CARBON BEHAVIOR AND FORMATION OF WATER CHEMICAL COMPOSITION IN THE DRAINAGE SYSTEM OF THE DRAINED EUTROPHIC PEATLAND

Peatlands are recognized as one of the most critical ecosystems for long-term carbon sequestration, although they cover approximately 3 % of the Earth's surface. However, drainage and peat extraction significantly disrupt the carbon balance of peatlands. Specifically, the drainage network, an integral component of drained peatlands, contributes substantially to greenhouse gas emissions and lateral carbon transport. In eutrophic peatlands, the drainage system also serves as a source of nutrients for receiving water bodies. To predict changes in the carbon balance, develop effective reclamation measures, and implement climate-related projects, it is essential to understand the processes governing the chemical composition of drainage waters. In this study, we examined the chemical composition of drainage water in the eutrophic Tarmanskoe peatland (Western Siberia) using historical and contemporary data. Seasonal dynamics of dissolved carbon and fluxes of carbon dioxide (CO) and methane (CH) to the atmosphere were analyzed for 2024. The findings revealed an increasing role of evaporation in the formation of water composition since the commissioning of the drainage system. This trend is evidenced by the rising proportions of chloride and sodium ions, along with shifts in water-rock equilibrium from kaolinite towards montmorillonite and carbonates. The equilibria in the carbonate system and the ratios of major ions indicate that carbon redistribution occurs through the dissolution and precipitation of carbonates during the drainage system's operation. Seasonal dynamics of dissolved carbon and greenhouse gas fluxes revealed distinct patterns. In summer, CO and CH fluxes from waterlogged drainage ditches increased, while CO emissions from ponds decreased due to the activity of photosynthetic organisms. Notably, a dry drainage ditch exhibited unique dynamics: summer CO fluxes from its oversaturated sediments decreased more than fivefold, and CH fluxes remained near zero, comparable to spring levels. Meanwhile, both CH and CO accumulated in pore waters in dissolved forms. The results underscore the importance of studying carbon biogeochemistry in waterlogged soils and sediments and the factors driving CO and CH accumulation in pore waters. These findings provide critical insights for developing novel approaches to reclamation and climate projects for drained peatlands.