Fine-tuning of Pb-210-based methods for dating vegetated saltmarsh sediments

Saltmarshes, wetlands, inter-tidal mudflats are highly productive natural ecosystems with significant ecological value. 210Pb and 137Cs have been used for establishing chronologies at a centennial scale in these sediments. They are relevant for assessing how saltmarshes are vulnerable to climate change, natural hazards and contamination from human inputs. This paper aims to review and adapt existing methods for the 210Pb-based radiometric dating of these sediments where the subterranean production and decay of OM are sources of achronicity. This limits the use of the basic assumption of considering the sediment as a continuous medium. From the available evidence, 210Pb fluxes onto sediments may be mediated by the activities bound to the mass flows, suggesting that models assuming a constant flux should be handled with care. The activity concentrations of excess 210Pb required by CF-CS, CIC and TERESA radiometric models must be those of the sediment mineral fraction, while CRS and PLUM can work with the composite sediment matrix. A review of these issues and application of the models is illustrated with new data from two recent saltmarsh sediment cores. The effects of non-ideal boundary conditions in radiometric dating and the system time-average of 137Cs fluxes are discussed. Although specific to vegetated saltmarshes, this topic and the present results have generic applications for other vegetated coastal sediments

Sampling soil and sediment depth profiles at a fine resolution with a new device for determining physical, chemical and biological properties : the Fine Increment Soil Collector (FISC)

Purpose Many environmental investigations (empirical and modelling) and theories are based on reliable information onthe depth distribution of physical, chemical and biological properties in soils and sediments. However, such depth profilesare not easy to determine using current approaches, and, consequently, new devices are needed that are able to samplesoils and sediments at fine resolutions. Materials and methods We have designed an economic, portable,hand-operated surface soil/sediment sampler—the FineIncrement Soil Collector (FISC)—which allows for the close control of incremental soil/sediment sampling and for easyrecovery of the material collected by a simple screw-thread extraction system. This innovative sampling system was developedoriginally for the beryllium-7 (7Be) approach in soil and sediment redistribution research. To ensure reliable estimatesof soil erosion and sediment deposition from 7Be measurements, the depth distribution of this short-lived fallout

Modelling Deposition and Erosion rates with RadioNuclides (MODERN) – Part 1: A new conversion model to derive soil redistribution rates from inventories of fallout radionuclides.

The measurement of fallout radionuclides (FRN) has become one of the most commonly used tools to quantify sediment erosion or depositional processes. The conversion of FRN inventories into soil erosion and deposition rates is done with a variety of models, which suitability is dependent on the selected FRN, soil cultivation (ploughed or unploughed) and movement (erosion or deposition). The authors propose a new conversion model, which can be easily and comprehensively used for different FRN, land uses and soil redistribution processes. The new model MODERN (Modelling Deposition and Erosion rates with RadioNuclides) considers the precise depth distribution of any FRN at the reference site, and allows adapting it for any specific site conditions. MODERN adaptability and performance in converting different FRN inventories is discussed for a theoretical case as well as for two already published case studies i.e. a 137 Cs study in an alpine and unploughed area in the Aosta valley (Italy) and a 210 Pb ex study on a ploughed area located in the Transylvanian Plain (Romania). The tests highlight a highly significant correspondence (i.e. correlation factor of 0.91) between the results of MODERN and the published results of other models currently used by the FRN scientific community (i.e. the Profile Distribution Model and the Mass Balance Model). The development and the cost free accessibility of MODERN (see modern.umweltgeo.unibas.ch) will ensure the promotion of wider application of FRNs for tracing soil erosion and sedimentation

Fallout Pb-210 as a soil and sediment tracer in catchment sediment budget investigations : a review

Increasing anthropogenic pressures coupled with climate change impacts on natural resources have promoted a quest for innovative tracing techniques for understanding soil redistribution processes and assessing the environmental status of soil resources. Among the different existing tracers, the fallout component of the radioisotope lead-210, also termed unsupported or excess lead-210 (Pb-210(ex)) when referring to its presence in soil or sediment, arguably offers the broadest potential for environmental applications, due to its origin and relatively long half-life. For more than five decades, Pb-210(ex) has been widely used for dating sediments, to investigate sedimentation processes and, since the 1990s, to provide information on the magnitude of soil and sediment redistribution. The aim of this review is to provide a comprehensive evaluation and discussion of the various applications of Pb-210(ex) as a tracer in terrestrial and aquatic environments, with particular emphasis on catchment sediment budget investigations. This paper summarizes the state-of-the-art related to the use of this tracer, the main assumptions, the requirements (including the need for accurate analytical measurements and for parallel validation), and the limitations which must be recognised when using this fallout radionuclide as a soil and sediment tracer. Lessons learned and current and future research needs in the environmental and radiochronological application of Pb-210(ex) are also presented and discussed. (C) 2014 Elsevier B.V. All rights reserved