Research On Water Environmental Management Based On Assimilative Capacity In Lan River Watershed

Assimilative capacity calculation and total amount control implementation were the most important component of water environmental management, as well as protection of water environment security and promotion for economic and social sustainable development of watershed. Thus the calculation and allocation of water assimilative capacity has become one of the focuses of the water environmental management science at present. In order to study water assimilative capacity and allocate pollution of watershed, taking Lan River watershed in Lanxi City as an example. The characteristic of water pollution was analysised, the assimilative capacity of COD and ammonium nitrogen was calculated based on WASP7.3 model(Water Quality Analysis Simulation Program, Version 7.3), and a comprehensive water management mode based on TMDL (Total Maximum Daily Loads) was developed. The main results are summarized as follows.(1) It was estimated that the loads of COD and ammonia nitrogen were 19418.75 t.a-1 and 702.97 t.a-1 respectively in 2007. The main COD source of pollutant loads was non-point sources of agricultural, accounted for 58% of the total COD loads. The main ammonia nitrogen sources were domestic pollution, accounted for 77.8% of the total ammonia nitrogen loads. The order of source contribution ratio from high to low as following:domestic pollution sources>industrial pollution sources> livestock pollution sources>aquaculture pollution sources.(2) The capacities to assimilate COD and ammonia nitrogen were studied using two methods based on WASP7.3 model, the first is empirical foumulas method and the second is trial-and-error method. The total COD and ammonia nitrogen assimilative capacity of Lan River watershed is 10616.9 t·a-1 and 157.6 t·a-1 respectively under 90% confidence instream flow condition based on the empirical foumulas method, it decreased in the following order:Mein River Segment>Lan Segment> Jinhua Segment> Gan River Segment> Chi River Segment> Youbu River Segment. The total COD and ammonia nitrogen assimilative capacity of Lan River watershed is 11208.3 t·a-1 and 184.7 t·a-1 respectively under 90% confidence instream flow condition based on the trial-and-error method, and it's decreased order is the same to the empirical foumulas method.(3) According to TMDL concept, the mothods of proportional allocation and contribution rate allocation were used to allocate point and non-point pollutant load in Lan River watershed. Load reduction based on proportional allocations showed that Jinhua segment had residual capacity to assimilate COD and ammonia nitrogen, but pollutant load reduction for COD and ammonia nitrogen in Lan segment reached 46.3% and 83.8% respectively, and pollutant load reduction for COD and ammonia nitrogen in Qu segment reached 4.0% and 81.8% respectively, the water quality of Lan River watershed matched its designated use. Load reduction based on contribution rate allocation showed that, to guarantee the water quality in Lan segment matched its designated use, the maximum point and non-point COD reduction should reached 58.9% and 61.9% respectively, and the maximum point and non-point ammonia nitrogen reduction reached 72.5% and 96.9% respectively. To guarantee the water quality in Qu segment matched its designated use, the maximum point and non-point COD reduction should reached 4.0% and 11.2% respectively, and the maximum point and non-point ammonia nitrogen reduction reached 71.3% and 92.2% respectively.