Evaluation of high‐flow rate continuous‐flow centrifugation and filtration devices for sampling and concentrating fine‐grained suspended sediment

Abstract

Fine‐grained (<63 μm) suspended sediment is an important vector for transporting contaminants in aquatic systems. Characterization of physical and biogeochemical properties of suspended sediment usually requires bulk samples to assess its quality and to determine its source. Low‐flow rate (~2 to 4 L min−1) continuous‐flow centrifugation (CFC) systems may need a time period from several hours to one day to collect such samples, and thus, due to their low inflow rate, limits application of these devices. A field study was conducted in three different freshwater systems in Manitoba, Canada to examine and compare the performance of two high‐flow rate systems as alternative approaches: the M512 continuous‐flow centrifuge (M512); and continuous filtration using PENTEK 1 μm filtration bags (filtration system). It was determined that the mass collection efficiency (MCE) for the M512 (in absolute terms) was similar to low‐flow rate CFC systems. As with low‐flow rate CFC systems, the M512 preferentially collected particles of a certain size range (i.e., in the case of M512, particles ≥ 0.83 μm) and accordingly this may affect the collection of a truly geochemically and physically representative sample in waters containing a high proportion of finer particles (≤1 μm). Several filtration systems in series improved its MCE performance and, in terms of total collected mass, this configuration appears to be as efficient as the low‐flow rate CFC systems in an equivalent sampling time. The results of this study confirmed that, in nearly all cases, the filtration system collected a representative sample of ambient suspended sediment, in terms of particle size composition, and geochemical and colour properties. In practice, it is suggested that the filtration systems in series have advantages over M512 as the filtration system is more portable and cost‐effective with a lower power demand.

Sediment sources and transport dynamics in large, regulated river systems with multiple lakes and reservoirs in the subarctic region of Canada

“…All source and suspended sediment samples were placed in prelabeled plastic bags and stored in coolers (i.e., the Red River and the BR samples) or in a refrigerator (at 4°C) on board the Namao (i.e., Lake Winnipeg samples) for further analyses. In the laboratory, suspended sediments were recovered from the filters as described by Goharrokhi et al (2020) and the approach described by Perks et al (2014) was used to obtain samples from the time‐integrated sediment sampler. All the samples were dried at 40°C and manually disaggregated with a mortar and pestle.…”

“…Discrete or point‐in‐time suspended sediment samples at the Lake Winnipeg outlets were collected from the Namao using high‐flow rate continuous‐flow centrifugation and filtration devices (for details on these samplers see Goharrokhi et al, 2020). Suspended sediment samples were collected during whole‐lake spring, summer, and fall cruises of the Namao and, thus, are representative of any seasonal variability in the contribution of sediment sources.…”

“…Winnipeg samples) for further analyses. In the laboratory, suspended sediments were recovered from the filters as described by Goharrokhi et al (2020) and the approach described by Perks et al (2014) was used to obtain samples from the time-integrated sediment sampler.…”

Polycyclic aromatic hydrocarbons in terrestrial and aquatic environments following wildfire: a review

“…There are a number of methods for the collection of fluvial sediment including time integrated passive samplers (Figure 7, Box 3a), resuspension of bed sediments, collection of bed scrapes, or pointin time samples (Figure 7, Box 3b), which include continuous-flow centrifuge (CFC) or grab samples. The use of passive sediment samplers (Phillips et al, 2000) or high-volume filtration devices (Goharrokhi et al, 2020) are recommended here due to their low cost, minimal maintenance, and because they capture sediment that is actively being transported over a longer duration (i.e., numerous hours to months) than other methods that are often snapshots in time.…”

“…However, depending on the sediment load of a particular stream or river, passive samplers may not collect enough sediment for PAH analysis (>10 g dry weight) and thus, methods like the CFC or resuspension of finegrained channel bed-stored sediment may be a better option. With the exception of the CFC and high-volume filtration device (Goharrokhi et al, 2020), all of these methods collect a large quantity of water with the sediment samples, which must be removed in order to isolate the sediment for analysis. After collecting the water-sediment mixtures, they should be left undisturbed to allow the sediment to settle, after which the excess water should be siphoned off and the sediment at the bottom moved into clean glassware in preparation for lab analysis.…”