Assessment Of Water Ecological Carrying Capacity And Its Response To Land Use In Northwestern Yunnan

Northwestern Yunnan is located in the southeast of Qinghai-Tibet Plateau,where the ecological environment is sensitive and fragile.It is of great importance to upper Yangtze River water protection.With increasingly intensified human activities,land use in Yanggongjiang watershed located in Lijiang of Northwestern Yunnan has been altered significantly,leading to water exhaustion of Heilongtan springs and river net in the region.It is particularly necessary to analyze the pattern of land use and optimize the regional development pattern from the perspective of water ecological carrying capacity.Current water ecological carrying capacity study has not included habitat assessment,and in this study a new concept and model of water ecological carrying capacity based on water quantity,water quality and habitat is established.The Yanggongjiang watershed is selected as a case study to assess its water ecological carrying capacity evolution and its relationship with land use.A system dynamic model of water ecological carrying capacity was built to predict its potential change under different scenarios,and based on which land use policy was drawn.Main Results are showed as followed:(1)Forest is the dominant land use in the region based on five land use datasets from 1980 to 2015,and its area and proportion had been increasing mostly derived from cropland and pasture.Urban is also increasing with the decrease of cropland.At the landscape level,the number of patches decreased first and then increased.With the increase of landscape diversity,the complexity of patch shape is basically stable.On the one hand,the proportion of forestland and water area in the catchment showed an upward trend during the study period,which reflected the remarkable effect of the policy of returning farmland to forest in Yunnan Province.But on the other hand,the main ecosystem services value in the basin decreased by 815 million RMB yuan,indicating that the artificial forest structure and function were single and the ecological restoration effect was not very effective.(2)Based on conventional water quality and water quantity,habitat factors are innovatively incorporated into the concept of water ecological carrying capacity,and an index system based on water quantity,water quality and habitat is established.From1980 to 2015,the habitat quality index of the watershed showed a deteriorating trend by4.5%,and the increase of land use intensity was the main reason.The optimum range of ecological water demand in Yanggongjiang River is 3.43-5.72 m~3/s.The index of ecological water demand shows an upward trend,and the low discharge of Yanggongjiang River is significantly increased by water diversion project.The water quality of Yanggongjiang River has undergone an improvement period followed by a deterioration period.The change of the carrying index of the watershed is approximately inverted U-shaped,which can be divided into three stages:rising,stable and declining.The health status of the aquatic ecosystem fluctuates greatly.(3)An evaluation criteria system of economic and social development of watershed was built to calculate the pressure index,and to analyze the contribution of different pressure indicators to the pressure index.From 1995 to 2016,the pressure index of the watershed showed a fluctuating upward trend,and the social and economic pressure was continuously increasing.The proportion of tertiary industry contributes most to the pressure index,followed by urbanization.Therefore,we should pay attention to the coordinated development within the industry,excavate the development potential of special tourism,and promote the transformation of economic structure.(4)The index model of water ecological carrying capacity is constructed to evaluate the index and its coordination degree.The index of water ecological carrying capacity of Yanggongjiang River watershed shows a parabolic change,which has experienced the stages of"average","better","good"and"better"development successively.At present,the protection of aquatic ecosystem and the development of socioeconomic system are in a state of inconsistency.(5)A multiple linear regression model of land use,carrying capacity index and pressure index was constructed to quantitatively analyze the overall impact of land use on water ecological carrying capacity.The index of water ecological carrying capacity were altered by land use in the watershed mainly by influencing both carrying index and pressure index.LUCC had a significant impact on most of the water ecological carrying capacity indicators.Habitat quality suffered the biggest influences.The overall impact of LUCC on the change of water ecological carrying capacity is 53.3%.Land use change is the main driving force for the evolution of water ecological carrying capacity.(6)A system dynamic model connecting driving factors and land use change was constructed,and the water ecological carrying capacity under different scenarios was predicted.The low carrying capacity index in the watershed in the future is mainly responsible for the low water ecological carrying capacity.Habitat quality,guarantee rate of ecological water demand and water quality are the main limiting factors for water ecological carrying capacity.Since the protection of aquatic ecosystem lags behind the level of economic and social development,the aquatic ecosystem can hardly bear the pressure of socioeconomic development,and the risk of ecological security increases.Land use and economic and social regulation suggestions based on water ecological carrying capacity constraints are put forward.