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Humic substances from deposits of a natural laboratory : A blue lake on the ice-cap (Greenland)
The Science of the Total Environment, 62 (1987) 107-109 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands
107
HUMIC SUBSTANCES FROM DEPOSITS OF A NATURAL LABORATORY : A BLUE LAKE ON THE ICE-CAP (QREENLAND). F. GADEL’ , 0. TORR12and A. BRUCHET3 1 Laboratoire de Sdimentologie et Geochimie Marines - Universite de Perpignan - France 2 Laboratoire de Chimie Marine - Universite de Toulon et du Var - France 3 Laboratoire Central - Lyonnaise des Eaux - Le Pecq - France SUHMARY The structural analysis of humic compounds from depostts of a blue lake in Greenland, a parttcular environment on the ice-cap isolated from any terrestrial influence, shows their relatively specific nature, resulting from growing blue algae. Fulvic acids are essentially of polysaccharidic nature ; humic acids, more hetercqenous in composition, show, with polysaozharides and peptidic fragments, an aromatic character certainly due to amino-acid residues. INTRODUCTION The blue lakes are situated just above the arctic circle in Greenland on the ice-cap more than I km thick (30 km from the side of the Sondrestromfjord glacier on the western coast). These lakes, about ten meters deep, are practically isolated from terrestrial influences and the bottom deposits result principally from meteoric dusts. The sediments are scattered on the rough bottom of lakes into a multitude of shallow holes which shelter them against currents. They are composedof a black mud with small bell particles from cosmic origin and rare terrestrial white quartz. The organic matter originates exclusively from a blue elgw growth (Cyanophyceae). The entanglement of algal fibers constitutes cocoonswhich trap the cosmic dust. The organic matter content is high (6.6 X org. C.). Whe have studied the distribution and nature of humic substances in this particular environment. RESULTS AND DISCUSSION Due to its algal nature, the organic matter Is very hydrolysable (73 % - 6N HCl I 10%) and the sediment relatively high in nitrogen wntent (0.6 X N). The humic compounds (extractable whith 0.1 N NeOH+ 1 X Ne4P207) ere abundant (50 X) and the fulvic acid/humic acid ratio is close to 2. The e/&i?&Y8/&@& of fulvic and humic acids show that the H/C atomic ratios are very high, giving evidence of a high aliphatic character (FA : 2.02 and HA : 1.62). The N/C ratio is relatively high In HA (0. I 15), but very low in FA (0.014). Therefore the nitrogenous wmpounds ere principally concentrated in humic acids. The O/C ratio which is intermediate in I-LA(O.SOO), is particularly high in FA (0.97 1), due to the abundance of oxygenated groups. The fn/rccdgfastfa (Fig. I ) account for a high aliphatic character of FA, with a marked absorption band corresponding to carbohydrates ( 1050 cm- ’ ) end e higher content of nitrogenous and aromatic compounds in HA. The ‘Ifffff~sjwcira (Fig. 2) show the essentially polysaccharidic nature of FA (93 X) and the 0048-9697/8’7/.$03.50
0 1987
Elsevier
Science
Publishers
B.V.
humic
acids
\
v fulvic
4cl--00
3400
wawwnber
'ig.I-F.T.infrared humic
humic
2000
acids
ki-
spectra
Fig.2-(ItI of
)nuclear magnetic humic compounds.
resonance
00 %A I
spectra
fulvic acids : : ? E :
of
compounds.
SCAN
acids
hmic acids
fulvic
acids I
Fig.3-(13C) nuclear resonance CP/mass humic compounds.
magnetic spectra of
Fig.4-A
et humic
B Pyrolysis compounds.
