Abstract
Cyanobacteria may adversely impact aquatic ecosystems through oxygen depletion and cyanotoxin production. These cyanotoxins can also harm human health and livestock. In recent years, cyanobacterial blooms have been observed in several drinking water reservoirs in Kentucky, United States. In Kentucky, the paradigm is that phosphorous is the limiting nutrient for cyanobacteria growth. To explore this paradigm, an indoor microcosm study was conducted using hypereutrophic Guist Creek Lake water. Samples were collected and spiked with various combinations of locally used agricultural grade fertilizers, including ammonium nitrate, urea, and triple phosphate (calcium dihydrogen phosphate). Samples were incubated indoors for the photoperiod-specific to the time of the year. Cyanobacteria density, measured by phycocyanin, did not demonstrate increased growth with the addition of phosphate fertilizer alone. Cyanobacteria growth was enhanced in these conditions by the combined addition of ammonium nitrate, urea, and phosphorus fertilizer. Growth also occurred when using either ammonium nitrate or urea fertilizer with no additional phosphorus input, suggesting that phosphorus was not limiting the cyanobacteria at the time of sample collection. The addition of both nitrogen fertilizers (ammonium nitrate and urea) at the concentrations used in this study, in the absence of phosphorus, was deleterious to both the Chlorophyta and cyanobacteria. The results suggest further studies using more robust experimental designs are needed to explore lake-specific dual nutrient management strategies for preventing cyanobacterial blooms in this phosphorus-rich hypereutrophic lake and possibly other hypereutrophic lakes.
Highlights
Cyanobacterial blooms in aquatic ecosystems are known to periodically produce harmful toxins [1] [2]
Cyanobacteria growth was enhanced in these conditions by the combined addition of ammonium nitrate, urea, and phosphorus fertilizer
The ability to tolerate carbon-limited conditions has been linked to cyanobacteria dominance in hypereutrophic conditions [46], and the results from this study demonstrate that a more complicated study design that includes carbon would be needed to better understand cyanobacterial bloom dynamics in Guist Creek Lake under the study conditions that were created
Summary
Cyanobacterial blooms in aquatic ecosystems are known to periodically produce harmful toxins [1] [2]. Small human-made freshwater lakes (reservoirs) are frequently impacted by cyanobacteria growth as such lakes are readily impacted by surface runoff and more rapid temperature changes [7]. Beyond having their fisheries impacted, lakes (large and small) may have their local communities adversely effected from blooms due to decreased recreation and tourism, increased drinking water treatment costs, lower property values, lower quality of life, and environmental stigma [8] [9] [10]. Recent national assessments of cyanobacteria bloom formation implicate both nitrogen and phosphorus as major drivers of US freshwater blooms [18] [19]
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