Sedimentary humic substances from lakes in Latvia

Humic and fulvic acids, isolated from sediments of lakes in different trophic states (Latvia) were studied. The humic substances (HS) were characterized by their elemental and functional composition, their spectral properties, and molecular mass. The humus properties strongly depend on the origin of the sedimentary HS. Substantial similarity between sedimentary HS from oligotrophic and dystrophic water bodies was found, unless the biology of these lakes greatly differs. Humic molecules from sediments of oligotrophic and dystrophic lakes are smaller, more uniform, and contain lower amounts of carboxyl-and hydroxyl-groups than HS from meso- and eutrophic water bodies. On the other hand, sedimentary HS from meso- and eutrophic lakes are dominated by aliphatic structures, and, possibly chromophore groups are present, and they are rich in polar groups. The macromolecules of HS from meso- and eutrophic lakes show the highest polydispersity. (C) 1997 Elsevier Science Ltd.