Disentangling the evolution of trophic state of San Roque reservoir (Córdoba, Argentina) by paleolimnological reconstruction and land-use history

MENGO LUCIANA; HALAC SILVANA; COSTAMAGNA INGRID; FORAY GABRIELA; LOIZEAU JEAN LUC; DEON JOAQUIN; CHIAVASSA SERGIO; PIOVANO EDUARDO

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

INTERNATIONAL ASSOCIATION OF LIMNOGEOLOGY and INTERNATIONAL PALEOLIMNOLOFY ASSOCIATION

Paleolimnology has become a valuable tool for assessing the environmental degradation suffered by reservoirs during the last decades. Water quality in reservoirs of central Argentina has been affected by the progressive eutrophication as a consequence of the land use change and climatic variability. The San Roque reservoir (SRr; 31° 22? S, 64° 27? W) has reached a hypereutrophic state in the last two decades. Multi-proxy analyses (MS, grain size, TOC, TIC,P, fossil pigments) of the paleolimnological record of radiodated sediment cores allow to reconstruct the 20th-21st century environmental history of the SRr and the identification of four main environmental stages.The record of stage 1 (1914?1958 CE) can be considered as the environmental base level of the reservoir when anthropic activity was low. Stage 2 (1958?1978 CE) includes a volume increase of SRr, due to a second dam construction, while the trophic state remained low. Stage 3 (1978?2000 CE) is characterized by an increase in the internal primary production (eutrophic state), mainly caused by anthropic input of nutrients (e.g., sewage effluents) due to urban expansion in the SRr river watershed. Stage 4 (2000?2018 CE) corresponds to the highest trophic scenario, which has led to hypereutrophic conditions associated with increased urbanization in the littoral zone of the reservoir. SRr environmental reconstruction indicates that the system has been impacted by multiple factors: a) structural modifications (e.g., changes in the base level by the second dam construction) and b) land use changes (e.g., increase in nutrient load). In addition, precipitation increase after the 70s is an additional factor affecting eutrophication. Our results mostly highlight that the generalized degradation of SRr water quality has been promoted by the synergistic action of anthropic and natural forcing. These results can provide tools for modeling future scenarios and improving watershed management policies.