CANADA INSTITUT OCEANOGRAPHIQUE DE ~BEDFORD,~ ~AA INSTITUTE OF OCEANOGRAPHY DARTMOUTH, N. S.

Transcription

1 f DFO - LibriiMPriliblrOque L1i E y CANADA INSTITUT OCEANOGRAPHIQUE DE ~BEDFORD,~ ~AA INSTITUTE OF OCEANOGRAPHY DARTMOUTH, N. S. ISOLATION AND CHARACTERIZATION OF ORGANIC MATTER FROM GLACIAL-MARINE SEDIMENTS ON THE SCOTIAN SHELF by Lewis H. King REPORT B. I. O JULY 1967 PROGRAMMED BY THE CANADIAN COMMITTEE ON OCEANOGRAPHY

2 BEDFORD INSTITUTE OF OCEANOGRAPH Y DARTMOUTH, N. S. - CANADA g This is a technical report to our Headquarters which has received only limited circulation. On citing this report in a bibliography, the title should be followed by the words "UNPUBLISHED MANUSCRIPT", in accordance with accepted bibliographic custom. ISOLATION AND CHARACTERIZATION OF ORGANIC MATTER FROM GLACIAL-MARINE SEDIMENTS ON THE SCOTIAN SHELF by Lewis H. King REPORT B.I.O JULY 1967

3 ii ABSTRACT Humic and fulvic acid fractions have been isolated from the organic matter of glacial-marine sediments obtained on the Scotian Shelf. The sediment is extracted with 0.5 M NaOH under a nitrogen atmosphere, and then treated with 0.5 M HC1 and re-extracted with NaOH. The total yields of the isolated material range from per cent of the original organic content, and the ash contents are on the average about 5 per cent. The yields of humic acid are doubled as a result of the acid treatment. The organic matter is characterized by means of group and elemental analysis. The experimental data indicate small but apparently significant differences in the character of the organic matter from various sedimentary facies on the shelf, but a comparison with soils on the basis of the literature indicates substantial differences. These differences suggest a much higher degree of condensation of the aromatic rings in the terrestrial material.

4 111 TABLE OF CONTENTS Page INTRODUCTION 1 DESCRIPTION OF SAMPLES 3 EXPERIMENTAL PROCEDURE 5 DISCUSSION OF RESULTS 7 ELEMENTAL COMPOSITION 11 CONCLUSIONS 15 ACKNOWLEDGEMENTS 16 REFERENCES 17

5 ISOLATION AND CHARACTERIZATION OF ORGANIC MATTER FROM GLACIAL-MARINE SEDIMENTS ON THE SCOTIAN SHELF INTRODUCTION The isolation of organic matter from soils and marine sediment constitutes one of the major problems in its chemical investigation. Because of low extraction yields, measurements are.-commonly made on only a small portion of the organic matter present, and the fractions studied are probably not representative of the total organic matter. It is also difficult to avoid chemical alteration during the extraction process, as well as to obtain low ash-content products whereby reliable physical and chemical properties can be measured. Soil scientists generally isolate humic substances from the soil by treatment with alkali solutions as these solutions effect the most complete extraction and, as shown by,kononova (1961), this method does not change the nature of the humic substances essentially. More recently Mehta, et. al. (1963) detected changes in the molecular weight distribution ofeumic substances and noted an increase in molecular weight with HC1 treatment and an even more marked decrease with NaOH. At the present time it appears impossible to obtain a high degree of extraction of humic substances from soils and marine sediments without causing some alteration of the material. Extraction conditions should be kept as mild as possible and should be carried out under an inert atmosphere. For a more complete extraction of soil organic matter Than (1945) and Zyrin (1948) extracted humic substances in dilute alkalis after treatment of the soil alternately with acid and alkali. Degens and Hunt (1964) have subsequently found that this treatment is effective in the partial removal of kerogen from shales. The technique of alternate acid-base treatment has been employed in this investigation to remove organic matter from four glacial-marine sediments from the Scotian Shelf. By analogy with the classification of organic matter in soil the following definitions are adapted for these studies. The term humic acid represents the group of organic substances that are extractable from soil by alkali solution and precipitated upon acidification. Fulvic acids are the alkali soluble compounds that stay in solution upon acidification. The insoluble organic fractions of the soil are termed humins. According to Kononova (1961) the humin group is represented mainly by humic acids which have lost the capacity to dissolve in alkali solutions because of a more stable linkage with the mineral part of the soil. For marine sediments this latter fraction is heterogeneous as considerable quantities of spore and pollen grains can be microscopically observed, and it is probable that other insoluble petrographic components exist as well. These petrographic entities result in apparent lower yields of the soluble humic substances.

