CONSEQUENCES OF CLIMATE WARMING AND LAKE ACIDIFICATION FOR UV-B PENETRATION IN NORTH-AMERICAN BOREAL LAKES

CLIMATE warming, acid deposition and increasing exposure to ultraviole t radiation are all regarded as widespread problems in boreal ecosyste ms. Here we report observations from twenty years of whole-lake acidif ication experiments, which show that these three problems are intimate ly linked, In our study area in northwestern Ontario, both climate war ming and lake acidification led to declines in the dissolved organic c arbon content of lake waters, allowing increased penetration of solar radiation, We suggest that some of the changes in aquatic ecosystems t hat have been attributed to lake acidification may in fact have involv ed increased exposure to ultraviolet light. Moreover, it seems that-pa rticularly in clear, shallow lakes and streams-climate warming and/or acidification can be more effective than stratospheric ozone depletion in increasing the exposure of aquatic organisms to biologically effec tive UV-B radiation.