Effects of the summer monsoon on the distribution and loading of organic carbon in a deep reservoir, Lake Soyang, Korea

Seasonal and vertical patterns of organic carbon concentration, and an organic carbon budget were studied in a deep reservoir in Korea. Dissolved organic carbon (DOC) and particulate organic carbon (POC) were measured in the river inflow and at the dam. Autochthonous production of carbon was estimated from phytoplankton primary productivity. Variations in POC were greater than for DOC, reflecting pronounced changes in algal biomass during the study period. Before the monsoon, in spring and early summer, DOC concentrations consistently were low (ca. 1.5 mg l−1). Heavy rains associated with the summer monsoon had substantial impacts on the lake’s carbon budget. Turbid storm runoff supplied large quantities of nutrients and organic carbon to the metalimnion. Some of these substances were advected into the epilimnion, and may have contributed to a seasonal increase in primary productivity. Although annual rates of carbon supply from allochthonous and autochthonous sources were similar, the autochthonous carbon appears to be a more important energy source in the lake because most allochthonous carbon was discharged from the dam without affecting the epilimnion.