CHANGES IN LAKE CARBON ACCUMULATION RATES IN SOUTHWESTERN CANADA SINCE THE MID-1800S

Lake sediments have been shown to contribute up to 15% of total amount of carbon stored in the boreal forest biome. However, estimates of carbon accumulation rates in lake sediments vary widely by region. Little is known about how lake carbon accumulation rates have changed through time and what factors influence these changes. We quantified total organic carbon accumulation rates over the industrial period (1860-2010) in 19 lakes located in the southern boreal/temperate forest regions of western Canada (48-55°N, 99-127°N). We also examined processes that could potentially affect these rates, focusing on climate, lake morphology, and surrounding land use. Ten of the lakes sampled were from protected areas, and in four instances, lakes were sampled from nearby areas that were not protected to help quantify the potential effects of land management practices on lake carbon accumulation.

Significant increases in C accumulation rates are observed at 13 out of the 19 lakes examined for the 1830-1860 and the 1980-2010 time periods. Carbon accumulates rates increase 3.6-fold on average in these 13 lakes between 1830-1860 and 1980-2010, with increases ranging from 80 to 1300%. In contrast, no lake shows a significant decrease in carbon accumulation rates since 1830. These results suggest C accumulation in lakes has increased over the past 180 years. In all instances, changes in sediment rates play a dominant role in driving the observed increases, with sedimentation rates increasing 11.3-fold on average between 1820-1860 and 1980-2010, with increases ranging from 65 to 3972%. This work will also examine processes that could potentially influence these rates, focusing on climate, lake morphology, and surrounding land use.