Spatial distribution and temporal trends of butyltin compounds (TBT, DBT & MBT) in short sediment cores of the SW Portuguese Shelf (western Iberian Margin, NE Atlantic).

Spatial patterns and temporal trends of the butyltin compounds tributyltin (TBT), dibutyltin (DBT), and monobutyltin (MBT) were investigated in a set of sediment samples collected along the SW Portuguese continental shelf. This region did not reach the Good Environmental Status (GES) in accordance with the Marine Strategy Framework Directive (MSFD) during a first evaluation carried out in 2012. Overall, MBT and DBT were the predominant organotin species detected, but high concentrations of TBT were found in and around disposal sites for dredge sludge derived from the dredging in navigation channels, harbours, and shipyard facilities of the Tagus and Sado estuaries. Although Portuguese regulations for monitoring sediment quality in relation to dredging activities consider only PAH, PCB and HCB, they also dictate that other organic contaminants such as butyltin compounds (BTs) should be monitored if suspicion of high values exists, but no action limits are defined for these (MAOTDR, 2007). Without action limits, the monitoring recommendation given in the regulations is not put into practice. Considering their toxicity, BT derivates should be integrated in the legislation, because they represent an environmental threat in the relocation of dredged material, especially when derived from harbour and shipyards areas. Based on this study, we recommend giving more attention to the amounts and impacts of BTs in sediments at dredged material disposal sites (DMDS) and their surroundings. Or even better, in order to be more efficient, monitoring should be done at the source of the dredged materials and not at the sink. In case it is not done, the monitoring of concentrations of TBT (and other BTs) in sediments and organisms, including imposex studies, at all Portuguese sites for disposal of dredged material receiving slightly to strongly contaminated dredged material must be developed.

Influence of diagenetic processes and terrestrial/anthropogenic sources in the REE contents of the Cascais submarine canyon (Iberian western coast).

Temporal variations of rare earth elements (REE) and their fractionation patterns, major elements, Pb and Hg were determined in two multicores collected at 445 and 2100 m water depth (mwd) in the Cascais submarine canyon (CSC). The PAAS-normalized REE patterns suggest mixing of Tagus estuarine and marine sediments, marked by MREE (Nd-Dy series) enrichment and by positive Eu-anomaly, with marine sediments. The positive Eu/Eu* implies incorporation of detrital feldspar minerals derived from the estuary. Ce/Ce*, (La/Yb)PAAS and (Nd/Yb)PAAS show differences between the two cores. Core 252-35 from the shallower site is enriched in HREE (Ho-Lu series) over LREE (La-Pr series), a pattern also found in the Tagus estuary in the vicinity of an abandoned chemical complex, where the environment is affected by the legacy of massive-sulfide ores processing. There seems to be only limited down-canyon sediment transport to the deeper reaches where core 252-32 was collected. This deeper site shows Ce/Ce* peaks coinciding with low (La/Yb)PAAS values suggesting preferential diagenetic remobilization of LREE relative to HREE. Upcore Pb/Al and Hg/Corg trends observed in both cores indicate dispersion of the anthropogenic component from the estuary through the CSC, which is less obvious from the ∑REE/Al trends particularly in the deeper site. This may suggest the influence of diagenetic processes in the REE signal, associated with relatively low sediment accumulation rates.

Heavy metal pollution in a reforested mangrove ecosystem (Can Gio Biosphere Reserve, Southern Vietnam): Effects of natural and anthropogenic stressors over a thirty-year history.

In order to assess the impact of recent industrialization and land-use changes in the Can Gio Mangrove Forest, a Biosphere Reserve in Southern Vietnam, we analyzed heavy metal (HM), total organic carbon (TOC) and total nitrogen (TN) concentrations in a 210Pb-dated sediment core, allowing for the environmental reconstruction of the last three decades. C/N ratios were very high (>20) until ~1990, reflecting highly refractory organic matter. Sediment Quality Guidelines (SQG's) violations were observed particularly after the establishment of industries in the area in the late-1990s. Chromium (Cr) and copper (Cu) exceeded the threshold effect levels (TEL); whereas nickel (Ni) was above the probable effects level (PEL), identifying the risk of potential adverse biological effects. Moderate contamination, mainly from cobalt (Co) and lead (Pb), was detected by the contamination factor (CF) index, with Pb levels likely originating from mainly anthropogenic sources, particularly after ~1992, as indicated by elevated enrichment factor (EF) values. A high positive correlation was found between Pb, Cr, Cu and Ni (r ≥ 0.8), while Co, cadmium (Cd) and TOC were highly positive correlated (r = 0.9). We identified evidence of point sources, atmospheric pollution and erosion as the main contributors to enhanced HM levels. However, negative values of the Geo-accumulation index (I-geo) indicated uncontaminated sediments. This discrepancy in pollution indices was likely due to the use of shale averages instead of regional levels as background values, as well as the influence of multiple stressors.

