Investigation of a Sequential Filtration Technique for Particle Fractionation I A N G . DROPPO,* B O M M A N N A G . KRISHNAPPAN, SALEM S. RAO, AND EDWIN D . O N G L E Y National Water Research Institute, 867 Lakeshore Road, P. 0. Box 5050, Burlington, Ontario, Canada L 7R 4A6
introduction The ecology of an aquatic environment is strongly mediated by the suspended and bottom sediments within the system. Many nutrients and environmentally sensitive contaminants have environmental pathways that are primarily or exclusively associated with aquatic sediments ( 1 ) . Therefore, sediments may represent important components for contaminant transport and for bio-uptake by various filter feeders. Investigations into the chemically active fraction ('63 pm), the effects of particle size on the adsorption of contaminants, and the association of microbial organic matter with aquatic sediment among others often require that the sediment be separated into a number of size fractions. Such separation or fractionation can be achieved in a number of ways. Some of the common fractionation methods include centrifugation ( Z ) , cyclosizer (3), air elutriation ( 4 ) ,water elutriation (9,and sequential filtration (6-11), The objective of this paper is to evaluate the sequential filtration methodology's propensity to effectively separate targeted size classes of a sediment suspension.
Materials and Methods Sample Preparation. Flocs or aggregates are inherently unstable, and the act of sampling and analyzing them may result in their disaggregation or further flocculation. Because of the difficulty in maintaining the integrity of flocculated material, the sediment used for the study was a fully dispersed (primary particle) inorganic bottom sediment from Lake Erie offshore of Port Stanley and Port Burwell. The use of primary particles was necessary to avoid erroneous distributions caused by aggregation or disaggregation during the filtration and sizing procedures and to allow for accurate comparisons between fractional distributions. The organic content of the sediment was 2.9% as measured by the process of loss on ignition (3 g of sediment at 500 "C for 3 h). The sediment was wet sieved through a 62-um mesh to ensure an upper size limit and a size distribution in the silt and clay range. The
