The past and present role of fires on sedimentary dynamics in a central Argentina reservoir: A two centuries paleolimnological reconstruction

Abstract

A multi-proxy, spatial-temporal analysis of the fluvial catchment and sedimentary record from the San Roque Reservoir (SRr; Cordoba, ´ Argentina) over the last ca. 170 years, reveals the close interaction between fires, erosion, and sedimentary fluxes. Sedimentological characteristics and physical and geochemical proxies were integrated with the charcoal record to decipher the interplay between catchment disturbances and reservoir sedimentary dynamics. Sediment composition is mainly influenced by the Achala batholith, with coarser clastic deposits near-river mouths reflecting textural control and fluvial competence while pelagic sedimentation and inner-lake processes dominate in the central-lake domain. The charcoal record reveals that fires are strongly linked to increased clastic inputs derived from post-fire erosion.The environmental evolution based on multi-proxy analyses of SRr reveal a progressive transformation due to landscape anthropization driven by the conversion of wetland into a reservoir which has been significantly influenced by land-use changes and disturbances in the catchment. The environmental trajectory over the time includes four phases: (i) Fluvial wetland (1850–1870 CE): the depression functioned as a wetland with recurrent flooding and riverine influences, with high clastic and organic inputs derived from deforestation and fire events, (ii) Onset of reservoir infilling (1870–1950 CE): represents the transition to a lacustrine system. Fires, deforestation and structural changes enhanced clastic and organic inputs, (iii) Stabilized lacustrine system (1950–2006 CE): the system functioned as a lacustrine environment, with increasing dominance of pelagic sedimentation over coarser fluvial influence and (iv) Hypereutrophic lake with episodic erosion events (2006–2022 CE): reservoir sedimentation is primarily driven by inner-lake processes with episodic clastic inputs linked to fire activity in the catchment.The environmental reconstruction provides a long-term perspective that is useful for reservoir management and for highlighting the critical role that land-use changes and fires play in the environmental condition of aquatic systems in general.