Nanofibrils and other colloidal biopolymers binding trace elements in coastal seawater: Significance for variations in element size distributions

Abstract

Colloidal size spectra of Fe, Cu, Ag, La, and Pb were determined by asymmetrical flow field-flow fractionation coupled to high-resolution inductively coupled plasma mass spectrometry, in samples from 0.5-40-m depth profiles from the Gullmarsfjord on the Swedish west coast, at nine occasions between February 2004 and July 2005. Trace elements were quantified in unfiltered and 0.45-μm filtered samples, and total organic carbon and transparent exopolymer particles were measured. Atomic force microscopy was used to determine sizes and shapes of colloids. Most Fe was associated with Al-rich particles that were resuspended from the sediment or derived from a local river. Dissolved Fe and Cu had depth profiles similar to total organic carbon and transparent exopolymer particles, and highest concentrations occurred in the surface and the upper mixed-water layer, where the in situ biological production and the inputs of water from the Baltic Sea and a local river were high. The colloidal size spectra of the elements, and the atomic force microscopy images, revealed that three to four classes of colloids were present in the samples, differing in size, shape, and element-binding properties. Small (0.5-3 nm) spherical macromolecules of chromophoric dissolved organic matter, binding most elements, occurred at all depths and on all sampling occasions. Populations of 3-7-nm globular or slightly elongated colloids, binding Cu, Ag, and Pb, and 7-40-nm fibrillar colloids, binding Fe and Pb, appeared in the upper mixed-water layer during late spring and summer, thereby changing the colloidal size spectra of associated elements in June-July. © 2010, by the American Society of Limnology and Oceanography, Inc.