Monitoring of Expansion and Withering of Salix subfragilis Communities in Namgang Dam Reservoir

Abstract

The water depth of Namgang Dam Reservoir is shallow and the water level fluctuation is relatively small, because it is located in a midstream plain of the Nam River. These conditions of Namgang Dam led to the growth of Salix subfragilis communities. Initially, they were distributed over small areas but over time, they rapidly proliferated to cover large areas. They generate large amounts of leaf debris particularly in the dry season, so that water quality could be deteriorated. And, in the flood season, they raise water levels by obstructing the water flow in tributary streams, this consequently leads to flooding damages. In addition, Salix subfragilis periodically undergoes self-thinning and the withered trunks and branches turn into driftwood. These problems pose difficulties to dam management. By the way, these communities began to wither in areas lower than the highest water level, after a long-term period of inundation in 2012. To determine the reason for the withering phenomena in this study, the relationship between water level(turbidity) and the withering of Salix subfragilis in dam reservoir was investigated, and the withering characteristics of Salix subfragilis communities were analyzed through aerial photographys and field surveys. Results of this study show that disruption of photosynthesis due to high turbidity during the long-term inundation is what was caused their withering.