Biotic Community Response to Stress
Since the development of the saprobian index nearly a century ago (Kolkwitz and Marsson, 1908, 1909), practitioners of bioassessment have accumulated information on the effects of anthropogenic stress on aquatic communities. While every metric supplies some information, no single metric presents all the information needed. The amount of information obtained per unit effort can vary widely from one metric to the next. Metrics that never vary, vary without reference to any observable impact, or are difficult to measure well or with consistency have been discarded in favor of more practical metrics with more discriminatory power. Investigators have occasionally been humbled by looking for effects in one metric and missing devastating effects in another.