Response of nephelometric turbidity to hydrodynamic particle size of fine suspended sediment |
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| Affiliation: | 1. State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau, Institute of Soil and Water Conservation, Northwest Agricultural and Forestry University, Yangling, Shannxi, 712100, China;2. State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau, Institute of Soil and Water Conservation, Chinese Academy of Science and Ministry of Water Resources, Yangling, Shaanxi, 712100, China;3. University of Chinese Academy of Sciences, Beijing, 100049, China;4. College of Life Sciences, Guizhou University, Guiyang, Guizhou, 550025, China;1. Institution of Land Utilization, Technology and Regional Planning, Faculty of Agricultural and Food Sciences and Environmental Management, University of Debrecen, Debrecen, Hungary;2. Administration of Natural Resources Management, General Commission for Scientific Agricultural Research (GCSAR), Damascus, Syria;3. Department of Soil Sciences and Land Reclamation, Faculty of Agriculture, Al-Baath University, Homs, Syria;4. Department of Soil and Environment, Swedish University of Agricultural Sciences (SLU), Uppsala, Sweden;5. Institute of Research and Development, Duy Tan University, Danang, 550000, Viet Nam;6. Faculty of Environmental and Chemical Engineering, Duy Tan University, Danang, 550000, Viet Nam;7. Faculty of Water Resource Engineering, Thuyloi University, Hanoi, Viet Nam;8. Ho Chi Minh City University of Technology (HUTECH), 475A, Dien Bien Phu, Ward 25, Binh Thanh District, Ho Chi Minh City, Viet Nam;9. Sustainable Management of Natural Resources and Environment Research Group, Faculty of Environment and Labour Safety, Ton Duc Thang University, Ho Chi Minh City, Viet Nam;1. Department of Civil Engineering, National Institute of Technology, Warangal, India;2. School of Engineering, University of Glasgow, Glasgow, UK;3. School of Civil Engineering, Beijing Jiaotong University, Beijing, China;4. Department of Civil Engineering, Institute of Infrastructure Technology Research and Management, Ahmedabad, India;5. College of Agriculture, Waraseoni District, Balaghat M.P., India;1. College of Harbour, Coastal and Offshore Engineering, Hohai University, Nanjing 210098, China;2. School of Civil and Environmental Engineering, Nanyang Technological University, Singapore 639798, Singapore |
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| Abstract: | Turbidity is used as a surrogate for suspended sediment concentration (SSC), and as a regulatory tool for indicating land use disturbance and environmental protection. Turbidity relates linearly to suspended material, however, can show non-linear responses to particulate organic matter (POM), concomitant with changes in particle size distribution (PSD). In the paper the influence of ultra-fine particulate matter (UFPM) on specific turbidity and its association with POM in suspended sediment are shown for alpine rivers in the Southern Alps of New Zealand. The approach was two-fold: a field-based investigation of the relations between SSC, POM, and turbidity sampled during event flow; and experimental work on hydrodynamic particle size effects on SSC, POM, PSD, and turbidity. Specific turbidity changes over event flow and are sensitive to increasing proportional amounts of sand, UFPM, and POM in suspension. Furthermore, the UFPM is the size fraction (<6 μm) where POM increases. The implications of the current study are that the slopes of turbidity-SSC relations are undesirable in locations that may be dominated by cyclic release of POM or distinct pulses of fine-grained material. At locations where the turbidity-SSC slopes approximate 2, the POM proportion is usually <10% of the total suspended load. However, when turbidity-SSC slopes are <1 this is likely caused by high amounts of side-scatter from UFPM concomitant with higher proportions of POM. Thus, the use of turbidity as a proxy for determining SSC may have serious consequences for the measurement of representative suspended sediment data, particularly in locations where POM may be a significant contributor to overall suspended load. |
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| Keywords: | Turbidity Nephelometry Suspended sediment concentration Particle size distribution Particulate organic matter |
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