STABLE CARBON AND NITROGEN ISOTOPIC EVIDENCE FOR ECOTONAL COUPLING BETWEEN BOREAL FORESTS AND FISHES

As a result of water turbulence effects on boundary layer diffusion re sistance and carbon isotopic discrimination, the delta(13)C values (ra tios of C-13:C-12) of attached algae may often overlap those of terres trial plants, thereby making it impossible to distinguish between the relative importance of these two potential food sources for aquatic an imals. The present study used a dual isotope approach (delta(13)C and delta(15)N) to refine measurements of the incorporation of allochthono us organic matter into freshwater fishes; The dependence of five speci es of littoral fishes on terrestrial detritus for part of their energy sustenance was demonstrated. The littoral zones of boreal Canadian Sh ield lakes are, therefore, not isolated from their surrounding riparia n forests in terms of carbon flow as present day timber management gui delines erroneously assume, but instead exhibit a measurable degree of ecotonal land-water coupling. As a result, clearcut logging of ripari an forests to the lakeshore edge, permissible by law in most Canadian provinces containing boreal forests, may have to be reassessed as a fo rest harvesting strategy.