CLIMATE-INDUCED CHANGES IN THE DISSOLVED ORGANIC-CARBON BUDGETS OF BOREAL LAKES

During 20 years of climatic warming, drought and increased forest fire s between 1970 and 1990, DOC concentrations declined by 15-25% in lake s of the Experimental Lakes Area, northwestern Ontario, allowing incre ased penetration of both UV and photosynthetically-active radiation (P AR), and causing deeper euphotic zones and thermoclines. Decreased inp ut to the lakes of DOC from terrestrial catchments and upstream lakes was the primary reason for the decline, although in-lake removal also increased slightly. Decreased streamflow caused by drought was more im portant than forest fires in affecting DOC exports from catchments. Ex perimental acidification of lakes caused even greater losses in DOG, b y enhancing rates of in-lake removal. DOC in Lake 302S, acidified to p H 4.5 during the 1980's, declined to less than 10% of preacidification values.