6 2 Although studies of the portion of marine sediments soluble in organic solvents have been extensive, detailed study of the humic portion has been neglected. In a recent Russian review on the accumulation and transformation of organic matter in bottom sediments Bordovskiy (1965) indicates that the study of humic acids of bottom deposits is as yet in its infancy even though soils and solid fuels have been the subject of detailed investigation. The geological and biological significance of detailed studies is discussed by both Bordovskiy (1965) and Degens (1965). Investigations at the Bedford Institute of Oceanography are concerned mainly with the relation of the composition of organic matter to sediment type and the depositional environment. Studies are also in progress on the oxygen-containing functional groups of the organic matter.

7 3 DESCRIPTION OF SAMPLES The samples used in this investigation are described in Table 1. Organic carbon and nitrogen were determined on the whole sample with a Leco Carbon Determinator and a Coleman Nitrogen ' Analyzer. Carbon, hydrogen and nitrogen on the purified organic extracts were determined with Coleman Analyzers, while oxygen and sulphur were obtained by difference. The textural parameters of the sediments were determined by means of screen'and pipette. The samples were collected with a modified van Veen grab sampler of 23 - litre capacity, and they were stored at 0 C. For a description of the geological setting the reader is referred to papers by King (1965 and 1967). TABLE 1 - Description of samples KC-66 KC-84 KC-34 Glacial Till Sample Clay, LaHave Clay, Emerald N. flank of Designation Basin Basin Sambro Bank KC-9 Silt, W. flank of Emerald Bank Latitude 43 45'N ui 'N 44 00'N 'N Longitude 63 45'W 63 05'W 63 18'W 62 46'W Depth,metres Median diam.mdp Wentworth gradea Gravel Sand Silt Clay Organic carbon* Nitrogen* C/N ratio * Run on carbonate-free sample

8 5 EXPERIMENTAL PROCEDURE The samples were thawed, treated with 0.1 M HC1 for carbonate removal and thoroughly washed several times with the aid of a continuous-flow centrifuge. They were then freeze-dried, weighed and a few grams were removed for organic carbon determination on the Leco Carbon Determinator. Sample weights varied from 375 g. for the clays with relatively high organic content to 1,000 g. for the silt and till of lower carbon content. The organic matter was then extracted with 0.5 M NaOH using an extractant to sediment ratio of 10:1 (WM. All extractions were carried out under a nitrogen atmosphere at room temperature and the samples were shaken on a mechanical shaker for approximately 18 hours. The extractions were repeated seven times at which point the supernatent solutions were a pale yellow. After each extraction the supernatent solution was removed and acidified with concentrated HC1 to ph 3. The acid treatment precipitated the humic acid fraction and left the fulvic acid in solution. After completion of the consecutive extractions the total humic acid precipitate was separated from the fulvic acid fraction by centrifuging, and washed several times with water. The sample residue was retained for further extraction by the alternate acid-base treatment. The humic acid fraction is purified by redissolving it in 0.5 M NaOH and passing it several times through a column of Rexyn 101 exchange resin in the H form. Values of ph for the purified extract are variable after immediate passage through the column, but stabilize at 4-7 in approximately one week. This is a stable suspension and a portion is removed for storage because once the humic acid is dried it cannot be completely redissolved in NaOH. The remaining portion is further purified by freezing and thawing, a technique suggested by Forsyth and Fraser (1947). This treatment destroys the colloidal properties of the suspension and the humic acid can be removed by centrifuging and washing. Soluble contaminants including siliceous materials are removed and a considerable degree of purification is attained. During the separation of sample KC-84 (Table 1) the humic acid failed to precipitate completely upon freezing and thawing, so that two fractions were collected at this stage. The soluble fraction (Fraction B) showed a higher ash content. Upon completion of the freezing and thawing treatment the organic matter was freeze-dried and designated Humic Acid Fraction 1. The fulvic acid solutions (ph 3) were passed over a column of chromatographic alumina ( mesh) to remove the fulvic acid and eliminate the large volume of acid solution. The fulvic acid was then eluted from the column with 0.5 M NaOH. Unfortunately, rather large amounts of alumina were dissolved from the column. This alumina was removed by adjusting the ph to 6.5 and centrifuging, but much of the organic matter was retained by the alumina so the process was repeated several times. Even then, the bulk of the fulvic acid was retained by the alumina. The alumina-organic complex

