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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]

Working on an experimental dataset to derive descriptive parameters with well-known procedures appears to be a straightforward process. However, due to the complexity of environmental systems, the procedures cannot be completely defined, and commonly hypothesis are required to obtain final results. These degrees of freedom cause a spread in results that is often wider than the experimental uncertainties and that should be taken into account in the measurement accuracy estimation. As an example of this issue, the sources of uncertainty, including reproducibility, that occur in dating marine and lacustrine sediment cores with the 210Pb methodology are discussed in this paper. The IAEA Coordinated Research Project (CRP) "Study of Temporal Trends of Pollution in Selected Coastal Areas by the application of Isotopic and Nuclear Tools" promoted this discussion, its main objective being the determination of a streamlined, harmonised and validated methodology for marine sediment dating. The uncertainties estimated from experimental data and mathematical propagated must be complemented with reproducibility contribution: some elements are specific for the 210Pb method (mixed layer, finite thickness of layers and identification of the equilibrium depth), while others are more general (exponential fitting and data interpolation). The final spreading of results can be mainly controlled by reproducibility, and efforts are needed to standardise procedures to reduce the effect of reproducibility and to better estimate the overall uncertainty of measurements. It is necessary to underline the importance of a thorough (a-priori) cost-effective analysis of the uncertainty evaluation of the measurement results in relation to the aim of the study, taking primarily into account the overall accuracy required case by case. • In 210 Pb dating models, there is low reproducibility of uncertainties. • Data interpolation and equilibrium depth choice affect constant flux dating results. • Procedures to fit 210 Pb data and surface mixed layer affect CFCS dating results. • The final spreading of dating uncertainties can be controlled by reproducibility. [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: The DYFAMED site (Ligurian Sea, 43°25′N; 7°52′E) has been the subject of multidisciplinary research since 1987, including the study of atmospheric deposition of metals and their association with marine particles in the water column. On the other hand, the attention paid to the underlying sediments as the ultimate repository of elements, particularly pollutants, has been considerably lesser. Through the combined use of 210Pb chronologies and elemental analysis, we studied the concentrations and fluxes of trace metals (Zn, Pb, Ni, Cu, Cr) in a sediment core collected from ∼2300m water depth at the seafloor beneath DYFAMED. Surface metal enrichment during the 20th century is apparent in the case of Pb, Zn and Cu (maximum enrichment factors 1.5, 1.2 and 1.4, respectively). A comparison with published data suggests that atmospheric deposition is the main entrance route of anthropogenic trace metals accumulated in the recent sediments, while lateral advection of sediments by currents and sediment gravity flows is proposed to account for the pre-industrial concentrations of metals. Recent atmospheric inputs of Pb and Cu are more efficiently stored in sediments with respect to Zn, most of which is apparently advected elsewhere. [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]

Laboratories from 14 countries (with different levels of expertise in radionuclide measurements and 210Pb dating) participated in an interlaboratory comparison exercise (ILC) related to the application of 210Pb sediment dating technique within the framework of the IAEA Coordinated Research Project. The laboratories were provided with samples from a composite sediment core and were required to provide massic activities of several radionuclides and an age versus depth model from the obtained results, using the most suitable 210Pb dating model. Massic concentrations of Zn and Cu were also determined to be used for chronology validation. The ILC results indicated good analytical performances while the dating results didn't demonstrate the same degree of competence in part due to the different experience in dating of the participant laboratories. The ILC exercise enabled evaluation of the difficulties faced by laboratories implementing 210Pb dating methods and identified some limitations in providing reliable chronologies. • Interlaboratory comparison exercise (ILC) finds difficulties of the Pb-210 method. • ILC results indicate good analytical performance of the participants. • ILC dating results did not show the same degree of confidence. [ABSTRACT FROM AUTHOR]

The 210Pb sediment dating is the most widely used method to determine recent (~100–150 years) chronologies and sediment accumulation rates in aquatic environments and has been used effectively for reconstruction of diverse environmental processes associated with global change. Owing to the relative accessibility of the 210Pb methodology, many environmental chronologies have been produced, but not always critically assessed. Sometimes, sedimentary processes such as compaction, local mixing, erosion, or episodic sedimentation are not taken into account, nor the validity of the fundamental premises and proper estimation of uncertainties assessed. A Pb-210 dating interlaboratory comparison modelling exercise was designed within the framework of the IAEA (International Atomic Energy Agency) Coordinated Research Project "Study of temporal trends of pollution in selected coastal areas by the application of isotopic and nuclear tools" (CRP K41016), to identify potential problems associated with the use of 210Pb dating models and to suggest best practices to obtain reliable reconstructions. The exercise involved 14 laboratories worldwide with different levels of expertise in the application of the 210Pb dating methods. The dating exercise was performed using 210Pb, 226Ra and 137Cs activity data from two sediment cores (coastal and lacustrine sediments), and the participants were requested to provide their 210Pb chronologies based on dating models. This modelling exercise evidenced the limitations and constraints of 210Pb method when supplementary and validation information is not available. The exercise highlighted the relevance of solid understanding of the fundamentals, assumptions and limitations of the 210Pb dating method and its validation, and allowed identifying key aspects to improve the reliability of 210Pb dating process, including: a critical examination and interpretation of the 210Pb activity depth profile; an appropriate selection of the 210Pb dating model according to the characteristics of the 210Pb activity profile and the environmental setting taking into account sediment compaction in the calculations; a sound identification of the 210Pb equilibrium depth and the estimation of the 210Pb inventory ensuring the best possible estimation of interpolated 210Pb values when needed; and the use of independent markers to corroborate the age models. • Potential constraints and limitations of the 210Pb dating method are evidenced. • The 210Pb dating method is far to be a straightforward tool for dating sediment cores. • Reliable 210Pb chronologies require a proper understanding of the dating methodology. [ABSTRACT FROM AUTHOR]

The development of the Grijalva-Usumacinta river basin exerts modifications on its discharge area. A sediment core was studied to reconstruct environmental changes and trace element contamination status during the past 45 years. 210Pb-derived mass accumulation rates indicate higher sediment input to the area since 1995, related to increased precipitation and floodings in the catchment area. Sediments show finer particles from the late 1970s on, likely related to dams construction upriver and/or land use changes. Heavy metal enrichment factors (EF < 2) suggest minimum contamination. Benthic foraminifera and redox-sensitive - elements (As, Ba, Co, Cr, Cu, Ni, Pb, V and Zn) indicate the sediments before 2000 were deposited under oxygenated conditions. Afterwards, environmental conditions changed and benthic foraminifera and dinocysts assemblages changed suggesting eutrophication and lower oxygen conditions during the last 20 years. Monitoring should be continued to assess eutrophication/hypoxic/pollution trends that could become deleterious to the marine biota. • Sediments from past 45 years record environmental changes in the marine area off the largest river in southern Gulf of Mexico • Mass accumulation rates indicate higher sediment input to the area since 1995. • Higher sediment input related to increased precipitation and flooding in Tabasco City and the catchment area. • Grain size variation reflects land use change and damming since the 1980s. • Benthic Foraminifera and Dinocysts indicate a process of eutrophication in bottom waters during the last 20 years. [ABSTRACT FROM AUTHOR]

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]