Numerical Simulation For Ammonia Nitrogen, Phosphate And Algal Production In The Dalian Bay

The dominating pollutants in the Dalian bay, such as ammonium nitrogen and phosphate, were the focus of attention in this paper. Based on the analysis of historical records and measured data, the three-dimensional hydrodynamics and water quality model have been established with numerical simulation technique. The distribution and variation of the hydrologic features and the main pollutants in the Dalian bay were repeated in the model. Qualitative analysis was applied on the influence of nutrient (as ammonium nitrogen and phosphate mainly) structure on alga production. The spatial distribution and seasonal variation of phytoplankton were simulated. The influence of the wastewater loads and the discharge stations on the water quality was predicted. The visualization of the water quality model was developed with Tecplot tools. It could be adopted in the coastal management of Dalian Bay.The simulation results implied that for the poor flow capacity of water in the existing outlet, the discharged pollutants are not diluted in time but accumulated and result in sea water pollution. In Bay tip diffusion is the main factor affecting the concentration of ammonia nitrogen, phosphate and alga carbon. In Bay mid, the nitrification consumption and the phytoplankton mortality decides the concentration of ammonia nitrogen and phosphate and the phosphate limits the alga production. Land loads supply the ammonia nitrogen primarily in Bay and the sea bed humus supplies the phosphate primarily in Bay mid and Bay mouth.The region of nutrient load influence on water quality is chiefly located in outlet area in Bay tip. The concentration of pollutant increases along with the load rapidly and the effect of the nutrient on alga production becomes weak gradually.The total land loads and the phosphate play the similar role on the algal production; they are stronger than ammonia nitrogen on the algal production. In the Bay tip the year average N/P value was higher than 16. The influence of ammonia nitrogen and phosphate on alga production indicated that phosphate is the limiting nutrient in algal production in Bay tip. Due to high nitrogen input, the N/P value will be very high; in case the high phosphorus input added, some kind algae blooming will be initiated. The alga production could be controlled through reducing the phosphate load.The different influence of various outlet positions on the water quality reflects water's self-purification in different region. If the outlet position was changed into the bay mouth with therich flow capacity, the pollution will be diffused and transported promptly by marine environmental dynamic effect but not accumulated around the point sources.