Biological processes in running waters and their implications for the assessment of ecological integrity

Although biomonitoring approaches are being increasingly used in the measur ement of stream and river health, critical assumptions about the nature of biological populations and communities that underpin them are often ignored . Many approaches based on pattern detection in plant and animal communitie s assume high temporal persistence in the absence of anthropogenic disturba nces. However, this has been rarely tested with long-term data sets and the re is evidence that this assumption is not true in some river systems. Biol ogical processes, such as predation and recruitment, can account for consid erable spatial and temporal variation in the structure of some stream commu nities. These processes may prevent the development of robust predictive mo dels or indices based on pattern detection. Measurements of population or c ommunity attributes also are often used to infer ecosystem processes, yet t he link between pattern and process has rarely been demonstrated. Many goal s of river management relate to the maintenance of natural ecological proce sses and ecosystem function; direct measurement of these processes is, howe ver, often neglected in assessment programs. Such measures are often sensit ive to causal factors that are known to affect river health and it is possi ble to develop simple but powerful predictive models. Perhaps more importan tly, should an impact to be detected, strategies for remediation are more o bvious as the causal processes are generally better known. The ultimate suc cess of biomonitoring approaches depends on how well we understand the biop hysical processes that influence the structure and dynamics of stream and r iver systems, and the way they function.