SEARCH · USGS Science

Results for “Agricultural Systems”

Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 541 records · Page 30Linked to original sources

USGS2007

Effects of Agricultural Land-Use Changes and Rainfall on Ground-Water Recharge in Central and West Maui, Hawai`i, 1926-2004

Concern surrounding declines in ground-water levels and an increase in the chloride concentration of water pumped from wells in the Iao aquifer system on the Island of Maui has prompted an investigation into the long-term sustainability of current (2006) and future ground-water withdrawals. As part of this investigation, a water budget for central and west Maui was calculated from which (1) ground-water recharge was estimated for the period 1926-2004 and (2) the effects of agricultural land-use changes and drought were analyzed. Estimated mean ground-water recharge decreased 44 percent from 1979 to 2004 in central and west Maui. Reduction in agricultural irrigation, resulting from more efficient irrigation methods and a reduction in the acreage used for agriculture, is largely responsible for the declining recharge. Recently, periods of lower-than-average rainfall have further reduced recharge. During the period 1926-79, ground-water recharge averaged 693 Mgal/d, irrigation averaged 437 Mgal/d, and rainfall averaged 897 Mgal/d. During the period 2000-04, ground-water recharge averaged 391 Mgal/d, irrigation averaged 237 Mgal/d, and rainfall averaged 796 Mgal/d. Simulations of hypothetical future conditions indicate that a cessation of agriculture in central and west Maui would reduce mean ground-water recharge by 18 percent in comparison with current conditions, assuming that current climatic conditions are the same as the long-term-average conditions during the period 1926-2004. A period of drought identical to that of 1998-2002 would reduce mean recharge by 27 percent. Mean recharge would decrease by 46 percent if this drought were to occur after a cessation of agriculture in central and western Maui. Whereas droughts are transient phenomena, a reduction in agricultural irrigation is likely a permanent condition.

Scientific Investigations Report↗

USGS2013

Agricultural sources of contaminants of emerging concern and adverse health effects on freshwater fish

Agricultural contaminants of emerging concern (CECs) are generally thought of as certain classes of chemicals associated with animal feeding and production facilities. Veterinary pharmaceuticals used in animal food production systems represent one of the largest groups of CECs. In our review, we discuss the extensive increase in use of antibiotics in animal feeding operations (AFOs) around the world. AFOs are a major consumer of antibiotics and other veterinary pharmaceuticals and over the past decade there has been growing information on the occurrence, release, and fate of CECs from animal food production operations, including the application of pharmaceutical-containing manure to agricultural fields and releases from waste lagoons. Concentrations of CECs in surface and ground water in proximity to AFOs correspond to their presence in the AFO wastes. In many cases, the environmental concentrations of agriculturally-derived CECs are below toxicity thresholds. Hormones and hormone replacement compounds are a notable exception, where chemical concentrations near AFOs can exceed concentrations known to cause adverse effects on endocrine-related functions in fish. In addition, some agricultural pesticides, once thought to be safe to non-target organisms, have demonstrated endocrine-related effects that may pose threats to fish populations in agricultural regions. That is, we have pesticides with emerging concerns, thus, the concern is emerging and not necessarily the chemical. In this light, one must consider certain agricultural pesticides to be included in the list of CECs. Even though agricultural pesticides are routinely evaluated in regulatory testing schemes which have been used for decades, the potential hazards of some pesticides have only recently been emerging. Emerging concerns of pesticides in fish include interference with hormone signaling pathways; additive (or more than additive) effects from pesticide mixtures; and adverse population-level effects at concentrations below predicted toxicity thresholds. Consequently, there is a need to evaluate the environmental concerns related to pesticide exposures to fish populations based on current biological and toxicological techniques. This presentation reviews some of the agricultural chemicals that have emerged as contaminants of concern and potentially threaten fish populations in agricultural watersheds.

