title: Is the wash-off process of road-deposited sediment source limited or transport limited?
abstract: An in-depth understanding of the road-deposited sediments (RDS) wash-off process is essential to estimation of urban surface runoff pollution load and to designing methods to minimize the adverse impacts on the receiving waters. There are two debatable RDS wash-off views: source limited and transport limited. The RDS build-up and wash-off process was characterized to explore what determines the wash-off process to be source limited or transport limited based on twelve RDS sampling activities on an urban road in Beijing. The results showed that two natural rain events (2.0mm and 23.2mm) reduced the total RDS mass by 30%-40%, and that finer particles (<105μm) contributed 60%-80% of the wash-off load. Both single- and multi-rain events caused the RDS particle grain size to become coarser, while dry days made the RDS particle grain size finer. These findings indicated that the bulk RDS particles wash-off tends to be transport limited, but that finer particles tend to be source limited. To further explore and confirm the results of the field experiment, a total of 40 simulated rain events were designed to observe the RDS wash-off with different particle size fractions. The finer particles have a higher wash-off percentage (Fw) than the coarser particles, and the Fw values provide a good view to characterize the wash-off process. The key conclusions drawn from the combined field and simulated experiments data are: (i) Finer and coarser particle wash-off processes tend to be source limited and transport limited, respectively. (ii) The source and transport limited processes occur during the initial period (the first flush) and later periods, respectively. (iii) The smaller and larger rain events tend to be transport limited and source limited, respectively. Overall, the wash-off process is generally a combination of source and transport limited processes.
authors.affiliation: State Key Laboratory of Urban and Regional Ecology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China. Electronic address: htzhao@rcees.ac.cn.
authors.forename: Hongtao
authors.initials: H
authors.lastname: Zhao
authors.affiliation: State Key Laboratory of Urban and Regional Ecology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China.
authors.forename: Xuefei
authors.initials: X
authors.lastname: Chen
authors.affiliation: State Key Laboratory of Urban and Regional Ecology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China; University of Chinese Academy of Sciences, Beijing 100049, China.
authors.forename: Shaonan
authors.initials: S
authors.lastname: Hao
authors.affiliation: State Key Laboratory of Urban and Regional Ecology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China.
authors.forename: Yan
authors.initials: Y
authors.lastname: Jiang
authors.affiliation: Zhenjiang Urban Planning and Design Institute, Zhenjiang 212132, China.
authors.forename: Jiang
authors.initials: J
authors.lastname: Zhao
authors.affiliation: State Key Laboratory of Urban and Regional Ecology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China; College of Environmental Science and Engineering, Qingdao University, Qingdao 266071, China.
authors.forename: Changliang
authors.initials: C
authors.lastname: Zou
authors.affiliation: College of Environmental Science and Engineering, Qingdao University, Qingdao 266071, China.
authors.forename: Wenxia
authors.initials: W
authors.lastname: Xie
mesh_terms: D000068476:Beijing; D004784:Environmental Monitoring; D004785:Environmental Pollutants / Q000032:analysis*; D019015:Geologic Sediments / Q000032:analysis*; D010316:Particle Size; D011891:Rain; D014186:Transportation
chemical_list: D004785:Environmental Pollutants
keywords: Build-up and wash-off; Particle grain size; Source limited; Transport limited; Urban surface runoff