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At least 1,009 records · Page 56Linked to original sources
USGS2011

Trends in suspended-sediment loads and concentrations in the Mississippi River Basin, 1950–2009

Trends in loads and concentrations of suspended sediment and suspended sand generally were downward for stations within the Mississippi River Basin during the 60-, 34-, and 12-year periods analyzed. Sediment transport in the lower Mississippi River has historically been, and continues to be, most closely correlative to sediment contributions from the Missouri River, which generally carried the largest annual suspended-sediment load of the major Mississippi River subbasins. The closure of Fort Randall Dam in the upper Missouri River in 1952 was the single largest event in the recorded historical decline of suspended-sediment loads in the Mississippi River Basin. Impoundments on tributaries and sediment reductions as a result of implementation of agricultural conservation practices throughout the basin likely account for much of the remaining Mississippi River sediment transport decline. Scour of the main-stem channel downstream from the upper Missouri River impoundments is likely the largest source of suspended sand in the lower Missouri River. The Ohio River was second to the Missouri River in terms of sediment contributions, followed by the upper Mississippi and Arkansas Rivers. Declines in sediment loads and concentrations continued through the most recent analysis period (1998–2009) at available Mississippi River Basin stations. Analyses of flow-adjusted concentrations of suspended sediment indicate the recent downward temporal changes generally can be explained by corresponding decreases in streamflows.

Mississippi River Basin↗
USGS2013

Concentration, flux, and the analysis of trends of total and dissolved phosphorus, total nitrogen, and chloride in 18 tributaries to Lake Champlain, Vermont and New York, 1990–2011

Annual concentration, flux, and yield for total phosphorus, dissolved phosphorus, total nitrogen, and chloride for 18 tributaries to Lake Champlain were estimated for 1990 through 2011 using a weighted regression method based on time, tributary streamflows (discharges), and seasonal factors. The weighted regression method generated two series of daily estimates of flux and concentration during the period of record: one based on observed discharges and a second based on a flow-normalization procedure that removes random variation due to year-to-year climate-driven effects. The flownormalized estimate for a given date is similar to an average estimate of concentration or flux that would be made if all of the observed discharges for that date were equally likely to have occurred. The flux bias statistic showed that 68 of the 72 flux regression models were minimally biased. Temporal trends in the concentrations and fluxes were determined by calculating percent changes in flow-normalized annual fluxes for the full period of analysis (1990 through 2010) and for the decades 1990–2000 and 2000–2010. Basinwide, flow-normalized total phosphorus flux decreased by 42 metric tons per year (t/yr) between 1990 and 2010. This net result reflects a basinwide decrease in flux of 21 metric tons (t) between 1990 and 2000, followed by a decrease of 20 t between 2000 and 2010; both results were largely influenced by flux patterns in the large tributaries on the eastern side of the basin. A comparison of results for total phosphorus for the two separate decades of analysis found that more tributaries had decreasing concentrations and flux rates in the second decade than the first. An overall reduction in dissolved phosphorus flux of 0.7 t/yr was seen in the Lake Champlain Basin during the full period of analysis. That very small net change in flux reflects substantial reductions between 1990 and 2000 from eastern tributaries, especially in Otter Creek and the LaPlatte and Winooski Rivers that largely were offset by increases in the Missisquoi and Saranac Rivers in the second decade (between 2000 and 2010). The number of tributaries that had increases in dissolved phosphorus concentrations stayed constant at 13 or 14 during the period of analysis. Total nitrogen concentration and flux for most of the monitored tributaries in the Lake Champlain Basin have decreased since 1990. Between 1990 and 2010, flow-normalized total nitrogen flux decreased by 386 t/yr, which reflects an increase of 440 t/yr between 1990 and 2000 and a decrease of 826 t/yr between 2000 and 2010. All individual tributaries except the Winooski River had decreases in total nitrogen concentration and flux between 2000 and 2010. The decrease in total nitrogen flux over the period of record could be related to the decrease in nitrogen from atmospheric deposition observed in Vermont or to concurrent benefits realized from the implementation of agricultural best-management practices in the Lake Champlain Basin that were designed primarily to reduce phosphorus runoff. For chloride, large increases in flow-normalized concentrations and flux between 1990 and 2000 for 17 of the 18 tributaries diminished to small increases or decreases between 2000 and 2010. Between 1990 and 2010, flow-normalized flux increased by 32,225 t/yr, 78 percent of which (25,163 t) was realized during the first decade, from 1990 through 2000. The five tributaries that had decreasing concentration and flux of chloride between 2000 and 2010 were all on the eastern side of Lake Champlain, possibly related to reductions since 1999 in winter road salt application in Vermont. Positive correlations of phosphorus flux and changes in phosphorus concentration and flux in tributaries with phosphorus inputs to basins from point sources, suggest that point sources have an effect on stream phosphorus chemistry. Several measures of changes in agricultural statistics, such as agricultural land use, acres of land in farms, acres of cropland, and acres of corn for grain or seed, are positively correlated with changes in phosphorus concentration or flux in the tributaries. Negative correlations of the amount of money spent on agricultural best-management practices with changes in phosphorus concentration or flux in the tributaries, suggest that best-management practices may be an effective tool, along with point-source reductions, in making progress towards management goals for phosphorus reductions in Lake Champlain.

