The concentration and isotopic fractionation of gases dissolved in freshwater in equilibrium with the atmosphere. 1. Oxygen

Abstract

Equations and tables are presented from which accurate values can be obtained, in any of several sets of units, for the concentration of oxygen dissolve11 in freshwater in equilibrium with the atmosphere from 0" to 40°C and 0.5 to 1.1 atm. The y are based on values for the Henry coefficient of oxygen, k,,, which have an estimated accuracy of 0.02%. Equations are derived which relate k, to equilibrium concentrations in natilral waters. The equations include corrections for molecular interactions in the vapor pha.;e. Uncertainty about the best way to correct for these interactions limits the estimated act Iracy of the derived values to about & 0.07% at 0°C and 0.04% at 4O"C, but the new results are much more accurate than values from the UNESCO tables. Within their random errors, previous measurements agree very well with the new results. Under equilibrium conditions, and between 0" and 6O"C, the per mil difference between the 340,:3202 abundance ratio in t le dissolved gas and the air is given by 6 = -0.730 + (427/T), where T is in kelvin and the standard deviation is <0.02%0.

Dissolved oxygen concentrations in hypersaline waters

“…The effect of other salts on DO levels is also examined. Theory Gas solubi/ity and Henry's Iaw-Application of Hellry's law to the solubility of atmospheric gases in natural waters has been thoroughly outlined in papers by Benson and Krause (1980), Weiss (1974), and Weiss and Price (19 80). According to Henry's law the solubility of a gas, i, in a solvent of fixed composition .at constant temperature (T), is given by A= kix, (1) whereA is the fugacity of the gas in the vapor phase, Xi is its mole fraction in the liquid phase, and k, is the Henry's law coefficient (units given in list of notation).…”

“…Since then, equilibrium concentrations of dissolved oxygen (DO) in marine and estuarine waters have been measured over a range of salinity and temperature with his technique or minor modifications of it. In these saline waters, as well as in freshwaters, his basic technique has become the standard to determine the concentration of DO, and tables are available that document the relationship between salinity, temperature, and DO at equilibrium in such waters ' (Weiss 1970;Benson and Krause 1980;Mortimer 198 1). It is only relatively recently that other methods of measuring DO have been developed; they involve diffusion to a reducing electrode.…”

Deoxygenation of the deep water of Lake Victoria, East Africa

“…uration algorithm of Benson and Krause (1980). Talling ( 1966) followed the annual cycle of thermal and oxygen stratification at a deep (60 m) offshore station in Uganda in 1960-196 1 and compared his results with the earlier studies of Fish (1959) in 1952-1953, his own in 1956(Talling 1957,andthoseofNewell(l960) in 19 5 7-19 5 8.…”

Evaluation of the Eureka Manta2 Water-Quality Multiprobe Sonde

“…The DO concentrations for air-saturated water at four different temperatures (5, 15, 25, and 50 °C) were measured two times by each test sonde. Theoretical DO values for each of the 100-percent air saturation solutions tested were calculated (Benson and Krause, 1980). Two samples were collected from the ministand pipe's spigot immediately after each DO measurement and measured by Winkler titration.…”