Search

Abstract Trace element (As, Co, Cr, Cu, Ni, Pb, V and Zn) enrichment trends during the past century, were assessed in thirteen 210Pb-dated sediment cores from the southern Gulf of Mexico, with the purpose to evaluate the impact on the environment, and potentially on public health, of the offshore oil industry and of oil spills such as that of the Ixtoc1 well blowout in 1979. The trace element composition was quite homogeneous among cores; and the pre-industrial concentrations of Ba, Cr, Cu and Ni are naturally high in the region, as to reach levels of potential ecological concern. The influence of multiple and simultaneous processes (e.g. industrial activities, natural seeps, fluvial discharges) on the trace element concentrations is difficult to disentangle. Some cores suggested long-term preservation of putative oil spill traces, although it was not possible to attribute their origin. The Al-normalized redox element ratios, and the crude oil contamination ratio, suggested that these events occurred along almost four decades, and that the traces attributed to the Ixtoc1 spill were comparable to background conditions, most likely owing to active natural oil seeps in the area. In most cases there was a trend towards a lowering in the supply of trace elements; this might be associated with environmental controls in the region since the 1980s. This study highlights the relevance of using dated environmental archives to reconstruct the historical trends of trace metal contamination in areas where long-term environmental studies are scarce. Graphical abstract Unlabelled Image Highlights • Metal concentrations and enrichment trends were studied in southern Gulf of Mexico. • Metal enrichment evidenced weak to intense contamination within the past 100 years. • Metals result from simultaneous sources (oil industry, seeps, fluvial discharges). • Reducing metal concentrations since 1980s likely respond to environmental regulation. • Background and recent metal concentrations might be harmful to biota and humans. [ABSTRACT FROM AUTHOR]

Nutrient pollution causes environmental damages on aquatic ecosystems worldwide. Eutrophication produces impacts in coastal ecosystems, affecting biota and ecosystem services. The Urias coastal lagoon (SE Gulf of California) is a sub-tropical estuary under several environmental pressures such as nutrient inputs from shrimp farm effluents and dredging related to port operations, which can release substances accumulated in sediments. We assessed the water quality impacts caused by these activities and results showed that i) nitrogen was the limiting nutrient, ii) shrimp farm effluents increased particulate organic matter and chlorophyll a in the receiving stations, and iii) dredging activities increased nitrite and reduced dissolved oxygen concentrations. The co-occurrence of the shrimp farm releases and dredging activities was likely the cause of a negative synergistic effect on water quality which mainly decreases dissolved oxygen and increases nitrite concentrations. Coastal zone management should avoid the co-occurrence of these, and likely others, stressors in coastal ecosystems. [ABSTRACT FROM AUTHOR]

We present a study on the use of 239,240Pu as a chronostratigraphic marker to constrain 210Pb ages in young Holocene sediments from four coastal locations of Cuba (Caribbean Sea). The selected sites typify a variety of deposition environments such as a bay, a gulf, a coastal lagoon and a river estuary. The vertical distributions of 210Pb (and 226Ra), 239,240Pu and 137Cs in the sediment cores were determined in order to quantify the sedimentation processes. Mean activity ratios of 0.04 ± 0.01 for 238Pu/239,240Pu and 0.3 ± 0.2 for 241Am/239,240Pu indicated that atmospheric nuclear weapon tests (NWT) fallout was the main source of the anthropogenic radionuclides. Marine sites (Havana Bay and Gulf of Batabano) were characterized by low or negligible signals of 137Cs, which impeded its use as a chronostratigraphic marker. In the Sagua River Estuary and the Guanaroca Lagoon, where mixing of fresh and saline waters take place, depth profiles of 137Cs and 239,240Pu were in good agreement. A simple model that assumes a well-mixed reservoir in surface ocean waters and constant sediment accumulation was used to interpret the 239,240Pu profiles. The model corroborated the 210Pb ages, except in the case of the highly mixed sediment cores from the Gulf of Batabano. The apparent mean residence time of 239,240Pu in the well-mixed reservoir ranges from 5 to 50 years, with longer timescales for marine sites. 239,240Pu showed to be a useful time tracer in coastal sediments where the 137Cs signal is very low. [ABSTRACT FROM AUTHOR]

Abstract: Environmental archives, such as sediments, banded corals and tree rings, are widely used to reconstruct past environmental conditions of ecosystems. In particular, 210Pb has been used during more than 4 decades, through dating of undisturbed sediment cores, to study ecosystem changes during the last 100yr. Since its inception, diverse dating models have been proposed, developed, used and validated in numerous environments, but their nomenclature and formulation is not homogenous. In this work we emphasize that conceptual models used to date undisturbed sediment cores can be deduced from a single fundamental equation, which relates excess 210Pb concentration in sediment, its flux to the sediment surface and mass accumulation rate. From this equation, models were consistently named based on the main hypothesis used and, using a unified and logical nomenclature, dating equations were derived in detail. We applied in detail most of the described models to a sediment core from Mexico and uncertainty expressions were also included. Finally, some recommendations to use the models are proposed. We believe that this work can facilitate the use of 210Pb as a tool to date sediment cores in a more homogeneous way. [Copyright &y& Elsevier]

