A paleoenvironmental analysis of natural and anthropic events in the Caviahue area (Neuquén Province; Northern Patagonia) inferred from chironomids and other sediment proxies

WILLIAMS, N.; RIZZO, A.; DAGA, R.; ARRIBÉRE, MA.; RIBEIRO GUEVARA, S.

San Carlos de Bariloche

Congreso; IAL IPA 2022; 2022

Lacustrine sediments represent natural archives allowing the development of continuousrecords integrating local, regional, and global environmental signals by preserving diversepaleoenvironmental indicators. Our aim was to identify the occurrence and impact of natural(climatic fluctuations, volcanic eruptions) and/or anthropogenic (species introduction, fireactivity, transhumance, urbanization) events in an area affected by the Copahue VolcanicComplex (CVC). We present the results from Lake Portezuelo (central western Neuquén,Copahue-Caviahue region), a small and shallow environment with abundant emergentand submerged macrophytes and absence of fish (apparently since 2012, caused by aCVC eruption). This study was mainly based on chironomid remains observed along asedimentary sequence extracted in 2014, dated with 137Cs technique (sedimentation rate:0.307 cm yr-1) and comprising approximately the 200 last years. Chironomid community wascomposed of 22 taxa belonging to subfamilies Orthocladiinae, Tanypodinae, Podonominae,and Chironominae. A major change in assemblages occurred at ~1990, characterized by adecrease of Parapsectrocladius sp., Cricotopus sp., and some Tanypodinae members; andan increase of Parachironomus sp. This was coincident with temperature increases andprecipitation decreases recorded in Patagonia for recent decades. Previous decreases inchironomid abundance could reflect both lower temperatures (available from models) andeffects of anthropogenic fires during late 19th and early 20th centuries. Despite most volcanicdeposits (previously identified) caused immediate decreases in chironomid abundance andrichness, the greatest changes in midge assemblages were associated with decadal periods.To disentangle past environmental impacts, the analysis of the chironomid community wascomplemented with sedimentary, mineralogical and geochemical indicators (density, organicmatter, major/trace elements). By contrasting chironomid variations with temperature andprecipitation data from available meteorological models (CRU TS 4.01) for the last century,inferences to past periods are expected to be possible, enabling the development of precisepaleoclimatic and paleoenvironmental interpretations that will allow future projections in thePatagonian region.