Conference Paper↗

USGS1989

The hydrogeologic framework and a reconnaissance of ground-water quality in the Piedmont Province of North Carolina, with a design for future study

The U.S. Geological Survey is investigating the relation of ground- water quality and land use in the regolith and fractured rock ground-water system of the North Carolina Piedmont. The initial phase of this study provides a description of the ground-water flow system and a review of available ground-water data and formulates hypotheses that guide the design of a water-quality monitoring network for study of selected areas. In the Piedmont, the solid igneous and metamorphic bedrock grades upward into unweathered fractured rock that is covered by a transition zone of highly-fractured, partially weathered rock, clay-rich saprolite, and the soil. The fractured bedrock, transition zone, saprolite, and soil make up a complex flow system. A review of available ground-water quality data shows a lack of information about organic compounds and trace metals and changes in ground- water quality with depth. Land use, soils, and geology significantly influence ground-water quality. The hypotheses that need to be tested in the next study phase are: (1) that ground-water contamination can be related to land use, and (2) that the transition zone between bedrock and regolith serves as a primary transmitter of contaminants. Monitoring of basins containing industrial, urban, residential, and agricultural land uses in future studies will help define the relation of ground-water quality to land use. Water quality at different depths in the flow system and in streams during base flow needs to be identified.

North Carolina↗

USGS1988

Selenium accumulation in benthic bivalves and fine sediments of San Francisco Bay, the Sacramento-San Joaquin Delta, and selected tributaries

Spatial distributions of selenium were determined in fine-grained, oxidized, surface sediments and in two benthic bivalves ( Corbicula sp., a suspension-feeding freshwater clam, and Macoma balthica , a deposit-feeding brackish-water clam) within San Francisco Bay, the San Joaquin River and three river systems unlikely to be subject to selenium inputs. Biologically available selenium enters the middle reaches of the San Joaquin River from agricultural runoff. However, selenium concentrations in sediments and Corbicula in the lower San Joaquin, upstream from San Francisco Bay, were not significantly different from concentrations in rivers with no known selenium inputs. Biologically available selenium did not appear to enter the northernmost reach of San Francisco Bay from the San Joaquin River in levels which could measurably influence bioaccumulation by Corbicula . Selenium concentrations in Corbicula were enriched in the northernmost reach of San Francisco Bay compared with the rivers, but several lines of evidence suggested that local inputs (perhaps from urban/industrial waste discharges) were the most important sources. Selenium concentrations in Macoma balthica were also elevated at one station in the northern reach of the Bay and at one station in the extreme South Bay. However, no enrichment was evident at two other stations, suggesting a lack of bay-wide contamination. No significant correlation between selenium and mercury concentrations in Corbicula tissues was observed.

California↗

USGS2007

Global impacts of conversions from natural to agricultural ecosystems on water resources: Quantity versus quality

Past land use changes have greatly impacted global water resources, with often opposing effects on water quantity and quality. Increases in rain‐fed cropland (460%) and pastureland (560%) during the past 300 years from forest and grasslands decreased evapotranspiration and increased recharge (two orders of magnitude) and streamflow (one order of magnitude). However, increased water quantity degraded water quality by mobilization of salts, salinization caused by shallow water tables, and fertilizer leaching into underlying aquifers that discharge to streams. Since the 1950s, irrigated agriculture has expanded globally by 174%, accounting for ∼90% of global freshwater consumption. Irrigation based on surface water reduced streamflow and raised water tables resulting in waterlogging in many areas (China, India, and United States). Marked increases in groundwater‐fed irrigation in the last few decades in these areas has lowered water tables (≤1 m/yr) and reduced streamflow. Degradation of water quality in irrigated areas has resulted from processes similar to those in rain‐fed agriculture: salt mobilization, salinization in waterlogged areas, and fertilizer leaching. Strategies for remediating water resource problems related to agriculture often have opposing effects on water quantity and quality. Long time lags (decades to centuries) between land use changes and system response (e.g., recharge, streamflow, and water quality), particularly in semiarid regions, mean that the full impact of land use changes has not been realized in many areas and remediation to reverse impacts will also take a long time. Future land use changes should consider potential impacts on water resources, particularly trade‐offs between water, salt, and nutrient balances, to develop sustainable water resources to meet human and ecosystem needs.

Water Resources Research↗

USGS2009

RESIS-II: An Updated Version of the Original Reservoir Sedimentation Survey Information System (RESIS) Database

The Reservoir Sedimentation Survey Information System (RESIS) database, originally compiled by the Soil Conservation Service (now the Natural Resources Conservation Service) in collaboration with the Texas Agricultural Experiment Station, is the most comprehensive compilation of data from reservoir sedimentation surveys throughout the conterminous United States (U.S.). The database is a cumulative historical archive that includes data from as early as 1755 and as late as 1993. The 1,823 reservoirs included in the database range in size from farm ponds to the largest U.S. reservoirs (such as Lake Mead). Results from 6,617 bathymetric surveys are available in the database. This Data Series provides an improved version of the original RESIS database, termed RESIS-II, and a report describing RESIS-II. The RESIS-II relational database is stored in Microsoft Access and includes more precise location coordinates for most of the reservoirs than the original database but excludes information on reservoir ownership. RESIS-II is anticipated to be a template for further improvements in the database.

