Showing papers on "Nonpoint source pollution published in 1995"

Controlled versus Conventional Drainage Effects on Water Quality

Abstract: Fertilized cropland is a potential nonpoint source of nitrogen and phosphorus, which can contribute to the nutrient enrichment of surface water ecosystems. Research has shown that agricultural drainage water may contain fertilizer nutrients and pesticides. Nitrogen and phosphorus are present in drainage outflow primarily because of the addition of fertilizer, which results from the change in land use following drainage improvements instead of from the mere installation of drainage. Yet, public concern for the environment has led to a general criticism of agricultural drainage for degrading water quality. Controlled drainage has been recognized in some states as a best management practice to reduce the transport and delivery of nitrogen and phosphorus to sensitive surface waters. This article summarizes and compares water quality impact associated with conventional and controlled drainage practices. Nitrogen and phosphorus reductions of 30% to 50%, resulting from controlled drainage are reported in several...

Economic and Environmental Implications of Soil Nitrogen Testing: A Switching-Regression Analysis

Abstract: A simultaneous equations, or "switching-regression," model is developed to assess the impact of soil nitrogen (N) testing on N fertilizer use, crop yields, and net returns in corn growing areas of Nebraska. The results indicate that when there is uncertainty about the quantity of available "carry-over" N, N testing enables farmers to reduce fertilizer use without affecting crop yields. However, the value of information from N tests depends critically on cropping history and soil characteristics. These findings have implications for environmental and technology transfer policies designed to reduce nonpoint source water pollution.

Regulating Nonpoint Source Pollution Under Heterogeneous Conditions

Abstract: Because of difficulties in measuring effluent from nonpoint pollution, proposals for regulating agricultural runoff often suggest instruments applied to inputs or management practices. When pollution functions vary across sources, uniform input instruments cannot achieve a least-cost pollution reduction, but efficient instruments may be difficult to administer. In this paper we analyze lettuce production on two soils in California's Salinas Valley to consider empirical costs associated with uniform input taxes and regulations. The results suggest that uniform instruments may not be costly relative to an efficient baseline. Though taxes are more efficient, farmers have higher profits with regulations.

Non-point-source Nutrient Losses to the Aquatic Environment in Denmark: Impact of Agriculture

Abstract: As part of a coordinated programme for nationwide monitoring of the Danish aquatic environment, initiated in 1988, nutrient fluxes are measured in 270 rivers, and nutrient cycling is studied in six agricultural catchments. This enables assessment of the degree of non-point-source nutrient loading of Danish surface water and groundwater as well as of the impact of agriculture practised under different climatic and physiographic conditions and with different farming practices. Comparison of annual median losses of total nitrogen and total phosphorus in agricultural catchments and undisturbed catchments revealed an average loss ratio of 14:l for total nitrogen (23.4 and 1.7 kg N ha-1, respectively) and 4:1 for total phosphorus (0.29 and 0.070 kg P ha-1, respectively). Assessment of nitrogen cycling in six small agricultural catchments with either sandy soil or loamy soil revealed marked differences in annual net input to the soil (142 v. 77 kg N ha-1), annual leaching from the root zone (154 v. 78 kg N ha-1), and annual riverine loss of nitrogen (13 v. 25 kg N ha-1). The differences in the rates of leaching and riverine loss in the two soil types reflect the different potential for surface-water and groundwater pollution with nitrogen and also the fact that the denitrification potential is higher in both the soil and the riparian areas of sandy ecosystems. Modelling of data from 77 small representative river basins revealed significant empirical relationships (P <0.001) between annual loss of both nitrogen and phosphorus and various predictor variables (e.g. runoff, proportion of agricultural land, soil type). Runoff and proportion of agricultural land explained, respectively, 41% and 26% of the variance in the nitrogen-model and 45% and 8%, of the variance in the phosphorus model. Such loading models are valuable tools for systems analysis and management at the catchment level, such as when assessing measures implemented to reduce non-point-source nutrient pollution.

