The effect of agricultural intensification and water-locking on the world's largest coastal lagoonal system.

The palaeolimnological conditions of Mirim Lagoon, a large coastal shallow lagoon under the influence of historical human impacts related to the development of the primary sector of the economy were reconstructed. The first significant human impact consisted of locking the estuarine system to induce the transition from brackish to freshwater conditions. During this transition, the sedimentation rate consistently increased from pre-disturbance values of 0.25 cm yr-1 to >1 cm yr-1. A concomitant increase in nitrogen and carbon values was recorded indicating a related eutrophication process. The highest nutrient levels were achieved during the 1990s after the incorporation of cutting-edge technologies for agricultural production such as high-yielding varieties of rice resistant to climate variability and pests, and the use of inorganic fertilisers, pesticides and water supply controlled by irrigation. After 2011, the soybean production boosted and the area cultivated with this oilseed equalled the area of rice paddies, i.e., 2 × 105 ha. A sharp decrease in δ13C from -19 to -24‰ and in δ15N from 6 to 2‰ were observed in the sedimentary record, indicating a major shift in the composition of the organic matter after the agricultural intensification. Trace elements Cr, Cu, Ni and Zn showed a high positive correlation with Al and Fe, and enrichment factors near 1, indicating a natural and terrigenous source of these elements and also unpolluted conditions. However, the increase of As after 1990 and the positive correlation with Pb was associated with agricultural practices. All elemental ratios (K/Al, Ti/Al and V/Cr) showed constant pre-disturbance trends and a turning point ca. the 1990s. Microplastics were detected from the beginning of the 1990s and increased towards recent sediments, thus corroborating an anthropogenically impacted scenario. Therefore, the development of the primary sector of the economy exerted clear impacts on the environmental quality of the system.

Background levels of trace elements in brown and red seaweeds from Trindade, a remote island in South Atlantic Ocean.

Trace elements in organisms are normally higher in well-developed coastal areas than on oceanic islands. Few studies have used seaweeds as their sentinels on islands. This study established background levels of trace elements (As, Cd, Pb, Zn, Cu and Hg) for four seaweed species (Dictyopteris delicatula and Canistrocarpus cervicornis, brown algae; Ceratodictyon variabile and Palisada perforata, red algae) from Trindade, an oceanic Brazilian island, and verified potential differences associated to distinct environmental conditions. Spatial differences were not detected for As, Hg and Cd in samples, although the highest concentrations of these elements were observed in brown seaweeds. The highest Zn, Pb and Cu concentrations in seaweeds from the only inhabited beach may be a signal of the onset of human footprints on this still pristine, remote island. By comparison with background described in the literature, concentrations of trace elements in seaweeds were low, thus, allowing them to be considered reference levels.

Accumulation and elimination of trace metals in a transplantation experiment with Crassostrea rhizophorae.

Oysters, Crassostrea rhizophorae, were reciprocally transplanted to two different sites: a contaminated site in the Cotegipe Channel at Aratu Bay and an uncontaminated site at Cacha-Prego, inside and outside of Todos os Santos Bay (Brazil), respectively. Trace metal accumulation was measured after 0, 15, 30, and 60 days of exposure at the contaminated site. Oysters transplanted for 60 days from the clean to the contaminated site had accumulated cadmium and lead to similar concentrations as found in the native oysters. They had also accumulated copper and zinc, but to lower levels compared to native specimens. Elimination experiments were carried out by transplanting oysters in the reverse direction. After 30 days, concentrations of cadmium and lead had decreased to levels comparable to those in the native specimen, whereas concentrations of copper and zinc did not diminish. A second elimination experiment, bringing back to Cacha-Prego oysters that had been exposed 60 days at Cotegipe Channel, indicated stronger decreases of copper and lead, but no clear changes of cadmium and zinc concentrations. The accumulation experiment with C. rhizophorae is useful to estimate trace metal bioavailability and changes in concentrations as a function of time at the contaminated site. The different results of elimination experiments in the uncontaminated site suggest different degrees of trace metal fixation after long-term and short-term accumulation periods.