Potential effects of climate change on ion chemistry and phytoplankton communities in prairie saline lakes

Abstract

Shallow, closed‐basin saline lakes found in semiarid areas of Canada tend to be sensitive to changes in precipitation: evaporation ratios. Historical climatic information indicates that the area is becoming increasingly arid and this trend is expected to continue under current climate‐change scenarios. The water chemistries and phytoplankton of six Alberta saline (>1 g liter‒1 total dissolved solids) lakes were studied over a 12‐yr arid period to evaluate potential chemical and biological effects of climate‐induced increases in brine conductivity. Major ion concentrations, relative proportions of major ions, chlorophyll a concentrations, and the relative importance of different phytoplankton phyla were evaluated with respect to the increasing conductivity profiles of the lakes and with respect to the range of conductivities represented in the lake series. When the data were combined, concentrations of Na+, K+, Mg2+, SO42‒, Cl‒, and alkalinity were positively correlated with conductivity and Ca2+ was negatively correlated with conductivity. The relative proportions of Na+, SO42‒, and Cl‒ increased significantly with brine conductivity (2,900–30,900 µS), and the proportions of other ions decreased. The variability of these relationships suggests that the brine compositions in some of these lakes are strongly influenced by local surface water and groundwater chemistry. Increases in conductivity were usually accompanied by decreases in Chl a concentration and a shift away from cyanophyte species in favor of chlorophytes, cryptophytes, and chrysophytes. This change in the importance of these phytoplankton phyla, which occurs at relatively low salinities (∼3,500 µS cm‒1), acts to limit phytoplankton biomass in these P‐sufficient systems by restricting the growth of nitrogen‐fixing species. Salinity‐linked shortages of nutrients other than P may account for these changes.