Modeling nitrate in tile-drained watersheds of east-central Illinois
Walker, Sharyl Elise
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https://hdl.handle.net/2142/23338
Description
Title
Modeling nitrate in tile-drained watersheds of east-central Illinois
Author(s)
Walker, Sharyl Elise
Issue Date
1996
Doctoral Committee Chair(s)
Mitchell, J. Kent
Department of Study
Agricultural and Biological Engineering
Discipline
Agricultural and Biological Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Hydrology
Engineering, Agricultural
Environmental Sciences
Language
eng
Abstract
Reservoirs in east-central Illinois are subject to nitrate contamination due to the agricultural nature of their watersheds. Field tile systems provide direct links between leached nitrate and surface drainage systems. The purpose of this study was to develop a model for predicting flow and nitrate loading in a surface drainage ditch at the outlet of a tile-drained watershed. In particular, relationships were developed for the upper portion of the Little Vermilion River Watershed in Champaign County, Illinois. The Root Zone Water Quality Model (RZWQM) was used as a tool in model development.
A sensitivity analysis was performed for RZWQM to identify input parameters with the greatest influence on simulated tile drain flow, tile nitrate, and crop yield. Results guided calibration of the model for two tile-drained sites, using 1993 measurements of tile flow and nitrate loading. Linear regression models were presented for relating measured surface drainage ditch response to measured tile system response. The analysis led to consideration of watershed outlet response as a linear combination of field tile system inputs and drainage flowing directly to the surface drainage system. Coefficients for the linear model are related to drainage characteristics of the watershed and appear to be influenced by rainfall patterns. Use of the linear model for evaluating alternative fertilizer practices was demonstrated. Recommendations were made for improving RZWQM and for applying the model to Georgetown Reservoir, located downstream of the site investigated.
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