Assessment of recent benthic invertebrate community health declines around a municipal wastewater outfall

The Capital Regional District (CRD) regularly monitors the effects of the region’s eight municipal wastewater outfalls that discharge into the Salish Sea. Benthic invertebrate community health assessments have been a component of the Macaulay Point outfall monitoring program since the 1990s, with annual monitoring occurring from 2000 to 2012. Declines in benthic invertebrate community health were observed following detailed statistical analyses of the 2008 to 2010 Macaulay Point dataset relative to the 2002 to 2007 time period when generally stable or improving community health conditions were observed. Over the same time frame, no significant concurrent declines in sediment or wastewater chemistry were observed. These apparently contradictory trends led CRD staff to consult with various benthic invertebrate experts in the hopes of receiving guidance on how to investigate potential causes of the declines. One of the early hypothesized causes was increased volumes of Pacific Ocean waters containing low concentrations of dissolved oxygen entering the deep waters of the Salish Sea. To determine whether these low oxygen levels were impacting the Macaulay Point benthic invertebrate communities, the CRD entered into a collaborative study with Ocean Networks Canada to deploy fixed moorings with continuous dissolved oxygen sensors. In addition, detailed assessments of the 2011 data have led to some questions about field and laboratory procedures employed from year-to-year; methodological variations could be confounding the CRD’s interpretation of the benthic invertebrate community health declines. This presentation will provide an overview of findings to date of both the oxygen monitoring and the field and laboratory method validations