Monitoring ecological flows in the Miramichi River, NB using the Canadian Ecological Flow Index (CEFI) and aquatic insect traits

Background/Question/Methods

Globally, river ecosystem integrity is threatened by the pervasive effects of hydrological alteration. Identifying and maintaining the ecologically sensitive components of a dynamic flow regime for river biota has become a management priority. Effective tools to identify sites impacted by hydrological alteration are required. The Canadian Ecological Flow Index (CEFI) was developed to detect potential hydrological alteration using a benthic macroinvertebrate metric derived from standardized, routine biomonitoring samples collected as part of the Canadian Aquatic Biomonitoring Network Program. CEFI is based on empirically-derived velocity optima for taxa that occur throughout Canada. Currently, the taxonomic scope and resolution of CEFI is limited. Applications of CEFI are also restricted by the availability of benthic data paired with long-term hydrological records. Our objective was to use the relationship between benthic macroinvertebrate traits and hydrological variables to describe a mechanistic taxon-trait framework to expand the taxonomic resolution and scope of CEFI. We paired hydrological gauging stations with biomonitoring samples at 20 sites across the Miramichi River Basin (New Brunswick, Canada) to include a range of hydrological and hydraulic conditions. Taxonomic identity and associated trait properties were assessed for four dominant orders of aquatic insects: Ephemeroptera, Plecoptera, Trichoptera, and Odonata obtained in our samples.

Results/Conclusions

CEFI values were calculated for the 2011 samples and estimated stream velocities for the sites ranged from 0.36 (+/- 0.04) m/s to 0.42 (+/- 0.03) m/s. The largest rivers (wetted width >100m) had the lowest estimates of velocity based on CEFI values. Rivers of moderate size (wetted width >30m) had moderate CEFI values but the highest recorded velocity values. The smallest rivers (wetted width <20m) had the highest variability in CEFI values and measured velocity. We compared the body size of EPTO taxa to their predicted velocity optima and observed a positive relationship between mean body size of taxa and their velocity optima. Based on this relationship, we can estimate the velocity optima for individuals or taxa used in the calculation of CEFI. We will use independent data to test the performance of the estimated velocity optima for the CEFI metric calculation. By substituting body size for taxonomic identity, we can expand the number of taxa, and improve taxonomic resolution within the CEFI metric. Moreover, using trait information can reduce the taxonomic barrier that restricts application of this tool, thus improving our ability to assess ecohydrological impairment.