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

GUILLERMINA SÁNCHEZ VUICHARD; LUCIANA MENGO; HALAC, SILVANA R.; SILVINA STUTZ

Congreso; Lagos, Memorias del Territorio-Lakes, Memories of the Landscape IAL-IPA 2022; 2022

A multi-indicator analysis, including pollen, non-pollen palynomorphs, paleopigments, totalphosphorus -TP, organic matter, plant macrofossils and associated fauna, was performed toreconstruct the paleoenvironmental history of Siete Lomas lake (37º08’S, 57º38’W) duringthe last ca. 1000 years. During the early period of the lake history, changes in dominantcommunities were mainly controlled by climate, and later, changes probably resultedfrom a combination of both climate and human impacts that generated an acceleratedeutrophication. Three scenarios in lake’s evolution were recognized. Since ca. 1050 AD aclear and ephemeral/small shallow lake with a low primary productivity and low nutrientswas indicated by low TP concentrations, the dominance of submerged macrophytes(angiosperms and charophytes) and low abundance of phytoplankton, probably associatedwith a dry period. At ca. 1880 AD a transition towards a turbid, eutrophic perennial lakewith higher primary productivity, increased nutrients (i.e., TP levels) and water level and adiverse community composed by plants, algae and zooplankton was denoted, likely relatedto the onset of a wet period. During this time the aquatic community was dominated bythe phytoplanktonic algae (e.g., Pediastrum and Gloeotrichia), which was confirmed byfossil pigments indicators of chlorophyte, cyanobacteria and diatom algae. On the otherhand, 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, asindicated by fucoxanthin increase. The abundance of cladocera (Daphnia sp., Ceriodaphniasp., Simocephalus sp. and Moina sp.) and bryozoans (Plumatella sp.) also indicated the lakeeutrophication. During the last century, the main drivers of changes in the lake history werethose related to eutrophication: the agriculture and the cattle breeding implemented in thislandscape as well as the foundation and settlement of cities.