Geochemical features of humic acids extracted from sediments of urban lakes of the Arctic

The study focuses on the comprehensive research of geochemical and environmental roles of humic acids isolated from sediments of the urbanized lakes of Kola Peninsula, the Arctic. The sediments were collected from 5 water bodies located in the different parts of Murmansk city. The elemental analysis (C, H, N, and O percentage) of the samples was conducted. The molecular structure of the acids was investigated using solid-state CP/MAS 13C-NMR and FTIR spectroscopy methods. The findings revealed the specific geochemical and environmental features of the sediment humic acids in the urbanized aquatic ecosystems of the Arctic region. The process of humification in the studied lakes is slowed down due to cold climatic conditions and the high level of the pollution of the water bodies. The molecules of the humic acids are immature and high-oxygen. Therefore, on the one hand, they can actively leach the toxic metals from the components of the sediments. On the other hand, despite the relatively low content of chelate-forming groups in the structure of the humic acids, the stable organometallic compounds form due to high percentage of dispersed organic matter in the sediments and structural flexibility of the molecules of the acids. Furthermore, the geochemical composition of the sediments and their enrichment by the trace elements and hydrocarbons significantly influence on the character of the interaction between metals and humic acids.