Cadmium in the North Sea—a mass balance

Abstract

Based on recently published data on cadmium concentrations in the different compartments of the North Sea ecosystem, i.e. water, suspended particulate matter, biota and sediments, and based on 3D circulation simulations, a (preliminary) mass balance for cadmium in the North Sea was worked out by estimating the contents in the compartments as well as the advective and other fluxes into/out of and within the system. It turns out that the total cadmium content in the water of 810 ± 320 t is in the same order of magnitude as the amount of cadmium in the sediment 1000 ± 500 t. The net deposition flux of cadmium to the sediments (8 t/yr) amounts only to about 3% of the annual anthropogenic input. The amount of cadmium in the biota is about 63 ± 12 t, but the annual turnover of cadmium due to primary production, herbivorous grazing and remineralisation is at least of the same order. The anthropogenic cadmium input from rivers, atmosphere and direct discharges of 310 ± 185 t/yr would add again the total cadmium content in the water in about 2.6 yr. The flushing of the North Sea circulation is very effective: in about 0.7 yr the cadmium contained in the water of the North Sea would be washed out, if no new cadmium would be introduced. The net outflow of cadmium across the northern boundary (307 t/yr) is equal to the anthropogenic input. Thus, in the mid eighties, the mass balance of cadmium in the North Sea has reached a steady-state within the error bars given.