title: Light attenuation - a more effective basis for the management of fine suspended sediment than mass concentration?
abstract: Fine sediment continues to be a major diffuse pollution concern with its multiple effects on aquatic ecosystems. Mass concentrations (and loads) of fine sediment are usually measured and modelled, apparently with the assumption that environmental effects of sediment are predictable from mass concentrations. However, some severe impacts of fine sediment may not correlate well with mass concentration, notably those related to light attenuation by suspended particles. Light attenuation per unit mass concentration of suspended particulate matter in waters varies widely with particle size, shape and composition. Data for suspended sediment concentration, turbidity and visual clarity (which is inversely proportional to light beam attenuation) from 77 diverse New Zealand rivers provide valuable insights into the mutual relationships of these quantities. Our analysis of these relationships, both across multiple rivers and within individual rivers, supports the proposition that light attenuation by fine sediment is a more generally meaningful basis for environmental management than sediment mass. Furthermore, optical measurements are considerably more practical, being much cheaper (by about four-fold) to measure than mass concentrations, and amenable to continuous measurement. Mass concentration can be estimated with sufficient precision for many purposes from optical surrogates locally calibrated for particular rivers.
authors.affiliation: National Institute of Water and Atmospheric Research Ltd (NIWA), Hamilton, New Zealand E-mail: r.davies-colley@niwa.co.nz.
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Davies-Colley
authors.affiliation: Department of Environmental Science, Xi'an Jiaotong Liverpool University, Dushu Lake Higher Education Town, Suzhou Industrial Park, Jiangsu, China.
authors.forename: Deborah J
authors.initials: DJ
authors.lastname: Ballantine
authors.affiliation: National Institute of Water and Atmospheric Research Ltd (NIWA), Hamilton, New Zealand E-mail: r.davies-colley@niwa.co.nz.
authors.forename: Sandy H
authors.initials: SH
authors.lastname: Elliott
authors.affiliation: National Institute of Water and Atmospheric Research Ltd (NIWA), Hamilton, New Zealand E-mail: r.davies-colley@niwa.co.nz.
authors.forename: Andrew
authors.initials: A
authors.lastname: Swales
authors.affiliation: National Institute of Water and Atmospheric Research Ltd (NIWA), Hamilton, New Zealand E-mail: r.davies-colley@niwa.co.nz.
authors.forename: Andrew O
authors.initials: AO
authors.lastname: Hughes
authors.affiliation: National Institute of Water and Atmospheric Research Ltd (NIWA), Wellington, New Zealand.
authors.forename: Mark P
authors.initials: MP
authors.lastname: Gall
mesh_terms: D011232:Chemical Precipitation; D019015:Geologic Sediments / Q000737:chemistry*; D008027:Light; D009520:New Zealand; D045483:Rivers; D014865:Waste Disposal, Fluid / Q000379:methods*; D014867:Water / Q000737:chemistry; D014874:Water Pollutants, Chemical / Q000737:chemistry
chemical_list: D014874:Water Pollutants, Chemical; D014867:Water