Showing papers on "Nonpoint source pollution published in 2001"

Validation of the SWAT Model on a Large River Basin With Point and Nonpoint Sources

Abstract: The State of Texas has initiated the development of a Total Maximum Daily Load program in the Bosque River Watershed, where point and nonpoint sources of pollution are a concern. Soil Water Assessment Tool (SWAT) was validated for flow, sediment, and nutrients in the watershed to evaluate alternative management scenarios and estimate their effects in controlling pollution. This paper discusses the calibration and validation at two locations, Hico and Valley Mills, along the North Bosque River. Calibration for flow was performed from 1960 through 1998. Sediment and nutrient calibration was done from 1993 through 1997 at Hico and from 1996 through 1997 at Valley Mills. Model validation was performed for 1998. Time series plots and statistical measures were used to verify model predictions. Predicted values generally matched well with the observed values during calibration and validation (R2≥ 0.6 and Nash-Suttcliffe Efficiency ≥ 0.5, in most instances) except for some underprediction of nitrogen during calibration at both locations and sediment and organic nutrients during validation at Valley Mills. This study showed that SWAT was able to predict flow, sediment, and nutrients successfully and can be used to study the effects of alternative management scenarios.

Chesapeake Bay Eutrophication: Scientific Understanding, Ecosystem Restoration, and Challenges for Agriculture

Abstract: Chesapeake Bay has been the subject of intensive research on cultural eutrophication and extensive efforts to reduce nutrient inputs. In 1987 a commitment was made to reduce controllable sources of nitrogen (N) and phosphorous (P) by 40% by the year 2000, although the causes and effects of eutrophication were incompletely known. Subsequent research, modeling, and monitoring have shown that: (i) the estuarine ecosystem had been substantially altered by increased loadings of N and P of approximately 7- and 18-fold, respectively; (ii) hypoxia substantially increased since the 1950s; (iii) eutrophication was the major cause of reductions in submerged vegetation; and (iv) reducing nutrient sources by 40% would improve water quality, but less than originally thought. Strong public support and political commitment have allowed the Chesapeake Bay Program to reduce nutrient inputs, particularly from point sources, by 58% for P and 28% for N. However, reductions of nonpoint sources of P and N were projected by models to reach only 19% and 15%, respectively, of controllable loadings. The lack of reductions in nutrient concentrations in some streams and tidal waters and field research suggest that soil conservation-based management strategies are less effective than assumed. In 1997, isolated outbreaks of the toxic dinoflagellate Pfiesteria piscicida brought attention to the land application of poultry manure as a contributing factor to elevated soil P and ground water N concentrations. In addition to developing more effective agricultural practices, emerging issues include linking eutrophication and living resources, reducing atmospheric sources of N, enhancing nutrient sinks, controlling sprawling suburban development, and predicting and preventing harmful algal blooms.

Toward Quantifying Water Pollution Abatement in Response to Installing Buffers on Crop Land