New York;Vermont↗
USGS2014

Water withdrawals, use, and trends in Florida, 2010

In 2010, the total amount of water withdrawn in Florida was estimated to be 14,988 million gallons per day (Mgal/d). Saline water accounted for 8,589 Mgal/d (57 percent) and freshwater accounted for 6,399 Mgal/d (43 percent). Groundwater accounted for 4,166 Mgal/d (65 percent) of freshwater withdrawals, and surface water accounted for the remaining 2,233 Mgal/d (35 percent). Surface water accounted for nearly all (99.9 percent) saline-water withdrawals. An additional 659 Mgal/d of reclaimed wastewater was used in Florida during 2010. Freshwater withdrawals were greatest in Palm Beach County (707 Mgal/d), and saline-water withdrawals were greatest in Hillsborough County (1,715 Mgal/d). Fresh groundwater provided drinking water (public supplied and self-supplied) for 17.33 million people (92 percent of Florida’s population), and fresh surface water provided drinking water for 1.47 million people (8 percent). The statewide public-supply gross per capita use for 2010 was 134 gallons per day, whereas the statewide public-supply domestic per capita use was 85 gallons per day. The majority of groundwater withdrawals (almost 62 percent) in 2010 were obtained from the Floridan aquifer system, which is present throughout most of the State. The majority of fresh surface-water withdrawals (56 percent) came from the southern Florida hydrologic unit subregion and is associated with Lake Okeechobee and the canals in the Everglades Agricultural Area of Glades, Hendry, and Palm Beach Counties, as well as the Caloosahatchee River and its tributaries in the agricultural areas of Collier, Glades, Hendry, and Lee Counties. Overall, agricultural irrigation accounted for 40 percent of the total freshwater withdrawals (ground and surface), followed by public supply with 35 percent. Public supply accounted for 48 percent of groundwater withdrawals, followed by agricultural self-supplied (34 percent), commercial-industrial-mining self-supplied (7 percent), recreational-landscape irrigation and domestic self-supplied (5 percent each), and power generation (less than 1 percent). Agricultural self-supplied accounted for 51 percent of fresh surface-water withdrawals, followed by power generation (25 percent), public supply (11 percent), recreational-landscape irrigation (9 percent), and commercial-industrial-mining self-supplied (4 percent). Power generation accounted for nearly all (99.8 percent) saline-water withdrawals. Of the 18.80 million people who resided in Florida during 2010, 41 percent (7.68 million people) resided in the South Florida Water Management District (SFWMD), 25 percent each resided in the Southwest Florida Water Management District (SWFWMD) and the St. Johns River Water Management District (SJRWMD) (4.73 and 4.70 million people, respectively), 7 percent (1.36 million people) resided in the Northwest Florida Water Management District (NWFWMD), and 2 percent (0.33 million people) resided in the Suwannee River Water Management District (SRWMD). The largest percentage of freshwater withdrawals was from the SFWMD (47 percent), followed by the SJRWMD (21 percent), SWFWMD (18 percent), NWFWMD (9 percent), and SRWMD (5 percent). Between 1950 and 2010, the population of Florida increased by 16.03 million (580 percent), and the total water withdrawals (fresh and saline) increased by 12,334 Mgal/d (465 percent). More recently, total freshwater withdrawals decreased by more than 1,792 Mgal/d (22 percent) between 2000 and 2010, while the population increased by 2.82 million (18 percent), and total freshwater withdrawals decreased by more than 474 Mgal/d (7 percent) between 2005 and 2010, while the population increased by 0.88 million (8 percent). The recent trend of decreases in freshwater withdrawals is a result of increased rainfall during this period, the development and use of alternative water sources, water conservation efforts, more conservative regulations and mandates, changes in economic conditions, and losses of irrigated lands. Fresh-water withdrawals for public supply, agricultural self-supplied use, and commercial-industrial-mining self-supplied use all decreased between 2000 and 2010 and between 2005 and 2010, whereas freshwater withdrawals for domestic self-supplied use, recreational-landscape irrigation use, and power generation use either remained the same or changed slightly during the decade. The use of highly mineralized groundwater (referred to as nonpotable water) as a source of drinking water has increased in Florida. Nonpotable water use for public supply has increased from nearly 2 Mgal/d in 1970 to about 165 Mgal/d in 2010. Nonpotable water is either blended or treated to meet drinking-water standards and is mostly used along the east and west coasts of central and southern Florida. The use of reclaimed wastewater increased from about 206 Mgal/d in 1986 to nearly 659 Mgal/d in 2010. More than three-quarters (79 percent) of reclaimed wastewater in 2010 was used to supplement potable-quality water withdrawals for urban irrigation, agricultural irrigation, and industrial use.

Florida↗
USGS2015

Potentiometric surfaces and water-level trends in the Cockfield (upper Claiborne) aquifer in southern Arkansas and the Wilcox (lower Wilcox) aquifer of northeastern and southern Arkansas, 2012

