COMPARATIVE LIMNOLOGY OF LAKES SPANNING THE BOREAL FOREST-TUNDRA TRANSITION ZONE, MEALY MOUNTAINS, LABRADOR, CANADA

Lake sediments are an important source of paleoenvironmental information and play a significant role in the global carbon cycle. The composition of lake sediment is governed by a variety of factors acting both within and outside of lakes. Understanding these factors is critical to interpreting long-term sedimentary records in terms of their environmental significance and for predicting how lakes will respond to future changes in climate. This study examines modern limnologic, morphometric, and watershed controls on the composition of lake sediments in a suite of lakes spanning the boreal forest and tundra biomes in the Mealy Mountains of southeastern Labrador, Canada (57.58 °N, 58.60 °W). Surface sediment samples were collected from nine lakes in combination with bathymetric and water quality measurements in July and August 2014. Sediment composition was evaluated by loss on ignition (LOI) and a geographic information system (GIS) was used to define watershed characteristics. The lakes varied in physical and chemical characteristics, ranging in area from 0.02 to 3.6 km², ranging in maximum depth from 0.6 to 91 m, and had catchments ranging in area from 0.01 to 31 km². The study set included both thermally stratified and non-stratified lakes with surface water temperatures that ranged from 14.1 to 19.8 °C; pH ranged from 4.6 to 7.1; and the study lakes included both fully saturated and highly depleted dissolved oxygen profiles. Percent LOI of surface sediments ranged from 5.6 to 86.9 %. Comparison of percent LOI values to lake and watershed characteristics suggests that lake depth is a primary control of lake temperature and dissolved oxygen content which in combination with watershed relief play a prominent role in determining the composition of lake sediments. Continued work will further examine water chemistry along with stable carbon and nitrogen isotope composition of the sediments. This study will complement ongoing work examining long-term changes recorded in sediment cores from these lakes.