| Soil moisture is an important factor of affecting plant growth,and plays a key role in vegetation restoration and ecological construction in karst rocky desertification regions.Taking Huajiang Gorge as the study area,and based on the Landsat-8 data and Temperature Vegetation Dryness Index(TVDI)and situ monitoring method,we try to reveal the temporal variation characteristics of soil moisture of different vegetation types was analyzed in this study.The main conclusions are as follows:(1)The underlying surface characteristics of Huajiang Gorge can be a basis for the analysis of soil moisture variation characteristics.The characteristics of the underlying surface shows that:(1)In terms of terrain,the elevation of most areas was from 500m to 1300m,the slope was from6°to 25°(the area of gentle slope was 18.80 km~2,the area of gradient slope was 15.66 km~2).The aspect was dominated by sunny slope and semi-sunny slope(the area of sunny slope was 16.77km~2,and the area of semi-sunny slope is 19.17km~2).(2)The land use was dominated by woodland,cultivated land and garden land,and with the largest distribution area of woodland(17.86km~2),followed by cultivated land(10.89km~2)and garden land(8.67km~2).(3)The karst rocky desertification occupied the most area of the study area.The karst area accounts for 87.88%of the whole region,and the rocky desertification area accounts for 61.15%of the karst area.The mild and moderate rocky desertification are the main types in the area of rocky desertification,which account for 77.51%of the area of rocky desertification,respectively.(2)Based on the Landsat-8,TVDI method was used to analysis the dry and wet condition of soil moisture.The results show that:(1)It is feasible to use TVDI and Landsat-8 data to retrieve surface soil moisture in karst rocky desertification areas.The TVDI was negatively correlated with the measured soil moisture(0-10cm)data at the same time,and passed the significance test(P<0.05).(2)The spatial distribution of surface soil moisture in Huajiang Gorge is characterized by light drought from 2013 to 2018,and low surface soil moisture in most areas(light drought,drought and severe drought account for more than 80%in rainy season and more than 60%in dry season).The spatial distribution of topography,land use and rocky desertification grade has the following characteristics:(1)On the topography,the areas with high soil moisture content are mainly distributed on the gentle steep slopes,steep slopes,semi-sunny slopes and sunny slopes in the rainy season of 900m-1100m,25°-90°,while in the dry season,the gentle slopes,slopes,shady slopes and semi-sunny slopes of 900m-1100m,6°-25°,and the areas with low soil moisture content are mainly distributed on the 500 m-900m slopes.Slopes,slopes,shady slopes and semi-sunny slopes of 6°-25°.(2)In land use types,the soil moisture content of woodland is higher than other land use types,and the soil moisture content of garden land and Cultivated land is relatively low.(3)On the level of rocky desertification:the lower the level of rocky desertification,the higher the soil moisture content.(3)The spatial and temporal variations of soil moisture in different vegetation were analyzed,which used to examine the spatial distribution characteristics of soil moisture.The results show that:(1)In terms of the average soil moisture content,the soil moisture in rainy season is significantly higher than that in dry season,and the soil moisture content decreases with the deeper vertical profile of soil layer.In the rainy season,the difference of 0-10cm in Zanthoxylum planispinum var.dintanensis,Koelreuteria bipinnata Franch.and Broussonetia papyrifera is small,10-40cm Zanthoxylum planispinum var.dintanensis and Broussonetia papyrifera are higher than Koelreuteria bipinnata Franch.In the dry season,the soil moisture in all soil layers of Broussonetia paniculata and Zanthoxylum planispinum var.dintanensis were significantly higher than Koelreuteria bipinnata Franch.(2)On the stability of soil moisture content,the coefficient of variation of soil moisture content of Zanthoxylum bungeanum var.dintanensis,Koelreuteria bipinnata Franch.and Broussonetia papyrifera belongs to the moderate degree of variation(10%<CV<100%);in rainy season,the soil moisture content of 5-20 cm of Zanthoxylum bungeanum var.dintanensis,Koelreuteria bipinnata Franch.and Broussonetia papyrifera is relatively stable,and the fluctuations of 0-5 cm and 20-40 cm are large;in dry season,the fluctuations of 0-5 cm of three Vegeta.(3)Under rainfall condition,the response time,infiltration depth and soil moisture subsidence time of vegetation to rainfall are affected by rainfall,rainfall duration and rainfall intensity.Overall presentation:the greater the rainfall,the greater the infiltration depth,the greater the variation range of soil moisture content and the later the regression time;the longer the rainfall duration,the greater the infiltration depth,the smaller the variation range of soil moisture content and the later the regression time;the greater the rainfall intensity,the greater the infiltration depth and the greater the variation range of soil moisture content,but the earlier the soil water regression time under high-intensity rainfall.(4)The redistribution of rainfall by vegetation canopy affects soil moisture change.Soil moisture content has a certain correlation with throughfall,stemflow and rainfall interception.It increases with the increase of throughfall,stemflow and rainfall interception in a certain range.And becomes less affected by throughfall,stemflow and rainfall interception when it reaches saturation.This study reveals the temporal variation of soil moisture in different vegetation types,topography,land use and rocky desertification grade in rocky desertification gorge region,which can provide some references on the tree species selection,spatial site optimization and soil water resource management in rocky desertification area. |
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