Guidelines for monitoring of turbidity.

Abstract

Turbidity estimates the impact of light scattering due to particles on the level of light attenuation in the water column. It is affected by total suspended solids (i.e., organic and inorganic particles) in the water, and thus differs from water transparency, which is also dependent on the amount of chromophoric dissolved organic matter (CDOM). Organic particles are mainly autochthonous (phytoplankton, zooplankton, bacterial cells) and thus are related to the trophic state whereas inorganic particles are largely allochthonous (e.g., resuspension, fluvial sediment load). This source of error has to be taken into consideration whenever eutrophication status is assessed using turbidity in the Baltic Sea that is optically classified as a Case II water body (Morel and Prieur 1977), i.e., the body where concentrations of colour producing substances (e.g. phytoplankton, inorganic particles and CDOM) vary independently from each other. For turbidity, this feature is emphasized in coastal areas subject to fluvial impact. The representativeness of turbidity as an eutrophication metrics increases towards offshore areas; here, an increasing share of particles causing turbidity is of autochthonous origin. This has been utilized in the ship-of-opportunity (SOOP) approach. The scope of this guideline is turbidity, measured either with turbidity meters in a laboratory or with turbidity sensors on board research vessels or in the SOOP and other autonomous systems. 1.2 Purpose and aims The purpose for turbidity monitoring is to describe spatiotemporal trends in total suspended solids. Turbidity provides information of total suspended solids that can serve as a diagnostic of eutrophication (with certain limitations mentioned above). It is thus an element of eutrophication monitoring, although only as a supporting parameter.