-mass
spectra
of
109 extremely high aliphaticity. The aliphatic nature of HA (87 W) is characterized by a large proportion of saturated CH groups with a predominance of CH3 on CH2-CH groups, indicative of high branching of aliphatic chains (HATCHERet al., 1980). The polysaccherides are also abundant (38 X). The 13CN~fRs~&~ (Fig. 3) depict that in fulvic acids appear mainly the peeks corresponding to carbons of carbohydrates or aliphatic alcohols and the anomeric carbons of polysfccharides. In humic acids the CH3 and CH2 groups are abundant. The peptide peak appears clearly as the anomeric carbons of polysaccherides and the aromatic carbons The PY-&‘-MS spectm (Fig. 4 A-B) give more precise information on the structure of humic compounds. Fulvic acids are clearly dominated by fragments of carbohydrate origin. The anhydrosugars detected are known to be formed during the initial steps of pyrolysis of cellulose and other polyhexoses (SHAFIZADEH and FU, 1973). Their further degradation leads to the furans and various carbonyl compounds. Some products can result from non-reducing xylopyranasyl residues or carbohydrates (MIYAZAKI, 1975). The cyclic ketone (cyclopent-2-en- l-one) constitutes a fragment of polycarboxylic acids (BRACEWELL et al., 19801, resulting from pyrolysis of mono- and polysaccharidas. The low phenolic peek could be the result of uncontrolled secondary reactions which often occur in Severe elcaline or dehydrating matrix conditions. Humic acids show a much more heterogeneous character. Fragments from peptidic origin are present as pyrrole and methylpyrrole, indole from tryptophan residues, toluene from phenylalanine, pyridine and acetonitrile. The a&amide peak is characteristic of N-acetylaminosugars present in bacterial or fungal cell walls. Humic acids also show a marked aliphatic character indicated by the SerleS of n-alkanes ranging from CT9 to C23 which are certainly volatilization products rather than pyrolysis fragments. The phenolic peaks are derived from tyrosine residues rather than polyhydroxyaromatics as confirmed by the predominance of phenol and p-cresol and the absence of other cresol isomers (BRUCHET, 1985). This natural laboratory isolated from terrestrial influence generates abundant and specific humic compounds very rich in carbohydrates, related to the growth of blue algae, active in these drastic wnditions. The phenolic content of such equatic humic substances seems exclusively due to tyrosin residues. Algae may thus represent an alternatlve source of phenolic compounds. ACKNOWLEDBEHENTS The authors thank Dr. M. Meurette (Laboretoire R. Bernas, Orsay, France) for the sampling of these valuable deposits. REFERENCES 1 P.G. Hatcher, R. Rowan and M.A. Mattingly, ‘H and ’ 3C NMR of marine humic acids. Org. Gecchem., 2 (1980),77-85. 2 F. Shafizadeh and Y.L. Fu, Pyrolysis of cellulose. Carbohydrate Research, 29, Elsevier, Amsterdam, 1973,pp. 113-123. 3 K. Miyazaki, Effect of the thermal treatment on wood-hemicellulase. A new compound, 4-hydroxy-5,6dihydro-2 H-pyran-2-one, from xylan on heating, Mokuzai Gakkaiski, 2 t(5) ( 1975) 305-308. 4 J.M. Bracewell, G.W. Robertson and D.I. Welch, Polycarboxyllc acids as the origin of some pyrolysis products characteristic of soil organic matter. J. of Analytical and Applied Pyrolysis, 2 ( 1980) 239-248. 5 A. Bruchet, Applications da la technique da pyrolyse-CG-SM a I’btude des matieres organiques non voletiles des eaux naturelles ou en wurs de traitement, These 3lrme cycle, Universite de Poitiers, 64 p.
107
HUMIC SUBSTANCES FROM DEPOSITS OF A NATURAL LABORATORY : A BLUE LAKE ON THE ICE-CAP (QREENLAND). F. GADEL’ , 0. TORR12and A. BRUCHET3 1 Laboratoire de Sdimentologie et Geochimie Marines - Universite de Perpignan - France 2 Laboratoire de Chimie Marine - Universite de Toulon et du Var - France 3 Laboratoire Central - Lyonnaise des Eaux - Le Pecq - France SUHMARY The structural analysis of humic compounds from depostts of a blue lake in Greenland, a parttcular environment on the ice-cap isolated from any terrestrial influence, shows their relatively specific nature, resulting from growing blue algae. Fulvic acids are essentially of polysaccharidic nature ; humic acids, more hetercqenous in composition, show, with polysaozharides and peptidic fragments, an aromatic character certainly due to amino-acid residues. INTRODUCTION The blue lakes are situated just above the arctic circle in Greenland on the ice-cap more than I km thick (30 km from the side of the Sondrestromfjord glacier on the western coast). These lakes, about ten meters deep, are practically isolated from terrestrial influences and the bottom deposits result principally from meteoric dusts. The sediments are scattered on the rough bottom of lakes into a multitude of shallow holes which shelter them against currents. They are composedof a black mud with small bell particles from cosmic origin and rare terrestrial white quartz. The organic matter originates exclusively from a blue elgw growth (Cyanophyceae). The entanglement of algal fibers constitutes cocoonswhich trap the cosmic dust. The organic matter content is high (6.6 X org. C.). Whe have studied the distribution and nature of humic substances in this particular environment. RESULTS AND DISCUSSION Due to its algal nature, the organic matter Is very hydrolysable (73 % - 6N HCl I 10%) and the sediment relatively high in nitrogen wntent (0.6 X N). The humic compounds (extractable whith 0.1 N NeOH+ 1 X Ne4P207) ere abundant (50 X) and the fulvic acid/humic acid ratio is close to 2. The e/&i?&Y8/&@& of fulvic and humic acids show that the H/C atomic ratios are very high, giving evidence of a high aliphatic character (FA : 2.02 and HA : 1.62). The N/C ratio is relatively high In HA (0. I 15), but very low in FA (0.014). Therefore the nitrogenous wmpounds ere principally concentrated in humic acids. The O/C ratio which is intermediate in I-LA(O.SOO), is particularly high in FA (0.97 1), due to the abundance of oxygenated groups. The fn/rccdgfastfa (Fig. I ) account for a high aliphatic character of FA, with a marked absorption band corresponding to carbohydrates ( 1050 cm- ’ ) end e higher content of nitrogenous and aromatic compounds in HA. The ‘Ifffff~sjwcira (Fig. 2) show the essentially polysaccharidic nature of FA (93 X) and the 0048-9697/8’7/.$03.50
0 1987
Elsevier
Science
Publishers
B.V.
