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Effects of Low Bioavailable Nitrogen and Phosphorus on Cyanobacteria Dynamics in Eutrophic Lake Erie | Ohio Sea Grant

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Effects of Low Bioavailable Nitrogen and Phosphorus on Cyanobacteria Dynamics in Eutrophic Lake Erie

OHSU-TD-1510: Effects of Low Bioavailable Nitrogen and Phosphorus on Cyanobacteria Dynamics in Eutrophic Lake Erie

Published: May 1, 2013
Last Modified: May 11, 2016
Length: 211 pages
Direct: Permalink

Contributors

Justin David Chaffin Ph. D

Justin Chaffin, Ph. D

Senior Researcher, Research Coordinator, Stone Laboratory

Abstract

The growth and abundance of phytoplankton in freshwater lakes has long been
attributed to the concentration of phosphorus (P), and this idea of P-limitation has been a
paradigm accepted by limnologists. Hence, lake managers have relied on the strategy of
reducing P to restore water quality of eutrophic lakes. Recently however, several
researchers have proposed that nitrogen (N) is equally important as P, and have stated
that the P paradigm has eroded. These researchers suggest that both P and N inputs need
to be constrained. In spite of the evidence that suggests N-limitation, there are still
several researchers that hold onto the paradigm that only P regulates phytoplankton
biomass. Limnologists need more data to solve this hotly debate topic. The goal of this
dissertation is to provide insights into the dual nutrient management strategy controversy
by studying how western Lake Erie cyanobacteria responded to low concentrations of N
and P. In western Lake Erie nitrate concentrations decrease throughout the growing
season to very low levels. Nutrient enrichment bioassays conducted monthly during the
summers of 2010 and 2011 indicated that N (and not P) constrains cyanobacterial growth
during August and September when nitrate concentrations are very low. Experiments conducted during 2012 showed that N-limited cyanobacterial blooms are able to utilize
many forms of N. However, nutrient dilution assays indicated that N-limitation could not
be induced during early summer when P is the primary limiting nutrient. Following Nlimitation,
the cyanobacterial bloom shifted from Microcystis to the N-fixing Anabaena.
Furthermore, during 2011, the concentration of the cyanotoxin microcystin was highly
correlated with Anabaena biovolume. Genetic diversity of the Microcystis population
was assessed during 2011 and showed that diversity was very similar spatially and
temporally in spite of the wide range of N, indicating that Lake Erie Microcystis can
survive in low N waters. Finally, long-term data sets show that annual summer nitrate
concentrations in western Lake Erie have been declining since 1995, and yet
cyanobacterial blooms are prevalent. Overall the results suggest that additional N inputs
will likely exacerbate cyanobacterial blooms, however, reducing N inputs will not be
effective in ameliorating eutrophication.