Impacts of Artificial Dam Construction on Phytoplankton Communities in the Meishan Bay, Zhejiang Province

Meishan Bay became a semi-enclosed artificial bay after the construction of the North Dam and South Dam at the entrances of Meishan Bay between 2012 and 2017. Following the dam construction, Meishan Bay has become a concentrated area primarily for tourism, leisure, and ecological protection, with a significant increase in the frequency of red tides. To investigate the impact of artificial dam construction on the structure of phytoplankton communities in the Meishan Bay, this study conducted surveys of water bodies at nine stations both inside and outside the bay. Results showed that the abundance of phytoplankton within the bay was higher than outside, while the average species diversity index and evenness index were lower within the bay compared to outside, reflecting weaker ecosystem stability within the bay. The construction of dams in the Meishan Bay reduced the water flow velocity, leading to a decrease in the concentration of suspended solids, increased water transparency, and reduced limitations on algal photosynthesis, thus favoring algal reproduction. On the other hand, the convergence of multiple terrestrial rivers within the bay provided a large amount of nutrients for algae, promoting their proliferation but also exacerbating pollution within the bay. The dam construction also altered the content and ratio of nutrients within the bay, resulting in a higher proportion of dinoflagellates. Skeletonema sp., Guinardia delicatula, and Prorocentrum minimum became dominant species in the water. It was clearly showed by this study that Meishan Bay was influenced simultaneously by artificial dam construction and maritime tourism, resulting in a low stability ecosystem. There is a need to enhance pollution management within the bay, guide the development of the tourism industry, and monitor red tides. This research provides a scientific basis for understanding the ecological and environmental impacts of artificial dam construction.