Impact of Artificial Aeration on Phytoplankton Growth and Seasonal Succession in a Eutrophic Lake
Valkov, Veselina Aleksandrova
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Excessive phytoplankton growth caused by increased loadings of nitrogen (N) and phosphorus (P) is the most visible symptoms of eutrophication. At higher densities phytoplankton creates water quality problems such as offensive taste and odor, impaired aesthetics, depletion of dissolved oxygen (DO), and cyanotoxicity concerns. Artificial aeration is commonly used to eliminate thermal-stratification, to increase DO levels in lakes and reservoirs, and to control P-release from sediments. This research was conducted to evaluate the impact of aeration on sediment nutrient release, nutrient availability for phytoplankton growth, phytoplankton seasonal succession and Cyanobacterial growth. Water samples for nutrient and phytoplankton analysis were taken from a eutrophic reservoir in North Dakota under aerated and non-aerated conditions, where sediment nutrient release was identified as a major source of N and P. Aeration eliminated thermal stratification and increased DO concentrations throughout water column. When aerated, aerobic condition at the sediment-water interface reduced sediment P-release by nearly 50%. However, phosphorus release due to degradation of organic matter continued and was likely enhanced by increased DO levels. Induced mixing from aeration made nutrients equally distributed in the water column and more available for phytoplankton growth, which led to more phytoplankton growth measured as higher chlorophyll-a concentration and phytoplankton biovolume. Results of this study reveal that increased mixing and nutrient availability due to aeration are the major reasons for changes in phytoplankton seasonal succession resulting in favoring growth and shifting growth-periods of diatoms, dinoflagellates, and Cyanobacteria. Seasonal succession of phytoplankton community was also affected by nitrogen limitation in the reservoir. Ability of Cyanobacteria to grow at low N concentrations and low N:P ratios stimulated nitrogen-fixing cyanobacterial species to bloom and maintained higher cyanobacterial growth. Aeration did not reduce algal and cyanobacterial growth in the reservoir.