A preliminary investigation into the ecological significance of headwater drainage features in Southern Ontario
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Within Southern Ontario urban development is rapidly devouring headwater systems, and this can have significant repercussions to the health of entire river networks. The ecological contributions of headwaters to downstream aquatic systems are poorly understood. The relationships between exported organic material (invertebrates, organic detritus) and land use were examined from 16 headwater systems (13 ephemeral channels, 3 intermittent channels) located in and around the Toronto Region. Drift traps, precipitation and crest stage gauges were installed at each location to capture exported materials, measure rainfall and estimate peak flow, respectively. Samples were collected during runoff events, snow melt or precipitation from March through November 2008. The amount of snow melt or precipitation necessary to trigger surface runoff was found to be highly dependent on land use and antecedent conditions. Invertebrates of aquatic and terrestrial origin were collected, with aquatic animals comprising 43% and 87% of the total from ephemeral and intermittent headwaters, respectively. The mean export of organic materials was 963 invertebrates per event (0.65 g) and 32.0 g of plant matter per event. The amount of materials transported was highly variable among samples (1 – 13,751 invertebrates per event). Within ephemeral channels, Annelida, Insecta and Chironomidae were the most numerous aquatic taxa (representing 40%, 24% and 23% of the total number of invertebrates transported per event, respectively), while Mollusca, Arachnida and Insecta were the most numerous terrestrial taxa (representing 35%, 21% and 16% of the total number of invertebrates transported per event, respectively). Earthworms contributed 64% of the total invertebrate volume collected per event. Chironomidae, Crustacea and Trichoptera were the most numerous aquatic taxa collected from intermittent channels (representing 55%, 27% and 8% of the total number of invertebrates transported per event, respectively), whereas Arachnida, Insecta, and Collembola were the most numerous terrestrial taxa (representing 52%, 19% and 13% of the total number of invertebrates transported per event, respectively). Trichoptera accounted for 59% of the total aquatic invertebrate volume collected per event. Preliminary results suggest that the ecological contributions of headwaters to downstream systems are considerable and their importance should not be overlooked.