The distribution of organic carbon (OC) and of some metals (Cu, Mn) amongst
the particulate (>0.2 mu m), colloidal (10 kDa-0.2 mu m) and the truly dis
solved (<10 kDa) fractions of the River Marne was investigated during the p
hytoplankton spring bloom. A tangential ultrafiltration (UF) device was uti
lized to separate the colloidal fraction. On average, 22% of the OC, 31% of
the Cu and 53% of the Mn, usually assigned to the so-called dissolved frac
tion, were found in the colloidal fraction. The colloidal fraction exhibite
d a behaviour different from that of the particulate and truly dissolved fr
actions. Autochthonous production led to enrichment in the colloidal and pa
rticulate OC pools: up to 47% of the total dissolved OC was in the colloida
l fraction. An increase in the colloidal metal fraction, concomitant with a
fall in the truly dissolved fraction, coincided with peaks in phytoplankto
n during the bloom. These phenomena might be related either to an increase
in pH associated with photosynthetic activity, resulting in the precipitati
on of truly dissolved forms into the colloidal fraction, or to scavenging o
f the truly dissolved metals by the algal species of colloidal size.
The interaction between the colloidal and the truly dissolved phases was ve
ry important. The partition coefficients of the Cu and Mn between the collo
idal and truly dissolved fractions were higher than between the particulate
and the truly dissolved fractions. This pattern is consistent with a great
er specific surface area of colloids than macroparticles. Consequently, the
adsorption and complexation capacities are enhanced in the colloidal fract
ion of the particulate matter.
The extraction of hydrophobic complexes with Cu using C-18 Sep-Pak columns,
showed that the Cu occurring in colloidal, total dissolved or truly dissol
ved forms was significantly complexed by the organic matter. The truly diss
olved fraction might be complexed up to 100% during a phytoplankton bloom.
Copyright (C) 1999 John Wiley & Sons, Ltd.