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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]

Coastal vegetated habitats can be important sinks of organic carbon (C org ) and mitigate global warming by sequestering significant quantities of atmospheric CO 2 and storing sedimentary C org for long periods, although their C org burial and storage capacity may be affected by on-going sea level rise and human intervention. Geochemical data from published 210 Pb-dated sediment cores, collected from low-energy microtidal coastal wetlands in El Salvador (Jiquilisco Bay) and in Mexico (Salada Lagoon; Estero de Urias Lagoon; Sian Ka'an Biosphere Reserve) were revisited to assess temporal changes (within the last 100 years) of C org concentrations, storage and burial rates in tropical salt marshes under the influence of sea level rise and contrasting anthropization degree. Grain size distribution was used to identify hydrodynamic changes, and δ 13 C to distinguish terrigenous sediments from those accumulated under the influence of marine transgression. Although the accretion rate ranges in all sediment records were comparable, C org concentrations (0.2–30%), stocks (30–465 Mg ha −1 , by extrapolation to 1 m depth), and burial rates (3–378 g m −2 year −1 ) varied widely within and among the study areas. However, in most sites sea level rise decreased C org concentrations and stocks in sediments, but increased C org burial rates. Lower C org concentrations were attributed to the input of reworked marine particles, which contribute with a lower amount of C org than terrigenous sediments; whereas higher C org burial rates were driven by higher mass accumulation rates, influenced by increased flooding and human interventions in the surroundings. C org accumulation and long-term preservation in tropical salt marshes can be as high as in mangrove or temperate salt marsh areas and, besides the reduction of C org stocks by ongoing sea level rise, the disturbance of the long-term buried C org inventories might cause high CO 2 releases, for which they must be protected as a part of climate change mitigation efforts. [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 measured Cd and Pb in the muscle and stomach contents of Thunnus albacares and Katsuwonus pelamis to define the distribution of the elements in the tissues and their degrees of biomagnification. 210 Po was measured in the livers of both species and compared to the results of similar studies. The trophic position of the tuna species was determined by N isotope measurements. The average activity of 210 Po in the liver ranged from 119 to 157 (Bq kg −1 wet weight) in K. pelamis and T. albacares . The trophic position of T. albacares (4.60) was higher than that of K. pelamis (3.94). The Cd content of the muscle increased significantly with the trophic position of the tuna. δ 13 C in T. albacares and K. pelamis varied, with values of 3.13 and 1.88‰, respectively. The δ 15 N values in yellowfin tuna were higher than in skipjack tuna. The trophic position of T. albacares (4.60 ± 0.67) was therefore more elevated than that of K. pelamis (3.94 ± 1.06). Pb was biomagnified in T. albacares (transfer factor = 1.46) . [ABSTRACT FROM AUTHOR]

Abstract: The accumulation, enrichment and provenance of selected trace metals (Ag, As, Cd, Cr, Cu, Hg, Ni, Pb, V and Zn) were studied in sediment cores collected from three lakes located in the Central Mexican Plateau, selected on the basis of their contrasting degree of urbanization: Santa Elena Lake, in a rural and remote area; El Tule Lake, in a rural and slightly urbanized area; and Chapala Lake, in a highly urbanized area. Grain size, magnetic susceptibility and sedimentary constituents such as organic carbon, calcium carbonate, as well as major (Al, Fe, Mn) and minor (Ca, Li, Rb, Sr, Th) elements were analyzed to explain the concentration trends of trace metals. Factor analysis (FA) was used to assess the provenance of the trace elements. The highest metal enrichment factor (EF) above natural concentration levels was found at Chapala Lake for Ag (EF=3.9), although other trace element EF in all lakes was <2.0, indicating slight contamination. However, the concentration levels of Cr and Ni in all lakes, Hg and Zn in Chapala Lake, Cu in El Tule Lake and As in Santa Elena Lake were above international benchmarks for which adverse effects are expected to occur frequently, even for those metals only slightly enriched (e.g. As, Cr). Through FA, the terrigenous contribution was identified as the most important source of trace metals to the three lakes, most likely related to deforestation and erosion of the surrounding areas, followed by atmospheric transport of volcanic ashes, rather than to direct sources. [Copyright &y& Elsevier]

Highlights: [•] Nine macroalgal blooms were examined in five lagoons from SE Gulf of California. [•] Shrimp farms were the main point source of nutrients loads to the lagoons. [•] Biomass as phytoplankton ranged 40–792mgm−2 and macroalgal of 1–296 g m−2. [•] Biomass (phytoplankton+macroalgae) was the same tendency that nutrient loads. [•] Phytoplankton and macroalgal biomass were a significant correlation with N:P ratio. [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: 210Pb is widely used for dating recent sediments in the aquatic environment; however, our experiences working in shallow coastal environments in the Pacific coast of Mexico have demonstrated that the potential of 210Pb for reliable historical reconstructions might be limited by the low 210Pb atmospheric fallout, sediment mixing, abundance of coarse sediments and the lack of 137Cs signal for 210Pb corroboration. This work discusses the difficulties in obtaining adequate sedimentary records for geochronological reconstruction in such active and complex settings, including examples of 210Pb geochronologies based on sediment profiles collected in two contrasting areas coastal areas (mudflats associated to coastal lagoons of Sinaloa State and the continental shelf of the Gulf of Tehuantepec), in which geochemical data was used to support the temporal frame established and the changes in sediment supply recorded in the sediment cores which were related to the development of land-based activities during the last century. [Copyright &y& Elsevier]

