Numerical Simulation Of Nitrogenous Migration And Transformation In Tianzhuang Reservoir

Tianzhuang Reservoir is an exclusive large-scale reservoir in Yiyuan county. With the continual development of society and economy, large numbers of companies were constructed around the reservoir, which discharged more and more contaminations into it. It aggravated the water pollution of the reservoir, and restrained the reservoir from exploiture. Although there were numerous rivers in Yiyuan County, many of them were seasonal rivers. Increase in population made freshwater in the county scarcity. Therefore, it's necessary to meliorate water quality of Tianzhuang Reservoir, for which could be use as drinking water resource.Based on fieldwork and data collection, the study monitored and sampled in the field in July and November 2005, April and September 2006 respectively, analyzed all the samples in the lab, and investigated water pollution states both in Tianzhuang reservoir and pollution sources systemically. And then two-dimensional water quality model was developed to simulate the important level of the different pollution sources for ammonia and nitrate by applying sensitivity analysis and model the temporal-spatial distribution of ammonia and nitrate of the reservoir in different hydrological years. Towards the main pollution sources the relevant measures were raised and predicted by the model respectively. Some new understanding and conclusions are drawn.⑴The concentration of nitrogen in Tianzhuang Reservoir is high, and the concentration of ammonia preponderate over the III grade of'environmental quality specification of surface water'(GB 3838-2002) 1.5 times. The different forms of nitrogen in the reservoir transformed more obviously in cross section than in longitudinal profile.⑵By sensitivity analyze of the main pollution sources, it's indicates that nitrogen releasing from sediments and agricultural diffuse are the most important pollution resource of ammonia and nitrate respectively. The sensitive sequence of ammonia pollution sources in high water season is nitrogen releasing from sediments, pollutants discharging from fertilizer plant, agricultural diffuse, leachate from fly ashes, and in least water season is nitrogen releasing from sediments, agricultural diffuse, pollutants discharging from fertilizer plant, leachate from fly ashes. The sensitive sequence of nitrate pollution sources is agricultural diffuse, leachate from fly ashes, pollutants discharging from fertilizer plant.⑶The simulate results of the nitrogen concentration in different hydrological years indicate that the ammonia concentration in dry year is highest, in mean year takes the second place, in wet year is lowest. The concentration of nitrate in high water season in wet years is highest, in mean year take the second place, and in dry year is lowest. The concentration of ammonia and nitrate in least water season is higher than in high water season in the same hydrological years. In different hydrological years the concentration of ammonia in the eastern region of the reservoir is higher than the western region of the reservoir. The concentration of ammonia in region with larger nitrogen fluxes releasing from sediments is higher than in region with less nitrogen fluxes.⑷When the agricultural diffuse loading released 30% or 60%, the concentration of nitrate would reduced 21% or 49%. The mid-eastern field of the reservoir is affected greatly by leachate from fly ashes, the difference in nitrate concentration is 0.20~0.50mg/L, before and after the stacking area was relocated. The stacking area which accumulates fly ashes should be migrated from the bank of the reservoir.⑸When the fertilizer plant stop discharging pollutions into the reservoir, the concentration of ammonia would reduced 0.13~0.27mg/L. When sediment capping is taken in partial region, the concentration of ammonia in high water season is up to par. The north and middle oscula are important for discharging, it's significant for improving the water quality to adopt sediment capping in these areas.⑹On basis of hydrological data of three typical hydrological years, nitrogen fluxes releasing from sediments and the concentration of ammonia in rivers, ammonia environment capacities in high water season of wet, mean and dry years are calculated by model trial method, which respectively are 569.35 kg/d,383.58kg/d,278.19kg/d,ammonia environment capacities in least water season respectively are 216.05kg/d,159.94 kg/d,144.76kg/d. It's showed that there is no superfluous ammonia environment capacity in least water season, and the ammonia pollution in least water season in dry year is most serious.