Cyanobacteria like it hot, nutrient-rich, and a little salty: increased chloride alters phytoplankton and zooplankton community structure in lakes and reservoirs

JONATHAN P. DOUBEK; SAMANTHA M. BURKE; JAMIE C. SUMMERS; SARAH L. BARTLETT; HILARY A. DUGAN; FLORA E. KRIVAK-TETLEY; NICHOLAS K. SKAFF; KAITLIN J. FARRELL; IAN M. MCCULLOUGH; FACUNDO SCORDO; PAUL C. HANSON; KATHLEEN C. WEATHERS

Lunz

Workshop; GLEON 18 Lunz & Gaming, Austria; 2016

Global Lake Ecological Observatory Network - WasserCluster Lunz Biologische Station GmbH, Austria - University of Vienna - University of Innsbruck - U.S. National Science Foundation

In many regions, freshwaters are becoming saltier as a result of global changes. Increased salt in lakes and reservoirs has the potential to alter freshwater ecosystem functions and services. Although there have been laboratory and small-scale studies that examine the effects of salt on a single or a few biota, less is known about changes in community structure at large spatial scales that may be influenced by salinization. We used data collected as part of the U.S. Environmental Protection Agency?s 2007 National Lakes Assessment to examine how salt affects phytoplankton and zooplankton densities, richness, and community structure in >1000 lakes and reservoirs across the continental U.S. Chloride concentrations ranged from ~0 to >10,000 mg/L. Indicator species analyses identified many green algal and diatom taxa as characteristic of lower chloride concentrations. Cyanobacteria, such as Limnothrix, Phormidium, and Planktothrix, which are known toxin-producing taxa, were characteristic of higher chloride concentrations. Only one green algal taxon (Oedogonium) was affiliated with higher chloride conditions. Chloride concentrations also altered zooplankton community structure, with taxa such as the gelatinous Holopedium affiliated with lower chloride concentrations, and the halophilic taxa Eurytemora, Moina, and Artemia characteristic of higher chloride concentrations. Overall, macrozooplankton appeared to be more tolerant of high chloride concentrations compared to phytoplankton, and both were more tolerant of high concentrations than rotifers. Chloride thresholds for biotic changes were much lower than prescribed acute and chronic toxicity standards (860 mg/L and 230 mg/L, respectively), suggesting that even slight increases in chloride may significantly alter freshwater planktonic communities.