Agricultural Structure Optimization Based On The Multi-objective Control In Tiaoxi Watershed

With the effective control of point source pollution in China,the influence of agricultural non-point source(AGNPS)pollution on water quality become more and more prominent.As a typical agricultural watershed,the water quality of Tiaoxi watershed was mainly impacted by AGNPS.To adjust agricultural structure was an important way in controlling the AGNPS pollution.In this study,a multi-objective programming model was employed to optimize the agricultural structure in Tiaoxi watershed to minimize AGNPS pollution load.The adjusted structure was evaluated by the impact on water quality.The results are shown as follows:(1)Based the data of socioeconomic-statistics in Tiaoxi watershed,the NPS pollutant discharge load of agriculture was estimated by the export coefficient method.The results showed that the pollutant discharge load of CODcr,TN,TP,NH3-N reached 14786t,6273t,1109t,2578t,respectively.Rural domestic sewage was the main pollution contributor for the CODcr and NH3-N in the watershed,which accounted for 43%and 57%of total AGNPS discharge load respectively.The croplands was the main pollution source of TN,with the proportion of 33%of total AGNPS discharge load,while the livestock was the main pollution contributor for the TP,with the proportion of 57%.The spatial distribution of NPS pollution showed that the overall trend of pollutant intensity increased from west to east.The regions with higher nutrient discharge intensity were mainly concentrated in the middle reaches of east Tiaoxi watershed;those with lower intensity were concentrated in the upstream region of East Tiaoxi watershed;and the lowest nutrient discharge intensity were in the West and southwest of Tiaoxi watershed.(2)A multi-objective programming model based on LINGO was used to optimize the agricultural structure in Tiaoxi watershed,with the objective of minimizing AGNPS discharge load.The development of agricultural economy and the demand for agricultural products were chosen as the constraints in the model.Under three scenarios,the agricultural economic output,pollution discharge load and agricultural structure composition were predicted with the model..The results showed that equal standard pollution load increased with the increase of the total agricultural output.The optimized results showed that it should vigorously promote the transformation of traditional vegetable cultivation to modern vegetable cultivation.The breeding scale of pig and cattle should be significantly decreased while that of sheep should be increased.However,the adjustment of cropland and aquaculture in the optimization result was slight.Compared with the control of NPS pollution and the agricultural economic output under different scenarios,the stable production scenario was chosen as the optimization scenario for Tiaoxi watershed in the recent years.The amount of CODcr,TN,TP,NH3-N of stable production scenario can be reduced by 9.3%,7.5%,11.5%,7.6%,respectively.(3)The WASP model was employed to predict the concentration of NH3-N and TP of three scenarios.The results showed that the water quality of the less output scenario was best,but it was not obviously comparing with the stable output scenario.According to the results of the multi-objective programming model,some agricultural adjustment strategies for Tiaoxi watershed were suggested,such as to rationally configure the proportion of croplands,to develop the facilities agriculture,to strictly control the breeding scale of livestock,and to develop ecological aquaculture.