Accumulation patterns of rare earths and other elements in coastal lake sediments under different land uses

Abstract

The elemental composition of sediments can provide valuable records of environmental changes, including land-use impacts. This study evaluates the role of major, trace, and rare earth elements (REE) in sediment cores from three coastal lakes in southern Brazil which have been influenced by varying land-use pressures. These differing influences range from intensive agriculture to near-pristine wetlands. Using Instrumental Neutron Activation Analysis, we quantified 25 elements in dated sediment cores and calculated enrichment factors (EF) to differentiate natural from anthropogenic contributions. The La-Sc-Th ternary diagram was employed to trace sediment provenance. Our results revealed contrasting impacts of land-use changes. Mirim Lagoon showed barium enrichment which was previously attributed to coal mining and combustion, while Mangueira Lagoon exhibited increased REE concentrations post-1950, likely linked to the use of agricultural fertiliser. Nicola Lake, by contrast, demonstrated minimal anthropogenic influence. Sediment dilution and resuspension in larger systems, such as Mirim Lagoon, mitigated observable changes despite intense land-use activities. These findings highlight the distinct responses of lake systems to land-use pressures, providing insights into their sedimentary dynamics and potential for environmental monitoring.