Abstract Cyanobacterial blooms are a potential threat to human communities and ecosystems. Since the late 1980s, researchers have reported harmful cyanobacterial colonies in Patos Lagoon (PL), the largest coastal lagoon in South America. Most studies concerning harmful blooms in PL have focused on its biology and on its southernmost estuarine region, with little information about its displacement inside the lagoon and the influence of physical forces on its dynamics. This study uses satellite-derived information (normalized difference chlorophyll-a index – NDCI), river discharge data, and meteorological data (wind speed and direction, rainfall, and air temperature) to analyze two bloom episodes in PL, during the austral summer of 2019/2020, specifically in its larger, limnic portion. A 30-year meteorological time series was used to contrast the same summer period. Two remote sensing images from Sentinel-2 were taken of PL margins, near their central portion. The summer of 2019/2020 was drier when compared with the historical data, characterizing low river discharge. This environmental condition was coupled with high temperature, which implies thermal stratification in summer even at 2-m depth sites, which might have promoted cyanobacterial growth and accumulation inside PL. Moreover, weak winds (<<6 m s−1) seemed to accumulate cyanobacterial patches on the water surface, including after vertical mixing caused by strong winds (>6 m s−1). The NDCI values represented the two days of blooms, with higher values occurring under higher water temperatures and low wind speeds.

OBJETIVO: Avaliar a qualidade da água de três lagos presentes em uma área abandonada de mineração de carvão. MÉTODOS: Foram amostrados em perfil três lagos presentes na bacia de drenagem do rio Morozini (Treviso, Santa Catarina, Brasil), com coletas em duas épocas do ano (fevereiro - verão e julho - inverno). RESULTADOS: De maneira geral, os três lagos estudados apresentaram elevadas concentrações de SO4-2, Mg, Fe, Al, Ca, Ba, Si, Zn, Ni, Na, K, Sr, B, Cd, Cr, Pb e Cu. CONCLUSÕES: Esta pesquisa sugere que a atividade de mineração e a prática de disposição de rejeitos adotada pelas companhias de mineração afetaram drasticamente a qualidade da água dos lagos estudados, tornando-os inapropriados a diversos usos humanos, tais como lazer, pesca e natação.

AIM: To assess water quality of three lakes located in an abandoned coal mining area, in the Morozini River basin (Treviso, Santa Catarina State, Brazil). METHODS: The study sites were three lakes mining pits flooded after deactivation, near the drainage basin of the Morozini River (Treviso City, Santa Catarina State, Brazil). Samplings were carried out in profile in the limnetic region during two seasons (Summer in February and Winter in July). RESULTS: In general, the three lakes showed high concentrations of SO4-2, Mg, Fe, Al, Ca, Ba, Si, Zn, Ni, Na, K, Sr, B, Cd, Cr, Pb and Cu. CONCLUSIONS: Coal mining activity and waste disposal practices adopted by the mining companies in the Morozini River basin have drastically affected the water quality of the examined lakes and made them inappropriate for diverse human uses, such as leisure, swimming and fishing.