Stream habitat analysis at differing temporal and spatial scales : a study of the relationship between human disturbance and fish habitat in Manitoba Escarpment streams
Forster, Maureen G. M.
Stream habitat analysis was conducted on five different stream systems that originate in the Manitoba Escarpment to collect information on the existing fish communities and to explore potential relationships among the chemical, biological and physical habitat features of the streams in relation to differing levels of human disturbance among the watersheds. The study was modelled on an integrated watershed approach to stream habitat analysis that has been undertaken in several regions of the United States. Nine sites were selected to represent three levels of human disturbance at three spatial scales. The disturbance levels were assigned as "minimally", "moderately" or "highly" disturbed based on an assessment of the amount of human activity (e.g., industry, agriculture, urbanization) in each stream system. The spatial scale categories were defined by drainage area and position within the watershed as "headwater sites" (20-30 km2), "sub-catchment sites" (60-70 km2) and "catchment sites" (200-300 km2). Sample collections of fish, aquatic macroinvertebrates, and stream habitat variables were gathered from each site during the open-water season for a two-year period. Water samples for nutrient and pesticide analyses were collected year-round on a biweekly basis for the same two-year period as the biological and habitat data. The data were examined using summary statistics, cluster analysis and Principal Component Analysis (PCA). Eighteen regionally used pesticides were detected from samples collected during spring, summer, and fall application periods, and in winter samples collected outside of application periods. Low levels of pesticides were detected in streams located within Riding Mountain National Park that are upstream of agricultural activities. The study identified nineteen fish species and provided new locality records for sixteen fish species, some of which may be relict populations from post-glacial recolonizations of southern Manitoba's waterways. Data analysis indicated higher nutrient concentrations, increased pesticide detections and a higher number of channel alterations or barriers to fish passage in the "moderately" and "highly" disturbed sites in comparison to the "minimally" disturbed sites. Fish species diversity was lowest in the "highly" disturbed sites and highest at the "moderately" disturbed headwater site, "minimally" disturbed sub-catchment site and "minimally" disturbed catchment site. These results suggested that the proximity and presence of human disturbances, particularly activities related to agricultural practices and land-clearing, has affected these stream habitats, but these effects can be ameliorated by the maintenance of perennial flows, fish access to upstream and downstream areas, riparian zone integrity, and instream habitat heterogeneity.