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1.
    
ABSTRACT: Agricultural and urban activities in the West Wellfield Interim Protection Area (WWIPA), located in West Dade County in South Florida, have the potential to impact both the environmentally sensitive Everglades and the Biscayne Aquifer. The Hydrological Simulation Program-FORTRAN (HSPF) is used to simulate surface runoff, ground water recharge, and transport of sediments, nutrients, and pesticides in the WWIPA, as a basis to quantify impacts and evaluate alternatives. Presented are four model test runs that consider current conditions, the effect of future urbanization of the agricultural land, as well as two preventive actions to minimize pollution levels. Preventive actions include application of minimum required rates of fertilizers and replacement of fertilizers by sewage sludge. Model results show that under current practices, sediments, nutrients, and pesticides are present in surface runoff and nutrients enter the ground water, and that both urbanization and preventive actions result in pollutant reductions.  相似文献   

2.
    
ABSTRACT: An extensive base of water quality information emphasizing the effects of land use and hydrology was obtained in the karstified Fountain Creek watershed of southwestern Illinois to help resolve local water quality issues. Agrichemicals dominate the loads of most water quality constituents in the streams and shallow karstic ground water. Only calcium (Ca), magnesium (Mg), Aluminum (A1), and sulfate (SO4) ions are predominantly derived from bedrock or soils, while agrichemicals contribute most of the sodium (Na), potassium (K), chlorine (Cl), nitrate (NO3), fluorine (F), phosphorus (P), and atrazine. Concentrations of individual ions correlate with discharge variations in karst springs and surface streams; highly soluble ions supplied by diffuse ground water are diluted by high flows, while less soluble ions increase with flow as they are mobilized from fields to karst conduits under storm conditions. Treated wastewater containing detergent residues dominates the boron load of streams and provides important subordinate loads of several other constituents, including atrazine derived from the Mississippi River via the public water supply. Average surface water concentrations at the watershed outlet closely approximate a 92:8 mixture of karst ground water and treated wastewater, demonstrating the dominance of ground water contributions to streams. Therefore the karst aquifer and watershed streams form a single water quality system that is also affected by wastewater effluent.  相似文献   

3.
ABSTRACT: Areas of low topographic relief have low water-table gradients and make the direction of movement of contaminants from land fills in the ground water difficult to predict from regional gradients alone. The landfill, nearby free-flowing ditches or canals, variations in hydraulic conductivity, and the influence of nearby pumping wells can all affect the direction of flow. In low-gradient areas the concepts of “upgradient” and “downgradient” are less useful in planning the location of monitoring wells than in areas of higher relief. Low-relief areas also may be affected by the discharge of mineralized water from deeper aquifers, naturally or through irrigation, which can mask geochemical surveys intended to detect landfill leachate. Examples of effects of low topographic relief are noted in southeast Florida where water-table gradients are 7×10?-4 to 5×10?-4 feet per foot. Water-table mounding beneath the landfill and the drainage effects of nearby ditches and well have created multiple leachate plumes in Stuart where one plume migrated in a direction opposite to the apparent regional gradient. In Coral Springs analysis suggests a bifurcating plume migrating along two narrow zones. In Fort Pierce it was difficult to detect leachate because of mineralized irrigation water and fertilizer runoff from an adjacent citrus grove.  相似文献   

4.
    
ABSTRACT: Twenty‐three stream sites representing a range of forested, agricultural, and urban land uses were sampled in the South Platte River Basin of Colorado from July through September 2002 to characterize water quality during drought conditions. With a few exceptions, dissolved ammonia, Kjeldahl nitrogen, total phosphorus, and dissolved orthophosphate concentrations were similar to seasonal historical levels in all land use areas during the drought. At some agricultural sites, decreased dilution of irrigation return flow may have contributed to higher concentrations of some nutrient species, increased primary productivity, and higher dissolved oxygen concentrations. At some urban sites, decreased dilution of base flow and wastewater treatment plant effluent may have contributed to higher dissolved nitrite‐plus‐nitrate concentrations, increased primary productivity, and higher dissolved oxygen concentrations. Total pesticide concentrations in urban and agricultural areas were not consistently higher or lower during the drought. At most forested sites, decreased dilution of ground water‐derived calcium bicarbonate type base flow likely led to elevated pH and specific‐conductance values. Water temperatures at many of the forested sites also were higher, contributing to lower dissolved oxygen concentrations during the drought.  相似文献   

5.
    
