Abstract
Qingcaosha Reservoir, an estuary reservoir on the Yangtze River and a drinking water source, is facing phytoplankton blooms and the factors driving changes in phytoplankton composition and distribution have not been well understood so far. To facilitate the understanding of this problem, we collected surface water samples from January to December 2014 monthly at 12 sampling sites. A total of 205 taxa classified into eight major taxonomic groups were identified. Cyclotella meneghiniana, Melosira varians, Melosira granulata, Cryptomonas ovata and Chlorella vulgaris were the species dominating at least one season. The long stratification period and high nutrient concentration resulted in high chlorophyll a concentration (36.1 ± 18.5 μg L−1) in the midstream and downstream during summer, and mass phytoplankton growth and sedimentation process led to nutrients decrease. In the reservoir, neither P or N limitation was observed in the study period. We observed that water temperature, nutrient concentrations and light availability (Zeu/Zmix) are critical in selecting functional groups. These results highlight that the functional groups characterized the water body well and showed a good ecological status based on the assemblage index (Q average = 4.0). This work also highlights that mixing regime, water temperature and light availability were the driving factors that determine phytoplankton dynamics.
Highlights
Estuarine embedded reservoirs, serving as essential drinking water sources for adjacent cities, are sensitive to estuary and coastal environmental changes [1,2,3]
Considering that the reservoir located in the Yangtze River estuary and salt water may flow into this reservoir during high tides, EC was affected by saline water in the dry season, with mean values of
Our phytoplankton analysis revealed a significant increase in phytoplankton biomass along with significant decrease in nutrient concentration at the midstream and downstream of the reservoir
Summary
Estuarine embedded reservoirs, serving as essential drinking water sources for adjacent cities, are sensitive to estuary and coastal environmental changes [1,2,3]. Due to eutrophication and their unique geographical locations, nutrients from land and rivers, salt water invading the estuary [3] and other changes in other variables may influence phytoplankton succession in the reservoir and lead to algae blooms, as eutrophication is a natural process occurring in aquatic systems and eutrophic reservoirs are frequently being dominated by cyanobacteria for considerable periods of time [4]. The acceleration of this process can cause serious threats to water quality and habitat, drinking water supplies, food webs and all aspects of freshwater ecosystems [5]. An emphasis on phytoplankton functional group dynamics provides new insights into phytoplankton species adaptation strategies to environmental changes and assessment of the reservoir’s ecological status [7]
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