DISSOLVED FORMS OF MIGRATION OF HUMIC SUBSTANCES IN SURFACE WATER BODIES OF THE YAMAL-NENETS AUTONOMOUS DISTRICT

Abstract

The relevance. The river and lake waters of the Arctic regions of Western Siberia are enriched with dissolved organic matter, primarily humic acids, which are characterized by a good ability to form stable organomineral complexes. When studying the formation of the chemical composition of such waters, it is necessary to take into account the complex compounds that shift the equilibrium in geochemical processes (in dissolution, leaching, sedimentation and co-precipitation, etc.) towards the aqueous phase, thereby directly affecting the composition of waters. In the case of humic acids, a sufficient data on thermodynamic constants have been accumulated which made it possible to conduct numerical modeling. The main aim is to consider the features of the distribution of humic substances (fulvic and humic acids) in the surface waters of the region and to calculate the migration forms based on the available new data on the chemical composition. Other issues are to study in what quantity and what elements are bound by humic substances; and whether there are differences between the waters belonging to different river basins. We also determine the role of organic matter, mainly humic substances, in the formation of the chemical composition of waters. Objects: surface water bodies of the tundra and forest-tundra natural zones of the Yamalo-Nenets Autonomous District. The authors tried to cover the main stages of the surface water evolution in the direction of depression – large lakes – rivers, as well as consider the water bodies of different drainage basins of four main rivers – Taz, Pur, Ob, Nadym. As a result, 23 watercourses (large and small rivers) and 24 reservoirs (20 lakes of different sizes and 4 depressions) were studied. Methods. Chemical composition of water was determined by standard methods at the Basic Research Laboratory of Hydrogeochemistry of the Tomsk Polytechnic University, the analysis of fulvic acids and humic acids was carried out by titration to account for bichromate consumed for the oxidation of carbon of fulvohumic acids. The migration forms of humic substances and chemical elements were calculated using the HydroGeo software. Results. The features of distribution of humic substances in the direction of depression–lake–river in the main drainage basins of rivers in the north of Western Siberia were studied. The dissolved migration forms of humic acids relative to their concentrations were determined by thermodynamic calculations, and the forms of migrations of the main ions and trace elements were determined taking into account the content of humic acids, i. e. it is shown which part of them binds into organomineral complexes. It was determined that compounds with fulvohumic acids are the most common in all the described waters, but their maximum proportion is typical for depressions. Some of the trace elements are more prone to form organomineral forms than others: Cu, Ni, Mn, Li, Zn, Fe. Fulvic acids are more susceptible to complex formation. The patterns obtained must be taken into account when considering the conditions for the formation of these waters.

Keywords

• dissolved migration forms
• thermodynamic modeling
• humic substances
• organomineral complexes
• surface waters
• arctic
• yamalo-nenets autonomous district