大阪湾と紀伊水道における水質観測結果に基づいて, 大阪湾における懸濁・溶存態物質の収支をボックスモデルにより解析した。その結果, 夏季, 冬季ともに表層では懸濁物質(TSM), 懸濁態有機炭素(POC), 懸濁態有機窒素(PON)および懸濁態リン(PP)の生成量は分解を上回り, 中層と底層では分解が生成を上回っていた。表層におけるPOC, PONおよびPPの生成量の夏季と冬季の平均はそれぞれ1, 300, 175および27td^<-1>であり, 河川等からの負荷量と比較してそれぞれ約10, 8および16倍大きい。表層で多量の懸濁態有機物が生成されるにもかかわらず, これらのうち約60%は大阪湾内で分解され, 湾外への流出は20～30%であった。一方, 溶存態無機窒素(DIN)と溶存態無機リン(DIP)は両季節ともに表層で消費, 中層と底層では生成が上回っていた。表層で栄養塩が消費されて懸濁態の有機物が生成され, 中層と底層では懸濁態有機物が分解を受けて溶存態の栄養物質へと移行し, 海水中へ回帰している。夏季では, 下層の栄養塩が再び表層に輸送されて基礎生産に利用される循環が認められた。In order to clarify the budgets of organic matter and nutrient in Osaka Bay, distributions of salinity, total suspended matter(TSM), particulate organic carbon(POC), particulate organic nitrogen(PON), particulate phosphorus(PP), dissolved inorganic nitrogen(DIN) and dissolved inorganic phosphorus(DIP) were investigated in Osaka Bay and the Kii Channel in summer(August 29 and September 5)and winter(December 11 and 17)in 1996. The budgets of TSM, POC, PON, PP, DIN and DIP in summer and winter were estimated by box model analysis. The mean net generation rates of POC, PON and PP in the surface layer during summer and winter were 1, 300, 175 and 27 t d^<-1> respectively. These values of POC, PON and PP were larger than those supplied from the land and others by factors of 10, 8, and 17, respectively. This means that large amounts of POC, PON and PP were produced in the water column in the bay. The amounts of each decomposed in the bay were about 60% of the totals, while 20～30% were transported outside the bay. On the other hand, the mean net generation rates of DIN and DIP in the lower layer(middle and bottom layers)during summer and winter were 130 and 17 t d^<-1> respectively. In summer, the DIN and DIP transports from the lower layer to the surface layer were 171 and 31 t d^<-1> respectively. They are utilized by primary production in the surface layer and, therefore, the residence times of total nitrogen and total phosphorus were prolonged in Osaka Bay.