Design basis for Everglades stormwater treatment areas

Abstract: The State of Florida (1994) has adopted a plan for addressing Everglades eutrophication problems by reducing anthropogenic phosphorus loads. The plan involves implementation of Best Management Practices in agricultural watersheds and con­ struction of regional treatment marshes (Stormwater Treatment Areas or STA's). This paper describes the development, testing, and application of a mass-balance model for sizing STA's to achieve treatment objectives. The model is calibrated and tested against peat and water-column data collected in Water Conservation Area- 2A (WCA-2A), where phosphorus dynamics and eutrophication impacts have been intensively studied. The 26-year-average rate of phosphorus accretion in peat is shown to be proportional to average water-column phosphorus concentration, with a proportionality constant of 10.2 mJyr (90 percent Confidence Interval = 8.9 to 11.6 m/yr). Spatial and temporal variations in marsh water-column data suggest that drought-induced recycling of phosphorus was impor­ tant during periods of low stage in WCA-2A. Maintaining wet con­ ditions will be important to promote phosphorus removal in STA's. Sensitivity analysis of STA performance is conducted over the range of uncertainty in model parameter estimates to assess the adequacy of the model as a basis for STA design. (KEY TERMS: wetlands; phosphorus; modeling/statistics; stormwa­ ter management; peat; nonpoint source pollution; Everglades; eutrophication; wetland treatment.)

Estimating Nonpoint Source Pollution Loads With a GIS Screening Model

Abstract: The St. Johns River Water Management District (SJR-WMD) is using a Geographic Information System (GIS) screening model to estimate annual nonpoint source pollution loads to surface waters and determine nonpoint source pollution problem areas within the SJRWMD. The model is a significant improvement over current practice because it is contained entirely within the district's GIS software, resulting in greater flexibility and efficiency, and useful visualization capabilities. Model inputs consist of five spatial data layers, runoff coefficients, mean runoff concentrations, and stormwater treatment efficiencies. The spatial data layers are: existing land use, future land use, soils, rainfall, and hydrologic boundaries. These data layers are processed using the analytical capabilities of a cell-based GIS. Model output consists of seven spatial data layers: runoff, total nitrogen, total phosphorous, suspended solids, biochemical oxygen demand, lead, and zinc. Model output can be examined visually or summarized numerically by drainage basin. Results are reported for only one of the SJRWMD's ten major drainage basins, the lower St. Johns River basin. The model was created to serve a major planning effort at the SJRWMD; results are being actively used to address nonpoint source pollution problems.

Stormwater Runoff and Receiving Systems: Impact, Monitoring, and Assessment

Abstract: Stormwater, Urban Runoff, and Receiving Systems A Context for Understanding Stormwater Effects in Receiving Systems, EE Herricks Urban Runoff in an Integrated Landscape Context, J Cairns, Jr Impacts Section Summary, EE Herricks Analysis of Effects and Management of Urban Runoff, L Lijklema and RH Aalderink Factors in Controlling Nonpoint Source Impacts, PH Davies Stream Power: A Unifying Theme for Urban Fluvial Geomorphology, BL Rhoads Stream Stability under a Changing Environment, B Urbonas and B Benik Channel and Habitat Change Downstream of Urbanization, W James Ecotoxicological Approaches and Criteria for the Assessment of Urban Runoff Impacts on Receiving Waters, JB Ellis, RB Shutes, and DM Revitt Biological Effects of Urban Runoff Discharges, RE Pitt The Impact of Combined Sewer Overflow Discharges on the Biological and Chemical Quality of Receiving Streams: Two Case Studies from the Northwest of England, PS Davis, J Seager, and I Milne The Environmental Impact of Stormwater Ponds, TR Schueler and J Galli Uncertainty and Risk Section Summary, EE Herricks Uncertainty and Risk: Receiving System Issues, BR Parkhurst and W Warren-Hicks Risk Analysis and Engineering Design in Water Resources, JP Heaney Computing TMDLs for Urban Runoff and Other Pollutant Sources, LA Rossman The Uncertainties of Urban Storm Water Regulation, SJ Koorse Study Design Section Summary, AC Rowney Integrated Watershed Analysis and Study Design, C Richards Quality Assurance Issues in Assessing Receiving Water, GA Burton, Jr Design of Assessment Programs and Use of Water Quality Indices, MA House Impact Mitigation Section Summary, JE Jones Design Practices for Channels Receiving Urban Runoff: Examples from the River Thames Catchment, UK, A Brookes Urban Channel Systems-The Engineering Issues of Impact Mitigation, TN Debo Analysis and Development of Fisheries Habitat and Stormwater Management Options for an Urban Stream, AW Johnson and JE Caldwell Lessons Learned from a Decade of Stormwater Treatment in Florida, EH Livingston Toward Ecologically Based Urban Runoff Management, RR Horner Sand Filter Design for Water Quality Treatment, E Shaver and R Baldwin Issues Analysis (Federal, State, Local, Industrial, and International) Section Summary, S Tucker EPA's Permit Program for Storm Water, M Cook Regulatory Issues Related to Natural Design Systems, JJ Scherer Stormwater Quality Issues Faced by Industry, DR Van Sickle Stormwater Quality Issues Facing Local and State Government, D Harrison Regulatory Issues from the US Perspective: NPDES Permits for Discharges from Municipal Separate Storm Sewer Systems, K Weiss Permitting of Combined Sewer Overflows (CSO)-Best Management Practice in the United Kingdom, IT Clifforde Institutional Issues in Urban Pollution Managment in England and Wales, JM Tyson Index

