Numerical Study of the Three Gorges Dam Influences on Chlorophyll-a in the Changjiang Estuary and the Adjacent East China Sea

• Published in: Journal of Ocean University of China Vol. 20; no. 1; pp. 10 - 22
• Main Authors: Chen, Dongxing, Liu, Qianqian, Yin, Kedong
• Format: Journal Article
• Language: English
• Published: Heidelberg Science Press 01-02-2021; Springer Nature B.V; School of Marine Sciences/Guangdong Key Laboratory of Marine Resources and Coastal Engineering, Sun Yat-sen University, Guangzhou 510275, China; Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai), Zhuhai 510275, China%Department of Physics and Physical Oceanography, University of North Carolina Wilmington, Wilmington, NC 28403, USA
• Subjects: Algal blooms; Biogeochemistry; Biological fertilization; Canyons; Chlorophyll; Chlorophyll a; Dam construction; Dams; Earth and Environmental Science; Earth Sciences; Ecological effects; Estuaries; Estuarine dynamics; Fertilization; Fertilizers; Hydrology; Isobaths; Mathematical models; Meteorology; Modelling; Nitrogen; Oceanography; Oceans; Phosphates; Phosphorus; Seasonal variation; Seasonal variations; Sediment discharge; Spatial variations; Watersheds; Three Gorges Dam; East China Sea; coastal ecosystem; physical-biogeochemical model; East China Sea; Chl; Chl-a
• ISSN: 1672-5182; 1993-5021; 1672-5174
• DOI: 10.1007/s11802-021-4430-z

The impoundment of the Three Gorges Dam (TGD) has altered downstream hydrological characteristics and sediment discharge, and it has caused ecological impacts, such as changes in chlorophyll-
a
(Chl-
a
) in estuaries and coastal oceans. To investigate the TGD’s influence on Chl-
a
’s interannual and seasonal variations in the Changjiang Estuary and the adjacent coastal East China Sea, a physical-biogeochemical model was developed with numerical experiments covering a decade, including TGD’s pre-period (pre-TGD, 1999–2003) and post-period (post-TGD, 2004–2008). The modeling results demonstrate an annual increase in the regional average Chl-
a
from pre- to post-TGD, with the largest increase reaching up to 20.8% in spring in the nearshore region beyond the Changjiang mouth. The spatial variations in Chl-
a
are high, with the largest variation being observed around the 20–40 m isobaths. The increase in Chl
-a
is influenced by improved light and nutrient conditions, which is attributed to dam construction and fertilization by human activities. A decline in nitrogen-phosphorus fertilizer usage ratio along the Changjiang River watershed after the TGD’s impoundment is another factor that influences the Chl-
a
’s variation. The modeling results also show severe NO
3
and PO
4
imbalances with a larger N/P ratio during the post-TGD period, especially in regions with large Chl-
a
increases. Moreover, the greater increase in the usage of phosphorus fertilizer than nitrogen fertilizer influences Chl
-a
’s variation and has potential promotion effects on the outbreak of harmful algal bloom events.