Spatiotemporal Variability in Lake-Atmosphere Net CO2 Exchange in the Littoral Zone of an Oligotrophic Lake

Lakes may function as either sinks or sources of CO2. Their response to climate change is uncertain, as we lack continuous data of lake CO2 efflux and its drivers. This is especially true in the littoral zone of lakes, which can be very dynamic from the continuous injection and remobilization of terrestrial nutrients. This study used high-frequency measurements of CO2 exchange during the ice-free season by prototype low-power floating forced diffusion autochambers. We quantified the net surface flux of CO2 across a transect of the littoral zone of a small deep oligotrophic lake in eastern Nova Scotia, Canada, and examined potential drivers. The littoral zone was a net source for CO2, on average emitting 0.171 +/- 0.023 mu mol CO2 . m(-2) . s(-1), but we did observe significant temporal variation across diel and seasonal periods, as well as with distance from shore. While no pelagic environmental driver appeared to explain this variability in CO2 exchange, our study suggests that factors that vary on a fine spatial scale within the littoral zone may effectively regulate CO2 exchange. If environmental drivers of pelagic CO2 exchange are unrelated to CO2 exchange in the littoral zone, this may have large implications for current mechanistic understandings of lake carbon dynamics and for upscalings of fluxes. This work shows the spatial and temporal variability of littoral CO2 efflux, as well as the utility of low-power forced diffusion automated chambers for observing lake-atmosphere net CO2 exchange. Plain Language Summary Lakes influence global climate change by exchanging gases with the atmosphere. We lack detailed data sets of such exchanges, especially in the shallow littoral zone of lakes. We employed a novel technique to measure the release of carbon dioxide from the surface waters of the littoral zone of a clearwater lake in Nova Scotia, Canada. We discovered that the littoral zone had a net release of CO2, which varied over time on daily to seasonal scales, as well as over space with distance from the shore. We were unable to find a relationship between the factors known to promote gas exchange in the deeper part of lakes and gas exchange in the shallow littoral zone. Our findings suggest that current mechanistic understandings of lake carbon dynamics may need to be adapted to better reflect dynamics within the shallow littoral zone. Our work also demonstrates the utility of our cost-effective novel technique in observing the exchange of CO2 between the lake and atmosphere.