Characterization of suspended particulate matter surrounding a salmonid net-pen in the Broughton Archipelago, British Columbia

A held study was carried out on the central coast of British Columbia in Ma rch 1999 to determine particle fluxes arising from a salmonid net-pen durin g feeding. Water samples were collected within, beside, and at two depths r elative to a net-pen and analysed for suspended particulate matter (SPM), m ajor and minor elemental abundance, carbon/nitrogen content, and stable car bon isotopes. Sediment traps were also deployed immediately beside the bott om of the net-pen. The highest mean concentration of SPM (0.6 mg 1 (1)) dur ing the feeding cycle was observed within the central region of the net-pen . Approximately 87% and 30% of the mean SPM were observed at depth and besi de the net-pen, respectively. suggesting that transport of suspended partic ulates was predominantly in the Vertical direction. Sediment trap deploymen ts revealed that sedimentation fluxes of total SPM. carbon. and nitrogen we re higher below the farm than ar the control sire located 500 m away. Major and minor elemental analyses of feed pellets and sediment trap contents sh owed that calcium, phosphorus, sulphur, and strontium were removed within t he net-pen system. The feed-specific carbon isotope signature (delta C-13 = -21.4 to -22.0 parts per thousand) was not evident in the trap samples dep loyed beside the bottom of the net-pen (delta C-13 = -23.4 parts per thousa nd). suggesting the relative absence of feed pellet particles, isotopic alt eration through fish assimilation and/or dilution of the isotope signature with other carbon sources. However, a feed-signature was evident in samples collected in the upper water column (depth 5 m). suggesting that delta C-1 3 might serve as a useful tracer of feed particles.