Volcanic and environmental impacts on subfossil chironomids from Northern Patagonia (Argentina) over the last 700 years.

Southern South America, especially Patagonia, presents numerous glacial lakes holding proxies of past environmental and climate changes. This is useful to reconstruct past environmental changes, key for understanding Southern Hemisphere variability and the present. Our aim was to identify the volcanic and environmental impact that occurred during the last 700 year in Northern Patagonia (Argentina) using subfossil chironomids, organic matter content, and tephrochronology from short sediment cores of two lakes located between Los Alerces National Park and Esquel city. Both lakes have similar watershed characteristics and were affected by the same volcanic events, making them an excellent tool for study environmental changes. Although changes in chironomid assemblages were subtle along both cores, enviromental variations and faunal responses to volcanic ash (tephra) could be inferred. In the last 50 years, an increase of organic matter, chironomids typical of productive environments, and the presence of macrophytes, point towards an increase in lake productivity. Probably linked to the establishment of Esquel city and fisheries starting in 1966 AD. Four tephra were recorded along cores affecting chironomid abundance differently, showing that the effects of volcanic events are not unique onefold but are related to the characteristics of the ash, the effect of wind, rain, and/or macrophytes. [ABSTRACT FROM AUTHOR]