Temporal and spatial patterns in salinity and suspended solids in a reservoir influenced by the Asian monsoon

Between April 1993 and November 1994, conductivity, cations, anions and suspended solids were measured at multiple sites in Taechung Reservoir, Korea. The major mechanism regulating ionic composition was dilution by monsoon rain and a resulting interflow current; these forces caused marked spatial and temporal heterogeneity. Ionic dilution was most pronounced in the headwaters during an intense monsoon in 1993 and was accompanied by an increase in the proportion of Na+ and Cl-, presumably from rainwater. A decrease of > 25% in conductivity and cations occurred during summer 1993 at the plunge-point due to a temperature difference between the lake water and an interflow. In contrast, the 1994 monsoon was weak, ionic dilution was not apparent, and spatial-temporal variation was modest. Overall reservoir salinity was a direct function of water residence time which is regulated by monsoon intensity. Differences in hydrology between years also influenced seston composition; inorganic suspended solids dominated total suspended solids in 1993, but in 1994 the organic fraction was the major component.