Stream fauna and bed stability

Posted on March 27, 2012

Invertebrate taxa are often used as indicators of stream health.  However, because animal abundance and diversity in streams tend to be low when bottom substrates are unstable, there’s a need to allow for the complicating effects of bed stability when assessing the ecological impacts of water quality.  Physical methods for assessing bed stability can be time-consuming and the corresponding measures may have limited ecological meaning.    As a result, there are advantages to be gained from the use of biologically-based indicators of bed stability, especially if they can be based on data collected during routine stream sampling operations.  Working in 46 stream riffle reaches onNew Zealand’sNorthIsland, researchers measured streambed stability by following the movements of variously-sized tracer stones marked with 23-mm radio tags over a six month period.  Over the course of the study all sites experienced several spates and at least one flood event.  The occurrence of 60 animal taxa at the various sites was then related to the stone mobility data to award a bed stability score to each taxon.  While some species of caddisflies and beetles were associated with the most stable conditions, other caddis and beetles were indicators of unstable conditions.  At each site, a macroinvertebrate index of stability was calculated by multiplying the abundance of each taxon by its stability score and dividing the sum of these by the total number of individuals.  The macroinvertebrate index was significantly related to  measured bed stability at the study sites (rank correlation = – 0.6), but not at eight randomly selected validation sites (rank correlation = – 0.5).  Therefore, the approach offers promise but there is a need for further testing over a broader geographical scale.

Reference:  Schwendel, A.C., Joy, M.K., Death, R.G. & Fuller, I.C.  2011.  A macroinvertebrate index to assess stream-bed stability.  Marine and Freshwater Research  62, 30–37.