製鋼スラグ-堆肥施肥材による磯焼け海域の藻場再生技術における鉄のスベシエーシヨンとその生物利用性に関する研究

摘要

Recently, the lack of dissolved iron has emerged as a primary reason for seaweed depletion which is a serious problem worldwide. The solubility and bioavailability of iron in seawater depend on a dissolved organic matter(DOM). Based on the concepts, the restoration of seaweed beds is being accomplished using a fertilizer composed of steelmaking slag and compost as sources of iron and DOM, respectively. To better understand the restoration process, the present study focused on the role of seawater extractable organic matter(SWEOM) that is derived from compost. First, extraction and purification methods for SWEOM were established, and the novelty of SWEOM was discussed by comparing its structural features with those of humic substances. Next, the binding abilities for SWEOM to Fe(Ⅱ) were elucidated by means of an analytical technique based on a ligand-exchange reaction between SWEOM and ferrozine. In addition, the effects of SWEOM on supplying the bioavailable Fe species to seaweed were indicated by oogenesis assay using female gametophytes of Laminaria japonica. The findings in the present study indicated that SWEOM is an effective chelator for use in supplying bioavailable Fe to L. japonica, and will contribute to a better understanding of the restoration process when using Fe fertilizer.%藻場は，水産資源としてのみならず，沿岸域の生態系保全及び炭素固定において重要な役割を担っているが，近年，沿岸開発及び環境変化による藻場の減少が世界的な問題となっている.日本では，沿岸環境変化による藻場の消滅は"磯焼け"として古くから知られており，各地の沿岸域で深刻な問題となっている.コンブ胞子体の形成阻害及びウニ等の食害耐性の脆弱化の観点から，溶存鉄の欠乏が磯焼けの原因の一つに考えられている.コンブ等の大型褐藻類の巨視的形態である胞子体は，微視的な形態の配偶体の生殖生長及び配偶子の受精を経て形成される.ここで，配偶体の生殖生長への移行は鉄の摂取がきっかけとなる.また，高濃度の溶存鉄環境下(10〜50nM)におけるコンブ胞子体の生長速度は，溶存鉄欠乏環境下(2nM未満)と比べ著しく高くなる.