The four seasons nutrients distribution in Changjiang River Estuary and its adjacent East China Sea

The distribution of nitrate(NO-3)、nitrite(NO-2)、ammonium(NH+4)、phosphate(PO3-4)、 silicate(SiO2-3) recorded during the four cruises(2006 summer and winter,2007 spring and autumn),indicates that surface nutrients were high in west and low in east,NO-3、PO3-4 and SiO2-3 in Changjiang River Estuary and Hangzhou Bay behaved as double tongue pattern in all seasons,which was regulated by Changjiang River dilution water and offshore water mixing.In summer,nutrients expanded northeast at the river mouth due to Changjiang River dilution water turning northeast,while there was no such behavior in other seasons.NO-2 and NH+4 was obvious point source diffusion effected by Shanghai City sewage outfall.The high value area of NO-2 at 122.5°E to 125°E in autumn was caused by high concentration nutrients that regenerated from bottom organic matter and brought to the surface through vertical mixing.In winter,the nutrients contour was closer to coast than that in summer due to Kuroshio water invasion into the shelf.Section distribution of NO-3、PO3-4 and SiO2-3 was mainly controlled by vertical mixing in spring,while the seawater stratification was obvious in summer,which began to be broken up in autumn,and vertical mixing turned to be dominated.In winter,the nutrients distribution was almost uniform from surface to bottom.NO-2 and NH+4 didn't present fierce seasonal variation like other nutrients.Influenced by the sewage outfall diffusion,the coastal areas of M1 and M4 sections presented high concentration of NO-2 and NH+4.