Regulation of Algal Bloom Hotspots Under Mega Estuarine Constructions in the Changjiang River Estuary

Abstract

Massive large-scale engineering projects have been built in river estuaries around the world, but their effects on environments in the surrounding coastal waters were less emphasized compared to those due to the watershed projects. In this study, we used the Changjiang River Estuary as an example to show that a significant consequence can be resulted in such a situation. Through analyzing the harmful algal bloom events data and the chlorophyll satellite data, we investigate the spatiotemporal variations of algal blooms in the estuary and its adjacent water. The results indicate that the location of algal bloom hotspot changed over the period of the estuarine constructions. Furthermore, using a well-validated numerical model, we explored the mechanisms responsible for such an ecosystem regime shift. It was found that after the estuarine constructions were built, the surface chlorophyll maximum was attenuated and part of it migrated landward north of the river mouth but was strengthened south of the river mouth and extended seaward. Alternations of the nutrient concentration distribution and turbidity distribution induced by river plume deviation are responsible for the redistribution of the high chlorophyll concentration area. By contrast, the direct impact of the Three Gorges Dam through changing the runoff and sediments flux, which has been highlighted in numerous studies, was less important than expected. Given the fact that Three Gorges Dam and mega estuarine constructions were built in a similar period, any observed regime shift of hydrodynamic and ecological status outside the estuary should be interpreted with particular caution.

Rapid variations of phytoplankton blooms and their dynamics off the Changjiang River Estuary

“…The simulated components included nutrients (dissolved inorganic nitrogen and phosphate), phytoplankton (dinoflagellates and diatoms), zooplankton, and detritus as well as their photosynthesis, respiration, mortality, and grazing activities under specific conditions. The model performance of phytoplankton and nutrients has been well validated in our previous studies (Wang et al, 2019a;He et al, 2022;Wang et al, 2023), exhibiting reasonable spatiotemporal distribution of phytoplankton and nutrients.…”

Tidal Variability of Phytoplankton Distribution in the Highly Turbid Changjiang River Estuary: Mechanisms and Implications

“…The model was validated previously, which showed reasonable performance in reproducing inter‐tidal results of hydrodynamic structure, including tidal dynamics, plume dynamics, and temperature distributions in the Changjiang River Estuary over multiple time scales (e.g., Huang et al., 2018; T. Wu & Wu, 2018; H. Wu et al., 2011, 2014, 2018; Yuan et al., 2016; Z. Zhang et al., 2018). The model results also revealed sediment and phytoplankton dynamics and adequately simulated their variability over seasonal time scales (He et al., 2022; Luo et al., 2017; Y. Wang, Wu, Lin, et al., 2019).…”

“…Zhang et al, 2018). The model results also revealed sediment and phytoplankton dynamics and adequately simulated their variability over seasonal time scales (He et al, 2022;Luo et al, 2017;Y. Wang, Wu, Lin, et al, 2019).…”

Impact of the Construction of New Port Facilities on Primary Production of Plankton in the Neva Estuary (Baltic Sea)

“…The large-scale construction of mega-engineering facilities can have a greater impact on estuarine ecosystems than the facility itself (He et al, 2022). This usually leads to an increase in turbidity and nutrient concentration, which affects phytoplankton (Wang et al, 2019).…”

“…Moreover, nutrients that have accumulated in the sediment over time can be recycled back into the water because of the intrusion of nutrient-rich pore water from sediments or bottom water layers into the whole water column (Su et al, 2015). This may release phytoplankton from nutrient limitation and stimulate plankton primary production (Su et al, 2015;He et al, 2022), but its response depends on the season and the species composition of the algae (Lagus et al, 2007;Su et al, 2015).…”