SEDIMENTARY HUMIC SUBSTANCES ISOLATED FROM A COASTAL LAGOON OF THE NILE DELTA - PHYSICAL AND CHEMICAL CHARACTERISTICS

Humic substances extracted from the sediments of Lake Edku (Egypt) wer e fractionated to their humic and fulvic acid constituents; their phys ical characteristics [ratio of optical density at 465 and 665 nm (E4/E 6), infra-red spectra (IR)] and chemical composition (elemental compos ition, functional groups) were measured. Fulvic acids were characteriz ed by their lower E4/E6, lower carbon content and higher oxygen conten t. C/H and C/O ratios were lower in fulvic acids, but the C/N ratio wa s comparable in both components. Fulvic acids were also more acidic in nature, due to a higher carboxyl group content which constituted the major part of the total acidity. Carboxyl group concentrations average d 10.6 mu eq mg(-1) C and 6.1 mu eq mg(-1) C in fulvic and humic acids , respectively. Infra-red spectra revealed a similar structural config uration. The geographical distribution of the physical and chemical ch aracteristics did not reveal distinct and systematic features that cou ld be related to the origin of the material. This was mainly attribute d to the predominance of the internally produced humic substances over the land-derived material, and the relative distribution of humic and fulvic acids in both of them. Observed geographical variations appear ed to be the product of varying conditions in the local depositional e nvironment. (C) 1996 Academic Press Limited