to which water will rise in a well). The potentiometric surface map shows the direction of ground-water flow from higher to lower altitude. The study area extends beyond the aquifers of the Edwards-Trinity system to hydrologic divides, including the Colorado River and the Rio Grande (fig. 2). The data used to compile this map were obtained from the Texas Natural Resources Information System on magnetic tape and from Rees and Buckner (1980). The winter of 1974-75 (December 1974 through February 1975) was selected for mapping for two reasons: (1) More water-level data were available throughout the study area for this winter season than for other winter seasons, and (2) during winter there is almost no loss of ground water as a result of evaporation, irrigation withdrawals, and transpiration.

Texas↗
USGS1936

Summary of investigations on the morphometry of the cisco, Leucichthys artedi (Le Sueur), in the lakes of the northeastern highlands, Wisconsin

The morphometric studies on the cisco or lake herring, Leucichthys artedi (Le Sueur), which are briefly summarized in this paper are part of a program of investigation of the fishes of the lakes in the northeastern highland district, Wisconsin. For the morphometric studies, 1,548 specimens were employed, all of them collected in the summers of 1931 and 1932 from four 'type' lakes, selected on the basis of their size, depth, and physicochemical and biological characteristics. Of this number 753 individuals were used to determine the general nature of the morphological variations in the Trout Lake, Muskellunge Lake, Silver Lake, and Clear Lakes cisco populations, while 795, collected from Muskellunge Lake in 1932 were employed in a detailed examination of certain morphological differences between the 1928 and 1929 year classes of that population. An attempt is made in this paper to present all the important conculsions, together with a small amount of illustrative material.

Papers of the Michigan Academy of Science, Arts, a↗
USGS2010

Evaluation of the extent of contamination caused by historical mining in catchments of central Colorado

The U.S. Geological Survey conducted an assessment of stream water and sediment quality in central Colorado, an area of about 54,000 km2. The study area is focused on small tributary catchments in the Rocky Mountains. The Colorado Mineral belt, a northeast-trending mineralized zone that experienced base- and precious-metal mining at the beginning of the late 1800s and early 1900s, cuts diagonally across the geologic trend in the study area. The goal of this study was to compare water and sediment quality in background catchments with those which have been mined. Water and sediment data from 200 catchments, and data from macroinvertebrates from more than 100 catchments, provided ample data for evaluation of the effects of mining on water and sediment quality. Focused sampling was conducted during low-flow conditions in the summers of 2004-2007. Samples were collected from catchments that (1) were underlain largely by a single lithologic unit, (2) contained hydrothermally altered rock and had been prospected, and (3) contained historical mines. Geochemical data determined from catchments that did not contain hydrothermal alteration or historical mines met water-quality criteria and recommended sediment-quality guidelines and showed small variations in base-metal concentrations. Hydrothermal alteration and mineralization typically are associated with igneous rocks that have intruded older bedrock. Base-metal concentrations were elevated in sediment from catchments underlain by hydrothermally altered rock. Catchments affected by historical mining contained highly elevated base-metal concentrations. Classification of catchments on the basis of mineral deposit types proved to be an efficient and accurate method for discriminating catchments that had degraded water and sediment quality. Only about 4.5 percent of the study area has been affected by historical mining, whereas a larger portion of the study area is underlain by hydrothermally altered rock. Weathering of QSP-altered catchments release metals and result in naturally elevated geochemical background concentrations in both sediment and water. The presence of hydrothermal alteration is shown to be a major consideration in the selection of sites for the determination of geochemical background.

Conference Paper↗