Study On The Assessment Of Water Quality And Water Environmental Capacity Of Lai-Xi River In Lu-Zhou City

The pollution sources and characteristics, the water quality and the environmental capacity of Lai-xi River in Lu-zhou were studied in this paper. Firstly, the pollution status was studied based on field survey and information collection, it was shown that the total discharge of sewage, COD_cr and NH₃-N in 2003 was 3061.4×l0⁴t/a, 9118.0t/a and 943.5t/a, respectively. By analyzing the discharge proportion, it was found that Lu County was the main of pollution zones, causing about 96% of sewage, 92% of COD_cr, and 90% of NH₃-N; non-point source was the main of pollution sources, causing about 54% of sewage, 79% of COD_cr, and 86% of NH₃-N.Based on the monitoring results of water quality in 2003, the status and trend of water quality, and the violation proportion of pollution indices were sequentially analyzed by fuzzy aggregative index method, single factor index method and mean synthetical indicator method, the result showed that the water quality of Lai-xi River was bad at large, the other belonged to order V except the entry and boundary section meeting order III; the main pollution index was COD_Mn, thus Lai-xi River was the typical river with organic pollutants. Based on the monitoring results in 1999～2003, the water quality was predicted to be worsening by fitted cubic polynomial.The water quality at flow direction was numerically simulated by one-dimension steady-state model, and according to the principle of maximal contamination tolerance, Lai-xi River was found to have been seriously polluted, the environmental capacity of C0D_cr and NH₃-N was 3406t/a and 316t/a, then the reduced load was 4335t/a and 3103 t/a.Lastly, achieving standard analysis of the environmental capacity was studied. Target of the yearly reduced load was offered from different zones and control elements, the result showed that Lu County was polluted worse, in which the reduced load of COD_cr and NH₃-N was 5254t/a and 79t/a, while Long ma-tan Zone still had accordingly excess capacity of 4730 t/a and 57 t/a; the control element from Shi-ya Bridge to E-xiang Well was polluted worst, in which the reduced load of COD_cr and NH₃-N was 4730 t/a and 57 t/a, while the control element from E-xiang to Hu-shi Bridge still had excess capacity of 746 t/a and 32 t/a. Thus, countermeasures of pollution control were put forward to secure the water quality and environmental capacity achieve standard from management side.This study can offer important information for the programming of the water environment comprehensive recondition of Lai-xi River, in the meanwhile, its thought and method can be used in the similar work of other areas for reference.