Channelization and Habitat Heterogeneity: How does Stream Morphology Affect Community Structure?

Stream channelization is a common form of anthropogenic disturbance, and its effects on streams (such as altered discharge and increased sedimentation) are well documented. It is also believed that channelization reduces habitat diversity within a stream; however, it is not yet clear how this loss of habitat diversity affects native and introduced salmonid assemblages. In the current study we examine the relationship between habitat diversity (heterogeneity) and stream morphology, and how this relationship affects fish and invertebrate communities of the Crowsnest River in Southern Alberta. The first objective of this study is to assess how habitat heterogeneity is affected by alterations to stream morphology associated with stream channelization. We accomplish this by observing and analyzing the instream habitat composition across two unaffected stream sections featuring high stream sinuosity and two channelized stream sections featuring low stream sinuosity, using a geographic information system (GIS). The four study reaches were mapped and digitized using geo-referenced aerial photos, and unique habitat types within reaches (patches) were transformed into polygons. Each polygon was then given attribute values corresponding to various habitat metrics, allowing the GIS to assign habitat values to individual patches. The unique capabilities of a GIS also made it possible to quantify individual and combined patch area, distances between patches and frequency of patch occurrence, along with various other metrics which provide us with a clear depiction of the in stream habitat heterogeneity within the study reaches.  We then examine the relationship between habitat heterogeneity and fish and invertebrate assemblages. Here we compare the community structure of the fish and invertebrate populations between the aforementioned unaffected (high habitat heterogeneity) and channelized (low habitat heterogeneity) stream reaches. We also compare the salmonid communities of 19 stream reaches of the Crowsnest River which depict various degrees of sinuosity, to determine if stream morphology has an effect on native and non-native assemblages. Invertebrate samples were collected using a stratified random technique and quantitative methods, while fish data was collected from both electro-shocking and snorkel surveys. Preliminary analysis of the four primary stream reaches suggest that pristine meandering reaches feature greater habitat heterogeneity, and support higher abundances of fish and invertebrates than do channelized reaches. Also, initial analysis of the salmonid communities across the secondary 19 stream reaches suggest that stream morphology plays a potential role in the re-colonization of native Cutthroat Trout (Oncorhynchus clarki) into the main channel of the Crowsnest River.