Reconsidering Dissolved Organic Carbon as a Passive Reservoir: Active Biogeochemical Cycling and Priming Effects in Anthropogenically Perturbed Riverine Systems

Abstract

Dissolved organic carbon (DOC) has long been conceptualized as a quasi-stable reservoir within riverine biogeochemical frameworks, yet mounting empirical evidence challenges this paradigm. This study integrates high-frequency optical proxy sensing, isotopic mass-balance modeling (δ¹³C, Δ¹⁴C), and metagenomic profiling across fourteen anthropogenically impacted catchments in Central Europe and Southeast Asia to interrogate the dynamic reactivity of riverine DOC pools. Our results demonstrate that allochthonous DOC fractions exhibit priming-induced mineralization rates up to 3.7-fold greater than previously documented under elevated nutrient loading conditions. Furthermore, microbial community composition—particularly the proliferation of Bacteroidota and Proteobacteria lineages—exerts a dominant regulatory control over DOC turnover kinetics. These findings necessitate a fundamental revision of DOC residence-time parameterizations in coupled hydrological-biogeochemical models, with profound implications for regional carbon budget assessments and river water quality governance frameworks.