Composition of water and suspended sediment in streams of urbanized subtropical watersheds in Hawaii |
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| Institution: | 1. Department of Physics, University of the Free State, Qwa Qwa Campus, Private bag X13, Phuthaditjhaba, 9866, South Africa;2. Materials and Engineering Research Institute, Sheffield Hallam University, S1 1WB, Sheffield, United Kingdom;1. Arup, 13 Fitzroy Street, London W1T 4BQ, UK;2. Institute of Energy Futures, Howell Building, Brunel University, London UB8 3PH, UK;3. School of Informatics, University of Edinburgh, 10 Crichton Street, Edinburgh EH8 9AB, Scotland, UK;4. Institute of Land Water and Society, Charles Sturt University, PO Box 789, Albury, NSW 2640, Australia;5. Executive in Residence, INSEAD Social Innovation Center, Europe Campus, Boulevard de Constance, 77305 Fontainebleau, France;1. Department of Textile and Polymer Engineering, Yazd Branch, Islamic Azad University, Yazd, Iran;2. Physics Department, Faculty of Science, Yazd University, P.O. Box 89195-741, Yazd, Iran;1. Beijing Advanced Innovation Center for Food Nutrition and Human Health, Beijing Technology and Business University, Beijing 100048, China;2. Department of Chemistry, School of Science, Beijing Technology and Business University, Beijing 100048, China;3. School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing, 100083, China |
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| Abstract: | Urbanization on the small subtropical island of Oahu, Hawaii provides an opportunity to examine how anthropogenic activity affects the composition of material transferred from land to ocean by streams. This paper investigates the variability in concentrations of trace elements (Pb, Zn, Cu, Ba, Co, As, Ni, V and Cr) in streams of watersheds on Oahu, Hawaii. The focus is on water and suspended particulate matter collected from the Ala Wai Canal watershed in Honolulu and also the Kaneohe Stream watershed. As predicted, suspended particulate matter controls most trace element transport. Elements such as Pb, Zn, Cu, Ba and Co exhibit increased concentrations within urbanized portions of the watersheds. Particulate concentrations of these elements vary temporally during storms owing to input of road runoff containing elevated concentrations of elements associated with vehicular traffic and other anthropogenic activities. Enrichments of As in samples from predominantly conservation areas are interpreted as reflecting agricultural use of fertilizers at the boundaries of urban and conservation lands. Particulate Ni, V and Cr exhibit distributions during storm events that suggest a mineralogical control. Principal component analysis of particulate trace element concentrations establishes eigenvalues that account for nearly 80% of the total variance and separates trace elements into 3 factors. Factor 1 includes Pb, Zn, Cu, Ba and Co, interpreted to represent metals with an urban anthropogenic enrichment. Factor 2 includes Ni, V and Cr, elements whose concentrations do not appear to derive from anthropogenic activity and is interpreted to reflect mineralogical control. Another, albeit less significant, anthropogenic factor includes As, Cd and U and is thought to represent agricultural inputs. Samples collected during a storm derived from an offshore low-pressure system suggest that downstream transport of upper watershed material during tradewind-derived rains results in a 2-3-fold dilution of the particulate concentrations of Pb, Zn and Cu in the Ala Wai canal watershed. |
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