Relationships Between Long-Term Trend of Satellite-Derived Chlorophyll-a and Hypoxia Off the Changjiang Estuary

Date of Issue:2022-04-12 Reading:127

The Changjiang Estuary is one of the largest estuaries in the world, where hypoxia frequently occurs during the summer season. Recent routine surveys in the observed area found that the low dissolved oxygen (DO) in the summer bottom water was not rapidly expanding with increasing nutrient loads in Changjiang diluted waters. Based on the remote sensing data and in situ data, we examined the historic seasonal hypoxia observations for the bottom waters of the Changjiang Estuary and investigated the short- and long-term effects that runoff had on variations in DO and chlorophyll-a (Chl-a). Our analysis indicated that the recent areal variation in hypoxia was due to the changing Chl-a distribution and stratification conditions. The correspondence between hypoxia and surface Chl-a concentration showed that remotely sensed Chl-a larger than 3.0 mg L−1 was an essential condition for the formation of hypoxia off the Changjiang Estuary. The trend of Chl-a concentration was significantly impacted by the Three Gorges Dam (TGD), and the interannual variation of Chl-a was weakly affected by global-scale climate variability. After the TGD impoundment, the sediment loading in the Changjiang runoff and suspended sediments in Changjiang Estuary in August decreased, and the high Chl-a concentration moved landward. These shifted the hypoxia from its optimal forming conditions.

Citation:Jianyu Chen, Delu Pan, Mingliang Liu, Zhihua Mao, Qiankun Zhu, & Ninghua Chen, et al. (2017). Relationships between long-term trend of satellite-derived chlorophyll-a and hypoxia off the changjiang estuary. Estuaries and Coasts,DOI:10.1007/s12237-016-0203-0.


The trends (a ten panels), average surface Chl-a concentration (units, mg/L; b upper right), and the occurrences of hypoxia (c bottom right, white
for 0: without hypoxia; red for 1: hypoxia occurrence; gray for 2: no observations) in August over each region during 1998–2013.

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