Multi‐Dimensional Tracing of Particulate Organic Matter Sources in a Deep‐Water Reservoir: Coupling Temporal Dynamics, Water Depth Stratification, and Particle‐Size Effects
Mingming Gao, Shuguang Lv, Yuying Li, Minli Guo, Danyang Miao, Yufan He, Rongxin Wang, Yun Zhang, Shiming Ding, B. Larry Li, Nicola FohrerABSTRACT
Particulate organic matter (POM) constitutes an important component of aquatic organic matter, with significant spatiotemporal variations in its sources and composition. However, a comprehensive understanding of the POM sources with different particle sizes in deep‐water reservoirs under spatiotemporal changes remains limited. This study investigated the sources of various POM size classes in the Danjiangkou Reservoir across seasonal and vertical gradients using stable isotope of carbon (δ 13 C) analysis and the Iso‐Source mixing model. The δ 13 C values of Pico‐ and Nano‐POM were depleted in 13 C (mean: −30.6‰; range: −35.0‰ to −21.3‰), exhibiting the typical isotopic signature of phytoplankton and terrestrial C 3 plants. Combined with the Iso‐Source model, these values indicate that they were primarily derived from phytoplankton and C 3 plants, accounting for 58.04% of the total contribution, of which phytoplankton made a larger contribution (66.49%). Micro‐ and Net‐POM showed δ 13 C values enriched in 13 C (mean: −26.5‰; range: −35.9‰ to −15.1‰), with higher contributions from phytoplankton and C 4 plants (56.14%). The coefficient of variation (CV) for phytoplankton was significantly lower in spring and summer than in autumn and winter across all POM size classes. The lowest CV was observed for Pico‐ and Nano‐POM, indicating that the source of smaller‐sized POM was more stable. Across different layers, the δ 13 C values of Pico‐ and Nano‐POM showed significant correlations with total organic carbon (TOC) ( p < 0.01), reflecting autochthonous production control; Micro‐ and Net‐POM were significantly correlated with nitrogen species (NO 3 − ‐N, NH 4 + ‐N, and TN) ( p < 0.05), highlighting the influence of allochthonous inputs. This study reveals the source apportionment characteristics and environmental response mechanisms of different POM size classes in a subtropical deep‐water reservoir at spatio‐temporal scales, thereby providing a scientific basis for understanding the carbon cycling processes in aquatic ecosystems.