Changes in Water Quality After the Construction of an Estuary Dam in the Geum River Estuary Dam System, Korea

We investigated long-term (1985-2009) changes in water quality due to the construction of an estuary dam in the Geum River Estuary Dam System, Korea. Both the upstream reservoir and downstream estuarine sides of the dam were examined. Water quality conditions for nutrients and chlorophyll a (Chl-a) have deteriorated considerably since the dam construction in 1994, with the reservoir water damaged more severely than the estuarine water. Improved water clarity and an enhanced level of nutrients resulted in an order of magnitude increase in Chl-a, indicating excessive phytoplankton growth in the reservoir after dam construction. The hydrology-related principal component (precipitation and discharge) was the most important and the autochthonous primary production-related principal component (nutrients and Chl-a) was the second most important factors affecting the postdam water quality conditions in both the reservoir and estuary. The cumulative load difference analysis revealed that the reservoir was a sink site for PO43- and NH4+ as well as a source site for Chl-a owing to excessive phytoplankton growth in the reservoir. The discharge from the reservoir dominated the estuarine water quality during wet seasons.