Oxygen transfer across the air‐water interface by natural convection in lakes

Abstract

Oxygen transfer associated with natural convection in lakes and reservoirs was examined in a series of laboratory experiments. A thin, cool surface water layer (2-3 mm in thickness) was formed by chilling the air overlying a tank of surface area 0.6 m 2 and depth 0.6 m. The surface water layer became gravitationally unstable, resulting in the formation of negatively buoyant thermal plumes, which penetrated through the total depth of the water column. The spatial distribution of oxygen concentration at the air-water interface in the tank was visualized using a fluorescence imaging technique to quantify the oxygen transfer driven by only natural convection. Pyrenebutyric acid (PBA) at a concentration of 3.0 ϫ 10 Ϫ6 mole L Ϫ1 was used as the fluorophore, and the quenching of the fluorescence by oxygen was used to produce a spatial distribution of dissolved oxygen. A light plane was generated across the tank by the refraction of a laser light beam, and two-dimensional images were continuously acquired with an intensified charge coupled-device (ICCD) camera. Analysis of these images revealed the sinking of cooled water to transport oxygen, and the experiments enabled the quantification of the oxygen transferred from the air into water at a range of heat fluxes. The results confirm that vertical penetration of cold-dense water can be a significant source of oxygen for lakes and reservoirs.''Oxygen is the most fundamental parameter of lakes, aside from water itself. . . '' (Wetzel 1975), and an improved understanding of water quality issues is dependent on understanding how dissolved oxygen (DO) enters and is distributed through these systems. Oxygen and other gases enter and leave a water body across the air-water interface. The rate at which this occurs is frequently parameterized as being a function of the wind speed across the surface and on the gas concentration in the water, relative to its saturation level (Broecker et al. 1978;O'Connor 1983). At times of high wind speed and low DO concentration, the transfer rate into the aqueous phase will be relatively high.The study of gas transfer across an air-water interface has generally been conducted with reference to the ocean (for example, Watson et al. 1991;Wanninkhof 1992). Here, sus-

CO2 exchange between air and water in an Arctic Alaskan and midlatitude Swiss lake: Importance of convective mixing

“…In contrast, most lakes are well embedded within a terrestrial environment, with which they are strongly interacting [e.g., Kocsis et al, 1999;Schladow et al, 2002]; and the atmospheric conditions near the lake's surface are only partially determined by the exchange processes that occur over the lake itself. From the standpoint of regional and local meteorology, the fractional cover of the lakes examined in this paper is small compared to the terrestrial surface surrounding them.…”

“…The contribution of heat flux has been included in one formulation for gas fluxes Schluessel, 1994, 2001], but this was derived for the oceans and has not been satisfactorily applied to small lakes [Anderson et al, 1999]. Lakes are often topographically sheltered, affording them protection against strong winds [Schladow et al, 2002;Kocsis et al, 1999], which makes the application of oceanographically derived formulations questionable under such conditions [Schladow et al, 2002]. Cole et al [1994] showed that CO 2 flux from small lakes to the atmosphere can be a large component of the carbon budget, and even of the surrounding landscape [Kling et al, 1991[Kling et al, , 1992Richey et al, 2002].…”

Regime térmico e a dinâmica do oxigênio em um lago meromítico de águas pretas da região amazônica

“…Trabalhos recentes realizados em regiões temperadas têm abordado a questão da mistura parcial ou total do oxigênio na coluna de água pela ação dos ventos (Nishri et al, 2000;Antenucci & Imberger, 2001, 2003Schladow et al, 2002). Na região amazônica, pesquisas sobre a dinâmica do oxigênio em lagos ainda são modestas, principalmente em face às dimensões e a grande variabilidade de sistemas lacustres da região.…”

Direct numerical simulation of turbulent scalar transport across a flat surface

“…Non-intrusive optical measurement techniques such as Particle Image Velocimetry (PIV) have been used in order to understand the near surface hydrodynamics (e.g. Tamburrino & Gulliver 2002;Banerjee et al 2004;McKenna & McGillis 2002, 2004bSugihara & Tsumori 2005;Turney & Banerjee 2013), while Laser Induced Fluorescence (LIF) enabled visualization of the gas concentration fields (e.g Wolff & Hanratty 1994;Münsterer et al 1995;Schladow et al 2002;Woodrow & Duke 2002;Herlina & Jirka 2004;Walker & Peirson 2008). Various research groups (such as Lu & Hetsroni (1995); Handler et al (1999); Nagaosa (1999); Yamamoto et al (2001)) conducted direct numerical simulations (DNS) of passive heat/mass transfer across the free surface of an open-channel flow.…”