[Show abstract][Hide abstract] ABSTRACT: Variations in the abundance of fossil charcoals between rocks and sediments are assumed to reflect changes in fire activity in Earth's past. These variations in fire activity are often considered to be in response to environmental, ecological or climatic changes. The role that fire plays in feedbacks to such changes is becoming increasingly important to understand and highlights the need to create robust estimates of variations in fossil charcoal abundance. The majority of charcoal based fire reconstructions quantify the abundance of charcoal particles and do not consider the changes in the morphology of the individual particles that may have occurred due to fragmentation as part of their transport history. We have developed a novel application of confocal laser scanning microscopy coupled to image processing that enables the 3-dimensional reconstruction of individual charcoal particles. This method is able to measure the volume of both microfossil and mesofossil charcoal particles and allows the abundance of charcoal in a sample to be expressed as total volume of charcoal. The method further measures particle surface area and shape allowing both relationships between different size and shape metrics to be analysed and full consideration of variations in particle size and size sorting between different samples to be studied. We believe application of this new imaging approach could allow significant improvement in our ability to estimate variations in past fire activity using fossil charcoals.
[Show abstract][Hide abstract] ABSTRACT: Climate change is projected to have a strongly negative effect on water supplies in the arid mountains of South America, significantly impacting millions of people. As one of the poorest countries in the region, Bolivia is particularly vulnerable to such changes due to its limited capacity to adapt. Water security is threatened further by glacial recession with Bolivian glaciers losing nearly half their ice mass over the past 50 years raising serious water management concerns. This review examines current trends in water availability and glacier melt in the Bolivian Andes, assesses the driving factors of reduced water availability and identifies key gaps in our knowledge of the Andean cryosphere. The lack of research regarding permafrost water sources in the Bolivian Andes is addressed, with focus on the potential contribution to mountain water supplies provided by rock glaciers.
[Show abstract][Hide abstract] ABSTRACT: The Baurières plain within the upper Drôme River basin was used to reconstruct recent changes in sediment supply in relation to changes in land use within an alpine catchment. A considerable body of archival information is available. Furthermore, the plain acts as a natural sediment trap and the reach–basin interaction has not been disrupted by human activity. Based on archival data, channel geometry measurements, dendrogeomorphological and radionuclide analysis (Cs137 and unsupported Pb210), the trends in channel change and sediment supply over the past two centuries are assessed and their causes are interpreted.Dendrogeomorphology and radionuclide profiles show that the floodplain is characterised by a decrease in sedimentation rate in the 1960s. The ex-Pb210 profiles also suggest a spatial modification of the relative contribution in sediment supply of the catchment. Bedload yields are estimated to be at least 26 m3 km−2 year−1 between 1928 and 1996 based on an estimate of storage over a channel length of 11.5 km. Archival data concerning bedload removal from traps yields an estimate of 25.6 m3 km−2 year−1 between 1993 and 2001. These two values are very comparable suggesting no major modification in bedload transport within the reach during the 20th century. If the bedload supply has not strongly decreased in the studied reach during this period, the bedload sources have changed. The volume of sediment stored in the Beaurières area between 1928 and 1996 corresponds to at least 40% of the sediment delivered by channel degradation from an upstream alluvial reach.Both changes in floodplain sedimentation as well as changes in bedload and suspended contributions from catchment sources are interpreted as responses to land use but also flow regime. Hillslope sediment production strongly decreased due to planned hillslope afforestation and torrent regulation at the end of the 19th century, and spontaneous hillslope afforestation resulting from grazing decline, mainly in the two decades following World War II. The observed change in suspended sediment supply which occurred around 1960–1965 has a clear synchronicity with spontaneous catchment afforestation following World War II. After this period, a decrease in sediment supply, a change in source, but also a decrease in peak flow, were observed.Changes in run-off are complex and cannot be caused with only land use change. Flood hydrographs underwent peak decreases and duration increases through the 20th century because of increase in water retention capacity of the forested catchment. In addition flood seasonality has changed, with September and October flood events being much less frequent in the last part of the 20th century.
[Show abstract][Hide abstract] ABSTRACT: Information on rates of soil loss from agricultural land is a key requirement for assessing both on-site soil degradation and potential off-site sediment problems. Many models and prediction procedures have been developed to estimate rates of soil loss and soil redistribution as a function of the local topography, hydrometeorology, soil type and land management, but empirical data remain essential for validating and calibrating such models and prediction procedures. Direct measurements using erosion plots are, however, costly and the results obtained relate to a small enclosed area, which may not be representative of the wider landscape. In recent years, the use of fallout radionuclides and more particularly caesium-137 ((137)Cs) and excess lead-210 ((210)Pb(ex)) has been shown to provide a very effective means of documenting rates of soil loss and soil and sediment redistribution in the landscape. Several of the assumptions associated with the theoretical conversion models used with such measurements remain essentially unvalidated. This contribution describes the results of a measurement programme involving five experimental plots located in southern Italy, aimed at validating several of the basic assumptions commonly associated with the use of mass balance models for estimating rates of soil redistribution on cultivated land from (137)Cs and (210)Pb(ex) measurements. Overall, the results confirm the general validity of these assumptions and the importance of taking account of the fate of fresh fallout. However, further work is required to validate the conversion models employed in using fallout radionuclide measurements to document soil redistribution in the landscape and this could usefully direct attention to different environments and to the validation of the final estimates of soil redistribution rate as well as the assumptions of the models employed.
