Distribution Patterns And Bigeochemical Implications Of Oxygen Isotope Composition In Dissolved Phosphate And Phosphate Of Different Species In Sediment In Jiulong River Estuary

Phosphorus is a essential nutrient for all living organism, but analytical tools to trace phosphorus sources and cycle are limited. In the absence of biological activity and enzymatic hydrolysis, isotope exchange between phosphate oxygen and water is slow and can be considered negligible for the time scales for concern of most environmental applications. Oxygen isotopes composition in phosphate (δ18Op) as a tracer can be utilized to determine the phosphorus sources and the degree of phosphorus cycling within the biomass. In the past decade,δ18Op has been well applied in tracing phosphorus cycle in open ocean, estuary and soil. Riverine input as the main source for the ocean can be easily influenced by the phosphorus cycle in the estuary. Most studies focus on the distribution patterns of phosphorus of different species in estuary, but few studies report the phosphorus source and transformation in different species in the estuary.This study has developed the measurement of oxygen isotopes composition in phosphate of4inorganic species in sediment in estuary. In order to determine no oxygen isotopes fractionation in phosphate in the procedure of extractions, separation and purification, we choose KH2PO4solution and international phosphorite standard (NBS-120c) to achieve pure Ag3PO4through this procedure. To determine the accuracy of δ18Op of different species in sediment, we choose a natural sediment sample in Shishi coastal area. The results show that the accuracy is sensitive and different δ18Op values are variable in phosphate of different species.An analysis assessing variations in the oxygen isotopes composition of dissolved inorganic phosphate (DIP) in surface water was conducted in Jiulong river estuary in October,2013. The results show that the δ18O values of DIP in the river end-member and ocean end-member are closely to the equilibrium value. According to the δ18O values of DIP retaining the original values of sources, phosphate point source inputs can be find in the Longhai city (station A5), the South river (station A8), Xiamen first wharf (station X2), tributary in Humao Bay (station X7). The δ18O values of DIP in groundwater near Jiulong river estuary are close to the equilibrium value. But the δ18O values of DIP in surface water during rainstorm event are much higher than the equilibrium value. Those results show that δ18O values of DIP in Jiulong river are sensitive to the environmental changes.High concentration of phosphorus is in surface sediment, especially organic phosphorus, in Jiulong river estuary after rainstorm (10days later) in July,2013. The δ18O values of loosely-sorbed phosphate and Fe-bound phosphate have the characteristic of low value in river end-member and high value in ocean end-member, with same change trend with the δ18O values of DIP. The δ18O values of authigenic phosphate and detrital phosphate are close at the same station, but lower than δ18O values of DIP, with the no clear deviation in river and end-member and terrigenous characteristics.