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At least 343 records · Page 19Linked to original sources

USGS1999

Prediction of episodic acidification in North-eastern USA: An empirical/mechanistic approach

Observations from the US Environmental Protection Agency's Episodic Response Project (ERP) in the North-eastern United States are used to develop an empirical/mechanistic scheme for prediction of the minimum values of acid neutralizing capacity (ANC) during episodes. An acidification episode is defined as a hydrological event during which ANC decreases. The pre-episode ANC is used to index the antecedent condition, and the stream flow increase reflects how much the relative contributions of sources of waters change during the episode. As much as 92% of the total variation in the minimum ANC in individual catchments can be explained (with levels of explanation >70% for nine of the 13 streams) by a multiple linear regression model that includes pre-episode ANC and change in discharge as independent variable. The predictive scheme is demonstrated to be regionally robust, with the regional variance explained ranging from 77 to 83%. The scheme is not successful for each ERP stream, and reasons are suggested for the individual failures. The potential for applying the predictive scheme to other watersheds is demonstrated by testing the model with data from the Panola Mountain Research Watershed in the South-eastern United States, where the variance explained by the model was 74%. The model can also be utilized to assess 'chemically new' and 'chemically old' water sources during acidification episodes.Observations from the US Environmental Protection Agency's Episodic Response Project (ERP) in the Northeastern United States are used to develop an empirical/mechanistic scheme for prediction of the minimum values of acid neutralizing capacity (ANC) during episodes. An acidification episode is defined as a hydrological event during which ANC decreases. The pre-episode ANC is used to index the antecedent condition, and the stream flow increase reflects how much the relative contributions of sources of waters change during the episode. As much as 92% of the total variation in the minimum ANC in individual catchments can be explained (with levels of explanation >70% for nine of the 13 streams) by a multiple linear regression model that includes pre-episode ANC and change in discharge as independent variables. The predictive scheme is demonstrated to be regionally robust, with the regional variance explained ranging from 77 to 83%. The scheme is not successful for each ERP stream, and reasons are suggested for the individual failures. The potential for applying the predictive scheme to other watersheds is demonstrated by testing the model with data from the Panola Mountain Research Watershed in the South-eastern United States, where the variance explained by the model was 74%. The model can also be utilized to assess `chemically new' and `chemically old' water sources during acidification episodes.

Hydrological Processes↗

USGS2022

Optical properties of dissolved organic matter in throughfall and stemflow vary across tree species and season in a temperate headwater forest

Tree-derived dissolved organic matter (DOM) comprises a significant carbon flux within forested watersheds. Few studies have assessed the optical properties of tree-derived DOM. To increase understanding of the factors controlling tree-derived DOM quality, we measured DOM optical properties, dissolved organic carbon (DOC) and calcium concentrations in throughfall and stemflow for 17 individual rain events during summer and fall in a temperate deciduous forest in Vermont, United States. DOC and calcium fluxes in throughfall and stemflow were enriched on average 4 to 70 times incident fluxes in rain. A multiway model was developed using absorbance and fluorescence spectroscopy to further characterize DOM optical properties. Throughfall contained a higher percentage of protein-like DOM fluorescence than stemflow while stemflow was characterized by a higher percentage of humic-like DOM fluorescence. DOM absorbance spectral slopes in yellow birch ( Betula alleghaniensis ) stemflow were significantly higher than in sugar maple ( Acer saccharum ) stemflow. DOM optical metrics were not influenced by rainfall volume, but percent protein-like fluorescence increased in throughfall during autumn when leaves senesced. Given the potential influence of tree-derived DOM fluxes on receiving soils and downstream ecosystems, future modeling of DOM transport and soil biogeochemistry should represent the influence of differing DOM quality in throughfall and stemflow across tree species and seasons.

