CO2 Emissions from a small Arctic Pond

Abstract:

Although arctic ponds are likely to be important sources of greenhouse gases, measurements of their CO₂ and methane emissions are scare. This is especially critical because arctic ponds are abundant and have large variability in their hydrodynamic and biological properties due to varying catchment area, meteorology, bathymetry, and the presence or absence of cyanobacterial mats. We present results of CO₂ measurements from a characteristic small arctic pond (Lake S4, Alaska) with a surface area of approximately 0.3 ha and a depth of 1 m. Its outlet flows into a larger lake, and inflows are dispersed through a wetland around the pond. We installed continuously measuring CO₂ concentration, dissolved oxygen, and temperature loggers at different locations and deployed a meteorological station on the shore. We computed gas transfer velocities (k) using the surface renewal model with input of modeled turbulence from the surface energy budget; we used these k values in computing CO₂ fluxes between water and air. We compared the computed k and the fluxes to chamber measurements. CO₂ fluxes were into the pond in the beginning of the time series when concentrations in the pond fell below saturation. Later, the lake acted consistently as a CO₂ source. Higher CO₂ concentrations were measured near wetland areas. Estimated fluxes increased by an order of magnitude in response to rainfall events. Therefore, changes in precipitation and resultant inflows from the catchment play an important role in the carbon budget of small arctic ponds. Overall, considerable variability in both gas transfer velocities and CO₂ concentrations were observed. Hence, even for a small system, knowledge of hydrodynamic boundary conditions, and CO₂ concentrations in the water are necessary to determine greenhouse gas emissions.