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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]

Coastal lagoons provide important ecosystem services worldwide but are subject to high and multiple environmental stresses. Little information exists on the inner creeks of low-flow coastal lagoons, where the low-exchange rates may exacerbate anthropogenic impacts. In this work, we used a model with high spatio-temporal resolution to describe the hydrodynamics and to estimate the accumulation of conservative contaminants in the upper estuary of the Urias sub-tropical coastal lagoon, in northwestern Mexico. The lagoon shows a weak anti-estuarine behavior and its hydrodynamics is governed by astronomical tides and topography. The mean steady-state water age in the three lagoon areas was ∼15, ∼30 and ∼70 days in the Harbor, Intermediate and Upper Areas, respectively. Thus, the Upper Area, which shelters a mangrove forest, is the most vulnerable to pollution due to the high potential for accumulation. As a best case scenario, the simulation of the release of conservative substances in the Upper area indicated that, 50 days after the release started, conservative pollutants mostly remained in the Upper Area and were not significantly exported to the open ocean. This methodology can be used to model the impact of conservative substances in coastal lagoons worldwide, and can be complementary and useful for the optimization of long-term coastal zone management activities. [ABSTRACT FROM AUTHOR]