Deciphering the intricate link between watershed-level land use changes and reservoir eutrophication in central Argentina over the 20th-21st century

In Anthropocene, unbalances of the water cycle have created a severe threat to the supply of this crucial element for current and future generations. In addition, water quality degradation has been promoted by the land-use change from natural ecosystems to urbanized and industrialized areas, favoring the nutrient input into water bodies. In the last two decades, the San Roque reservoir (SRr), situated in central Argentina, has become hypereutrophic. In this work, we proposed an integrated study strategy that included a multiproxy examination of the reservoir sedimentary record and a study of land-use changes, in order to: 1) link land-use change to primary productivity of the SRr over the last 100 years; and 2) identify the processes involved in the SRr's environmental evolution prior and after urban expansion occurred by 1980 CE. Results allow to recognize two distinctive scenarios: a) Pre-urban scenario (1898–1983 CE) reflected by a dominance of allochthonous organic matter in the sedimentary record derived from the catchment's deforestation and, b) A transition towards increasing lake internal productivity (1984–2018 CE), resulting in a eutrophic state with cyanobacteria dominance due to catchment urban densification, particularly in the peri-lacustrine area. This work constitutes a novel tool by combining a paleolimnological approach with demographic analysis to accurately track the consequences of land use change on the water body and, in addition, provide the basis for modeling future scenarios.