Influence of stratification in near-surface water layer on intensity of gas exchange between atmosphere and water

Little is known concerning the influence of the temperature field in the near-water layer on gas exchange between the atmosphere and water. During periods of calm the transfer of oxygen from the air to water is sometimes impeded and large numbers of fish may die. A laboratory experiment was carried out in glass thermostated containers, in each of which the temperature was maintained with great accuracy. One was heated to 39 to 40 C; another was cooled to 12 to 13 C; a third was kept at ambient temperature. In each case the aeration coefficient and rate of mass transfer were computed. Air and water temperatures were varied to determine temperature gradients in the near-water and near-surface layers. A copper constantan thermocouple was used in measuring temperatures above and below the interface. The influence of petroleum films on the rate of mass transfer was also determined. The rate of evaporation at different temperatures was ascertained. The greatest influence was observed in experiments with cooled air. It was found that temperature stratification in the near-surface water layer exerts a considerable influence on water-air gas exchange. In certain cases a petroleum film increases the temperature gradient and causes an even greater decrease in mass transfer rate.