Acid functional group content of aquatic humic matter: Its dependence upon origin, molecular weight and degree of humification of the material

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Abstract
The acididic functional group content was investigated of molecular weight fractions of fulvic and humic acids sampled at various locations of a watershed within the Laurentide provincial park, Quebec. In order to study the effect of humification, also humic material produced by a streptomycete culture and sampled at regular intervals during a 6 months’ incubation period was investigated. The equivalent weights and the number of COOH and phenolic OH functional groups measured on the fulvic and humic acid molecular weight fractions were compared with data reported for humic material from other aquatic and terrestrial environments. Also investigated were seasonal and environmental effects on the equivalent weights and the COOH and phenolic functional group values as well as the influence of humification on these parameters. It was shown that although aquatic humic compounds have several properties in which they are quite distinct from soil humus, in their acidic functional groups aquatic humic compounds differ very little from humus terrestrial origin. The only dissimilarity observed was that aquatic humic acids normally contain more COOH and fewer phenolic OH groups than their terrestrial counterparts. The results obtained from chemical analysis were well in agreement with evidence obtained from infrared absorption spectra. Furthermore with increasing molecular weight the number of acidic functional groups was observed to decrease whereas with progressive humification the number of COOH groups augmented for fulvic acids and diminished in the case of humic acids. Hence, the former were normally richer in acidic functional groups than the latter.