| Popis: |
Fluxes and pathways of silicon in a marine rainbow trout cage farm were studied. The measured fluxes included those carried by fish food, juveniles, harvest, fish loss (death and escape), sedimentation from the cages, and benthic release measured with flux chambers in-situ. Two different types of Si mass balances for the farm were constructed. The mass balance according to the flux method was based on the measured fluxes and constructed for each of two consecutive growing seasons. The mass balance constructed according to the accumulation method was based on the total input and removal of Si to the cages of the farm since it was started, and the recovery of Si in the sediment originating from the farm. In both types of mass balances external input was the major source of Si, contributing a minimum of 55–80% of the total biogenic silica in the material collected in sediment traps below the farm and of the material accumulated in the farm-derived sediment. The Si removed from the farm with harvest contributed a very small part, ∼0.3%, of the amount of Si supplied to the farm with fish food and juveniles. The loss of Si to the environment was 2.4 kg (1985), 2.5 kg (1986) and 2.5 kg (1980–1986) for each ton of fish produced. On a seasonal basis, about 4.5% of the sedimented biogenic Si was returned in dissolved form from the sediment to the overlying water. This constituted about 0.3% of the biogenic Si content in the farm-derived sediment. The flux of reactive silicate from sediment below the fish farm was enhanced about 2.5 times compared to nearby sediments unaffected by the farm. |
