Sedimentation and Carbon Flux in a Scottish Sea Loch, Loch Linnhe

Sediment traps were deployed in the upper basin of Loch Linnhe in 120 m of water at depths of 20, 60, 90 and 110 m below the surface. They were serviced over 13 months during 1991–92 at intervals ranging from a week to a month and the following parameters measured: dry weight and concentrations of carbon, nitrogen and chlorophyll. The average sedimentation rates of total dry weight over a year at 20, 60, 90 and 110 m were 12•4, 20•4, 31•0 and 48•5 g m−2day−1respectively. The historical net sedimentation rate, calculated from the depth profile of210Pb, was 12•7 g m−2day−1, suggesting that the sedimentation rate at 20 m is probably a good estimate of the present net sedimentation rate. On this basis the (estimated) sedimentation at the sediment surface (120 m) was composed of approximately 80% resuspended material. The estimate of input of organic carbon of phytoplankton origin was based on chlorophyll sedimentation rates and yielded a figure of 0•082 g C m−2day−1. A summary diagram indicating our estimate of the pathways of particulate organic carbon is presented.