Watershed planning groups and action agencies seek to understand how lake water quality responds to changes in watershed management. This study developed and demonstrated the applicability of an integrated modeling approach for providing this information. An integrated model linking watershed conditions to water-quality of the receiving lake incorporated the following components: (1) an event-based AGNPS model to estimate watershed pollutant losses; (2) annualization of AGNPS results to produce annual lake pollutant loadings; (3) a base flow separation package, SAM, to estimate base flow; (4) estimates of nutrients in base flow and point sources; and (5) linkage of watershed loadings directly to EUTROMOD lake water quality algorithms. Results are presented for Melvern Lake, a 28-km2 multipurpose reservoir with a 900-km2 agricultural watershed in east central Kansas. Reasonable estimates of current lake quality were attained using an average phosphorus availability factor of 31 percent to calibrate model results to measured in-lake phosphorus. Comparison of a range of possible scenarios, including all cropland changed to no-till (best case) and all CRP and good-condition grasslands changed to cropland (worst case), indicated only a (4 percent change for in-lake phosphorus and a (2 percent change for chlorophyll a. These results indicated that this watershed is not sensitive to projected changes in land use and management.  相似文献   

6.
    
ABSTRACT: . Under a watershed based approach being examined by the Quebec Ministry of Agriculture to accelerate the adoption of conservation practices, a study on the impacts of agricultural practices on the St. Esprit watershed was initiated in the fall of 1993. The water quality of this 26 km2 intensive agricultural watershed was studied over an 18 month period. Water samples taken at the outlet of the watershed were analyzed for nitrate, phosphate, suspended sediment, and atrazine. Water quality data were analyzed to establish seasonal trends in pollutant concentration and load in the watercourse. Spring snowmelt was identified as a significant period of pollutant material export. All pollutant materials displayed seasonal variability in the export process. Peak pollutant concentrations were associated with high flow events. Mean observed pollutant concentrations did not exceed drinking water quality standards.  相似文献   

7.
    
ABSTRACT: Since 1991, the U.S. Geological Survey has been conducting the National Water Quality Assessment (NAWQA) Program to determine the quality of the Nation's water resources. In an effort to obtain a better understanding of why pesticides are found in shallow ground water on a national scale, a set of factors likely to affect the fate and transport of two herbicides in the subsurface were examined. Atrazine and metolachlor were selected for this discussion because they were among the most frequently detected pesticides in ground water during the first phase of the NAWQA Program (1993 to 1995), and each was the most frequently detected compound in its chemical class (triazines and acetanilides, respectively). The factors that most strongly correlated with the frequencies of atrazine detection in shallow ground‐water networks were those that provided either: (1) an indication of the potential susceptibility of ground water to atrazine contamination, or (2) an indication of relative ground‐water age. The factors most closely related to the frequencies of metolachlor detection in ground water, however, were those that estimated or indicated the intensity of the agricultural use of metolachlor. This difference is probably the result of detailed use estimates for these compounds being available only for agricultural settings. While atrazine use is relatively extensive in nonagricultural settings, in addition to its widespread agricultural use, metolachlor is used almost exclusively for agricultural purposes. As a result, estimates of agricultural applications provide a less reliable indication of total chemical use for atrazine than for metolachlor. A multivariate analysis demonstrated that the factors of interest explained about 50 percent of the variance in atrazine and metolachlor detection frequencies among the NAWQA land‐use studies examined. The inclusion of other factors related to pesticide fate and transport in ground water, or improvements in the quality and accuracy of the data employed for the factors examined, may help explain more of the remaining variance in the frequencies of atrazine and metolachlor detection.  相似文献   

8.
    