The Cockfield aquifer, located in southern Arkansas, is composed of Eocene-age sand beds found near the base of the Cockfield Formation of Claiborne Group. The Wilcox aquifer, located in northeastern and southern Arkansas, is composed of Paleocene-age sand beds found in the middle to lower part of the Wilcox Group. The Cockfield and Wilcox aquifers are primary sources of groundwater. In 2010, withdrawals from the Cockfield aquifer in Arkansas totaled 19.2 million gallons per day (Mgal/d), and withdrawals from the Wilcox aquifer totaled 36.5 Mgal/d. A study was conducted by the U.S. Geological Survey in cooperation with the Arkansas Natural Resources Commission and the Arkansas Geological Survey to measure water levels associated with the Cockfield aquifer and the Wilcox aquifer in northeastern and southern Arkansas. Water levels were measured at 43 wells completed in the Cockfield aquifer and 47 wells completed in the Wilcox aquifer in February and March 2012. Measurements from 2012 are presented as potentiometric-surface maps and in combination with measurements from 2006 as water-level difference maps. Trends in water-level change over time within the Cockfield and Wilcox aquifers were determined using the water-level difference maps and selected well hydrographs. The Cockfield aquifer study area in southern Arkansas is bounded on the east by the Mississippi River and on the west by the area that contains outcrops and subcrops of the Cockfield Formation. The northern boundary of the Cockfield aquifer study area is defined by the area that contains observation wells completed in the Cockfield aquifer and the southern boundary is the Louisiana State line. The Wilcox aquifer study area in northeastern Arkansas is bounded on the east by the Mississippi River and on the north by the Missouri State line. The southern and western boundaries are defined by areas containing observation wells completed in the Wilcox aquifer or by outcrop areas on or near Crowleys Ridge. The Wilcox aquifer study area in southern Arkansas is defined by observation wells completed in the Wilcox aquifer or by areas that contain outcrops of the Wilcox Group, or both. The potentiometric-surface map of the Cockfield aquifer shows the regional direction of groundwater flow was generally toward the east-southeast, except in areas of intense groundwater withdrawals such as southwestern Ashley County, where groundwater flows toward the town of Crossett. The highest water-level altitude measured was 350 feet (ft) above National Geodetic Vertical Datum of 1929 (NGVD 29) in central Columbia County. The lowest water-level altitude measured was 40 ft above NGVD 29 in southeastern Lincoln County. The water-level difference map for the Cockfield aquifer in Arkansas was constructed using 42 water-level measurements made during 2006 and 2012. The difference in water levels for the Cockfield aquifer ranged from 27.4 ft to -10.4 ft. The largest water-level rise was in Calhoun County, and the largest water-level decline was 10.4 ft in Union County. Of the 42 wells, 13 wells had a rise in water level, and the remaining 29 wells had a decline in water level. Hydrographs for 32 wells in the Cockfield aquifer with historical water-level data were evaluated using linear regression to calculate the annual rise or decline for each well. These data were aggregated by county and statistically evaluated for the range, mean, and median of water-level change in each county. Hydrographs for Bradley, Calhoun, Chicot, Columbia, and Union Counties indicated both rising and declining water levels. The mean annual water-level rise or decline for Calhoun County was 0.00 foot per year (ft/yr) or unchanged. The mean annual water-level for Ashley, Bradley, Chicot, Cleveland, Columbia, Lincoln, and Union Counties show declines ranging from -0.02 to -1.10 ft/yr. Two potentiometric-surface maps, one for the southern area and one for the northeastern area, were constructed to show the altitude of the water surface in the Wilcox aquifer. The direction of groundwater flow in the northeastern area was generally towards the south-southwest except for some areas immediately adjacent to the Mississippi River where the flow was more eastward towards the river. The highest water-level altitude was 219 ft in northern Mississippi County, and the lowest water-level altitude was 123 ft near West Memphis in Crittenden County. The direction of groundwater flow in the northern part of the southern area was generally towards the southwest. The direction of groundwater flow in the southern part was in all directions because of two cones of depression and two water-level mounds. The highest water-level altitude measured was 394 ft at the center of a water-level mound in eastern Hot Spring County and a water-level mound in southwestern Hempstead County. The lowest water-level altitude measured was 145 ft at the center of the cone of depression in Clark County. Water-level difference maps for the Wilcox aquifer in Arkansas were constructed using 47 water-level measurements made during 2006 and 2012. The difference in water levels for the Wilcox aquifer in the northeastern area ranged from 22.0 ft to -17.9 ft. The largest rise in water level occurred in Crittenden County, and the largest decline occurred in Lee County. Twenty-one wells had rising water levels, and 10 wells had declining water levels. The difference in water levels for the Wilcox aquifer in the southern area ranged from 18.1 ft to -4.2 ft. The largest rise and the largest decline in water level occurred in Nevada County. Twelve wells had rising water levels, and 4 wells had declining water levels. Linear regression analysis of long-term hydrographs was used to determine the mean annual water-level rise and decline in the Wilcox aquifer in the northeastern and southern areas of Arkansas. In the northeastern area, the mean annual water level declined in all seven counties. The mean annual declines ranged from -0.55 ft/yr in Craighead County to -1.46 ft/yr in St. Francis County. In the southern area, the annual rise and decline calculations for wells with over 20 years of records indicate rising and declining water levels in Clark, Hot Spring, and Nevada Counties. The mean annual water level declined in all counties except Hot Spring County.

Arkansas↗
USGS2017

Water-level trends and potentiometric surfaces in the Nacatoch Aquifer in northeastern and southwestern Arkansas and in the Tokio Aquifer in southwestern Arkansas, 2014–15

The Nacatoch Sand in northeastern and southwestern Arkansas and the Tokio Formation in southwestern Arkansas are sources of groundwater for agricultural, domestic, industrial, and public use. Water-level altitudes measured in 51 wells completed in the Nacatoch Sand and 42 wells completed in the Tokio Formation during 2014 and 2015 were used to create potentiometric-surface maps of the two areas. Aquifers in the Nacatoch Sand and Tokio Formation are hereafter referred to as the Nacatoch aquifer and the Tokio aquifer, respectively. Potentiometric surfaces show that groundwater in the Nacatoch aquifer flows southeast toward the Mississippi River in northeastern Arkansas. Groundwater flow direction is towards the south and southeast in Hempstead, Little River, and Nevada Counties in southwestern Arkansas. An apparent cone of depression exists in southern Clark County and likely alters groundwater flow from a regional direction toward the depression. In southwestern Arkansas, potentiometric surfaces indicate that groundwater flow in the Tokio aquifer is towards the city of Hope. Northwest of Hope, an apparent cone of depression exists. In southwestern Pike, northwestern Nevada, and northeastern Hempstead Counties, an area of artesian flow (water levels are at or above land surface) exists. Water-level changes in wells were identified using two methods: (1) linear regression analysis of hydrographs from select wells with a minimum of 20 years of water-level data, and (2) a direct comparison between water-level measurements from 2008 and 2014–15 at each well. Of the six hydrographs analyzed in the Nacatoch aquifer, four indicated a decline in water levels. Compared to 2008 measurements, the largest rise in water levels was 35.14 feet (ft) in a well in Clark County, whereas the largest decline was 14.76 ft in a well in Nevada County, both located in southwestern Arkansas. Of the four hydrographs analyzed in the Tokio aquifer, one indicated a decline in water levels, while the others remained relatively unchanged. Compared to 2008 measurements, the largest rise in water levels was 21.34 ft in Hempstead County, and the largest water-level decline was 39.37 ft in Clark County. Although changes in water levels since 2008 are spatially varied; long-term trends indicate an overall decline in water levels in both aquifers.

