Effect Of Ecological Management On Soil And Water Loss In The Loess Plateau Of China

Although the ecological environment of the Loess Plateau has improved significantly after a long period of large-scale soil erosion control,but the nature of ecological fragility has not changed completely,and has arisen some new management problems.For example,due to the inappropriate vegetation restoration mode,large areas of artificially restored vegetation began to degrade,and the indiscriminate vegetation restoration resulted in unbalanced regional management.In the past,many scholars have conducted a lot of research on soil erosion in the Loess Plateau,but most of them are mainly concentrated on the runoff plot scale or a certain watershed,and fewer studies on the regional scale.There is a lack of analysis on the overall management effectiveness and its influencing factors from a regional perspective.This paper takes the Loess Plateau of China as the study area,based on soil erosion monitoring data,literature data,yearbook data,and hydrological data,and combined with regional meteorological,soil,terrain,land use,vegetation,and other data.Then using Arc GIS,Matlab,Open MEE,and other technologies,through Meta-analysis,ANOVA,posterior distribution,cluster analysis,correlation analysis,etc.,to explore the effectiveness of regional-scale ecological management and the effective control of runoff and soil erosion,and comprehensively analyze the future management pattern of the Loess Plateau.The main results are as follows:（1）Revealed the effects of land use characteristics on runoff and soil erosion at the runoff plots scale.The Loess Plateau runoff plot database includes 55 measurement points,of which 461 plots measured runoff and 535 plots measured soil erosion.The correlation of soil and water loss with plot length and slope gradient is determined by land use type,while for all land use types the runoff and soil erosion varied with rainfall.Only the annual runoff coefficient of the shrubland was significantly correlated with the the slope length and slope gradient（p<0.05）.Bare soil was found to have the highest average annual runoff(58.57 mm·a^-1)and annual soil loss(122.06 t·ha^-1·a^-1).Natural grassland and mixed forest had the lowest annual runoff(<15 mm·a^-1)and annual soil loss(<20 t·ha^-1·a^-1),exhibiting a better effect on soil and water conservation when the precipitation was<200 mm and>600 mm,respectively.When the precipitation was 400–600 mm,shrubland showed the lowest mean annual runoff(21.36 mm·a^-1)and annual soil loss(13.36 t·ha^-1·a^-1),which is conducive to reducing water and sediment.Therefore,shrubland could be selected as the recovery vegetation type in the semi-humid climatic region.（2）Clarified the effect of vegetation coverage changes on soil and water loss at the watershed scale.Vegetation coverage has a negative exponential function with runoff and soil erosion modulus,and vegetation restoration has a greater impact on soil erosion than runoff.The database includes 59 small watershed data with statistics on vegetation coverage（2.51%–86.3%）,runoff modulus(155.7–780431.8 m³·km^-2·a^-1),and soil erosion modulus(400–58285 t·km^-2·a^-1),and the average coverage level increased by33.12%after ecological management.The erosion modulus of recovery period at 15–20 yr is significantly different with the other recovery periods for all climatic regions（p<0.05）.Three specific vegetation coverage thresholds were identified for soil erosion:the lower threshold（0%–35%）,the transition（35%–65%）,and the upper threshold（65%–100%）;four specific vegetation coverage thresholds were identified for runoff:the low threshold（0%–20%）,the transition（20%–50%）,the high threshold（50%–75%）,and the upper threshold（75%–100%）.In the Loess Plateau,the effective vegetation coverage in the cold and arid regions is 25.12%,in the semi-humid region is 51.02%,in the semi-arid region is 45.92%,and in the arid region is 26.53%,and corresponding vegetation restoration strategies should be adopted in different climatic regions.（3）Clarified the effect of soil and water conservation measures at the regional scale on soil and water loss.Agricultural measures had the lowest impact on soil and water loss among all the soil and water conservation measures.At a different time,biological measures had the best effect on reducing flow,while biological+engineering had the best effect on soil erosion control.The effect of reducing flow and sediment is the lowest for the>30 years of engineering measures.Based on the relative reduction evaluation index,afforestation+grass cover,afforestation+natural recovery,grass cover+natural recovery,afforestation+grass cover+natural recovery,afforestation+grass cover+level ditching,afforestation+grass cover+warping dam,afforestation+grass cover+terracing,afforestation+grass cover+natural recovery+warping dam,afforestation+grass cover+no-tillage,afforestation+grass cover+natural recovery+no-tillage are evaluated as efficient measures.For individual soil and water conservation measures,terracing has the largest reducing runoff and sediment cost,while for the comprehensive measures,engineering has the largest reducing runoff and sediment cost,followed by biological+engineering,agricultural,biological+agricultural,and biological measures.（4）Clarified the impact of regional ecological management on soil and water loss.The accumulated treatment degree of the Loess Plateau has reached about 51%.The management areas from the first management stage to the fifth stage were about 7600km²,17800 km²,62000 km²,212200 km² and 30400 km²,accounting for 2.3%,5.4%,18.8%,64.3%and 9.2%of the management degree,respectively.The average vegetation coverage increased by 33.6%,the average soil erosion modulus decreased by 83.07%,and the average runoff modulus decreased by 84.05%after the ecological management.The mutation time of runoff and sediment in the middle regions is later than that in the upstream regions,and the mutation year of runoff is earlier than sediment.The sediment at Tongguan station has the largest reduction（79.79%）,and the runoff at Longmen Station has the largest reduction（33.16%）.The soil erosion intensity（SEI）index was 3.36 in group a1,where the water storage and soil conservation capacity and the soil erosion intensity are both low.The SEI index was 13.88 in group a2,where the water storage and soil retention are low and the soil erosion intensity is high.The SEI index was 9.48 in group a3,where the water storage and soil retention are large and the soil erosion intensity a low.The SEI index was 14.57 in group a4,where both the water storage and soil retention capacity and the water and soil loss intensity are high.Among the seven key national soil and water conservation areas,Shannxi province has the highest SEI（average Ⅰ value of 5.29）,and the SEI level is extremely serious erosion.In summary,ecological management control soil and water loss by changing the connectivity of water and sediment.While the land use type determines the runoff-sediment tradeoff relationship between different measures.At present,the management of soil and water loss on the Loess Plateau has entered a period of synergistic promotion of protection and control.Although the regional ecological environment has improved significantly,the ecosystem is still very fragile,and some areas are not yet capable of self-healing.The future management direction should still focus on biological measures,but the optimal land use type should be selected in different climatic regions,while the effect of vegetation coverage threshold should be considered,and the most efficient measures and combinations should be selected in different management regions.In addition,according to the status quo and governance of soil erosion in different governance areas,corresponding governance strategies are formulate.In addition,corresponding strategies should be formulated according to the current management situation of soil and water loss in different areas.The above research results provide a theoretical basis for the future multi-scale research of soil erosion prevention in the Loess Plateau,and have important reference value for regional soil and water conservation planning and macro-policy formulation.