ABSTRACT: Phosphorus (P) in runoff from long term animal waste application fields can contribute to accelerated eutrophication of surface waters. Manure when applied at nitrogen (N) agronomic rates generally increases soil P concentrations, which can increase runoff of soluble P. Along the North Bosque River in central Texas, dairy waste application fields are identified as the most controllable nonpoint source of soluble P in a total maximum daily load. To evaluate P reduction practices for fields high in soil extractable P, edge‐of‐field runoff was measured from paired plots of Coastal bermudagrass (Cynodon dactylon) and sorghum (Sorghum bicolor)/ winter wheat (Triticum spp.). Plots (about 0.4 ha) received manure at P agronomic rates following Texas permit guidelines and commercial N during the pretreatment period. During the post‐treatment period, control plots continued to receive manure at P agronomic rates and commercial N. Treatment plots received only commercial N during the post‐treatment period. Use of only commercial N on soils with high extractable P levels significantly decreased P loadings in edge‐of‐field runoff by at least 40 percent, but runoff concentrations sometimes increased. No notable changes in extractable soil P concentrations were observed after five years of monitoring due to drought conditions limiting forage uptake and removal.  相似文献   

9.
    
ABSTRACT: Pesticides in stormwater runoff, within the Sacramento River Basin, California, were assessed during a storm that occurred in January 1994. Two organophosphate insecticides (diazinon and methidathion), two carbamate pesticides (molinate and carbofuran), and one triazine herbicide (simazine) were detected. Organophosphate pesticide concentrations increased with the rising stage of the hydrographs; peak concentrations were measured near peak discharge. Diazinon oxon, a toxic degradation product of diazinon, made up approximately 1 to 3 percent of the diazinon load. The Feather River was the principal source of organophosphate pesticides to the Sacramento River during this storm. The concentrations of molinate and carbofuran, pesticides applied to rice fields during May and June, were relatively constant during and after the storm. Their presence in surface water was attributed to the flooding and subsequent drainage, as a management practice to degrade rice stubble prior to the next planting. A photo-degradation product of molinate, 4-keto molinate, was in all samples where molinate was detected and made up approximately 50 percent of the total molinate load. Simazine, a herbicide used in orchards and to control weeds along the roadways, was detected in the storm runoff, but it was not possible to differentiate the two sources of that pesticide to the Sacramento River.  相似文献   

10.
    
ABSTRACT: This paper illustrates a method of using a hydrologic/water quality model to analyze alternative management practices and recommend best management practices (BMPs) to reduce nitrate-nitrogen (NO3--N) leaching losses. The study area for this research is Tipton, an agriculturally intensive area in southwest Oklahoma. We used Erosion Productivity Impact Calculator (EPIC), a field-scale hydrologic/water quality model, to analyze alternative agricultural management practices. The model was first validated using observed data from a cotton demonstration experiment conducted in the Tipton area. Following that, EPIC was used to simulate fertilizer response curves for cotton and wheat crops under irrigated and dryland conditions. From the fertilizer response functions (N-uptake and N-leaching), we established an optimum fertilizer application rate for each crop. Individual crop performances were then simulated at optimum fertilizer application rates and crop rotations for the Tipton area, which were selected based on three criteria: (a) minimum amount of NO3--N leached, (b) minimum concentration of NO3--N leached, and (c) maximum utilization of NO3--M. Further we illustrate that by considering residual N from alfalfa as a credit to the following crop and crediting NO3--N present in the irrigation water, it is possible to reduce further NO3--N loss without affecting crop yield.  相似文献   

11.
    
ABSTRACT: A study of stream base flow and NO3‐N concentration was conducted simultaneously in 51 subwatersheds within the 116‐square‐kilometer watershed of East Mahantango Creek near Klingerstown, Pennsylvania. The study was designed to test whether measurable results of processes and observations within the smaller watersheds were similar to or transferable to a larger scale. Ancillary data on land use were available for the small and large watersheds. Although the source of land‐use data was different for the small and large watersheds, comparisons showed that the differences in the two land‐use data sources were minimal. A land use‐based water‐quality model developed for the small‐scale 7.3‐square‐kilometer watershed for a previous study accurately predicted NO3‐N concentrations from sampling in the same watershed. The water‐quality model was modified and, using the imagery‐based land use, was found to accurately predict NO3‐N concentrations in the subwatersheds of the large‐scale 116‐square‐kilometer watershed as well. Because the model accurately predicts NO3‐N concentrations at small and large scales, it is likely that in second‐order streams and higher, discharge of water and NO3‐N is dominated by flow from smaller first‐order streams, and the contribution of ground‐water discharge to higher order streams is minimal at the large scale.  相似文献   