Arkansas↗
USGS2023

Assessment of conservation management practices on water quality and observed trends in the Plum Creek Basin, 2010–20

The U.S. Geological Survey and University of Wisconsin–Green Bay collected hydrologic and water-quality data to assess the effectiveness of agricultural conservation management practice (CMP) implementation at mainstem Plum Creek and west Plum Creek in northeastern Wisconsin. These two subbasins cover 88 percent of the Plum Creek Basin (Hydrologic Unit Code 12), which is a subbasin of the lower Fox River Basin. A published total maximum daily load report for the lower Fox River Basin rated Plum Creek as one of the greatest contributors of total suspended solids (TSS) and total phosphorus (TP) draining into the lower Fox River. To reduce TSS and TP exports from Plum Creek, additional cropland conservation practices and watercourse protections were applied between 2012 and 2020. To detect water-quality trends, data were collected during 2010 to 2020 at mainstem Plum Creek and 2013 to 2020 at west Plum Creek. The project used two methods to evaluate CMP effectiveness. The first method focused on evaluating water-quality changes between initial and post-CMP implementation periods during rain- or snowmelt-induced runoff events (hereafter referred to as “events”). In this approach random-forest models were developed to account for environmental factors which influence water quality. Model residuals from the two time periods were compared to determine the significance of water-quality changes associated with CMP implementation for mainstem and west Plum Creek Basins. The second method used a Weighted Regressions on Time, Discharge, and Season time-series approach to examine changes in water quality during the entire study period in mainstem Plum Creek. Results from both methods indicated there were minimal water-quality changes in TSS concentrations and flow-normalized delivery during runoff events during the 10-year period from 2010 to 2020; however, TP concentrations during low streamflow (less than 3 cubic feet per second [ft 3 /s]) may have decreased. The lack of observed improvement may be attributable to any of the following: variability in weather and hydrologic conditions, insufficient post-treatment data, additional cropland being converted to corn production, above average rainfall, streambank degradation, acute and legacy sources of phosphorus from farm fields, excessive/vulnerable manure applications and spills, and point-source discharges.

Wisconsin↗
USGS2024

Streamflow characteristics and trends in New Jersey, water years 1903–2017

As New Jersey’s population density remains high, so does its requirements for water management. Understanding the streamflow conditions throughout the state and how they may have changed over time is an important part of managing the water resources within the state. The New Jersey Department of Environmental Protection has many responsibilities related to protecting the environment and natural resources and among them is protecting the waters in the lakes, rivers, and streams of New Jersey for current and future use. To support this mission, the U.S. Geological Survey updated high- and low-streamflow statistics for 97 continuous-record streamgages and low-streamflow statistics for 719 partial-record streamgages throughout the state. The continuous-record streamgages included in the study had a minimum of 20 years of record, spanning from 1903 to 2017. This study is an update to previous studies that documented the high- and low-streamflow statistics for New Jersey streams in the 1970s and in 2005. The 1982 report by Gillespie and Schopp documented low-flow characteristics and flow duration for about 400 continuous and partial-record streamgages. The U.S. Geological Survey computed streamflow statistics including, but not limited to, maximum, minimum, and means for period of record, flow durations, nonexceedance high- and low-flow frequencies, base flow, runoff, peak-to-mean flow ratios, and September median streamflow. Overall, both high and low flows are generally increasing in New Jersey, though the results are not uniform across the State. Streamflow trends and changes to duration and frequency statistics can be influenced by local water use, in addition to climate variables. The resulting computations at some streamgages indicated considerable positive change while others showed considerable negative change. Water managers and regulators can use the data provided here and in the companion data release to assess individual stream reaches and watershed management areas to evaluate the available resources and changes, which may have developed during the periods for which streamflow statistics are available.

New Jersey↗
USGS2026

Decadal trends in the quality of groundwater used for public drinking-water supply in California, 2004–23, California Groundwater Ambient Monitoring and Assessment Program, Priority Basin Project

This study provides a comprehensive assessment of decadal changes in the quality of groundwater used for public drinking-water supply at 444 monitoring sites across California during 2004–23. We assessed decadal step trends in groundwater quality for 145 water-quality constituents and geochemical indicators statewide and across geographic and land-use based network groups. We evaluated the statistical significance of directional changes (predominant increase or decrease of constituent concentrations) and the magnitude of those changes across all network groups. Uranium showed the most widespread directional and high-magnitude increases of all constituents with regulatory benchmarks statewide, particularly in the agriculture-dominated Central Valley as well as urban-and desert-dominated regions of Southern California. Fluoride and perchlorate showed the most widespread directional and high-magnitude decreases of all constituents with regulatory benchmarks statewide, which were also most pronounced in Southern California. Although arsenic and nitrate did not often register significant directional changes across network groups, they showed widespread, high-magnitude changes in both directions (increase and decrease) at levels often exceeding 10 percent of respective regulatory benchmarks statewide. Triazine herbicides (atrazine and simazine) and the gasoline oxygenate methyl tert -butyl ether showed significant directional decreases statewide, but not at levels considered to be of high magnitude compared to respective regulatory benchmarks. We observed significant directional and high-magnitude increases of total dissolved solids statewide, which were most pronounced in agricultural areas. Analysis of explanatory geochemical indicators indicated that prevalent statewide increases of alkalinity and calcium were the predominant components of the observed statewide increases in total dissolved solids by mass. Widespread increases in groundwater alkalinity and calcium across agricultural and urban areas may be related, in part, to warm-season irrigation and other anthropogenic factors that have shifted soil weathering dynamics over the long term. Increasing alkalinity concentrations were related to increasing uranium concentrations, particularly in areas with aquifer materials derived from granitic rocks. Conversely, increasing calcium concentrations were related to decreasing fluoride concentrations, particularly in areas where fluoride occurred naturally at elevated concentrations. Decrease of perchlorate, triazine herbicides, and methyl tert -butyl ether are likely related to decreased anthropogenic source inputs over time and natural attenuation in aquifers.