9 6 was dried and analyzed for organic carbon in order to obtain the total fulvic acid content of the sample. The fulvic acid fraction removed from the alumina was reduced in volume by flash evaporation, transferred to dialysis bags and dialized exhaustively against distilled water. 'The sample was then freeze-dried and designated Fulvic Acid Fraction 1. The residue from the NaOH extraction was treated with 0.5 M HC1 using a 4:1 (W/W) ratio of acid to sediment and shaken for 18 hours. The supernatent solution which contained both iron and aluminum was neutralized to remove these constituents. Upon completion of the entire extraction these constituents were dried and analyzed for organic carbon. The residue was extracted with 0.5 M NaOH and the humic and fulvic acids were recovered and purified according to the procedure for Fraction 1 above. The alternate acidbase treatment was repeated seven times at which point the extraction was essentially complete. The humic and fulvic acid fractions were designated as Fraction 2. The residue was washed and dried for carbon determination.

10 7 DISCUSSION OF RESULTS One of the main objectives of this investigation was to define conditions for the maximum extraction of organic matter and to maintain a high degree of purity in the extracts. The results are shown in Table 2. The total organic material obtained by the combined NaOH and NaOH-HC1 extractions is per cent for the clays, 47 per cent for the silt and 49 per cent for the till. In all cases the alternate acid-base extraction (Fraction 2) doubled the yield of humic acid. The fulvic acid yield, including both the recovered and calculated portions, decreases considerably in Fraction 2. The degree of purification attained for the humic acid fractions is quite satisfactory as indicated by the ash contents which average about 5 per cent. Only a small fraction of the fulvic acid was recovered as pure material because most was, lost to the organo-alumina complex formed during the purification process. The calculated fulvic acid content represents the amount of fulvic acid on. the organo-alumina complex and was obtained by measuring the carbon content of the complex and multiplying this value by the appropriate organic factor obtained from the elemental analysis of the pure fulvic acid.. The total fulvic acid for each sample is the sum of the pure and calculated fractions. The humin fraction was calculated from the carbon content of the sample residues using an organic factor of 1.7. The unaccounted organic matter is obtained by difference and varies from per cent. These values include all mechanical losses in handling, as well as losses on the resin columns. The wide variation tends to suggest that losses are mainly mechanical; however, the possibility of some loss due to chemical alteration of the organic matter cannot be ignored. Since the data of Table 2 were obtained the isolation procedure has been modified. After extraction with NaOH the solutions are passed over the H resin column to remove sodium before precipitation of the humic acid. This eliminates NaCl in the subsequent fulvic acid solutibn and this improves the purification procedure. After separation of the humic and fulvic acid fractions with HC1 the supernatent liquid containing the fulvic acid is flash evaporated to dryness to remove HC1. Unfortunately, the HC1 cannot be removed by passage over an OH resin as the fulvic acid is absorbed by the resin and cannot be recovered. After evaporation the fulvic acid is dissolved in dilute NaOH and passed over the H resin for further purification, and the neutral solution is centrifuged to remove additional inorganic constituents. It is then placed in dialysis bags, dialized

11 Sample Organic Matter in carbonate free sample % TABLE II Humic acid, fulvic acid and Humin content of samples (yields expressed as per cent of total organic matter). Humic Acid, Fulvic Acid, Fulvic Acid, Recovered % Recovered % Calculated Total Total (Ash-free) (Ash-free) % Humic Fulvic Humin, Unaccounted Ash Ash Acid Acid Calculated Organic Humic Acid F. 1 F. 2 % F. 1 F. 2 %- F. 1 F. 2 % % % Matter l'ulvic Acid KC C ' A B KC KC , 14.9

