Paleolimnological records in the Southeastern Pampa plain

Abstract

South Eastern Pampa plain (SEPP) lakes are very sensitive to environmental changes.Paleoenvironmental studies performed in these lakes allowed reconstructing changes inclimate and hydrological dynamics since the Early Holocene to the present. Thesepaleoenvironmental inferences were based on compositional and taphonomic analyses of aseries of biological proxies, such as diatoms, mollusks, pollen, non-pollen palynomorphs, plantmacroremains and associated fauna. Up to date, the seven studied records in the regionincluded lakes Nahuel Rucá, Hinojales San Leoncio, Lonkoy, Tobares, Hinojales, La Brava andKakel Huincul. In this chapter, the results of these seven records are integrated and discussedin a regional context. This integration demonstrated that the influence of external climatictriggers over intrinsic limnological processes constitute the major causes ofpaleoenvironmental changes modulating the evolution of these lakes during the last ca. 12 calka BP. During the Early Holocene, the records suggest that the SEPP was characterized by a dryclimate, even drier than the inferred for the Late Pleistocene-Holocene boundary, andsignaling a strong influence of precipitation changes on lakes dynamics. Climate became evendrier during the Middle Holocene, and while some of these lakes completely desiccated duringthat period (Lake Tobares) others remained active, probably as a consequence of the input ofgroundwater related to the elevation of the phreatic levels during the marine transgressiveregressivecycle that occurred during the Middle and Late Holocene in the area. In the last ca.2500 cal yr BP, freshwater input in the lakes increased, as a consequence of an increase inrainfall. Lakes acquired their modern configurations towards ca. 600 cal yr BP. Since ca. 1670CE, lakes started to experience changes related to anthropic impacts, first by cattle and thenby intensive agriculture, which was accentuated in the last 25 years, promoting a significantincrease in lakes eutrophication.