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Primary productivity was determined by using 13C tracer according to different cell size of phytoplank-ton through in situ incubation experiments in upper stream of the Lake Shihwa. The average concentration of chlorophyll a was 14 μg L- 1 demonstrating an eutrophic water. The ratio of POC/Chl-a was lower than 30, reflecting that the origin of organic matter might be mainly phytoplankton. The primary productivity was 93.9 mgC m-2 d-1 at St. 1, which was about 40-fold lower than the average value of the lake (3,972 mgC m-2 d-1) determined by Choi et al. (1997) before opening of gate but it was higher than the average primary productivity (3.98 mgC m-2 d-1) reported by KOWACO in 1993 before constructing dam. The fractionated size (20~53 μm) of phytoplankton community account for 51% of total primary productivity, indicating the highest assimilation rate. This study suggest that 13C tracer methodology should be applied as a useful approach for the water ecological research in the future.


Primary productivity was determined by using 13C tracer according to different cell size of phytoplank-ton through in situ incubation experiments in upper stream of the Lake Shihwa. The average concentration of chlorophyll a was 14 μg L- 1 demonstrating an eutrophic water. The ratio of POC/Chl-a was lower than 30, reflecting that the origin of organic matter might be mainly phytoplankton. The primary productivity was 93.9 mgC m-2 d-1 at St. 1, which was about 40-fold lower than the average value of the lake (3,972 mgC m-2 d-1) determined by Choi et al. (1997) before opening of gate but it was higher than the average primary productivity (3.98 mgC m-2 d-1) reported by KOWACO in 1993 before constructing dam. The fractionated size (20~53 μm) of phytoplankton community account for 51% of total primary productivity, indicating the highest assimilation rate. This study suggest that 13C tracer methodology should be applied as a useful approach for the water ecological research in the future.