Chapter VII — 105 — Activities in Deposits 



The hydrogen-ion concentration may be decreased or the pK increased 

 by the following microbiological reactions: (/) Utilization of CO2 by either 

 chemosynthetic or photosynthetic autotrophs, chiefly diatoms and algae, 

 (2) oxidation or decarboxylation of the salts of organic acids such as 

 formate, acetate, propionate, lactate, etc., (j) reduction of sulfate to sul- 

 fur or H2S, {4) reduction of nitrate or nitrite, and (5) the formation of 

 ammonia from nitrogenous compounds such as amino acids, proteins, urea, 

 purine bases, etc. 



Microorganisms capable of activating the aforementioned reactions 

 have been demonstrated in sedimentary materials. The hydrogen-ion 

 concentration of bottom deposits at depths to which CO2 does not diffuse 

 from the atmosphere is probably largely a function of the interrelated 

 factors which influence the abundance, kinds, and activity of bacteria. 

 An appraisal of these factors will require much additional quantitative in- 

 formation. According to Miyadi (1934), bacterial activity has a pro- 

 nounced effect upon the hydrogen-ion concentration of lake mud. 

 KusNETZOW (1935a) reports that bacterial activity may affect the hydro- 

 gen-ion concentration as well as the oxidation-reduction potential of an 

 entire water basin. The influence of bacterial activities on the pK of 

 water is discussed by Enevoldsen (1927). 



Besides influencing the solubiHty and reactivity of calcium, magne- 

 sium, iron, manganese, and other sedimentary constituents, the hydrogen- 

 ion concentration also influences the oxidation-reduction potential of the 

 sediments. Its effects on base exchange and on the properties of clay are 

 discussed in the symposium volume edited by Trask (1939). 



ZoBell (19426) records that the hydrogen-ion concentration of the 

 topmost layers of bottom deposits is usually nearly the same as that of 

 immediately overlying water. The hydrogen-ion concentration of sea 

 water ranges from pH 7.6 to 8.3, depending primarily upon the depth of 

 the overlying water and its origin. In some cores from the Gulf of Cali- 

 fornia and the Channel Island region off the coast of southern CaUfornia 

 it increases to as much as ^H 8.9, and in other cores it decreases with 

 depth to as low as pH. 7.2. In fresh- water lakes the range is much greater, 

 varying considerably from lake to lake (Allgeier el a I., 1941). 



Effect on oxidation-reduction potential : — The oxidation-reduction 

 (0/R or redox) potential of a system may be defined as its relative oxidiz- 

 ing or reducing power or its electron-escaping tendency. The higher the 

 concentration of free electrons in a solution the greater is its reducing 

 power (or the lower its Eh), and the lower the concentration of free elec- 

 trons the greater its oxidizing power (or the higher its Eh). The reducing 

 power, oxidizing power, or redox potential of a solution containing a re- 

 versible oxidation-reduction system can be expressed conveniently in 

 terms of Eh measured in volts as E.M.F. compared with the E.M.F. of a 

 normal solution of hydrogen ions (Hewitt, 1936). Buchanan and Ful- 

 mer (1928) point out that, in general, any system having an Eh value 

 less than another system will tend to reduce it, and the system having the 

 higher value will tend to oxidize the lower. 



INIost bacteria tend to create reducing conditions or to lower the Eh of 

 culture media from an initial Eh of + 0.2 or + 0.3 volt to Eh — o.i or — 0.2 

 volt at pK 7.0 (Hewitt, 1936). Anaerobes generally require a lower Eh 

 for the initiation of growth, and they create more reducing conditions or 

 a lower Eh than do aerobes (Reed and Orr, 1943). Not only do bac- 



