| Summary: | Prairie saline lakes are unusual ecosystems with major ecological, economic and
recreational importance. Despite their ecological value, anthropogenic activities are
conducted with little knowledge of their impacts. Early studies conducted between the
1940s and 1980s were semi-quantitative and limited by available technology. Historical
quantitative data sets collected between 1989 to 1995 for nine Saskatchewan prairie lakes
whose salinity ranges from 0.2-170.3 g TDS·L-1 were analyzed to determine if there was
any relationship between salinity, nutrient concentrations, plankton biomass and
community composition.
Prairie saline lakes are characterized by high N and P concentrations which increase
along a specific conductivity gradient. Specific conductivity is significantly related to
total phosphorus, soluble reactive phosphorus, sum nitrogen, ammonia and dissolved
oxygen concentrations. Chlorophyll α concentrations were significantly correlated with
total phosphorus, sum nitrogen, silica, temperature, surface area and Secchi depth.
Sestonic ratios suggest N- and P-limitation for phytoplankton were present in all of the
study lakes, but were less severe in the higher salinity lakes.
In eutrophic fresh water lakes, elevated nutrients are correlated with high phytoplankton
biomass. In prairie saline lakes, phytoplankton biomass is low relative to N and P
concentrations. In addition, crustacean zooplankton biomass is high and phytoplankton
biomass alone does not appear sufficient to support this zooplankton biomass. The
phytoplankton community composition is most strongly affected by salinity, with a
greater proportion of flagellate phytoplankton taxa occurring as salinity increases. There
is also an unexpected decrease in the proportion of cyanobacteria in the phytoplankton
community. As salinity increases, the crustacean zooplankton community shifts from a
mixed community to one exclusively dominated by Artemia.
Regression models of phyto- and zooplankton biomass developed in fresh water systems
were applied to the study lakes to investigate their applicability. Total phytoplankton
biomass and inedible phytoplankton biomass were overestimated by TP, while edible phytoplankton biomass was underestimated TP. Zooplankton biomass was not accurately
predicted by ch1 α concentrations or total phytoplankton biomass, but predictions based
on TP were accurate. The saline lakes tend to have a greater proportion of small,
flagellate phytoplankton taxa which are a prime food source for crustacean zooplankton.
In these lakes the total phytoplankton biomass was lower than would be expected based
on TP concentrations. It is possible that these phytoplankton taxa are capable of
withstanding the zooplankton grazing pressure while still managing to outcompete larger,
slower growing phytoplankton taxa for nutrients. It is also possible that there is an
alternate food source available to the zooplankton, such as benthic algae and/or bacteria.
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