| Abstract/Description or Keywords |
Continuous flow centrifugation (CFC) is used in water studies for the bulk collection of suspended sediment, thus allowing a broad range of sediment quality analysis. However, various studies have demonstrated issues associated with CFC such as: particle distribution change; contamination of sediments from instrument components or a restricted cleansing ability; and a lack of comparable efficiency rates of sediment collection. Experiments were undertaken to establish the efficiency of collection and potential changes of organic matter (OM) and particle size (PS) by CFC using the US M-512 manual centrifuge. The experiment included three different sediment types with two varied concentrations that were completed in a controlled experiment. Samples of the water-sediment mixture were collected systematically throughout the experiments and processed for various characteristics. The collection efficiency was evaluated using suspended sediment concentration variation between the influent and effluent samples collected. OM change was calculated using loss-on-ignition of the filtered sediment and PS was analysed using a LISST-ST (Laser in Situ Scatter and Transmissometry) particle size analyser. Sediment collection efficiency recorded for all sediments was < 50%, a value much lower than previous literature for different manufacturer’s centrifuges. Furthermore, time-series of sediment retention indicated consistent collection efficiency. The centrifuge preferentially retained the mineral component of fluvial sediment but there was no significant change of OM in kaolinite or agricultural sediments caused by centrifugation. An increase in the fine fraction (<63 _m) of the PS distribution for all sediments was observed. Given the usefulness of CFC to collect adequate quantities of sediment for analysis, even in low concentration water bodies, the continued use of the US M-512 centrifuge instrument is acceptable when the associated limitations are acknowledged. As a consequence of this paper, OM content values and effective PS distributions must be considered carefully whilst there are actions that may be taken to improve the efficiency of sediment collection in future applications. |
