Changes Of Gully Erosion Intensity After Drainage In The Zoige Peatland

Zoige plateau is in the eastern part of Qinghai-Tibetan Plateau,which occupies the largest alpine peatland in China.In the 1970 s,artificial drainage was conducted to enlarge pastures.A large area of peatlands had been transformed into meadow,so that it showed degradation syndrome,with gully erosion occurring where around ditches especially.In this study,in order to illuminate the response mechanism of gully erosion to artificial drainage,based on fieldwork in 2014 and 2015,we take gully erosion on Riganqiao in Hongyuan as the research object to investigate its distribution characteristics by using field survey,remote sensing interpretation,GIS analysis and experimental analysis.We also study the effect of artificial drainage on land subsidence and ecological effects,reveal the mechanism of gully erosion occurrence and development under drainage stress,and discuss the influences of gully erosion on Zoigepeatland.The main conclusions are as follows:（1）Compared with the earlier measurements of peat thickness in 1983,current peat thickness is thinner.The rate ranged from 0.37 mm/a to 2.22 mm/a.It is larger than 1 mm/a in un-drained sites,and less than 1 mm/a in drained sites.Moreover,the variation of peat thickness had an obvious dissimilarity（p<0.05）.This suggested that drainage intensified peatland surfacerecession.（2）Based on the results of fieldwork,gully can be divided into four types for different causes of gully formation: the ditch wall is trampled by animals;the ditch bank collapses forits lower part erodes;the head-cut of ditches;soil pipes collapse.In addition,the dominant process of gully erosion is associated with lateral erosion near ditches,while incision in areas with larger distance from ditches.（3）For the analysis of gully morphologic characteristics,the volume（V）-length（L）relationship for gully has been established: V = 0.2465L¹.2094（n = 72,R² = 0.7762）（n =72,R² = 0.7762）.Moreover,the gully lengthening rate is faster than gully widening rate.（4）Based on the results of remote sensing interpretation and GIS analysis,in the past 50 years,erosion gully density has increased from 0.34±0.13 km/km² to 1.87±0.13 km/km²,and the erosion rate has risen from 0.35+0.15 mm yr^-1 to 1.67±0.07 mm yr^-1.Comparison betweendifferent sub-watersheds indicated the greater the drainage intensity,the more obvious changes in erosion density and erosion rate,such as sub-watershed 1 and 2.Combined with DEM,the coefficient b is >0.2 in S-A equation,which indicated the process of erosion by surface runoff is the dominant process of gully erosion.（5）Comparing soil physical and chemical properties,at different sites,showed that soil organic content（SOC）,total nitrogen content（TN）and soil porosity（SP）rise as the distanceincreases from ditches,but bulk density（BD）and degree of decomposition decrease.In addition,one-way ANOVA revealed that they are different significant（p<0.05）.Based on vegetation survey results,the plant communities showed a succession sequence from hydrophyte to mesophyte.The changes of soil and community type illuminate Zoige peat mire has been degenerating.（6）For the consequences of peat mire erosion,in this study,we focus on two areas where the characteristics of erosional system have significant implications.These are: gully erosion and carbon loss;and release of stored contaminants from eroding peat mires.The results demonstrated that the rate of POC loss is 3.95 gm^-2yr^-1,DOC loss is 2.00 gm^-2yr^-1,and the loss of primary Productivity is 0.25 in gullied areas.Above all,C loss rates contribute to 1/3 of C accumulation rates(20.4 gm^-2yr^-1)h and extremely influence peatland carbon balance.What’s more,Erosion promoted the release of stored contaminants from soils by changing micromorphology and hydrology of peatlands,which leads to the ecological pollution in the downstream.The developing degree,erosion type and distribution characteristics of gullies are influenced strongly by geomorphology and the composition of ground materials.Drainages lead to land subsidence and changes of peat properties,which is beneficial to gully erosion.This research reveals the influencing factors and mechanisms of changes gully intensity in Zoige peatland under drainage,which provides a reliable theoretical reference for the restoration of erosion peatlands and the evaluation of erosion effect...