The Study On The Exchange Characteristics Of Nutrients At The Sediment-Water Interface On The Coastal Waters Of Bohai Bay

Bohai Bay is a typically semi-enclosed sea bay with shallow water and mud silting. The water exchange between Bohai Bay and the outside sea is weak. Thus, it is difficult for the pollutants released in this water body to transport to the outside sea. In recent years, the economy has developed rapidly around the coastal zone of Bohai Bay. As a result, the water has been heavily polluted and the eutrophication problem has become more serious. Sediment serves as the source and sink of nutrients, and plays an important role in the budget and dynamics of nutrients recycling in the marine water. Therefore, the study on the exchange fluxes of nutrients between sediment and water interface in this typical sea area is necessary, and it has great significance for controlling the eutrophication and improving the water quality.In this study, the nutrients exchange flux between sediment and water interface at five stations in Bohai Bay was determined from the end of May in 2011, and the lab incubation experiment was adopted to simulate and measure the nutrients exchange flux under different conditions, like DO、pH、biological disturbance. It turned out that NO₃^--N was -0.65-5.00 mmol/（m²·d）; NH₄⁺-N was 0.85-6.85 mmol/（m²·d）; NO₂^--N was -0.18-1.61 mmol/（m²·d）; DIN was 0.96-10.70 mmol/（m²·d）; PO₄^3--P was -0.036-0.064 mmol/（m²·d）. The exchange flux of NO₃^--N, NO₂^--N, NH₄⁺-N and DIN in all stations were in oxygen-rich condition more than in oxygen-poor condition, while PO₄^3--P in all stations showed the opposite. The exchange flux of NO₃^--N, NO₂^--N and PO₄^3--P increased with the increase of pH value, while NH₄⁺-N showed the opposite, and there was no uniform relationship between DIN and pH value. The exchange flux of all the dissolved inorganic nitrogen salts showed under the condition without inhibitors above with inhibitor, and PO₄^3--P expressed the opposite.The eutrophication of the water quality at this collection stations in the Bohai Bay coastal were evaluated roughly according to the eutrophication evaluation model. The evaluation results showed that in spring the water in the sampling area of Bohai Bay coastal was still in the potential eutrophication stage. According to the Redfield ratio, we could use the average exchange flux of nutrients in all sampling stations to estimate that the DIN, PO₄^3--P from the release of the sediment and water interface in Bohai Bay can provide 174.5 % nitrogen, 0.3 % phosphorus for the primary production in the sampling stations, which received by the laboratory culture method. It indicated that only the dissolved inorganic nitrogen salts in the release of nutrients between sediment and water interface has an important contribution on the maintenance of primary production.