The effects of salinity on plankton and benthic communities in the Great Salt Lake, Utah, USA: a microcosm experiment

Abstract

Saline lakes change in size and salinity because of natural climate variability and especially from inflow diversions, which threaten life in these waters. We conducted a microcosm experiment in 12 L containers using organisms from the Great Salt Lake to determine how salinities ranging from 10 to 275 g·L−1 influenced the ecosystem. After 30 days, brine shrimp (Artemia franciscana) were nearly absent in salinities of 10 g·L−1 (where fish survived) and >225 g·L−1. As salinities increased from 75 to 225 g·L−1, final masses decreased 60% and their total biomass decreased fourfold. Copepod and rotifer biomasses were negligible at salinities >50 g·L−1. Brine fly (Ephydra gracilis) final biomass decreased 45% as salinity increased from 50 to 250 g·L−1. When Artemia and other grazers were abundant, phytoplankton chlorophyll levels were near 4.0 μg·L−1, but when grazing rates declined at higher salinities, phytoplankton chlorophyll increased to 130 μg·L−1. Mean periphyton chlorophyll levels showed the reverse pattern. Denitrification decreased total N concentrations during the experiment, resulting in final N:P ratios indicative of algal nitrogen limitation. The microcosm experiment demonstrated the strong influence of salinity on the entire ecosystem and highlighted the need for careful management of salt lakes to maintain appropriate salinities.