Abstract: The scientific research literature is reviewed (i) for evidence of how much reduction in nonpoint source pollution can be achieved by installing buffers on crop land, (ii) to summarize important factors that can affect this response, and (iii) to identify remaining major information gaps that limit our ability to make probable estimates. This review is intended to clarify the current scientific foundation of the USDA and similar buffer programs designed in part for water pollution abatement and to highlight important research needs. At this time, research reports are lacking that quantify a change in pollutant amounts (concentration and/or load) in streams or lakes in response to converting portions of cropped land to buffers. Most evidence that such a change should occur is indirect, coming from site-scale studies of individual functions of buffers that act to retain pollutants from runoff: (1) reduce surface runoff from fields, (2) filter surface runoff from fields, (3) filter groundwater runoff from fields, (4) reduce bank erosion, and (5) filter stream water. The term filter is used here to encompass the range of specific processes that act to reduce pollutant amounts in runoff flow. A consensus of experimental research on functions of buffers clearly shows that they can substantially limit sediment runoff from fields, retain sediment and sediment-bound pollutants from surface runoff, and remove nitrate N from groundwater runoff. Less certain is the magnitude of these functions compared to the cultivated crop condition that buffers would replace within the context of buffer installation programs. Other evidence suggests that buffer installation can substantially reduce bank erosion sources of sediment under certain circumstances. Studies have yet to address the degree to which buffer installation can enhance channel processes that remove pollutants from stream flow. Mathematical models offer an alternative way to develop estimates for water quality changes in response to buffer installation. Numerous site conditions and buffer design factors have been identified that can determine the magnitude of each buffer function. Accurate models must be able to account for and integrate these functions and factors over whole watersheds. At this time, only pollutant runoff and surface filtration functions have been modeled to this extent. Capability is increasing as research data is produced, models become more comprehensive, and new techniques provide means to describe variable conditions across watersheds. A great deal of professional judgment is still required to extrapolate current knowledge of buffer functions into broadly accurate estimates of water pollution abatement in response to buffer installation on crop land. Much important research remains to be done to improve this capability. The greatest need is to produce direct quantitative evidence of this response. Such data would confirm the hypothesis and enable direct testing of watershed-scale prediction models as they become available. Further study of individual pollution control functions is also needed, particularly to generate comparative evidence for how much they can be manipulated through buffer installation and management.

Application of a watershed model to evaluate management effects on point and nonpoint source pollution

Abstract: A Total Maximum Daily Load (TMDL) program has been initiated in the North Bosque River Watershed in Texas, USA, where point and nonpoint sources of pollution are of a concern. The Soil and Water Assessment Tool (SWAT), which had been validated for flow and sediment and nutrient transport, was applied to quantify the effects of Best Management Practices (BMPs) related to dairy manure management and municipal wastewater treatment plant effluent. Results are presented for the period from 1960 through 1998 for three sites along the North Bosque River. Results are presented as annual time–weighted concentrations (average of the daily load divided by daily flow over a year) and annual flow–weighted concentrations (total cumulative load divided by total cumulative flow over a year). The wastewater treatment plant BMPs resulted in greater improvement in time–weighted instream soluble phosphorus concentrations than dairy BMPs. On the other hand, dairy BMPs made greater differences in flow–weighted concentrations. This study showed that SWAT could be a useful tool for studying the effects of alternative management scenarios for pollution control from point and nonpoint sources in large watersheds.

Effectiveness of a constructed wetland for retention of nonpoint-source pesticide pollution in the Lourens River catchment, South Africa.

Abstract: Constructed wetlands have been widely used to control both point- and nonpoint-source pollution in surface waters. However, our knowledge about their effectiveness in retaining agricultural pesticide pollution is limited. A 0.44-ha vegetated wetland built along a tributary of the Lourens River, Western Cape, South Africa, was studied to ascertain retention of runoff-related agricultural pollution. Total suspended solids, orthophosphate, and nitrate were retained in the wetland in the proportions 15, 54, and 70%, respectively, during dry weather conditions (with rainfall less than 2 mm/d) and 78, 75, and 84% during wet conditions (with rainfall between 2 and 35 mm/d). Retention of water-diluted azinphos-methyl introduced via runoff at a level of 0.85 microg/L was between 77 and 93%. Chlorpyrifos and endosulfan were measured during runoff in inlet water at 0.02 and 0.2 microg/L, respectively. However, both pesticides were undetectable in the outlet water samples. During a period of 5 months, an increased concentration of various insecticides was detected in the suspended particles at the wetland inlet: azinphos-methyl, 43 microg/kg; chlorpyrifos, 31 microg/kg; and prothiofos, 6 microg/kg. No organophosphorus pesticides were found in the outlet suspended-particle samples, highlighting the retention capability of the wetland. A toxicological evaluation employing a Chironomus bioassay in situ at the wetland inlet and outlet revealed an 89% reduction in toxicity below the wetland during runoff.

