広島湾, 江田内湾, 周防灘北東部海域および太田川における尿素の濃度について

Urea Concentrations in Waters of Hiroshima Bay, Etauchi Bay, Northeast Suo Nada and the Ohta River.

Yamamoto Tamiji

Yamazaki Tohru

Fujimori Satoshi

Matsuda Osamu

生物生産学研究

Journal of the Faculty of Applied Biological Science, Hiroshima University

広島湾、江田内湾、周防灘北東部海域および太田川において、水中の尿素態窒素(Urea)、溶存態有機窒素(DON)および溶存態無機窒素(DIN)濃度の測定を行った。尿素の濃度は広島湾で0.08-3.32(平均0.67)μg atNℓ-1、江田内湾で0.00-5.01(平均0.85)μg atNℓ-1、周防灘では0.15-2.50(平均0.91)μg atNℓ-1であった。太田川河川水中尿素の濃度範囲は他の3海域と同程度であったが(0.23-3.15μg atNℓ-1)、平均値1.49μg atNℓ-1は3海域のものよりも有意に高く、海域に対する尿素の供給源の1つとして陸域からの流入が考えられた。さらに、太田川のDON(平均41.6μg atNℓ-1)およびDIN(平均30.7μg atNℓ-1)濃度も海域で得られた値より有意に高かった。太田川河川水は広島湾水に比べて相対釣にUreaよりもDINの濃度が高いことから、太田川河口域(広島湾奥部)に生息する植物プランクトンの増殖に対してはUreaよりもDINの負荷の方が大きな影響を与えていると推測された。また、この研究で得られた平均Urea/DON(%)は5.7-12.9%で、溶存態有機窒素全体に占めるUreaの割合は河川水中、海水中とも大きいものではなかった。広島湾、江田内湾、周防灘北東部海域および太田川におけるUreaの分布は不規則で、とくに一定の傾向は見られなかった。しかしながら、変動係数はUreaが34.2-89.4%、DONが77.2-103.7%、DINが50.2-75.3%で、Ureaの濃度のばらつきが他の形態の窒素に比べて必ずしも大きいというわけではなかった。広島湾、江田内湾および周防灘北東部海域の平均Urea/DIN(%)は34.4-42.8%であり、当該海域において一次生産に利用される全窒素(DIN+Urea)のうち、平均して7.2-8.4%が尿素によるものであろうと推算された。

Urea, dissolved organic nitrogen (DON) and dissolved inorganic nitrogen (DON) concentrations in waters of Hiroshima Bay, Etauchi Bay, northeast Suo Nada and the Ohta River were measured. Range and average concentration of urea were 0.08-3.32 (0.67) μg atNℓ-1 in Hiroshima Bay, 0.00-5.01 (0.85) μg atNℓ-1 in Etauchi Bay, and 0.15-2.50 (0.91) ,μg atNℓ-1 in Suo Nada, respectively. Although the range in urea concentration observed in the water of the Ohta River (0.23-3.15 μg atNℓ-1)was in the same level as those in the other coastal areas, the average value (1.49 μg atNℓ-1)was significantly higher than those in the other coastal areas. This means that the river inflow is one of the important supply source of urea for the coastal area. In the Ohta River water, DON (41.6 μg atNℓ-1 in the average) and DIN (30.7 μg atNℓ-1 in the average) concentrations were also high. Judging from the low Urea/DIN (%) in the Ohta River water, it was supposed that, compared to urea, DIN would be principal nitrogen source for the growth of phytoplankton in the estuary of Hiroshima Bay. The Urea/DON (%) observed in this study was 5.7-12.9%, which revealed the contribution of urea in the total DON load was not so high both in the river and the coastal waters. The distribution of urea in the coastal environments is heterogeneous, not showing any regular distribution, as has already been shown in several papers. However, the coefficient of varitaion was not always high in urea (34.2-89.4%) compared to those of DON (77.2-103.7%) and DIN (50.2-75.3%). From the Urea/DIN (%) in the three coastal areas (34.4-42.8%), the contribution of urea in all nitrogen forms (DIN+Urea) used for the primary production was estimated 7.2-8.4% in the average.

海水

河川水

尿素

溶存態無機窒素

溶存態有機窒素

DIN

DON

river water

seawater

urea

Fishing industry. Fisheries [ 660 ]

jpn

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