Distribution in the stable nitrogen isotope of the suspended particulate organic matter in the Yangtze River(Changjiang) estuary,China and its biogeochemistry implications

In this paper,δ15N of suspended particulate matters(SPM) in surface water was studied during four seasons of 2006 in the Yangtze River estuary.Based on the variations of δ15N in different seasons and geographical regions,the biogeochemical processing of nitrogen transformation was studied and its environmental implications were also revealed.In this paper,the mechanism of nitrogen cycle was explored in the Yangtze River estuary.The results show that δ15N of SPM was in a wide range of 0.6‰ and 8.2‰,varying with seasons and geographic regions.The temporal and spatial variation reflected different influences of terrigenous inputs and nitrogen biogeochemical processing.In the inner estuary,δ15N was affected mainly by riverine inputs from the Yangtze River.In the turbidity maximum zone,SPOM was affected by microbial degradation obviously,indicating the control of the decomposition processing of SPOM in δ15N during four seasons.In the adjacent marine area,the influence of terrigenous inputs weakened and δ15N was controlled by inorganic nitrogen assimilation by phytoplankton and the decomposition of SPOM.