Abstract
<jats:p>Northern permafrost landscapes store large amounts of organic carbon that can enter lakes as dissolved organic matter (DOM), but links among shoreline terrestrial sources, lake-water DOM composition, and catchment configuration remain uncertain in low-precipitation Shield landscapes. We combined shoreline soil-porewater and lake-water sampling across a 5°C climate gradient spanning discontinuous and continuous permafrost in the Northwest Territories, Canada, with dissolved organic carbon concentration measurements, ultra-high-resolution mass spectrometry (FT-ICR-MS), stable carbon isotope composition (δ¹³C-DOM), radiocarbon (Δ¹⁴C-DOM), and whole-catchment geospatial analyses. Soil porewater had higher dissolved organic matter carbon (DOM-C) concentrations and more aromatic molecular composition than lake water, supporting its use as a nearshore terrestrial endmember. Lake-water DOM had lower aromaticity, higher H/C, greater relative intensity of aliphatic formulae, and higher Δ¹⁴C-DOM than soil porewater, consistent with reduced expression of the terrestrial molecular signature in lakes. Across lakes, soil-to-lake DOM-C differences, aromaticity, H/C, compound-class patterns, and Δ¹⁴C-DOM were associated with aquatic-to-terrestrial ratio, calculated as total lake and surface-water area divided by terrestrial watershed area. Water residence time was not correlated with aquatic-to-terrestrial ratio and explained less variation in soil-to-lake DOM-C differences and aromaticity. Permafrost extent was also reflected in molecular composition, with lower O/C and nominal oxidation state of carbon in continuous-permafrost sites after accounting for aquatic-to-terrestrial ratio. Together, these results show that shoreline terrestrial DOM, catchment configuration, and regional permafrost-gradient characteristics jointly structure lake-water DOM composition. The aquatic-to-terrestrial ratio provides a first-order metric for identifying lakes where DOM composition is likely to reflect stronger terrestrial influence versus greater aquatic-network influence.</jats:p>