Data Series↗

USGS2000

Identifying wells downstream from Laguna Dam that yield water that will be replaced by water from the Colorado River, Arizona and California

This report summarizes a comprehensive study and development of the method documented in Owen-Joyce and others (2000). That report and one for the area upstream from Laguna Dam (Wilson and Owen-Joyce, 1994) document the accounting-surface method to identify wells that yield water that will be replaced by water from the Colorado River. Downstream from Laguna Dam, the Colorado River is the source for nearly all recharge to the river aquifer. The complex surface-water and ground-water system that exists in the area is, in part, the result of more than 100 years of water-resources development. Agriculture is the principal economy and is possible only with irrigation. The construction and operation of canals provides the means to divert and distribute Colorado River water to irrigate agricultural lands on the flood plains and mesas along the Colorado and Gila Rivers, in Imperial and Coachella Valleys, and in the area upstream from Dome along the Gila River. Water is withdrawn from wells for irrigation, dewatering, and domestic use. The area downstream from Laguna Dam borders additional areas of agricultural development in Mexico where Colorado River water also is diverted for irrigation.

Arizona;California↗

USGS1993

Ground-water quality at the Management Systems Evaluation Area (MSEA) near Princeton, Minnesota, 1991

The northern cornbelt sand-plains Management Systems Evaluation Area (MSEA) program is a multiagency, multistate initiative to evaluate the effects of modified and prevailing fanning systems on water quality in a sand-plain area in Minnesota and at satellite areas in North and South Dakota, and Wisconsin (Delin and others, 1992). The primary objective of the northern cornbelt sand-plains MSEA is to evaluate the effects of ridge-tillage practices in a corn and soybean farming system on ground-water quality. The Minnesota MSEA program is a cooperative study primarily between the U.S. Department of Agriculture-Agricultural Research Service, the University of Minnesota Soil Science Department, and the U.S. Geological Survey. The Minnesota Pollution Control Agency and the Department of Geology and Geophysics at the University of Minnesota are also cooperating in the evaluation of ground-water quality at the MSEA.

Minnesota↗

USGS2015

Particle tracking for selected groundwater wells in the lower Yakima River Basin, Washington

The Yakima River Basin in south-central Washington has a long history of irrigated agriculture and a more recent history of large-scale livestock operations, both of which may contribute nutrients to the groundwater system. Nitrate concentrations in water samples from shallow groundwater wells in the lower Yakima River Basin exceeded the U.S. Environmental Protection Agency drinking-water standard, generating concerns that current applications of fertilizer and animal waste may be exceeding the rate at which plants can uptake nutrients, and thus contributing to groundwater contamination. The U.S. Geological Survey (USGS) recently completed a regional scale transient three-dimensional groundwater-flow model of the Yakima River Basin using MODFLOW-2000. The model was used with the USGS particle-tracking code MODPATH to generate advective flowpaths and associated travel times. Analyses used particle backtracking in time from September 2001 through 504 monthly stress periods to October 1959 or until pathlines terminated at a model boundary. The particle starting locations were assigned to 1,000 foot square computational model cells containing one or more of the 121 sampling locations with measured nitrate concentrations greater than the U.S. Environmental Protection Agency drinking-water standard for nitrate (10 milligrams per liter [mg/L]). Of the 2,403 particles, the simulated pathlines for 2,080 reached the water table within the 42-year simulation period, thus identifying the predicted recharge areas for those particles. The median horizontal straight-line distance was 13,194 feet between starting and ending locations for these particles and the median time-of-travel for particles that intersected the water table was 984 days. Well to water-table travel times for 75.4 percent of the particles were less than the average travel time of 3,749 days. Predicted recharge locations for all particles, including those that did not reach the water table in 42 years, were between 50 feet and 34 miles horizontal distance from their starting locations, with a median distance of less than 3 miles away. Generalized groundwater-flow directions in unconsolidated basin-fill deposits were towards the Yakima River, which acts as a local sink for shallow groundwater, and roughly parallel to topographic gradients. Particles backtracked from more shallow aquifer locations traveled shorter distances before reaching the water table than particles from deeper locations. Flowpaths for particles starting at wells completed in the basalt units underlying the basin-fill deposits sometimes were different than for wells with similar lateral locations but more shallow depths. In cases where backtracking particles reached geologic structures simulated as flow barriers, abrupt changes in direction in some particle pathlines suggest significant changes in simulated hydraulic gradients that may not accurately reflect actual conditions. Most groundwater wells sampled had associated zones of contribution within the Toppenish/Benton subbasin between the well and the nearest subbasin margin, but interpretation of these results for any specific well is likely to be complicated by the assumptions and simplifications inherent in the model construction process. Delineated zones of contribution for individual wells are sensitive to the depths assigned to the screened interval of the well, resulting in simulated areal extents of the zones of contribution to a discharging well that are elongated in the direction of groundwater flow.

