Lake Okeechobee Performance Measure - Diatom / Cyanobacteria Ratio

http://www.evergladesplan.org/pm/recover/recover_docs/et/lo_pm_cyano-diatom.pdf

Lake Okeechobee Performance Measure

Diatom/Cyanobacteria Ratio

Last Date Revised: March 7, 2007

Acceptance Status: Accepted

1.0 Desired Restoration Condition

The target is to substantially reduce the dominance of cyanobacteria relative to diatoms. This can be expressed as a numeric target of having a long-term pelagic ratio of biovolume (diatoms: cyanobacteria) greater than 1.5:1.

2.0 Justification

Studies of phytoplankton taxonomic structure of Lake Okeechobee in the 1970s indicated that the community was dominated by diatoms; today the community is dominated by pollution-tolerant bloom-forming cyanobacteria (Havens et al. 1996). The five-year mean diatom to cyanobacteria ratio for 2000-2005 was 0.63 (SFER, 2006). If phosphorus loads are substantially reduced the percentage of the community comprised of cyanobacteria should decline (LATHROP et al., 1998).

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The target of this approach is to reduce phosphorus to reduce the cyanobacteria population. The alternative of increasing Silica to increase Diatoms population is not being discussed. This is an easier solution.

Silicate as regulating nutrient in phytoplankton competition

http://www.int-res.com/articles/meps/83/m083p281.pdf

Vol. 83: 281-289, 1992
MARINE ECOLOGY PROGRESS SERIES
Published July 16
Silicate as regulating nutrient in phytoplankton competition
J. K. Egge, D. L. Aksnes
Department of Fisheries and Marine Biology. University of Bergen. Heyteknologisenteret, N-5020 Bergen. Norway

ABSTRACT- The development of phytoplankton communities was studied in floating enclosures. The enclosures were supplied with either surface water or water from 40 m depth. Nutrients with or without silicate were added in some of the experiments, while others received no artificial fertilization. It is shown that diatom dominance occurred irrespective of season if silicate concentration exceeded a threshold of approximately 2 PM. Flagellate dominance changed to diatom dominance within a few days after nutrient addition resulting in silicate concentrations above this threshold. Dominance of Phaeocystis sp. appeared on several occasions after the bloom of another species, but never at high silicate concentrations. The success of the diatom group seemed to be due to a high inherent growth rate at non-limiting silicate concentrations. Calculations indicated that the inherent growth rate for the diatom group had to be 5 to 50 % higher than for the flagellate group in order to explain the outcome of our experiments.