| The security of the ecological environment is the cornerstone of Cathay Pacific's people's security.However,with the development of the economy,China's ecological security has great challenges.The South-to-North Water Diversion Project is the world's largest water transfer project.However,in the past two decades,China's society,economy and population have grown rapidly.The improvement of people's quality of life has promoted the development of various industries.The pollution of agricultural non-point source pollution has also become more serious and put a lot of pressure on the water quality of the reservoir.Mastering the ecological safety status of the water source area is of great significance to the South-to-North Water Transfer Project.Based on this,in this study,through the characteristics of spatio-temporal changes of water quality in typical watersheds in the water source area of the South-to-North Water Diversion Project,the impact of agricultural production activities on the water environment in the water source area,the characteristics of soil fertility under different land uses in the water source area,and the impact of surface water source pollution on the soil environment The current water and soil environment assessment and risk assessment of the water source area,combined with the economic and social factors of the water source area,comprehensively evaluate the ecological security of the water source area,and predict the ecological security according to the model.The specific research results are as follows:(1)The comprehensive evaluation of the water quality of each typical watershed in the water source area is in good condition throughout the four seasons,and the watershed as a whole has met the target requirements of drinking water quality.The seasonal variation characteristics of water quality in typical watersheds of water source areas are as follows: the p H value of water quality is consistent with the change trend of dissolved oxygen,and both decrease with the increase of temperature,and the value is significantly lower in summer than in other seasons.The changes of total nitrogen,ammonia nitrogen,electrical conductivity,nitrate nitrogen,total phosphorus and chemical oxygen demand of water bodies are similar.Affected by the non-point source pollution caused by rain erosion in early summer,they all show a slightly higher summer law than other seasons.The dissolved oxygen in the water body of the water source is kept above the three types of water in all seasons,and the standard rate of dissolved oxygen in the four seasons is 100%.In summer,5.37% and 15.81% of ammonia nitrogen and total nitrogen,respectively,failed to meet the standard.The areas that failed to meet the standard were mainly concentrated in Shiyan Basin,Lianshui River Basin,and Danjiangkou Reservoir Area.Some rivers in these areas had nitrogen caused by non-point source pollution.Excess risk.In the early summer,the phosphorus content of the water source area was 15.81%,which did not meet the standards of the three types of water.The areas that failed to meet the standards were concentrated in the Lianshui River Basin and Nanyang Basin in Hanzhong City.Some rivers in these areas have the risk of excessive phosphorus caused by non-point source pollution.(2)Agricultural production activities have little impact on the water environment.The total amount of nitrogen and phosphorus produced by agricultural production activities in water sources is between 5900-7000 t and 690-880 t respectively.The total pollution of the planting industry,aquaculture industry and life sources is increasing.Among the three different types of pollution,the nitrogen and phosphorus from the planting industry are the largest,followed by the aquaculture industry,and the smallest source of life.The average pollution production ratio of the three is 40.33%,15.11% and 44.56%,respectively.The gray water footprint of agricultural production pollution has shown an increasing trend in the past 18 years.The pollution generated by agriculture requires 119-140 billion cubic meters of water to be diluted to meet the three types of water quality standards.The total gray water load index of agricultural production activities is 0.24-0.29,that is,pollutants from agricultural production activities entering the river need to be diluted by 24%-29% of the total water volume of the water source,and the water resources of the water source are sufficient to dilute it.(3)The soil fertility level of the water source area is generally at a medium level,the fertility index of paddy fields and farmland is the best,both are at a good second level,and the rest of the land use types are at the third level of medium fertility.The characteristics of soil nutrients in the water source are: the soil p H is generally neutral and acidic.The p H range of different land use types is between 4.47-8.37.The order of p H value is farmland>forest land>paddy field>vegetable field>tea garden.The value of soil organic matter in the water source area is at a moderately low level.The total nitrogen value of the water source soil is in the range of 0.65-2.62 g/kg.The content of farmland paddy fields is higher than that of the other three types of land.The total nitrogen is generally at the third level and medium level.The total phosphorus value of the water source soil is in the range of 0.13-1.85 g/kg,and the total phosphorus content of vegetable fields,farmland and tea gardens is higher than that of forest land and paddy field,and it is generally at the medium level.The content of alkali-decomposed nitrogen in the water source area is in the range of 88.14-182.84 mg/kg.The content of alkali-decomposed nitrogen in paddy fields,vegetable fields and tea gardens is higher than that of farmland and forest land,and is generally at a moderately high level.The coefficient of variation of the soil available phosphorus in the water source area is large,with the content in the range of 3.41-37.76 mg/kg,which is in the third level of medium level.(4)The application of nitrogen and phosphate fertilizers poses a greater risk to water sources,and livestock and poultry manure and domestic sewage have great potential for fertilizing farmland.The nitrogen and phosphorus densities of cultivated land for chemical fertilizers in water sources are within the range of 195.59-710.49 kg/ha and 63-229.54 kg/ha.The overall nitrogen and phosphorus load showed a slow growth trend.The application of nitrogen and phosphate fertilizers poses a greater risk to water sources,and the risk level has changed from a low-risk state in 2000 to a medium-risk state.In the Shangluo area of Shangluo City,there is less application of chemical fertilizers,and there are many mountainous areas in the city.The crop multiple cropping index is low,and the average load for the unit cultivated area is large.However,Nanyang is located in the Nanyang Basin,with flat terrain,a large crop planting area and a high multiple cropping index,so that the nitrogen and phosphorus load per unit of cultivated area is large,and the risk index is gradually approaching a serious risk state.The nitrogen and phosphorus farmland load of livestock and poultry manure in the water source area was in the range of 84.66-117.67 kg/ha and 13.45-18.92 kg/ha,respectively.The nitrogen and phosphorus load of livestock and poultry increased by 40.64% and 38.99% from 2000 to 2017,respectively.The risk assessment of livestock and poultry manure on the environment is in the range of 0.48-0.61,which is a slightly risky state.The load of nitrogen and phosphorus produced by domestic sewage in the water source area on the cultivated land is in the range of 29.82-33.96 kg/ha and 5.56-6.39 kg/ha,and the nitrogen and phosphorus production of sewage accounts for 9.5-11.22% and 20.5-2.33% of the environmental capacity.(5)The overall safety of the water source area is in a relatively safe three-level state,the state is relatively stable,and the ecological security state is improving year by year.From a city perspective,the ecological security status is ranked as Shangluo>Ankang>Shiyan>Hanzhong>Nanyang.Among them,Shangluo City has a high ecological security status and always maintains a three-level status,while Nanyang City's ecological security status is mostly at the fourth-level sensitivity due to the development of planting industry,the prosperity of livestock and poultry farming and the relatively low forest coverage rate.The state of the level is easily damaged.According to the prediction and simulation of the GM(1,1)model,it is found that the safety level of each area of the water source area can reach three levels in the next ten years. |
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