Estimation of the impact of semi-labile dissolved organic nitrogen on the nutrient cycle in the coastal sea

2019 Fiscal Year Final Research Report

• Project/Area Number: 17K15302
• Research Category: Grant-in-Aid for Young Scientists (B)
• Allocation Type: Multi-year Fund
• Research Field: Aquatic bioproduction science
• Research Institution: Kyoto University
• Principal Investigator: Kobayashi Shiho 京都大学, フィールド科学教育研究センター, 助教 (60432340)
• Project Period (FY): 2017-04-01 – 2020-03-31
• Keywords: 溶存有機物 / 難分解性溶存有機物 / 準易分解性溶存有機物 / 栄養塩循環 / 沿岸海域

Outline of Final Research Achievements

The increase of refractory dissolved organic nitrogen (DON) in aquatic area, which is not decomposed after 100 days, has recently treated as a problem because it has put a load on water quality management but may not contribute as nutrient. Moreover, it is not clear the influences of the semi- labile DON, which is decomposed within 100 days but not decomposed after 20 days, on the nutrient cycle. It is important to investigate such DON because the water exchange rate of the upper layer of major bay with freshwater influences is within 20 days, then the DON may possibly flow out of the bay before it contributes as nutrient. In this study, we first measured the rate of semi- labile DON by the repeated field observations and decomposition experiments. We then estimated the outflow flux of semi- labile DON to out of the bay using numerical flow simulation and the inflow flux of nutrient from main river, and finally quantified the impact of semi- labile DON on nutrient cycle in the bay.

Free Research Field

海洋環境学

Academic Significance and Societal Importance of the Research Achievements

これまでに水域の生物生産環境への影響が注目されていた難分解性溶存有機窒素に加え，本研究では分解に要する期間が海水交換時間よりも長いために栄養塩に戻るより早く湾外に流出すると考えられる準易分解性溶存有機窒素のフラックスを算出し，それが陸域から流入した栄養塩の流入フラックスの何割にあたるかを示した．生物生産性を維持するための栄養塩濃度レベルの管理は沿岸海域で急務となっており，その成果は沿岸海域における持続的な生物生産と沿岸漁業の発展に，将来にわたって役立てることができる．また同時に，沿岸―陸棚海域においてCOD(化学的酸素要求量)などの水質指標の改善が進まない原因の解明にもつながると考えられる．