POTENTIAL EFFECTS OF CLIMATE-CHANGE ON ION CHEMISTRY AND PHYTOPLANKTON COMMUNITIES IN PRAIRIE SALINE LAKES

Shallow, closed-basin saline lakes found in semiarid areas of Canada t end to be sensitive to changes in precipitation : evaporation ratios. Historical climatic information indicates that the area is becoming in creasingly arid and this trend is expected to continue under current c limate-change scenarios. The water chemistries and phytoplankton of si x Alberta saline (> 1 g liter(-1) total dissolved solids) lakes were s tudied over a 12-yr arid period to evaluate potential chemical and bio logical effects of climate-induced increases in brine conductivity. Ma jor ion concentrations, relative proportions of major ions, chlorophyl l a concentrations, and the relative importance of different phytoplan kton 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, concentra tions of Na+, K+, Mg2+, SO42-, Cl-, and alkalinity were positively cor related with conductivity and Ca2+ was negatively correlated with cond uctivity. The relative proportions of Na+, SO42-, and Cl- increased si gnificantly with brine conductivity (2,900-30,900 mu S), and the propo rtions of other ions decreased. The variability of these relationships suggests that the brine compositions in some of these lakes are stron gly influenced by local surface water and groundwater chemistry. Incre ases in conductivity were usually accompanied by decreases in Chi a co ncentration and a shift away from cyanophyte species in favor of chlor ophytes, cryptophytes, and chrysophytes. This change in the importance of these phytoplankton phyla, which occurs at relatively low saliniti es (similar to 3,500 mu S cm(-1)), acts to limit phytoplankton biomass in these P-sufficient systems by restricting the growth of nitrogen-f ixing species. Salinity-linked shortages of nutrients other than P may account for these changes.