Ecological Survey of Sediment Flux in Coastal Fish Farms I : Decomposition Features of the Flux

In order to know the decomposition mechanisms of sedimented matters in coastal fish farm, chemical features of the sediments were observed in comparison with non-fish farm. The observations were conducted in December 1980 and August 1981 in the vicinity of Fisheries Research Laboratory, Kagoshima University. Two-liter-traps were submerged at 1m, 5m and 10m from the sea bottom. The periods of suspension were appointed to be 1 day, 2 days, 4 days, 7 days and 10 days. Organic carbon, organic nitrogen and total phosphate were analyzed in each observation. Tipical examples of the sediment decomposition were observed in 1-day-suspension of the traps. In August, average organic carbon in fish farm and non-fish farm were 15.6 and 5.6 g/㎡/day, respectively. Organic nitrogen in August were 1.7 g/㎡/day in fish farm and 0.7 g/㎡/day in non-fish farm. Total phosphate, 1.9 g/㎡/day, in fish farm was nineteen times higher than that in non-fish farm. The results obtained in December showed almost same trends as mentioned above. The decomposition coefficient of organic flux in deep layer, however, was 30~70% higher than that in case of August