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311 results on '"Blake,William H"'

14. An Exploratory Data Analysis (EDA) Tool for Tracer Selection in Sediment and Pollution Fingerprinting Studies.

Author

Ovando-Fuentealba, Luis, Blake, William H., Taylor, Alex, Clason, Caroline, and Bravo-Linares, Claudio

Subjects
*DECISION trees, *DATA analysis, *WORK design, *POLLUTION, *PRIOR learning, *POLLUTION source apportionment
Abstract

Tracer selection is a critical step for any mixing model that uses the information of multiple variables to find the most likely solution for sediment or pollution source apportionment. The purpose of this work was to design an Exploratory Data Analysis (EDA) tool for qualitative and quantitative interpretation of tracer selection based on boxplots. This tool establishes a set of conditions presented as a decision tree to support the user in tracer selection decisions where current systems are either too statistically driven, which limits user interaction with the data, or rely too heavily on judgement and prior knowledge of tracer behaviour. This method extends upon the classical "range test" by incorporating a set of conditions and thresholds, creating a semi-quantitative method with a visual component to improve the tracer selection process and enable targeted consideration of geochemical behaviours for conservativism purposes. We present the results from experimental mixtures using the mixing model MixSIAR to demonstrate the method and illustrate the value of this approach for improved tracer selection. The tool, which is written in R, is freely available for use across a wide range of source apportionment applications. [ABSTRACT FROM AUTHOR]

Published
2024
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15. Anthropogenic and climatic impacts on historic sediment, carbon, and phosphorus accumulation rates using 210Pbex and 137Cs in a sub-watershed linked to Zarivar Lake, Iran.

Author

Khodadadi, Maral, Gibbs, Max, Swales, Andrew, Toloza, Arsenio, and Blake, William H.

Subjects
ANTHROPOGENIC effects on nature, CLIMATE extremes, WATERSHED management, TERRACES (Geology), CLIMATE change, LAKE sediments
Abstract

To estimate a watershed's response to climate change, it is crucial to understand how human activities and climatic extremes have interacted over time. Over the last century, the Zarivar Lake watershed, Iran, has been subjected to various anthropogenic activates, including deforestation and inappropriate land-management practices alongside the implementation of conservation measures like check dams. To understand the effects of these changes on the magnitude of sediment, organic carbon (OC), and phosphorus supplies in a small sub-watershed connected to the lake over the last century, a lake sediment core was dated using 210Pbex and 137Cs as geochronometers. The average mass accumulation rate (MAR), organic carbon accumulation rates (OCAR), and particulate phosphorus accumulation rates (PPAR) of the sediment core were determined to be 6498 ± 2475, 205 ± 85, and 8.9 ± 3.3 g m−2 year−1, respectively. Between the late 1970s and early 1980s, accumulation rates were significantly higher than their averages at 7940 ± 3120, 220 ± 60, and 12.0 ± 2.8 g m−2 year−1 respectively. During this period, the watershed underwent extensive deforestation (12%) on steep slopes, coinciding with higher mean annual precipitations (more than double). Conversely, after 2009, when check dams were installed in the sub-watershed, the sediment load to the lake became negligible. The results of this research indicate that anthropogenic activities had a pronounced effect on MAR, OCAR, and PPAR, causing them to fluctuate from negligible amounts to values twice the averages over the last century, amplified by climatic factors. These results imply that implementing climate-smart watershed management strategies, such as constructing additional check dams and terraces, reinforcing restrictions on deforestation, and minimum tillage practices, can facilitate protection of lacustrine ecosystems under accelerating climate change conditions. [ABSTRACT FROM AUTHOR]

Published
2024
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18. Suitability of 210Pbex, 137Cs and 239+240Pu as soil erosion tracers in western Kenya

Author

Dowell, Sophia M., Humphrey, Olivier S., Gowing, Charles J.B., Barlow, Thomas S., Chenery, Simon R., Isaboke, Job, Blake, William H., Osano, Odipo, Watts, Michael J., Dowell, Sophia M., Humphrey, Olivier S., Gowing, Charles J.B., Barlow, Thomas S., Chenery, Simon R., Isaboke, Job, Blake, William H., Osano, Odipo, and Watts, Michael J.