12 9 against distilled water for one week and freeze-dried (Fulvic Acid, Fraction A). Some of the inorganic components are precipitated in the bags during the early stages of the dialysis and these are removed by centrifuging. During the dialysis a portion of the fulvic acid passes through the membrane and this fraction is recovered by flash evaporation and freeze-dried (Fulvic Acid, Fraction B). The entire procedure is summarized in Figure 1. Using this procedure all organic matter extracted from the sediment can be recovered as pure material. It is possible that the pure fractions of fulvic acid obtained by the earlier purification process are fractionated so the elementary analyses must be accepted with caution. Fulvic acid from soils is generally concentrated and partially purified by absorption on charcoal with subsequent removal by NaOH. This procedure was tried with the marine material but the fulvic acid was held so strongly by the charcoal that it could not be eluted with NaOH. This indicates a marked difference between the fulvic acids of soil and marine material. The fulvic acid portion of the marine sediment is about half that of the recoverable humic acid. The humic acid-fulvic acid ratios vary from and are similar to those found in chernozem soils. According to Kononova (1961) the humic profile in the chernozem soils is a complex organo-mineral system and is stable and homogeneous. Lack of a fractionated profile is caused by the absence of a leaching-type water regime. Water circulation under marine conditions is also probably limited, therefore, little chance exists for leaching and fractionation of the more mobile fulvic acid fraction until such time as the connate water is expelled upon compaction of the sediment. The fulvic acid of soils is noted for its high degree of mobility because of its high degree of dispersion and resistance to electrolytes. These properties could be significant during the compaction phase of shale development. In addition to its high mobility, fulvic acid in soil is active in the decomposition of the mineral part of the soil (Kononova, 1961), so by analogy the fulvic acid in marine sediment is probably important with respect to diagenetic changes in the minerals.

13 ISEDIMEN4 Treat with 0.1 M HC1 to remove carbonates Wash, dry Id weigh Sample Extract with 0.5 M Nal for 18 hours in nitrogen atmosphere (repeat 7 times) Sample for carbon determination for carbon determination SOLUBLE HUMIC AND FULVIC ACID,( FRACTION 1 1 Extract passed over Rexyn 101 exchange resin in the H form to remove Ne Adjust to ph 3 with HC1 to precipitate Humic Acid SEDIMENT CONTAINING THE LESS' SOLUBLE HUMIC FRACTIONS Treat with 0.5 M HC1 for 18 hours and wash free of acid Extract with 0.5 M NaOH several times Repeat alternate acid-base treatments several times SOLUBLE HUMIC AND FULVIC ACID FRACTION 2 Extract passed over Rexyn 101 exchange resin in the H form to remove Ne Adjust to ph 3l withhc1 SEDIMENT AND RECOVERABLE ORGANIC MATTER Wash,weigh and determine carbon content Purification procedure same as Fulvic acid fraction 1 FULVIC ACID FRACTION 2AI I FULVIC ACID FRACTION 2B Purification procedure same as Humic acid fraction 1 HUMIC ACID FRACTION 2AI I HUMIC ACID FRACTION 2B Flash evaporate to dryness to remove HC1. Redissolve in NaOH, pass over resin in H form Dialyze against distilled water Sample passing through membrane Flash evaporate and freeze-dry FULVIC ACID FRACTION 1B Fraction remaining in bags, centrifuge to remove inorganic precipitate, freeze-dry FULVIC ACID ( FRACTION IA Wash, redissolve in 0.5 M NaOH, pass over resin column Coagulate by freezing and thawing for further purification and centrifuge. Freeze-dry HUMIC ACID FRACTION 1B ( Soluble fraction, higher in inorganic constituents; not always obtained. Portion can be removed for storage as this is a stable suspension. Once the Humic acid is dried it is difficult to redissolve completely Freeze-dry HUMIC ACID FRACTION IA

14 ELEMENTAL COMPOSITION Elemental analyses for the different humic and fulvic fractions are shown in Table 3. These analyses show certain regular changes between fractions from the same sample, as well as between samples. The carbon content of the humic acid fractions ranges from per cent while the hydrogen varies from per cent. Between fractions of humic acid from the same sample, carbon and hydrogen tend to increase slightly from Fraction 1 to Fraction 2, and the atomic H/C ratios remain more or less constant with some erratic variation. Between samples the carbon shows no consistent trend but the hydrogen tends to decrease in the glacial till and silt samples. The H/C ratios, which range from , decrease in the till and silt as compared with the clay samples. This increase in degree of condensation from the clays to the till and silt possibly results from a respective increase in age, or it might arise as a result of a closer association of the till and silt with a former terrestrial environment. Fulvic acids from all samples show lower carbon values than the humic acids and vary from ,2 per Cent while the hydrogen values show no definite trend. The atomic H/C ratios of the fulvic acids are higher than those of the humic acids and range from Because of the difficulties encountered in the purification of the fulvic acids and the possibility of fractionation, it is doubtful if these analyses are representative of the whole fulvic acid fraction. These data suggest a decrease in degree of condensation as compared with humic acid. The carbon and hydrogen results shown in Table 3 for the humic acids compare well with results obtained by Bordovskiy (1965) on recent Bering Sea sediments. The atomic H/C ratios on the Bering Sea results range from On the other hand, the composition of the marine material shows a marked difference with that of soil. The H/C ratios on soil extracts can range from suggesting on the average a much greater degree of condensation of the aromatic rings in the terrestrial material. The oxygen content of the humic fractions ranges from per cent for all the samples, but there is no consistent trend between samples. Oxygen generally decreases a few per cent from Fraction 1 to Fraction 2. For the fulvic acid fractions the oxygen ranges between limits of per cent and is thus considerably higher than the humic acids. Nitrogen contents of the humic acid fraction range from per cent for all the samples. Within samples the nitrogen content decreases on the average about one per cent for humic acid fractions 1 and 2 with the exception of sample KC-66 in which a slight increase is shown. The atomic N/C ratios range from for the humic acids, and show no significant trends between