Washington↗

USGS2000

Distribution, movement, and fate of nitrate in the surficial aquifer beneath citrus groves, Indian River, Martin, and St. Lucie Counties, Florida

The surficial aquifer system beneath citrus groves in Indian River, Martin, and St. Lucie Counties, Florida, was studied to determine the effects of citrus agriculture on ground-water quality. The surficial aquifer is the primary drinking-water source for Martin and St. Lucie Counties and furnishes about 33 percent of the drinking-water for Indian River County. Water-quality samples and water-level data were collected from December 1996 through October 1998. Nitrate concentrations in ground water exceeded 10 milligrams per liter (mg/L), the U.S. Environmental Protection Agency's maximum contaminant level for nitrate reported as nitrogen, in 5 percent of the samples from citrus groves. These exceedances occurred in samples from wells with depths of 10 feet or less at citrus groves, and mostly in samples collected during or immediately following fertilizer applications. Samples from wells with depths of 20-25 feet contained little or no nitrate. The decreased nitrate concentrations in ground water with depth was not consistent with chloride and dissolved-solids concentrations, two other common indicators of agricultural activity. Chloride and dissolved-solids concentrations remained elevated in ground-water samples from all depths at citrus groves; median chloride and dissolved-solids concentrations in samples from citrus sites were 125 and 779 mg/L, respectively. In comparison, samples from the reference site had maximum chloride and dissolved-solids concentrations of 61 and 366 mg/L, respectively. Based on the age of ground water at 20-25 foot depths (3-50 years, measured with tritium and helium-3 concentration ratios), nitrate concentrations also should have remained elevated with depth because fertilizers have been used for at least 20-30 years at these citrus groves. Nitrate concentrations decreased with depth as a result of denitrification. This could have occurred because favorable conditions for denitrification existed in the aquifer, including high concentrations of dissolved organic carbon and iron (median concentrations of 25.5 and 1.75 mg/L, respectively at citrus sites) and low concentrations of dissolved oxygen (median concentration of 0.9 mg/L at citrus sites), which indicates that reducing conditions were present. Evidence that denitrification occurred included the enrichment of ground water with depth in the heavier isotope of nitrogen, nitrogen-15 ( 15 N). Ground water from wells screened 10-15 feet below land surface had a median d 15 N value of 24.6 per mil, whereas ground water from wells screened 5-10 feet below land surface had a median d 15 N value of 9.4 per mil. Fertilizer samples had a median d 15 N value of 3.0 per mil. Increased d 15 N values coincident with decreased nitrate concentrations with depth indicates that fractionation occurred during denitrification reactions. Finally, excess nitrogen gas, a byproduct of denitrification reactions, was detected at concentrations ranging from 0-8 mg/L in samples from wells screened 10-25 feet below land surface.

Florida↗

USGS1996

Geohydrology and water quality of the unconsolidated deposits in Erie County, Pennsylvania

