Claude E. Zobell

Studies on Redox Potential of Marine Sediments

The redox potential of sediments may be used advantageously in the study and interpretation of the morphology, general nature, and chemical processes in unconsolidated sediments. The redox potential is believed to have a pronounced effect on the diagenesis of sedimentary materials, including the conversion of organic matter into petroleum. The modern concepts of oxidation, reduction, and redox potentials are discussed. The redox potential is measured in volts and is expressed as an Eh value, Eh being the e.m.f. of an oxidation-reduction system referred to a standard hydrogen half-cell. The Eh of a system is a quantitative expression of its oxidizing or reducing intensity. Redox potential may be defined as the electron-escaping tendency of a reversible oxidation-reduction system, and thus is an intensity factor. The reducing or oxidizing capacity of sediments is independent of the redox potential, although there is a relation between the intensity and capacity factors. The pH and temperature at which measurements are made influence the redox potential of sediment samples. The Eh of sediments, like the pH, can be measured either colorimetrically or electrometrically. A description of the methods of measuring the Eh of sedimentary materials helps to clarify the concepts of redox potentials. Methods of measuring the capacity as well as the intensity factor are given. Data on more than 1,000 samples of bottom deposits indicate that each type of sediment has its own characteristic Eh and pH. Eh values ranging from +0.350 to -0.500 volt have been observed in samples of recent sediments in which the pH ranged from 6.4 to 9.5. As a very general rule, the pH of sediments increases with core depth and the Eh decreases, or conditions become more alkaline and more reducing with core depth. The reducing capacity decreases with core depth. Positive Eh values are generally characteristic of bottom deposits which are well oxygenated, those which consist of coarse sediments, or those which are poor in organic matter. Negative Eh values are characteristic of bottom deposits rich in organic matter and which consist largely of fine sediments. An abundance of readily decomposable organic matter appears to promote reducing conditions. In the presence of organic matter, bacteria and allied microorganisms create reducing conditions. Such conditions are maintained by certain organic compounds, ferrous iron, reduced manganese, hydrogen sulphide, and other inorganic constituents of sediments. End_Page 477------------------------------

OBSERVATIONS ON THE MULTIPLICATION OF BACTERIA IN DIFFERENT VOLUMES OF STORED SEA WATER AND THE INFLUENCE OF OXYGEN TENSION AND SOLID SURFACES

The storage of sea water is accompanied by a great increase in the number of bacteria and a decrease in bacterial species.Appreciably more bacteria per cc. appear in small volumes of sea water than in large volumes of identical water.Although the oxygen content of sea water is a factor which influences the activity of bacteria, it does not account for the denser bacterial populations which appear in the smaller volumes.The favorable influence of small volumes is attributed to the contact of the water with the larger solid surface area in the small receptacles. Between ten and a hundred million bacteria per cc. have been demonstrated in sea water stored in sand which presents an enormous surface area whereas less than three hundred thousand bacteria per cc. appearing similar water stored in 10-liter bottles presenting relatively little surface area.The beneficial effect of small volumes and their large surface areas occurs only in dilute nutrient solutions. Upon the addition of 10 to 100 mgm. of organic ma...

Occurrence of bacteria in pelagic sediments collected during the mid-Pacific expedition

Abstract Bacterial populations ranging from hundreds to thousands per gram wet weight were demonstrated in pelagic sediments (red clay and globigerina ooze) taken during the Mid-Pacific Expedition. The abundance of viable bacteria in these sediments decreased with core depth. Although certainly most important as geochemical and biological agents in surface sediments at the mud-water interface, living bacteria were found at the bottom of the longest cores examined, nearly 8 metres, representing material believed to have been deposited more than a million years ago. A few explanations are offered to account for the presence of bacteria in this material of great antiquity.

Microbial Modification Of Crude Oil In The Sea

Abstract Virtually all kinds of hydrocarbons and crude oils from many fields are susceptible to microbial oxidation. More than a hundred species of bacteria, yeasts, and fungi are able to oxidize h...

