Taking the pulse of the ecosystem: progress in quantifying aquatic ecosystem health

Ecosystem health metrics quantify the cumulative effects of stressors on ecosystem structure and function, and inform management, restoration, and policy decisions. Freshwater ecosystems, in particular, face numerous stressors, and as a result, there is an increasing array of health metrics applied to their management. In this chapter, we review the current use of ecosystem health metrics, develop a preliminary framework for metric selection, and identify gaps in the current suite of metrics. The existing metrics typically characterize the biological, physical, or chemical attributes of ecosystems, whereas a few additional metrics integrate across these categories. Metrics vary in complexity, ranging from simple, visual assessments that can be completed by volunteers, to complex numerical models with extensive data and expert input requirements. Overall, ecosystem health metrics are well developed and useful with metrics available to fit both general and specialized management needs. However, common challenges include difficulty in establishing suitable reference conditions, a lack of uncertainty estimates, and a lack of inter-metric comparisons. Recent technological improvements, such as remote sensing, computational models, and new genetic sequencing techniques, are facilitating the development of novel and more holistic metrics, including early warning metrics, coupled complex systems models, and the inclusion of public input data. *Corresponding author: E-mail: roleysar@msu.edu