MICROELEMENTS IN RIVER WATER OF MOUNTAIN-FOREST BASINS (SOUTHERN RUSSIAN FAR EAST)

Abstract

Relevance: study of the migration of chemical elements from mountain-forest ecosystems into rivers in the runoff formation zone. Purpose: assessment of microelements content and the ranges of their variability in the water of background streams at mountainous headwaters, and detecting the probable pathways and mechanisms of their geochemical migration. Objects: Pravaya Sokolovka R. (the Ussuri R. system) and its four tributaries. Methods. The concentrations of trace elements and rare earth elements were determined by ICP-MS Agilent 7700 x (Agilent Techn., USA). The content of the main anions (Cl–, SO42–, NO3–) was determined on a Shimadzu LC 10Avp liquid chromatograph, the main cations (Ca2+, Mg2+, K+, Na+) – on a Shimadzu AA 6800 atomic absorption spectrometer; dissolved organic carbon (DOC) – using a TOC analyzer (Shimadzu TOC-VCPN). When processing quantitative data, the standard statistical methods of analysis were used. Results. During the warm period in 2012, 2019 and 2020, there were carried out the integrated hydrochemical studies at five research catchments located in the middle mountain belt of the Southern Sikhote-Alin. In river water samples, the main chemical components and the microelements dissolved forms (<0,45 µm) were determined. The analysis of about 80 samples made it possible to assess the spatial-temporal variability of the measured concentrations of trace elements and to establish the probable factors driving their migration in small river catchments differing in landscape patterns. A comparative analysis of found trace elements concentrations showed their similar relevant values for conventionally clean rivers of the Sikhote-Alin mountain country and over the world. To reveal possible mechanisms of microelements migration into rivers, the authors accomplished a conjugate correlation analysis for the dataset of macrocomponent and microelement composition of the river water. We assumed that during rainfall events, the leaching of dissolved organic carbon and related elements from soil cover is the main mechanism for concentrating low-mobile (Al, Sc, Ti, Cr, Ga, Y, Zr, Hf, and Rare Earth Elements), some heavy (Fe, Mn, and Co), and anion-generating (Cr, Se, V, and Ge) trace elements. This suggests the migration of organic carbon and related elements from the catchment during heavy rains and the simultaneous presence of a certain proportion of elements in the composition of complexes with organic matter. A preliminary analysis of the peculiarities of the moistening regime and the landscape structure of watersheds revealed trends in the interannual variability of dissolved forms of Fe and Al in the rivers draining watersheds with the different structural organization of forest ecosystems. It is shown that the distribution of mountain taiga soils in river basins determines the lowest seasonal and interannual variability of dissolved forms of typomorphic elements, as well as their more stable relationship with organic carbon. In the case of dominance of coniferous-deciduous ecosystems in a catchment, the content of Fe and Al soluble forms depends on river water acidity, which varies associated with the processes of organic substances accumulation and leaching from the soil.

Keywords

• microelements
• rare earth elements
• macro-composition
• organic-mineral complex
• stream
• sikhote-alin