Wetland and its degradation in the yellow river source zone

Abstract

Plateau wetlands in the Yellow River Source Zone are distributed in a wide range of geomorphic zones. They can be classified as alpine, piedmont, valley, floodplain, lacustrine, riverine and terrace wetlands on the basis of this geomorphic association. Some wetland types have shown signs of degradation triggered by environmental desiccation and improper land management strategies. The degradation process is characterized by four stages: intact, slight (dryland), severe (wasteland) and extreme (badland). Wetland degradation can be reversible or irreversible, depending on whether the tolerant threshold of the wetland ecosystem has been exceeded. The change from healthy wetland to dryland is considered quantitative and reversible, in that only the water reserve in the wetland system has been reduced whilst most of its ecosystem functions are retained. Beyond the dryland stage, degradation is considered irreversible in that external intervention is essential to rehabilitate the degraded system via minimizing human disturbance, and even engineering work may be needed. Both the process and the severity of degradation can be considerably accelerated by the joint effect of multiple degradation drivers that far exceeds the sum effect of individual factors. The severity of wetland degradation is commonly assessed from biological and hydrological indicators, including vegetative cover and proportion of original plants, surface water reserve and soil moisture, and the level of soil erosion induced by rodent burrowing. To be effective, any rehabilitative measures of degraded wetland must target the roots of the degradation problem, which are likely to be site-specific.