DETERMINATION OF BEST TIMING FOR POULTRY WASTE DISPOSAL: A MODELING APPROACH1

ABSTRACT: Confined production of poultry results in significant volumes of waste material which are typically disposed of by land application. Concerns over the potential environmental impacts of poultry waste disposal have resulted in ongoing efforts to develop management practices which maintain high quality of water downstream of disposal areas. The timing of application to minimize waste constituent losses is a management practice with the potential to ensure high quality of streams, rivers, and lakes downstream of receiving areas. This paper describes the development and application of a method to identify which time of year is best, from the standpoint of surface water quality, for land application of poultry waste. The procedure consists of using a mathematical simulation model to estimate average nitrogen and phosphorus losses resulting from different application timings, and then identifying the timings which minimize losses of these nutrients. The procedure was applied to three locations in Arkansas, and three different criteria for optimality of application timing were investigated. One criterion was oriented strictly to water quality, one was oriented only to crop production, and the last was a combination. The criteria resulted in different windows of time being identified as optimal. Optimal windows also varied with location of the receiving area. The results indicate that it is possible to land-apply poultry waste at times which both minimize nutrient losses and maximize crop yield.     

POTENTIAL FOR REDUCING NITROGEN POLLUTION THROUGH IMPROVED AGRONOMIC PRACTICES1

ABSTRACT: According to the 1990 National Water Quality Inventory nutrient runoff from agriculture is one of the largest contributors to watershed contamination. Nutrient balance studies suggest that many farmers use more fertilizer than necessary because of insufficient crediting for nutrients coming from manure and legumes. Using data from the USDA's 1990 Farm Costs and Returns Survey, we found that farmers raising only conventional crops spend between $470 to $624 million more per year on fertilizer than necessary. This accounts for a range of 24 percent to 32 percent of total annual nitrogen (N) purchases. The excess N amounts to between 2.5 to 3.3 billion pounds N and has considerable water pollution potential. Farmers and the fertilizer industry have responded positively to highly focused research and education programs which support improved crediting of these nutrients.     

TESTS OF THE CREAMS MODEL ON AGRICULTURAL FIELDS IN VERMONT1

ABSTRACT: The computer model, CREAMS, has been developed for field-sized agricultural areas to aid in best management practices evaluation and planning. A test of CREAMS was performed by comparing monthly observed and simulated values for runoff, sediment, and phosphorus exports from two agricultural fields in Vermont to determine the applicability of the model in cold climates. Water quality samples were collected from field runoff and analyzed for both total suspended solids and total phosphorus. Generally, exports were overestimated during low flow months and underestimated during high flow months. Significant r²values (p <0.05), ranging from 0.78 to 0.90, between simulated and observed data were found for all comparisons except for sediment export from one field. Comparisons of the slopes of the regressions between observed and simulated values and the ideal slope of one using t-tests revealed significant differences between simulated and observed monthly runoff, sediment, and phosphorus exports. It is postulated that this lack of adequate prediction could be attributed to the use of average monthly, instead of daily, temperature and solar radiation in calculations of evapotranspiration and snowmelt, and the use of static parameter values for parameters that vary seasonally.     

Integrated Modular Modeling of Water and Nutrients From Point and Nonpoint Sources in the Patuxent River Watershed1

Abstract: We present a simple modular landscape simulation model that is based on a watershed modeling framework in which different sets of processes occurring in a watershed can be simulated separately with different models. The model consists of three loosely coupled submodels: a rainfall‐runoff model (TOPMODEL) for runoff generation in a subwatershed, a nutrient model for estimation of nutrients from nonpoint sources in a subwatershed, and a stream network model for integration of point and nonpoint sources in the routing process. The model performance was evaluated using monitoring data in the watershed of the Patuxent River, a tributary to the Chesapeake Bay in Maryland, from July 1997 through August 1999. Despite its simplicity, the landscape model predictions of streamflow, and sediment and nutrient loads were as good as or better than those of the Hydrological Simulation Program‐Fortran model, one of the most widely used comprehensive watershed models. The landscape model was applied to predict discharges of water, sediment, silicate, organic carbon, nitrate, ammonium, organic nitrogen, total nitrogen, organic phosphorus, phosphate, and total phosphorus from the Patuxent watershed to its estuary. The predicted annual water discharge to the estuary was very close to the measured annual total in terms of percent errors for both years of the study period (≤2%). The model predictions for loads of nutrients were also good (20‐30%) or very good (<20%) with exceptions of sediment (40%), phosphate (36%), and organic carbon (53%) for Year 1.     

RELATION BETWEEN STREAM-WATER QUALITY AND GEOHYDROLOGY DURING BASE-FLOW CONDITIONS,ROBERTS CREEK WATERSHED,CLAYTON COUNTY,IOWA1

ABSTRACT: An investigation to determine the relation between stream water quality and geohydrology in the Roberts Creek watershed, Clayton County, Iowa, was conducted during selected base-flow periods in 1988–90. Discharge measurements were made and water samples collected for analyses of nutrients and selected herbicides in 19 subbasins along the main stem and tributaries of Roberts Creek. The areal extent of unconsolidated and bedrock units subcropping in each subbasin was quantified. The hydrologic data were correlated statistically with the geologic data to determine relations. Roberts Creek generally gained water and had larger nitrogen concentrations in subbasins in which bess and alluvial material were underlain primarily by low-permeability till and shale units. Roberts Creek generally lost water and had lower nitrate concentrations in subbasins with subcroppmg karstic units. Nitrogen concentrations decreased in streams underlain by the karstic units because the nitrogen removed by biological processes was not replaced by ground-water inflow. Seepage from Roberts Creek to ground water in areas of subcropping karstic carbonate rocks reduced the flow, which reduced the velocity, causing increased residence time of water in the stream. The additional residence time may allow additional time for biological processes to remove nitrogen from solution. There was no significant relation between dissolved orthophosphate or atrazine and the underlying geology.     

MODELING THE BUILDUP AND WASHOFF OF POLLUTANTS ON URBAN WATERSHEDS1

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.     

URBAN INFLUENCE ON PHOSPHORUS AND SEDIMENT LOADING OF WEST POINT LAKE,GEORGIA1

ABSTRACT: West Point Lake is a 10,360 ha mainstream impoundment of the Chattahoochee River located 95 kilometers downstream of Atlanta, Georgia. Origins and magnitude of external total phosphorus (TP) and total suspended solids (TSS) loads from the West Point Lake basin were estimated over a one-year period. Partitioning the drainage basin allowed the sources of these loads to be determined. The upper subbasin area, from Franklin, Georgia, to the headwaters of the Chattahoochee River, contributed 96 percent of the discharge and 97 percent of the TP and TSS loads into West Point Lake. The lower subbasin area, from Franklin to West Point Lake dam, only contributed 3 percent of the TP and TSS loads. Ninety-one percent and 87 percent of the TP and TSS loads, respectively, from the upper subbasin originated from the Atlanta area. Point sources discharged 70 percent and 3 percent of the upper subbasin TP and TSS loads, respectively. A large portion (66 percent) of the TP from the upper subbasin was in the bioavailable form.