Numerical Simulation Of DIN&DIP Distribution In Yueqing Bay And Their Response To Important Coastal Engineerings

Yueqing Bay, one of the most large three bays of Zhejiang, is rich in resource, which is exploited more and more frequently with the increasingly development of the social economy. In the past thirty years, with reclaimed area in the bay increasingly growing, contaminants excluded into the bay increasing rapidly and going up of fertilizer used for agriculture, cage culture and fishpond cultivation, the total nutrients amount in Yueqing Bay was growing speedily which resulted in the eutrophication in the bay becoming serious.The Delft3D Modal was used in the paper. First, the region tidal current field was calculated and by comparing with the matched monitoring data, it proved that the result of calculation tallied well with the fact. According to water quality monitoring data in the bay, NO₃^- and PO₄^3- are selected to be studied to represent the DIN and DIP in the bay. Based on the above, the distribution of COD_cr, NO₃^- and PO₄^3- after the Xuanmen First-stage & Second-stage Engineerings are simulated, the result of which was compared with the mean concentration of monitoring points in the bay which proved that the simulation was successful.Using the above information, the distribution before and after the Xuanmen Blocking Engineer and the reclamation engineerings planned in the near future in Yueqing Bay of the water exchange half-life time, mean concentration of NO₃^- and PO₄^3- were calculated. Furthermore, the the response of DIN, DIP and water exchange half-life time to these important coastal engineerings were analyzed. In the end, it came out the result as followed:The influence of the Xuanmen Blocking Engineering on the water exchange half-life time was mainly near the bugle-like area to the west of the construction site, the most increment of which was about 36h. In the rest area of the bay the increment is no more than 12h and near the bay-mouth existed reducing area because of the increment of water flux there; after the engineering, the flow route and direction of the material in the bugle-like area to the west of the construction site and part of the northern bay was changed, the biochemical change in which would adjust correspondingly, the concentration amplitude of NO₃^- was 50%(0.2mg/l⁰.3mg/l). And in the mouth of the bay, the concentration of NO₃^- increased about 35%(0.1mg/l). In Xuamen Bay, the concentration of NO₃^- reduced 90%(0.1 ⁰.3mg/l) corresponding to the blocking; Moreover, as a result of the change of transportation and biochemical progresses, the concentration of PO₄^3- in the middle and top of the bay increased 45%(0.01mg/l⁰.015mg/l) and the most amplitude, 55%, was near the blocked mouth. In area near the bay-mouth the increment of its concentration was about 0.005mg/l, the relative amplitude of which was about 50%. And in the Xuanmen Bay, the concentration reduced 85 %(0.01mg/l⁰.025mg/l).After the reclamation engineerings planned in the near future, the water exchange half-life time in the top of Yueqing Bay increased 5 days, that in the middle were 2³ days and 1 day in the mouth, which indicated that the water exchange capability was obviously weakened because of the reduced sea area and storage capacity for tidal water. After the reclamation engineerings, the mean...