Douglas A. Haith

Nonpoint Source Pollution Control by Soil and Water Conservation Practices

ABSTRACT THERE has been a tendency to equate best manage-ment practices, as defined in water quality legisla-tion, with soil and water conservation practices. The effectiveness of SWCPs at controlling potential pollut-ants other than sediment depends on the characteristics of pollutants. Pollutants have been categorized in groups having distinctly different soil adsorption properties which have been related to the effect of SWCPs on water and soil movement.

Pesticide decay in turf: a review of processes and experimental data.

Decay rates are central parameters in modeling pesticide fate and transport in the environment. Pesticide decay is usually modeled as a first-order process, and variations in half-life can have significant impacts on model predictions. Decay rates for the foliage and thatch components of turf are scarce, and most simulation efforts must resort to values based on pesticide behavior in soil. This paper describes the main dissipation processes affecting pesticides applied to turf and compares aerobic soil decay rates from the USDA-Agricultural Research Service Pesticide Properties Database (ARS PPD; USDA-ARS, 2006) and from The Pesticide Manual (Tomlin, 2003) to dissipation values in turf found in the literature for 18 pesticides currently registered for turf. Median half-lives were 39.5 d for the ARS values, 35.8 d for Tomlins values, and 5.7 d for the turf-specific values. The turf dissipation half-lives are considered to be representative of the microbial decay processes occurring in the foliage and thatch layers of well established turf, where the majority of the pesticide is intercepted and retained.

An Event-based Procedure for Estimating Monthly Sediment Yields

ABSTRACT Asimple model is proposed for estimating the short-term sediment yields often needed in studies of nonpoint source water pollution and sediment control. The model consists of a two-stage computation which separately considers the generation of sediment supply and its subsequent transport by runoff. Inputs include daily temperature and precipitation records and parameters for the Universal Soil Loss and curve number equations. Testing over a 25-month period for an 850 km2 New York watershed indicated that the model explained 95% of the observed monthly variation of sediment yields

Ecological risk assessment of pesticide runoff from grass surfaces.

An ecological risk assessment was performed for runoff of 37 pesticides registered for use on grass surfaces (lawns and golf courses) in the U.S. The assessment was based on 100-yr simulations using TPQPond, a newly developed model of pesticide runoff and subsequent accumulation in a receiving pond. One-in-10 yr pond concentrations were compared with acute toxicity end points for fish, invertebrates, and algae. Simulations were performed for pesticides applied at label rates on lawns, fairways, and greens using weather data for nine U.S. locations. Runoff of 4 of the 37 pesticides produced potential acute risk to invertebrates or fish. Two chemicals posed a comparable danger to plants. Risk was highest with fairways and lowest for greens. Locations with long growing seasons and large amounts of precipitation produced the highest risks. The risk assessment followed the general protocols recommended by USEPA, but with different models, weather data, and scenarios. In spite of the differences, the results confirmed that most but not all of the pesticides which had survived the USEPA registration process were also demonstrated safe, with respect to acute risks, by this independent assessment. The five exceptions were explained by differences in models, simulation scenarios, and input data. These results do not mean that the studied pesticides are free of any ecological dangers. In particular, no attempt was made to evaluate chronic risk.

Models for Analyzing Agricultural Nonpoint-Source Pollution

Mathematical models are useful means of analyzing agricultural nonpoint-source pollution. This review summarizes and classifies many of the available chemical transport and planning and management models. Chemical transport models provide estimates of chemical losses from cropland to water bodies; they include continuous simulation, discrete simulation, and functional models. A limited number of transport models have been validated in field studies, but none has been tested extensively. Planning and management models, including regional impact, watershed planning and farm management models, are used to evaluate tradeoffs between environmental and agricultural production objectives. Although these models are in principle the most useful for policy making, their economic components are much better developed than components for predicting water pollution.

Evaluation of a Daily Rainfall Erosivity Model

ABSTRACT Amodel proposed by Richardson et al. (1983) for calculating erosivity from daily rainfall data was tested at 23 locations in eastern and central United States. Testing involved comparison with erosivities determined from hourly rainfall data by Wischmeier and Smith (1978). Model results for annual erosivities were generally consistent with Wischmeier and Smith values. Event erosivities produced by the model averaged approximately 80% of the Wischmeier and Smith values for 2, 5 and 20-year events. The model is easily calibrated and is an operational tool for erosion, sediment yield and nonpoint source pollution studies.

Nutrient Loads to Cayuga Lake, New York: Watershed Modeling on a Budget

AbstractNutrient loads were estimated for the 34 watersheds draining into Cayuga Lake, New York, through use of a watershed model. Financial and human resources were very limited for the project, but significant cost savings were achieved through project decisions. Chief among these were selection of a watershed model that did not require calibration and use of historic water quality monitoring data for model testing. Savings were also obtained by extrapolating soil properties from related information (nutrient contents from organic matter), substituting literature concentrations for missing point source data, extrapolating septic system performance from one area to another, and use of synthetic weather data generated from a model. None of the decisions was remarkable in itself, but together, they permitted a watershed study and its associated modeling to be accomplished with modest resources.

Volatilization of pesticides from golf courses in the United States: mass fluxes and inhalation health risks.

Golfers may be subject to chronic health risks from inhalation of vapors from pesticides applied to turf surfaces. The objective of this study was to provide a comprehensive evaluation of the volatilization potential of pesticides used on golf courses in the United States and to assess the resulting inhalation health risks. Long-term exposures were simulated using a fate and transport model for inhaled concentrations. The model was tested using data from field experiments for eight pesticides. Mean concentrations were overestimated by a factor of two, and the model explained 82% of observed variations. The model was subsequently used to estimate volatilization mass fluxes and air concentrations for 37 chemicals using weather information from nine climatic zones in the United States. Simulation results indicated substantial regional variations in volatilization fluxes, concentrations, and health risks, largely due to weather and pesticide application variations. Hazard quotients associated with chronic noncarcinogenic health risks were found to be less than 10 for all chemicals and locations. Similarly, carcinogenic health risks for the 10 pesticides considered likely or possible carcinogens were determined to be less than 10. Based on currently available levels of chronic toxicity endpoints for human health (chronic reference doses and cancer potency factors), we could find no evidence of health risk to golfers from inhalation of these 37 pesticides.

A Corn Yield Model for Operational Planning and Management

ABSTRACT A simple model is proposed for predicting corn yields as a function of hybrid, planting timeliness, growing season temperatures, moisture stress and frost occur-rence. The model is used in conjunction with a daily soil moisture balance model. Required meterologic data are daily temperatures, precipitation, and pan evaporation rates. Additional yield data such as hybrid factor and timeliness penalty are obtained from state field trial in-formation. Moisture stress parameters for each of three stress periods are estimated by model calibration. The model was tested in a two-stage calibration and valida-tion application in New York. Comparison of model predictions with measured crop yields showed errors of 3 to 8 percent in predicted yields.

A SIMULATION MODEL FOR ASSESSING THE SUCCESS OF AGRICULTURAL BEST MANAGEMENT PRACTICES ON SURFACE WATER QUALITY

A simulation model was used to assess how agricultural practices used to reduce soil erosion, such as no-till cropping, affect the plant nutrient and suspended sediment levels in streams. The model...