Optimization and quality control of suspended particulate matter concentration measurement using turbidity measurements

Abstract

The dry weight concentration of suspended particulate material, [SPM] (units: mg L -1 ), is measured by passing a known volume of seawater through a preweighed filter and reweighing the filter after drying. This is apparently a simple procedure, but accuracy and precision of [SPM] measurements vary widely depending on the measurement protocol and experience and skills of the person filtering. We show that measurements of turbidity, T (units: FNU), which are low cost, simple, and fast, can be used to optimally set the filtration volume, to detect problems with the mixing of the sample during subsampling, and to quality control [SPM]. A relationship between T and 'optimal filtration volume', V opt , is established where V opt is the volume at which enough matter is retained by the filter for precise measurement, but not so much that the filter clogs. This relationship is based on an assessment of procedural uncertainties in the [SPM] measurement protocol, including salt retention, filter preparation, weighing, and handling, and on a value for minimum relative precision for replicates. The effect of filtration volume on the precision of [SPM] measurement is investigated by filtering volumes of seawater ranging between one fifth and twice V opt . It is shown that filtrations at V opt maximize precision and cost effectiveness of [SPM]. Finally, the 90% prediction bounds of the T versus [SPM] regression allow the quality control of [SPM] determinations. In conclusion it is recommended that existing [SPM] gravimetric measurements be refined to include measurement of turbidity to improve their precision and quality control.

Shellfish Aquaculture from Space: Potential of Sentinel2 to Monitor Tide-Driven Changes in Turbidity, Chlorophyll Concentration and Oyster Physiological Response at the Scale of an Oyster Farm

“…Seawater samples were stored in 1 l bottles until they were filtered in the laboratory in the evening. The turbidity, T (in Formazin Nephelometric Unit, FNU), of each water sample was determined in triplicate using a 2100Q portable turbidimeter (Hach Company, Loveland, CO, USA) in order to optimize the volume of filtered seawater as in Neukermans et al (2012). SPM, defined as the dry mass of particles per unit volume of seawater, was then determined using a standard gravimetric technique.…”

Physical, Bio-Optical State and Correlations in North–Western European Shelf Seas

“…In this paper the focus is on assessing the quality of fit (R), statistical significance F-statistic (p-value), measure of average uncertainty in model prediction MAPD and UPD as widely presented in literature [8,21,[42][43][44].…”

“…The color of seawater driven by high SPM concentrations produces mostly reddish to brown waters although different shades can result from varying mineral compositions [15,19]. Measuring SPM is not challenging but accuracy, as well as precision of measurements varies depending on skills, instrumentation and approach implemented and therefore turbidity can also be used to assess the type of SPM [20,21]. Water turbidity is a proxy for transparency or scattering material and is driven by the amount of scattering suspended material at a location, the particulate material physical properties and medium refractive index.…”

Suspended matter concentrations in coastal waters: Methodological improvements to quantify individual measurement uncertainty

“…Standard procedures exist for [TSM] determination in fresh and sea water (Strickland and Parsons, 1968;Pearlman et al, 1995). Further improvements of these standard procedures have been described and evaluated most recently by Stavn et al, 2009 andNeukermans et al, 2012b. However, no evaluation of the determination uncertainty for individual samples is available.…”

“…This salt cannot be washed out completely as the margin of the filter is covered by the edge of the filtration funnel during washing. Attempts were made to remove the salt from the margins by rinsing additionally the rim of the filter after the funnel has been removed (Strickland and Parsons, 1968, Tilstone et al, 2002, Neukermans et al, 2012b. The salt water enters the margin by capillary forces, as often the seawater is poured onto dry filters.…”