humic
acids
\
v fulvic
4cl--00
3400
wawwnber
'ig.I-F.T.infrared humic
humic
2000
acids
ki-
spectra
Fig.2-(ItI of
)nuclear magnetic humic compounds.
resonance
00 %A I
spectra
fulvic acids : : ? E :
of
compounds.
SCAN
acids
hmic acids
fulvic
acids I
Fig.3-(13C) nuclear resonance CP/mass humic compounds.
magnetic spectra of
Fig.4-A
et humic
B Pyrolysis compounds.
-mass
spectra
of
109 extremely high aliphaticity. The aliphatic nature of HA (87 W) is characterized by a large proportion of saturated CH groups with a predominance of CH3 on CH2-CH groups, indicative of high branching of aliphatic chains (HATCHERet al., 1980). The polysaccherides are also abundant (38 X). The 13CN~fRs~&~ (Fig. 3) depict that in fulvic acids appear mainly the peeks corresponding to carbons of carbohydrates or aliphatic alcohols and the anomeric carbons of polysfccharides. In humic acids the CH3 and CH2 groups are abundant. The peptide peak appears clearly as the anomeric carbons of polysaccherides and the aromatic carbons The PY-&‘-MS spectm (Fig. 4 A-B) give more precise information on the structure of humic compounds. Fulvic acids are clearly dominated by fragments of carbohydrate origin. The anhydrosugars detected are known to be formed during the initial steps of pyrolysis of cellulose and other polyhexoses (SHAFIZADEH and FU, 1973). Their further degradation leads to the furans and various carbonyl compounds. Some products can result from non-reducing xylopyranasyl residues or carbohydrates (MIYAZAKI, 1975). The cyclic ketone (cyclopent-2-en- l-one) constitutes a fragment of polycarboxylic acids (BRACEWELL et al., 19801, resulting from pyrolysis of mono- and polysaccharidas. The low phenolic peek could be the result of uncontrolled secondary reactions which often occur in Severe elcaline or dehydrating matrix conditions. Humic acids show a much more heterogeneous character. Fragments from peptidic origin are present as pyrrole and methylpyrrole, indole from tryptophan residues, toluene from phenylalanine, pyridine and acetonitrile. The a&amide peak is characteristic of N-acetylaminosugars present in bacterial or fungal cell walls. Humic acids also show a marked aliphatic character indicated by the SerleS of n-alkanes ranging from CT9 to C23 which are certainly volatilization products rather than pyrolysis fragments. The phenolic peaks are derived from tyrosine residues rather than polyhydroxyaromatics as confirmed by the predominance of phenol and p-cresol and the absence of other cresol isomers (BRUCHET, 1985). This natural laboratory isolated from terrestrial influence generates abundant and specific humic compounds very rich in carbohydrates, related to the growth of blue algae, active in these drastic wnditions. The phenolic content of such equatic humic substances seems exclusively due to tyrosin residues. Algae may thus represent an alternatlve source of phenolic compounds. ACKNOWLEDBEHENTS The authors thank Dr. M. Meurette (Laboretoire R. Bernas, Orsay, France) for the sampling of these valuable deposits. REFERENCES 1 P.G. Hatcher, R. Rowan and M.A. Mattingly, ‘H and ’ 3C NMR of marine humic acids. Org. Gecchem., 2 (1980),77-85. 2 F. Shafizadeh and Y.L. Fu, Pyrolysis of cellulose. Carbohydrate Research, 29, Elsevier, Amsterdam, 1973,pp. 113-123. 3 K. Miyazaki, Effect of the thermal treatment on wood-hemicellulase. A new compound, 4-hydroxy-5,6dihydro-2 H-pyran-2-one, from xylan on heating, Mokuzai Gakkaiski, 2 t(5) ( 1975) 305-308. 4 J.M. Bracewell, G.W. Robertson and D.I. Welch, Polycarboxyllc acids as the origin of some pyrolysis products characteristic of soil organic matter. J. of Analytical and Applied Pyrolysis, 2 ( 1980) 239-248. 5 A. Bruchet, Applications da la technique da pyrolyse-CG-SM a I’btude des matieres organiques non voletiles des eaux naturelles ou en wurs de traitement, These 3lrme cycle, Universite de Poitiers, 64 p.