Vermont↗

USGS2019

An integrated statistical and deterministic hydrologic model for analyzing trace organic contaminants in commercial and high-density residential stormwater runoff

Urbanization can dramatically alter stormwater, both the quantity and quality, by engendering larger peak flows and through the introduction of contaminants into runoff. The current study builds on previous research that developed relationships between a suite of nonpoint source contaminants, known as trace organic contaminants (TOrCs), and hydrologic measurements for a series of storms (one site had 15 storms and the other had 19 storms) in Madison, WI, by creating statistical and deterministic models. Correlations and regressions were calculated between TOrC loads and hydrologic measurements for a series of storms for both a commercial site and a high-density residential site. From the regressions, it became evident that loading responses to precipitation were not the same between the two land covers for some TOrCs, indicating varying load responses for TOrCs depending on land cover. The regressions were utilized in the Source Loading and Management Model for Windows (WinSLAMM), an event-based hydrologic and water-quality model, to demonstrate that it can be used to model novel contaminants. The regressions were also used to estimate mean annual loads of TOrCs from all commercial and high-density residential areas in Madison, WI, for the watersheds to which Madison discharges its stormwater. The mean annual loads varied between grams per year to tens of thousands of grams per year depending on the TOrC and watershed. This work will ultimately allow managers to simulate the presence of, establish total maximum daily loads for, and mitigate the loads of TOrCs through stormwater best management practices.

Wisconsin↗

USGS2014

Hydrogeology, water resources, and water budget of the upper Rio Hondo Basin, Lincoln County, New Mexico, 2010

The upper Rio Hondo Basin occupies a drainage area of 585 square miles in south-central New Mexico and comprises three general hydrogeologic terranes: the higher elevation “Mountain Block,” the “Central Basin” piedmont area, and the lower elevation “Hondo Slope.” As many as 12 hydrostratigraphic units serve as aquifers locally and form a continuous aquifer on the regional scale. Streams and aquifers in the basin are closely interconnected, with numerous gaining and losing stream reaches across the study area. In general, the aquifers are characterized by low storage capacity and respond to short-term and long-term variations in recharge with marked water-level fluctuations on short (days to months) and long (decadal) time scales. Droughts and local groundwater withdrawals have caused marked water-table declines in some areas, whereas periodically heavy monsoons and snowmelt events have rapidly recharged aquifers in some areas. A regional-scale conceptual water budget was developed for the study area in order to gain a basic understanding of the magnitude of the various components of input, output, and change in storage. The primary input is watershed yield from the Mountain Block terrane, supplying about 38,200 to 42,300 acre-feet per year (acre-ft/yr) to the basin, as estimated by comparing the residual of precipitation and evapotranspiration with local streamgage data. Streamflow from the basin averaged about 21,200 acre-ft/yr, and groundwater output left the basin at an estimated 2,300 to 5,700 acre-ft/yr. The other major output (about 13,500 acre-ft/yr) was by public water supply, private water supply, livestock, commercial and industrial uses, and the Bonito Pipeline. The residual in the water budget, the difference between the totals of the input and output terms or the potential change in storage, ranged from -2,200 acre-ft/yr to +5,300 acre-ft/yr. There is a high degree of variability in precipitation and consequently in the water supply; small variations in annual precipitation can result in major changes in overall watershed yield. Changing water-use patterns, concentrated areas of groundwater withdrawal, and variations in precipitation have created localized areas where water-table declines and diminished surface flow are of concern.

Lincoln, New Mexico↗

USGS1999

Water budget and water quality of Ward Lake, flow and water-quality characteristics of the Braden River estuary, and the effects of Ward Lake on the hydrologic system, west-central Florida