Applied radiation and isotopes: including data, instrumentation and methods for use in agriculture, industry and medicine 06/2012; 70(10):2451-9.
[Show abstract][Hide abstract] ABSTRACT: Floodplain sedimentation removes particles from fluvial transport and constructs stratigraphic records of flooding, biogeochemical sequestration and other aspects of the environmental history of river basins-insight that is enhanced by accurate geochronology. The natural fallout radionuclide (210)Pb, often employed to date lacustrine and marine sediments, has previously been used to determine floodplain accumulation rates over decadal-to-century time scales using the assumption that both input concentration and sediment accumulation rates are constant. We test this model in approximately 110 cores of pristine floodplains along approximately 2000 km of the Rios Beni and Mamore in northern Bolivia; over 95 per cent of the (210)Pb profiles depict individual episodic deposition events, not steady-state accumulation, requiring a revised geochronological methodology. Discrete measurements of down-core, clay-normalized adsorbed excess (210)Pb activity are coupled with a new conceptual model of (210)Pb input during floods: constant initial reach clay activity, unknown sedimentation (CIRCAUS). This enhanced methodology yields (210)Pb dates that correspond well with (i) dates determined from meteoric caps, (ii) observed dates of river bar formation, (iii) known flood dates, and (iv) dates from nearby cores along the same transect. Similar results have been found for other large rivers. The CIRCAUS method for geochronology therefore offers a flexible and accurate method for dating both episodic (decadal recurrence frequency) and constant (annual recurrence) sediment accumulation on floodplains.
Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences 05/2012; 370(1966):2040-74.
[Show abstract][Hide abstract] ABSTRACT: Stable isotope analysis of cellulose is an increasingly important aspect of ecological and palaeoenvironmental research. Since these techniques are very costly, any methodological development which can provide simultaneous measurement of stable carbon and oxygen isotope ratios in cellulose deserves further exploration. A large number (3074) of tree-ring α-cellulose samples are used to compare the stable carbon isotope ratios (δ(13)C) produced by high-temperature (1400°C) pyrolysis/gas chromatography (GC)/isotope ratio mass spectrometry (IRMS) with those produced by combustion GC/IRMS. Although the two data sets are very strongly correlated, the pyrolysis results display reduced variance and are strongly biased towards the mean. The low carbon isotope ratios of tree-ring cellulose during the last century, reflecting anthropogenic disturbance of atmospheric carbon dioxide, are thus overestimated. The likely explanation is that a proportion of the oxygen atoms are bonding with residual carbon in the reaction chamber to form carbon monoxide. The 'pyrolysis adjustment', proposed here, is based on combusting a stratified sub-sample of the pyrolysis results, across the full range of carbon isotope ratios, and using the paired results to define a regression equation that can be used to adjust all the pyrolysis measurements. In this study, subsamples of 30 combustion measurements produced adjusted chronologies statistically indistinguishable from those produced by combusting every sample. This methodology allows simultaneous measurement of the stable isotopes of carbon and oxygen using high-temperature pyrolysis, reducing the amount of sample required and the analytical costs of measuring them separately.
Rapid Communications in Mass Spectrometry 01/2012; 26(2):109-14.
[Show abstract][Hide abstract] ABSTRACT: This paper presents the design and development of an open source web-based Geographical Information System allowing users to visualise, customise and interact with spatial data within their web browser. The developed application shows that by using solely Open Source software it was possible to develop a customisable web based GIS application that provides functions necessary to convey health and environmental data to experts and non-experts alike without the requirement of proprietary software.
International Journal of Health Geographics 01/2012; 11:2.
[Show abstract][Hide abstract] ABSTRACT: a b s t r a c t Engineering and improved road safety education has resulted in an overall decrease in road traffic acci-dent numbers in Christchurch, New Zealand. The temporal trends of crash data from 1980 to 2004 reveal that lowering of crash rates is not occurring at a uniform rate throughout the day, with comparative increases in crash rates occurring during morning rush hour, and during the 'school run'. No spatial clus-tering around schools was identified. This suggests that policies to reduce school travel related road acci-dents need to be focused on reducing overall traffic levels rather than focusing geographically on areas in the immediate vicinity of schools.
Journal of Transport Geography 07/2011; 19(4).
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