As a link in the chain of effective utilization programs of sea-bottom sediment (i.e. HEDORO), a survival-type seaweed culturing concrete block (which is hereinafter referred to simply as “block”) was designed. The block is quite different from the existing kind, and it has such a distinctive feature that a scanty detrition takes place on the block at all times so that its surface could be always renovated. The HEDORO collected from the coastal sea bottom off Tomioka-Machi, Fukushima Pref. consisted of clay and silt, and a volume mean diameter of those composites was 11.3μm; and its moisture content was 100%.
In the water standing still, the detrition degrees of the specimen block mixed with varied Portland cement rates differed one after another, indicating that the lower degrees was inversely proportional to the cement rates from 10% to 50%. For example, the degree showed 9.10×10
-6cm/day when the cement rate was 10%, and 1.16×10
-6cm/day when it was 30%. Any changes in the detrition degree were not observed from 40 days after setting on the blocks in the water. The block detrition degree had not any correlation with the growth rate of gametophyte as well as sporophyte of brown algae
Eisenia bicyclis; and such a degree was in inverse correlation to the survival rate of algal sprouts. For instance, in case of the higher detrition degree of 6.07×10
-6cm/day, the survival rate of those sprouts on 16 days was smaller showing the value of 23.2%; on the contrary, in case of the lower degree of 9.15×10
-7cm/day, it stood for the larger value of 56.6%.
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