SEDIMENTATION OF EXPERIMENTALLY ADDED CADMIUM AND CD-109 IN LAKE-382,EXPERIMENTAL LAKES AREA, CANADA

From 1987 to 1992, Cd was added during the ice-free season to Experime ntal Lakes Area (ELA) Lake 382 at loadings of 1.7-4.2 mg . m(-2). year (-1). Cd was lost rapidly from the water column to sediments. Sediment cores (1987-1993) document increasing (from <1 to >5 mg . kg dry mass (-1)) sediment Cd concentration over time, sediment storage accounting for 90-95% of added Cd. Sedimentation of Cd occurred in both depositi onal and erosional sediment zones. Sandy sediments at shallow sites, d espite having low sediment Cd concentrations, were important sinks for Cd because of their great mass per unit area. Progressive transport o f Cd into the mixed sediment layer (8-10 cm thick, mixing in a decade or more) at deep sites was another important sink. Selective extractio ns suggest weak surface adsorption of Cd to Mn and Fe oxyhydroxides in periphyton and sedimenting particles, with high K-d Bottom sediments have lower K-d, although Cd tends to be associated with more strongly bound organic or sulfide fractions. This may indicate loss of easily m obilized Cd from bottom sediment during diagenesis. Because Cd is read ily released from fresh sediment, we hypothesize that recycling of sed iment Cd to the water column will slow the recovery of Lake 382 to pre manipulation conditions.