NITROGEN AND PHOSPHORUS RELATIONSHIPS TO CHLOROPHYLL A IN 139 RESERVOIRS OF CHINA

Some reservoirs in China have recently become polluted and eutrophic. Few studies have focused on the relationships between chlorophyll a (CM) and the nutrients or nutrient limitation in reservoirs. We analyzed the relationships of nitrogen and phosphorus with CM in 139 reservoirs in China using data from the China Knowledge Resource Integrated Database to reveal the response regulation of CM to the nutrients in reservoirs and to identify the effects of phosphorus and nitrogen on Chl at varying total nitrogen (TN): total phosphorus (TP) ratios. Results of linear least square regression and stepwise multiple regression predicted lower Chl concentrations from nutrition than in lakes, and Chl was found to be significantly related to TP or TN whether the reservoirs were divided into three categories based on their sizes (large, medium, small) or based on their regions (South, Middle, North). TN was found to be a better predictor of CM than TP in small reservoirs and in reservoirs in southern China, which differs from the nutrient limitation assessment criterion by Sakamoto (10-17). The difference can also be found in reservoirs in the middle categories (17 < TN:TP <= 25) based on the TN:TP ratio. We can therefore argue that the TN:TP ratio is not always an appropriate index for determining nutrient limitation in some reservoirs in China.