Nutrient, chlorophyll and zooplankton seasonal variations on the southern coast of a subtropical saline lake (Mar Chiquita, Cordoba, Argentina)

Mar Chiquita is the largest salt lake in South America. Because of its rich and diverse biodiversity, it has been designated a world site of the Ramsar Convention on Wetlands. Despite its importance, its limnological characteristics are poorly documented. Here we report a baseline assessment of the seasonal variations of several limnological parameters on the southern coast of the lake. Samples were obtained at two lake sites (pelagic and coastal) and an additional site in the Laguna del Plata estuary lagoon. We found that Mar Chiquita is a well-mixed eutrophic shallow lake with significant spatial and seasonal variations in its limnological parameters. Of particular relevance are the spring turnover and the clear water phase in summer, being characterized by nutrient peaks (total nitrogen, total phosphorus (P) and soluble reactive P) in early spring, followed by peaks in zooplankton and ammonia in late spring and summer, together with a decrease in chlorophyll and pH. These events appear related to seasonal variations in water temperature and the shallowness of the lake that allows strong biochemical interactions with sediments. Correlations among the studied parameters indicate a significant role of zooplankton (particularly the brine shrimp) in controlling phytoplankton abundance. Laguna del Plata has typical estuary characteristics, including high variability in salt concentrations (13-63 g.L-1), high nutrient levels (0.48 mg P.L-1) (hypereutrophic) and higher phytoplankton biomass than the main lake. Mar Chiquita characteristics show interesting similarities with those recorded in the Great Salt Lake in the USA.