Paleoecology of thePampa plain, southeastern South America: long term records of shallow lakes as a basis toelucidate their functioning duringthe Holocene

TONELLO, M; NAVARRO D.; STUTZ, S.; FONTANA, S.; GONZALEZ SAGRARIO MA

San Salvador de Bahía

Congreso; International Palinological Congress; 2016

Paleolimnological studies based on multi-proxy analysis constitute the best tool to reconstruct evolution of aquatic systems as well as evaluating their responses to natural and anthropogenic stressors. Additionally to this, multi-site studies with a dominant focus on the detection of common trends by which lakes respond in a coherent way physically, chemically and biologically as well intrinsic as to extrinsic forcings is a good example of the Ecological Paleoecology target. In order to integrate shallow lakes evolution at Pampa plain (33°-39°S and 57°-66°W Argentina, South America) during the Holocene, we review published paleoecological evidence for middle and late-Holocene, and present new evidence for the early-Holocene. Pollen, non-pollen palynomorphs (NPPs) and plant macroremains and associated fauna were analyzed from five shallow lakes located in the southeastern of Pampa plain. Regarding their modern functioning, they present two alternative states of equilibrium (Scheffer y Jeppesen, 2007; Scheffer y van Ness, 2007). Some of them are turbid lakes due to the high amount of algae, while others are clear macrophyte-dominated lakes. Long-term records indicated that during the Holocene, Pampa plain shallow lakes underwent different states related to light penetration, nutrient charge, sediment suspension and water depth. These lakes were active from the early Holocene as clear and brackish lakes, dominated by charophytes and some submerged macrophytes. During middle and the beginning of late Holocene, lakes remained clear but resting structures of algae and invertebrates suggest very shallow and small lakes, with alternance of drougths and flooded. Since ca. 2000 yrBP, nutrient increase allowed rising on diversity and number of submerged macrophyes, in lakes still clear. From ca. 700 yrBP to present, lakes became predominately turbid alternating with clear phases as indicated by increased in phytoplankton. Integrating these records offers a unique opportunity to provide long-term data based on multiple locations and multiple proxies and to elucidate ecological processes that operated at the scale of centuries-millennia in these systems. The theory of Alternative Stable States, ASS (which comes from the Ecology; Scheffer 1993) resulted a good tool to interpret in a complete way the dynamics of these systems on time scales much longer (unlike what ecology offers). In turn, as feedback to the ecological theory, paleoenvironmental data realize the rates of change this type of aquatic ecosystems, state of resilience and permanence, and possible ecological thresholds.