Distribution features of nutrients and nutrient structure in the Changjiang estuary in spring and summer

Based on the data of surveys during spring(May) and summer(August) from the Changjiang Estuary in 2009,the distribution characteristics of nutrients(DIN,SiO32——Si,PO43——P) and nutrient structure and its influencing mechanism were analyzed,meanwhile,the pollution level was evaluated.The results showed that: the distribution characteristics of DIN,SiO32——Si decreased from inshore areas to the open sea in surface and bottom waters,in spring and summer,the distribution of PO43——P was characterized by the buffer mechanism.The concentrations of nutrients were lower in spring than in summer.NO3-_N was the predominant species of DIN;DIN、SiO32——Si was sourced by runoff,PO43——P was regulated by many kinds of source.SiO32——Si/PO43——P,DIN/PO43——P value was higher than Redfield value with the characteristic of ratio of nutrient imbalance.The distribution of three kinds of nutrients was uneven in the Changjiang Estuary.Analyzed on the ratio of phytoplankton to absorb DIN/PO43——P,PO43——P was the potential limited factor in spring and summer.The eutrophication index of the Changjiang Estuary was higher than eutrophication threshold.