The effect of biotope-specific sampling for aquatic macroinvertebrates on reference site classification and the identification of environmental predictors in Mpumalanga, South Africa

Abstract

The classification of reference sites based on macroinvertebrate assemblages sampled in different aquatic biotopes in Mpumalanga, South Africa, was examined. Environmental variables that best predicted group membership for each of four classifications (stones, vegetation, sand and these three biotopes combined) were identified. Variables at several scales, including catchment, site and habitat, contributed to observed spatial patterns in macroinvertebrate assemblages. Altitude and longitude were important for combined, stones, and vegetation classifications, reflecting the importance of longitudinal zonation and geographic location, respectively. The characteristics of the substratum, including type (bedrock rapid versus cobble riffle), depth, and quality (deposition of silt on stones), were important at habitat scale. Canopy cover was identified as an important predictor in the stones classification. Geological type, which affects overall water chemistry, was important in the stones and combined classification, and temperature was important in the combined classification. Whilst this study is based on correlative data only, it demonstrates that the structure of macroinvertebrate assemblages is a function of both large-scale variables measured at catchment scale and smaller-scale variables measured at site and habitat scale. The study highlights the importance of measuring environmental variables within bioassessment programmes, especially when classifying and assessing reference sites.