広島湾底泥からの無機態窒素溶出フラックスの見積り

Estimation of inorganic nitrogen flux from the sediment of Hiroshima Bay, Japan

金 道煕

山本 民次

松田 治

生物生産学研究

Journal of the Faculty of Applied Biological Science, Hiroshima University

広島湾奥部と湾中央部の2測点において、1994年8月から1995年5月の間に季節別に4回、底泥からのアンモニア態窒素および亜硝酸態+硝酸態窒素の溶出フラックスの測定を行った。測定は間隙水と直上水中のそれらの濃度勾配から計算する間接的方法で行った。アンモニア態窒素の溶出は、常に湾中央部より湾奥部で高く、湾奥部で22.2～60.8μg atN m-2 h-1、湾中央部で18.2～41.Oμg atN m-2 h-1であった。季節的には8月に最高値、1月に最低値が見られた。亜硝酸態+硝酸態窒素の溶出には、アンモニア態窒素の溶出に見られたような場所による違いは見られず、湾奥部で0.47～17.1μg atN m-2 h-1、湾中央部で0.24～18.2μg atN m-2 h-1であった。季節的には1月に最高値、10月に最低値が見られた。アンモニア態窒素の溶出には泥温、酸化還元電位、直上水中の溶存酸素濃度などの環境因子と密接な関係が見られた。すなわち、泥温が上昇して有機物の分解速度が加速され、分解にともなって溶存酸素が消費されて底泥が還元状態になり、間隙水中のアンモニア態窒素濃度が増加することで、溶出フラックスが高まるものと推察された。一方、亜硝酸態+硝酸態窒素の溶出は基本的に間隙水中のそれらの濃度に依存しており、他の環境因子との間に明瞭な関係は見られなかった。

Seasonal variation of ammonium flux and nitrite+ nitrate flux from the sediments at two stations located in the inner and central areas of Hiroshima Bay, Japan were studied from August, 1994 to May, 1995. The ammonium and nitrite +nitrate fluxes were calculated from the concentration gradient between the sediment porewater and the overlying water. Ammonium flux was always higher in the inner area than in the central area, showing 22. 2-60. 8μg atN m-2 h-1 in the inner area and 18. 2-41. 0 μg atN m-2 h-1 in the central area, respectively. These fluxes were the maximum in August and the minimum in January at both stations. Nitrite + nitrate flux did not show any significant difference between locations, showing 0. 47— 17. 1 μ g atN m-2 h-1 in the inner area and 0. 24 —18. 2 μg atN m-2 h-1 in the central area. These fluxes were the highest in January, and the lowest in October at both stations. Ammonium flux showed significant relationships to the environmental parameters, such as temperature, and redox potential of the sediment and dissolved oxygen concentration in the overlying water. It was assumed that the am mounium flux might increase with increasing of the ammonium concentration in the porewater accompanied by the increase in decomposition rate of organic material in the sediment. The increase of mud temperature might have accelerated the decomposition of organic material in the sediment, resulting the consumption of oxygen and reduced condition of the sediment. On the other hand, nitrite +nitrate flux showed no relationships to the environmental parameters, although it depends on the nitrite +nitrate concentration in the porewater. From these results, the mechanisms of nitrite+nitrate release was assumed to be mainly governed by the gradient between their concentration in the sediment and those in the overlying water.

亜硝酸

アンモニア

フラックス

硝酸

広島湾

溶出

ammonia

flux

Hiroshima Bay

nitrite

nitrate

release

地球科学・地学・地質学 [ 450 ]

日本語

広島大学生物生産学部

農林水産研究情報センター

[ISSN] 1341-691X

[NCID] AN10409040