Characteristics of nitrogen cycle on a muddy tidal flat and shallow water area of Ariake Bay — Results of field study and laboratory experiments for Shiota River & Kashima River estuary —

Abstract

A comprehensive field study concerning a mud tidal flat and shallow-water area in Ariake Bay demonstrated distinct nature of nitrogen cycle in the mud flat system. Fine particles, low percolation and anoxic environments in sediments determined the relative abundance of inorganic nitrogen compounds in sediments. Ammonium was highly accumulated in interstitial water of sediments. Denitrification appeared to be limited by low nitrification in thin oxidized layer of sediments, together with the limited supply of nitrate from the overlying water. The composition of benthic biomass in terms of nitrogen were characterized by abundant bacteria and less abundant macro-benthos in comparison with those reported in sandy tidal flats. Bivalves were however observed to be dense in artificially intervened area, such as bivalve grounds and oyster beds.