Abstract

Land degradation resulting from soil erosion is a global concern, with the greatest risk in developing countries where food and land resources can be limited. The use of fallout radionuclides (FRNs) is a proven method for determining short and medium-term rates of soil erosion, to help improve our understanding of soil erosion processes. There has been limited use of these methods in tropical Africa due to the analytical challenges associated with 137Cs, where inventories are an order of magnitude lower than in the Europe. This research aimed to demonstrate the usability of 239+240Pu as a soil erosion tracer in western Kenya compared to conventional isotopes 210Pbex and 137Cs through the determination of FRN depth profiles at reference sites. Across six reference sites 239+240Pu showed the greatest potential, with the lowest coefficient of variation and the greatest peak-to-detection limit ratio of 640 compared to 5 and 1 for 210Pbex and 137Cs respectively. Additionally, 239+240Pu was the only radionuclide to meet the ‘allowable error’ threshold, demonstrating applicability to large scale studies in Western Kenya where the selection of suitable reference sites presents a significant challenge. The depth profile of 239+240Pu followed a polynomial function, with the maximum areal activities found between depths 3 and 12 cm, where thereafter areal activities decreased exponentially. As a result, 239+240Pu is presented as a robust tracer to evaluate soil erosion patterns and amounts in western Kenya, providing a powerful tool to inform and validate mitigation strategies with improved understanding of land degradation.

Published
2024

34. Optimisation of plutonium separations using TEVA cartridges and ICP-MS/MS analysis for applicability to large-scale studies in tropical soils

Author

Dowell, Sophia M., Barlow, Thomas S., Chenery, Simon R., Humphrey, Olivier S., Isaboke, Job, Blake, William H., Osano, Odipo, Watts, Michael J., Dowell, Sophia M., Barlow, Thomas S., Chenery, Simon R., Humphrey, Olivier S., Isaboke, Job, Blake, William H., Osano, Odipo, and Watts, Michael J.

Abstract

The analysis of plutonium (Pu) in soil samples can inform the understanding of soil erosion processes globally. However, there are specific challenges associated for analysis in tropical soils and so an optimal analytical methodology ensuring best sensitivity is critical. This method aimed to demonstrate the feasibility of sample preparation and analysis of Pu isotopes in African soils, considering the environmental and cost implications applicable to low-resource laboratories. The separation procedure builds upon previous work using TEVA columns, further demonstrating their usefulness for the reduction of uranium (U) interference in ICP-MS analysis with enhanced selectivity for Pu. Here several steps were optimised to enhance Pu recovery, reducing method blank concentration, and improving the separation efficiency through the determination of the elution profiles of U and Pu. The elimination of the complexing agent in the eluent, increased the spike recovery by improving matrix tolerance of the plasma, and simplified the separation procedure, improving throughput by 20%. The subsequent method was validated through the analysis of Certified Reference Material IAEA-384, where high accuracy and improved precision of measurement were demonstrated (measured value 114 ± 12 versus certified value 108 ± 13 Bq kg−1). Optimisation of the column separation, along with the analysis of the samples using O2 gas in ICP-MS/MS mode to mass shift Pu isotopes away from interfering molecular U ions provided a simple, robust, and cost-effective method with low achievable method detection limits of 0.18 pg kg−1 239+240Pu, applicable to the detection of ultra-trace fallout Pu in African soils.

Published
2023

45. A deconvolutional Bayesian mixing model approach for river basin sediment source apportionment

Author

Blake, William H., Boeckx, Pascal, Stock, Brian C., Smith, Hugh G., Bodé, Samuel, Upadhayay, Hari R., Gaspar, Leticia, Goddard, Rupert, Lennard, Amy T., Lizaga, Ivan, Lobb, David A., Owens, Philip N., Petticrew, Ellen L., Kuzyk, Zou Zou A., Gari, Bayu D., Munishi, Linus, Mtei, Kelvin, Nebiyu, Amsalu, Mabit, Lionel, Navas, Ana, and Semmens, Brice X.

Published
2018
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