Watershed ecological risk assessment is an important research subject of watershed eco-environmental protection and management, which also uses distinct watershed characteristics compared with regional ecological risk assessment. In this paper, we firstly present the concept and definition of watershed ecological risk assessment based on existing research. The watershed ecological risk assessment is a complicated dynamic process, taking eco-spatial pattern formed by physical landform differentiation and hydrological process as evaluation region, in order to assess the possibility and its harmful levels of the negative influence caused by natural hazard, artificial interference as well as some other risk sources on each ecosystem and its components in the watershed. The process of ecological risk assessment has great ambiguity, uncertainty and relativity. Thus, the focal point is to investigate the relationship and ecological risk effects among the water, soil, vegetation, biodiversity as well as human activity in different hydrologic compartments of the whole watershed.
Secondly, we analyze its spatial-temporal characteristics, heterogeneity, regional correlation and integrity and discuss the research hotspot region at present. Based on the properties, the quantity and the extent of risk sources, ecological receptor and ecological endpoint(defined as the damage to ecological receptor), we divide the ecological risk assessment into several types. Through an overview of the development and related research about the watershed ecological risk assessment, the main research subjects related to watershed ecological risk assessment are classified into three kinds. The first subject is about ecological risk of freshwater system, which concerns mainly about eco-toxicological research of one or more contaminants in different compartments of the hydrologic system. The second subject is about ecological risk of natural disasters in watershed, especially the risks of flood, drought, soil erosion on the ecosystem and its components. The third subject is application of comprehensive evluation model for watershed ecological risks involving multiple receptors and risk sources like land use, soil erosion, pollution emission, etc.
Thirdly, based on the EPA framework and watershed characters, we build a conceptual model of watershed ecological risk assessment which considers the environmental characteristics of a watershed and can reflect the spatial and temporal changes of the assessment parameters. According to the successive steps of risk assessment as "problem formation, risk analysis and characterization, risk management and its feedback", we construct an index system which includes the hazard indicators of risk sources, the vulnerability indicators of habitats as well as the potential loss of risk receptors based on the three basic elements of ecological risk assessment consist of risk sources, habitat and effect. Finally, problems and perspectives are discussed, expecting to make contribution to the further research in this field.