Growth of Bloom-Forming Cyanobacteria Under Different Forms of Nitrogen in Summer and Autumn

Timothy Y Wong, Fordham University


Cyanobacteria Harmful Algal blooms (cHABs) are a global issue threatening the stability of freshwater habitats, leading to water quality deterioration and human health complications. The scope and spread of these blooms have become increasingly frequent, adversely impacting society’s ability to use water for recreation and consumption. My project aimed to understand how the growth of bloom-forming cyanobacteria species (Aphanizomenon flos-aquae, Microcystis sp., Planktothrix agardhii) respond to different N compounds in P-rich conditions in summer and autumn lakewater assemblages. Using 4L lake water microcosms, I manipulated natural phytoplankton communities and examined the specific nutrient conditions that most strongly influenced their growth. Growth of the summer assemblage in the Microcystis experiment was influenced by N input, where algae exhibited a greater uptake affinity for NH4+ than NO3-. The N2-fixing cyanobacterium Aphanizomenon flos-aquae proliferated with and without supplemental N. However Microcystis sp. growth increased significantly across N treatments, especially from NH4+ input. The experiment with an autumn assemblage, which included Planktothrix agardhii, responded less to N additions. Although the algal community was less productive than the summer assemblage, the autumn assemblage was sensitive to P addition. Planktothrix agardhii had the greatest cell density from urea (+P) addition, although effects were non-significant. Seasonal turnover in Calder Lake likely had a significant role in community composition and its response to N and P treatments. Although the experiments highlighted how N had varying significance in algal growth between seasons, N was an important nutrient in algal productivity, where the different affinities across N compounds influenced the growth and composition of the summer assemblage (when cyanobacteria were most abundant). The results of this study suggest that different N compounds may lead to eutrophication in varying ways. Aphanizomenon flos-aquae, Microcystis aeruginosa and Planktothrix agardhii are a few of many cyanobacteria species that threaten freshwater communities by dominating plankton assemblages in freshwater ecosystems, leading to concerns of human exposure to neurotoxins and hepatotoxins. Results of this study also suggest that to effectively control and mitigate the magnitude of cHABs, the inputs of both P and N should be mitigated year round.

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Recommended Citation

Wong, Timothy Y, "Growth of Bloom-Forming Cyanobacteria Under Different Forms of Nitrogen in Summer and Autumn" (2021). ETD Collection for Fordham University. AAI28263289.