Three essays on watershed modeling, value of water quality and optimization of conservation management.

摘要

Conservation management practices are considered one of the best answers to escalating water quality deterioration by nonpoint source pollution. Integrated watershed economic model (IWEM) offers a multidisciplinary framework by addressing both the biophysical and the economic (cost and benefit) aspects of water quality improvement. An IWEM can be conceptualized as three sub-models: a watershed model, an economic model, and an optimization tool to integrate the watershed and economic models together. The present study is an attempt in this direction, by translating the three sub-models of IWEM into three essays of the dissertation. The Upper Big Walnut Creek (UBWC) watershed in central Ohio was selected for applying the IWEM framework.;The modeling of the UBWC watershed was performed in the first essay. For this study the Soil and Water Assessment Tool (SWAT) was used to predict the nutrient export associated with land management practices. Nitrate fluxes, calibrated using the field measured values at the two paired sub-watersheds, predicted nitrate loading was statistically not different from the measured values. Additionally, sensitivity and uncertainty of the model for flow and nitrate load were analyzed in detail. The uncertainty analysis showed that the model predicted flow and nitrate load was with the lowest uncertainty. Following calibration and validation of SWAT for UBWC, the SWAT model is qualified for predicting the impact of different management scenarios on nutrient loading.;Recreational value of water quality improvement is one of the major shares of economic benefits derived from water quality enhancement. Thus, recreational demand analysis was applied to UBWC watershed, which was described in the second essay. A survey method was used, in which 1400 registered anglers and licensed boaters in 5 surrounding counties of the watershed were selected for the study. The survey gathered a wide range of information from the visitors, which included the number of times they had visited the different zones of UBWC watershed during 2008, demographic variables, and details about trip activities. The results showed that the new information about water impairments in the watershed would shift the demand curve downwards, and that about water quality improvement would shift the demand curve upwards. The baseline average number of trips was 2.35, which was reduced to 1.72 with more information about pollution level in the watershed. However, water quality improvement would increase the number of trips to 2.78. The average annual consumer surplus was ;In the third essay, an integration tool was used for integrating the watershed and economic models presented in the above two essays. The watershed modeling results from essay 1 and the benefit estimates from essay 2 were used to specify the objective and transition functions of the dynamic program. The social cost of the pollution is parameterized with benefit estimates of water quality improvement. Model is developed for the entire watershed by considering it as a single homogeneous one hectare unit. The watershed model was used to simulate the baseline, and crop rotation and conservation technology-specific production functions. Two sets of conservation technologies were developed for the watershed. One with cover cropping, conservation tillage and vegetative buffer stripes and the other with split nitrogen fertilizer application, cover cropping, conservation tillage and vegetative buffer stripes. The analysis revealed that under no restriction on pollution loading, farmers would apply a maximum of 170.51kg/ha of N and the value function would be