Recent oxygen depletion in the Pearl River Estuary, South China: geochemical and microfaunal evidence

We examined a suite of geochemical and microfaunal indicators in ²¹⁰Pb-dated sediment cores from the Pearl River Estuary, South China, to determine the historical course of oxygen conditions. The results revealed a substantial increase in nutrient elements and primary production in the sediment over the last 3 decades, which could be interpreted as a recent increase in the extent of eutrophic condition in the Pearl River Estuary. Furthermore, total foraminifers decreased abruptly in abundance while the species Ammonia beccarii, which is tolerant of low-oxygen conditions and high organic fluxes, showed a marked increase in relative abundance after the 1970s. These faunal changes implied that significant deterioration had occurred in the bottom water oxygen conditions since the late 1970s. This degradation could be caused by the increased nutrient and organic loading to the estuarine system, which is likely related to the rapid urbanization and industrial development in the Pearl River Delta during this period.