QUALITATIVE DIFFERENCES IN INTERSTITIAL ORGANIC-MATTER AND THEIR EFFECT ON HYPORHEIC COLONIZATION

Sterile substrates seeded with FPOM derived from one of two different riparian leaf types (maple or cedar) were inserted into perforated met al pipes permanently installed in the hyporheic zone of the Speed Rive r, Ontario. After 8 weeks in the river, a total of 42 taxa had colonis ed; however taxon richness was greater in the maple-detritus substrate s than in the cedar-detritus substrates (35 taxa vs 22). In the cedar substrates, the highest overall density occurred at 10-30 cm depth, bu t invertebrate densities were high to 50 cm in the maple substrates. O verall, significantly more hyporheic organisms colonised the maple sub strates, and this was largely due to greater numbers of mayflies and c hironomids belonging to the subfamily Chironominae. There were no diff erences in the densities of the two other most common taxa, the elmid beetles and tanypodine chironomids, between the two detritus types. So me visual differences in the two detritus types were evident after the ir time in the river, but there were no numerical differences between associated bacterial populations. Although, the mean total organic car bon content of the two detritus types was the same, the C/N ratio, a m easure of potential nutritional value, was significantly higher in map le (42:1 vs 30:1).