Long-Term Hydrologic Impact of Urbanization: A Tale of Two Models

Abstract: At a watershed scale, land-use change can increase runoff, flooding, and nonpoint source pollution and degrade downstream water bodies. Thus it is important to assess the potential hydrologic impacts of land-use change prior to watershed development. The L-THIA (Long-Term Hydrologic Impact Assessment) model is a tool to initially assess how land-use change affects annual average runoff and is based only on readily available data. Because L-THIA is relatively new, it is important to test it against other, well-accepted methods. The U.S. Environmental Protection Agency's SWMM (Storm Water Management Model), a well-known and widely used model, was used to perform runoff calculations for comparison with L-THIA. Applications of L-THIA and SWMM to two small watersheds in Chicago show that L-THIA predicts annual average runoff between 1.1 and 23.7% higher than SWMM. The agreement between the results is higher for larger watersheds. Both models predict a linear relationship between average annual runoff and incre...

Influences of land use on water quality of a diverse New England watershed.

Abstract: Analysis of variations in major ion chemistry in the Mill River watershed reveals the importance of anthropogenic activities in controlling streamwater chemistry. Average concentrations of NO3- and SO4(2-) show a positive correlation with percent catchment area altered by human land uses, and concentrations of Cl- increase with road density. Water removal from municipal reservoirs increases the downstream concentration of NO3- and SO4(2-) over that predicted by land use changes, showing that removal of high quality upstream water concentrates pollutants downstream. In salt-impacted streams, Cl- exceeds Na- by 10-15% due to cation exchange reactions that bind Na+ to soil. The net effect of nonpoint source pollution is to elevate ANC in the most developed areas, which impacts the natural acidity of a large swamp. The sum of base cations (C(B)) exceeds ANC for all samples. Plotting C(B) against ANC and subtracting Cl- quantifies the impact of road salt from the impact of the addition of strong acids.

Linking Water Quality with Agricultural Intensification in a Rural Watershed

Abstract: Agricultural intensification was linked to streamwater pollution in a case study watershed using GIS and nutrient budgeting techniques. The results showed that surplus nitrogen applications from fertilizers and manure averaged 120 kg ha 1 yr 1 . In some parts of the watershed surplus applications exceeded 300 kg ha 1 yr 1 . A consistent increase in pig and chicken numbers (59 and 165% increase between 1986 and 1996) is considered the main reason for the surplus. Water quality was impacted in two ways: nitrate contaminated groundwater contributed to high nitrates in a major tributary during the summer, while in the wet winter season ammonia, phosphate and coliform levels were high throughout the drainage system. Significant negative relationships were found between surplus nitrogen applications and dissolved oxygen while ammonia and nitrate concentrations during the wet season were positively correlated to surplus applications. Soil texture and drainage type were also significantly correlated with the water quality indicators suggesting that it is possible to use the budget/GIS linked techniques for pollution risk assessment from agricultural non-point sources.

Contribution of Base Flow to Nonpoint Source Pollution Loads in an Agricultural Watershed

Abstract: Nonpoint source pollution of surface water from overland flow, drainage tiles, and ground water discharge is a major cause of water quality impairment in Iowa. Nonpoint source pollution from base flow ground water was estimated in the Walnut Creek watershed by measuirng chemical loads of atrazine, nitrate, chloride, and sulfate at 18 tributary creeks and 19 tiles. Loads were measured during a stable base flow period at creeks and tiles that discharged into Walnut Creek between two stream gauges. Chemical concentrations of atrazine (< 0.1−12 μg/L), nitrate (0.1 to 15 mg/L, and chloride (1.5 to 26 mg/L) in water were similar for creek and tile samples. Water draining predominantly agricultrural row crop areas had much higher concentrations than water draining restored prairie areas. Three methods were used to estimate base flow discharge in the watershed: (1) Darcy flux; (2) watershed discharge budget; and (3) discharge-drainage area; each yielded similar results (31.2 L/s to 62.3 L/s). Base flow loads to the main channel were esteimated by subtracting the loads from the upstream gauge; creeks and tiles, from the total load measured at the downstream gauge station. Base flow concentration for atrazine ranged from 0.15 to 0.29 μg/L and sulfate concentration ranged from 32 to 64 mg/L, whereas concentrations for nitrate and chloride were negative (−1 to −4 mg/L). Calcultaed base flow concentrations of atrazine and sulfate appeared to be reasonable estimates, but negative concentrations of nitrate and chloride imply either loss of chemical mass in the stream from upstream to downstream sampling points or measurment error. Load data suggest little contribution from base flow pollutants to Walnut Creek water quality, with most of the pollutant load derived from major tributary creeks. Results from this study have implication for dtermining total maximum daily loads in agricultural watersheds where contributions from point sources (creeks and tiles) can be used to estimate loads from nonpoint source ground water inputs.

