Holocene dynamics of macrophytes and algal dominance in Pampa plain shallow lakes, Argentina

STUTZ, S.; GONZALEZ SAGRARIO, M. A.; FONTANA, S.

Malargüe, Mendoza

Simposio; 6th Symposium of the Internarnational Research Group of Charophytes; 2012

International Research Group on Recent and Extant Carophites (IRGC)

Pampa plain, situated in the southern part of South America, has a great number of shallow lakes. In the southeastern part, these lakes have similar characteristics like origin, geomorphology, plant communities and trophic state. Studies performed in the last years indicated that these lakes have a great potential as paleoecological and paleoclimatic archives due to the abundance and good preservation of fossils: diatoms, plant remains, mollusks, ostracods, pollen and NPPs. Multi-proxy studies reveal that these lakes have been active since early Holocene and have changed from clear to turbid states during late Holocene. The modern plant communities and limnological conditions have developed recently, 1000-700 yr BP. In particular, between ca. 5000-700 yr BP, high abundance of oospores and gyrogonites of Charophytes are recorded in Lonkoy, Hinojales and Nahuel Rucá lakes. In Lonkoy and Hinojales lakes, a succession of three species of Chara is recognized. This sequence of changes in assemblage composition, in combination with other proxies, indicates saline - brackish environmental conditions. Two possible explanations are proposed to support saline - brackish conditions. One is the intrusion of seawater into the former freshwater lakes during the maximum Holocene sea level stand (ca. 6000?5000 yr BP); the other possibility is that arid conditions, inferred for the area during the middle-late Holocene, could caused a higher ratio of evaporation to precipitation in the aquatic systems, leading to salinization, low water levels and possibly temporary desiccation. This study shows that the long-term dynamics of macrophytes and algal dominance in shallow lakes within the Pampa plain can be reconstructed, and that changes in assemblage composition may be linked to regional environmental conditions.