| In view of the underlying surface change for the implement of soil erosioncontrol and the Grain for Green Programme on the Loess Plateau, the paper took theHe-Long Region as typical study area, utilized the field survey, RS/GIS analysissimulation, and the hydrological statistics methods to analyse the spatiotemporaltrends of environment including precipitation, vegetation, etc., discuss the erosion andsediment yield variation characteristicon, and analyse the driving factors. The resultsof this research are as follows:(1) Spatial and temporal evolution of soil erosion and sediment yieldenvironment1) Precipitation and rainfall erosivity: Precipitation was not significantly reducedfrom1981to2010at interannual scales. Areas of showing decreasing trend ofprecipitation took81.80%of the whole region. Rainfall erosivity was not significantlyreduced at interannual scales. Areas of rainfall erosivity showing decreasing trend was7.72×104km~2. Overall, rainfall erosivity at Yanhe and Shiwangchuan reduced. Areasof rainfall erosivity decreased took26.62%and57.13%of the corresponding basinrespectively at Kuyehe and Huangfuchuan.2) Soil erodibility: Areas of soil erodibility decreased occupied79.80%of thewhloe region from the late1970s to2010. Soil erodibility reduced in Kuyuhe andHuangfuchuan. Areas of soil erodibility decreased constituted58.65%and14.03%ofthe Yanhe and Shiwangchuan areas.3) Vegetation cover: Vegetation cover increased highly significantly in thegrowing season from2000to2010. And vegetation cover increased the most significantly in July, August and September. The improve situation of vegetation wasbest in Yanhe.4) Soil and water conservation measures: The total area of soil and waterconservation measures increased from12600km~2to34300km~2during1979and2011,which was mainly for the increase of afforestation and grass. The largest change ofarea was in Kuyehe, followed by Yanhe. The relative change of areas was largest inQingjianhe, and followed by Xinshuihe, Yanhe, and Kuyehe.(2) Spatial and temporal variation of erosion and sediment load1) Soil erosion: The soil erosion modulus was2205.4t/km~2·a at2011on theHe-Long Region. Area of suffering soil erosion was5.26×104km~2which occupied46.72%of the whole area. Among of that, area of suffering moderate soil erosion waslargest with1.70×104km~2which takes15.08%of the whole area. The soil erosionmodulus was1033.5t/km~2·a in Hufuchuan,1487.2t/km~2·a in Kuyehe,2986.7t/km~2·ain Yanhe,1026.2t/km~2·a in Shiwangchuan. The proportion of soil erosion area in thebasin area of the He-Long Region is largest inYanhe.The soil erosion area reduced significantly with22783.6km~2and a decrease of30.22%, the erosion intensity descended, and the severe erosion changed the mostdramatic on the He-Long Region from2000to2011. The the very strong and violenterosion area reduced very severely at typical basins of different underlying surfaceand the mild erosion increased significantly. And the erosion area variation degreewas largest in Shiwangchuan.2) Sediment load: The multi-year average sediment load is31044.8×104tonsfrom1980to2010, and16020×104tons from2000to2010. The annual averagesediment transport modulus is2747.3t/km~2·a from1980to2010, and is1417.7t/km~2·a from2000to2010. Transition time is around1998on the He-Long Regionand typical watersheds.The sediment showed a decreasing trend over time on the He-Long Region andeach typical basin, especially on the time period during1998and2010, the the degreeof reduction is more dramatic and the zero sediment discharge days showed aobviously growing trend. The sediment load reduced50.2%after the Grain for GreenProgramme compare with that before the programme at wet period, and the change value was-47.6%at dry period. The change of erosion and sediment yield is verydramatic in Kuyehe and Huangfuchuan where the erosion and sediment yield is mostserious.(3) Erosion and sediment yield driving factors as environment and humanactivities.1) Effect of precipitation to vegetation: Areas of NDVI being positivelycorrelated with precipitation constituted73.3%of the whole region, among of which,areas of showing significantly positive correlation occupied22.14%.Vegetation is positively correlated with precipitation on Huangfuchuan andKuyehe. On the contrary, the correlate relation is mainly negative on Yanhe andShiwangchuan where the precipitation is reduced, which illustrates that humanactivities play an effective role.2) Effect of precipitation to sediment load: Transition time of annualprecipitation was not significant. The fluctuating state of preicpitation is similar tothat of sediment load at the He-Long Region and the four typical basins, however thechange degree is small overall. The annual sediment load is small and shows areducing trend after1998.The sediment yield coefficient of precipitation changed dramatically on thewhole region and the four typical basins, and the significant of correlation coefficientis very low after1998which illustrates that the sediment load is mainly influnced byhuman activities3) Land use change driving by human activities: The Grain for GreenProgramme achieved good ecological benefits for the forestland increasedsignificantly, the sandland and farmland changed to grassland and forestland, and thelanduse types changed violently. Number of Patches increased severely, mean patchareas increased significantly. The Land use structure are by beginning tocentralization from fragmentation and heterogeneity. The human activities increasethe forestland effectively on the He-Long Region.The case of landuse change at the four basins is similar to the whole regionwhere the farmland reduced and grassland and forestland increased. Among of that,the change degree is least in Shiwangchuan. 4) Effect of conservation measures to soil erosion: Conservation measuresaveragely reduce the soil erosion modulus by471.9t/km~2·a, and the soil erosion areaby14.52%. The conservation measures can reduce the extremely strong and strongsoil erosion area effectively. Soil erosion area reduced by55.22%in Huangfuchuanwhose change degree is largest. |
PDF Full Text Request