Abstract

Boreal freshwater ecosystems are supersaturated with CO2 because of the respiration of forest-derived dissolved carbon in open waters, and represent a vector for the transfer of a significant portion of forest carbon to the atmosphere. In general, freshwater ecosystems contribute an estimated 0.65 Pg (in CO2 equivalents) and 1.4 Pg yr-1 of methane (CH4) and carbon dioxide (CO2), respectively, towards global carbon© emissions. But there is considerable variability in CO2 and CH4 production rates both within and among Boreal lakes, and this may be related to largely-overlooked C cycling in nearshore sediments, where forest-derived organic matter is expected to have a larger relative influence. Integrating controlled biogeochemical experiments, isotopic mixing models, DNA sequencing, and fluorescence spectroscopy, I investigate the effects of forest-derived C on CO2 and CH4 production in Boreal lake sediments. I find that CO2 production rates are increased where a larger proportion of the C pool is forest-derived, and that leaf litter inputs may suppress rates of CH4 production because of the inhibitory effects of available polyphenols. As climate change is predicted to shift plant community composition in forests and lakes, and alter hydrologic regimes and delivery rates of forest-derived C to freshwater ecosystems, this change in the quality of inputs into lake habitats can have far-reaching consequences for global C emissions.