LAKE AND WATERSHED CONTROLS ON THE ACCUMULATION AND COMPOSITION OF SEDIMENT IN LAKES AT THE BOREAL FOREST-TUNDRA ECOTONE, LABRADOR, CANADA

While lakes cover less than 2% of the Earth’s surface they play a critical role in the earth’s carbon cycle. This study examines lake and watershed controls on the accumulation and composition of lakes spanning the boreal forest-tundra ecotone in order to gain insight into the factors that influence organic carbon burial in lakes. The study area comprises a network of lakes of various sizes and watershed characteristics in the Mealy Mountains of southeastern Labrador, Canada (53.6° N, 58.6° W). Current and recent trends in the vegetation cover of each study lakes’ watersheds were determined based on calculations of Normalized Difference Vegetation Index (NDVI) values from Landsat data. GIS analysis of digital elevation models was used to further characterize the watersheds of individual lakes and define morphometric variables. Field observations of lake bathymetry, water temperature, conductivity, dissolved oxygen, and pH were used to further characterize the lakes. Short-term sediment accumulation rates for individual lakes will be determined based on analysis of sediment recovered in traps placed in the lakes between 2014 and 2015. Surface sediment cores were collected to determine the composition of recent sediments as defined by loss on ignition (LOI), total organic carbon, total nitrogen, stable isotopes of carbon and nitrogen, and Rock-Eval pyrolysis. Our results should help define the sensitivity of lake sedimentation to various environmental forcings and help guide the interpretation of long-term environmental reconstructions based on sediment cores collected from some of the study lakes.