Relationships between dissolved organic carbon concentrations, weather, and acidification in small Boreal Shield lakes

We used multiple linear regression analyses to explore empirical relationships between dissolved organic carbon ( DOC) concentrations, weather, and acidification in long- term data sets from 12 small Boreal Shield lakes in Ontario, Canada. In two lakes in which pH changes have been very large ( 4.5 to similar to 6.0), pH explained most of the temporal variation in DOC concentrations. In the remaining lakes, long- term average previous temperature ( on the scale of a decade or more) was usually the best explanatory variable for DOC concentrations. Lake- specific multiple regression models constructed from long- term and short- term attributes of weather ( long- term average previous temperature and precipitation, winter- spring precipitation, summer precipitation, summer sunshine) and pH explained between 41% and 96% of the temporal variation in DOC concentrations during the entire monitoring period for these lakes ( n = 16-26 years). Multiple regression models considering only the period common to all lakes, 1987 to 2003 ( n = 1617 years), explained 35%- 96% of the variation in DOC concentrations. The importance of long- term and short- term attributes of weather in explaining temporal variations in DOC concentrations suggests that changes in climate will have large effects on lake clarity; however, the interactions between weather- related effects may be very complex.