Voluntary Incentives for Reducing Agricultural Nonpoint Source Water Pollution M. Feather

Abstract: In this report... Agricultural chemicals and sediment from cropland may reduce the quality of America’s surface and ground water resources. The Clean Water Act stipulates that individual States are responsible for controlling agricultural nonpoint source pollution. Most State plans rely chiefly on education and technical assistance to promote the adoption of less polluting practices. Because profitability drives production decisions, these programs tend to be most successful when they promote inexpensive changes in existing practices. This report presents recent research findings on the success of existing incentive programs to control agricultural nonpoint source pollution. Impaired surface water quality from cropland erosion alone has resulted in $2-$8 billion in annual losses to recreational and commercial fishing, boating, municipal treatment plants, water storage facilities, and navigable waterways (Ribaudo, 1987). Both voluntary and mandatory policies have been implemented and studied to reduce agricultural pollution. Voluntary incentives rely on providing the farm operator with an incentive to adopt less polluting technologies. These approaches commonly use cost-sharing or education and technical assistance to encourage farm operators to use less polluting practices. Regulations or taxes to force farm operators to reduce pollution levels are two examples of mandatory approaches. Because nonpoint source pollution is not directly measurable, regulations would consist of design standards governing farmers’ land management and cropping practices. Although this option may appear to be a simple solution, administrative costs may be high. When taxes are levied on a polluting input (such as a chemical pesticide), farmers will reduce their use of that input and substitute other, less polluting inputs to reduce costs. The extent of the change in input use depends on the sensitivity of the demand for the polluting input to price changes, which can change from one area to another. Education, Technical, and Financial Assistance, a component of the U.S. Department of Agriculture’s (USDA) Water Quality Program, is a national effort to encourage the adoption of less polluting farm management practices. Research findings indicate that the adoption of an improved management practice is most strongly influenced by producer perceptions of its effect on profitability. Other important factors include familiarity with the practice and beliefs that it will improve onfarm water quality. This indicates that educational programs are best targeted toward inexpensive, familiar practices with tangible environmental benefits. The 1990 Food, Agriculture, Conservation, and Trade Act authorized USDA to create the watershed-based Water Quality Incentive Program (WQIP). WQIP encouraged the adoption of less polluting practices via direct incentive payments to farmers. The findings in this report suggest that the adoption of some less polluting practices is highly influenced by the payment level, while the adoption of others is not. Payments that are too low will have little effect on adoption, while those that are too high will result in the same level of adoption that could be accomplished by a lower payment. These findings suggest that WQIP payments should reflect changes in costs of production due to the adoption of an improved management practice.

Water quality impacts from on-site waste disposal systems to coastal areas through groundwater discharge

Abstract: This report summarizes research studies linking on-site waste disposal systems (OSDS) to pathogen and nutrient concentrations in groundwater with the potential to impact coastal embayments. Few studies connect OSDS to coastal water quality. Most studies examined pathogen and nutrient impacts to groundwater and omitted estimations of contaminants discharged to surface water. The majority of studies focused on nitrogen, with little information on pathogens and even less on phosphorus. Nitrogen discharged from OSDS poses the greatest threat to water quality. Vertical distance of septic tank infiltration system from the water table, septic system design, and siting remain the key components in minimizing potential impacts from OSDS for control of both pathogens and nutrients. The most comprehensive information connecting nutrient contributions from OSDS to surface water quality was the study conducted on Buttermilk Bay in Massachusetts where 74% of nitrogen to the bay was attributed to onsite disposal systems. In conclusion, further studies on the viability and transport of pathogens and nutrients through the groundwater aquifer and across the groundwater/surface-water interface are needed. Additional research on the importance of septic system design on the availability of contaminants to groundwater as well as the minimum distance between the septic system and water table necessary to protect groundwater are also indicated.

