Increased nutrient loads from the Changjiang (Yangtze) River have led to increased Harmful Algal Blooms

• Published in: Harmful algae Vol. 39; pp. 92 - 101
• Main Authors: Li, Hong-Mei, Tang, Hong-Jie, Shi, Xiao-Yong, Zhang, Chuan-Song, Wang, Xiu-Lin
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier B.V 01.10.2014; Elsevier
• Subjects: Algae; algal blooms; Animal and plant ecology; Animal, plant and microbial ecology; Autoecology; autumn; Bacillariophyceae; Biological and medical sciences; Brackish; Brackish water ecosystems; Changjiang River estuary; community structure; dissolved inorganic nitrogen; East China Sea; estuaries; Eutrophication; Flux; Fresh water ecosystems; Freshwater; Fundamental and applied biological sciences. Psychology; Harmful Algal Blooms; Miozoa; nutrient content; Nutrients; phytoplankton; Plant cytology, morphology, systematics, chorology and evolution; Plants and fungi; pollution load; rivers; seasonal variation; silicon; summer; Synecology; Thallophyta; winter; Pacific Ocean; West Pacific; Asia; East China Sea; China; INW, China, People's Rep., Changjiang Delta; INW, China, People's Rep., Changjiang Estuary; INW, Donghai Sea; China, People's Rep., Changjiang R; Flux; Nutrients; Changjiang River estuary; Harmful Algal Blooms; East China Sea; Eutrophication; Brackish water environment; Load; Algae; Estuaries; Freshwater environment; Marine environment; Bloom; Nutrient; Stream; Harmful alga
• DOI: 10.1016/j.hal.2014.07.002
• ISSN: 1568-9883

•Field and historical data on nutrients and HABs from 1950s to 2007s.•Variations of dissolved inorganic nutrients in the Changjiang River Estuary.•The characteristics of HABs in the past fifty years.•The importance of nutrient fluxes and DO variation in HABs in research area.•Nutrient composition and phytoplankton community were also analyzed. Based on observations collected during 15 cruises from 2002 to 2007 and on historical data, annual and seasonal variations in dissolved inorganic nutrients in the Changjiang (Yangtze) River estuary and the adjacent area were investigated. The importance of nutrients and nutrient fluxes to Harmful Algal Blooms (HABs) in the East China Sea (ECS) was also studied. The results showed an increasing trend in dissolved inorganic nitrogen (DIN) over the past fifty years. The changes in the PO4-P concentration fluctuated from 1959 to 2000, but the level has been almost stable since then. By contrast, the SiO3-Si concentrations decreased significantly over the past fifty years. Regarding seasonal variations, nutrients usually exhibited high values during autumn and winter, and the lowest values occurred in mid-summer. A strong positive relationship was observed between the DIN and PO4-P concentrations and the frequency or scale of HABs, indicating that eutrophication played a crucial role in the occurrence of HABs. As for nutrient fluxes, DIN and PO4-P fluxes have climbed sharply since 1980. In the ECS, the DIN increased sharply, but PO4-P concentrations only changed slightly. The increased nutrient discharges, especially DIN, could also have caused the strong increase in the frequency and area of HABs. The areas of hypoxic bottom water off the Changjiang River estuary presented an increasing trend over the past fifty years, which may also be attributable to eutrophication. Changes in the nutrient composition were also investigated in the present study. The N/P ratio increased dramatically over the past fifty years, while the Si/N ratio decreased. The percentage of diatoms decreased from 99% to 73%, while dinoflagellates increased from less than 1% to over 25% during the past fifty years. Therefore, long-term changes in nutrients, especially excess DIN and increasing N/P, could be responsible for the shift in the phytoplankton community structure.