[Show abstract][Hide abstract] ABSTRACT: The distribution of farmland shelterbelts and their effects on different manners of water erosion in the lands between them were analyzed on the basis,of three years field. investigations and two years plot observations of runoff and sediment yields. The results showed that tillage direction of the area was decided by distribution pattern of the shelterbelts because of the local special topographical characteristics and the tillage practices by big machines, which led to about 1/3 of the lands in the small catchments under up and down slope cultivation, and made rill erosion in the furrows more severely, meanwhile, the shelterbelts played an important role in alleviating the intensity of ephemeral gullies and gullies. So the conclusion is that the shelterbelts will exert positive effects on soil and water conservation only when their distributions are reasonable.
[Show abstract][Hide abstract] ABSTRACT: According to the characteristics of water and erosion environments of different natural zones on the Loess Plateau, this paper
studies changes of vegetation types, distribution boundaries of forest and grass as well as restoration capacity of vegetation
in different natural zones in the middle Yellow River. The annual precipitation of 530 mm is the critical annual precipitation
for forest and grass distribution in the middle Yellow River. Among the zonal and azonal environmental factors affecting watershed
sediment yield, the intermediate diameter D50 (mm) of suspended load and forest coverage (V, %) play the leading role. Of them the effect weight of forest coverage (V,
%) on catchments sediment yield is only 3.4% less than the role of the intermediate diameter (D50, mm), they are almost the same. To effectively control soil erosion in semiarid, especially in hilly-gullied areas and make
sediment transport modulus reduce to less than 6000 t/km2, it is rather difficult by merely relying on natural restoration of forest. In the process of cultivated land conversion
into forest land and grassland, measures suiting local conditions should be adopted in tree species selection and artificial
afforestation (grass planting) based on management with biological measures for slopeland and engineering measures for hilly-gullied
areas, so that watershed forest coverage in key counties can reach at least over 30%. Compared with the standard period of
precipitation prior to the 1960s, with the decrease of annual precipitation at various periods, plant productivities decline
to different degrees under natural conditions. The main reason accountable for the low survival rate of new seedlings and
grass over years is due to precipitation decrease. In light with regression models of annual precipitation and natural vegetation
productivities, it is possible to obtain estimated values of watershed natural vegetation productivity and eco-water consumption
needed for the restoration to the standard period respectively for the present time or arbitrary period since the 1970s, thus
providing a scientific basis for forest and grassland restoration in the middle Yellow River and the management prospect.
No preview · Article · Jun 2005 · Science in China Series D Earth Sciences
[Show abstract][Hide abstract] ABSTRACT: Threshold of environmental elements in drainage basin sediment yield refers to, under effect of climate, underlying surface
and human activity, a turning point of abrupt changes in drainage sediment yield related to environmental element characteristics.
Previous studies on threshold of sediment yield of relevant drainage basins were mainly concentrated on impact of natural
zones with a few researches on impact of other environmental elements. Particularly studies on compound environmental element
threshold in drainage basin sediment yield remain blank today. Studies indicate that sediment yield in drainage basins is
affected by compound interactions and complex actions. Based on single element analysis, the present paper gives quantitatively
compound threshold of environmental elements affecting sediment yield of the drainage basin between Hekouzhen and Tongguan
in the middle Yellow River by the method of multi-variant, polynomial formula regression analysis.
No preview · Article · · Science in China Series D Earth Sciences