12.
ABSTRACT: A model for urban stormwater quality was developed in this study. The basis for the model is the process by which pollutants build up on the watershed surface. For the wet climate of the study site, it was assumed that there exists an interval of time over which the pollutant buildup equals the pollutant washoff (no accumulation of pollutant). The buildup model was represented by a linear function of the antecedent dry time. The buildup function was then linked with a pollutant washoff model represented by a power function of the storm runoff volume. Various time intervals for no net accumulation were tested to calibrate the model. The model was calibrated to observed data for two small urban basins in Baton Rouge, Louisiana, and model results were used to analyze the behavior of phosphorus concentrations in storm runoff from these basins over a long period of time.  相似文献   

13.
    
ABSTRACT: The impact on water quality by agricultural activity in karst terrain is an important consideration for resource management within the Appalachian Region. Karst areas comprise about 18 percent of the Region's land area. An estimated one-third of the Region's farms, cattle, and agricultural market value are on karst terrain. Nitrate concentrations were measured in cave streams draining two primary land management areas. The first area was pasture serving a beef cow-calf operation. The second area was a dairy. Nitrate-N concentrations were highest in cave streams draining the dairy and a cave stream draining an area of pasture where cattle congregate for shade and water. The dairy contributed about 60 to 70 percent of the nitrogen load increase in the study section of the cave system. It was concluded that agriculture was significantly affecting nitrate concentrations in the karst aquifer. Best management practices may be one way to protect the ground water resource.  相似文献   

14.
ABSTRACT: The impact on water quality by agricultural activity in karst terrain is an important consideration for resource management within the Appalachian Region. Karst areas comprise about 18 percent of the Region's land area. An estimated one-third of the Region's farms, cattle, and agricultural market value are located on karst terrain. Nitrate concentrations were measured in several karst springs in Southeastern West Virginia in order to determine the impact of animal agriculture on nitrate pollution of the karst ground water system. Karst basins with 79, 51, 16, and 0 percent agriculture had mean nitrate concentrations of 15.8, 12.2, 2.7, and 0.4 mg/l, respectively. A strong linear relationship between nitrate concentration and percent agricultural land was shown. Median nitrate concentration increased about 0.19 mg l-1 per percent increase in agricultural land. Weather patterns were also found to significantly affect the median nitrate concentrations and the temporal variability of those concentrations. Lower nitrate concentrations and lower temporal variability were observed during a severe drought period. It was concluded that agriculture was significantly affecting nitrate concentrations in the karst aquifer. Best management practices may be one way to protect the ground water resource.  相似文献   

15.
    
The “Measured Annual Nutrient loads from AGricultural Environments” (MANAGE) database was published in 2006 to expand an early 1980s compilation of nutrient export (load) data from cultivated and pasture/range land at the field or farm scale. Then in 2008, MANAGE was updated with 15 additional studies, and nitrogen (N) and phosphorus (P) concentrations in runoff were added. Since then, MANAGE has undergone significant expansion adding N and P water quality along with relevant management and site characteristic data from: (1) 30 runoff studies from forested land uses, (2) 91 drainage water quality studies from drained land, and (3) 12 additional runoff studies from cultivated and pasture/range land uses. In this expansion, an application timing category was added to the existing fertilizer data categories (rate, placement, formulation) to facilitate analysis of 4R Nutrient Stewardship, which emphasizes right fertilizer source, rate, time, and place. In addition, crop yield and N and P uptake data were added, although this information was only available for 21 and 7% of studies, respectively. Inclusion of these additional data from cultivated, pasture/range, and forest land uses as well as artificially drained agricultural land should facilitate expanded spatial analyses and improved understanding of regional differences, management practice effectiveness, and impacts of land use conversions and management techniques. The current version is available at www.ars.usda.gov/spa/manage-nutrient .  相似文献   

16.
    
