Mechanisms controlling acidification resilience in the Yangtze River estuary: an index from buffering capacity

Published 15 May 2024 Science Leave a Comment
Tags: chemistry

Highlights

• Estuarine minimum buffer salinity is positively correlated with river DIC:TA ratio.
• The dam construction makes the minimum buffer zone move to lower salinity.
• Anthropogenic CO₂ invasion leads to a decline in the estuarine buffering capacity.
• Eutrophication exacerbates the decline in the estuarine bottom buffering capacity.

Abstract

Ocean acidification poses a substantial threat to global marine ecosystems, estuaries are more vulnerable to ocean acidification compared to open oceans due to their weaker buffering capacity. This study examined the carbonate parameters off the Yangtze River estuary (YRE) during summer 2019 and investigated seasonal variations in total alkalinity (TA) and dissolved inorganic carbon (DIC) transports in the lower Yangtze River in 2019. Monthly DIC (1566–2164 μmol/kg) and TA (1471–2128 μmol/kg) in the Yangtze River were negatively correlated with water discharge. Buffer factor (β_DIC) was calculated and used to evaluate the buffering capacity, which ranged from 64 to 256 μmol/kg and increased seaward along the YRE. Conservative mixing models indicated that the estuary had a minimum buffer zone (MBZ) at salinity of 2–9 during the high discharge periods. And the salinity of the MBZ was positively correlated with the riverine DIC: TA ratio. The construction of the Three Gorges Dam has resulted in a decrease in the Yangtze River’s DIC:TA ratio, leading to the migration of the estuarine MBZ towards lower salinity regions. The effect of anthropogenic CO₂ invasion on estuarine buffering capacity was opposite to that of dam construction, leading to the migration of the estuarine MBZ towards higher salinity regions. Biological influences on the buffering capacity in the YRE were also quite considerable. Net autotrophy slightly enhanced the buffering capacity of the estuarine surface water, while net heterotrophy significantly weakened the buffering capacity of the estuarine bottom water. Eutrophication could intensify the biological influences on the buffering capacity. Globally, mid-latitude estuaries, such as the YRE, generally exhibit the strongest buffering capacity, while estuaries in Arctic regions tend to have the weakest buffering capacity.

Liu Q., Wang J., Miao Y., Li D., Wang B., Jin H. & Chen J., 2024. Mechanisms controlling acidification resilience in the Yangtze River estuary: an index from buffering capacity. Marine Chemistry: 104400. doi: 10.1016/j.marchem.2024.104400. Article.

Related