Influence of a geological transition on lotic macroinvertebrate communities

Low-order lotic systems of the Canadian Precambrian Shield include an extensive portion of Ontario’s many waterways that remain relatively unstudied.  The Precambrian metamorphic and igneous geology of the Canadian Shield has a significant influence on the abiotic conditions of aquatic systems.  These differences are especially striking in comparison to non-Shield areas, particularly in the transition zone in south-central Ontario.  The purpose of this study is to examine corresponding biological changes across the Canadian Shield transition.  We used aquatic invertebrate data from small-order streams in central Ontario to assess community composition of Shield and off-Shield lotic systems in this area.  Multivariate methods were used to elucidate biotic patterns between sites, particularly to examine changes in macroinvertebrate community composition along the transition zone of the Shield.  These analyses show distinct differences between Shield and non-Shield sites, most strikingly that these two geological regions appear to have distinct macroinvertebrate communities.