The water cycle is maddeningly difficult to pin down with the level of detail that is desired for resolving issues about the fate of pollutants, nutrient cycling and the global carbon balance, etc. “Connectivity” is increasingly talked of in hydrology and water resources management as a way to better conceptualize how different parts of the catchment dynamically interact to influence runoff generation and water quality. Runoff is a major C flux (aquatic conduit) that is particularly sensitive to changes in climate and hydrological regimes. This paper uses three dimensions of connectivity (vertical, latitudinal and longitudinal), to plumb the sources of carbon leaving a boreal landscape via the aquatic conduit. We used the distributed sources and age of aquatic C export to help assess the role and stability of a boreal landscape in the global C cycle. We combined hydrometric data and mass balances with isotopic tracers of water and carbon, including both radiogenic (¹⁴C) and stable carbon isotopes (δ¹³C) of DOC, CO₂ and CH₄ in catchment soils and the stream network to define the connectivity of riparian, peatland and upland sources to the carbon in runoff throughout the year. The radiocarbon age of DOC, CO₂ and CH₄ were predominantly modern, even in peat catotelm, but with localized excursions to millennial ages. The sources and processes that transport dissolved C species varied strongly with flow rates and the associated patterns of connectivity, mediated by seasonal variation that influence carbon cycling. The age of the C and other tracers exported to streams enabled us to “connect” the aquatic C exports to their origins in the mosaic of landscape elements. The effort also identified ways in which the concept of hydrological connectivity can be refined to strengthen the testing of biogeochemical hypotheses across temporal and spatial scales in specific landscapes.

Aquatic Carbon, Connectivity, 14C, Riparian Zone

Kevin Bishop

ORAL