Water in unconsolidated deposits is used for the water supplies of homes, farms, municipalities, and industries in Erie County. The unconsolidated deposits cover most of the bedrock of Erie County. Thickness of the unconsolidated deposits ranged from 60 to 400 feet at 30 sites surveyed by seismic refraction and reflection methods. Water wells, mostly in the unconsolidated deposits, provide adequate domestic supplies. Wells in fractured bedrock can generally provide small domestic supplies; however, droughts can affect some of the domestic water wells. Ground-water withdrawals accounted for 10 million gallons per day of the water used in Erie County in 1984. Mean annual precipitation ranged from 42 to 47 inches per year in Erie County from 1961 through 1990; the southeastern region of the county generally receives more precipitation than the lake shore region to the north. Overland runoff to three segments of the French Creek watershed in the upland area ranged from about 13 to 19 in. per year and base flow ranged from 14 to about 18 in. per year from 1975 to 1992. Evapotranspiration ranged from about 13 to 16 in. per year for those segments. Beach and outwash deposits generally provide the largest supplies of water to wells in Erie County. A median specific capacity of 17 (gal/min)/ft (gallons per minute per foot) of drawdown was determined from records of nondomestic wells in beach deposits and 9 (gal/min)/ft of drawdown in outwash. Mean specific capacity for wells in till deposits was 1.5 (gal/min)/ft. The range in yield and specific capacity, however, was great for the unconsolidated deposits and high yielding outwash deposits are sometimes difficult to locate beneath till and valley-fill deposits. Hydraulic conductivities from three aquifer tests of outwash deposits (sand and gravel) at separate sites ranged from 110 to 2,030 ft/d (feet per day). Hydraulic conductivities from another aquifer test of sand and silt in the water table at Presque Isle ranged from 120 to 215 ft/d. Transmissivities from a third aquifer test of beach sand and gravel ranged from 235 to 262 feet squared per day. Laboratory analyses of stream samples collected during base flows in 1987 and 1988 indicate that concentrations of arsenic, barium, cadmium, chromium, fluoride, lead, mercury, and selenium did not exceed the maximum contaminant levels (MCL's) established for drinking water by the U.S. Environmental Protection Agency (USEPA). Concentrations of two nontoxic elements, iron and manganese, exceeded USEPA secondary maximum contaminant levels (SMCL's) in samples from selected stream sites. Manganese concentrations exceeded the SMCL of 0.05 milligrams per liter at 19 of 30 stream sites sampled in the Upland Plateau Section of Erie County. Twenty-one wells were sampled for inorganic constituents and selected pesticides. Some samples from three of the wells exceeded the MCL for nitrate. Total arsenic concentrations above the MCL of 50 micrograms per liter were documented intermittently in three water wells in North East Township. Water from six of seven tile drains sampled in agricultural fields contained detectable concentrations of herbicides. These samples document the transport of the herbicides from the shallow ground-water system to local streams. Herbicide concentrations were at or more than minimum reporting levels for atrazine, cyanazine, prometone, and simazine. Atrazine concentrations in all seven samples from tile drains did not exceed the USEPA MCL of 3.0 micrograms per liter.

Water-Resources Investigations Report↗

USGS1997

Evaluation of agricultural best-management practices in the Conestoga River headwaters, Pennsylvania: A summary report, 1982-90

Pipe-outlet terracing was effective in reducing sediment losses from a field site, but total nitrogen and phosphorus losses with runoff were not significantly different before and after terracing. Median concentrations of dissolved nitrate in several ground-water sampling locations increased after terrace installation. Dissolved nitrate concentrations in ground water decreased significantly after nutrient-management implementation. Findings indicate that agricultural-management practices to improve water quality are most effective if their overall design effects on surface- and ground-water systems are considered in their design.

Pennsylvania↗

USGS2021

Wetlands

During the last decades, soil organic carbon (SOC) attracted the attention of a much wider array of specialists beyond agriculture and soil science, as it was proven to be one of the most crucial components of the earth’s climate system, which has a great potential to be managed by humans. Soils as a carbon pool are one of the key factors in several Sustainable Development Goals, in particular Goal 15, “Protect, restore and promote sustainable use of terrestrial ecosystems, sustainably manage forests, combat desertification and halt and reverse land degradation and halt biodiversity loss” with the SOC stock being explicitly cited in Indicator 15.3.1. This technical manual is the first attempt to gather, in a standardized format, the existing data on the impacts of the main soil management practices on SOC content in a wide array of environments, including the advantages, drawbacks, and constraints. This manual presents different sustainable soil management (SSM) practices at different scales and in different contexts, supported by case studies that have been shown with quantitative data to have a positive effect on SOC stocks and successful experiences of SOC sequestration in practical field applications Volume 2 includes a description of hot spots of SOC stocks. This manual defines hot spots of SOC as areas that represent a proportionally little of the global land surface but on which SOC storage is highly effective; bright spots as large land areas with low SOC stocks per km2 that represent a potential for further carbon sequestration.

