Study On Water Environmental Capacity Of Shaxi River (Reaches In Shaxian County), Fujian Province

Water Environmental Capacity(WEC) is an important concept inenvironmental science which inflects the bearing capacity for region andwatershed to the pollutant under certain environmental targets, and it isrenewable resource. Study on the WEC has important practicalsignificance for water quality simulation, water pollution controlplanning and total amount control in region and watershed.Presently, water quality in Shaxi River (reaches in Shaxian County)has been improved as local government pays more attention to it, butthere are still some pollutant beyond environmental quality standards forsurface water on some sections. It is important to get the WEC forfuther improving water quality and providing firm managementmeasures.In this study, the index of water quality simulation are identified bywater quality assessment process. The QUAL2K water quality model isapplied to calculate the WEC with the trial and error method in ShaxiRiver (reaches in Shaxian County). According to the current pollutantdischarge and WEC research results, the reaches which need reducedischarge pollutants were identified, and total amount control measureswere put forword. The main conclusions are as follows:1) The water quality in Shaxi River (reaches in Shaxian County) is goodaccording to the water quality trend for eight years, but theconcentration of ammonia nitrogen and total phosphorus is ascendingas the time passing.2) The main pollution index are identified through water qualityassessment with environmental impact of each individualenvironmental parameter, including biochemical oxygen demand,Permanganate Index, ammonia nitrogen and total phosphorus, whichare the indictors of the water quality simulation. 3) The model parameters, including the oxidation rate of fast CBOD, thenitrification rate of ammonia nitrogen, the sedimentation rate ofinorganic phosphorus, and the oxidation rate of Permanganate Indexare calibrated by parameter estimation which is according to thecomparison with the measure value and model simulation value onJanuary4,2009. According to model validation with the data onJuly6,2004, the result shows that the QUAL2K model has goodsimulation, and it is suitable for the Shaxi River (reaches in ShaxianCounty) water quality simulation.4) In this study, in order to consider the influence of time and flow rate on thepara mete r values, the parameters for different months in2004werevalued using QUAL2K model. The result shows water qualitydegradation parameters were in a stable condition with time andflow-varying in the Shaxi River(reaches in Shaxian County).5) Taking an example of CODcr and ammonia nitrogen, The WEC forShaxi River(reaches in Shaxian County) was calculated by the trialand error method with QUAL2K model and river system WEC analysissoftware which was designed by Chinese Academy for EnvironmentalPlanning(CAEP) on the base of data on January4,2009. Taking totalquantity into consideratiom, the WEC results by QUAL2K model trialand error method is more reseanable than by river system WECanalysis software. The model trial and error method was applied forcalculating the WEC in the further study.6) Comparing the calculated WEC and pollutant discharge quantity, thequantity of cutting down for every reach is identified. The WEC issurplus for the whole reach, the surplus WEC of CODcr is14668.380t/a, ammonia nitrogen is1051.011t/a, total phosphorus is131.163t/a. The discharged pollutants in some reaches need to be cutdown. In the Dongxi-Luoxi reach, CODcr need to be cut down64.624t, ammonia nitrogen need to be cut down16.792t/a, totalphosphorus need to be cut down4.954t/a. In the Sha11-Mapuxireach, total phosphorus need to be cut down5.482t/a, In theMapuxi-Sha12reach, CODcr need to be cut down1858.673t/a.Finally, according to the results of the WEC in Shaxi River(reaches in Shaxian County), the article promotes the measures to implement totalamount control, which includes reducing pollutants dischargeconcentration, promoting the clean production, establishing emissiontrading institution, partitioned managing water resource, and so on.These measures could fullfill to improve the main stream environment byimproving reach water quality, and it is helpful to reasonably manage andutilize water resource.