Possible Amazonian contribution to Sargassum enhancement on the Amazon Continental Shelf.

The Amazon Continental Shelf (ACS) has a coastline of ∼1000 km and is situated in a humid equatorial region with two distinct seasons, wet and dry, and two transitional climatic periods. A total of eight oceanographic cruises were conducted to investigate the dynamics of the inorganic nutrients dissolved in the surface layer of the water column of the ACS and their associations with Sargassum blooms. An excess of nitrogen-N* (NH4+ = 0.01-9.30 µmol l-1) was verified through the salinity gradient from the continent to the ACS, mainly during the period of maximum discharge of the Amazon and Tocantins-Pará rivers. The highest NH4+ concentrations coincided with the occurrence of macrophyte (Sargassum sp.) blooms in the mesohaline and oceanic regions. During this period the high values of NH4+ accompany the low values of Sea Surface Salinity (SSS), indicating the advection of the Amazonian plume towards the Caribbean Sea. In the Sargassum belts we observed a N:P ratio = 60:1 during wet period, while outside this region, the N:P ratio was 34:1. According to DIN vs. AOU ratio, we observed that heterotrophic processes prevail over productive processes, mainly in the mesohaline and low salinity regions. Nitrogen concentrations from runoff, mainly from hydrographic basins, showed significant increases in the last decade, mainly due to anthropogenic factors such as agriculture, deforestation, livestock, urban sewage (domestic and industrial), and demographic growth of the population in the Tocantins-Pará Basin. Additionally, associations of diatoms and cyanobacteria provide more nitrogen in the mesohaline and oceanic regions that nourishes Sargassum blooms. Seasonal comparisons (October and April) of Sargassum belts with other studies, indicated that currents play a fundamental role in the transport of these macrophytes from the east edge (Africa) to the west edge (Brazil and French Guiana) towards the Caribbean Sea in the tropical Atlantic.

First assessment of microplastic and artificial microfiber contamination in surface waters of the Amazon Continental Shelf.

The composition and distribution of microplastics (MPs) in the Brazilian Amazon Continental Shelf surface waters are described for the first time. The study was conducted during the 2018 rainy and dry seasons, using 57 water samples collected with aluminum buckets and filtered through a 64-µm mesh. The samples were vacuum-filtered in a still-air box, and the content of each filter was measured, counted, and classified. A total of 12,288 floating MPs were retrieved; particles were present at all 57 sampling points. The mean MP abundance was 3593 ± 2264 items·m-3, with significantly higher values during the rainy season (1500 to 12,967; 4772 ± 2761 items·m-3) than in the dry season (323 to 5733; 2672 ± 1167 items·m-3). Polyamides (PA), polyurethane (PU), and acrylonitrile butadiene styrene (ABS) were the most common polymers identified through Fourier Transform Infrared Spectroscopy (FTIR) analysis. Cellulose-based textile fibers were also abundant (~40%). Our results indicate that the Amazon Continental Shelf is contaminated with moderate to high levels of MPs; the highest abundances were recorded at stations near land-based sources such as river mouths and large coastal cities.

Long-term water quality conditions and trends in 12 tropical coastal rivers in Northeast Brazil.

The water quality and trends in 12 tropical rivers in northeastern Brazil over a 27-year period (1990-2016; N = 39,008 samples) were evaluated. The analyzed parameters included temperature, conductivity, pH, dissolved oxygen (DO), biochemical oxygen demand (BOD), nitrogen (NH4+), total phosphorus (P), and fecal coliforms. Densely populated basins (> 1000 inhab km-2) presented lower DO values (average 3.4 mg l-1; 43% DO saturation), while those with low demographic density (< 100 inhab km-2) presented values that aligned well with the recommendations of environmental legislation (average 5.8 mg l-1; 75% DO saturation). The NH4+ and P compound concentrations were typical of water bodies affected by urban inputs. The average p values were above the allowable limit (< 0.1 mg l-1) at all stations. The NH4+ values were high at the stations showing low DO concentrations, which suggested that due to reducing conditions after NH4+ accumulation was favored in those aquatic systems. In densely populated basins, the average fecal coliform concentrations were > 40,000 MPN 100 ml-1, indicating the input of improperly treated domestic/industrial liquid wastes. For the period from 1990 to 2016, 45% of the stations (N = 19) showed a rate of DO reduction that ranged from 0.01 to 0.17 mg l-1.O2 year-1. An increase in NH4+ concentrations was observed in 33% of the stations (N = 14), with an estimated average increase rate from 0.013 to 1.8 mg l-1 NH4+ year-1. These results demonstrated that the rates of increase in anthropogenic factors were significant (p < 0.05), while the natural factors remained constant.

Spatial distribution of butyltins and imposex in eastern Brazilian Amazon.

Spatial distribution of Butyltins (BTs) in surface sediments and gastropod tissues were quantified, with samples taken from an estuarine system of the Eastern Amazon, Brazil. The imposex incidence was also assessed using Thaisella coronata (Gastropoda, Mollusca). The sediment sampling was carried out at 19 sites and T. coronata in 6 of those. The highest BTs levels were detected in sediments of a Marine Extractive Reserve (27.1 ng Sn g-1) and in an urban area (19.8 ng Sn g-1). In T. coronata tissues, BTs levels ranged from <5 to 142 ng Sn g-1. Imposex incidence ranged from 0% to 100% and VDSII (penile papillae) was registered in gastropods from 5 out of 6 sampled sites. The results suggest that BTs concentrations are related to sampled area use, but also to the local hydrodynamics, highlighting the importance of an effective control in the use of TBT-based antifouling paints in the Eastern Amazon.