Temporal And Spatial Dynamic Evolution And Driving Factors Of Soil Salinity In The Ogan Kucha River Oasis

The problem of soil salinization in the Ogan Kucha River Oasis is outstanding.Soil salinization is a slowly changing environmental problem that seriously jeopardizes the soil and the organisms that live on it,accelerates the degradation of the oasis ecosystem service function,and exacerbates desertification.The temporal and spatial dynamics of long-term sequence of soil salinization and the comprehensive mechanism of driving factors in this region are still not perfect.Therefore,in order to better develop and implement adequate soil reclamation plans and prevent any further salinization to maintain farmland and natural ecosystem stability and soil environmental remediation,spatial dynamics of soil salinization and driving factor information become very important.This study takes the Ogan Kucha River Oasis as the research object,and uses the field sampling in 2006,2008,2011,2013,2014,2015 and 2017 to clarify the Ogan Kucha River Oasis from 0-10,10-20,20-40 cm in 2006-2017.Temporal and spatial dynamic evolution characteristics of soil salinity in 40 cm soil layer,quantitative analysis of soil water content,pH,vegetation coverage,topographic moisture index,groundwater level,groundwater salinity comprehensive effect on soil salinity.The main conclusions of this study are as follows:?1?Most of the EC_1:5 coefficient of variation is greater than 100%,with strong spatial variability,and its distribution pattern is greatly affected by human factors such as irrigation.The soil moisture content,groundwater level,groundwater mineralization degree is second,and the pH is final.?2?In 2006-2017,the soil salinity content of the Ogan Kucha River Oasis increased from northwest to southeast.The soil salinity of the 0-10,10-20,20-40 cm section showed a downward trend.As the depth of the soil profile deepens,the decline in soil salinity continues to diminish.Salinization occurs mostly in the east,northeast and southeast of the study area,on the edge of the oasis and in the desert interlaced zone,and most of them are severe salinization and extreme salinization.As the depth of the soil profile deepens,the soil salinization area is relatively reduced and the degree of salinization is relatively weakened.?3?As a whole,the groundwater level in the study area gradually decreases from southwest to northeast,and the oasis is higher than the interlaced zone.The groundwater level in the lower part of the Shaya irrigation area and the southern part of the Yuejin Reservoir is generally higher than other areas.Although the groundwater level in the oasis is shallow,the salinization phenomenon is not obvious.The groundwater level in the interlaced zone is relatively deep relative to the oasis,but the soil salinization is obvious.The dynamic change of groundwater level in the sampling period from 2006 to 2015 is consistent with the dynamic change of the annual groundwater level.The groundwater level showed a downward trend in 2006-2015.?4?The groundwater salinity of the study area in 2006-2015 is>1 g/L as a whole,which is brackish water and salt water.The groundwater in the oasis is about 1-3 g/L,and the salinity of groundwater in the interlaced zone is generally higher than that in the oasis,both>3 g/L.Compared with the spatial dynamics of soil salinization,soil salinization occurred in the area of groundwater salinity>1 g/L,and mild and moderate salinization occurred in the groundwater salinity of 1-3 g/L,severe and extreme salinization occurred in the area of groundwater salinity>3 g/L.The groundwater mineralization degree in 2006-2015 showed an upward trend in the upper reaches of the oasis and in the northeastern part of the interlaced zone,and it showed a downward trend in the interlaced zone of the lower and southeastern oasis.?5?The soil moisture content of the surface layer of the Ogan Kucha River Oasis in 2008-2017 did not show a consistent spatial distribution.As the depth of the soil deepens,the soil moisture content increases.In the 2008-2017 sampling period,the soil salinity of the 0-10,10-20,and 20-40 cm sections showed an increasing trend.The surface soil water content increase trend is the most obvious,10-20,20-40 cm profile level.?6?In the 2006-2017 sampling period,the vegetation coverage of the study area was generally covered by medium and high coverage.In the sampling period of July,August and September,the high vegetation coverage area in the study area is about 40%,mainly distributed in the oasis.The middle,middle and low coverage areas are around 10%,mainly distributed on the edge of oasis.The vegetation types are mainly shrubs,and the low coverage area is about30%,mainly distributed in the interlaced zone.The vegetation types are mainly sparse forests and grasses.Contrary to the trend of soil salinization,the vegetation coverage of the study area in 2006-2017 is mainly on the rise,and the trend of the oasis edge and the interlaced zone is the most obvious.Vegetation coverage in July,August and September was higher than October.?7?Vegetation coverage?FVC?,pH,groundwater salinity?GWS?,groundwater level?GWL?,topographic wetness index?TWI?,and soil moisture content?SMC?are good explanatory variables.The soil driving factors?FVC,pH,GWS,GWL,TWI,SMC?have the same order of influence on soil salt content change,which are:FVC>pH>GWS>GWL>SMC>TWI.Vegetation coverage,pH,and groundwater mineralization have the greatest impact on soil salinization in the study area.The comprehensive interpretation ratio of soil salinity change by FVC,pH,GWS,GWL and SMC in 0-10 cm soil layer reached 46%.The comprehensive interpretation ratios of soil salinity changes of FVC,pH,GWS,GWL,SMC and TWI in 10-20 and 20-40 cm soil layers reached 54%.