Iron availability allows sustained cyanobacterial blooms: a dual-lake case study

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2021-05-14
Authors
Leung, Tania
Wilkinson, Grace
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Swanner, Elizabeth
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Geological and Atmospheric Sciences

The Department of Geological and Atmospheric Sciences offers majors in three areas: Geology (traditional, environmental, or hydrogeology, for work as a surveyor or in mineral exploration), Meteorology (studies in global atmosphere, weather technology, and modeling for work as a meteorologist), and Earth Sciences (interdisciplinary mixture of geology, meteorology, and other natural sciences, with option of teacher-licensure).

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The Department of Geology and Mining was founded in 1898. In 1902 its name changed to the Department of Geology. In 1965 its name changed to the Department of Earth Science. In 1977 its name changed to the Department of Earth Sciences. In 1989 its name changed to the Department of Geological and Atmospheric Sciences.

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1898-present

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  • Department of Geology and Mining (1898-1902)
  • Department of Geology (1902-1965)
  • Department of Earth Science (1965-1977)
  • Department of Earth Sciences (1977-1989)

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Lakes dominated by cyanobacterial harmful algal blooms (CyanoHABs) are geographically widespread. These blooms are associated with fish kills and toxin production, which have negative impacts on human health. There is compelling evidence that iron (Fe) can also regulate CyanoHABs besides nitrogen and phosphorus. Low iron concentrations (tens of ng L-1) has been documented to limit CyanoHABs in freshwaters whereas high Fe concentrations (hundreds of μg L-1) can promote CyanoHABs. However, it is unclear the extent which Fe influences CyanoHABs in lakes that lack an extensive anoxic zone and where the magnitude of Fe concentration ranges from tens to < 400 μg L-1. The aim of this study was to assess Fe trends, measured as dissolved Fe (DFe), associated with cyanobacteria dynamics in lakes in northwestern Iowa. We utilized a multi-wavelength fluorometer to monitor and classify phytoplankton based on their unique fluorescence spectra from chlorophyll a (Chl-a) and accessory pigments. Here we report a declining DFe trend (drawdown) potentially due to phytoplankton uptake in East Okoboji and its effect on CyanoHABs. Multi-wavelength fluorescence show cyanobacteria peaked (> 50% cyanobacteria Chl-a) during a DFe minimum. The drawdown in DFe inversely correlated with phosphorus, suggesting decoupled Fe and phosphorus cycling. The strong positive correlation between phosphorus and cyanobacteria Chl-a supports a role for phosphorus in triggering the CyanoHAB. This study suggest an underlying mechanistic role of Fe on CyanoHABs: the intermediate range of Fe concentrations investigated here may be sufficient to sustain CyanoHABs.

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This is a manuscript of an article published as Leung, Tania, Grace M. Wilkinson, and Elizabeth D. Swanner. "Iron availability allows sustained cyanobacterial blooms: a dual-lake case study." Inland Waters (2021). doi:10.1080/20442041.2021.1904762. Posted with permission.

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Fri Jan 01 00:00:00 UTC 2021
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