Spatiotemporal Variability of Carbon Dioxide in and Emissions from a Headwater Stream in Central New York.

Atmospheric CO₂ contributions from rivers and streams, known as CO₂ evasion, are estimated to be an order of magnitude greater than CO₂ outgassed from volcanoes. Headwater (1^st and 2^nd order) streams in the Northeastern United States are expected to provide a net efflux of CO₂ to the atmosphere. Headwater ecosystems are highly productive and metabolize considerable quantities of both terrestrially-derived (allochthonous) and stream-formed (autochthonous) organic carbon, which is respired as CO₂. The goal of this research was to identify spatiotemporal patterns of and environmental controls on CO₂ in a headwater stream in Central New York and determine implications on CO₂ emissions. Results from in-situ monitoring of dissolved carbon dioxide (pCO₂), water quality parameters, and environmental conditions combined with biophysical modeling suggests that pCO₂ is controlled by allochthonous carbon in the spring and autochthonous carbon following the peak emergence of aquatic vegetation and decline in volumetric stream flow in late July. Dissolved CO₂ was highly variable. Diurnal fluctuations in pCO₂ exceeded 3000 ppm both near the stream source and downstream near the mouth. pCO₂ generally decreased longitudinally downstream and could vary by nearly 5000 ppm between sites. Stream reaches in wetlands and those draining agricultural land had the highest pCO₂. Sites downstream of culvert outlets and storm- and waste-water outfalls were identified as potential hotspots for CO₂ evasion and suggest that humans could be adding to CO₂ emissions from inland waters through land modification and the installation of transportation and water infrastructure. Continued direct and coupled monitoring of pCO₂ and dissolved oxygen at the regional scale could help improve our understanding of the carbon footprint of inland waters and terrestrial-aquatic linkages, quantify anthropogenic impacts on carbon reallocation and CO₂ evasion from inland waters at the global scale, and make informed land management and infrastructure design decisions under future climate scenarios.