A diagnostic biotic index for assessing acidity in sensitive streams in Britain

Despite the history of freshwater biomonitoring, there is still a dearth of proven indices that allow accurate status assessment while simultaneously diagnosing the cause of impairment, particularly when stressors are multiple. Here, we present an approach to developing diagnostic indices where the sensitivity of biota is quantified using multivariate ordination. We applied the approach to the development of an index to detect acidity in British streams.