Influencing pathways of meteorological factors on particulate organic carbon concentrations in Lake Hongze and its inflowing rivers

Abstract

Lakes play an important role in the regional and global carbon cycle, acting as both sources of carbon emissions and carbon sinks. The sedimentation of particulate organic carbon (POC) represents an important pathway for carbon sink in lakes, and variations in POC concentration are strongly regulated by environmental factors. In this study, we investigated the spatiotemporal variations of POC concentrations in Lake Hongze and its 13 inflowing rivers. Based on the relationships among meteorological factors, nutrients, chlorophyll a, and POC, a structural equation model was established to quantify the effect sizes of different influencing pathways. The results showed that POC concentrations exhibited distinct seasonal fluctuations, with significantly higher values in summer and autumn. POC concentrations in Lake Hongze were higher than those in Inner Mongolia–Xinjiang lakes and Tibetan Plateau lakes, and represented a medium-to-high level among Eastern Plain lakes. In inflowing rivers, precipitation affected POC not only by directly transporting allochthonous POC, but also by indirectly promoting autochthonous POC production through nutrient inputs; and temperature mainly increased POC by enhancing endogenous POC synthesis. Within Lake Hongze, precipitation delivered allochthonous organic matter and river-derived chlorophyll a, but had no significant effect on nutrient levels. In contrast, temperature increased lake POC mainly by accelerating nutrient release from sediments. These findings reveal distinct response mechanisms of POC to meteorological factors between inflowing rivers and the lake interior, providing a scientific basis for lake carbon sink management under climate change.