California↗
USGS2000

Status and trends in suspended-sediment discharges, soil erosion, and conservation tillage in the Maumee River basin: Ohio, Michigan, and Indiana

The relation of suspended-sediment discharges to conservation-tillage practices and soil loss were analyzed for the Maumee River Basin in Ohio, Michigan, and Indiana as part of the U.S. Geological Survey’s National Water-Quality Assessment Program. Cropland in the basin is the largest contributor to soil erosion and suspended-sediment discharge to the Maumee River and the river is the largest source of suspended sediments to Lake Erie. Retrospective and recently-collected data from 1970–98 were used to demonstrate that increases in conservation tillage and decreases in soil loss can be related to decreases in suspended-sediment discharge from streams. Average annual water and suspended-sediment budgets computed for the Maumee River Basin and its principal tributaries indicate that soil drainage and runoff potential, stream slope, and agricultural land use are the major human and natural factors related to suspended-sediment discharge. The Tiffin and St. Joseph Rivers drain areas of moderately to somewhat poorly drained soils with moderate runoff potential. Expressed as a percentage of the total for the Maumee River Basin, the St. Joseph and Tiffin Rivers represent 29.0 percent of the basin area, 30.7 percent of the average-annual streamflow, and 9.31 percent of the average annual suspended-sediment discharge. The Auglaize and St. Marys Rivers drain areas of poorly to very poorly drained soils with high runoff potential. Expressed as a percentage of the total for the Maumee River Basin, the Auglaize and St. Marys Rivers represent 48.7 percent of the total basin area, 53.5 percent of the average annual streamflow, and 46.5 percent of the average annual suspended-sediment discharge. Areas of poorly drained soils with high runoff potential appear to be the major source areas of suspended sediment discharge in the Maumee River Basin. Although conservation tillage differed in the degree of use throughout the basin, on average, it was used on 55.4 percent of all crop fields in the Maumee River Basin from 1993–98. Conservation tillage was used at relatively higher rates in areas draining to the lower main stem from Defiance to Waterville, Ohio and at relatively lower rates in the St. Marys and Auglaize River Basins, and in areas draining to the main stem between New Haven, Ind. and Defiance, Ohio. The areas that were identified as the most important sediment-source areas in the basin were characterized by some of the lowest rates of conservation tillage. The increased use of conservation tillage was found to correspond to decreases in suspended- sediment discharge over time at two locations in the Maumee River Basin. A 49.8 percent decrease in suspended-sediment discharge was detected when data from 1970–74 were compared to data from 1996–98 for the Auglaize River near Ft. Jennings, Ohio. A decrease in suspended-sediment discharge of 11.2 percent was detected from 1970–98 for the Maumee River at Waterville, Ohio. No trends in streamflow at either site were detected over the period 1970–98. The lower rate of decline in suspended-sediment discharge for the Maumee River at Waterville, Ohio compared to the Auglaize River near Ft. Jennings, may be due to resuspension and export of stored sediments from drainage ditches, stream channels, and flood plains in the large drainage basin upstream from Waterville. Similar findings by other investigators about the capacity of drainage networks to store sediment are supported by this investigation. These findings go undetected when soil loss estimates are used alone to evaluate the effectiveness of conservation tillage. Water-quality data in combination with soil-loss estimates were needed to draw these conclusions. These findings provide information to farmers and soil conservation agents about the ability of conservation tillage to reduce soil erosion and suspended-sediment discharge from the Maumee River Basin.

Indiana, Michigan, Ohio↗
USGS2001

Historical trends and concentrations of fecal coliform bacteria in the Brandywine Creek basin, Chester County, Pennsylvania

The Brandywine Creek in Chester County is used for recreation and as an important source of drinking water. For this study, 40 sites were established for collection of water samples for analysis of fecal coliform and Escherichia coli bacteria in 1998-99. Samples were collected during base-flow conditions and during five storms in which rainfall exceeded 0.5 inch. During base- flow conditions, the median concentrations of fecal coliform bacteria exceeded 200 col/100 mL at 26 of the 40 sites (65 percent). During stormflow conditions, the median concentration of fecal coliform bacteria exceeded the Pennsylvania Department of Environmental Protection (PaDEP) criterion of 200 col/100 mL at 30 of 33 sites sampled (91 percent). Trends in fecal coliform bacteria concentrations were downward for the period 1973-99 at three long-term water-quality monitor stations, the result of upgrades in wastewater treatment plants, decreases in point-source discharges, and a decrease in agricultural land. A positive relation exists between streamflow and concentrations of fecal coliform bacteria at two of the long-term stations, but concentrations are elevated in base flow and stormflow at all three stations. Factors affecting bacteria concentrations in the Brandywine Creek Basin include nonpoint-source contaminants, reservoirs, seasonality, and stormflow. Nonpoint sources of bacterial contamination in the basin include, but are not limited to, land-surface runoff, urbanization, agricultural processes, groundwater contamination, and wildlife. Bacteria concentrations in streams that flow directly from the reservoirs are much lower than the concentrations in the streams flowing into the reservoirs. During March, April, May, October, and November, the Brandywine Creek tends to have lower water temperatures and bacteria concentrations than during June, July, August, and September. The 10-year median concentrations of bacteria at West Branch Brandywine Creek at Modena and East Branch Brandywine Creek below Downingtown exceed the criterion of 200 col/100 mL established by the PaDEP during the swimming season. The 10-year median concentrations of bacteria at Brandywine Creek at Chadds Ford exceed the criterion of 200 col/100 mL only during June. None of the stations exceed the criterion of 2,000 col/100 mL as established by the PaDEP for the remainder of the year.

