Continuous measurement of CO2 for estimation of air‐water fluxes in lakes: An in situ technique

Abstract

Three parameters must be known to use the thin boundary-layer model (or other bulk transfer models) for CO, flux between water and air: the concentration of dissolved CO*, CO,,,,,, the concentration of CO, in the air immediately above the water, COZ(atm), and the wind velocity, which is used to determine the appropriate transfer coefficient. These parameters change hourly and from day to day in a nonlinear fashion, so the frequency of measurements is an important factor in determining the accuracy of flux estimates for any period. To achieve a high frequency measurement, we developed a self-contained, solar-powered, in situ sampling system that continuously measures and records CO,,,,,, COZ(atm), and windspeed. Unique to this technique is an underwater in situ equilibration chamber (ISEC). The ISEC was tested in a shallow wetland pond in which changes in both CO,,,,, and COZ(ntm) were large. The data obtained showed that large errors may result from extrapolating flux calculations made from short-term data (e.g. daily) to longer time periods.The most commonly used method for estimating gas flux across the air-water interface is the thin boundarylayer (TBL) model, which requires measurements of windspeed and of the concentrations of the gas in air and water. Gas concentration data are usually acquired by periodic sampling, and the frequency of sampling is usually limited by accessibility to the site and the time available for analyses.When measurements are made for the purpose of calculating CO2 flux in lakes where diel changes in water and air arc small, limitations on sampling frequency may not be serious. However, there are two common situations in which very frequent measurements in both air and water may be necessary: eutrophic lakes and shallow ponds-both of which have strong diel changes due to high rates of photosynthesis and respiration. Even where diel changes are not so strong (as in oligotrophic lakes), other considerations, such as large changes in windspeed, may make sampling frequency important.Because CO2 flux is proportional to the dzjkwzce bcAcknowledgments

Diurnal sampling reveals significant variation in CO2 emission from a tropical productive lake

“…Sellers et al, 1995;Cole and Caraco, 1998;Hanson et al, 2006) but generally showed small variation. Cole and Caraco (1998) for instance, recorded small CO 2 changes within a day in midsummer and even smaller ones during the spring in Mirror Lake.…”

High‐frequency measurements of productivity of planktonic algae using rugged nondispersive infrared carbon dioxide probes

“…We did not face biofouling problems, but in longer measuring campaigns, the silicone rubber tubing must be cleaned or replaced regularly in order to avoid decrease in gas diffusion. The CO 2 concentration dynamics with a peak during morning and minimum near dusk resembled that recorded by Sellers et al (1995) with a more costly system of in situ equilibrium chamber (ISEC) connected to IRGA in August 1992 in Lake 979 at the Experimental Lakes Area (ELA). Our diel cycle in CO 2 concentration is also very similar to that measured by Hanson et al (2003) in mid-July in the mesotrophic Cranberry lake using a Li-Cor IRGA.…”

Influence of weather variables on methane and carbon dioxide flux from a shallow pond

“…In a study by Sellers et al (1995), higher CO2 concentrations were recorded around 09:00, followed by lower values around 20:00 and it was demonstrated that more frequent sampling is necessary. Diel changes in CO2 concentration was reported in a Finnish lake and the importance of accounting for diel changes has been emphasized in a study by Huotari et al (2009).…”

“…and CO2 fluxes (Mattson and Likens 1990;Hamilton et al 1994;Sellers et al 1995;Bastviken et al 2004Bastviken et al , 2010Huotari et al 2009). Additional studies of variability between days-weeks would be very valuable to understand and predict how rapidly fluctuating environmental variables affect GHG fluxes from inland waters (beyond the connection between air pressure changes and CH4 ebullition; e.g.…”