The Quantitative Characterization Of Human Factors Effecting The Soil Erosion Environment

With the progress of human history, the human being has changed the world so widely thathuman being has touched every corner of the world. Soil erosion is a natural process, however,due to human activities, great changes has taken place in erosion forms, the degree of loss, thespatial distribution and evolution processes. Understanding how human beings influence thesoil erosion and related mechanism and processes and quantifying this influence is of greatimportance to readjustment of the human activities and soil and water conservation policymaking.This paper, took the Yanhe River watershed and Zhifanggou watershed as case study areas,analyzed surface morphology and vegetation cover using PE-factor (soil and waterconservation engineering measures) and C-factor (vegetation and management factor) andquantified the impact of human activities on soil erosion environment, and clarified thevariation in the vegetation pattern at the landscape scale. Meanwhile, taking a typical smallwatershed of Zhifanggou watershed as an example, reconstructed artificial terrain DEM ofdifferent time series using Hc-DEM method, and analyzed the evolution of the topographicfactors such as slope degree, and slope length and related environmental factors. After that,a quantitative evaluation of the evolution of soil erosion in Zhifanggou in past70years andthe impact of human activities on this evolution was done. The main conclusions are asfollows:(1) Delineated the surface morphology using the factor value of soil and water conservationengineering measures, studied the extent of the impact of human activities on topography bybuilding an index of human activities topographic effects, and quantitatively analyzed thehuman impact on the evolution of surface morphology in Zhifanggou watershed and YanheRiver watershed The values of engineering measures factor value linearly decreased withtime in Zhifanggou watershed and Yanhe River watershed, and the changes in surfacemorphology changes could help control soil erosion. The trends of topographic index Htof human activities in different periods showed that the extent and scope of surface morphologyresulted from human activities continued to increase in Zhifanggou watershed from1938to1987, then to decrease except for a slight increasing during the period from1999to2003. Theextent and scope of changes in surface morphology due to human activities increased first andthen decreased, but the most obvious impact had been observed in in period from1997to2000. The analysis of man-made terrain DEM in Zhifanggou watershed showed that slope,slope length, slope factor, slope length factor, slope of slope length factor showed adecreasing trend as to the impact of human activities on terrain continued, which the slopechanges with minimal degree, the slope length changes with largest degree. The change inslope length was bigger than that in slope. The average annual decreasing rate was3.58%and11.94%respectively, and the terrain factor valued decreased with the increase of basicfarmland and residential area.(2) Described the surface cover(vegetation) using the value of cover-management factor,analyzed the extent and scope of the impact of human activities on surface cover by buildinghuman activities vegetation effects indexes, and quantitatively analyzed the human impact onvegetation cover in Zhifanggou watershed and Yanhe River watershed. Thecover-management factor values of Zhifanggou watershed showed a4times parabolarelations with time, and increased first then decreased in Yanhe River watershed. The analysisof the variation of the vegetation index Hcsuggested that human activities impactedvegetation by destruction in Zhifanggou watershed from1938to1958, then by restoringactivities, and this restoring effect was most obvious from1987to1999. The disruptiveimpact of vegetation due to human activities decreased, and the restoring impact increased inYanhe River watershed from1986to2006. Big changes occurred in the landscape pattern ofvarious vegetation factors in Zhifanggou watershed and Yanhe River watershed, the area ofwoodland and farmland changed significantly in Zhifanggou watershed, and the area ofgrassland changed a little, the landscape diversity and evenness index decreased first and thenincreased, while the woodland, grassland and farmland changed greatly in Yanhe Riverwatershed, the landscape diversity index and evenness index increased year by year.(3) During the studying period from1938to2010, soil erosion experienced a dramaticincreasing period and then a decreasing one. Soil erosion modulus was the largest, and fromthen on showed a generally downward trend. In1938, soil erosion of middle degree was themainly erosion type, while severe erosion was the mainly erosion type during period from1958to1978. Nevertheless, soil erosion declined in years from1978to1998. From1999, thearea associated with slight erosion averaged3.85km2, while extreme erosion accounted for8.96%of the total area of the watershed. Erosion was significantly influenced by topography at a watershed-scale and increased dramatically with slope increase. The soil erosion mainlyoccurred in slopes above25°. Noticeably, more soil erosion was from slopes more than35°and south facing slopes produced more erosion than north facing ones. Among various landuse types, the slightest erosion was associated with forestland, and the strongest one withdeserted land. Farmland was the major source of erosion during1958-1998, while in thefollowing period, the key area for soil conservation switched to grassland. Though theeco-environment of Zhifanggou watershed has been markedly improved through30years ofcomprehensive management, severe soil erosion on steep slope of gullies and hills remained aproblem demanding attention.(4) We took1938as a base period with exacerbation of soil erosion by human beings, andanalyzed the role of human activity in the increase of soil erosion by comparing thedifferences of soil erosion in1958and1938; we then took1958as a base period with thedecrease of soil erosion by human activities, quantitatively analyzed the impact of humanactivity on the decease of soil erosion in different periods by comparing the differences of soilerosion between1978-2010and1958, Compared to1938, the increased soil erosion was249111.57t in1958due to the human activities, of which the increase of soil erosion due tovegetation cover changes was310890.84t while the changes in surface morphology reducedsoil erosion by61779.27t. Compared to1958, the soil erosion decreased year by year due tothe human activities from1978to2010.The reduced erosion was about11870.47-140085.99t,of which7078.48-14442.88t was reduced by the increase of vegetation cover, and4971.98-25301.57t was reduced due to surface morphology change. Compared to the changesin surface morphology, vegetation cover changes reduced more soil erosion.