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-mm 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.

Fractionation of iron species and iron isotopes in the Baltic Sea euphotic zone

“…Other phytoplankton exudates not detected by this method may be of importance though, since they exist over a continuum of size ranges (Verdugo et al, 2004), and the TEP method only measures those >0.45 µm. Stolpe and Hassellöv (2010) found significant amounts of Fe associated to colloidal biopolymers in surface seawater in the Skagerrak Sea after periods of high primary production. However, FFF-ICPMS data (Fig.…”

“…1) suggest that terrestrial fulvic acid associated Fe is a major colloidal component in the Baltic Sea. In addition, FFF-ICPMS detected that larger (3-50 nm) colloidal biopolymers form in surface seawater after periods of high primary production (Stolpe and Hassellöv, 2010). In the Bothnian Sea, although these types of biopolymers occurred during summer, iron was found to be exclusively associated to fulvic acid (0.5-4 nm size fraction) from terrestrial sources (Fig.…”

“…1e). By the use of Atomic Force Microscopy (AFM) the sizes of these nanofibrils were determined to 50-250 nm in length and 0.5-1.1 nm in thickness and associated with TEP (Stolpe and Hassellöv, 2010).…”

“…1) and other elements have been determined by Field Flow Fractionation coupled to Inductively Coupled Plasma Mass Spectrometry (FFF-ICPMS) in a number of studies, ranging from river water (Dahlqvist et al, 2007;Lyvén et al, 2003), and surface water from the brackish Bothnian Sea (Salinity ∼4.7) through the Baltic Proper (this study, Salinity ≥7) and the Skagerrak coast (Salinity >20) at the North Sea boundary (Stolpe and Hassellöv, 2010). In river water, colloid-associated iron is mainly distributed between 0.5-4 nm macromolecules of humic-type fluorescent organic matter (presumed fulvic acid) and 3-50 nm iron rich colloids (presumed Fe(III)-hydroxide/oxyhydroxide; Hassellöv and von der Kammer, 2008).…”

Iron biogeochemistry across marine systems – progress from the past decade

“…Stolpe and Hassellöv (2010) coupled Flow Field Flow Fractionation (FlFFF) with ICPMS, on-line "humic" fluorescence and UV-absorbance detectors, and subsamples for Atomic Force Microscopy (AFM) to fractionate and identify different colloidal size classes and associated trace metals during phytoplankton bloom events in a Fjord on the North Sea coast of Sweden. They found both seasonal and vertical variations in the colloidal size distributions for iron and other trace elements and could use these in order to explain the apparent iron solubility and vertical distribution to a large extent (Stolpe and Hassellöv, 2010). During the winter season colloidal size distribution for iron (and many other elements) were only appearing in the CDOM fraction (∼0.5-3 nm), while during the spring bloom and summer bloom in two consecutive seasons the colloidal size distributions for iron were shifting dramatically.…”