Studies on the Bacterial Flora of Marine Bottom Sediments

ABSTRACT The bacteriological analysis of 126 sediment samples collected in the Channel Island region along the coast of Southern California from bottoms as deep as 2,000 meters reveals the presence of several physiological types of bacteria which may influence the diagenesis of recent sediments. Strict aerobes recovered from the bottoms of cores over 50 cm long where there is no free oxygen may have been buried in the sediments in a dormant state for a long time. Core depth, organic-matter content, and the median particle size of the sediments are the chief factors which influence the bacterial populations. Most of the bacteria are capable of multiplication and biochemical activity at 0° C. Bacteria which decompose proteins, cellulose, starch, chitin, and other complex organic compounds ar quite abundant in the bottom deposits. The occurrence of lipoclastic species which utilize the glycerol from fats and leave long-chain fatty acids may help account for the genesis of petroleum.

Vertical Distribution of Bacteria in Marine Sediments

Off the coast of Southern California bacteria are more abundant in marine sediments than in the overlying water, there being thousands to millions per gram of sediment and only a few hundred or less per milliliter of water. The distribution of bacteria in the sediment is more or less independent of the depth of the overlying water, the temperature of the ocean floor, and the distance from mainland. The bacterial population seems to be influenced more greatly by the organic content of the sediments than by other factors. Vertical sections from cores 40 to 75 cm. in length show that the number of bacteria in the sediments decreases greatly with depth in the upper 5 cm. of the core and more slowly beyond. In the surface slime, aerobes are 5 to 100 times more plentiful than a aerobes, but at depths exceeding 15 centimeters about as many anaerobes as aerobes are present. Both anaerobes and aerobes have been demonstrated at all depths analyzed. The oxidation-reduction potential (intensity factor expressed as Eh) increases with core depth, although the oxygen-absorbing capacity decreases with depth. Both properties are ascribed primarily to bacterial activity. Bacteria recovered from marine sediments exhibit many biochemical processes such as ammonification, proteolysis, nitrate reduction, nitrification, urea fermentation, chitin digestion, methane production, fat hydrolysis, cellulose decomposition, glucose, xylose, and arabinose fermentation and starch hydrolysis.

Microbial Transformation of Molecular Hydrogen in Marine Sediments, with Particular Reference to Petroleum

Molecular hydrogen is produced by a large number of bacterial species, many of which occur in marine sediments. Such bacteria have been demonstrated in marine bottom deposits, oil-bearing sands, and in reservoir fluids from oil wells. Up to 10,000 hydrogen-producing bacteria were found per gram of mud from the floor of the Pacific Ocean. Pure or enrichment cultures of such bacteria have been shown to liberate hydrogen from organic compounds at temperatures ranging from near 0°C. to as high as 65°C. Hydrogen is liberated from virtually all kinds of organic compounds, and most readily from carbohydrates or polyhydroxy alcohols. Redox potentials more reducing than Eh -0.05 volt and reactions ranging from pH 5.5 to 9.8 favor hydrogen formation. It is poss ble to demonstrate the production of hydrogen in samples of marine mud by inhibiting the activities of hydrogen-oxidizing bacteria. The latter are believed to account for the general exiguity or lack of molecular hydrogen in marsh gas and other natural gases, although traces of hydrogen have been reported in such gases. The rapid consumption of hydrogen by samples of soil and sediments is attributed to the activities of bacteria or their enzymes which catalyze its oxidation. Listed are several species of autotrophic aerobes which oxidize hydrogen to water. Of greater geological importance are various kinds of anaerobes which oxidize hydrogen with the formation of methane, simple organic acids, ammonia, and hydrogen sulphide. Evidence is presented that bacteria produce methane by catalyzing the reduction of carbon dioxide or other one-carbon-atom compounds with hydrogen. Other types of bacteria catalyze the reduction of carbon dioxide by hydrogen with the formation of formic, acetic, and possibly other carboxylic acids. Amino acids and other organic compounds are also reduced by hydrogen-activating ba teria. Certain bacteria found in sediments utilize energy from the oxidation of molecular hydrogen for the reduction of sulphate. Others reduce nitrate and nitrite. The hypothesis is advanced that various kinds of hydrogen-oxidizing bacteria, in conjunction with radioactivity and other catalytic agents in sediments, may contribute to the formation of petroleum hydrocarbons. Different sources of hydrogen and the energetics of some hypothetical reactions are considered. End_Page 1709------------------------------

