Analysis of the effectiveness of an urban stormwater Best Management Practice on Weracoba Creek, Georgia, using the Rapid Bioassessment Protocol

An off-line stormwater treatment facility was placed adjacent to Weracoba Creek to control fecal coliform bacteria levels.  The BMP facility operates continually with pretreatment, a compressed media filter, and ultra-violet treatment for both wet- and dry-weather events.  Using the Rapid Bioassessment Protocol (RBP) with benthic macroinvertebrates as bioindicators of stream health, we compared sites upstream and downstream of the proposed BMP to a reference condition for that sub-ecoregion.    All samples were collected in consecutive “index periods” between September and March, 2006, 2007, and 2008.  Prior to stormwater treatment, benthic communities were dominated by the Cricotopus/Orthocladius complex, Physidae, and Planorbidae, all tolerant taxa.   Concurrent chemical analysis and coliform monitoring indicated a substantial improvement in the quality of water downstream of the BMP.  RBP analysis also indicated a measurable improvement in stream health at the two downstream sampling sites while there was no difference in metrics at the upstream site.  There was a shift in downstream benthic community composition, exemplified by a six-fold increase (or greater) in Hydropsyche sp..  Critical metrics (most notably, percentage of Trichoptera) indicated an improvement in the structure of the benthic community and a re-evaluation of stream health from “class B” to “class A” status.