Study On The Landscape Pattern Of Hydrogen And Oxygen Isotopes And Its Key Impact Factors In Multiple Water In The Lashi Lake Basin,Yunnan

Isoscapes are useful tools for studies concerned with hydroclimatic processes,at multiple scales,and their effects on water resources and it is also a visual technology.In this paper,the typical bazi watershed in Lashi Lake,Yunnan Province was selected as the research object,and isotope samples of atmospheric precipitation,surface water and groundwater were collected in July,2021.Using isoscape mapping,landscape pattern analysis methods and gradient analysis methods in landscape ecology,isoscape mapping of surface water and groundwater isotopes in Lashi Lake watershed was mainly carried out at different spatial scales,to further explore the characteristics of isotope landscape pattern for regional multi-water bodies and its key impat factors,and analyze the transformation relationship between multi-water bodies.The specific conclusions are as follows.In terms of the characteristics of multi-scale land use pattern in the watershed,the semi-variogram determines that the radius of 210m moving window is an appropriate scale to reflect the inherent spatial variation characteristics of land use pattern.The land use pattern index of the whole watershed is mainly controlled by the land use pattern in the dam area,which is highly homogeneous in the mountainous area above 2500m above sea level,while the dam area below 2500m is diversified,fragmented,and complicated in shape,especially in the surrounding areas of construction land such as villages and highways in the dam area.The land use landscape in the dam area is fragmented by high-intensity human activities.With the increase of sampling point buffer from 50m to 300m,the fragmentation and aggregation of landscape in the buffer gradually decreased,and 100m～200m was an important buffer zone for landscape changes.In terms of the characteristics of stable hydrogen and oxygen isotope composition of atmospheric precipitation and its impacting factors:the range of atmospheric precipitation isotopeδ¹⁸O andδD are-17.11‰to～-11.55‰and-118.2‰to～-77.45‰respectively,which is consistent with the global atmospheric circulation.The slope and intercept of local meteoric water lines are small,indicating that water vapor is subjected to strong evaporation and fractionation during precipitation.With the extension of sampling time,δ¹⁸O andδD value shows a trend of increasing first and then decreasing,and then continuously dilution.Theδ¹⁸O has a significant positive correlation with temperature,which affects precipitation in short time scale,but it is not significantly related to rainfall,and may be affected by local water vapor cycle and water vapor transport during rainfall.In terms of multi-scale surface water hydrogen and oxygen isoscape characteristics and its impacting factors,the stable isotope values of surface water are generally positive,among which the Lashi Lake water is highly evaporating,and the isotope has undergone unbalanced fractionation.The stable hydrogen and oxygen isotope of lake water is more positive than other types of water in surface water,and the slope and intercept of the evaporation line equation are the smallest.In isoscape mapping,through precision comparison,the interpolation methods with the highest precision at dam area scale,lake scale and watershed scale are Kriging interpolation,radial basis function and Kriging interpolation respectively.The maps at three scales reflect that the isotope values in the lake are positive,especially in the center of the lake,where the isotope values are the highest,and the surface water isotope valuesδ¹⁸O andδD value decreases from the lake area to the north,south and east,while the western edge of the dam area is positive.The spatial distribution of d-excess shows that the value is high in the north and east,and low in the lake area and reservoir area.In terms of impacting factors,100m～200m is the scale that the land use pattern has the strongest impact on the surface water isotope.The fragmentation of land use landscape structure,the patch area of the largest land use landscape type,diversity and dispersion affect the isotopic composition change of Lashi Lake to a certain extent.Based on gradient analysis,the correlation betweenδ¹⁸O and altitude is significant,and the altitude effect on the northern transect of Lashi Lake is more obvious than that on the southern transect.For the characteristics of isoscape in groundwater and its influencing factors,the groundwater isotope values are generally negative,δ¹⁸O andδD value gradually decreases from south to north and from east to west.The high value area is close to residential areas,buildings and roads.The isotope value of groundwater in the area with river water recharge is relatively negative.The isoscape pattern has a significant relationship with the land use pattern,especially in the buffer zone with a radius of150m～200m.The isotope values of all kinds of zones are highly correlated with the altitude,among which,due to the influence of surface water recharge,there are different pattern characteristics in the southern sample zone and the northern and eastern sample zones.In terms of the transformation relationship of multi-water types,precipitation is the common recharge source of surface water and groundwater in Lashi Lake watershed,and there is a mutual recharge relationship between surface water and groundwater,and groundwater is more affected by the recharge of surface water.The Lashi Lake water is subject to strong evaporation,and its isotope value is more positive than that of other water types.The relationship between isoscape pattern of groundwater and land use pattern and altitude is stronger than that of surface water.There is a positive spatial correlation between the isotopes of surface water and groundwater,and the spatial distribution is agglomerated.The agglomeration areas are mainly located in areas with high human activity intensity,and the agglomeration hotspots are mainly controlled by groundwater isotopes.