Variation of Riverine Material Loads and Environmental Consequences on the Changjiang (Yangtze) Estuary in Recent Decades (1955−2008)

TLDR

Anthropogenic changes in the Changjiang basin have altered riverine material loads, degrading the estuary and adjacent seas. The study analyzes long‑term material‑load data to identify changing trends and their driving factors. Over the past five decades, dam construction has reduced dissolved silicate and suspended sediment loads, while population growth and fertilizer use have increased dissolved nitrogen and phosphate, lowering the DSi/DIN ratio and raising the DIN/DIP ratio, which may promote red‑tide blooms and hypoxia in the estuary.

Abstract

With intense anthropogenic perturbations in the Changjiang (Yangtze) River basin, the riverine loads and compositions of materials into the Changjiang Estuary have greatly changed, resulting in dramatic deterioration in the Changjiang Estuary and adjacent sea environments. Based on a long-term data set of the material loads into the Changjiang Estuary, changing trends and associated impacted factors were presented. The results showed downward trends concentrations and loads of dissolved silicate (DSi) over the past 50 years due to dam constructions in the Changjiang River. However, dissolved nitrogen (DIN) and dissolved inorganic phosphate (DIP) exhibited remarkable upward trends due to the increase of the population and the use of large-scale chemical fertilizer in the Changjiang River basin. The sharp decrease in the ratio of DSi/DIN and the increase in the ratio of DIN/DIP could cause increased Red tide bloom and decreased dissolved oxygen in the Changjiang Estuary. In addition, even though water discharge has remained almost constant, the suspended sediment discharge was shown to be sharply decreased due to the construction of dams.