To quantify organic matter mineralization at estuarine intertidal flats, we measured in situ sediment respiration rates using an infrared gas analyzer in estuarine sandy intertidal flats located in the northwestern Seto Inland Sea, Japan. In situ sediment respiration rates showed spatial and seasonal variations, and the mean of the rates is 38.8 mg CO 2 -C m -2 h -1 in summer. In situ sediment respiration rates changed significantly with sediment temperature at the study sites (r 2 = 0.70, p \ 0.05), although we did not detect any significant correlations between the rates and sediment characteristics. We prepared a model for estimating the annual sediment respiration based on the in situ sediment respiration rates and their temperature coefficient (Q 10 = 1.8). The annual sediment respiration was estimated to be 92 g CO 2 -C m -2 year -1 . The total amount of organic carbon mineralization for the entire estuarine intertidal flats through sediment respiration (43 t C year -1 ) is equivalent to approximately 25% of the annual organic carbon load supplied from the river basin of the estuary.

Water quality of Osaka Bay is greatly influenced by freshwater discharge from rivers, to the effect of salinity playing a major role in forming the stratification. The tidal front is expected to appear in such an area even in winter considering the theory of the formation of a tidal front. From the field observation, we recognized a tidal front in winter for the first time in Osaka Bay. The critical value of a parameter log(H/U 3 ) for generation of a tidal front is obtained as a function of river discharge and cooling effect through sea surface. Differences of nutrients (NH 4 -N, PO 4 -P) concentration across the front are not clear, probably because they are utilized by phytoplankton easily. But in (NO 2 -N)+(NO 3 -N), DIN, PP and T-P, there is a discontinuity structure across the front, even if the absolute value of concentration difference is small.

No abstract

We have studied nitrogen and phosphorus distributions across the thermohaline front in Kii Channel in winter by using engine-cooling sea water of a ferry boat. On Dec. 1986 and Jan. 1987, differences of PO 4 -P and DIN across the front are recognized. Especially in the latter case, differences of nutrients concentrations across the front are very obvious. But differences of nutrients across the front on Feb. 1986, Feb. and Mar. 1987 are not obvious. Inspite of winter, Akashiwo had happened in Osaka Bay, nutrients mostly have already been utilized by phytoplankton in inner part of Osaka Bay. Consequently, differences of nutrients concentrations across the front are nearly zero.