Effects of Land Use and Cover Change on Ecological Environment in Black Soil Region

Black soils, located mainly in Heilongjiang and Jilin provinces of China, cover a broad area from 43° to 48°N and from 124° to 127°E, with a total area of 5.93 × 106 ha. The black soils were cultivated about 200 years in south, 50 years in north and 100 years in central parts of the black soil area. These soils are one of the most fertile soils in China. These soils were cultivated for a relatively short time as compared to the soils in southern China. The vegetation changed from natural vegetation to crop-weed, to rotation of corn-soybean-wheat, or to rotation of corn-soybean. Steppified herbosa were flourished in black soil area under the proper weather condition for plant growth where the precipitation of about 500mm to 600mm mainly from April to September is synchronized with heat. The water status has changed dramatically with the use of land. If we take the water storage in the depth of 1m in spring in natural soil under the Steppified herbosa vegetation as control, the water storage un- der crops decreased to 20.4% , 20.6% , 22.6% , 27.2% , 29.3% , 27.3% after 2, 8, 15, 30, 50, and 100 years cultivation, respectively. The decrease of water storage was around 17.6% to 30. 8% in summer investigation and about 19.7% to 29.9% in autumn measurement. According to the data from the three times measurement, we make a simulated calculation. The result showed that, the storage of water in this area was as high as a 24. 9 × 109t reservoir in spring. The storage of water has decreased to 19. 2 × 109 t after a hundred year cultivation. The impact of land use/cover on the soil water status is great. The capacity of land for storing water is decreased by 20% when cultivated for crops in contrast to natural soil. After the second year when the land was initially cultivated, the capacity decreased 6.9% every year with the cultivated time. So we concluded that the effect of soil use/cover is bigger than the time effect. The effect on black soil C pool of land use method and land cover is decisive, the C pool has a increase trend under original soil condition and steppified herbosa, it will decrease when black soil were reclaimed from its original state to farmland covered with crops. Compared with the capacity on soil C pool in 1 m soil layer under original soil condition and steppified herbosa, however, the organic C pool were decreased slowly by 23.71% on farmland after cultivation of 100 years. Plants need nitrogen as a macro-element. Method of land use and land cover affected the N pool in black soil in the same trend as for the C pool. Nevertheless the change in C pool in the layer from 50cm to 100cm is not significant in the period of 100 years; it is expected that much longer time is needed to have a significant change. It is land use/cover that makes tremendous influence on water and soil losses, but there is a litde relationship of water and soil losses with the cultivation time. Compared with the original soil and natural vegetation, the annual water loss of reclaimed farmland increased 27t/( ha·a) ; and there are as much as 50. 93 × 106 t of water loss for the whole black soil area. Also the annual soil loss of reclaimed farmland increased about 38 t/ha; and there are 78. 87 × 106 t soil loss for the whole black soil area. The over-cultivation not only resulted in the soil and water loss but also deteriorated the human living environment.