Centennial environmental evolution and human activity impacts recorded by sedimentary diatoms in the Pearl River...

Sedimentary diatom assemblages are sensitive bio-archives that can be used to reconstruct past environmental conditions in aquatic ecosystems. However, quantitative sedimentary records capable of precisely resolving anthropogenic impacts from natural variability in highly dynamic estuaries remain poorly understood. Here, we conducted a high-resolution diatom analysis of two ²¹⁰Pb-dated sediment cores (Z4-2 and Z5-2) from the Pearl River Estuary (PRE), covering the period 1938-2023 and 1893-2023, respectively. Our results identified a total of 66 diatom species and revealed a profound ecological shift. Prior to 2000, the diatom assemblage was dominated by planktonic taxa such as Cyclotella striata and C. stylorum, whose fluctuations reflected natural climate variability. In contrast, the period after 2000 was characterized by the dominance of the benthic species Paralia sulcata, which exceeded 50% abundance, accompanied by a sharp decline in freshwater species. This trajectory quantitatively demonstrates that anthropogenic forcing, including industrial pollution and coastal development, has surpassed natural climate variability as the primary driver of environmental change in the estuary in recent decades. These findings provide a critical baseline for distinguishing natural cycles from human-induced shifts, thereby offering a scientific basis for informed management decisions in the PRE and other anthropogenically influenced estuary ecosystems.