Abstract
Changes in the nitrogen budget between the sediment and overlying water, were evaluated using
a benthic ecosystem model for the shallow area of Mikawa bay, Japan. The model was run for the
period between June to July (1996) when a water mass, severely deficient in dissolved oxygen,
developed and resulted in drastic benthic community changes.
The model result indicated that the nitrogen budget changed greatly as a dissolved oxygen defi
cient water mass developed. The shallows had the capability of reducing the particulate organic
nitrogen at higher efficiency than the rate of elution of dissolved inorganic nitrogen when ambient
oxygen conditions were normal. But, After the oxygen deficient water mass developed, the re
moval rate of particulate organic nitrogen decreased with the death of macrobenthic suspension
feeders more rapidly than the elution rate in dissolved inorganic nitrogen and consequently, the
budget of total nitrogen swinged from sink to source.
It is very important to keep the dissolved oxygen saturation level that the benthicfauna can
survive to maintain the water purification capacity of the shallows.
