Guanabara Bay Brazil Research Articles

Microbial community shift under exposure of dredged sediments from a eutrophic bay.

Microbial communities occur in almost every habitat. To evaluate the homeostasis disruption of in situ microbiomes, dredged sediments from Guanabara Bay-Brazil (GB) were mixed with sediments from outside of the bay (D) in three different proportions (25%, 50%, and 75%) which we called GBD25, GBD50, and GBD75. Grain size, TOC, and metals-as indicators of complex contamination-dehydrogenase (DHA) and esterase enzymes (EST)-as indicators of microbial community availability-were determined. Microbial community composition was addressed by amplifying the 16S rRNA gene for DGGE analysis and sequencing using MiSeq platform (Illumina).We applied the quality ratio index (QR) to the GB, D, and every GBD mixture to integrate geochemical parameters with our microbiome data. QR indicated high environmental risk for GB and every GBD mixture, and low risk for D. The community shifted from aerobic to anaerobic profile, consistent with the characteristics of GB. Sample D was dominated by JTB255 marine benthic group, related to low impacted areas. Milano-WF1B-44 was the most representative of GB, often found in anaerobic and sulfur enriched environments. In GBD, the denitrifying sulfur-oxidizing bacteria, Sulfurovum, was the most representative, typically found in suboxic or anoxic niches. The canonical correspondence analysis was able to explain 60% of the community composition variation and exhibit the decrease of environmental quality as the contamination increases. Physiological and taxonomic shifts of the microbial assemblage in sediments were inferred by QR, which was suitable to determine sediment risk. The study produced sufficient information to improve the dredging plan and management.

Geohabitats characterization in areas of dredge sediment disposals on Rio de Janeiro continental shelf, adjacent to Guanabara Bay: Brazil

Disposal of dredged sediments from harbor areas is often carried out without prior characterization and diagnosis of the benthic ecosystem and its relationships with the physical environment. Geohabitats studies contribute to this previous characterization, showing how geological and geomorphological features are associated with the benthic ecosystems of a given location. To investigate these relationships, acoustic geophysical methods (echobatimetry, sonography, and high-resolution seismic) and direct observation methods (underwater video and geological sampling) were used in two distinct areas on the Rio de Janeiro continental shelf, adjacent to Guanabara Bay: Area I (degraded with dredging disposal) and Area II (control, without disposal). After the acquisition, processing, and integrated data interpretation, it was possible to determine 5 (five) classes of geohabitats: class I, areas with high acoustic reflectivity, with little or any presence of benthic organisms, under the direct influence of discarded material; class II, areas of high acoustic reflectivity, with predominance of quartzose sand mixed with calcareous fragments (shells), with abundance and diversity of benthic organisms; class III, areas of very high acoustic reflectivity (backscattering), with high abundance and diversity of benthic organisms, indicative of semi-consolidated seafloor (articulated algal “reefs”); class IV, areas with high acoustic backscattering, with strong presence of bed forms (megaripples), associated with the quartzose sand; and class V, areas of low acoustic reflectivity, with sand-muddy textures, low abundance, and relative diversity of benthic organisms. It was verified that the use of these noninvasive GEOHAB techniques had an excellent correlation between the obtained results and proved to be an important tool for the characterization of Geohabitats in areas of dredge sediment disposals on Rio de Janeiro continental shelf, adjacent to Guanabara Bay—Brazil.