Study On Agricultural Grey Water Footprint In Swan Lake Basin

Water resources are indispensable natural resources involved in almost all human activities.With the continuous development of human society,global water consumption is constantly increasing,the shortage of water is increasing,and the pressure from water for human activities is increasing very fast.In all kinds of water resources consumption,agricultural water accounts for the vast majority of global water resources consumption.According to statistics,global agricultural water consumption accounts for more than 70%of total water consumption.While human activities consume water resources,they also cause a certain degree of pollution to water resources.Especially in recent years,for high yields,agricultural activities of human often apply a large amount of fertilizers and pesticides to farmland.Fertilizers and pesticides that are not absorbed by crops will flow into the water body along with the rainfall runoff,resulting in water pollution.The study area is located in the Jianghan Plain,which is a typical farming area,and there is basically no industrial production.The unique plum rain season in the Jianghan Plain is just at a critical period for crop growth.A large amount of concentrated rainfall will produce a large amount of farmland runoff.Therefore,agricultural production is one of the main factors causing the water pollution in the basin.There are two national reserves in the basin,the Baiji Dolphin Nature Reserve and the Elk Nature Reserve.The safety of the water environment in the basin plays a very important role in the survival of baiji dolphin and elk.Therefore,it is necessary to choose a scientific method to assess the runoff pollution of the farmland and the water environment of the river basin.The grey water footprint proposed by the water footprint theory provides an effective and quantifiable evaluation index for the pollution of the water environment.Based on the water footprint theory and combined with field experiments,this study studied the differences of gray water footprint of two major crops?rice and cotton?under different water and fertilizer management modes;The total gray water footprint of two major crops were analyzed and characterized in RS and GIS software;Monthly monitoring and analysis of water conditions in various parts of the watershed were carried out for a period of one year;From the perspective of catchment,simulated the years of rainfall and runoff based on the hydrological model?DHSVM?,so as to study the trend of gray water footprint,and analyze the difference of gray water footprint in different typical characteristics of hydrological years.The main conclusions are as follows:?1?In field experiments of rice planting,two different water management modes were selected:conventional flood irrigation treatment?F1?and Optimized irrigation treatment?F2?,and three different fertilization treatments were selected:Conventional fertilization?P1?,mixed fertilization?P2?and optimized fertilization?P3?.there are six combination treatment,namely F1+P1,F1+P2,F1+P3,F2+P1,F2+P2,F2+P3.The gray water footprint of the six combined modes are:309m³/t,225m³/t,224m³/t,200m³/t,158m³/t,154m³/t.respectively.Compared with F1+P1 treatment,the F2+P3 treatment reduced the gray water footprint by 51.2%.The gray water footprint of rice production in the study area under the traditional water and fertilizer treatment was about 50%higher than the average of hubei province,which is 215m³/t in the global water footprint database.while the gray water footprint of F2+P3 model was less than the average of hubei province.If conditions permit,the selection of suitable water and fertilizer management mode can greatly reduce the gray water footprint of rice production.?2?In field experiments of cotton planting,four different fertilization treatments were selected:conventional fertilization?T1?,80%reduced fertilization?T2?,60%reduced fertilization?T3?and no fertilization?CK?.With the four fertilization treatments,the runoff loss rate of TN was 6.4%?7.7%and that of TP was 1.6%?2.1%.No fertilization treatment was significantly affect the yield of cotton.The gray water footprint of the three fertilization treatments are642m³/t,531m³/t and 499m³/t,respectively.among which there is no significant difference in the yield of farmers'conventional fertilization and 80%nitrogen reduction fertilization,while the treatment of 80%nitrogen reduction fertilization can reduce the gray water footprint by about 17%.The grey water footprint of conventional fertilization treatment in the study area is 8.4%higher than hubei province's average,which is 588 m³/t in the global water footprint database,while 20%nitrogen reduction fertilization can reduce the grey water footprint by 15.1%under the condition that the yield is not significantly affected.?3?According to the result of RS image classification extraction and GIS statistical analysis,the planting area of cotton and middle rice in 2014 was 26,900 mu and 10,900 mu?namely 17,397.79 hectares and 726.03 hectares?in the catchment,and that area in 2015 was 24,400mu and 15,600 mu?1,625.76 ha and 1,039.41 ha?.Under the conventional planting treatment,the total gray water footprint of rice planting in the Swan Lake Basin in 2014 and 2015 was 185*10⁴m³ and 265*10⁴m³,respectively,which under the optimized water and fertilizer treatment significantly reduced the gray water footprint of rice production in the basin.And Under the conventional fertilization treatment,the total gray water footprint of cotton production in the basin was392*10⁴m³ and 366*10⁴m³ in 2014 and 2015,respectively,while the total gray water footprint was reduced by about 15%under the 20%nitrogen reduction fertilization treatment?80%conventional?which did not significantly affect the yield.?4?The Swan Lake Basin consists of two catchment areas,Jiaozi river and Swan lake,and there are some difference in water condition of the two catchment.The monitoring data throughout the year showed that the water quality level of Jiaozi river catchment is generally between the level II?IV according to the China standard in surface water environment quality.The average content of NH³-N and COD_Mn in water body were according with the water quality standard of level?.The average content of TN in water body reached level?.The average content of TP in water body meeted level?.The monitoring data throughout the year showed that the water quality level of the Swan lake watershed was generally between level II?IV according to the China standard in surface water environment quality.The average content of NH³-N and COD_Mn in water body were according with the water quality standard of level?.The average content of TN and TP in water body were all at level?.In general,the water environment of the basin was in good condition.?5?According to the analysis,the gray water footprint of the swan lake basin is on the rise year by year.The average gray water footprint is 4478.3*10⁴m³ per year.During 1999?2014,the year with the largest gray water footprint is 2010 and the gray water footprint is 7500.6*10⁴m³.The year with the smallest gray water footprint is2005 and the gray water footprint is 1784.9*10⁴m³.For different typical hydrological year?abundant water year,normal water year,drought year?,the gray water footprint most in the three seasons,which is 2225.9*10⁴m³ in summer,1190.1*10⁴m³ in spring,and 764*10⁴m³ in autumn,respectively.In general,the correlation between typical characteristic hydrological years and grey water footprints is not obvious.the gray water footprint may not be the largest in abundant water year,on the contrary,the gray water footprint may not be the least in drought year.?6?The water footprint assessment manual defines the watershed pollution degree index as the ratio of the grey water footprint of the watershed to the watershed runoff per unit time.According to the above analysis,the pollution degree index of the basin does not exceed 20%,so the water condition of basin is better on present.Based on the water footprint theory,this paper makes a preliminary analysis of the gray water footprint of the watershed from the two aspects of the main agricultural production and the catchment.The research would make a certain role in guiding the sustainable development of the water environment of the basin and protecting the habitat safety of the baiji dolphin and elk.