Abstract: During the reoccupation of the WOCE transect A10 at 30°S by the BEAGLE2003 cruise, the SHOTS project partners collected a large number of samples for the analysis of isotopic tracers. 137Cs was mostly deposited on the oceans surface during the late 1950s and early 1960s, after the atmospheric detonation of large nuclear devices, which mostly occurred in the Northern Hemisphere. The development of advanced radioanalytical and counting techniques allowed to obtain, for the first time in this region, a zonal section of 137Cs water concentrations, where little information existed before, thus constituting an important benchmark for further studies. 137Cs concentrations in the upper waters (0–1000m) of the south-eastern Atlantic Ocean are similar to those observed in the south-western Indian Ocean, suggesting transport of 137Cs labeled waters by the Agulhas current to the Benguela Current region. In contrast, bomb radiocarbon data do not show this feature, indicating the usefulness of 137Cs as a radiotracer of water mass transport from the Indian to the South Atlantic Ocean. [Copyright &y& Elsevier]

Abstract: The vertical distribution of Hg and Pb were determined in a sediment core collected from the Sagua estuary (North Cuba) that receives input from the Sagua river, one of the most polluted rivers discharging into the Cuban coastal environment. Depth profiles of metal concentrations were converted to time-based profiles using the 210Pb dating method and confirmed with the 137Cs fallout peak. The mean mass accumulation rate was estimated to be 0.17±0.04gcm−2 y−1 (mean sediment accumulation rate 0.52±0.13cmy−1) and the core bottom was estimated to date back about 130years. The historical sedimentary record showed a strong enrichment of mercury concentrations in the past decades, caused by the incomplete treatment of industrial wastes from a chlor-alkali plant with mercury-cell technology in the Sagua river basin. Lead fluxes to sediments showed a gradual increase from the 1920s to present, which agrees with a population increase in Sagua la Grande City. Fluxes of both metals have increased the past 25years, with values reaching a maximum of 0.5 and 3.9μgcm−2 y−1 for Hg and Pb, respectively. [Copyright &y& Elsevier]

A reference material designed for the determination of anthropogenic and natural radionuclides in sediment, IAEA-384 (Fangataufa Lagoon sediment), is described and the results of certification are presented. The material has been certified for 8 radionuclides (40K, 60Co, 155Eu, 230Th, 238U, 238Pu, 239+240Pu and 241Am). Information values are given for 12 radionuclides (90Sr, 137Cs, 210Pb (210Po), 226Ra, 228Ra, 232Th, 234U, 235U, 239Pu, 240Pu and 241Pu). Less reported radionuclides include 228Th, 236U, 239Np and 242Pu. The reference material may be used for quality management of radioanalytical laboratories engaged in the analysis of radionuclides in the environment, as well as for the development and validation of analytical methods and for training purposes. The material is available from IAEA in 100 g units. [ABSTRACT FROM AUTHOR]

210Pb was analysed in samples collected from (16) sediment traps, deployed during 1 year on the Northwestern Mediterranean continental margins, within the framework of the (MTP I)-EUROMARGE-NB programme. The traps were moored within (5) submarine canyons and their adjacent open slope, corresponding to contrasting conditions of particle inputs (fluxes and constituents). The major meso-scale observation (at the margin) is the variation in 210Pb fluxes along the slope, increasing by a factor of 2–3 between the entrance and the exit of the slope, in relation to the general (water) circulation. At a smaller scale (canyon), the 210Pb fluxes showed trends which were common to the various sites, i.e. a seaward decrease at 500 m depth and an increase, with depth, in the canyons. All these features are related to mass flux variations, except for periods with huge mass fluxes, when 210Pb fluxes reached a constant value. 210Pb activities decreased with increasing mass flux; then did not show clear relationship with the concentration of the major constituents of the flux.210Pb fluxes, obtained from the traps were mainly in excess of the theoretical 210Pb flux, available in the overlying water column. Since 210Pb inventories, measured on the basis of the shelf and slope bottom sediments, were also in excess in relation to the available flux. The margin, as a whole, appears as a sink for 210Pb. This boundary-scavenging process appears to be controlled completely by the mass flux of particles. Differences were observed between 210Pb fluxes in the near-bottom traps and in the underlying sediments; there can be linked to mass flux and/or morphobathymetry (the trap flux is higher than the sediment flux in the canyon, but lower on the open slope). Overall, the differences were not in excess of 50%, confirming good representation of data collected by the sediment traps. However, this finding must be taken into account when comparing organic carbon or other constituent fluxes, between the traps and the sediment. [Copyright &y& Elsevier]

Spatial and temporal variability of mercury concentrations in sediments was evaluated in 210Pb-dated sediment cores from offshore and intertidal areas in the southern Gulf of Mexico. In offshore cores, mercury concentrations were comparable (11.2–69.2 ng g−1), and intermediate between concentrations in intertidal cores from the eastern (6.0–34.4 ng g−1) and the western (34.9–137.7 ng g−1) inlets of Términos Lagoon. The enrichment factor (EF) indicated minimal contamination (EF < 2) in most offshore cores, whereas in some intertidal cores steadily increasing mercury enrichment and fluxes were observed along the past century. No evidence of oil industry related mercury contamination was found, as the minor but increasing enrichment in intertidal cores is most likely related to land-derived sources such as catchment eroded soils and waste water runoff. Results highlight the importance to control catchment erosion and untreated sewage releases to reduce mercury loadings to the coastal zone. Unlabelled Image • Hg contamination trends were studied in sediment cores of southern Gulf of Mexico. • Null to minor Hg enrichment was observed during the past 100 years in the area. • Recent Hg concentrations in most offshore cores were close to preindustrial levels. • Minor Hg contamination in intertidal areas is likely associated to surface runoff. • Hg concentrations are not a risk to benthic biota in the region. [ABSTRACT FROM AUTHOR]