The Braden River is the largest tributary to the Manatee River. The river was dammed in 1936 to provide the city of Bradenton a source of freshwater supply. The resulting impoundment was called Ward Lake and had a storage capacity of about 585 million gallons. Reconstruction in 1985 increased the size of the reservoir to about 1,400 million gallons. The lake has been renamed the Bill Evers Reservoir and drains about 59 square miles. The Braden River watershed can be subdivided into three hydrologic reaches. The upper reach consists of a naturally incised free-flowing channel. The middle reach consists of a meandering channel affected by backwater as a result of the dam. The lower reach is a tidal estuary. Water budgets were calculated for the 1993 through 1997 water years. Mean surface-water inflow to Ward Lake for the 5-year period was 1,645 inches per year (equivalent depth over the surface of the lake), or about 81.8 percent of total inflow. Mean ground-water inflow was 311 inches per year, or about 15.5 percent. A mean of 55 inches of rain fell directly on the lake and accounted for only 2.7 percent. Mean surface-water outflow was 1,736 inches, or about 86.4 percent of total water leaving the lake. There was no net ground-water outflow from the lake. Mean surface-water withdrawal for public supply was 229 inches per year, or about 11.4 percent. Mean evaporation was 45 inches and accounted for only 2.2 percent of the mean outflow. Change in lake storage on the budget was negligible. Most chemical constituents contained in water flowing to Ward Lake meet the standards specified by the Florida Department of Environmental Protection and the U.S. Environmental Protection Agency. Phosphorus is the exception, exceeding the U.S. Environmental Protection Agency limits of 0.10 milligram per liter in most samples. However, the source of the phosphorus is naturally occurring phosphate deposits underlying the watershed. Organic nitrogen and orthophosphate are the dominant species of nutrients in the streams and the lake. A major source of water to the streams is the surficial aquifer system. Mineralized water pumped from the intermediate aquifer system and the Upper Floridan aquifer for irrigation of agricultural areas or golf courses has influenced the chemical composition of the surficial aquifer and surface-water systems. The Braden River estuary receives freshwater inflow from Ward Lake and from three major streams discharging downstream from the dam. Salinity levels in the estuary are affected by freshwater flow from these sources and by antecedent conditions in the estuary prior to flow events. The lowest salinity levels are often measured at the confluence with Williams and Gap Creeks rather than at the outfall from the lake. The chemical composition of water flowing from the tributaries to the estuary is similar to the chemical composition of water in the tributaries flowing to Ward Lake and does not appear to be affected by brackish water from high tides. Nitrogen concentrations in water from Glen Creek were greater than in water from all other tributaries in the watershed. Fertilizer from orange groves and stormwater runoff from urban and industrial areas affect the water quality in Glen Creek. The effects of the reservoir on the hydrology of the watershed were to change the middle reach of the river from a brackish water estuary ecosystem to a freshwater lake ecosystem, raise water levels in the surficial aquifer system adjacent to the river, change water quality, and reduce freshwater flow to the estuary during periods of low flow. The lake acts as a sink for total organic carbon, dissolved solids, calcium, chloride, and sulfate, thereby decreasing loads of these constituents to the estuary.

Water-Resources Investigations Report↗

USGS2025

Pyrethroid insecticide pollution of wetlands reduces amphipod density

Freshwater amphipods play a key role as forage for breeding and migrating waterfowl in wetlands throughout the Prairie Pothole Region (PPR) of North America. Amphipod populations declined in recent decades, but there is a limited understanding of mechanisms for their decline and their uneven distribution across the landscape. Row crop agriculture is abundant in the PPR, but the sensitivity of amphipods and wetland ecosystems to agrochemical pollution has rarely been studied. We investigated relationships among amphipod abundances (specifically, Gammarus lacustris and Hyalella azteca ), land uses, water quality, and pyrethroid insecticide contamination of wetland sediments. Our study design targeted a large gradient of amphipod abundances and accounted for water quality, hydrology, and habitat metrics that commonly influence amphipods. We found a significant, negative relationship between pyrethroid concentrations and the abundance of the two amphipod species. Pyrethroids were detected at relatively low concentrations (<2.5 ng/g sediment) in 44% of study wetlands and occurred most frequently in intensively cropped watersheds with low vegetative filter strip coverage. Interestingly, wetlands on state and federal wildlife reserves had regular occurrence of pyrethroids, demonstrating the pervasive transport of these compounds and the intensity of agriculture in the PPR. The pyrethroids are likely entering these wetlands through overland transport during rain events or aerial spray drift, and our results show that forest patches and vegetative filter strips may reduce pyrethroid exposure to both wetlands and amphipods.

Ecotoxicology↗

USGS2026

Using sediment chemical fractions and multivariate statistics on water to identify sources, mobility, and bioavailability of aluminum in the Florida River near Durango, Colorado

