Characteristics Of Vegetation And Erosion Sediment Yield In The Yanhe Watershed

The Loess Hilly-gully region is the most serious soil erosion area on the Loess Plateau,and is the major sediment source place of the Yellow River. Vegetation is the key factor tocontrol soil and water loss and recover eco-environment. Since the implementation of the“Grain for Green” project at1999, the vegetation coverage has increased obviously, andthe soil and water loss has decreased also. However, it is still not clear that which stage ofthe vegetation pattern on the Loess hilly-gully region has recovered? Whether the soilerosion has been controlled? What is the focus place of the soil and water conservation,vegetation rebuilding and ecological restoration in future? Therefore, in the present study,the Yanhe watershed on the Loess hilly-gully region was selected as the research object,the habits environment, the vegetation pattern, the soil erosion characters of differentvegetation types were studied, and the amount of channel deposition and the landslide andcollapsing erosion were survey, based on the above researches, the erosion sediment yieldcharacters of small watersheds and Yanhe watershed were analyzed. The main results asfollows:1. There are33vegetation formations in the9typical small watersheds of Yanhewatershed at the present stage including6artificial forest formations,2artificial bushformations,4natural forest formations,6natural bush formations and15subshrub-herbaceous formations. Among there are24vegetation formations in thesouthern area with the natural forest and bush vegetation formations such as Quercusliaotungensis formation, Platycladus orientalis formation, Acer buergerianum formation,Syringa pekinensis formation, and Sophora viciifolia formation distributed widely. Thereare19vegetation formations in the middle area with the Robinia psendoacacia formationand Artemisia gmelinii formation dominantly distributed, and other formations such asArtemisia capillaris formation, Stipa bungeana formation, Bothriochloa ischaemunformation, S. viciifolia formation, Caragana intermedia formation, and Hippophae rhamnoides formation widely distributed also. There are25vegetation formations in thenorthern area with the A. gmelinii formation dominantly distributed, and the R.psendoacacia formation, H. rhamnoides formation, B. ischaemun formation, S. bungeanaformation, A. capillaris formation, and Artemisia giraldii formation widely distributed.2. The distribution of the artificial vegetation in the slope displayed randomnesscharacteristic. The Q. liaotungensis formation, S. viciifolia formation, A. gmeliniiformation, A. giraldii formation, and B. ischaemun formation mainly distributed on thegully slope, and the formation of the early stage of succession, such as A. capillarisformation and S. bungeana formation, mainly distributed on the Liang/Mao slope. The B.ischaemun formation and S. viciifolia formation mainly distributed on the south-facingslopes, the Q. liaotungensis formation and S. pekinensis formation mainly distributed onthe north-facing slopes, and the other formations were not obvious sensibility for aspects.The vegetation coverage of small watersheds displayed increasing trend from southern areato northern area ranged from33.3%to40.3%in the northern area, and ranged from38.1%to42.5%in the middle area, and exceeded60%in the southern area.3. According to the erosion pin plots analysis, the soil erosion intensity of14vegetaiton types was ranged from805.7t/km2.a to5149.6t/km2.a. The ability of vegetationto control erosion was displayed as the natural forest vegetiaton larger than natural bushvegetiaton, than artificial bush vegetation, the herbaceous vegetation of the late stage ofsuccession and15-years artificial R. psendoacacia formation, and than the herbaceousvegetation of the early stage of succession and6-8-years artificial R. psendoacaciaformation.4. In the condition of rainstorm in2013, the average soil erosion intensity of all smallwatersheds were below2500t/km2.a, The erosion intensity was mainly in the category ofslightly erosion in the small watersheds of the southern and northern areas, and was mainlyin the category of mild and moderate erosion in the small watersheds of the middle area. Inthe all9small watersheds, the area which the erosion intensity was above2500t/km2.awas mainly distributed in the gully slope covered by the artificial forest-bush vegetationand the herbaceous vegetation of the early stage of succession.5. Due to the influence of the rainstorm in2013, the landslide and collapsing erosionin the small watersheds was serious. The average landslide and collapsing erosion intensitywas reached7357.66t/km2in the southern area, was3706.93t/km2in the middle area, andwas1678.04t/km2in the northern area. 6. In2013, the erosion yield and sediment deposition of Yanhe watershed was about0.27×108t and0.04×108t, respectively, and the calculated value of the sediment dischargeof Ganguyi hydrologic control area was about0.23×108t with the measured value of0.24×108t. The hillslope-gully erosion of Yanhe watershed with the average of1614.5t/km2was most serious in the middle area, then in the northern area, and the slightest in thesouthern area. The landslide and collapsing erosion of Yanhe watershed with the average of3354.2t/km2displayed decreasing trend from southern to northern. The area which theerosion intensity was above5000t/km2was mainly distributed in the sub-region ofXichuanhe watershed, Nanchuanhe watershed and Panlongchuan watershed, and the upperreaches of Xingzihe watershed and Yanhe watershed.7. At the present stage, good vegetation cover of the hillslope-gully slope could controlrainstorm erosion effectively. The erosion types of the sediment source of Yanhe watershedwas dominated by gravitational erosion in the condtion of rainstorm. Therefore, in thepremise of protecting the achievements of the “Grain for Green” project, it should bestrengthen the construction of the storage and drainage measures of inter-gully, reduce theslope runoff flowing down the gully, prevent the gravitational erosion of gully slope, andcontrol the gully erosion. Then, it might effectively prevent soil erosion, and promote therealization of landscape engineering in future.