Report↗

USGS2023

Characterizing historic streamflow to support drought planning in the upper Missouri River basin

This project combined tree-ring based paleo and modern climate and hydrologic research aimed at understanding the primary influences on drought risk and water reliability in basins critical for western U.S. water resources. New paleohydrologic datasets and analyses were developed and applied to contextualize future streamflow projections and address specific water management questions. These questions centered around optimizing future water management protocols for numerous objectives ranging from improving agricultural water allocation during drought while maintaining instream flows for aquatic ecosystem health, to the testing of operations across large river systems with complex infrastructure critical for downstream flood control, navigation, and hydropower generation. USGS scientists worked closely with the Bureau of Reclamation to estimate both past and future drought risk at key management locations throughout the Missouri basin, the Milk and St. Mary River system, and across the major managed river systems in the western United States. These efforts provided a roadmap for future water management strategies under changing climate and water supply conditions, which are detailed in Reclamation’s newly completed Missouri Headwaters Basin Study, the 2021 SECURE Water Act Report, and the forthcoming update of the St. Mary and Milk Rivers Basin Study. Among the major scientific findings to emerge was a new understanding of the long-term (1200-year) history of drought variability for the Missouri River, which highlighted the unusual severity of the early 2000s drought across the Rocky Mountain headwaters and adjacent high plains. By combining the extended drought record with extensive modern and paleoclimate records, we document how warming exacerbates severities of naturally occurring droughts, with recent decades defined by “hot” droughts and the 2000s (2001-2010) drought ranking as the most severe event in 1200 years. Increasingly severe drought events such as this strain already over-allocated water resources that multiple sectors of society depend heavily upon.

upper Missouri River basin↗

USGS2023

Stream corridor sources of suspended sediment and sediment-bound phosphorus from an urban tributary to the Great Lakes

Potential sources of suspended sediment and sediment-bound phosphorus (sedP) were studied in the Kinnickinnic River (51 square kilometers), a heavily urbanized tributary to Lake Michigan (90% urban land use) in Milwaukee, Wisconsin. The river is 60% concrete lined channels, with few unlined reaches. From September 2019 through August 2020, an integrated study of sediment budget and sediment fingerprinting was conducted to quantify upland and stream corridor sources of suspended sediment and sedP using Sediment Source Assessment Tool (SedSAT) methods with a suite of trace elements. Passive suspended sediment samplers were installed at three sites. Soft, fine-grained streambed sediment was collected at 10 rapid geomorphic assessment (RGA) sites. An inventory of bank erosion and soft-sediment deposition was done at each of the 18 RGA sites, which were selected to represent a range of stream sizes and geomorphic conditions. Sources of suspended sediment varied with streamflow; the primary source was from roadways in residential areas followed by eroding streambanks. Industrial/commercial areas contributed 1% of the suspended sediment at the streamgage during the study period, whereas green space contributed 18% of the suspended sediment at a mid-basin monitoring location downstream of an unlined reach. The dominant sources of streambed sediment, like suspended sediment, throughout the basin were eroding banks and residential areas, with green space and industrial/commercial area signatures present locally. In contrast with previous studies in agricultural and mixed-use basins, the urban Kinnickinnic River had limited storage of soft sediment, due to the hydrologically flashy system and concrete lined channels. However, eroding streambank sources contribute 50% of the streambed sediment, but only 9% of suspended sediment within this tributary to the Great Lakes.

Wisconsin↗

USGS2020

Could a freshwater fish be at the root of dystrophic crises in a coastal lagoon?

Eutrophication has a profound impact on ecosystems worldwide. Grass carp Ctenopharyngodon idella , an herbivorous fish, has been introduced to control aquatic plant overgrowth caused by eutrophication, but could have other, potentially detrimental, effects. We used the Po di Volano basin (south of the Po River delta, northern Italy) as a test case to explore whether grass carp effects on canal aquatic vegetation could be at the root of historical changes in N loads exported from the basin to the Goro Lagoon. We modeled the aquatic vegetation production and standing crop, its denitrification potential, and its consumption by introduced grass carp. We then examined whether changes in historical nitrogen loads matched the modeled losses of the drainage network denitrification function or other changes in agricultural practices. Our results indicate that introduced grass carp could completely remove submerged vegetation in the Po di Volano canal network, which could – in turn – lead to substantial loss of the denitrification function of the system, causing in an increase in downstream nitrogen loads. A corresponding increase, matching both timing and magnitude, was detected in historical nitrogen loads to the Goro Lagoon, which were significantly different before and after the time of modeled collapse of the denitrification function. This increase was not clearly linked to watershed use or agricultural practices, which implies that the loss of the denitrification function through grass carp overgrazing could be a likely explanation of the increase in downstream nitrogen loads. Perhaps for the first time, we provide evidence that a freshwater fish introduction could have caused long-lasting changes in nutrient dynamics that are exported downstream to areas where the fish is not present.