The Florida River in southwestern Colorado, USA, flows through the Southern Ute Reservation and is a cultural and water resource to Tribal and non-Tribal communities. High concentrations of total Al, up to 16 400 µg l –1 , have been detected in the Florida River. Elevated Al concentrations in water may affect aquatic organisms’ ability to regulate ions and inhibit respiratory functions. Water chemistry collected during three sampling events in 2022 from the Florida River and two of its tributaries are used here to better understand the spatial distribution, seasonality, and sources of Al concentrations in the Florida River. Streambed sediment and rock chemistry is also used to infer geologic sources of Al in the watershed. A five-stage sequential extraction was performed on streambed sediment and rock samples to help determine Al transport processes. We assessed relations between major and trace elements in water using a principal component analysis, finding that high Al concentrations in the Florida River (>3500 µg l –1 total Al) are caused by the erosion of Al-laden sediments. We used a stepwise multiple linear regression to investigate the relationship between land use and Al concentrations. Land use did not reliably predict Al concentration, though increased streamflow connected to reservoir releases – particularly in the Salt Creek tributary – were found to contribute Al to the Florida River during the irrigation season. In this study, we demonstrate that successful metal source appropriation may be achieved through limited field sampling when performed with sufficient water chemistry analysis, sequential chemical extraction of stream sediments, and statistical and land-use analysis.

Colorado↗

USGS2016

High-resolution records detect human-caused changes to the boreal forest wildfire regime in interior Alaska

Stand-replacing wildfires are a keystone disturbance in the boreal forest, and they are becoming more common as the climate warms. Paleo-fire archives from the wildland–urban interface can quantify the prehistoric fire regime and assess how both human land-use and climate change impact ecosystem dynamics. Here, we use a combination of a sedimentary charcoal record preserved in varved lake sediments (annually layered) and fire scars in living trees to document changes in local fire return intervals (FRIs) and regional fire activity over the last 500 years. Ace Lake is within the boreal forest, located near the town of Fairbanks in interior Alaska, which was settled by gold miners in AD 1902. In the 400 years before settlement, fires occurred near the lake on average every 58 years. After settlement, fires became much more frequent (average every 18  years), and background charcoal flux rates rose to four times their preindustrial levels, indicating a region-wide increase in burning. Despite this surge in burning, the preindustrial boreal forest ecosystem and permafrost in the watershed have remained intact. Although fire suppression has reduced charcoal influx since the 1950s, an aging fuel load experiencing increasingly warm summers may pose management problems for this and other boreal sites that have similar land-use and fire histories. The large human-caused fire events that we identify can be used to test how increasingly common megafires may alter ecosystem dynamics in the future.

Alaska↗

USGS2004

Distribution of Holocene Sediment in Chesapeake Bay as Interpreted from Submarine Geomorphology of the Submerged Landforms, Selected Core Holes, Bridge Borings and Seismic Profiles

Overview -- We have interpreted the geomorphology of the submerged landforms to show thick Holocene sediment that accumulated from three different sources during on-going sea level rise that began 10,000 - 12,000 years ago at the end of Pleistocene. We used a variety of subsurface data from the literature and unpublished information to document thicknesses, materials, dates and duration of processes. Although the details of the true extent and thicknesses are unknown, the deposits of different sources have affinity for particular geographic and submerged geomorphic regions of the Chesapeake Bay and its tidal tributaries. During the last Pleistocene glacial event (Wisconsian), the area now occupied by the Chesapeake Bay was exposed, sea level being about 100 m lower than present. The Susquehanna River valley extended beyond the Bay well out on the exposed Atlantic Shelf. The Susquehanna transported glacial outwash from northern Pennsylvania and New York; the glacio-fluvial deposits were graded to the edge of the continental shelf (Colman et al., 1990; Hack, 1957). Other Piedmont and Appalachian Rivers including the Potomac and James Rivers transported large volumes of sediment to confluence with the Susquehanna channel. Locally, across the encompasing coastal plain landscape, intensive headward erosion, gullies, and slope failure, generated extensive debris flows, sheet wash, and terraces of braided alluvial channel deposits. Large volumes of sediment were moved through the river system to the continental shelf. This was accomplished by a cold, wet climate that included much freezing and thawing; steep eroding slopes resulted from the lowering of sea level from the previous high stand (Stage 5e) between glacial events. Across the Delmarva peninsula extensive wind-blown deposits of sand and loess were recycled onto low terraces and uplands from the unvegetated glacio-fluvial sediments moving through the system (Denny et al., 1979). The volume and distribution of sediment eroded and transported from the watershed surrounding the area of the Bay was several orders of magnitude greater than generally observed in transport and storage on the present day landscape.

