Study on nutrient limitation of phytoplankton growth in Xiangxi Bay of the Three Gorges Reservoir, China.

After the impoundment of the Three Gorges Reservoir (TGR), algal blooms in the sidearm tributaries have resulted from increasing nutrient loads along the major tributaries. Field sampling and in situ nutrient addition bioassay were implemented to examine the nutrient limitation of phytoplankton growth and bloom initiation during autumn in Xiangxi Bay of the TGR. Result shows that P is the primary limiting nutrient for algal growth and bloom in Xiangxi Bay during autumn. The treatment involving the combination of N, P and Si had a significant (p < .05) additional effect on the growth of phytoplankton. The N, P, Si combined treatment increased growth by 10-50% relative to the N and P treatments from day 1 to day 4, respectively. Trace metal additions involving Fe, Zn, Mn, and Cu and/or in combination with N, P, and Si initially resulted in an extremely low growth rate which later increased significantly (p < .05) towards the end of the study. The present study provides an insight into the responses of different phytoplankton taxa in autumn under nutrient conditions in the tributary bay. The nutrient limitation study is recognized as the first step to mitigating the bloom while proposing an effective nutrient control strategy. The outcome of which can provide the basis for formulating sustainable watershed management. Multiple nutrients reductions with P as primary concern are required for a lasting management solution to the risk of bloom in the TGR.