Optical characteristics of humic acids from bottom sediments of lakes with different mictic types

Optical properties of humic substances (HS) from bottom sediments of two dimictic and meromictic lakes with similar depth (25 m and 29 m) and different thermal circulation and oxygen condition of their water were carried out. Dimictic Marta Lake (ML) and meromictic Czarne Lake (CL) are situated not wide apart, in Drawno National Park, North Poland. Optical analysis: differences UV-VIS - absorption spectra and fluorescence emission spectra were analysed for characterisation of humic acids (HA). HA were taken from bottom sediments of three thermal zones of lakes. All HA from profundal bottom sediments have a bigger UV absorption than HA from littoral. They testify lower degree of oxidative transformation of HA from profundal zone. It was assumed that fluorescence yield of HA from profundal of CL is a few times bigger, than this from profundal of ML. In all humic acids (HA) from profundal zone chromofor (l = 405 nm) and fluorofor (l = 480 nm) originated probably from reduced cytochrom c structure is present. Humic acids molecules are characterised by some exciting and emission centers, which testify their possibility of intermolecular transfer of energy. Coefficients (Kf=IFL/A) proportional to FL yield were calculated. Observed difference of fluorescence yield level indicates the presence of a few time more fluorescent centers in HA from profundal of meromictic than dimictic lake.