The Changjiang Estuary represents an important link transporting the fluvial particulate organic matter (POM) to the marginal East China Sea. Intensified by global climate change, the severity of droughts is expected to increase. Yet, the effects of drought on the optical properties and composition of POM have not been fully understood. Herein we investigated the impact of extreme drought on the particulate organic matter based on the spectroscopic measurements of the base-extracted particulate organic matter (BEPOM) in 2021 ( hydrologically normal year) and 2023 (drought year) in the Changjiang River estuarine-coastal ocean continuum using absorption and fluorescence spectroscopy measurements. Parallel factor analysis (PARAFAC) recovered three components from the pooled dataset, including two terrestrial humic-like components (C1, C2) and one protein-like fluorescent component (C3). Results showed that, compared to the relative abundance of the three components in the hydrologically normal year, the fluorescence composition of BEPOM showed significant spatiotemporal heterogeneity in the surface water under drought conditions, with the most significant differences occurring in the summer season and specifically, in the inner estuary to the turbidity maximum zone (TMZ) . These findings highlight the role of droughts in altering the biogeochemical cycling of estuarine POM, which could have cascading effects on marine food webs and the health of coastal ecosystems.
 

drought, particulate organic matter, Changjiang Estuary and its adjacent marginal seas, PARAFAC