Mechanism Of Wetland Evolution On The Zoige Plateau

The Zoige Plateau is the main peat swamp wetland in China,and is also an important"reservoir" of the Yellow River.Problems such as the declination of swamps that have occurred in wetlands in the region since 1970 have aroused widespread concern.In this paper,Landsat 5,Landsat 7 and Landsat 8 satellite remote sensing data from 1990 to 2016 are used as the main data sources.Through field surveys and experiments,remote sensing images,meteorological and hydrological data and theoretical analysis,the temporal and spatial changes and characteristics of wetland evolution in the Zoige Plateau were studied over the past 30 years.In addition,we studied and analyzed the influencing factors of wetland from climate change,human activities and hydrodynamic factors,further explored the development and changes of natural channels and artificial ditches,and the mechanism of degradation of marsh wetlands.The following main results were obtained:(1)The change in construction land and desert area is most obvious.The area in 2011 was 5.84 times and 1.35 times of the 1990 area respectively;the forest area was decreasing at a rate of 0.66 km2/a;the peat bog wetland area was 78.62 km2/a.The rate of water continued to decrease,and the fluctuation of water area was mainly affected by the change of rainfall.The change of vegetation coverage decreased first and then increased and tended to be uniform.(2)From 1967 to 2012,the annual rainfall showed a slight decrease at a rate of 0.4 mm/a,and the temperature showed an increasing trend;at the end of the 1990s,the reference crop evaporation ET0 increased,and the growth rate of the actual evaporation amount ETc in the past 45 years was small.(3)The area of desertification increased at a rate of 2.17 km2·a-1 from 1990 to 2016 with the increase from 1990 to 2004,decrease from 2004 to 2011,and increase from 2011 to 2016.It was mainly distributed around margins of the peat bog,rivers,lakes,and pastures;severe desertification is mainly distributed on the edge of peat bog on the northern bank of the first bend of the Yellow River and on the peat bog area from the Zoige County to the junction of the Heihe River and the Yellow River;its internal formation and expansion is the geological structure of the area with loose and unstable deposits and sediments.The external causes are insufficient hydrological conditions due to climate change and regional drainage,as well as human activities(excessive grazing)and rodent damage to the surface vegetation.(4)The degradation of the plateau wetland is essentially due to various reasons to break the original water balance of the wetland and turn the wetland irreversibly into dry land.The main reasons are likely to be due to factors such as traceability of natural water systems,artificial ditches,and overgrazing.Artificial ditches are the most rapid and effective external force.