15 TABLE 3 Elemental analyses and atomic ratios of samples Sample Designation Elemental analysis, weight % (ash free) N 0 + S -6 Atomic Ratios KC-66 Humic Acid, Fl Humic Acid, F Fulvic Acid,Fl Fulvic Acid,F KC-84 Humic Acid, Fl Humic Acid, F2A Humic Acid, F2B Fulvic Acid,F KC-34 Humic Acid, Fl Humic Acid, F Fulvic Acid,F KC-9 Humic Acid, Fl Humic Acid, F Fulvic Acid,Fl Fulvic Acid,F '

16 samples. Between humic acid fractions 1 and 2 the N/C values generally decrease by 0.01 to The relationship between the carbon and nitrogen contents of sediments are generally expressed in the literature as weight C/N ratios rather than atomic N/C ratios, therefore these values are also included in Table 3 for comparative purposes. The C/N ratios for the original sediments are shown in Table 1. A comparison of the sediment values with those of the extracted organic matter shows an average increase from 7.2 to 11.3 because of a loss in nitrogen. The 11.3 average probably represents a minimum value as the average is not weighted and the contribution of the humin content cannot be taken into account. The difference between these average values indicates that at least 35 per cent of the nitrogen was lost during the extraction of the organic matter. Large losses in nitrogen have previously been reported by Emery (1956) and Foreman and Hunt (1958) when marine sediments and shales are extracted with HF. The nitrogen loss could be caused by alteration of the organic matter during extraction; however, it is more likely caused by the loss of inorganic nitrogen. Stevenson (1962) investigated the influence of fixed ammonium on the C/N ratios of sedimentary rocks and determined that per cent of the nitrogen found in sedimentary rocks occurs in this form. Therefore, the average 35 per cent lost in nitrogen found in this investigation is probably due to loss of fixed ammonium. Stevenson (1962) emphasizes that C/N ratios reported in the literature for sediments and sedimentary rocks are low, and that the ratio should not be considered a characteristic of indigenous organic matter unless the fixed ammonium is taken into account. The average C/N ratio for the humic acid fractions of Table 3 is This value is lower than the 16.4 value for humic acids from the Bering Sea reported by Bordovskiy (1965). The difference arises from lower nitrogen values reported by Bordovskiy,

