Graduation date: 1998Land application of industrial wastewater with high levels of nitrogen requires\ud adequate management practices to prevent groundwater pollution by nitrates. In this study\ud a predictive computerized model was developed for nitrate leachate concentrations\ud resulting from land application of wastewater onto crop systems including poplars. The\ud study included a literature review, development of a computer program that could serve\ud this purpose, and a field investigation to test the validity of the computed predictions. The\ud literature review focused on poplar water and nitrogen uptakes, and suggested that mature\ud poplars could uptake up to 400 lb of nitrogen /acre/year and 2 3 million gallons of water\ud per acre per year.\ud The computer model, based on 10-day water and nutrient balances, takes into\ud account a number of parameters such as wastewater quality, evapotranspiration and\ud precipitation data, irrigation volumes, soil water holding capacities, fertilization, crop\ud nutrient uptakes and crop coefficients. This study involves a number of assumptions\ud selected to give conservative (i.e., worst case approach) model predictions.\ud Attempts to validate the model were conducted through soil and groundwater\ud sampling along with precipitation data collection in four distinct fields in Brooks, Oregon,\ud from October 1996 to April 1997. The variations in nitrogen soil profiles from October to\ud April helped determine the amount of nitrogen leaving the soil, and groundwater samples\ud from 5 feet deep wells gave nitrate concentrations in groundwater below the root zone.\ud A sensitivity analysis of the program demonstrated how important nitrogen and\ud water uptakes values were to the model predictions. An increase of 1% in nitrogen uptake\ud or of 0.4% in crop coefficients generated 1% decrease in nitrogen concentration of the\ud leachate. These results are important to consider when adopting highly uncertain literature\ud values for crop uptakes -especially with poplars.\ud The field validation of the model showed promising results in terms of estimating\ud average yearly leachate concentrations in nitrogen resulting from land application of\ud wastewater, but also suggested that more groundwater wells were needed to obtain a\ud statistically significant validation of the model. These preliminary field results indicate that\ud the model can provide an indication of groundwater nitrogen concentration trends but\ud needs to further verified to be used confidently as a predictive tool
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