Impact of Landscape Feature and Feature Placement on Agricultural Non-Point-Source-Pollution Control

Abstract: Management of agricultural non-point-source pollution in watersheds requires an integrated approach involving implementation of on-field and off-field management practices. An off-field management practice that is widely used to control sediment and water-borne pollutants from entering surface waters is vegetated buffer (or filter) strips. When situated between a potential pollutant source and a surface water body that receives runoff, vegetated buffer strips have been shown to be very effective in removing substantial amounts of sediment and nutrients (primarily nitrogen and phosphorus) from the runoff. However, the effectiveness of vegetated buffer strips depends not only on their hydrologic and hydraulic characteristics but also on their physical characteristics (e.g., width and placement within the agricultural landscape). This paper examines the influence of width and placement of vegetated buffer strips on sediment yield in an agricultural watershed. The AGNPS hydrologic/water-quality model was link...

Recreational swimming benefits of New Hampshire lake water quality policies: an application of a repeated discrete choice model.

Abstract: Water pollution control policies generally direct sources (i.e., industry, agriculture) to reduce loadings of certain pollutants. Thus, evaluating the relative net recreation benefits of policies to improve water quality requires establishing a linkage between the sources, the resultant water quality degradation at the affected water bodies, and, ultimately, the effect on recreation behavior. This linkage is rarely present in the empirical literature which is, thus, deficient for water pollution control policy assessment purposes. In this paper, we estimate the relative recreational swimming benefits that may result from controlling point and nonpoint sources of pollution, respectively, in New Hampshire's lakes. We use a repeated discrete choice framework to model swimming behavior as a function of each lake's level of eutrophication, bacteria, and oil and grease. For each pollutant, at each affected lake, we identify which source is responsible for the pollution, and we conduct scenarios controlling each pollution source independently, and then, taken together. Seasonal benefit estimates are presented for each scenario. Coupled with information on the most cost effective means of generating the scenarios, these estimates provide a useful starting point for a quantitative assessment of the net recreation benefits of policies to improve the quality of New Hampshire lakes.

GIS-based nonpoint source pollution modeling: Considerations for wetlands

Abstract: Over the past several years, a coupled model-GIS approach has been used extensively to identify areas with a high pollution potential and to estimate loading rates for a variety of pollutants (Table 1). Studies have assessed surface water movement of sediments and nutrients (e.g., DeRoo et al. 1989; Sivertun et al. 1988; Walker et al. 1992; Levine et al. 1993) and subsurface leaching of pesticides and nitrogen (e.g., Halliday and Wolfe 1991; Petach et al. 1991; Wylie et al. 1994). Various aquatic systems have been examined including lakes, streams, reservoirs, and groundwater aquifers (Table 1). Wetland ecosystems often occupy transition zones in a landscape, frequently occurring between terrestrial land uses and surface water bodies such as streams and lakes (Brinson 1993). Because of their intermediate position and their dependence on water originating from upland areas, these systems are highly vulnerable to inputs of nonpoint source (NPS) pollutants. Wetlands located in human-dominated landscapes now receive sediments, nutrients, and other NPS pollutants in excess of historical inputs (Neely and Baker 1989), and studies have shown negative effects on wetland species and ecosystem hnctioning with such impacts (Ehrenfeld 1983; Morgan and Philipp 1986; Moore et al. 1989; Ehrenfeld and …

Introduction to Water Pollution Biology

Abstract: Overview of Water Pollution. The Nature of Water and the Hydrologic Cycle. Overview of Aquatic Ecosystems. Bacteria and Water Pollution. Dissolved Oxygen and Natural Purification. Algae and Eutrophication. The Estuarine Environment. The Nitrogen and Phosphorous Cycles. Thermal Pollution. The Sulfur Cycle. Aquatic Toxicology. Pollution by Inorganic Materials and Metals. Pesticides and Water Pollution. Polychlorinated Biphenyls. Pollution from Petroleum Hydrocarbons. Pollution from Biological Sources. Index.

