Variations of nutrients concentration in surface seawater in adjacentarea of Weizhou Island in recent 10 years

Thedistnibution of nutrients in surface seawater in adjacent area of Weizhou Island was analyzed based ondata obtained from30 surveys from 2004 to 2013.Theresult showed that the concentrationsof DIN and PO4-Pinseawater decreased gradually in onder of winter,autumn,and summer.However,the concentration of SiO³-Sishowed no obvious seasomal vanation.Becauseof the terrestrial input,the inter-aunnual DIN waried greatly andshowed anupgrade tendency.NOz-N showed thesameannual fluctuationas DIN and contributed mostlyto DIN.The annual mean concentration of NH4-N and SiO¹-Si decreased slightlywhile theannual mean concentration of PO4-P increased fistly before it decreased.Further analysis of the nutrients limitation for phytoplankton gowthimplied that theadjacent waters of Weizhou Island was in oligotmophic status of PHimitation.In recent 10 years,Si/N ratio gradually decreased and N/P ratio decreased firstly and then increased,which may change the phyto-plankton community structure.