Open-File Report↗

USGS2008

Water-Quality Characteristics of Ledge Creek and Holman Creek Upstream from Lake Rogers, Granville County, North Carolina, 2005 and 2008

Water-quality and hydrologic data were collected during 2005 and 2008 to characterize potential source areas of nutrients and sediment within the Ledge and Holman Creek watersheds upstream from Lake Rogers in Granville County, North Carolina. Eight monitoring locations were established in all--five in Holman Creek and three in Ledge Creek--for collecting discharge and water-quality data during different streamflow conditions. Water-quality samples were collected during two sampling events in the fall of 2005 for analysis of major ions, nutrients, suspended sediment, and fecal-indicator bacteria. Water-quality samples were collected during three sampling events in the winter and spring of 2008 for analysis of nutrients and suspended sediment.

North Carolina↗

USGS2014

Extensive dispersal of Roanoke logperch ( Percina rex ) inferred from genetic marker data

The dispersal ecology of most stream fishes is poorly characterised, complicating conservation efforts for these species. We used microsatellite DNA marker data to characterise dispersal patterns and effective population size ( N e ) for a population of Roanoke logperch Percina rex , an endangered darter (Percidae). Juveniles and candidate parents were sampled for 2 years at sites throughout the Roanoke River watershed. Dispersal was inferred via genetic assignment tests (ATs), pedigree reconstruction (PR) and estimation of lifetime dispersal distance under a genetic isolation-by-distance model. Estimates of N e varied from 105 to 1218 individuals, depending on the estimation method. Based on PR, polygamy was frequent in parents of both sexes, with individuals spawning with an average of 2.4 mates. The sample contained 61 half-sibling pairs, but only one parent–offspring pair and no full-sib pairs, which limited our ability to discriminate natal dispersal of juveniles from breeding dispersal of their parents between spawning events. Nonetheless, all methods indicated extensive dispersal. The AT indicated unrestricted dispersal among sites ≤15 km apart, while siblings inferred by the PR were captured an average of 14 km and up to 55 km apart. Model-based estimates of median lifetime dispersal distance (6–24 km, depending on assumptions) bracketed AT and PR estimates, indicating that widely dispersed individuals do, on average, contribute to gene flow. Extensive dispersal of P. rex suggests that darters and other small benthic stream fishes may be unexpectedly mobile. Monitoring and management activities for such populations should encompass entire watersheds to fully capture population dynamics.

Ecology of Freshwater Fish↗

USGS2016

Historical water-quality data from the Harlem River, New York

Data specific to the Harlem River, New York, have been summarized and are presented in this report. The data illustrate improvements in the quality of water for the past 65 years and emphasize the importance of a continuous water-quality record for establishing trends in environmental conditions. Although there is a paucity of sediment-quality data, the New York City Department of Environmental Protection (NYCDEP) Bureau of Wastewater Treatment has maintained a water-quality monitoring network in the Harlem River (and throughout the harbor of New York City) to which 61 combined sewer outfalls discharge effluent. In cooperation with the NYCDEP, the U.S. Geological Survey evaluated water-quality data collected by the NYCDEP dating back to 1945, which indicate trends in water quality and reveal improvement following the 1972 passage of the Clean Water Act. These improvements are indicated by the steady increase in median dissolved oxygen concentrations and an overall decrease in fecal indicator bacteria concentrations starting in the late 1970s. Further, the magnitude of the highest fecal indicator bacteria concentrations (that is, the 90th percentile) in samples collected from the Harlem River have decreased significantly over the past four decades. Other parameters of water quality used to gauge the health of a water body include total suspended solids and nutrient (inorganic forms of nitrogen and phosphorus) concentrations—mean concentrations for these indicators have also decreased in the past decades. The limited sediment data available for one sample in the Harlem River indicate concentrations of copper, zinc, and lead are above sediment-quality thresholds set by the New York State Department of Environmental Conservation. However, more data are needed to better understand the changes in both sediment and water quality in the Harlem River, both as the tide cycles and during precipitation events. As a partner in the Urban Waters Federal Partnership, the U.S. Geological Survey has worked to address the chronic water-quality concerns of the Harlem River by compiling relevant data and studies, which is an important component for understanding and rectifying water-quality problems within a watershed.

