Researchers at University of Hawaii investigated carbon dioxide (C02
) exchange between pond water and the atmosphere. Although oxygen exchange is routinely
estimated in free water studies, far less attention has been given to diffusion of
carbon dioxide, which may be significant. Researchers analyzed data from their pond
research facility in the U.s. to quantify the rates of exchange of carbon dioxide
between pond water and the atmosphere in fertile earthen ponds, and to identify
factors which determine these rates of exchange. An analysis of these data showed
that total carbon dioxide concentrations varied little during the day, but showed a
perceptible dip during mid-day, reflecting photosynthetic uptake. Wind speeds
directly above the water surface were measured, and researchers observed that the
windiest periods occurred mainly during daylight hours. Analysis showed that the
concentration of free carbon dioxide and wind speed together accounted for 81 % of
the variation in the diffusion rates during the diel cycle. Thus, prediction of diffusion
rates requires only observed carbon dioxide concentrations and wind speed, although
photosynthetic demand can be the primary determinant of concentrations under
some conditions.