The impacts of Tongkong River Weir in Taiwan Pingdong on the groundwater contamination and aquaculture
台湾屏东县东港溪拦溪对其周边地下水水质及水产养殖的影响

Seawater intrusion problems occur along almost the entire western coast of Taiwan, and often cause ground water contamination and affect the health of cultured organisms. In the coastal town of Hsinyuan, Pingtung County, southwestern Taiwan, these problems progressed much faster. A river weir built to extract subsurface water from the Tongkong River was suspected of causing these problems, so a study evaluated the effect of the weir on groundwater quality. Hsinyuan and the nearby town of Chiatung were used for comparison. Groundwater quality and water table contour line data before and after construction of the weir were analyzed. Samples of well water, pond water, plankton, and cultured fish (Japanese eel Anguilla japonica) and shrimp from ponds in these five regions were collected and analyzed on a monthly basis. An aquarium test using groundwater from each region to raise Japanese eel fingerlings was also conducted. These results were combined to evaluate the influence of the groundwater quality of each region on the health of cultured fish. The results revealed that construction of the weir lowered the groundwater table, and caused contaminated river water and seawater to intrude into groundwater of the Hsinyuan area, adversely impacting the health of cultured fish. These results suggest that the groundwater drawdown rate of the Tongkong River should be reduced in the dry season. Additionally, aquaculture activities along the western coast must be reduced, especially in the Hsinyuan area. Some other solutions are also proposed. This study further shows that Japanese eel is a reliable environmental biomonitor.