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

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

San Salvador de Bahía

Congreso; International Palinological Congress; 2016

the evolution of aquatic systems as well asevaluating their responses to natural and anthropogenic effects. Additionally, multi-sitestudies help to detect common trends that respond to intrinsic as well as toextrinsic factors. For morethan a decade the authors have been investigatingshallowlake recordsfrom the Pampa plain in Argentina(33°-39°S; 57°-66°W) withthemain goal of elucidating theirevolutionary historyduring the Holocene.Here, wereview published palaeoecological evidence for the middleand late-Holocene, andpresent new results for the early-Holocene. Pollen, non-pollenpalynomorphs(NPPs), and plant macrofossil remains and associated fauna were analyzed fromfive shallow lakes located in the southeastern Pampa plain. Regarding theirmodern functioning, these lakespresent two alternative states of equilibrium.Some of them are turbid lakes due to the high amount of algae, while othersareclear macrophyte-dominated lakes.Long-term records indicatedthat during the Holocene, the shallow lakes of the Pampa plain underwentdifferent states related to light penetration, nutrient load, sedimentsuspension and water depth.These lakes were active sincethe early Holocene asclear and brackish lakes, dominated by charophytes and some submerged macrophytes.During the middle Holocene and the beginning of the late Holocene, lakes remainedclear but the presence of resting structures of algae and invertebrates suggestvery shallow conditionsand reduced size, with alternating periods of droughts andfloods. Since ca. 2000 yrBP, the increase in nutrientsfavoredarise in biodiversitysuch as the number of submerged macrophytes, remaining in a clearwater regime.From ca. 700yrBP to the present, lakes became predominately turbid alternatingwithclear phases as indicated by the increased in phytoplankton. Integratinglong-term multiproxy data from multiple-sitesoffersthe opportunity to elucidateecological processes that operate onthe timescale of centuriestomillennia.Thetheory of alternative stable statesprovides a good tool to interpret thedynamics of these systems on much longertime scales than ecology can offer. Inturn, as feedback to the ecological theory, palaeoecologicaldata explaintherates of changeof these aquatic ecosystems, the state of resilience andpermanence, as well as possible ecological thresholds.