SENSITIVITY OF HIGH-LATITUDE FRESH-WATER ECOSYSTEMS TO GLOBAL CHANGE - TEMPERATURE AND SOLAR ULTRAVIOLET-RADIATION

Freshwater ecosystems are a major component of the northern environmen t. The application of new limnological technologies and approaches to these ecosystems is producing a revised perspective on their structure and dynamics, and is leading to insights into their potential respons e to global change processes. The planktonic communities of northern l akes are dominated by microbial food webs, with components that are hi ghly sensitive to changes in temperature. North-south transects in Que bec, Yukon and the Northwest Territories show that takes beyond the no rthern tree line have concentrations of UV-screening dissolved organic carbon less than 5 mg.l(-1), rendering them vulnerable to changes in incident UVB and to climatic effects on catchment hydrology. The coupl ing of studies on the modern-day limnology of northern freshwater ecos ystems with paleolimnological approaches will allow the interpretation of short-term changes in these systems within the context of their hi storical variability.