Rethinking High Carbon Emissions Associated With Thick Accumulated Sediments in Reservoirs

Abstract Reservoirs with thicker sediments generally exhibit elevated carbon emissions; however, this relationship may not necessarily persist when emissions are assessed per unit thickness. A comprehensive understanding of this relationship is essential for accurately evaluating carbon emissions across various sedimentation patterns. This study proposes the concept of carbon emission intensity (CEI), defined as carbon emissions per unit mass or volume of sediment, evaluates its correlation with sediment thickness (ST) using 58 global data sets and clarifies the impact of ST on CEI through controlled incubation experiments. The results revealed a strong negative logarithmic correlation between CEI and ST ( R 2 = 0.88), indicating that increasing ST substantially reduces CEI values. The observed trend can be attributed to the potential of thicker sediment layers to restrict oxygen penetration, promoting organic carbon (OC) burial. The incubation experiments reinforced this mechanism, revealing that although thicker sediments generated higher absolute carbon emissions, their CEI values were consistently lower. Oxygen penetration and active OC decomposition were found to be limited to the top few centimeters of sediment, independent of the total ST. The findings indicate that dam construction in narrow river sections could be strategically favorable, as these areas are more likely to accumulate thicker sediments characterized by lower CEI, reducing overall carbon emissions.