RESUMO
N. Mirlean, L. Calliari, and K. Johannesson examined the REE paired La/Eu and Gd/Yb ratios in the region of Patos Lagoon estuary/Brazil and related coastal waters. They concluded that "the mud deposition events at the beach were most likely associated with dredging processes in the estuary especially where overflow is the source of fluid mud on the beach shoreface". In this response to that study, we reflect on several discrepancies in their methods, results and conclusions. In this work, we demonstrate that the approach adopted by the authors does not provide evidence that the selected REE ratios measured on muddy deposits on the beach were derived from dredged activities, particularly regarding overflow. On the contrary, based on their results, the REE ratios presented in the suspended sediments collected in the navigation channel are most likely associated to natural sediments.
Assuntos
Monitoramento Ambiental , Estuários , Brasil , Poluição Ambiental , Sedimentos GeológicosRESUMO
Deposits of fluid mud on wave-dominated beaches are rare. Where they happen frequently and periodically, they can be associated with anthropic processes that bring fluid mud to the shoreface and surf zone. To determine the reason for the frequent deposition of fluid mud at Cassino Beach (Southern Brazil) in the 2014-2020 period, the La/Eu and Gd/Yb ratios in marine, beach, and adjacent Patos estuary sediments were investigated. Mud from the beach showed similar ratios of REE to dredged sediments from the harbor basin and navigation channel within the estuary. Industrial and port activity changes REE ratio in sediments of the navigation channel, and they are distinct from naturally deposited marine and estuarine sediments. We conclude that the mud deposition events at the beach are most likely associated with dredging processes in the estuary especially where overflow is the source of fluid mud on the beach shoreface.