Spatial and temporal difference of primary productivity and its influencing factors in the Pearl River Delta

To evaluate the primary productivity in the Pearl River Delta, the spatio-temporal distribution of primary productivity and its relationship with environmental factors were investigated by multivariate statistical methods during March, June, September and December in 2015. The concentration of primary productivity (C) ranged from 98.81 mg·(m²·d)^-1 to 927.21 mg·(m²·d)^-1 with an annual average of 346.51 mg·(m²·d)^-1. The primary productivity varied in different seasons (spring> winter> summer> autumn).The annual average of primary productivity ranged from 232.60 mg·(m²·d)^-1 at Shiqiao to 600.61 mg·(m²·d)^-1 at Zhujiangqiao. Positive relationship was found between primary productivity and transparency, nitrogen and phosphorus as well as chlorophyll a(P < 0.01, n=52), whereas the primary productivity showed negative correlation with silicate(P < 0.01, n=52). The primary productivity and eutrophication composite index (EI) showed linear relationship. Compared with other watersheds, the Pearl River Delta was at medium or high eutrophication status with relative low primary productivity, so it is needed to prevent pollutions with a tendency towards heavy eutrophication.