Abstract
Elemental analysis, UV-VIS-IR light-absorption, and differential thermal analysis were carried out for characterization of humic acids (HAs). HAs were taken from bottom sediments of Lobelia Lake in Western Pomerania in Poland. Bottom sediments were sampled during summer stagnation from depths corresponding to three thermal zones of the lake: A - epilimnion (4.4 m), t A = 19.5°C; B - metalimnion (8.0 m), t B = 14.8°C; and, C - hypolimnion (49 m), t C = 6.0°C. Sediments were also taken from 0 - 35 cm depth. In each zone, three distinctly separate layers differing in colour were observed. HAs were extracted with 0.1 M NaOH from each layer of sediment. The elemental composition of sediments was similar to fulvic acids (FAs) from soil, but N concentration in the HAs was twofold higher. IR spectra showed that HAs from the epilimnion zone differed markedly in chemical structure from HAs of other zones. Comparison of the thermic destruction effect of HAs showed that their energetic values increased with depth from the epilimnion to the hypolimnion zone.
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