ENVIRONMENTAL HISTORY FOR THE LAST TWO MILENNIA IN THE CENTRAL ARGENTINEAN PAMPA PLAIN: A PALEOLIMNOLOGICAL APPROACH

The Central Pampa plain (36º–37º S; 60º–61º W) presents numerous shallow lakes subjected to climatic dynamics and anthropogenic impacts during the Late Holocene, but few were analyzed. New studies are essential to provide an integral and regional analysis of these lakes evolution. In this context, a multi-indicator analysis including sedimentary and palynomorph (pollen and non-pollen) indicators was performed to reconstruct the paleoenvironmental evolution of Blanca Chica shallow lake during the past 1700 years. Four main lake condition stages were identified. Natural forcing dominated the period prior to 1880 CE, followed by a scenario characterized by the combined action of anthropic and natural forcings. Between 260800 CE, laminated sediments and phytoplankton dominance point to a high-level, turbid, nutrient rich lake during a wet period. Between 800–1600 CE, massive sediments, increasing halophytic vegetation and decreasing phytoplankton indicate a lower water-lake level in a dry context. This drought scenario was intensified between 1660–1830 CE as suggested by massive mottled sediments, submerged macrophytes remains and filamentous chlorophytes. A shift to wetter conditions is indicated for 1830–2015 CE, by a perennial, turbid, eutrophic, high-level lake with massive organic sediments. The onset of agriculture and cattle was shown by a raise in pollen taxa (i.e., 1830) and increased sedimentation rates related to soils erosion which suggested intense anthropic activity. The change in the aquatic communities and sedimentology for the last 30 years allowed considering a shift to high anthropogenic impact combined with an increase in precipitation which generated an accelerated eutrophication of the lake.