浅い内湾底泥の巻き上げが栄養塩溶出に及ぼす影響

Abstract

The effect of resuspension on nutrient release from sediments was studied by field observations and laboratory experiments. Field observations were carried out in two shallow estuaries, Matsushima Bay and Shiogama Port. Three laboratory experiments reflecting the conditions of continuous resuspension, intermittent resuspension and a static state were carried out using estuarine sediment cores. In the estuary, a fluid mud layer was formed just above the sediment and an organic surface layer with an ignition loss of over 20% was found at the top of the sediment in the summer, which increased the concentration of suspended solids during resuspension. The resuspension caused by a tidal current began a little before the low tide and continued until the high tide. It was found that the release rate of dissolved inorganic nitrogen under conditions of continuous resuspension was higher than that under a static state, because the release of ammonium nitrogen from pore water in the sediments occurred simultaneously with that from the sediment in the former case. The nitrification rate under conditions of intermittent resuspension was lower than that in the other two systems. On the other hand, phosphate release was not observed under an aerobic static state. It was also recognized that the concentration of phosphate decreased at the beginning of resuspension, and increased thereafter.