Distribution and pollution assessment of nitrogen and phosphorus in surface sediments of Nanao Coast, Shantou

In order to understand the spatial distribution of nitrogen and phosphorus as well as the mechanism of nutriment cycle from sediments,28 surface sediments samples were collected from mariculture areas of Nanao island and its coastal waters.The concentrations of total nitrogen(TN),total phosphorus(TP)and their fractions were investigated by adopting the European standard SMT(The Standards, Measurements and Testing)method.Single standard index method was used to assess the pollution level of nitrogen and phosphorus in sediment. The results showed that the mean concentrations of TN and TP were(663.46 ± 106.06)mg/kg and(467.72 ± 113.00)mg/kg, respectively.Meanwhile,the mean TP content of fish culture zone was up to(858.25 ± 20.63)mg/kg,which was significantly higher than those of other coastal waters in China and abroad.Inorganic phosphorus(IP)was the dominant portion of TP in all sampling sites, which occupied 63.74%-88.52% of TP,whereas HCl-P was the major contributor of IP,which occupied 57.46%-71.72% of TP, followed by NaOH-P which accounted for 4.04%-32.71% of TP. NaOH-P including Fe-P and Al-P,which were the prevalent forms of bioavailable phosphorus,can be used to estimate the interior release capability of sediments.Single standard index method indicated that the content of TP was overall low in the sediments of Nanao coast,except the fish culture zone.However,the content of TN was high where all of the single standard indexes were above 1,indicating that nitrogen pollution was relatively serious.