| Public concern over groundwater quality has grown significantly in recent years and has focused increasingly on agriculture as a source of groundwater quality problems. Increasing evidence of nitrate contamination of groundwater beyond the maximum contaminant level has intensified the need for developing protection alternatives. Such alternatives include the restrictions on fertilizer use and manure handling. Through the adoption of these alternatives it is possible to satisfy the groundwater quality objectives in terms of reducing nitrate occurrences in groundwater.; To efficiently utilize the protection alternatives, it is important to evaluate the spatial distribution of on-ground nitrogen loadings and the corresponding nitrate leaching to groundwater. Regional management of groundwater quality is complicated by the fact that nitrogen sources are highly spatial. The knowledge of the spatial distribution of nitrogen loading can identify the areas where groundwater needs to be protected. This assessment is of great importance in designating areas that can benefit from pollution-prevention and monitoring programs. This proper discernment of on-ground nitrogen loadings enables the accurate quantification of nitrate leaching. Accurate quantification of nitrate leaching is difficult because of the complex interaction of land use, on-ground nitrogen loadings, recharge, soil nitrogen dynamics, soil characteristics, and depth of soil. When conducting a regional-scale analysis, it is essential to understand the interaction of the aforementioned factors to account for the transient and spatial variability in nitrate leaching to groundwater. The current research focused on developing an approach to determine aquifer sustainability in terms of optimal on-ground nitrogen loading distribution such that nitrate concentrations are below the maximum contaminant level. The proposed approach integrated on-ground nitrogen loadings from different sources, soil transformations of nitrogen, and a groundwater nitrate fate and transport model. Afterward, the integrated simulation models were utilized in developing an optimization framework to optimally determine the sustainable on-ground nitrogen loading distribution. By determining these sustainable limits, protection alternatives can be introduced to areas where nitrogen loadings exceed these limits. Protection alternatives were developed such that the on-ground nitrogen loadings will be reduced to the optimal loadings. (Abstract shortened by UMI.)... |
