Influence of the permafrost boundary on dissolved organic matter characteristics in rivers within the Boreal and Taiga plains of western Canada
Catchment export of terrestrial dissolved organic matter (DOM) and its downstream degradation in aquatic ecosystems are important components of landscape scale carbon balances. In order to assess the influence of peatland permafrost on river DOM characteristics, we sampled 65 rivers along a 900 km transect crossing into the southern discontinuous permafrost zone on the Boreal and Tundra Plains of western Canada. Catchment peatland cover and catchment location north or south of the permafrost boundary were found together to have strong influences on dissolved organic carbon (DOC) concentrations and DOM chemical composition. River DOC concentrations increased with catchment peatland cover, but were consistently lower for catchments north of the permafrost boundary. In contrast, protein fluorescence (PARAFAC analysis), was unrelated to catchment peatland cover but increased significantly in rivers north of the permafrost boundary. Humic and fulvic acid contribution to DOM fluorescence was lower in rivers draining catchments with large lakes than in other rivers, consistent with extensive photodegradation, but humic and fulvic acid fluorescence were also lower in rivers north of the permafrost boundary than in rivers to the south. We hypothesize that shifts in river DOM characteristics when crossing the permafrost boundary are related to the influence of permafrost on peatland hydrological connectivity to stream networks, peatland DOM characteristics and differences in DOM degradation within aquatic ecosystems.