Espinoza, J.M.A.; Alves, D.C.L.; Sales, D.A.; Albuquerque, M.G.; Espinoza, T.A.; Gonzaga, B.A.; Façanha, M., and Moreira, J., 2024. Monitoring water quality in coastal lagoons using orbital sensors: Case study for the north coast of Rio Grande do Sul, Brazil. In: Phillips, M.R.; Al-Naemi, S., and Duarte, C.M. (eds.), Coastlines under Global Change: Proceedings from the International Coastal Symposium (ICS) 2024 (Doha, Qatar). Journal of Coastal Research, Special Issue No. 113, pp. 569-573. Charlotte (North Carolina), ISSN 0749-0208.

Coastal lagoons can be defined as ecosystems surface aquatic species that develop at the interface between ecosystemscoastal terrestrial and marine. These may be permanently open or intermittently closed from the adjacent sea by deposition barriers. Coastal lagoons cover about 12% of the coast of North America.South and more than 40% of the coast of Rio Grande do Sul, Brazil. Due to the advancement of anthropogenic pressureson water resources, monitoringof changes in water quality with the aim of preventing pollution from compromising the useintegrated of these resources. Monitoring them is essential and requires the increasing use of instruments and technologies. However, costs make rapid monitoring with effective environmental protection unfeasible. This work presents a methodology for monitoring these water resources, aimed at analyzing the water quality of a set of coastal lagoons on the coast of Rio Grande do Sul, Brazil. Images from the MSI sensor on board the Sentinel-2 satellites were used and two indices were derived as indicators of water quality: (a) Total Suspended Solids - TSS and (b) Dissolved Organic Matter - DOM-Chl. The years 2022/2023 were monitored. The results demonstrate a low dispersion in TSS values in this period (2.53≤σ≤4.62), with the 2023 values showing greater amplitude (∼ 38.5 mg.L-1) and standard deviation (σ=4.16) compared to the results of 2022. However, in 2023 we observed a TSS plume concentrated near the bridge in the north area. This variation can be attributed to the water deficit in the summer of 2022/2023, resulting in discharge values lower than the historical regime. The DOM-Chl results showed values with small amplitude (0.43 – 1.25 mg.L-1) with the plume distribution similar to the TSS. The derived TSS and DOM-Chl maps provide a low-cost management resource, offering new tools for monitoring coastal environments.