THE ABUNDANCE, DISTRIBUTION, AND CONFIGURATION OF POREWATER ORGANIC COLLOIDS IN RECENT SEDIMENTS

The characterization and quantitation of aquatic organic colloids isolated from sedimentary porefluids was performed by size exclusion chromatography (SEC) with UV detection and ultrafiltration (UF) with total organic carbon analysis and UV detection. Separation of the samples and several well-characterized humic substances by SEC was found to be highly dependent upon the ionic strength of both the mobile phase and sample matrix. The elution of samples containing indifferent electrolyte concentrations by low ionic strength mobile phases yielded multipeak chromatograms and may be subject to misinterpretation as true molecular weight distributions. A dynamic coiling/uncoiling mechanism is offered as an explanation for the observed phenomenon. For well-characterized humic substances eluted with high ionic strength mobile phases, number- and weight-average molecular weights as well as the polydispersivities were calculated and were found to be in good agreement with other recently published values. Molecular weight distributions for Suwanee fulvate determined by both sizing techniques appeared to be in reasonable agreement. Ultrafiltration was used to separate organic colloids from low molecular weight components in sedimentary porewaters. Vertical profiles in the cores showed depletion of colloids near the sediment/water interface and accumulation of macromolecules with depth. Porewater colloids collected using glass fritted samplers appeared to confirm this trend, although lower values were recovered than when extracted by centrifugation methods.