A framework for biological criteria for Florida streams using benthic macroinvertebrates

Our study developed an approach to biological assessment that would document effects of pollution on benthic macroinvertebrate assemblages in Florida streams. The primary objectives were: (1) to classify streams for assessment of benthic assemblages and (2) to develop biological metrics and aggregated indices for biocriteria and assessment. Reference sites were selected throughout Florida (with the exception of the southernmost area, known as the Southern Florida Coastal Plain ecoregion) and sampled by biologists from the Florida Department of Environmental Protection. These sites were sampled during a summer index period (1 July through 30 September) from 1992 through 1994. Streams were classified using invertebrate species composition. Three geographic stream classes (bioregions) that were based on aggregations of subecoregions were determined from this analysis: the panhandle, peninsular Florida, and the northeastern portion of Florida. Stream types based on water source (i.e., calcareous or non-calcareous) were not useful as stream classes. From an initial suite of 32 macroinvertebrate metrics, 8 metrics were useful in composing the Stream Condition Index (SCI) for Florida for all 3 bioregions. Scores (5, 3, or 1) were developed for these metrics to allow for aggregation into an index. Aggregating the metrics into the SCT provided a biocriterion that improved discrimination between impaired and unimpaired sites over use of individual metrics.