Agricultural drainage effects on water quality in southeastern U.S

Abstract: A review of literature and summary of research results are presented on the effects of drainage on water quality in North Carolina, South Carolina, Georgia, and Florida. Principal findings from the predominate coarse-textured soils of the Atlantic Coastal Plain include increased nitrate-nitrogen losses associated with improved subsurface drainage. Benefits of drainage include potential reductions in organic nitrogen (N) and phosphorus (P) losses from these mineral soils. Results of drainage investigations on organic soils in the Everglades Agricultural Area of Florida indicate that phosphorus is the primary limiting factor for eutrophication problems in Lake Okeechobee. P losses can be potentially reduced by using slow versus fast drainage, retaining drainage water from vegetable and sugarcane fields (on sugarcane or fallow areas), and minimizing water-table fluctuations. Some of these potential practices and their resultant effects need additional verification for application to other areas and conditions.

Voluntary Incentives for Reducing Agricultural Nonpoint Source Water Pollution

Abstract: Agricultural chemicals and sediment from cropland may reduce the quality of America's surface and ground water resources The Clean Water Act stipulates that individual States are responsible for controlling agricultural nonpoint source pollution Most State plans rely chiefly on education and technical assistance to promote the adoption of less polluting practices Because profitability drives production decisions, these programs tend to be most successful when they promote inexpensive changes in existing practices This report presents research findings on the success of incentive programs to control agricultural nonpoint source pollution

An Economic Analysis of the Pre-sidedress Nitrogen Test for Pennsylvania Corn Production

Abstract: The impacts of agriculture on water quality are receiving a high level of public attention. For example, the U. S. Environmental Protection Agency recently concluded that agriculture is the leading contributor to nonpoint source pollution, and possibly the leading source of water pollution in the United States. Water quality issues associated with agriculture are nitrogen, phosphorous, soil, and pesticide pollution. This concern about the impact of agriculture on water quality has stimulated interest in production methods that reduce farm pollution. One approach to addressing the problem is adoption of Best Management Practices (BMP's) that would reduce water pollution relative to conventional practices. Assuming that farmers are motivated by profits, adoption of BMP's will occur only if farmers expect higher profits. If BMP's do not increase profits, then adoption requires regulatory measures. The usual assumption of BMP's is that conventional production practices are technically and/or allocatively inefficient relative to BMP's. Under this assumption, farmers may be able to both reduce pollution and improve farm profits. Soil testing is a BMP that has long been used t manage phosphorous and potassium availability for crop production. Until recently, soil tests were considered to be of little value in

Rural nonpoint source pollution control in Wisconsin : the limits of a voluntary program ?

Abstract: This paper examines the relationship between best-management practices, institutional needs, and improved water quality within the watersheds of Wisconsin's program for controlling rural nonpoint source pollution. The first section describes the federal requirements for state nonpoint source programs and the legislative and management methods the state of Wisconsin uses to put those requirements into practice. The emphasis of the paper, described in the second section, is the institutional difficulty in evaluating the success of a large, integrated water quality program. Measurements which are investigated include (1) watershed water quality before and after implementation of BMPs; (2) program participation as measured by eligible vs. participating landowners, BMPs considered necessary vs. BMPs implemented, or dollars allocated to the NPS program vs. dollars expended; and (3) institutional goal coordination and management effectiveness. It is found that, despite the size and sophistication of Wisconsin's NPS program, there is little if any improvement in ambient water quality in these watersheds, probably because of a general lack of adequate participation in this voluntary program.

Benefits of Protecting Rural Water Quality: An Empirical Analysis

Abstract: Concerns about the impact of farm production on the quality of the Nation's drinking and recreational water resources have risen over the past 10 years. Because point sources of pollution were controlled first, agricultural nonpoint sources have become the Nation's largest remaining single water-quality problem. Both public and private costs of policies that address the conflict between agricultural production and water quality are relevant, but measuring the off-farm benefits and costs of changing water quality is difficult. Many of the values placed on these resources are not measured in traditional ways through market prices. This report explores the use of nonmarket valuation methods to estimate the benefits of protecting or improving rural water quality from agricultural sources of pollution. Two case studies show how these valuation methods can be used to include water-quality benefits estimates in economic analyses of specific policies to prevent or reduce water pollution.

