Detection of coherent signals for river damming in shallow marine sediments along a 900-km inner shelf mud belt

Continental shelf sediments serve as valuable archives of environmental changes within river basins, providing critical insights into the transfer of terrestrial materials to marine environments. In many major river systems worldwide, large-scale dam constructions have significantly reduced downstream sediment delivery. While previous studies have primarily focused on the impacts of such interventions on river channels and estuaries, highlighting effects such as reduced deltaic sedimentation rates and localized erosion. However, it remains uncertain whether these changes leave detectable stratigraphic signals in more distal regions of the continental shelf. This study investigates whether sedimentary changes associated with the commissioning of the Three Gorges Dam and the Shuikou Hydropower Station are recorded in the 900-km-long Zhejiang–Fujian Mud Belt, located offshore from the Changjiang River mouth. To evaluate the preservation of long-range signals of man-made activities, five dated sediment cores were analyzed using a suite of non-destructive proxies, including grain size, clay mineral assemblages, γ-density, magnetic susceptibility, and color reflectance. A total of 302 downcore measurements were subjected to Empirical Orthogonal Function (EOF) analysis. Distinct shifts in sediment characteristics were observed around the year 2002. The first EOF mode reflected sediment contributions from the Changjiang River, while the second captured inputs from the Minjiang River and other regional sources, indicating that signals of upstream anthropogenic disturbances can be retained even in distal shelf deposits. These findings suggest that continental shelf sedimentary records may preserve not only natural processes but also basin-wide human influences. This underscores the need for caution when using modern shelf records to reconstruct past environmental conditions, as recent anthropogenic imprints may obscure paleoenvironmental signals. By integrating stratigraphic records with multivariate statistical techniques, this study demonstrates here an effectively approach for assessing the influence of land-based activities on offshore sedimentary systems, offering a new perspective on human-induced changes in modern depositional environments.