176 HILL 



organic matter. Some heterotrophic bacteria are also capable of oxidizing 

 reduced sulfur compounds, apparently without utilizing the resultant energy. 

 Certain photosynthetic bacteria can use H 2 S and other sulfide compounds as 

 electron donors. 



The relative importance of biological and nonbiological oxidation of sulfur 

 compounds in sulfur deposits 33 and in lakes 34 ' 35 has been investigated using 

 35 S-labeled sulfide. Depending on oxygen availability, bacteria may play an 

 important although perhaps secondary role in the oxidation of H 2 S. 



Transport of sulfide to the water surface may occur by a number of 

 mechanisms including molecular and turbulent diffusion. In the absence of 

 chemical or biological oxidation, the average distance through which a sulfide 

 ion or molecule with a diffusion coefficient D will diffuse during a time t is 

 (2Dt) 1/2 . Then during the 20-min lifetime of H 2 S in oxygen-bearing seawater 

 found by Ostlund and Alexander, 3 1 the sulfide could traverse distances of the 

 order of 1 mm by molecular diffusion (D =* 10" 5 cm 2 /sec) and 1 m by turbulent 

 diffusion [D — 10 cm 2 /sec (Ref. 36)] . As a first approximation, in the presence 

 of dissolved oxygen and sulfide-oxidizing bacteria, escape of H 2 S is then 

 conceivable from layers of stagnant water less than about 1 mm in depth and 

 from turbulent water bodies up to about 1 m in depth. H 2 S can conceivably also 

 be brought to the surface of water bodies by convective flow or in gas bubbles. 



The rates of movement of H 2 S out of the water will be a function of pH. At 

 low pH most of the sulfide will be present as undissociated H 2 S, resulting in a 

 high effective concentration driving force for transport. In basic waters the 

 opposite will be true. 



Rates of oxidation of H 2 S in the atmosphere are not well known. 

 Laboratory measurements exist for reactions with atomic oxygen and 

 ozone. 38 ' 39 Most authorities suggest, on the basis of these measurements, that 

 the oxidation of H 2 S in the atmosphere is rapid, probably resulting in a half-life 

 considerably less than 1 day. 2 ' 3 After emission into the atmosphere, H 2 S may 

 also be subject to removal from the atmosphere by absorption on terrestrial and 

 marine surfaces. 



From the foregoing description of the phenomena leading to H 2 S emission, 

 various writers have drawn some of the following conclusions regarding expected 

 locales of emission. Both land and marine sources of biogenic H 2 S have been 

 envisioned. On land H 2 S may be emitted from swamps and bogs, from lakes, and 

 from soils when wet and therefore in soils with a high water table. Johansson, 

 cited by Eriksson, 5 has obtained some data that provide indirect evidence for 

 the emission of I1 2 S from the soil of potted plants. Marine sources may include 

 marshes, intertidal flats, and polluted harbors. 



The suggestion that H 2 S may not be the missing link in the atmospheric 

 sulfur budget has recently come from Lovelock, Maggs, and Rasmussen. In 

 laboratory experiments these authors have found dimethyl sulfide in seawater 

 and have found its concentration to be of the order of 4 X 10 g/ml. Also, 



