Abstract
The effects of covering nutrient-rich sea sediment with sand and silicic calcium (iron slag) upon the release of nutrients into the overlying seawater were investigated by using 6-month indoor cultures under illumination, which contained sea sediment from a young yellowtail plantation, covering material and seawater. In the control tank without covering, the overlying water turned dark reddish brown, due to the mass production of Cryptomonas sp. No color appeared in the tanks with either silicic calcium or sand covering until the addition of phosphate to the former and sulfide as well as phosphate to the latter (Exp. 1), The prevention of the growth of Cryptomonas by covering seems to be due to the inhibition of.PO4-P and S2-S release from the sediment bed. These elements are concentrated in the deepest part of the iron rich sand layer adjacent to the sediment bed and distributed throughout the iron poor silicic calcium layer (Exp. 2), suggesting that the elements released from the sediment pass through the silicic calcium layer more easily than through the sand layer.
