Characterization of lake sediment humic acids from the Ćelije Lake system near Kruševac (Central Serbia) by13C and 1H solution NMR and 13C cpmas NMR

Abstract

Humic acids were extracted from the bottom sediment of the three lakes (Zlatari, Vasici and Vodozahvat) that together comprise Lake Celije a regional drinking water reservoir. The humic acids were examined by high resolution 13C and 1H solution NMR and 13C CPMAS. The aromaticity expressed as the number of benzene rings per 1000 g of humic acid is 1.8 for Zlatari, 2.3 for Vasici and 1.9 for Vodozahvat. Oxygen-substituted aromatic carbon structures in humic acids from the first two lakes (Zlatari and Vasici) are similar and resemble p-coumaryl units in lignin while those in Lake Vodozahvat more closely resemble coniferyl or sinapyl units in lignin. The aromatic rings of all three humic acids are highly substituted. Humic acids from the first two lakes have very similar carbohydrate carbon contents (19.9 and 19.5% respectively) compared to 23.3% for Vodozahvat humic acid. Zlatari and Vodozahvat humic acids have a higher alkyl chain content which indicates a greater potential for forming hydrophobic cavities. The carboxyl and aromatic OH group content of each humic acid influences their capacity for forming complexes with metal ions.