Hydrological and nutrient budgets of freshwater and estuarine wetlands of Taylor Slough in Southern Everglades, Florida (U.S.A.)

Abstract: Hydrological restoration of the Southern Everglades will result in increased freshwater flow to the freshwater and estuarine wetlands bordering Florida Bay. We evaluated the contribution of surface freshwater runoff versus atmospheric deposition and ground water on the water and nutrient budgets of these wetlands. These estimates were used to assess the importance of hydrologic inputs and losses relative to sediment burial, denitrification, and nitrogen fixation. We calculated seasonal inputs and outputs of water, total phosphorus (TP) and total nitrogen (TN) from surface water, precipitation, and evapotranspiration in the Taylor Slough/C-111 basin wetlands for 1.5 years. Atmospheric deposition was the dominant source of water and TP for these oligotrophic, phosphorus-limited wetlands. Surface water was the major TN source of during the wet season, but on an annual basis was equal to the atmospheric TN deposition. We calculated a net annual import of 31.4 mg m−2 yr−1 P and 694 mg m−2 yr−1N into the wetland from hydrologic sources. Hydrologic import of P was within range of estimates of sediment P burial (33–70 mg m−2 yr−1 P), while sediment burial of N (1890–4027 mg m−2 yr−1 N) greatly exceeded estimated hydrologic N import. High nitrogen fixation rates or an underestimation of groundwater N flux may explain the discrepancy between estimates of hydrologic N import and sediment N burial rates.

The effects of climate change on stream flow and nutrient loading1

Abstract: This study assesses the potential impact of climate change on stream flow and nutrient loading in six watersheds of the Susquehanna River Basin using the Generalized Watershed Loading Function (GWLF). The model was used to simulate changes in stream flow and nutrient loads under a transient cli- mate change scenario for each watershed. Under an assumption of no change in land cover and land management, the model was used to predict monthly changes in stream flow and nutrient loads for future climate conditions. Mean annual stream flow and nutrient loads increased for most watersheds, but decreased in one water- shed that was intensively cultivated. Nutrient loading slightly decreased in April and late summer for several watersheds as a result of early snowmelt and increasing evapotranspiration. Spatial and temporal variability of stream flow and nutrient loads under the transient climate scenario indicates that different approaches for future water resource management may be useful. (KEY TERMS: climate change; water quality; nonpoint source pol- lution; GWLF; simulation; modeling.)

Determining nutrient export coefficients and source loading uncertainty using in‐stream monitoring data

Abstract: Over a three-year period, flow and nutrients were monitored at 13 sites in the upper North Bosque River watershed in Texas. Drainage areas above sampling sites differed in percent of dairy waste application fields, forage fields, wood/range, and urban land area. A multiple regression approach was used to develop total phosphorus (TP) and total nitrogen (TN) export coefficients for the major land uses in these heterogeneous drainage areas. The largest export coefficients were associated with dairy waste application fields followed by urban, forage fields, and wood/range. An empirical model was then established to assess nutrient contribution by major sources using developed export coefficients and point source loadings from municipal wastewater treatment. This model was verified by comparison of estimated loadings to measured in-stream data. Monte Carlo simulation techniques were applied to provide an uncertainty analysis for nutrient loads by source, based on the variance associated with each export coefficient. The largest sources of nutrients contributing to the upper North Bosque River were associated with dairy waste application fields and forage fields, while the greatest relative uncertainty in source contribution was associated with loadings from urban and wood/range land uses.