17 15 - CONCLUSIONS The procedures used in this investigation for the extraction of humic acid appear to be satisfactory with regard to yield and purity of the isolated organic matter, and the revised procedure has eliminated many of the difficulties encountered in the isolation of the fulvic acid fraction. The extent of chemical alteration of the isolated fractions is an unknown factor, but extraction conditions have been kept as mild as possible to minimize alteration and strong enough to insure a high yield. Soil scientists are continually striving to develop milder and more selective extraction procedures with the use of neutral or slightly alkaline solvents, but these are usually demonstrated on podzol horizons which are relatively easy to isolate as compared to Grey Wooded soils reported on by Schnitzer and Gupta (1964). Marine sediment and Grey Wooded soils are probably similar with regard to their extraction behavior. Group analysis is important for comparison between samples, as well as with soils. For example, the, humic acid-fulvic acid ratios are similar in marine material to those found in the unfractionated chernozem soils. This suggests a fundamental relation between the origin of the humic and fulvic fractions of soil and marine material even though the respective fractions from the contrasting environments differ widely in chemical composition. Fulvic acid in soils is noted for its high degree of mobility because of its high degree of dispersion and resistance to electrolytes, and considerable information is available on its ability to decompose mineral constituents of the soil. By analogy, the fulvic acid component of marine sediment is probably important with regard to the migration of organic matter in marine sediment, as well as with respect to diagenetic changes in the minerals. Differences in the carbon and hydrogen content between humic acid fractions from the same sample appear to arise as a result of a concomitant change in oxygen content. Because their H/C atomic ratios are more or less constant the differences in the distribution of carbon, hydrogen and oxygen probably reflect changes in the distribution of the functional groups of the fractions. Between the clay samples and the silt and till samples, the H/C atomic ratios of the humic acid are different, suggesting differences in their skeletal structures. These differences in the degree of condensation of the samples might be related to differences in the age of the samples, or might arise as a result of a past terrestrial influence. Both the glacial till (KC-34) and the silt (KC-9), which is a proglacial deposit, are older than the top of the clay facies (KC-66 and KC-84), and both were probably influenced more strongly by a terrestrial environment even though they were deposited below sea level (King, 1967). The fulvic acid fractions of all samples show lower carbon

18 values than the humic acid while the oxygen contents are higher, and the hydrogen values are about equal with some erratic variation. The atomic H/C ratios of the fulvic acid fractions are higher than those of the humic acid fractions and show respective ranges from to These fractions probably differ both in their functional group content, as well as in their skeletal structure. The carbon-hydrogen data compare well with the values cited on the Bering Sea sediments. The atomic H/C ratios on the Bering Sea sediments range from (Bordovskiy, 1965), while the range for this investigation is Variations in the C/N ratios of the whole sediment and the extracted organic material indicate a loss in nitrogen during the extraction process. This loss might be due to chemical alteration, but it is more likely caused by the loss of fixed ammonium. A thorough investigation by Stevenson (1962) on the distribution of nitrogen in sedimentary rocks indicates that a high percentage of the nitrogen occurs as fixed ammonium. ACKNOWLEDGEMENTS Grateful acknowledgement is made to my associate Dr. M.A. Rashid, for helpful discussion, to my colleague Dr. R. Platford for critical review of the manuscript and to Mr. G. Duncan for technical support.

19 REFERENCES Bordovskiy, O.K Accumulation and transformation of organic substances in marine sediments. Marine Geology, 3: pp Degens, E.T., Geochemistry of Sediments. Prentice-Hall, New Jersey, 342 pp. Degens, E.T. and Hunt, J.M., Thermal stability of amino compounds in recent and ancient sediments, humic acids and kerogen concentrates. Intern. Meeting on Organic Processes in Geochemistry, Paris. Forsman, J.P. and Hunt, J.M., Kerogen in sedimentary rocks, in Habitat of Oil, Amer. Assoc. Petrol. Geol., Tulsa, Oklahoma: Forsyth, W.G.C. and Fraser, G.K., Freezing as an aid in the drying and purification of humus and allied materials. Nature, 160 : p Khan, D.V., A method of isolating the insoluble fraction (humin) from podzolic soils. Dokl. vsesoyuz. Akad. s.-kh. Nauk Lenina, 7-8 (quoted by Kononova, M.M., 1961). King, L.H., Use of a conventional echo-sounder and textural analyses in delineating sedimentary facies - Scotian Shelf. Bedford Institute of Oceanography Report 65-14, 27 pp., unpublished manuscript. Can. Jour. of Earth Sciences, in press. King, L.H., On the sediments and stratigraphy of the Scotian Shelf. Bedford Institute of Oceanography, Report 67-2, 32 pp., unpublished manuscript. Transactions Geological Association of Canada, in press. Kononova, M.M., Mehta, N Soil Organic Matter. Pergamon Press, New York, 450 pp. Ċ., Dubach, P. and Deuel, H., Investigation on the molecular weight distribution of humic substances by gel filtration through Sephadex. Z Pflanzenernahrung, Dung. Bodenk. 102: Orr, W.L. and Emery, K.O., Composition of organic matter in marine sediments. Bull. Geol. Soc. Amer., 67;

20 Schnitzer, M. and Gupta, U.C., Some chemical characteristics of the organic matter extracted from the 0 and B2 horizons of Gray Wooded soil. Proceedings Soil Science Society of America, 28; 377. Stevenson, F.J., Chemical state of the nitrogen in rocks. Geochimica et Cosmochimica Acta, 26: