Influence Of Groundwater Depth On Surface Ecological Environment In The Blown-sand Region Of Northern Shaanxi Province

Groundwater is an important water source for socio-economic development and ecological environment maintenance in northwest arid area.Therefore,taking the blown-sand region of northern Shaanxi Province as a typical region,in this paper,the technical route combining field investigation,theoretical analysis and statistical analysis has been used to analyze the relationship between the groundwater depth and natural vegetation,salinization and desertification,in this area.The following research conclusions are obtained:(1)This article analysed the temporal and spatial changes of groundwater depth and Fractional Vegetation Coverage(FVC)in the blown-sand region of northern Shaanxi Province,and studied the driving factors which cause the changes of it.The results show that in the study area groundwater depth has an increasing trend from 2004 to 2019,and it was increased by 0.77m in 2019(4.50m)compared with 2004(3.73m),The areas where the groundwater depth decreased and increased were 6549.33 and 9765.70 km2,respectively,with an area volume ratio of 40.14%and 59.86%.The increment area is mainly distributed in Dingbian County and Jingbian City.In Dingbian and Jingbian City,groundwater depth has a significant positive correlation with irrigation area and groundwater extraction.In Hengshan District,Yuyang District and Shenmu City,groundwater depth has a significant correlation with rainfall and evaporation.From 2004 to 2019,the vegetation coverage in the study area changed from medium-low coverage(30%<FVC≤45%)to medium coverage(45%<FVC ≤60%),showing an increasing trend from southwest to northeast,and the ecological environment improved significantly.(2)This article put forward the range of sensitive effects of groundwater depth on the FVC the range of groundwater depth for the suitable growth of typical dominant vegetation.The results show that the sensitive range of groundwater depth to FVC is 1.5～8.0 m in the blownsand region of northern Shaanxi Province.The suitable groundwater depth of Achnesis splendens,the pioneer plant,the Longgrass,Stipa grandis and Stipa breviflora and so on dominant species in the study area were 1.52～3.98m,1.53～2.97 m,3.14～6.44m,4.58～5.93m and 4.76～5.44m.(3)This article constructed a soil salinization detection Index model the blown-sand region of northern Shaanxi Province,analysis the spatial-temporal variation characteristics of regional soil salinization through the model,and further determine the upper limit of groundwater depth to meet the requirements of salinization prevention in different counties.The results showed that from 2004 to 2019,the salinization area of the blown-sand region of northern Shaanxi Province showed a decreasing trend.The most widely distributed salinization area is Yuyang District,followed by Dingbian County,Shenmu City,Jingbian County and Hengshan District.The upper limit of groundwater depth without salinization can be set as 5.04m in Dingbian County,5.12 m in Jingbian County,3.69m in Hengshan District,1.95 m in Yuyang District and 2.38 m in Shenmu City.(4)This article revealed the temporal and spatial variation of desertification the blownsand region of northern Shaanxi Province,analyzed the response relationship of desertification to groundwater depth,and evaluates the ecological environment situation in study area.The results showed that from 2004 to 2019,the desertification area showed a decreasing trend,and the desertification pattern distribution showed a decreasing trend from southwest to northeast.The desertification transformation types were mainly unchanged and reversed,and the areas were 7353.88 km2 and 4671.10 km2,respectively.The range of sensitive burial depth corresponding to mild desertification the blown-sand region of northern Shaanxi Province is 1～2m in Yuyang District and Shenmu City,2～3m in Dingbian City and Hengshan District,and 6～7m in Jingbian City.In 2019,the areas with excellent and good ecological environment quality the blown-sand region of northern Shaanxi Province were mainly distributed in the northeast of Shenmu City and the area around Mahuangliang-Niujialiang town in Yuyang District.Hengshan District Leilong Bay-Tawan town area;The medium quality areas are mainly distributed in the east of Dingbian City,Jingbian County and Xiaohaotu-Mengjiawan Township in Yuyang District.Poor quality scattered in Dingbian County Duiziliang Township and Jingbian City Dongkeng-Ningtiaoliang.