Water-Resources Investigations Report↗
USGS2002

Evaluation of trends in pH in the Yampa River, northwestern Colorado, 1950-2000

In 1999, the U.S. Geological Survey began a study of pH trends in the Yampa River from near its headwaters to its mouth. The study was prompted by an apparent historical increase in measured pH at the Yampa River near Maybell, from an average of about 7.6 in the 1950's and 1960's to about 8.3 in the 1980's and 1990's. If real, further increase could cause more frequent exceedances of the Colorado water-quality standard of 9.0 and adversely affect aquatic life in the Yampa River Basin, including Dinosaur National Monument. The principal conclusion of this study is that this apparent historical increase in measured pH was caused mostly by changes in measurement protocol. Synoptic sampling during August 16-19, 1999, a period of relatively warm weather and base flow, showed that late afternoon pH of the Yampa River ranged from 8.46 to 9.20. The largest pH (9.20) exceeded the Colorado water-quality standard and was measured at Yampa River above Elk River, about 1.8 miles downstream from the Steamboat Springs Regional Waste Water Treatment Plant outfall, where nutrient enrichment caused photosynthesis by algae to dominate. Here, the dissolved oxygen concentration was 161 percent of saturation and carbon dioxide (CO2 was at 26 percent of saturation. At Yampa River downstream from a diversion near Hayden, 16.3 miles downstream, the effects of photosynthesis were still dominant, though attenuated by reaeration and dilution with freshwater from the Elk River. About 37.2 miles farther downstream, at Yampa River below Craig, which is about 6.2 miles downstream from the Craig Waste Water Treatment Plant, the effects of photosynthesis increased slightly, and pH rose to 8.80. Respiration plus oxidation of organic matter became dominant at Yampa River at Deerlodge Park in Dinosaur National Monument, where pH was 8.51, dissolved oxygen concentration was at 109 percent of saturation, and CO2 was at 189 percent of saturation. Respiration plus oxidation of organic matter, though diminished, apparently extended to the mouth of the Yampa River. Diurnal measurements on the Yampa River during August 23-26, 1999, show that the effects of photosynthesis and respiration plus oxidation of organic matter decreased downstream with distance from the developed urban area in the eastern part of the basin. Larger night-time values of pH in Dinosaur National Monument at Deerlodge Park and at the mouth of the Yampa River indicate that source waters varied with respect to capacity for respiration plus oxidation and photo-synthesis, that photosynthesis was minor, and that pH was largely controlled by respiration plus oxidation of organic matter. Synoptic sampling was repeated during March 13-16, 2000, when discharge was larger in response to late-winter melting of snow and ice at lower altitudes in the basin. Concentrations of nitrite plus nitrate were about 9 times greater in the Yampa River during March 2000 than during August 1999, and the largest increase (greater than 1,200 percent) was at Yampa River below Craig. At and downstream from Steamboat Springs, Colorado, pH at Yampa River sites averaged 8.85 during synoptic sampling in March 2000 compared to 8.70 in August 1999, with the partial pressure of carbon dioxide gas (PCO2) averaging 67 percent of saturation (compared to 99 percent during August 1999). The apparently larger effects of photosynthesis on pH and dissolved oxygen concentrations during March 2000 compared to August 1999 probably were caused by (1) slower rates of exchange of CO2 into and dissolved oxygen out of the river because of colder and deeper water and (2) slower rates of CO2 production and oxygen consumption resulting from slower rates of respiration by organisms and from slower rates of aerobic decomposition of organic matter in the colder river water and streambed sediment. Hypothetical thermodynamic simulations were done for samples collected in the lower Yampa River Basin to simulate the same amount of photosynthesis th

Water-Resources Investigations Report↗
USGS2003

Concentrations and loads of suspended sediment and nutrients in surface water of the Yakima River basin, Washington, 1999-2000 [electronic resource] : with an analysis of trends in concentrations

Spatial and temporal variations in concentrations and loads of suspended sediment and nutrients in surface water of the Yakima River Basin were assessed using data collected during 1999?2000 as part of the U.S. Geological Survey (USGS) National Water-Quality Assessment (NAWQA) Program. Samples were collected at 34 sites located throughout the Basin in August 1999 using a Lagrangian sampling design, and also were collected weekly and monthly from May 1999 through January 2000 at three of the sites. Nutrient and sediment data collected at various time intervals from 1973 through 2001 by the USGS, Bureau of Reclamation, Washington State Department of Ecology, and Roza-Sunnyside Board of Joint Control were used to assess trends in concentrations. During irrigation season (mid-March to mid-October), concentrations of suspended sediment and nutrients in the Yakima River increase as relatively pristine water from the forested headwaters moves downstream and mixes with discharges from streams, agricultural drains, and wastewater treatment plants. Concentrations of nutrients also depend partly on the proportions of mixing between river water and discharges: in years of ample water supply in headwater reservoirs, more water is released during irrigation season and there is more dilution of nutrients discharged to the river downstream. For example, streamflow from river mile (RM) 103.7 to RM 72 in August 1999 exceeded streamflow in July 1988 by a factor of almost 2.5, but loads of total nitrogen and phosphorus discharged to the reach from streams, drains, and wastewater treatment plants were only 1.2 and 1.1 times larger. In years of ample water supply, canal water, which is diverted from either the Yakima or Naches River, makes up more of the flow in drains and streams carrying agricultural return flows. The canal water dilutes nutrients (especially nitrate) transported to the drains and streams in runoff from fields and in discharges from subsurface field drains and the shallow ground-water system. The average concentration of total nitrogen in drains and streams discharging to the Yakima River from RM 103.7 to RM 72 in August 1999 was 2.63 mg/L, and in July 1988 was 3.16 mg/L; average concentrations of total phosphorus were 0.20 and 0.26 mg/L. After irrigation season, streamflow in agricultural drains decreases because irrigation water is no longer diverted from the Yakima and Naches Rivers. As a result, concentrations of total nitrogen in drains increase because nitrate, which constitutes much of total nitrogen, continues to enter the drains from subsurface drains and shallow ground water. Concentrations of total phosphorus and suspended sediment often decrease, because they are transported to the drains in runoff of irrigation water from fields. In Granger Drain, concentrations of total nitrogen ranged from 2-4 mg/L during irrigation season and increased to about 6 mg/L after irrigation season, and concentrations of total phosphorus, as high as 1 mg/L, decreased to about 0.2 mg/L. In calendar year 1999, Moxee Drain transported an average of 28,000 lb/d (pounds per day) of suspended sediment, 380 lb/d of total nitrogen, and 46 lb/d of total phosphorus to the Yakima River. These loads were about half the average loads transported by Granger Drain during the same period. Average streamflows were similar for the two drains, so the difference in loads was due to differences in constituent concentrations: those in Moxee Drain were about 40-60 percent less than those in Granger Drain. Loads of suspended sediment and total phosphorus in Moxee and Granger Drains were nearly four times higher during irrigation season than during the non-irrigation season because with increased flow during irrigation season, concentrations of suspended sediment and total phosphorus are usually higher. Loads of nitrate in the drains were about the same in both seasons because nitrate concentrations are higher during the non-irrigation season.

