| Poyang Lake is the largest freshwater lake in China. It is noted that water quality of the lake water body has deteriorated obviously in recent years. Investigation of total phosphorus leaching is very important for protection and improvement of water environment of Poyang Lake. In this thesis, spatial and temporal variations of streamwater TP concentrations in Le’an River were analyzed. Meanwhile, the runoff and TP leaching process was simulated using HYPE model. The TP output load of the catchment was estimated using the simulation data of runoff and TP concentrations. Then, the TP concentrations and output load were simulated under different fertilizer application and precipitation conditions. Finally, the TP output load of the future 15 years were predicted using a MPI-ESM-LR climate model. The main work and conclusions of this thesis are summarized as follows:(1) TP concentrations changed obviously with seasons in Le’An River from October, 2010 to August,2011. Water quality was best in spring, and worst in summer. Spatially, streamwater TP concentrations increased gradually from upstream to downstream in summer, while there were no obvious trends in other seasons. Streamwater TP concentrations followed similar trends as rainfall. Intensive rainfall in July and August resulted in high TP concentrations, while the streamwater TP concentrations decreased accordingly with rainfall from February to April. TP concentrations were positively correlated with proportions of arable land, urban and rural areas, while negatively correlated with proportions of forest and grassland areas; TP concentrations were more sensitive to changes of proportions of arable land, urban and rural land areas as well as forest areas.(2) The runoff model for Le’an River was developed based on the meteorological and hydro logical data during January 1,1978 to December 31,1986. The model reached ideal accuracy both in calibrated and validated periods. In the calibrated period, daily NASH efficiency coefficients Ens and daily determination coefficients R2 of six hydrological stations were higher than 0.80. The highest runoff relative error RE of the six hydrological stations was-10.24 percent. During the validated period, daily NASH efficiency coefficients Ens and daily determination coefficients R2 of six hydrological stations were higher than 0.80, runoff relative error of Sandu Station was 14.53 percent, the rest of the stations were lower than 10 percent. The hydrological simulation performed well in general.(3) The TP leaching process was simulated by HYPE model on the basis of the established runoff model. The model performed well during the monitoring period. Daily NASH efficiency coefficients Ens and daily determination coefficients R2 of three water quality monitoring stations were higher than 0.50, while TP concentration relative errors were lower than 10 percent. The estimated TP output load was 926.98t from October,2010 to September,2011 according to output from the model.(4) TP concentrations and TP output load increased with the growth of applying quantity of fertilizer and manure, but changed slightly in general. TP concentrations and TP output load were influenced greatly by rainfall. When rainfall decreased by 20 percent, annual average TP concentrations and annual TP output load decreased by 35.6 percent and 48.4 percent, respectively. When rainfall increased by 20 percent, annual average TP concentrations and TP output load increased by 37.3 percent and 91.0 percent, indicating that rainfall and runoff played an important role in non-point phosphorus pollution.(5) The predicted results for future water quality in Le’an River Basin showed that:TP output load appeared a fluctuated upward trend from 2020 to 2035. Among them, the high emissions scenario had a maximum TP output load, while the low emissions scenario had a minimum TP output load. |
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