Major nutrients and chlorophyll dynamics in Korean agricultural reservoirs along with an analysis of trophic state index deviation

The main objectives of this study were to determine how Asian monsoon influences nutrient regime, suspended solids, and algal chlorophyll (CHL) in 182 agricultural reservoirs, and then to develop the empirical models of nutrients-chlorophyll. The intensity of summer monsoon directly determined the ambient concentrations of nitrogen (N) and phosphorus (P). Regression analysis of empirical model showed that CHL had a high linear relation (R2 = 0.716, p < 0.01) with total phosphorus but a weak relation (R2 = 0.041, p < 0.01) with total nitrogen. Seasonal empirical models of TP-CHL showed that the regression coefficients in premonsoon (R2 = 0.605) and postmonsoon (R2 = 0.554) were greater than that of the monsoon. Values of trophic state index (TSI) implied that phosphorus limitation was severe in the Korean agricultural reservoirs. Overall, our study of 182 reservoirs suggested that phosphorus was key nutrient regulating the phytoplankton growth. This phenomenon was supported by the analysis of trophic state index deviation relations of “TSI (CHL)−TSI (SD) < TSI (CHL) – TSI (TP)”.