Evaluation of soluble phosphorus loading from manure-applied fields under various spreading strategies

Abstract: A simple model was developed and applied to a dairy farm in the New York City (NYC) water supply watershed to evaluate the effectiveness of various manure spreading strategies for reducing non-point source, soluble phosphorus (SP) pollution. Phosphorus from manure-spread fields is recognized as one of the important non-point source pollutants in the region and there is acute interest in developing economically viable water quality management practices. The NYC watershed initiative, i.e. the Watershed Agriculture Program (WAP), mandated that water quality management practices would be scientifically justifiable based on the best information available (Walter and Walter, 1999). Thus, this project was carried-out to evaluate manure-handling strategies based on the currently available information. The model for predicting SP loading to perennial streams via surface runoff was developed by combining a mechanistic hydrological model with an empirical relationship for SP concentration in runoff. This study showed that, in the short term, because of soil P accumulation associated with a history of dairy farming, the maximum possible reduction in SP loading to perennial streams is about 50%. Exporting all manure from the NYC watersheds attains this. Utilizing the concept of hydrologically sensitive areas (Walter et al. 2000), this study suggests possible SP loading reductions of 25% with all manure remaining on-farm. This study supports and emphasizes the finding by Walter et al. (2000) that the timing and location of manure spreading strongly influences SP transport.

Identifying critical sources of phosphorus export from agricultural watersheds

Abstract: Surface runoff accounts for much of the phosphorus (P) input to and accelerated eutrophication of the fresh waters. Several states have tried to establish general threshold soil P levels above which the enrichment of surface runoff P becomes unacceptable. However, little information is available on the relationship between soil and surface runoff P, particularly for the northeastern United States. Further, threshold soil P criteria will be of limited value unless they are integrated with site potential for runoff and erosion. In response, the Natural Resource Conservation Service (NRCS) developed a P Index (PI), which ranks the vulnerability of fields as sources of P loss in runoff, based on soil P, hydrology, and land use. This study evaluated the relationship between soil and surface runoff P in a study watershed in central Pennsylvania. The relationship was then incorporated into the (PI), and its impact on the identification of critical source areas within the watershed was examined. Using simulated rainfall (6.5 cm h−1 for 30 min), the concentration of dissolved P in surface runoff (0.2–2.1 mg l−1) from soils was related (r 2=0.67) to Mehlich-3 extractable soil P (30–750 mg kg−1). Using an environmentally based soil P threshold level of 450 mg kg−1 determined from the soil-runoff P relationship, the PI identified and ranked areas of the watershed vulnerable to P loss. The vulnerable areas were located along the stream channel, where areas of runoff generation and areas of high soil P coincide, and where careful management of P fertilizers and manure should be targeted.

Storm Discharge, Loads, and Average Concentrations in Northwest Ohio Rivers, 1975-1995

Abstract: A computerized technique was developed to identify storm runoff episodes and calculate storm discharges, storm loads, and storm average concentrations for each event in datasets with up to 10,000 records. This technique was applied to four watersheds within the Lake Erie drainage basin and identified between 160 and 250 runoff events in each. Storm event loads and storm event mean concentrations were calculated for each runoff event for suspended solids, total phosphorus, soluble reactive phosphorus, nitrate, and total Kjeldahl nitrogen. The basic characteristics of the resulting data are described, as are systematic differences as a function of watershed size, seasonal differences, and trends over time. Many of the results of this study reflect the importance of nonpoint processes and improvements in agricultural best management practices in these watersheds.

