Paleoenvironmental history of Siete Lomas shallow lake (Southeast Pampa plain, Argentina) during the last 1000 years

SANCHEZ VUICHARD GUILLERMINA; MENGO LUCIANA; HALAC SILVANA; STUTZ SILVINA

Bariloche

Conferencia; IAL IPA 2022. Lagos, Memorias del Territorio; 2022

INTERNATIONAL ASSOCIATION OF LIMNOGEOLOGY and INTERNATIONAL PALEOLIMNOLOFY ASSOCIATION

A multi-indicator analysis, including pollen, non-pollen palynomorphs, paleopigments, total phosphorus -TP, organic matter, plant macrofossils and associated fauna, was performed to reconstruct the paleoenvironmental history of Siete Lomas lake (37º08?S, 57º38?W) during the last ca. 1000 years. During the early period of the lake history, changes in dominant communities were mainly controlled by climate, and later, changes probably resulted from a combination of both climate and human impacts that generated an accelerated eutrophication. Three scenarios in lake?s evolution were recognized. Since ca. 1050 AD a clear and ephemeral/small shallow lake with a low primary productivity and low nutrients was indicated by low TP concentrations, the dominance of submerged macrophytes (angiosperms and charophytes) and low abundance of phytoplankton, probably associated with a dry period. At ca. 1880 AD a transition towards a turbid, eutrophic perennial lake with higher primary productivity, increased nutrients (i.e., TP levels) and water level and a diverse community composed by plants, algae and zooplankton was denoted, likely related to the onset of a wet period. During this time the aquatic community was dominated by the phytoplanktonic algae (e.g., Pediastrum and Gloeotrichia), which was confirmed by fossil pigments indicators of chlorophyte, cyanobacteria and diatom algae. On the other hand, the local community of macrophytes (Myriophyllum; Ceratophyllum.; Potamogeton; Chara and Tolypella) was poorly represented. During the last scenario, since ca. 1975 AD, a hypereutrophic, turbid and enlarged lake was denoted by an exponential increase in TP, the dominance of Gloeotrichia; Pediastrum and Scenedesmus, and also of diatoms, as indicated by fucoxanthin increase. The abundance of cladocera (Daphnia sp., Ceriodaphnia sp., Simocephalus sp. and Moina sp.) and bryozoans (Plumatella sp.) also indicated the lake eutrophication. During the last century, the main drivers of changes in the lake history were those related to eutrophication: the agriculture and the cattle breeding implemented in this landscape as well as the foundation and settlement of cities