New York↗

USGS2016

Sediment load and distribution in the lower Skagit River, Skagit County, Washington

The Skagit River delivers about 40 percent of all fluvial sediment that enters Puget Sound, influencing flood hazards in the Skagit lowlands, critically important estuarine habitat in the delta, and some of the most diverse and productive agriculture in western Washington. A total of 175 measurements of suspended-sediment load, made routinely from 1974 to 1993, and sporadically from 2006 to 2009, were used to develop and evaluate regression models of sediment transport (also known as “sediment-rating curves”) for estimating suspended-sediment load as a function of river discharge. Using a flow-range model and 75 years of daily discharge record (acquired from 1941 to 2015), the mean annual suspended-sediment load for the Skagit River near Mount Vernon, Washington, was estimated to be 2.5 teragrams (Tg, where 1 Tg = 1 million metric tons). The seasonal model indicates that 74 percent of the total annual suspended‑sediment load is delivered to Puget Sound during the winter storm season (from October through March), but also indicates that discharge is a poor surrogate for suspended‑sediment concentration (SSC) during the summer low-flow season. Sediment-rating curves developed for different time periods revealed that the regression model slope of the SSC-discharge relation increased 66 percent between the periods of 1974–76 and 2006–09 when suspended-sediment samples were collected, implying that changes in sediment supply, channel hydraulics, and (or) basin hydrology occurred between the two time intervals. In the relatively wet water year 2007 (October 1, 2006, through September 30, 2007), an automated sampler was used to collect daily samples of suspended sediment from which an annual load of 4.5 Tg was calculated, dominated by a single large flood event that contributed 1.8 Tg, or 40 percent of the total. In comparison, the annual load calculated for water year 2007 using the preferred flow-range model was 4.8 Tg (+6.7 percent), in close agreement with the measured value. Particle size affects sediment transport, fate and distribution across watersheds, and therefore is important for predicting how coastal environments, particularly deltas and beaches, will respond to changes in climate and sea-level. Particle-size analysis of winter storm samples indicated that about one-half of the suspended-sediment load consisted of fines (that is, silt- and clay-sized particles smaller than 0.0625 mm in diameter), and the remainder consisted of mostly fine- to medium-sized sand (0.0625–0.5 mm), whereas bedload during winter storm flows (about 1–3 percent of total sediment load) was predominantly composed of medium to coarse sand (0.25–1 mm). A continuous turbidity record from the Anacortes Water Treatment Plant (water years 1999–2013), used as a surrogate for the concentration of fines ( R 2 = 0.93, p = 4.2E-10, n = 17), confirms that about one-half of the mean annual suspended-sediment load is composed of fines. The distribution of flow through the delta distributaries (that is, the channels into which the main stem splits as it approaches the delta) is dynamic, with twice as much flow through the North Fork of the Skagit River relative to the South Fork during low-flow conditions, and close to equal flows in the two channels during high-flow conditions. Turbidity, monitored at several locations in the lower river in spring 2009, was essentially uniform among sites, indicating that fines are well mixed in the lower Skagit River system (defined as the Skagit River and all its distributaries downstream of the Mount Vernon streamgage). A strong relation ( R 2 = 0.95, p = 3.2E-14, n = 21; linear regression) between the concentration of fines and turbidity measured at various locations in summer 2009 indicates that turbidity is an effective surrogate for the concentration of fines, independent of location in the river, under naturally well-mixed fluvial conditions. This relation is especially useful for monitoring suspended sediment in western Washington rivers that are seasonally dominated by glacier meltwater because glacial melting typically produces suspended-sediment concentrations that are not well correlated with discharge. These results provide a comprehensive set of tools to estimate sediment delivery and delta responses of interest to scientists and resource managers including decision-makers examining options for flood hazard mitigation, estuary restoration, and climate change adaptation.

Washington↗

USGS2003

Patterns and sources of fecal coliform bacteria in three streams in Virginia, 1999-2000

