Humic substances in the sediments of lake Edku, Egypt : I-occurrence and distribution

Abstract AR

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Humic substance (HS) as humic and fulvic acids were determined in the surface sediments of Lake Edku (Egypt).

Their sources, distribution and behavior were assessed.

The lake is geographically subdivided into eastern, central and western sub-basins; subdivision is based on the presence of natural barriers and proximity to the drains or to the sea-lake connection.

The central basin showed the highest concentrations of HS, which is attributed to intensive development of macrophytes and to enhanced phytoplankton primary production.

In the eastern basin, high turbidity and water turbulence downstream from the drains limit primary production.

In the western basin, however, water turbulence, sandy bottom, elevated salinity and decrease in nutrients due to mixing with seawater limit the growth of macrophytes as well as the phytoplankton productivity.

Introduction Humic substances (HS) are the largest reservoir of organic carbon in the aquatic and terrestrial environments (Gjessing 1976; Mantoura et al., 1978).

The bulk of the organic matter in most soils, waters and sediments consists of humic substances (Schnitzer and Khan 1972), which may constitute as high as 70% of the organic matter in the lake sediments (Kemp 1971).

This fairly stable and extremely complex copolymers have received a great deal of interest due to their active participation in the biogeochemical processes in the aquatic environment (Duursma 1963; Nissen-baum & Kaplan 1972; Prakash et al., 1973; Stumm & Brauner 1975; Frimmel & Christman 1988).

The origin of the HS is of great importance since it will determine their chemical composition and structural characteristics and both will define their fate and reactiv-