Disentangling the evolution of trophic state of San Roque reservoir (Córdoba, Argentina) by paleolimnological reconstruction

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

Congreso; IAL IPA 2022; 2022

IAL e IPA

Paleolimnology has become a valuable tool for assessing the environmental degradation sufferedby reservoirs during the last decades. Water quality in reservoirs of central Argentina has beenaffected by the progressive eutrophication as a consequence of the land use change and climaticvariability. The San Roque reservoir (SRr; 31° 22’ S, 64° 27’ W) has reached a hypereutrophicstate 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-21stcentury 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 thereservoir when anthropic activity was low. Stage 2 (1958–1978 CE) includes a volume increaseof 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 inthe 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 littoralzone of the reservoir. SRr environmental reconstruction indicates that the system has beenimpacted by multiple factors: a) structural modifications (e.g., changes in the base level by thesecond 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 resultsmostly highlight that the generalized degradation of SRr water quality has been promoted by thesynergistic action of anthropic and natural forcing. These results can provide tools for modelingfuture scenarios and improving watershed management policies.