Abstract: A sedimentary sequence from the Espejo de los Lirios lake in the Metropolitan Zone of Mexico City (MZMC) was analyzed in detail for 210Pb and 137Cs activities, allowing to assess the evolution of the accretion rates in the lake during the last ∼84±4 years. The core revealed the deposition of contemporaneously indigenous lake sediments to the site interspersed with eroded bedrock from the catchment, evidencing episodic increases in sediment accretion which varied from 0.14 to 0.93 cm year−1. Increasing trends in sedimentation rates were found to be closely related to demographic expansion of the Metropolitan Zone of Mexico City and explained on the basis of the erosive processes produced as a result of deforestation created as a consequence of the urban and industrial development of the MZMC. [Copyright &y& Elsevier]

Beginning in the middle of the 1980s, the Gulf of California ecoregion experienced a boom in shrimp aquaculture and became the second largest producer in the western hemisphere. The moderated, but continual development of shrimp farming, in conjunction with municipal and agriculture effluents has been accompanied by concern about: (a) depletion of fishing stocks, (b) reduction of mangrove forest, (c) frequent harmful algal blooms in coastal waters and shrimp ponds, and (d) water quality deterioration. We demonstrate that environmental degradation resulted from a conjunction of factors including agriculture, untreated municipal effluents, shrimp aquaculture, increasing number of fishermen, and an absence of an effective regulatory program. We recommend the immediate implementation of an integrated coastal management program to protect the integrity of the coastal ecosystems and operate upon the principle of environmental sustainability for the different economic activities including shrimp aquaculture. [Copyright &y& Elsevier]

• C org burial was evaluated in seagrass sediments at the northern Mexican Caribbean. • Thalassia testudinum seagrass meadows showed C org storage within ~ 40 to ~ 100 years. • C org stock increments were related with increasing sediment accumulation rates. • Seagrasses might be gradually impacted by population growth and land use changes. Carbon sequestration in seagrass meadows mitigates the currently rising CO 2 atmospheric levels, as these ecosystems are highly productive and preserve sediment organic carbon over long periods. Five 210Pb dated sediment cores, collected from seagrass meadows dominated by Thalassia testudinum in the northern Mexican Caribbean touristic corridor Cancun-Riviera Maya, were used to establish temporal trends of organic carbon (C org) content, burial rates and stock variation over the past 100 years. C org contents (0.17–1.94%) and burial rates (2.0–252 g m−2 yr−1) were generally within the lower end range reported for seagrass meadow sediments worldwide. C org stock gradually increased over the past decades, associated with increasing sediment accumulation, possibly caused by inland erosion promoted by agricultural and forestry activities and, in the recent decades, by a rapid increase of urban development due to a fast growth of the tourist industry and population, likely causing fertilization of coastal waters. Seagrass meadow sediments in the northern Mexican Caribbean coastline showed long-term C org storage and preservation, since ~ 40 to ~ 100 years depending on the core, which emphasizes the need to protect these ecosystems against impacts of global change, and their incorporation into climate change mitigation strategies should be considered. [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]

Two sediment cores, collected from the center of the Lake Melincué (Santa Fe, Argentina), were analyzed using rock magnetic results, element composition, Total Organic and Inorganic Carbon (TOC and TIC) and Total Nitrogen (TN) to reconstruct the environmental variations in the last three centuries, associated with climatic changes and/or human activities. 210Pb dating, chronostratigraphic markers, and paleomagnetic results were used to create the age model of the cores. Rock magnetic analyses suggest that (titano)magnetite and a low proportion of hematite are the main magnetic phases. In addition, geochemical results compared with rock magnetic analysis indicate the possible presence of diagenetic dissolution. Four well-differentiated environmental phases were found with variations from cold to more humid and warmer environmental conditions. Unit 0 from 1750 CE to 1783 CE with a cold environment and high lake level, Unit 1 from 1783 CE to 1878 CE with continuing cold environmental conditions but a low lake level, showing the end of the Little Ice Age (LIA) toward the top, Unit 2 from 1878 CE to 1874 CE with a wetter environment and Unit 3 from 1974 CE to 2016 CE with wet and warm conditions and a high lake level. • We report new paleoclimatic multiproxy results in Lake Melincue, Argentina. • The age model was validated by stratigraphic markers and Paleosecular Variations. • Four environmental scenarios were distinguished from dry to wet conditions. • The results are related to the anthropogenic activity (land use and fertilizers). [ABSTRACT FROM AUTHOR]