Po River basin↗

USGS2009

Monitoring for Pesticides in Groundwater and Surface Water in Nevada, 2008

Commercial pesticide applicators, farmers, and homeowners apply about 1 billion pounds of pesticides annually to agricultural land, non-crop land, and urban areas throughout the United States (Gilliom and others, 2006, p. 1). The U.S. Environmental Protection Agency (USEPA) defines a pesticide as any substance used to kill or control insects, weeds, plant diseases, and other pest organisms. Although there are important benefits from the proper use of pesticides, like crop protection and prevention of human disease outbreaks, there are also risks. One risk is the contamination of groundwater and surface-water resources. Data collected during 1992-2001 from 51 major hydrologic systems across the United States indicate that one or more pesticide or pesticide breakdown product was detected in more than 50 percent of 5,057 shallow (less than 20 feet below land surface) wells and in all of the 186 stream sites that were sampled in agricultural and urban areas (Gilliom and others, 2006, p. 2-4). Pesticides can contaminate surface water and groundwater from both point sources and non-point sources. Point sources are from specific locations such as spill sites, disposal sites, pesticide drift during application, and application of pesticides to control aquatic pests. Non-point sources represent the dominant source of surface water and groundwater contamination and may include agricultural and urban runoff, erosion, leaching from application sites, and precipitation that has become contaminated by upwind applications. Pesticides typically enter surface water when rainfall or irrigation exceeds the infiltration capacity of soil and resulting runoff then transports pesticides to streams, rivers, and other surface-water bodies. Contamination of groundwater may result directly from spills near poorly sealed well heads and from pesticide applications through improperly designed or malfunctioning irrigation systems that also are used to apply pesticides (chemigation; Carpenter and Johnson, 1997). Groundwater contamination also may come indirectly by the percolation of agricultural and urban irrigation water through soil layers and into groundwater and from pesticide residue in surface water, such as drainage ditches, streams, and municipal wastewater. To protect surface water and groundwater from pesticide contamination, the USEPA requires that all states establish a pesticide management plan. The Nevada Department of Agriculture (NDOA), with assistance from the USEPA, developed a management program of education (Hefner and Donaldson, 2006), regulation (Johnson and others, 2006), and monitoring (Pennington and others, 2001) to protect Nevada's water resources from pesticide contaminants. Sampling sites are located in areas where urban or agricultural pesticide use may affect groundwater, water bodies, endangered species, and other aquatic life. Information gathered from these sites is used by NDOA to help make regulatory decisions that will protect human and environmental health by reducing and eliminating the occurrence of pesticide contamination. This fact sheet describes current (2008) pesticide monitoring of groundwater and streams by the NDOA in Nevada and supersedes Pennington and others (2001).

Fact Sheet↗

USGS1999

Sources and chronology of nitrate contamination in spring waters, Suwannee River basin, Florida

