A test of the application of the river environment classification in the Auckland region

Abstract

The River Environment Classification (REC) was developed to provide a spatial framework for regional scale environmental monitoring, assessment and management. This research tests whether significant differences exist in physical and biological attributes between four dominant REC classes in the Auckland Region. It also assesses the accuracy of REC data that are used to classify, and appraises whether the Auckland Regional Council's habitat assessment scheme is an appropriate measure with which to differentiate the REC classes. The Auckland Regional Council's habitat assessment, and macroinvertebrate communities were analysed for 40 streams in the Auckland Region. Climate, topography, land cover and network position (as defined by the REC) were constant at all sites. Sites were grouped into two geology classes (hard and soft sedimentary rock type) and further divided into two valley landforms (high and low gradient respectively). Considerable overlap was found between the four REC classes and the physical and biological parameters. This overlap was the result of high variation within the REC classes, reflecting the range of biological and physical condition within each REC class. Macroinvertebrate communities were related to the organic and inorganic substrate within a given reach. However, application of the REC in its current form did not identify these differences in local substrate. Sites from one REC class which had the least range in aquatic substrate (i.e. coarse bed materials) were more similar than the others. There was no differentiation between the remaining REC classes. This research shows that stream classification procedures should include an assessment of biological and physical condition along with other attributes already used by the REC, if variability in habitat and macroinvertebrate communities are to be explained within and between classes. Identification of reference conditions for REC classes would help to explain and interpret the within class variability found within the REC.