Dose-response Relationships Between Landscape And River Health In Huai River Basin

Fluvial ecosystems are one of the most important ecosystems in the world.Human societies extract great quantities of water from rivers,lakes,wetlands,and underground aquifers to meet agricultural,municipal,and industrial demands.Yet,streams and rivers are also among the ecosystems most affected by human activities.The species composition,food web structure,nutrient cycling and utility of thousands of kilometers of streams and rivers worldwide have been greatly altered from their natural states.In order to protect and restore rivers,large amount of money have been invested on bioassessment and restoration projects,with stream or river assessment and restoration becoming a major part of water environment policy.However,most of them are set arbitrarily or opportunistically,and missing the restoration goal.Stream ecosystem is usually characterized by a set of environmental predictors and ecological responsors operating and interacting at various spatial scales.Each variable is driven by its own ecological process at different scale ranging from local to whole catchment.Thus,to increase the effectiveness and success of stream restoration,a deep understanding of the inherent mechanisms and basic processes of stream ecosystem is necessary.In this study,several typical fluvial ecosystems are selected in Huai River basin and land use/cover.Knoweledge and methods from landscape ecology,stream ecology,GIS,and statistics are utilized to investigate the dose-response curves which show measured responses to the cumulative ecological exposure,or dose,of all events and human activities within a river ecosystem at multiple scales.The main research contents and results as follows:(1)Aquatic ecological regionalization refers to the process of dividing a certain study area into various aquatic ecoregions according to the similarities and dissimilarities of regional eco-environmental characteristic.This was based on the application of modern ecology theory and GIS,on the analysis of regional eco-environmental characteristics(such as hypsography,physiognomy,climate,soil,water resource,vegetation,biodiversity,etc.)with their formation mechanisms,and also on the combination of qualitative methods and quantitative methods.Based on the above research,we then put forward the principles,criteria and index of Huai River basin eco-region system.As a result,Huai River Basin was divided into 5 aquatic eco-regions and 16 aquatic sub-ecoregions.For every aquatic ecoregion,specific eco-environmental characteristics and aquatic biology characteristics were illustrated.The achievements of the study would not only provide further selection of study area driven by similar natural factors,but also scientific foundation for decision-making such as regional eco-environmental conservation and construction,reasonable natural resources utilization,spatial allocation of agricultural and industrial production,and also to develop information and approach for environmental management department.(2)Agriculture land was the dominant land cove class in both Jialu and Sha River basins,whereas urban land just occupied a comparatively small percent of land area among all scales in the two basins.Urban land was determined as the primary land cover responsible for water pollution in Jialu River Basin with its characteristic scale at local 60 m buffer,suggesting that the extent and intensity of riparian urbanization are major factors to take into account when performing water quality improvement.Although urban land was also the primary land cover explaining most water quality in Sha River basin,its characteristic scale was the catchment scale.In-stream physical habitats was the major factors directly impacting macroinvertebrates in both two basins,so that increasing habitat complexity and heterogeneity at in-stream vertical scale is crucial for macroinvertebrates conservation.(3)The longitudinal scale analysis confirmed what we have found at lateral scale that urban land was the primary factor to explain the deterioration of water quality in the two basins.In Jialu River basin,the levels of water pollution were gradually reduced from headwater to downstream,indicating the upper stream reaches were the main source imputing water pollution.In Sha River basin,its water quality was comparatively better than that in Jialu River basin,but it was easily influenced by the surrounding urban land.The middle reach was the appropriate longitudinal responsible for the water eutrophication.The response curves of water pollution variables through GAM models displayed non-linear relationship with urban land percentage in both two basins,which indicate a critical threshold of 50%for the urban land cover in Jialu River basin,and a optimum scale of lower than 20%urban land percentage in Sha River basin.Over all,the most effective predictive variables and its characteristic scales varied among the ecological response variables,therefore multiple scales are important issues when studying the effect of landscape on river ecosystem.Collinearity and spatial autocorrelation may challenge the interpretation of land cover patterns.Independence tests may have influential effect on the final results and detection of relationships between land use and river ecosystem.Our work exhibits an example of using empirical model and multiple scales to understand the effects of landscape on river ecosystems,and then to target the most effective predictive factors and appropriate scales among different response variable,all of which may be useful to guide restoration projects in a case study catchment.