CARBON ACCUMULATION IN THE SYLVANIA WILDERNESS, MICHIGAN: A HIGH RESOLUTION RECORD

Predicting carbon (C) sequestration rates in light of increasing atmospheric carbon dioxide, land use conversions, and disturbances is unclear. Although disturbances exert a significant effect on C accumulation, long-term impacts on C cycling are poorly understood. Comparing impacts of landscape disturbances on C accumulation rates in lakes adjacent to undisturbed old-growth stands to lakes in managed forest stands provides baseline conditions, rates of change, and recovery times. We examined C accumulation rates in lakes external, bordering, and internal to the Sylvania Wilderness (Sylvania) in Michigan’s Upper Peninsula. We sampled lake sediments for C accumulation, organic content, and water content from three lakes that vary in disturbance history via their distance to the Sylvania border: Mule Lake, 1 kilometer (km) outside Sylvania; Helen Lake, adjacent to the Sylvania border; and Corey Lake, 1 km interior to Sylvania. We collected a well-preserved record of uppermost benthic lake sediments using cores that freeze the sediment column in situ. This method allows for precise, fine-interval analysis of recently deposited, contiguous sediments. Laboratory processing of lake sediments included microtoming 3-millimeter sections over the last two centuries with a resolution of 3 - 10 years.

Preliminary results illustrate changes in younger sediments (c. 1815 + 33 years) with annual sediment accumulation rates of 0.23 centimeters per year since 1900. Sediment accumulation increased to 1975 until a significant decrease to pre-European settlement rates. Further, we observed an unusually sharp increase in ²¹⁰Pb activity near the top of the core associated with an increase in inorganic content representing an iron-rich layer. These changes in sediment accumulation could illustrate significant environmental changes, including wilderness delineation and/or road construction. In anticipation of future ecological shifts due to changing climate conditions, research focusing on C accumulation rates and ecosystem recovery following land use changes is needed to accurately quantify the impacts of these changes. These results will aid in the development of management protocols to maximize carbon sequestration and focus long-term preservation of natural resources.