Since 2008, the ROC Environmental Protection Administration (EPA) has carried out various plans of water quality improvement for rivers and reservoirs in Taiwan. In order to achieve the goal, the tasks of this project include :(1) analyzing the data of water quality collected from reservoir in order to propose reservoir water quality index; (2) presenting water quality improvement strategies for eutrophication potential reservoirs; (3) establishing Total Maximum Daily Load (TMDL) procedures and developing a plan for TMDL implementation, (4) reviewing literature on trophic state index of reservoir; (5) holding consultations with the departments involved. Literature on trophic state index from USA, Japan, and Korea is reviewed. The monitoring data of the 20 reservoirs between 1995~2015 indicated that Carlson trophic state index is unsuitable for Taiwan reservoir water quality management due to the influence of suspended solids (SS) concentration. The water qualities of four eutrophication potential reservoirs (Mingde Reservoir, Shimen Reservoir, Jingmian Reservoir, and Mudan Reservoir) are investigated and evaluated based on the monitoring data in 2014 and the water quality improvement strategies of the four reservoirs are presented in this project. The EPA, local government of reservoirs, and the experts discussed the water quality improvement strategies and watershed management of the four reservoirs. The TMDL for phosphorus and a load reduction strategy were developed for Shimen Reservoir. The simulated results indicate that the average annual total phosphorus (TP) loading into the reservoir is 32,014 kg/year, which consists of non-point source loading of 27,044 kg/year, and point source loading of 4,990 kg/year. The Vollenweider mass balance model was used next to determine the trophic state under current pollutant loading and the load reduction needed to keep the reservoir from being eutrophic. It is estimated that Shimen Reservoir can become the mesotrophic state if its average annual TP loading is reduced by 30.7% or more. The results provide the basis on which an integrated control action plan for both point and nonpoint sources of pollution in the watershed can be developed.

Reservoir, Trophic State Index, TMDL