The objective of the study was to determine nutrition regime and limitation in the Boryeng Reservoir where there’s a water tunnel between Geum River and the reservoir. Evaluation was conducted through in situ algal bioassay experiments (in situ ABEs) using the cubitainer setting in the reservoirs. For in situ ABEs, we compared and analyzed variations in chlorophyll-a (CHL-a) and phosphorus concentrations in Boryeong Reservoir before and after the water tunnel construction. We then analyzed the nutrient effects on the reservoir. Analysis for nitrogen and phosphorus was done in the three locations of the reservoir and two locations of the ABEs. The in situ ABEs results showed that phosphorous and Nitrogen, the primary limiting nutrient regulating the algal biomass was not limited in the system. The treatments of phosphorus or simultaneous treatments of N+P showed greater algal growth than in the control of nitrate-treatments, indicating a phosphorus deficiency on the phytoplankton growth in the system. The water from the Geum River had 5 times higher total phosphorus (TP) than the water in the reservoir. Efficient management is required as pumping of the river water from Geum River may accelerate the eutrophication of the reservoir.

Trophic and tolerance gradients on the ranges of ambient nutrients (N, P) and other water quality were tested on two species of Zacco temminckii (Zt) and Zacco platypus (Zp). For water chemistry, trophic gradients and BIM model analysis, 76 streams and rivers were sampled during 2004 - 2005. The populations of Zt had a narrow tolerance with a low limit (< 300 μg L-1) over a phosphorus gradient, whereas the Zp occurred in high TP up to 1180 μg L-1. There was a 4-fold difference in mean TP between two species and the tolerance range of phosphorus in Zp was significantly greater than in Zt (t = 5.25, p < 0.001). The chemical tolerance of two species had a similar pattern in nitrogen and other chemical parameters. The proportion of insectivores co-occurred with Zt was > 40% and was nearly two times greater (p < 0.001) than was that co-occurred with Zp. The omnivores co-occurred with Zp were significantly greater (t = 9.74, p < 0.001) than those co-occurred with Zt. The model values of BIM co-occurred with Zt were significantly greater (t = 13.67, p < 0.001) than those of Zp. Overall data suggested that Zp have a wide range of chemical tolerance as tolerant species, trophic preference of omnivores, and survived even in degraded environments, whereas Zt have other trophic extremes of sensitive species, trophic preference of insectivores, and the low-nutrient regions with high BIM model values. This study was supported by the CAER (Center for Aquatic Ecosystem Restoration) of Eco-STAR project from MEK (Ministry of Environment, Korea).