Surface-water impairment by fecal coliform bacteria is a water-quality issue of national scope and importance. In Virginia, more than 175 stream segments are on the Commonwealth's 1998 303(d) list of impaired waters because of elevated concentrations of fecal coliform bacteria. These fecal coliform-impaired stream segments require the development of total maximum daily load (TMDL) and associated implementation plans, but accurate information on the sources contributing these bacteria usually is lacking. The development of defendable fecal coliform TMDLs and management plans can benefit from reliable information on the bacteria sources that are responsible for the impairment. Bacterial source tracking (BST) recently has emerged as a powerful tool for identifying the sources of fecal coliform bacteria that impair surface waters. In a demonstration of BST technology, three watersheds on Virginia's 1998 303(d) list with diverse land-use practices (and potentially diverse bacteria sources) were studied. Accotink Creek is dominated by urban land uses, Christians Creek by agricultural land uses, and Blacks Run is affected by both urban and agricultural land uses. During the 20-month field study (March 1999?October 2000), water samples were collected from each stream during a range of flow conditions and seasons. For each sample, specific conductance, dissolved oxygen concentration, pH, turbidity, flow, and water temperature were measured. Fecal coliform concentrations of each water sample were determined using the membrane filtration technique. Next, Escherichia coli (E. coli) were isolated from the fecal coliform bacteria and their sources were identified using ribotyping (a method of 'genetic fingerprinting'). Study results provide enhanced understanding of the concentrations and sources of fecal coliform bacteria in these three watersheds. Continuum sampling (sampling along the length of the streams) indicated that elevated concentrations of fecal coliform bacteria (maximum observed concentration of 290,000 colonies/100 milliliters (col/100mL) could occur along the entire length of each stream, and that the samples collected at the downstream monitoring station of each stream were generally representative of the entire upstream reach. Seasonal patterns were observed in the base-flow fecal coliform concentrations of all streams; concentrations were typically highest in the summer and lowest in the winter. Fecal coliform concentrations were lowest during periods of base flow (typically 200?2,000 col/100mL) and increased by 3?4 orders of magnitude during storm events (as high as 700,000 col/100mL). Multiple linear regression models were developed to predict fecal coliform concentrations as a function of streamflow and other water-quality parameters. The source tracking technique provided identification of bacteria contributions from diverse sources that included (but were not limited to) humans, cattle, poultry, horses, dogs, cats, geese, ducks, raccoons, and deer. Seasonal patterns were observed in the contributions of cattle and poultry sources. There were relations between the identified sources of fecal coliform bacteria and the land-use practices within each watershed. There were only minor differences in the distribution of bacteria sources between low-flow periods and high-flow periods. A coupled approach that utilized both a large available source library and a smaller, location-specific source library provided the most success in identifying the unknown E. coli isolates. BST data should provide valuable support and guidance for producing more defendable and scientifically rigorous watershed models. Incorporation of these bacteria-source data into watershed management strategies also should result in the selection of more efficient source-reduction scenarios for improving water quality.

Water-Resources Investigations Report↗

USGS2003

Late-Holocene climate andecosystem history from Chesapeake Bay sediment cores, USA

Palaeoclimate records from late-Holocene sediments in Chesapeake Bay, the largest estuary in the USA, provide evidence that both decadal to centennial climate variability and European colonization had severe impacts on the watershed and estuary. Using pollen and dinoflagellate cysts as proxies for mid-Atlantic regional precipitation, estuarine salinity and dissolved oxygen (DO) during the last 2300 years, we identified four dry intervals, centred on AD 50 (P1/D1), AD 1000 (P2/D2), AD 1400 (P3) and AD 1600 (P4). Two centennial-scale events, P1/D1 and P2/D2, altered forest composition and led to increased salinity and DO levels in the estuary. Intervals P3 and P4 lasted several decades, leading to decreased production of pine pollen. Periods of dry mid-Atlantic climate correspond to 'megadroughts' identified from tree-ring records in the southeastern and central USA. The observed mid-Atlantic climate variability may be explained by changes in atmospheric circulation resulting in longer-term, perhaps amplified, intervals of meridional flow. After European colonization in the early seventeenth century, forest clearance for agriculture, timber and urbanization altered estuarine water quality, with dinoflagellate assemblages indicating reduced DO and increased turbidity.

Holocene↗

USGS2011

A tree-ring reconstruction of the salinity gradient in the northern estuary of San Francisco Bay

