Alteration of carbon cycling by beaver: methane evasion rates from boreal forest streams and rivers

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Abstract
In boreal forest drainage networks, beaver (Castor canadensis) apparently influence the biogeochemical cycling of carbon by creating conditions for sediment accumulation in streams, providing anoxic conditions suitable for significant methanogenesis. To test this assumption we measured methane evasion rates in streams, ranging in size from first to sixth order, in the Matamek River drainage network, Quebec, Canada. Evasion rates varied between 0.04 and 4.41 g C (CH4) .cntdot. m-2 .cntdot. year-1. There was no correlation between stream size or water temperature and evasion rate. However, methane evasion was 33-fold greater in beaver ponds than at other sites, representing 3.6% of the measured annual carbon output. In contrast, methane evasion accounted for only 0.05-0.5% of the annual carbon output from sites not modified by beaver.