Spatial Variation Of Soil Physicochemical Properties In Water-level-fluctuation Zone:A Case Study In Nuozhadu Reservoir

Water-level-fluctuation zone(WLFZ)is a special periodic alternately drained area whose soil is periodically flooded and exposed due to seasonal water level alteration in nearly all rivers,lakes and reservoirs worldwide.Seasonal water storage leads to periodic change of water level,which has a huge impact on soil organic matter content,soil heavy metal content and other soil characters,then dominantly control the structure and function of aquatic ecosystems.The Lancang-Mekong River is a typical river in longitudinal range-gorge region,and WLFZs in this area has a characteristic of large drop and wide range.Currently researches in this area didn’t consider the effects of land uses on soil physicochemical properties,neither did soil vertical variation.In this study,Nuozhadu Resevior where located in Lancang-Mekong River was selected as case area.As for there were three main type of land use(forest,farmland and rubber land)before dam construction,so based on different land use,soil samples were collected along altitude.The purpose was to characterize spatial variation of soil physicochemical properties in WLFZ and main conclusions are as follows:(1)Soil physical propertiesIn general,soil sand content increased,silt and clay content decreased,soil bulk density and soil moisture content increased after dam construction.Soil physical properties show differences in different land use.Soil sand content,soil bulk density and soil moisture content increased along with altitude increments while soil silt and clay content decreased.(2)Soil chemical propertiesIn general,soil total phosphorus content(TP)and soil pH increased,soil organic carbon density(SOCd),total nitrogen content(TN),total potassium content(TK)and available nitrogen(AN)decreased after dam construction.Soil chemical properties show differences in different land use.SOCd,TN,AN decreased in forest along with altitude increments and showed no content change in farmland and rubber land.TP and TK increased in forest and decreased in farmland and rubber land along with altitude increments.Soil pH decreased in these three types of land use along with altitude increments.(3)Soil heavy metal contentIn general,Cu,Cr,Fe,Mn,Ni and Zn content increased after dam construction.Soil heavy metal content showed differences in different land use.Cr and Zn content decreased and Cu.Mn and Ni content increased along with altitude increments.Fe content decreased in farmland and increased in forest and rubber land along with altitude increments.(4)The results showed that seasonal water storage caused plants died and soil exposed which lead to huge change of soil physical and chemical properties.And these changes showed differences in different land use and altitude.WLFZs in Nuozhadu reservoir is still in the early stage and there’s no significant difference in soil properties,so further study is needed to investigate the effects of drowning on soil properties in long period of time.