| Soil erosion is a severe ecological problem in the Loess Plateau region of China and it has undergone tremendous changes under the influence of human activities.This paper use the landuse data(derived from the scanning aerial in 1977,Google Image in 2004,and the high-resolution image of 2015)and vegetation coverage data(extracted from the Landsat remote sensing images of 1977,2004 and 2015)based on the principle of soil erosion,combining the data of precipitation,soil,DEM,and soil conservation measures to calculated the soil erosion based on Chinese Soil Loss Equation(CSLE).The spatio-temporal changes of soil erosion in the Jiuyuangou watershed from 1977 to 2015 and comprehensive management of soil and water conservation in the Jiyuangou watershed.The results will support data and technology for soil erosion analyze.The anslysis shows that:(1)From 1977 to 2015,the cultivated land increased from 33.44 km2 in 1977 to 35.03 km2in2004,and decreased to 11.56 km2 in 2015.During this period,the grassland decreasing firstly and then rising.Its value decreased from 34.21 km2 in 1977 to 25.76 km2 in 2004 and decreased to 45.095 km2 in 2015.The forest land shows a slowly increasing trend,from 0.16km2 in 1977 to 8.18 km2 in 2015;the orchard has continued to increase slightly to 3.92 km2in2015;the construction land,roads and water areas have increased slightly.According to the land-use transfer matrix,the area of grassland transferred to cultivated land accounted for29.67% of the transferred area of grassland;the area of cultivated land converted to grassland and woodland accounted for 16.30% and 3.34% of the transferred area;the area of grassland converted to forest land accounted for the transfer.9.65% of the area.(2)From 1977 to 2004,soil erosion showed a trend of decreasing first and then increasing.From 2011 t/km2·a,where the soil erosion was most severe,to 164 t/km2·a in 2004,it increased slightly to 2015.320t/km2·a of the year.Above 1500~2500t/km2·a,the erosion modulus accounted for 22% of the erosion in the basin.Soil erosion was relatively weak in2004 and 2015,and the erosion modulus in 2004 was less than 300t/km2·a.(3)There is no obvious erosion,slight or moderate erosion type in the farmland of the Jiuyuangou watershed,and the increase of cultivated land will increase the occurrence of erosion.The impact of grassland on soil erosion first showed a trend of decreasing and then increasing.When the area of forest land expands,the intensity of erosion above slight erosion will decrease and the increase will be larger without obvious erosion.The increase of forest land and grassland has an effective control over erosion.(4)The relevance of the land use,slope,slope length and soil erosion show that the intensity of soil erosion increases with the increase of slope and slope length,and the effect of cultivated land on soil erosion is greater than that of non-cultivated land.The main cause of soil erosion is the cultivated land of high slope.(5)The ridge-projection slope land and gully slope land statistical analysis shows that: the erosion of the gully slope land accounted for 67% in 1977,and accounted for 43% after 2004.This shows that maybe the major part of erosion and sediment yield is ridge-projection slope land when the level of governance is relatively high. |
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