Blue oak tree-ring chronologies correlate highly with winter–spring precipitation totals over California, with Sacramento and San Joaquin river stream flow, and with seasonal variations in the salinity gradient in San Francisco Bay. The convergence of fresh and saline currents can influence turbidity, sediment accumulation, and biological productivity in the estuary. Three selected blue oak chronologies were used to develop a 625-year-long reconstruction of the seasonal salinity gradient, or low salinity zone (LSZ), which provides a unique perspective on the interannual-to-decadal variability of this important estuarine habitat indicator. The reconstruction was calibrated with instrumental LSZ data for the winter–spring season, and explains 73% of the variance in the February–June position of the LSZ from 1956 to 2003. Because this calibration period post-dates the sweeping changes that have occurred to land cover, channel morphology, and natural streamflow regimes in California, the reconstruction provides an idealized estimate for how the LSZ might have fluctuated under the seasonal precipitation variations of the past 625 years, given the modern geometry and bathymetry of the estuary and land cover across the drainage basin. The February–June season integrates precipitation and runoff variability during the cool season, and does not extend into the late-summer dry season when LSZ extremes can negatively affect Sacramento–San Joaquin Delta (Delta) agriculture and some aquatic organisms. However, there is such strong inter-seasonal persistence in the instrumental LSZ data that precipitation totals during the cool season can strongly pre-condition LSZ position in late summer. The 625-year-long reconstruction indicates strong interannual and decadal variability, the frequent recurrence of consecutive 2-year LSZ maxima and minima, large-scale ocean atmospheric forcing, and an interesting asymmetrical influence of warm El Niño–Southern Oscillation (ENSO) events.

California↗

USGS2010

Hydrogeology of the Markagunt Plateau, Southwestern Utah

The Markagunt Plateau, in southwestern Utah, lies at an altitude of about 9,500 feet and is capped primarily by Quaternary-age basalt that overlies Eocene-age freshwater limestone of the Claron Formation. Over large parts of the Markagunt Plateau, dissolution of the Claron limestone and subsequent collapse of the overlying basalt have produced a terrain characterized by sinkholes as much as 1,000 feet across and 100 feet deep. Numerous large springs discharge from the basalt and underlying limestone on the plateau, including Mammoth Spring, one of the largest springs in Utah, with a discharge that can exceed 300 cubic feet per second. Discharge from Mammoth Spring is from the Claron Formation; however, recharge to the spring largely takes place by both focused and diffuse infiltration through the basalt that caps the limestone. Results of dye tracing to Mammoth Spring indicate that recharge originates largely southwest of the spring outside of the Mammoth Creek watershed, as well as from losing reaches along Mammoth Creek. Maximum groundwater travel time to the spring from dye-tracer tests during the snowmelt runoff period was about 1 week. Specific conductance and water temperature data from the spring show an inverse relation to discharge during snowmelt runoff and rainfall events, also indicating short groundwater residence times. Results of major-ion analyses for samples collected from Mammoth and other springs on the plateau indicate calcium-bicarbonate type water containing low (less than 200 mg/L) dissolved-solids concentrations. Investigations in the Navajo Lake area along the southern margin of the plateau have shown that water losing to sinkholes bifurcates and discharges to both Cascade and Duck Creek Springs, which subsequently flow into the Virgin and Sevier River basins, respectively. Groundwater travel times to these springs, on the basis of dye tracing, were about 8.5 and 53 hours, respectively. Similarly, groundwater travel time from Duck Creek Sinks to Lower Asay Spring was about 68 hours. Dye-tracer studies conducted at the Mammoth Creek fish hatchery along the eastern margin of the Markagunt Plateau indicate that water losing through the channel of Mammoth Creek 3,000 feet upstream of the hatchery discharges from the hatchery springs in about 7.5 hours. Results of studies using soil bacteria and club moss spores as surrogate particle tracers for the whirling disease parasite also indicate that the potential exists for transport of the parasite to the springs from Mammoth Creek.

Book chapter↗

USGS1996

Charcoal deposition and redeposition in Elk Lake, Minnesota, USA

Sedimentary charcoal, diatom and phytolith records of the past 1500 years at Elk Lake, Minnesota, in combination with sediment trap studies and a transect of surface sediment samples, document the mechanisms by which previously deposited charcoal is redeposited and finally buried in this lake. The frequent correspon dence of high diatom concentrations and peaks of phytolith and charcoal fragments suggests that currents and turbulence related to lake circulation are responsible for winnowing charcoal and phytoliths from shallow water depositional sites to deeper areas of the lake. High diatom concentrations in the record relate to increased nutrient fluxes also supplied by circulation. Despite the fact that the watershed and area around Elk Lake has not been burned since AD 1922, charcoal continues to reach the profundal zone from littoral source areas in Elk Lake. The variable redeposition of within-lake charcoal requires evaluation before fire-history records can be related to global, regional or even local fire events.

Holocene↗