Study On Soil Physiochemical Properties And Assessment Of Soil Environmental Quality In Wetlands Of Dongting Lake

Soil physiochemical properties and environmental quality,especially soil organic carbon,nutrients, heavy metals in wetlands of Dongting Lake were researched.This scientific data can be provided for local indurstries,angriculture.Also,The evidence can be provided for environmental safety and ecological recovery projects of wetlands which have been recoveried areas.The main results were as follows:(1) The soil texture of wetlands of Dongting Lake was mostly sandy soil and loam.The variation of bulk density was obvious according to different areas,different soil depth,different communities.The soil bulk density were 0.42～1.90g·cm^-3.The particle density were 0.33～7.96 g·cm^-3.The soil water content were 22.00%～61.20%.The soil moisture content increased gradually along the direction from edge to centre of the wetlands.(2) There were significant differences of soil organic matter in 4 types wetlands.The horizontal distribution of soil organic matter was Carexspp-dominated wetlands(33.04±10.86g·kg^-1)＞Phragmites-dominated wetlands(23.23±4.78g·kg^-1)＞the man made populus-dominated wetlands(16.92±3.44g·kg^-1)＞mud and sand-dominated wetlands (4.6±0.59 g·kg^-1),and there were negative relationship between soil organic matter and human disturbances except for the mud and sand-dominated wetlands.The vertical variation of soil organic matter was reduced with increasing depth from 0 to 60cm except for the mud and sand-dominated wetlands.There were negative relationship(R=-0.594^*,p＜0.05)between soil organic matter and pH,a significant positive relationship(R=0.830^**,p＜0.01) between soil organic matter and soil water content,and a significant negative index relationship(p＜0.01) between soil organic matter and soil bulk density,the regression equation is y=367.308e^-2.462x(R=-0.885,n=43).(3) According to different vegetation succession law, there were significant variation of soil organic carbon and total N in 5 vegetation communities:The horizontal distribution of soil organic carbon and total N along the direction from centre to edge of the wetlands was Juncus effusus communities＞Cyperaceae brevicuspis communities＞Polygonum hydropiper communities＞Phragmites australis communities＞salix sp.communities.There were negative relationship between soil organic carbon,total N and elevation.(4) The horizontal distribution of soil nutrients under different vegetation communities was Cyperaceae brevicuspis communities＞Phragmites australis communities＞Miscanthus sacchariflorus communities＞Populus euramericana communities＞Polygonum hydropiper communities.Soil nutrients under different vegetation communities decreased first and then increased,or increased first and then decreased,or reduced with increasing depth from 0 to 60cm.There were apparent differences of soil nutrients in 5 different vegetation communities,specifically there are most obvious differences between Polygonum hydropiper communities and other communities.(5) The order of content of heavy metals in wetlands of Dongting Lake was Zn＞Cr＞Ni＞As＞Cu＞Pb＞Cd＞Hg.In this eight heavy metals,there were all samples of Cd,Hg and As elements exceeded the background value.The pollution was most.serious.In other heavy metals,there are parts of samples exceeded the background value.(6) Correlation exists in soil heavy metal elements.Most of it were positive correlation, element Hg and other soil elements were negative correlation relationships.There were a significant positive relationship between Fe,Mg,K and most of heavy metal elements.For instance,the regression equation of Fe and Mn was y(Fe)=7523.66+31.13x(R²=0.865^**,p＜0.01).Soil organic matter,pH,water content exert an influence over soil heavy metal elements.(7) According to soil single pollution index, the sequence of pollution index of soil heavy metals in wetlands of Dongting Lake was Cd＞As＞Hg＞Ni＞Zn＞Cu＞Cr＞Pb.According to Nemrow composite index,the order of pollution index of soil heavy metals in wetlands of Dongting Lake was Jingchengyuan＞tuanzhou＞liumenzha＞xiaoxihu for different areas,Populus euramericana communities＞Miscanthus sacchariflorus communities＞Phragmites australis communities＞Polygonum hydropiper communities＞Cyperaceae brevicuspis communities under different communities,Transition layer＞Gley horizon＞Peat horizon＞Sod layer by different depth.It can be seen,developed paper industry and many factories caused severe heavy-metal contamination.The most serious pollution were elements Hg,As and Cd.It also shows that the Hg,As and Cd were absorbed by the wetlands of Dongting Lake.So,wetlands of Dongting Lake plays a very important role in the absorption of heaw metals.