Study On Distribution Of Nutrients And Exchange Of Nutrients At Sediment-Water Interface In Tianjin Coastal Area

The exchange of nutrients at the sediment-water interface plays a crucial role inthe marine nutrients cycle. Bohai Bay is a typically semi-enclosed sea bay withshallow water and mud silting. As the rapid development of economy around BohaiBay, a huge amount of waste water is discharged into this sea bay every year, whichresults in the environment of the area being under great pressure. In this paper,nutrients exchange fluxes at the sediment-water were simulated using the sedimentcolumn samples collected from the Tianjin coastal zone in the Bohai Bay, and thedistribution of nutrients in this sea bay were evaluated through the field observation.Field survey were carried out in May2012, and the samples of bed sediment andwater were analyzed. The analyzed results show that in the pore water of the sediment,the concentrations of NO3-N, NO2-N and DIN decrease as the depth increases. Whilethe concentration of NH4-N and PO4-P increase with the increase of the depth at first,then, it decreases with the increase of the depth. The concentration of SiO3-Siincreases with the increase of the depth at first, then, it decreases slightly or stable asthe depth increases. At the four stations, the exchange flux of NO3-N is0.164-0.195mmol/(m2d), NH4-N is-0.0379-0.00266mmol/(m2d), DIN is0.18-0.267mmol/(m2d), PO4-P is0.000975-0.00217mmol/(m2d) and SiO3-Si is0.133-0.133mmol/(m2d). It was found that the exchange fluxes of nutrients evaluated with theconcentration gradient in the pore water are lower than the results of the laboratoryexperiment.The experimental results show that the sediment is a source of NO3-N, DIN andSiO3-Si. However, the sediment can be a source or a sink of NH4-N and PO4-P. Theexperimental results under different environment conditions show that under theaerobic condition the exchange fluxes of NO3-N, DIN and SiO3-Si at all stations aremuch higher than that under the anoxic condition, while NH4-N and PO4-P at allstations show the opposite trend. The exchange fluxes of NO3-N, NH4-N, DIN andSiO3-Si under the condition without inhibitors are higher than that with inhibitor, andPO4-P shows the opposite trend. The contribution of the exchange fluxes of nutrientsat sediment-water interface to the water body are obvious, with the potentialcontribution rate of NO3-N is6.67-10.7%, NH4-N is-10.1-20.0%; DIN is5.95-10.1%, PO4-P is6.55-14.8%and SiO3-Si is11.1-17.5%.