ABSTRACT: A synoptic sampling of five surface-water sites in central Nebraska was conducted by the U.S. Geological Survey as part of its National Water-Quality Assessment Program during storm runoff in May 1992 to relate transport, yields, and concentrations of atrazine to environmental setting. Atrazine was the most extensively applied pesticide in the study unit. Atrazine transport was related to the size of contributing drainage area, quantity of atrazine applied, amount of precipitation, and volume of stream-flow. Estimated yields and mean concentrations of atrazine were related to the percentage of cropland in a drainage area. The largest estimated yields and mean concentrations of atrazine in surface water were associated from drainage areas with the highest percentage of cropland, and the smallest was associated with the smallest amount of cropland. Atrazine concentrations increased as streamflow increased but decreased at or near the time of peak streamflows, perhaps due to dilution. Atrazine concentrations then increased and remained elevated far into the stream recession. Atrazine is a regulated contaminant in finished public-water supplies. Large concentrations of atrazine could affect the management of public-water supplies because atrazine remains in solution in contrast to many other pesticides that are more easily removed.  相似文献   

17.
ABSTRACT: Storm water detention basins have historically been employed for quantity (i.e., flooding) control only. However, recently it has been suggested that these basins may also provide a practical means of storm water quality control. This paper presents the formulation of a mathematical modeling approach which may be used by professionals to simultaneously design detention basins for the dual purpose of storm water quantity and quality control. Model simulations demonstrate that for a given basin, pollutant removal increases as storm frequency increases. The importance of particle size distribution and settling velocity for net pollutant removal is illustrated, The design procedure is demonstrated, and pollutant loading diagrams for estimating pollutant removal as a function of storm size are developed.  相似文献   

18.
    
ABSTRACT: Seventy to eighty percent of the water flowing in rivers in the United States originates as precipitation in forests. This project developed a synoptic picture of the patterns in water chemistry for over 300 streams in small, forested watersheds across the United States. Nitrate (NO3?) concentrations averaged 0.31 mg N/L, with some streams averaging ten times this level. Nitrate concentrations tended to be higher in the northeastern United States in watersheds dominated by hardwood forests (especially hardwoods other than oaks) and in recently harvested watersheds. Concentrations of dissolved organic N (mean 0.32 mg N/L) were similar to those of NO3～, whereas ammonium (NH4+) concentrations were much lower (mean 0.05 mg N/L). Nitrate dominated the N loads of streams draining hardwood forests, whereas dissolved organic N dominated the streams in coniferous forests. Concentrations of inorganic phosphate were typically much lower (mean 12 mg P/L) than dissolved organic phosphate (mean 84 mg P/L). The frequencies of chemical concentrations in streams in small, forested watersheds showed more streams with higher NO3? concentrations than the streams used in national monitoring programs of larger, mostly forested watersheds. At a local scale, no trend in nitrate concentration with stream order or basin size was consistent across studies.  相似文献   

19.
ABSTRACT: The objective of this study was to evaluate the effectiveness of various land-use practices upon the production of nonpoint source pollutants from small agricultural watersheds in Northern Virginia. Pollutant production at each watershed was determined by individual monitoring stations. Data analysis consisted of a determination of the site specific pollutant yield for similar watersheds subjected to differing crop management approaches. These collected data were then compared to those generated by a parametric, event model developed for this investigation. This synthetic data base was used to eliminate or reduce errors resulting from monitoring site differences and to extend the collected data for additional comparisons.  相似文献   

20.
    
ABSTRACT: CREAMS was applied to a field-sized watershed planted to cotton in the Limestone Valley region of northern Alabama. The field was cultivated for three years with conventional tillage (CvT) followed by three years of conservation tillage (CsT). CREAMS is composed of three components: hydrology, erosion, and chemistry. Surface runoff and losses of sediment, N and P were simulated and results were compared with the observed data from the watershed. Curve numbers recommended in the CREAMS user's guide were not adequate for the watershed conditions. The hydrology submodel improved runoff simulation from CvT and CsT when field-data based curve numbers were used. The erosion submodel demonstrated that CsT reduced sediment loss more than CvT, even though CsT had higher runoff than CvT. The nutrient submodel based on the simulated runoff and sediment underpredicted N loss for both CvT and CsT. This submodel, however, accurately predicted P loss for CvT, but underpredicted for CsT (50 percent lower than the observed). The results of CREAMS simulation generally matched the observed order of magnitude for higher runoff, lower sediment, and higher N and P losses from CsT than from CvT.  相似文献   

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