Nonpoint source pollution potential in an agricultural watershed in northwestern pennsylvania

Abstract: A 155,947 ha portion of the Shenango River watershed in western Pennsylvania was evaluated as to the potential impact of agriculture drainage on water quality. Approximately a third of the area is being used as either cropland or pasture with approximately an equal percentage in forest lands. Eleven subwatersheds were evaluated as to their potential for nonpoint source pollution according to the criteria established by the Pennsylvania Department of Environmental Resources for the Chesapeake Bay Pollution Abatement Program. The individual components and overall rating for each subwatershed were then evaluated as to their correlation with four water quality variables based on 104 samples collected at 26 sampling stations throughout the watershed. There was a significant correlation between the overall rating factor for each subwatershed and each of the four water quality variables. In general, the watershed delivery factor, animal nutrient factor, and management factors were correlated with fecal coliform and phosphorus in the receiving streams, whereas the ground water delivery factor appeared to be more important in determining nitrate concentrations in these streams. These results indicate that manure and nutrient management, along with the exclusion of livestock from streams and the enhancement and/or replacement of riparian wetlands, are important approaches in reducing agricultural impacts in fresh water ecosystems.

Using Constructed Wetland-Pond Systems to Treat Agricultural Runoff: A Watershed Perspective

Abstract: Long and Cross Lakes in the St. John Valley watershed of northern Maine have exhibited chronic algae blooms in past years. Survey data and modeling determined agricultural runoff to be die main source of phosphorus and sediments in both watersheds. “Nutrient/Sediment Control Systems” (NSCS) are being used to treat runoff from target subwatersheds. The systems consist of a sedimentation basin, grass filter strip, wetland, and detention pond in series. Annual removal efficiencies for one system were 85–88% for total phosphorus and 96–97% for total suspended solids. Seasonal removals varied considerably, with spring flows exporting more phosphorus and sediment from the system than was imported. Phosphorus loadings to Long Lake will be reduced between 10–33% with 20 NSCS and diversion of municipal wastewater effluent to a nearby river.

Comparative Evaluation of Land Cover Data Sources for Erosion Prediction

Abstract: A fundamental problem in protecting surface drinking water supplies is the identification of sites highly susceptible to soil erosion and other forms of nonpoint source (NPS) pollution. The New York City Department of Environmental Protection is trying to identify erodible sites as part of a program aimed at avoiding costly filtration. New York City's 2,000 square mile watershed system is well suited for analysis with geographic information systems (GIS); an increasingly important tool to determine the spatial distribution of sensitive NPS pollution areas. This study used a GIS to compare three land cover sources for input into the Modified Universal Soil Loss Equation (MUSLE), a model estimating soil loss from rangeland and forests, for a tributary watershed within New York City's water supply system. Sources included both conventional data (aerial photography) and Landsat data (MSS and TM images). Although land cover classifications varied significantly across these sources, location-specific and aggregate watershed predictions of the MUSLE were very similar. We conclude that using Landsat TM imagery with a hybrid classification algorithm provides a rapid, objective means of developing large area land cover databases for use in the MUSLE, thus presenting an attractive alternative to photo interpretation.

Erosion assessment of large watersheds in Taiwan

Abstract: The objective of this study is to integrate the Agricultural Nonpoint Source Pollution Model (AGNPS) and the technique of a geographic information system (GIS) to quantify erosion problems at the Bajun River Basin and the Tsengwen Reservoir Watershed in Taiwan. The estimated annual soil loss from the Bajun River Basin is about 259 t/ha and the Tsengwen Reservoir Watershed is about 903 t/ha. The annual sedimentation depth for the Tsengwen Reservoir is approximately 5.9 mm, which is not significantly different from the observed rate, but exceeds what is observed in the United States and in the Yellow River Basin. It is, therefore, necessary to prescribe appropriate soil and water conservation practices to control the volume of soil loss within acceptable (or tolerable) limits.

Modeling watershed water quality

Abstract: In recent years, a risk-based management approach to water quality protection is gaining increased popularity. This approach relies upon the identification and targeting of worst case problems as those needing initial emphasis. One of the currently available engineering tools that is believed to satisfy the greatest needs and provide the best foundation for future problem solving is the development and application of watershed1 models to understand and predict the relationship of watershed conditions and management activities to sediment and chemical loadings to rivers and lakes. Usable, scientifically-sound tools that predict combined point and nonpoint source pollution loadings must be coupled to riverine and lake models so that the results of various management and control scenarios and options can be simulated and predicted. These dynamic models must be able to evaluate changes in loadings over temporal and spatial scales, and must consider both the amounts and speciation of contaminants.