HOLOCENE SHALLOW LAKES EVOLUTION FROM SOUTH-EASTERN PAMPA GRASSLANDS, ARGENTINA

STUTZ S.* (1); BOREL C.M. (2); DEL PUERTO L. (3); INDA H. (3) AND GARCIA-RODRIGUEZ F. (3)

Bariloche, Argentina

Congreso; VI SOUTHERN CONNECTION CONGRESS; 2010

SOUTHERN CONNECTION

In south-eastern Pampa grasslands there is a large number of similar lakes developed in Pleistocene deflation basins. They are plain lakes, very shallow, polimyctic, eutrophic or hypertrophic which exhibit water renewal and fluctuating salinity. They have similar plant communities characterized by a defined ring of emergent plants (Schoenoplectus californicus), submerged plants (Myriophyllum, Ceratophyllum) and a carpet of floating-leaved plants. Pollen, NPPs, diatoms, phytoliths, ostracods, macro plants remains, organic matter and carbonate content, were used as proxies to evaluate lakes evolution and then integrate them in a regional environmental and climate history. In this work, we present results from Tobares, Loncoy, Nahuel Rucá and Hinojales lakes. The early Holocene is only represented in Lake Tobares where pollen and NPPs suggest a very shallow system without modern analogous. Around 5500 14C yr BP, Hinojales and Nahuel Rucá were affected by high standing sea level reflecting marine influence, indicated by almost all the proxies. After this, both lakes evolved similarly, showing shifts from clear to turbid states. During the late Holocene all lakes showed similar spectra indicating that modern lakes began to establish during this time, even though anthropogenic activity greatly modified them in the last two centuries.