Environmental change and human impact during the 20th century in a shallow pampean lake inferred through multiproxy analysis

CECILIA LAPRIDA; HÉCTOR PANARELLO, S; MONTES DE OCA, FERNANDA; RAMON MERCAU, J; PLASTANI, M.S.; MASSAFERRO, JULIETA; LAMI, ANDREA

JOURNAL OF PALEOLIMNOLOGY

SPRINGER

Año: 2020

0921-2728

The pampas is a fertile lowland plain comprising central east Argentina. There, several permanent and temporary shallow lakes occur, being the most important area for cropping in South America. Over the past 100 years, human activities have changed wetlands more rapidly and extensively than in any comparable period of time in the past. Additionally, the impact of environmental warming, projected to be a powerful stressor on freshwater ecosystems in the second half of the 21st century, is still poorly understood in the mid-latitude shallow lakes. The aim of the present contribution is to identify the main forcing factors behind the environmental changes in La Barrancosa, a shallow lake located in the southeastern pampas during the last 200 years by a multiproxy approach based on different biological (ostracods, chironomids, pigments), basic geochemical and sedimentological parameters. During the 19th century, La Barrancosa was a shallow, temporary subsaline wetland suggesting fairly dry conditions in coincidence with the end of the Little Ice Age. Thereafter, an extensive hiatus between ca. 1850-1940 can be attributed to denudation processes occurred during the Dust Bowl Pampas of 1930s. Since 1940, wetter conditions forced higher lake levels and the establishment of a perennial shallow lake. Thereafter, all proxies show significant variations during time periods associated with modifications in the land use, climatic changes and technological innovations. Since 1970s, human activities have played a significant role especially in the lakes? trophic state, gradually causing eutrophication. Since 1990, eutrophication processes were accelerated, probably as a consequence of the great increase in the planted area around the lake and the transition from the traditional to modern techniques of agriculture based on extensive use of fertilizers and pesticides in the region. This study provides an opportunity to better understand the effects and consequences of the ongoing environmental deterioration of shallow lakes of the pampas.