Effects Of Typical Slope-Gully Land Consolidation Project On Ecosystem Services Of Soil And Water Conservation In The Loess Plateau

The implementation of the large-scale "return of farmland to forest(grass)" project has significantly improved the ecological environment of the Loess Plateau,but at the same time there is also a high quality of arable land tension,the problem of the contradiction between people and land.As an innovative soil and water conservation management measure that can effectively increase high-quality agricultural land,gully land consolidation project(ditch treatment and land creation)has been tested,applied and promoted since 2010,and by now,nearly 500,000 mu have been implemented in Yan’an and other places.The year 2013 saw the worst rainstorm in 100 years caused damage to nearly one-third of the newly created land,leading to much social concern about its impact on the ecosystem service function of soil and water conservation in the watershed.To address this issue,this study selected the Yanhe River Basin on the Loess Plateau as the research object,and used a combination of field investigation,analysis of actual measurement data and model simulation to quantitatively assess the impact of typical slope-gully land consolidation project on the soil conservation and water supply functions of the watershed ecosystem under the new environment,and obtained the following conclusions:(1)Slope-gully land consolidation project has significant influence on water and sediment in Yanhe River basin.Changes in the runoff sediment of a watershed directly reflect its soil and water conservation ecosystem service function.This paper investigates the changes of runoff sediment in the watershed before "return of farmland to forest(grass)" project(1990-1999),during the period of "return of farmland to forest(grass)" project(2000-2010),and during the period of gully land consolidation project(ditch treatment and land creation: 2011-2017),The results show that the runoff-sediment relationship is obviously different in the three periods,and the order of water-sediment reduction under the same conditions is return of farmland to forest(grass)+ ditch treatment land,return of farmland to forest(grass),before return of farmland to forest(grass),indicating that return of farmland to forest(grass)+ ditch treatment land has better water and soil conservation service function.(2)In VEST ecological service assessment model of soil and water conservation was constructed and calibrated and validated.In order to further study the impact of the slope-gully land consolidation project of the Yanhe River basin on its soil and water conservation ecosystem service function,the In VEST soil and water conservation ecosystem service assessment model was constructed,the validation results show that the R2 of annual sand transport is 0.65 and 0.87 for the rate period(1990-2000)and validation period(2001-2017),respectively,and the NSE is 0.55 and 0.82,respectively,which meet the model requirements;when the sensitivity parameter Z coefficient(seasonal parameter)is in the range of 28-29,the difference between annual water production and measured runoff is the smallest for the rate period and validation period,and the The simulation effect is better.The constructed model can be used as a tool to study the effects of typical slope-gully land consolidation project on ecosystem services of soil and water conservation of the Yanhe River basin.(3)The temporal and spatial changes of watershed ecological services were significant due to typical slope soil and water conservation measures.The temporal and spatial changes of soil and water conservation ecosystem services in the Yanhe River Basin were studied by using the model above.The results show that: during the period 1990-2017,soil erosion modulus decreased by 299t/(km2·a)and soil conservation increased;the spatial distribution of soil retention showed a trend of gradual increase from northwest to southeast in all years;the main driving factor affecting the spatial variation of soil retention in the study area was land use change,with forest land and grassland having stronger soil retention capacity under different land use types,contributing more than 80% to the soil retention of the watershed;higher contribution to soil retention was achieved in the range of 15°-25°slope and1200-1500 elevation,all reaching over 70%.In terms of water supply function: the Yanhe River basin shows a fluctuating trend of increasing water production,with a range of18.51-74.79 mm water production depth;the spatial variation of water production depth from northwest to southeast shows a trend of first increasing and then decreasing;the spatial and temporal trends of water production are consistent with the changes in rainfall,which is the main driver of water production;the water production capacity of different land use types is inversely proportional to the evapotranspiration,with stronger water production capacity of about 83.34 mm for construction sites,and decreasing for arable land,grassland and forest land in order,with 51.37 mm,49.95 mm and 48.42 mm,respectively.The main contributor to water production,the total amount of water produced by both accounts for about 70% of the whole region,and the contribution of forest land gradually increases;in the range of slope 15°-25°and elevation 1200-1500,the contribution of water production is larger.Thus,the implementation of slope soil and water conservation measures significantly improves the water supply and soil conservation service function of the watershed soil and water conservation ecosystem,which is of great significance to the ecological environment construction.(4)The ecological service function of water and soil conservation was changed obviously by gully land consolidation project.The response of watershed soil and water conservation service functions to extreme rainstorms under current land creation scale conditions was studied.The results showed that the soil conservation amount increased by1097.14t/ km2 and the sediment transport modulus decreased from 3162 t/km2 to 2394t/km2,a decrease of 24%,compared with the current gully land consolidation project in 2013 under the condition of 100-year rainstorm.Further study of the land remediation project in the Yang juangou watershed showed that soil erosion in the watershed was gradually decreasing with the increase of the ditch land remediation ratio,and compared with the non-remediated ditch,soil erosion decreased by 0.57%,1.17%,3.15%,4.20%,and 3.36% at 2%,4%,6%,8%,and 10% remediation ratios,respectively,and soil retention gradually increased from4% remediation ratio to larger increase of 0.40% was observed at 6% remediation ratio.The amount of soil conservation increased by 90% before and after road land consolidation in Yan ’an New Area.The gully land consolidation project improves the ecosystem service function of soil and water conservation in the watershed,effectively alleviates the human-land conflict,and is of great importance to guarantee national food security.The above study comprehensively assessed the changing characteristics of watershed soil and water conservation ecosystem service functions during the period of typical slope-gully land consolidation project in the new environment of the Yanhe River Basin,and provided a theoretical basis for the next step of ecological and environmental restoration and spatial optimization of the national land in the Loess Plateau.