Water-Resources Investigations Report↗
USGS2003

External quality-assurance results for the National Atmospheric Deposition Program/National Trends Network, 1997-99

Five external quality-assurance programs were operated by the U.S. Geological Survey for the National Atmospheric Deposition Program/ National Trends Network (NADP/NTN) during 1997 through 1999: the intersite-comparison program, the blind-audit program, the field- audit program, the interlaboratory-comparison program, and the collocated-sampler program. The intersite-comparison program assesses the accuracy of pH and specific-conductance determinations made by NADP/NTN site operators. In two 1997 intersite-comparison studies, 83.7 and 85.8 percent of the pH determinations met the NADP/NTN accuracy goals, whereas 97.3 and 92.4 percent of the specific-conductance determinations met the NADP/NTN accuracy goals. The percentage of pH and specific-conductance determinations that met the accuracy goals in 1998 were, for the most part, higher than in 1997. In two 1998 studies, 90.9 and 90.3 percent of the pH determinations met the accuracy goals compared to 94.7 and 96.0 percent of the specific- conductance measurements meeting the accuracy goals. In one 1999 intersite-comparison study, 89.5 percent and 99.4 percent of pH and specific- conductance determinations, respectively, met the NADP/NTN accuracy goals. The blind-audit program evaluates the effects of routine sample handling, processing, and shipping on the analytical bias and precision of weekly precipitation samples. A portion of the blind-audit sample subject to the normal onsite handling and processing of a weekly precipitation sample is referred to as the bucket portion, whereas the portion receiving only minimal handling is referred to as the bottle portion. Positive bias in regard to blind-audit results indicates that the bucket portion has a higher concentration than the bottle portion. The paired t-test for the 1997 through 1999 blind- audit data indicates that routine sample handling, processing, and shipping introduced a positive bias (a=0.05) for calcium and chloride and a negative bias (cz=0.05) for hydrogen ion. During 1997 through 1999, the median paired differences between the bucket and bottle portions ranged from 0.00 milligram per liter for nitrate and ammonium to +0.010 milligram per liter for both chloride and sulfate. The median paired difference between the bucket and bottle portions for hydrogen ion was -1.086 microequivalents per liter, whereas for specific conductance, the median paired difference between the bucket and bottle portions was -0.200 microsiemen per centimeter during 1997 through 1999. Surface-chemistry effects due to variable amounts of precipitation contacting prewashed sample-collection and shipping-container surfaces were studied in the blind-audit program by using three different sample volumes. The sample- collection and shipping containers used for the blind-audit study were obtained from the site operator's supply and could have been used for precipitation samples. Results of a Kruskal-Wallis analysis of variance test of the relation between paired blind-audit sample differences in units of concentration and sample volume were statistically significant for magnesium, chloride, sulfate, and hydrogen ion during 1997 through 1999. Before 1994, at least 5 of the 10 analytes displayed a statistically significant difference between paired blind-audit differences in units of concentration and sample volume, supporting the premise that chemical reactions between the 13-liter bucket shipping container (primarily the butadiene o-ring lid of the shipping container) and the sample, which resulted in an increasing loss of hydrogen ion with increasing volume, have been eliminated by the new l-liter bottle sample- shipping protocol. The field-audit program measures the effects of field exposure, handling, and processing on the chemistry of NADP/NTN precipitation samples. In the field-audit program, the site operator is instructed to process and submit a quality- control sample following a standard 7-day, Tuesday-to-Tuesday sampling period with no

Water-Resources Investigations Report↗
USGS2004

Water quality in Big Cypress National Preserve and Everglades National Park — Trends and spatial characteristics of selected constituents

Seasonal changes in water levels and flows in Big Cypress National Preserve (BICY) and Everglades National Park (EVER) affect water quality. As water levels and flows decline during the dry season, physical, geochemical and biological processes increase the breakdown of organic materials and the build-up of organic waste, nutrients, and other constituents in the remaining surface water. For example, concentrations of total phosphorus in the marsh are less than 0.01 milligram per liter (mg/L) during much of the year. Concentrations can rise briefly above this value during the dry season and occasionally exceed 0.1 mg/L under drought conditions. Long-term changes in water levels, flows, water management, and upstream land use also affect water quality in BICY and EVER, based on analysis of available data (1959-2000). During the 1980's and early 1990's, specific conductance and concentrations of chloride increased in the Taylor Slough and Shark River Slough. Chloride concentrations more than doubled from 1960 to 1990, primarily due to greater canal transport of high dissolved solids into the sloughs. Some apparent long-term trends in sulfate and total phosphorus were likely attributable, at least in part, to high percentages of less-than and zero values and to changes in reporting levels over the period of record. High values in nutrient concentrations were evident during dry periods of the 1980's and were attributable either to increased canal inflows of nutrient-rich water, increased nutrient releases from breakdown of organic bottom sediment, or increased build-up of nutrient waste from concentrations of aquatic biota and wildlife in remaining ponds. Long-term changes in water quality over the period of record are less pronounced in the western Everglades and the Big Cypress Swamp; however, short-term seasonal and drought-related changes are evident. Water quality varies spatially across the region because of natural variations in geology, hydrology, and vegetation and because of differences in water management and land use. Nutrient concentrations are relatively low in BICY and EVER compared with concentrations in parts of the northern Everglades that are near agricultural and urban lands. Concentrations of total phosphorus generally are higher in BICY (median values, 1991-2000, were mostly greater than 0.015 mg/L) than in EVER (median values, 1991-2000, less than 0.01 mg/L), probably because of higher phosphorus in natural sources such as shallow soils, rocks, and ground water in the Big Cypress region than in the Everglades region. Conversely, concentrations of chloride and sulfate are higher in EVER (median values in Shark River Slough, 1991-2000, mostly greater than 2 mg/L sulfate and 50 mg/L chloride) than in BICY (median values, 1991-2000, less than 1 mg/L sulfate and at most sites less than 20 mg/L chloride), probably because of the canal transport system, which conveys more water from an agricultural source into EVER than into BICY. Trace elements and contaminants such as pesticides and other toxic organic compounds are in relatively low concentrations in BICY and EVER compared with concentrations in parts of the northern Everglades near agricultural and urban sources. Concentrations rarely exceeded aquatic life criteria in BICY and EVER. Atrazine was the only pesticide found in water that exceeded the criteria (in 2 out of 304 samples). The pesticides heptachlor expoxide, lindane, and p,p?-DDE exceeded criteria in canal bed sediments in 1, 2, and 16 percent of the samples, respectively.

