| As one of the three inland lakes in Inner Mongolia,Daihai used to be the"pearl of Cyprus"with abundant water and grass,and was also an autonomous region-level lake wetland nature reserve,and an important lake located in a typical agro-pastoral zone,which has an important position in the local ecosystem.In recent years,with the development and utilization of Daihai and its basin,the ecological environment quality of the Daihai basin has deteriorated.The water body is shrinking,the salt content continues to increase,and the surrounding tidal flats have formed saline-alkali land,which has a great impact on the local and surrounding natural environment.Therefore,the discussion of land use pattern change,watershed area change,vegetation distribution characteristics,nutrient content and reuse mode and removal effect in the river basin has certain guiding significance for the ecological restoration and governance in the later stage of Daihai.This study is based on six remote sensing images from 1980,1990,2000,2010,2020 and 2022as data sources,supplemented by the investigation of hydrological conditions in the surrounding lake area,and determines the current watershed range of Daihai Lake area.The soil salinity,vegetation characteristics,productivity and nutrient composition of major communities in the coastal area of the road network in Daihai Lake District were investigated and measured.The feasibility of reducing nutrient pollution in the Daihai Basin through vegetation management measures mainly harvested plants was analyzed and evaluated.The main results and conclusions of this study are as follows:(1)In recent years,with the change of land use pattern in the river basin,the area of natural forest land has decreased significantly,and the area of grassland and cultivated land has increased year by year;Among the original more than 20 tributaries,only 3 tributaries of the Bowba River,the Great River and the Tiancheng River(Shimen Reservoir)remain to collect water in the lake area,and the water collection capacity is weakened,and the construction of the road network has formed a trend of encircling the lake area,so that external water sources cannot converge in the lake area.As a result,the basin area was reduced to 297 km~2,including a land area of 242.49 km~2and a water area of 54.51 km~2.(2)At this stage,the following land use methods mainly exist in the river basin;The maximum area of cultivated land(returned farmland)is 169.73 km~2;The construction land area is 13.89 km~2,the woodland area is 0.4 km~2,the grassland and wetland area is 58.47km~2,and the main vegetation of the grassland is mutton grass-whisk thatch grassland,mutton grass-lai grass grassland,reed grassland,and alkali grass-pig hair grassland,covering an area of 13.38 km~2,18.71 km~2,12.72 km~2and 9.38 km~2,respectively.(3)The degree of land salinization in the river basin is serious.The results of the detection of soil in the coastal zone around the lake showed that the soil salt content decreased radially from the lake area.The soil salinity content near the water body was as high as 16.78 g/kg,and decreased to 1.36 g/kg on the far road side.(4)The vegetation productivity,regenerative and main plant nutrients in the watershed were measured.The yield of alfalfa land in farmland was 1120 g/m~2.Among the grasslands,the productivity of mutton grass-whisk thatch grassland,mutton grass-Lai grassland,reed grassland and Suaeda-pighair grassland were 227.49 g/m~2and 221.85 g/m~2,227.49 g/m~2,211.85 g/m~2,588.16 g/m~2and 654.74 g/m~2,respectively.The content of starch in the nutrients of herbs was 19.75%,total nitrogen content was 1.23%,total phosphorus content was 1.01%,and ash content was 7.8%.(5)Through the harvesting of plants in the basin,15352.98 t of salt,4236.87 t of nitrogen and 732.09 t of phosphorus can be removed per year. |
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