Hydrological continuums across climate and permafrost gradients: Spatial patterns of organic carbon, greenhouse gases, and major and trace elements

Organic and inorganic solute fluxes from soils to rivers follow a hydrological continuum linking terrestrial and aquatic compartments, yet this cascade remains poorly constrained in permafrost regions despite its importance for carbon and greenhouse gas (GHG) cycling. We investigated six hydrological continuums-soil water, fen, lake, riparian zone, stream, and river-across a 1500 km north-south transect of the Western Siberian Lowland, spanning the full gradient from permafrost-free taiga to continuous permafrost tundra. During summer baseflow, surface and soil waters were analyzed for dissolved organic carbon (DOC), CO₂, CH₄, and 40 major and trace elements. DOC, CO₂, and CH₄ concentrations systematically decreased from soils and fens toward lakes and rivers, highlighting headwaters as dominant sources of carbon and GHGs. Aluminum covaried with DOC, consistent with organic complexation and downstream pH increases, whereas Fe and Mn reflected local redox variability. In contrast, Ca, Mg, Sr, and soluble anions increased downstream in southern, permafrost-free systems, indicating active groundwater inputs, while no such trend was observed in tundra sites under continuous permafrost, pointing to strong hydrological isolation. DOC declined with increasing drainage area, whereas CO₂ and CH₄ showed no consistent dependence on watershed size. Nutrients (Si, P) increased downstream mainly within discontinuous permafrost zones, suggesting enhanced subsurface contributions. Principal component analysis revealed two dominant patterns of covariation: one linking DOC, Fe, Al, and low-mobility lithogenic trace elements, consistent with colloidal transport of organic and organo-ferric complexes, and a second associated with electrical conductivity and labile ions, reflecting variable groundwater influence and subsurface-surface connectivity. GHG concentrations were largely independent of these patterns and instead related to local redox conditions and subsoil CO₂-CH₄ inputs. Overall, this study provides the first integrated, pan-regional assessment of coupled organic carbon, greenhouse gases, and major-trace element dynamics along complete hydrological continuums spanning the full permafrost gradient of the Western Siberian Lowland. By combining multi-compartment sampling with a space-for-time framework, we identify two fundamental controls-colloidal transport limitation and groundwater-driven source limitation-that unify solute behavior across climate zones. The results demonstrate how permafrost extent governs hydrological connectivity, biogeochemical processing, and GHG regimes, offering a mechanistic basis for predicting Arctic river responses to thaw, warming, and changing water-groundwater exchange.