Utilization of landscape indicators to model potential pathogen impaired waters1

Abstract: Many water bodies within the United States are contaminated by non-point source (NPS) pollution, which is defined as those materials posing a threat to water quality arising from a number of individual sources and diffused through hydrologic processes. One such NPS pollutant that is of critical concern are pathogens derived from animal wastes, including humans. The potential presence of pathogens is identified by testing the water for fecal conform, a bacteria also associated with animal wastes. Water contaminated by animal wastes are most often associated with urban and agricultural areas, thus it is postulated that by utilizing land cover indicators, those water bodies that may be at risk of fecal coliform contamination may be identified. This study utilizes land cover information derived from the Multi-Resolution Land Characterization (MRLC) project to analyze fecal coliform contamination in South Carolina. Also utilized are 14 digit hydro-logic unit code (HUC) watersheds of the state, a digital elevation model, and test point data stating whether fecal coliform levels exceeded State Water Quality Standards. Proportions of the various land covers are identified within the individual watersheds and then analyzed using a logistic regression. The results reveal that watersheds with large proportions of urban land cover and agriculture on steep slopes had a very high probability of being impaired. (KEY TERMS: Geographic Information Systems; land use planning; nonpoint source pollution; statistical analysis; water quality; watershed management.)

A windows-based GIS-AGNPS interface

Abstract: ArcView Nonpoint Source Pollution Modeling (AVNPSM), an interface between ArcView GIS and AGNPS (Agricultural Nonpoint Source Pollution Model) is developed in support of agricultural watershed analysis and nonpoint source pollution management. The interface is PC-based and operates in a Windows environment. It consists of seven modules: AGNPS utility, parameter generator, input file processor, model executor, output visualizer, statistical analyzer, and land use simulator. Basic input data to the interface include: soil, digital elevation model, land use/cover, water features, climate, and information on management practices. Application of the AVNPSM to a sample watershed indicates that it is user friendly, flexible, and robust, and it significantly improves the efficiency of the nonpoint source pollution modeling process.

Mass balance of heavy metals in New Haven Harbor, Connecticut: Predominance of nonpoint sources

Abstract: A mass balance was constructed quantifying all known sources and sinks for the metals Ag, Cd, Cu, and Pb in New Haven Harbor, Connecticut, USA. Sources included direct atmospheric deposition, rivers, treated sewage effluent, combined sewer overflows, and permitted industrial discharge. Sinks were burial in sediments, tidal exchange with Long Island Sound, removal in salt marshes, and dredging. All of these fluxes were measured directly, rather than estimated, and uncertainties were quantified. The mass balance closed successfully within the uncertainty of the measurements. Riverine inputs account for most of the total yearly metal flux. Metal concentrations in the river can be approximated as a simple linear function of discharge. Salt marshes remove an amount of metal equivalent to 20%‐30% of the flux from the river before it reaches the harbor. Burial in sediments is the major sink for all metals examined, but dredging acts as a substantial short-circuit of this sink. Tidal exchange appears to be a relatively small term; however, it is also the least well quantified. Sewage treatment plant (STP) effluent and combined sewer overflow discharge are minor contributors to the overall metal balance, except in the case of Ag. Metal concentrations in STP effluent are a linear function of discharge. Atmospheric deposition is of minor importance but is comparable to sewage effluent. Lakes can be used as natural collectors and indicators of atmospherically deposited metals. Although heavy metals are among the most toxic and persistent contaminants of estuaries, we lack a quantitative understanding of their sources, distribution, transport, and fate. For estuarine systems located in industrialized areas, such as urban harbors, this lack of knowledge is complicated by numerous inputs of metal pollution from point and nonpoint sources and by removal and redistribution of contaminated sediments through dredging operations. In order to determine the relative importance of each of these factors to the distribution and fate of heavy metals in an industrialized estuary, a mass balance of Ag, Cd, Cu, and Pb was constructed for the Quinnipiac River/New Haven Harbor system located in south-central Connecticut. The information generated by this study can be used by ecosystem managers to improve water and sediment quality in the most cost-effective way.

Nonpoint Source Pollution, Uniform Control Strategies, and the Neuse River Basin

Abstract: This research investigates various policy options considered by the state of North Carolina for reducing nonpoint source pollution. Focusing on nitrogen runoff from cropping activities, we estimate and compare the control costs and estuarine nutrient loadings under both the initial proposed rules, which were quite uniform, and the more flexible final proposed rules. We then illustrate the magnitude to which the outcomes from models and policies can diverge depending upon the treatment of the application-specific environmental heterogeneity. Such an analysis illustrates the relative importance of certain types of heterogeneity associated with the environment on policy design and real-world outcomes.