The hidden threat of heavy metal pollution in high sedimentation and highly dynamic environment: Assessment of metal accumulation rates in the Thi Vai Estuary, Southern Vietnam.

Paleoecological assessment is challenging in highly dynamic environments such as estuaries, where sedimentation of material derived from the catchment interferes with marine processes. In this study we analyzed sedimentary heavy metal contents of the last decades to assess the impact of recent industrialization and changes in land use of the Thi Vai Estuary in Southern Vietnam. Two sediment cores (upstream and downstream) were dated using 210Pb, allowing the environmental reconstruction of the last three decades. Considering the recent and fast economic growth of this region these results are suitable for the evaluation of anthropogenic impacts. Mean sedimentation rates (9.2 cm yr-1 upstream, 4.7 cm yr-1 downstream) indicate high land erosion likely due to deforestation and dumping of dredged material. Sediment quality guidelines (SQG's) showed that Cr and Cu levels exceed threshold values (TEL) in both cores. Upstream Ni is above the probable effect level (PEL) suggesting risk of potential adverse biological effects. Geo-accumulation (I-geo), enrichment factor (EF) and contamination factor (CF) indices were calculated based on geogenic background values. Most indices show only moderate contamination for different elements, particularly by Cr and Pb. However, considering the historical land use impacts (such as discharge of untreated wastewater, intense agricultural practices, tanning operations, etc.), pollutant concentrations are lower than expected, presumably due to dilution by high sedimentation rates and tidal hydrodynamics. Nonetheless, heavy metal indices and SQG's indicate the ecological condition in the area is of concern, particularly upstream as corroborated by high metal fluxes, highlighting severe impacts in the region.

Internal wave turbulence at a biologically rich Mid-Atlantic seamount.

The turbulence regime near the crest of a biologically rich seamount of the Mid-Atlantic Ridge southwest of the Azores was registered in high spatial and temporal resolution. Internal tides and their higher harmonics dominate the internal wave motions, producing considerable shear-induced turbulent mixing in layers of 10-50 m thickness. This interior mixing of about 100 times open-ocean interior values is observed both at a high-resolution temperature sensor mooring-site at the crest, 770 m water depth being nearly 400 m below the top of the seamount, and a CTD-yoyo site at the slope off the crest 400 m horizontally away, 880 m water depth. Only at the mooring site, additionally two times higher turbulence is observed near the bottom, associated with highly non-linear wave breaking. The highest abundance of epifauna, notably sponges, are observed just below the crest and 100 m down the eastern slope (700-800 m) in a cross-ridge video-camera transect. This sponge belt is located in a water layer of depressed oxygen levels (saturation 63±2%) with a local minimum centered around 700 m. Turbulent mixing supplies oxygen to this region from above and below and is expected to mix nutrients away from this biodegraded layer towards the depth of highest abundance of macrofauna.

The role of transport processes of particulate mercury in modifying marine anthropogenic secondary sources, the case of Haifa bay, Israel.

We have assessed the redistribution of a secondary source of sedimentary anthropogenic mercury in the Haifa bay (HB) area (SE Levantine basin), which is the northern sink for Nile-driven sand. A long-term (30years) ~80% decrease of the total sedimentary mercury concentrations (THg) was recorded in the inner bay, while an up to 3-fold increase was recorded in the top sediments of the outer bay. Sedimentary THg depth profiles and their temporal variability were used to model the main re-distribution processes, mainly resuspension associated with winter storm-derived transport. This mechanism transforms a secondary, sandy and well-aerated sink into a tertiary, more silty and hypoxic source at adjacent peripheral areas, affecting mercury bioavailability. We revisited the concept of environmental relaxation, i.e. the rate of return of a polluted environment to an acceptable state, showing that sedimentary transport processes may affect the associated ecological risks, mainly at shallow-water coastal sites.

Temporal evolution of lead isotope ratios in sediments of the Central Portuguese Margin: a fingerprint of human activities.

Stable Pb isotope ratios ((206)Pb/(207)Pb, (208)Pb/(206)Pb), (210)Pb, Pb, Al, Ca, Fe, Mn and Si concentrations were measured in 7 sediment cores from the west coast of the Iberian Peninsula to assess the Pb contamination throughout the last 200 years. Independently of their locations, all cores are characterized by increasing Pb/Al rends not related to grain-size changes. Conversely, decreasing trends of (206)Pb/(207)Pb were found towards the present. This tendency suggest a change in Pb sources reflecting an increased proportion derived from anthropogenic activities. The highest anthropogenic Pb inventories for sediments younger than 1950s were found in the two shallowest cores of Cascais and Lisboa submarine canyons, reflecting the proximity of the Tagus estuary. Lead isotope signatures also help demonstrate that sediments contaminated with Pb are not constrained to estuarine-coastal areas and upper parts of submarine canyons, but are also to transferred to a lesser extent to deeper parts of the Portuguese Margin.