To obtain information on the threshold level of eutrophication inhibiting the reproduction of useful marine organisms in shallow waters, the relation between the organic matter content of bottom sediment and the benthic biomass was analyzed in Ise and Mikawa Bays.
Of the benthic biomass, Polychaeta was dominant, and occurred in 39 species in Ise Bay, 75 percent in individuals, 14.4 percent in wet weight; while in Mikawa Bay it was 40 species, 45.1 percent in individuals, 21.9 percent in wet weight. The benthos occurred densely at the mouth of both bays and the east-side of Chita peninsula. In Ise Bay, the organic matter content of the sediment, ranging from 1.9 to 30.5 mg/g in TOC, from 0.22 to 3.61 mg/g in TN, was lower than that in the neighboring bays. On the contrary, dissolved iron in the pore water of the sediment showed a remarkable high value, 0.4mg/
l in average. The ratio of C/N was also higher than in Mikawa Bay. Horizontal distribution of COD, TOC, and TN in the sediment was generally similar, and the organic matter contents were the highest in the coastal area from Tsu to Matsusaka in Ise Bay, the inner parts of the west and the north of the Mikawa Bay.
High correlations (>r=0.94) between COD, TOC, and TN in the sediment, were observed. Benthos was the most abundant in a range of 3 to 8mg/g of COD value, and became poor above 14mg/g in COD, 0.4mg/g in Total sulfide S content of the sediment. The results suggested that COD value, TOC, TN, and Total sulfide S contents were good indices of eutrophic level in shallow waters, and the threshold value for benthos production were about 14mg/g in COD value, cor-respond to 15.6mg/g in TOC, 1.65mg/g in TN, and the Total sulfide S content of 0.4 mg/g.
抄録全体を表示