Assessments and diagnoses of aquatic ecosystem integrity based on integrity requirements of ecosystem service targets

This paper critically reviews the progress in ecosystem integrity (health) assessment of inland waters and provides future directions for assessment. Current biotic integrity assessments mainly use multimetric indices and predictive models to evaluate overall health status; the criteria largely rely on pristine reference sites, but such an approach is not applicable to unique natural waters and irreversibly modified waters. Biotic diagnostic assessments are still in the exploratory stage and can only diagnose possible stressor types and wide-ranges of their intensities through empirical models linking stressors and species-trait-indices. Current chemical integrity assessments mainly use criteria determined by small-scale ecotoxicity tests, rather than quantitative relationships developed between chemical factors and biotic effects in real ecosystems, thus potentially under or over-estimating pollutant toxicity. Current physical integrity assessments focus on overall habitat quality, rather than quantitative habitat requirements, and thus cannot provide quantitative support for ecological restoration and conservation. Current hydrological integrity (environment flow) assessments largely depend on quantitative relationships between hydrological regimes with a few species and single groups, rather than with whole communities, and fail to comprehensively diagnose hydrological causes of biotic resource decline. In the future, integrity assessments need to be based on ecosystem integrity requirements of ecosystem service targets: first, there is a need to build quantitative relationships between biotic integrity and ecosystem services, assess requirements of community structure and function for service goals, and establish biotic integrity assessment methods; second, we must build quantitative relationships between biotic integrity and abiotic integrity in real ecosystems, assess chemical, physical, and hydrological integrity requirements of biotic needs, and establish diagnostic assessment methods.