Preliminary quantification of sediment contributions from land use sources to a natural turbid endorheic shallow lake (Barros Lake, Rio Grande do Sul, Brazil)

Shallow freshwater lakes near the coastline are often affected by sediment pollution. Sediment source fingerprinting (SSF) methods can aid catchment managers in identifying primary sediment sources that impact aquatic environments. This preliminary study aimed to estimate the contribution of sediment sources from the main land uses of a coastal catchment strongly influenced by wind and whose outlet is a eutrophic, endorheic lake with inflow from 11 affluents. The Barros Lake catchment (90 km2), located in southern Brazil, comprises grasslands (37.7%), croplands (32.2%), a mosaic of grasslands and croplands (12.4%), forests (12.6%), silviculture (3.8%), gravel mines (0.8%), and urban areas (0.5%). Two sediment sampling approaches were defined: (1) soil from land uses and (2) deposited sediments at the affluent banks. Suspended sediment samples were collected monthly from the lake between October 2021 and October 2022. Additionally, 22 geochemical elements were analyzed by ICP-OES after aqua regia digestion to select potential tracers using the three-step method of SSF in a mass balance model solved via Monte Carlo simulations. Agriculture (croplands + silviculture + grasslands) contributed 82% (± 4%) and 44% (± 10%) of the sediments for the soil and affluent source approaches, respectively, demonstrating the significant contribution of lowlands to lake sediment. The grouping method of affluent sources provided a useful alternative to soil samples when soil sources exhibitedsimilar properties. Despite the natural turbidity of the lentic water body, geochemical sediment tracing was feasible. Conservative soil management is essential for environmental protection, especially in the Pampa Biome.