Until recently, rivers and streams were thought to only transport carbon from the land to the ocean. However, in addition to exporting terrestrially derived carbon to the ocean, streams and rivers also release inorganic carbon in the form of carbon dioxide (CO2) and methane (CH4). A recent study estimates that 2.1 Pg of carbon is evaded to the atmosphere from inland waters in the form of CO 2. There is still much uncertainty in CO2 and CH4 evasion estimates because gas concentration calculations are very sensitive to uncertainties, especially in pH measurements. Direct measurements and watershed-specific carbon flux studies are needed to refine current models.
Current evasion estimates cannot be fully explained by terrestrial C-input to inland water. Fringing wetlands are potentially important sources of CO2, CH4, and organic carbon (from which in-stream respiration produces CO2 and CH4) to inland waters. Lateral C-fluxes from wetlands to freshwater has largely been ignored but could account for this additional C-input. Investigation into carbon inputs from fringing wetland to inland waters may help refine estimates and explain the ˜missing” carbon input that supports current higher CO2 evasion rates.
I will quantify aqueous CO2 and CH4 concentrations in the Salmon River Watershed along a stream order and percent wetland cover gradient. I will perform yearlong sampling to investigate potential season variation. In addition, I will monitor how CO2 concentrations vary during rainfall events to determine the dominant precipitation-induced mechanism (dilution or soil flushing) and if the mechanism varies with precipitation event magnitude. I will also measure the isotopic signature of in-stream dissolved inorganic carbon (DIC) to provide insight into aqueous CO2 and CH4 sources.