抄録
Nitrogen cycle in a sediment and nitrogen budget between a sediment and an overlying water
were evaluated by benthic ecosystem model at Isshiki tidal flat that is the most largest one in
Mikawa bay. Model analysis was carried out in two cases of 1994 and 1984 to compare them by
the difference of benthic community. The result of the fluxes between sediment and the upper
water was in good agreement with that of the budget calculated from particulate organic nitrogen
and dissolved organic nitrogen distributions by box model method. Nitrogen cycle greatly change
in time and space by the difference of benthic community. Especially, nitrogen budget is influ
enced by the mass balance between suspension feeding type macrobenthos and benthic
microalgae and seagrass (including seaweed). From the view point of water purelify function of
tidal flat, the removal ability of particulate organic nitrogen increased 10% than that of 10 years
ago, but the removal ability of total nitrogen decreased to 5% of that of 10 years ago. From the
numerical simulation in the case supposing that the standing stock of seagrass (including sea -
weed) of 1984 applies to 1994's case, it was shown that uptake of particulate organic nitrogen
by suspension feeder increased 9% and that of total nitrogen changes from slight sink about 11mg
N・m^-2・d^-1 to large sink about 200mg N・m^-2・d^-1. Seagrass includingseaweed is very important
to increase the water purerify function.
