Water quality assessment using sediment analysis and Sentinel-3-derived bio-optical variables in Lagoa da Conceição, Brazil.

Growing anthropogenic pressure on aquatic environments has intensified processes of water quality degradation; compromising ecosystems, the health and wellness of populations that depend on natural resources, and associated economic activities. This study aims to assess the water quality of Lagoa da Conceição, in Florianópolis, SC, Brazil, through two distinct and complementary approaches; the evaluation of potentially toxic chemical elements in nanoparticles (NPs) and ultrafine particles present in aquatic sediments collected between 2024 and 2025, and the analysis of the variables chlorophyll-a (CHL), total suspended matter (TSM), and absorption of dissolved organic matter at 443 nm (ADG443), obtained from Sentinel-3A/B OLCI satellite imagery between 2019 and 2025. Methodologically, aquatic sediments were collected at 18 sites across Lagoa da Conceição for the analysis of NPs and ultrafine particles. In parallel, the CHL, TSM, and ADG443 variables were retrieved from Sentinel-3A/B satellite imagery at 153 points processed in the Sentinel Application Platform (SNAP), with the resulting data subjected to K-means clustering and robust ANOVA to identify geospatial patterns. As a result, sediment analyses identified iron (Fe) nanoparticles containing up to 60% carbon, frequently associated with chromium (Cr), nickel (Ni), vanadium (V), zinc (Zn), and zirconium (Zr), in addition to the presence of plastic nanoparticles. Concurrently, the bio-optical variables of the water column exhibited elevated values of CHL (7.187 mg/m3), TSM (17.213 g/m3), and ADG443 (5.555 m⁻1) over the 2019-2025 period. The geospatial patterns obtained through K-means clustering revealed moderate-to-high concentrations of these indicators within the interior of Lagoa da Conceição and significantly lower values in the adjacent coastal areas. Taken together, these two distinct and complementary approaches provided evidence of water quality degradation in the study area.