∗Bactericidal Action of Sea-Water:

It has been shown by the author 1 that sea-water inhibits the multiplication of freshwater bacteria while marine bacteria require sea-water media for their initial isolation, although these differences rapidly disappear following the laboratory cultivation of the bacteria. Similar observations on the selective bacteriostatic action of sea-water have been reported by Berkeley, 2 Lipman, 3 and Korinek. 4 It is generally known that intestinal and other bacteria of public health interest do not survive very long when emptied directly into the sea unless there is appreciable organic matter present or considerable freshwater dilution. Colon bacilli are rarely recovered from the open sea and they occur far less frequently in the vicinity of sewage effluents than can be accounted for by dilution or oceanic circulation. The failure of freshwater bacteria to survive in the sea has been attributed by various investigators to predacious protozoa, lack of nutrients, bacteriophage, 5 or to the lethal effect of sunlight. The following experiments reveal that sea-water per se is bactericidal. In the first series of experiments sewage was appropriately diluted with “formula C”† and 1.0 cc. quantities of the resultant dilutions were transferred to 99 cc. water blanks consisting of different kinds of sea-water as well as a “formula C” control. After thorough mixing by shaking, 1.0 cc. quantities of the final dilutions were plated with nutrient agar. About one minute elapsed from the time the final dilutions were made in sea-water until the agar was poured. Additional 1.0 cc. samples were plated after 15 minutes and again after 30 minutes, and at 30-minute intervals thereafter. The plates were incubated 4 days at 37°C. and the colonies counted.

Changes produced by micro-organisms in sediments after deposition

Significant numbers of bacteria have been found in recent sediments wherever critical tests have been made for their presence. Total numbers as well as the kinds of microorganisms decrease with core depth. Several physiological types of bacteria together with fewer yeasts, molds and actinomyces have been found, some at depths exceeding 15 feet. The demonstrated ability of the microorganisms to function in sedimentary materials in the laboratory under conditions simulating those in nature indicates that they could be active in situ , and changes in certain properties of sediments suggest that the microorganisms have been active. Bacteria consume oxygen, and there are enough bacteria in sediments to account for the depletion of the dissolved oxygen. Similarly bacteria are probably responsible for the oxidation-reduction potential of sediments which ranges from Eh 0 to -0.5 volts whereas the overlying water is oxidizing in character. There are several ways in which the biochemical activities of microorganisms influence the hydrogen-ion concentration of sediments. Most types of organic matter are attacked by bacteria. The organic content and microorganisms influence the aggregation of particles. By altering the environmental conditions and by serving as a source of food, bacteria have a pronounced effect on the animal population of sediments. It is still indeterminate if bacterial activity plays a role in the genesis of petroleum, but there are several ways in which it might. The changes in the calcium, iron, manganese, sulfur, phosphate and carbonate content of sediments attributable to microorganisms are mentioned.

SOURCES AND BIODEGRADATION OF CARCINOGENIC HYDROCARBONS

ABSTRACT Carcinogenic hydrocarbons (CHC) are widely distributed in air, soil, marine mud, water, oils (vegetable as well as mineral), and other materials. Most organisms appear to contain little or no CHC, but from 1 to more than 1,000 µg/kg has been detected in certain plants and animals. A major source of CHC is the combustion or pyrolysis of carbonaceous materials, including fossil fuels, organic refuse, forest fires, etc. Airborne, liquid, or solid pollutants tend to find their way into soil, streams, lakes, and the sea. Pertinent to the problem of oil spills is the quantity of CHC contributed by such spills as compared with that from aerial transport, terrestrial drainage, biosynthesis of CHC, and other sources. Evidence is presented for the synthesis of carcinogenic hydrocarbons by various species of bacteria, algae, and higher plants. Although some may be retained by their tissues, a good many animals metabolize various carcinogenic hydrocarbons and excrete the oxidation products. In most aquatic e...