| The vicious circle formed by grassland degradation and soil erosion is gradually encroaching on grassland resources in Xinjiang,seriously threatening regional ecological security and restricting the sustainable development of agriculture and animal husbandry,and the impact is further deepened with global climate change.Rainwater harvesting technology has multiple benefits such as improving the utilization efficiency of water resources,soil and water conservation and accelerating the process of ecological restoration in arid areas,and its application prospect is broad.However,the research foundation of rainwater harvesting in Xinjiang is weak,and the ecological environment is relatively fragile.There is a strong uncertainty in the application of rainwater harvesting measures,so it is urgent to strengthen the basic research.This paper took the grassland in the hilly and gully area of Ili Valley as the research object.On the slope scale,we had observed the runoff and sediment yield characteristics,the development and change of soil and vegetation of four rainwater management measures(natural grassland,contour trench,infiltration hole and grass mulching)on the grassland underlying surface of two soils(gray calcareous soil and brown-red soil)for a long time in the field.Using 3S technology,multivariate index analysis and field investigation,we comprehensively and accurately evaluated the rainwater harvesting potential of gullies in this area and put forward the corresponding rainwater harvesting technology.In addition,the effects of flood detention,sediment retention and ecological restoration of"check dam+biological measures"of in-situ gully rainwater harvesting technology were observed for a long time.Finally,we comprehensively analyzed the impact of slope-gully rainwater harvesting technology on grassland ecological environment in hilly and gully areas,and judged its regional suitability.The main results were as follows:(1)Short duration and high intensity occasional rainstorm(C-type rainfall)was the dominant erosive rainfall of grassland water erosion in the hilly area of Ili Valley.Under this rainfall type,the runoff reduction effect of grass mulching on brown-red soil grassland was the best,and the contour trench could better reduce the runoff on gray calcareous soil grassland.The average runoff of infiltration hole and natural grassland under A-type rainfall(continuous rainfall with low rainfall and low rainfall intensity)was greater than that of B-type rainfall(high rainfall and long-lasting heavy rainfall),but the results of grass mulching and contour trench showed the opposite.Under the conditions of A-type and B-type rainfall,the average runoff depth of each measure was natural grassland>infiltration hole>contour trench>grass mulching,and gray calcareous soil grassland>brown-red soil grassland.The average sediment yield of each treatment was natural grassland>infiltration hole>contour trench>grass mulching under different rainfall types,and gray calcareous soil grassland<brown-red soil grassland.Therefore,the auxiliary management of the slope could effectively prevent and control the soil erosion of the grassland.Among them,the grass mulching and the contour trench had excellent effects of reducing runoff and sediment.The average annual benefit of reducing runoff was 75.64%and 65.17%respectively,and the average annual benefit of reducing sediment was 75.64%and 69.56%respectively.(2)The surface soil moisture variability of the two kinds of grassland had obvious differences.The contribution of each factor on the soil moisture variability of gray calcareous soil grassland was as follows:temperature(70.33%)>rainfall(18.36%)>management measures(7.10%)>rainfall days(4.21%).For brown-red soil grassland,the contribution of management measures(17.87%)was second only to temperature(68.05%),followed by rainfall(13.14%)and rainfall days(0.94%).The three rainwater harvesting measures could improve the soil water content of surface,and the grass mulching and contour trench were the best water retention measures for gray calcareous soil and brown-red soil respectively.(3)The ecological effects of rainwater harvesting measures were different due to the underlying surface of grassland.Rainwater harvesting technology significantly improved the soil quality and promoted the growth and rapid recovery of slope vegetation on gray calcareous soil grassland.The soil comprehensive index of grassland under different management was contour trench(0.686)>grass mulching(0.621)>infiltration hole(0.437)>natural grassland(0.133),the vegetation comprehensive index was grass mulching(0.990)>infiltration hole(0.645)>contour trench(0.339)>natural grassland(0.133),and the coupling coordination degree of vegetation-soil system was grass mulching(0.626)>infiltration hole(0.515)>contour trench(0.491)>natural grassland(0.240).The ecological restoration effect of grass mulching was the best.The underlying surface of brown-red grassland was relatively fragile and vulnerable to external interference.Rainwater harvesting measures might had a negative impact on grassland habitat.The vegetation comprehensive index of grassland under different management was as follows:infiltration hole(0.948)≈natural grassland(0.940)>contour trench(0.817)>grass mulching(0.100).The soil comprehensive index was as follows:contour trench(0.749)>infiltration hole(0.432)>natural grassland(0.266)≈grass mulching(0.262),and the coupling coordination degree of vegetation-soil system was as follows:contour trench(0.625)>infiltration hole(0.566)>natural grassland(0.500)>grass mulching(0.284).The ecological restoration effect of contour trench was the best.On the contrary,the grass mulching hindered the process of grassland restoration.(4)Based on the discussion of the relationship between erosion gully characteristics and catchment environment,it was pointed out that although the catchment area of weakly developed gully was small,the runoff potential was the highest,and the distribution of gully network was the densest.The development scale of strongly developed gully was the largest and had high runoff potential.The catchment of moderately developed gully was medium,but the runoff potential was the smallest.We proposed rainwater harvesting technology suitable for all kinds of erosion gullies,that was,the“check dam+plant measure”was suitable for weakly developed gullies,the“stone check dam+slope bottom vegetation restoration”was suitable for moderately developed gullies,and the“flood diversion channel+water storage system”was suitable for strongly developed gullies.(5)The multi-level check dam could intercept runoff and sediment layer by layer,reduced the amount of sediment out of the gully by more than 15%under a heavy rainfall,effectively controlled the intensity of gully erosion.Through soil improvement and artificial vegetation restoration on the water side of the check dam,the limitations of dry,barren and poor structure of the gully soil were overcome,and about 80 m~2forest and grass patches were successfully created in the gully,which greatly promoted the restoration and reconstruction of gully vegetation and improved the ecological environment of the gully.To sum up,based on the comprehensive effect analysis of soil and water conservation and ecological restoration,in-situ water retaining measures(such as contour trench)and mulching measures are arranged on the slope,in-situ rainwater harvesting systems(such as check dam and small dam)are set in the erosion gullies,supplemented by artificial vegetation construction,which can effectively prevent water erosion in hilly and gully areas and promote grassland ecological restoration.It provides technical reference for the management of grazing grassland and the conservation of water and soil resources in Xinjiang... |
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