A multi-tracer approach, which consisted of analyzing water samples for n aturally occurring chemical and isotopic indicators, was used to better understand sources and chronology of nitrate contamination in spring wate rs discharging to the Suwannee and Santa Fe Rivers in northern Florida. Dur ing 1997 and 1998, as part of a cooperative study between the Suwannee River Water Management District and the U.S. Geological Survey, water samples were collected and analyzed from 24 springs and two wells for major ions, nutrients, dissolved organic carbon, and selected environmental isotopes [18O/16O, D/H, 13C/12C, 15N/14N]. To better understand when nitrate entered the ground-water system, water samples were analyzed for chlorofluorocarbons (CFCs; CCl3F, CCl2F2, and C2Cl3F3) and tritium (3H); in this way, the apparent ages and residence times of spring waters and water from shallow zones in the Upper Floridan aquifer were determined. In addition to information obtained from the use of isotopic and other chemical tracers, information on changes in land-use activities in the basin during 1954-97 were used to estimate nitrogen inputs from nonpoint sources for five counties in the basin. Changes in nitrate concentrations in spring waters with time were compared with estimated nitrogen inputs for Lafayette and Suwannee Counties. Agricultural activities [cropland farming, animal farming operations (beef and dairy cows, poultry, and swine)] along with atmospheric deposition have contributed large quantities of nitrogen to ground water in the Suwannee River Basin in northern Florida. Changes in agricultural land use during the past 40 years in Alachua, Columbia, Gilchrist, Lafayette, and Suwannee Counties have contributed variable amounts of nitrogen to the ground-water system. During 1955-97, total estimated nitrogen from all nonpoint sources (fertilizers, animal wastes, atmospheric deposition, and septic tanks) increased continuously in Gilchrist and Lafayette Counties. In Suwannee, Alachua, and Columbia Counties, estimated nitrogen inputs from all nonpoint sources peaked in the late 1970's corresponding to the peak use in fertilizer during this time. Fertilizer use in Columbia, Gilchrist, Lafayette, and Suwannee Counties increased substantially during 1993-97. The heavy use of fertilizers in the basin is corroborated by nitrogen isotope data. Values of d15N of nitrate (d15N-NO3) in spring waters range from 2.7 per mil (SUW718971) to 10.6 per mil (Poe Spring) with a median of 5.4 per mil. The range of values indicates that nitrate in the sampled spring waters most likely originates from a mixture of inorganic (fertilizers) and organic (animal wastes) sources; however, higher d15N values for Poe and Lafayette Blue Springs indicate that an organic source of nitrogen probably is contributing nitrate to these spring waters. Water samples from two wells sampled in Lafayette County have high d15N-NO3 values of 11.0 and 12.1 per mil, indicating the predominance of an organic source of nitrate. These two wells are located near dairy and poultry farms, where leachate from animal wastes may contribute nitrate to ground water. Dissolved-gas data (nitrogen, argon, and oxygen) indicate that denitrification has not removed large amounts of nitrate from the ground-water system. Thus, variations in d15N-NO3 values of spring waters can be attributed to variations in d15N-NO3 values of ground-water recharge, and can be used to obtain information about source(s) of nitrate. Extending the use of age-dating techniques (CFCs and 3H) to spring waters in complex karst systems required the use of several different approaches for estimating age and residence time of ground water discharging to springs. These approaches included the use of a simple reservoir model, a piston-flow model, an exponential model, and a binary-mixing model. When age data (CFC-11, CFC-113, and 3H) are combined for all springs, models that incorporate exponential mixtures seem to provide reliable estimates of average residence times of ground water discharging to springs. Whereas, data for some individual springs fit a binary-mixing model with more than 50 percent young water (recharged within the past 5 years), data from other individual springs fit a piston-flow model with a water age of about 25 years. The young ages of several spring waters (such as SUW718971, SUW725971, and Ginnie Spring) indicate the high vulnerability of the springs to contamination. For most springs, CFCs suggest that a large fraction of the water is more than 20 years old. Springs with lower flows tend to have young ages (shallow ground-water flow systems), whereas springs with higher flows tend to have older ages (deep ground-water flow systems). The chemical composition of spring waters can be used as a qualitative indicator of age and ground-water residence time. Nitrate-nitrogen concentrations and dissolved oxygen in spring waters are inversely related to the apparent ages of spring waters and ground-water residence time in the basin. Silica concentrations increase as the age of spring waters increase. Long-term trends in nitrate concentrations in selected spring waters were compared with estimated inputs of nitrogen from various sources in Suwannee and Lafayette Counties. In both counties, trends in nitrate concentrations in spring waters closely followed the estimated contribution of nitrogen from fertilizers. Decreasing nitrate concentrations in spring waters from Suwannee County followed the decrease in estimated fertilizer use from the mid-1970's to the early 1990's. Increasing nitrate concentrations in sprin g waters from Lafayette County followed the steady increase in fertilizer use from the early 1960's to the mid-1990's The relation between the concentration of nitrate in ground water and the amount of nitrogen that is added to a ground-water contributing area for a spring is controlled by complex interactions among hydrogeologic, land-use, and climatic factors, as well as several other land-management factors. Spring waters represent mixtures of converging flow paths that contain ground water with a range of ages. Even if nitrogen inputs were reduced substantially, it may take decades for nitrate concentrations in the ground-water system to return to near background levels.

Florida↗