Effects Of Litter On Hydrology And Soil Erosion In The Sandy Land Of The Wind-Water Erosion Crisscross Region

The wind-water erosion crisscross region of the Loess Plateau is one of the most vulnerable areas in China and even the world.Due to topographic fragmentation,lack of soil moisture and nutrients,as well as slow recovery of natural vegetation,the eco-hydrographic benefits and erosion resistance of litter are particularly important.In this study,the litter-covered sites of three representative arbor,shrub,and grass plants Populus simonii,Caragana korshinskii and Bothriochloa ischaemum were selected as the research objects,and the bare sandy lands were taken as the control in the wind-water erosion crisscross region.By exploring the effects of litter on water conservation capacity,wind erosion reduction efficiency,runoff-reduction efficiency and sediment-reduction efficiency to reveal the soil and water conservation effects of litter in the sandy land.The main conclusions are as follows:(1)Litter cover significantly improves water conservation capacity.The comprehensive scores of water conservation capacity were calculated by using the entropy weight method as follows: litter-covered sites of Caragana korshinskii(0.889)> litter-covered sites of Populus simonii(0.484)> litter-covered sites of Bothriochloa ischaemum(0.228)> bare sandy lands(0.038).Among them,the weight ratio of stable infiltration rate,soil available water holding capacity and soil non-capillary porosity was the highest,which accounting for 15.3%,14.8%and 14.8%,respectively.Though the maximum water holding rate,maximum retention rate,effective retention rate and maximum hygroscopicity rate of litter showed that Bothriochloa ischaemum > Populus simonii > Caragana korshinskii,the water holding capacity and retention capacity of litter showed that Populus simonii > Caragana korshinskii >Bothriochloa ischaemum.Meanwhile,litter cover reduced the soil bulk density,increased total porosity,saturated water holding capacity,capillary water holding capacity and mean infiltration rate.(2)Litter cover increased the surface roughness by 70.8% and the friction velocity by36.9%.When the coverage of litter was fixed(100%)and the wind speed was adjusted from6 to 12 m/s,the wind erosion reduction efficiencies of litter-covered sites were 49.1% ～ 96.6%.When the wind speed was fixed(10 m/s)and the coverage of litter was changed from 5% to100%,the wind erosion reduction efficiencies of litter-covered sites were –10.2% ～ 80.6%.According to the trend,the critical coverage of litter of Populus simonii,Caragana korshinskii and Bothriochloa ischaemum to reduce soil erosion were 8.7%,8.2% and 9.1%,respectively.Different types of litter lead to different density of litter layer and surface roughness due to their various shapes,which ultimately affects the erosion reduction effect.The effect was particularly obvious at high wind speeds(10 m/s and 12 m/s).In general,the wind erosion reduction efficiency showed that litter-covered sites of Bothriochloa ischaemum > litter-covered sites of Caragana korshinskii > litter-covered sites of Populus simonii.(3)Litter cover significantly reduces runoff volume and sediment volume.The runoff-reduction efficiency was 58.3%～96.6% and the sediment-reduction efficiency was81.6%～96.9% on three types of litter-covered slopes,and the sediment-reduction effect of the litter cover was better than the runoff-reduction efficiency.At low rainfall intensity,slope runoff showed soil surface runoff > litter surface runoff;at high rainfall intensity,slope runoff showed litter surface runoff > soil surface runoff.Runoff was significantly related to characteristics of rainfall and litter(P<0.01),while sediment,runoff-reduction efficiency and sediment-reduction efficiency were only significantly related to litter characteristics(P<0.01).In general,runoff-reduction efficiency and sediment-reduction efficiency both showed that litter-covered slopes of Populus simonii > litter-covered slopes of Caragana korshinskii >litter-covered slopes of Bothriochloa ischaemum.In the process of vegetation restoration in the wind-water erosion crisscross region of the Loess Plateau,trees,shrubs and grasses should be reasonably planted according to the needs of different areas,and after comprehensively considering the characteristics of erosion,soil conditions,climate and hydrological,etc.,so as to maximize the value of the litter,which is an important guiding significance for the ecological restoration of sandy areas.