Abstract In Taiwan, non-point source (NPS) pollution is one of the major causes of the impairment of surface waters. The Kaoping River Basin is the largest and the most intensively used river basin in Taiwan. In the Kaoping River Basin, most of the upper catchment is used for agricultural activities including cropland and livestock farming. In this study, I-Liao Creek watershed, one the major sub-basin of Kaoping River Basin, was selected to study the impact of NPS pollution on river water quality. An integrated watershed management model was applied to investigate potential NPS pollution management plans in the I-Liao Creek watershed. Based on the results from the field investigation and model simulation, the overall ammonia-nitrogen loading to the I-Liao Creek watershed was approximately 92,117 kg/year. The following remedial strategies have been taken to reduce the impacts of NPS pollution on the water quality of Kaoping River and I-Liao Creek: application of best management practice for NPS pollutant control; application of natural treatment systems for stormwater runoff treatment; and construction of the watershed geographical information system (GIS) and real time water quality monitoring system to effectively manage the watershed. Linking land utilization information with the NPS pollution simulation model may further provide essential information of pollution potential of NPS pollution for all sub-regions in the river basin. Experience obtained from this study will be helpful in designing the watershed management and pollution control strategies for other similar river basins.

The Kaoping River watershed is the largest and the most intensively used river basin in Taiwan. It is 171-km long, drains a catchment of more than 3,250 km2. Both point and non-point source (NPS) pollutants are now the causes of biochemical oxygen demand (BOD), nutrients, and suspended solids (SS) in the river. The main water pollution sources are livestock wastewater from hog farms, municipal wastewater, industrial wastewater, and NPS pollutants from agricultural areas. After the implementation of the hog ban in the Drinking Water and Source Water Protection Area (DWSWPA), all of the half million hogs have been removed or relocated in 2001. Thus, the municipal wastewater and NPS pollutants become the major concerns after 2001. In this study, the potential NPS pollution sources located in the Kaoping River watershed are investigated. Investigation results show that there are 827 potential pollution incidents, which cover 2,610 hectors in the Kaoping River watershed. Orchard farms are the major potential pollutant sources, which cover 60% of the total area of the potential pollutant sources. Moreover, results reveal that mango and betel palm farms dominated the illegal farmland areas, and are scattered around the river corridors. Field investigations indicate that major BOD, total phosphate (TP), total nitrogen (TN), and SS loadings came from the betel palm and orchard farms. The calculated total loadings of BOD, TP, TN, and SS are 69,000, 9,200, 58,500, and 487,500 kg/yr, respectively. Among the four major reaches (Lo-Non, Chi-San, Chu-Ko, and I-Lao creeks), the Lo-Non creek discharge the major pollutant loadings into the Kaoping River. Thus, the highest degree of protection is given to the Lo-Non creek. An integrated watershed management model was applied to investigate potential NPS pollution management plans in the Kaoping River watershed. Based on the results from the field investigation and model simulation, the following remedial strategies have been taken to reduce the impacts of NPS pollution on the water quality of Kaoping River: application of best management practice for NPS pollutant control; application of natural treatment systems for stormwater runoff treatment; and construction of the watershed geographical information system (GIS) and real time water quality monitoring system to effectively manage the watershed. Linking land utilization information with the NPS pollution simulation model may further provide essential information of pollution potential of NPS pollution for all sub-regions in the river basin. Results and experience obtained from this study will be helpful in designing the watershed management and NPS pollution control strategies for the Kaoping River watershed and other similar river basins.