Colloidal trace metals, organic carbon and nitrogen in a southeastern U.S. estuary

We have used cross-flow ultrafiltration on eleven 0.45-μm-filtered samples taken across the salinity gradient in the Ochlockonee Estuary. We sequentially ultrafiltered the samples using 10- and 1-kD filters (1 kD = 1000 daltons). The results indicate that total Fe and Mn behave nonconservatively in the estuary and that the removal is from the high-molecular-weight (HMW; > 10 kD) fraction although Mn is removed at lower salinity than Fe. For Ni, Cu and Cd, the HMW fraction is very important in the river but these elements are quickly converted from HMW to low-molecular-weight (LMW) species with increasing salinity. Carbon in the HMW fraction is strongly correlated with Fe but only weakly correlated with Fe in the smaller size fractions. The two important processes controlling the behavior of metals, carbon and nitrogen in the estuary are colloid aggregation and desorption or dissociation.