農業からの拡散汚染による堆積物炭素隔離の制約：コア由来DOMからの証拠

Sediment dissolved organic matter (DOM) in river-lake transitional zones mediates nutrient, carbon, and contaminant cycling, yet the roles of anthropogenic and natural inputs in shaping vertical sediment composition and inferred carbon stabilization remain poorly understood. Here, we conducted a vertical profiling analysis of river-lake ecotone sediments in Poyang Lake by integrating physicochemical, spectroscopic, isotopic and modelling approaches within a dual-level end-member mixing analysis (EMMA) framework. The sediments were primarily composed of sand (44.7%) and silt (35.8%) and exhibited weak acidity, with phosphorus pollution (S_TP 0.57-2.97) exceeding nitrogen (S_TN 0.07-1.45), particularly in the inflowing rivers. Stable isotope-based EMMA applied to bulk sediment organic matter (SOM) revealed mixed source contributions dominated by fertilizer inputs, based on δ¹³C (-25.58‰ to -20.53‰) and δ¹⁵N (3.99‰ to 5.98‰) signatures. Subsequently, fluorescence-based EMMA identified livestock and poultry (57%), riparian vegetation (23%), and farmland leaching (9%) as the main contributors to sediment water-extractable organic matter (WEOM). LightGBM-SHAP analysis showed α₂₅₄ was strongly associated with optically inferred stability of WEOM, with distinct controls between surface and deep sediments. Overall, the dual-level EMMA analysis indicated that agricultural diffuse pollution enhanced the WEOM lability and constrained the sediment carbon sequestration potential in river-lake transitional zones. Interpretations derived from fluorescence-based EMMA for sediments may be affected by DOM transformation during sediment burial and by uncertainties associated with end-member representativeness. These findings underscore the necessity of integrated nutrient management and land-use practices to sustain carbon storage in large floodplain lake systems.