Florida↗
USGS2003

Spatial distribution and trends in trace elements, polycyclic aromatic hydrocarbons, organochlorine pesticides, and polychlorinated biphenyls in Lake Worth sediment, Fort Worth, Texas

In spring 2000, the Texas Department of Health issued a fish consumption advisory for Lake Worth in Fort Worth, Texas, because of elevated concentrations of polychlorinated biphenyls (PCBs) in fish. In response to the advisory and in cooperation with the U.S. Air Force, the U.S. Geological Survey collected 21 surficial sediment samples and three gravity core sediment samples to assess the spatial distribution and historical trends of selected hydrophobic contaminants, including PCBs, and to determine, to the extent possible, sources of hydrophobic contaminants to Lake Worth. Compared to reference (background) concentrations in the upper lake, elevated PCB concentrations were detected in the surficial sediment samples collected in Woods Inlet, which receives surface runoff from Air Force facilities and urban areas. Gravity cores from Woods Inlet and from the main part of the lake near the dam indicate that the concentrations of PCBs were three to five times higher in the 1960s than in 2000. A regression method was used to normalize sediment concentrations of trace elements for natural variations and to distinguish natural and anthropogenic contributions to sediments. Concentrations of several trace elements—cadmium, chromium, copper, lead, and zinc—were elevated in sediments in Woods Inlet, along the shoreline of Air Force facilities, and in the main lake near the dam. Concentrations of these five trace elements have decreased since 1970. Polycyclic aromatic hydrocarbons also were elevated in the same areas of the lake. Concentrations of total polycyclic aromatic hydrocarbons, normalized with organic carbon, were mostly stable in the upper lake but steadily increased near the dam, except for small decreases since 1980. The Woods Inlet gravity core showed the largest increase of the three core sites beginning about 1940; total polycyclic aromatic hydrocarbon concentrations in post-1940 sediments from the core showed three apparent peaks about 1960, 1984, and 2000. The concentrations of organochlorine pesticides were low relative to consensus-based sediment-quality guidelines and either decreased or remained constant since 1970. The two likely sources of hydrophobic contaminants to the lake are urban areas around the lake and the drainage area of Meandering Road Creek that contributes runoff to Woods Inlet and includes Air Force facilities.

Texas↗
USGS1976

Distribution and trend of nitrate, chloride, and total solids in water in the Magothy aquifer in southeast Nassau County, New York, from the 1950's through 1973

Concentrations of nitrate, chloride, and total solids in water in the Magothy aquifer, southeast Nassau County, N.Y., show a steadily increasing trend from the early 1950 's through 1973. Vertical distribution of nitrate, chloride, and total-solids concentrations as shown in cross sections of the study area indicate downward movement of these constituents from tens of feet to a few hundred feet in this time period. Maximum concentrations are in a zone underlying the areas of Westbury, Hicksville, and Plainview. Nitrate (as nitrogen) concentration increased from 4-5 mg/liter to 7 mg/liter in the area of Westbury and from 3 to 10 mg/liter in Plainview during the period 1950-73. Lowest nitrate concentrations are in the area south of a line running from North Merrick to South Farmingdale. Also, during the period analyzed (1950-73), a 10-mg/liter line of equal-chloride concentration on a cross section in the Westbury area moved downward a distance of less than 50 feet, and in the area of Hicksville, nearly 150 feet. Total-solids concentration doubled during the period 1950-73 in the area of Plainview, where maximum downward movement of pollutants was observed. (Woodard-USGS)

Water-Resources Investigations Report↗
USGS1987

Bias and precision of selected analytes reported by the National Atmospheric Deposition Program and National Trends Network, 1984

The U.S. Geological Survey operated a blind audit sample program during 1974 to test the effects of the sample handling and shipping procedures used by the National Atmospheric Deposition Program and National Trends Network on the quality of wet deposition data produced by the combined networks. Blind audit samples, which were dilutions of standard reference water samples, were submitted by network site operators to the central analytical laboratory disguised as actual wet deposition samples. Results from the analyses of blind audit samples were used to calculate estimates of analyte bias associated with all network wet deposition samples analyzed in 1984 and to estimate analyte precision. Concentration differences between double blind samples that were submitted to the central analytical laboratory and separate analyses of aliquots of those blind audit samples that had not undergone network sample handling and shipping were used to calculate analyte masses that apparently were added to each blind audit sample by routine network handling and shipping procedures. These calculated masses indicated statistically significant biases for magnesium, sodium , potassium, chloride, and sulfate. Median calculated masses were 41.4 micrograms (ug) for calcium, 14.9 ug for magnesium, 23.3 ug for sodium, 0.7 ug for potassium, 16.5 ug for chloride and 55.3 ug for sulfate. Analyte precision was estimated using two different sets of replicate measures performed by the central analytical laboratory. Estimated standard deviations were similar to those previously reported. (Author 's abstract)

Water-Resources Investigations Report↗
USGS1987

Estimation of streamflow characteristics and assessment of trends in the Niobrara River at Mariaville, Nebraska

A computer model was used to synthesize a long-term streamflow record for the Niobrara River at Mariaville, Nebraska. The record was developed on the basis of 30-plus years of streamflow data from 3 upstream sites, and the U. S. Geological Survey 's CONROUT model was calibrated using 294 days of measured flow at Mariaville; for the calibration period, 87% of the synthesized daily discharges were within 15% of the measured values. The synthesized record was analyzed for trends in streamflow characteristics. A marked decrease in the average consecutive-day, low-flow discharges was detected after 1964, ranging between 162 cu ft/sec less for the 1-day low flow and 200 cu ft/sec less for the 14-day low flow. The decrease probably was caused by the start-up of operations at Merritt Reservoir. (Author 's abstract)

Water-Resources Investigations Report↗