Effects of dredging activities and seasonal variation on coastal plankton assemblages: results from 10 years of environmental monitoring.

Coastal zones support the most productive marine ecosystems, yet they are increasingly threatened by anthropogenic stressors such as dredging. In this study, we investigated how seasonal variation and dredging activities conducted during the construction of a harbor and submarine base (Sepetiba Bay, RJ, Brazil) affected the phytoplankton and zooplankton assemblages. The observed temporal variability at five different sites over 10 years revealed that dredging exceeds the expected influence of dry and rainy seasons on plankton abundance and diversity. In general, the abundance of both groups increased during dredging due to the resuspension of nutrients and benthic organisms. This increase was particularly evident in the dinoflagellate Scrippsiellaa cuminata, the diatoms Thalassiosira rotula and Nitzschia longissima, and the herbivorous zooplankton Acartia clausii and Pseudevadne tergestina. Moreover, season and dredging activities synergistically influenced plankton assemblages, resulting in larger seasonal variations during dredging activities. After the end of the harbor construction, plankton abundance decreased and remained low until the end of the monitoring, which may indicate persistent changes in the biodiversity and ecosystem functioning of impacted areas.

Chronic oil spills revealed by the most important set of samples from the incident in northeastern Brazil, 2019.

In 2019, an oil spill of unprecedented dimensions and unknown source reached the Brazilian coast. Such incident, which occurred somewhere in the ocean and was detected only when the first oil patches reached the beaches in the northeastern region, is recognized as one of the most serious oil spills in the country. From the chromatographic analysis of the oily residues using n-alkanes, polycyclic aromatic hydrocarbons (PAH), and oil biomarkers, it was possible to characterize their coverage. The results confirmed that an oil of the same specification reached a length of coastline higher than 3,000 kilometers. However, were also found oily residues that did not match with the product involved in that incident, evidencing the occurrence of different discharges. This study documents the extension of the affected coastline during the incident and assesses the possible origin of such different oils from their geochemical characteristics by selecting 21 samples from more than 300 samples previously collected and analyzed during the response actions. The unexpected occurrence of these residues suggest chronic events. The results highlighted that unrelated oily residues were found even in a region far from the coast, indicating that discharges of oil in the open sea occur more regularly than initially expected.