Abstract :
Solid-phase and pore-water Cu have been determined for two cores in the low-salinity (2–3‰) Kalix River estuary, Sweden. The pore-water Cu concentration in the oxidized surface layer of the sediment (32–42 nmol l−1) exceeded the Cu concentration in the overlying bottom water (10–11 nmol l−1) by a factor of 3–4. Assuming that organic matter degradation follows first-order kinetics, a multi-G model with two organic matter fractions of different reactivity was used to describe the early diagenetic decomposition of organic matter. An estimated Cu/C mole ratio of 5.10−5 was obtained from sediment trap data. By combining this ratio with a steady-state pore-water Cu model, the early diagenetic remobilization of Cu was linked to the decomposition of organic matter. The rate constant for the reaction that releases Cu could be set equal to the decay constant of the highly reactive organic matter fraction (2.0 yr−1). This highly reactive fraction was decomposing under aerobic conditions close to the sediment-water interface. Early diagenetic remobilization of Cu in these sediments thus appears to be entirely controlled by aerobic decomposition of organic matter. An estimate of the diffusive benthic efflux of Cu (2.9 nmol cm−2 yr−1) suggests that ˜ 3% of the amount of Cu being deposited is released back into the water column.
The pore-water model supports the idea that the Redfield model for the biological control of nitrogen and phosphorus can be extended to certain bioreactive trace elements.
