In situ size measurements of suspended particles in estuarine and coastal waters using laser diffraction

Abstract

Introduction This chapter looks first at the sources and composition of particles in natural waters, with emphasis on estuarine and coastal environments, and highlights the importance of particles in geochemical and biogeochemical processes. It discusses the tendency of natural particles to form aggregates, and the influence this has on their transport. Recognizing the fragile nature of aggregates, the chapter then looks at the problems associated with the study of natural suspended particles using currently available techniques. Finally, it describes and assesses the performance of a recently developed laser diffraction instrument that allows particles to be sized in the water column, in real time and with minimal physical disturbance. Sources of particles in estuarine and coastal waters Suspended particles in estuaries and coastal waters comprise a heterogeneous mixture of mineral particles and biogenic debris as well as living organisms and their excretory products. Mineral particles originate from the weathering and erosion of crustal material and are transported mainly by rivers and, to a lesser extent, as airborne dust. Pollutant particles, such as fly ash and dust released directly into the water system or deposited from the atmosphere, are also observed (Deuser et al., 1983). The biogenic component comprises primarily the resident phytoplanktonic assemblage, diatoms, and their exoskeletal remains plus refractory land-derived biological material. By contrast, particles in the open oceans away from land sources are predominantly autochthonous and organic (Honjo et al., 1982), though Collier & Edmond (1984) found that traces of terrigenous material were always present at the remotest oceanic sites.