富山湾深層水を用いたスラグ系施肥材の海産藻類に対する効果実証実験(Effect of an Iron-Enriched Fertilizer on Marine Algae in Toyama Bay Deep Seawater)
- 標題
- 富山湾深層水を用いたスラグ系施肥材の海産藻類に対する効果実証実験(Effect of an Iron-Enriched Fertilizer on Marine Algae in Toyama Bay Deep Seawater)
- 作者
- 植木 知佳, 熊谷 敬之, 藤田 大介(Chika Ueki, Takayuki Kumagai and Daisuke Fujita)
- 文件屬性
- 日本研究
- 知識分類
- 基礎研究
- 出版年
- 2012
- 刊名
- 海洋深層水研究
- 卷
- 13
- 期
- 1
- 頁
- P7-16
- 點閱數
- 2560
摘要
海水中の鉄不足は藻場衰退の一因とされ，コンブ配偶体の成熟に鉄が必要なことが示されている ほか，海域でも製鋼スラグ系の鉄分供給施肥材の投入でコンブ群落が回復したとの報告もある． こ の施肥材の藻類への影響を詳細に調べるため，清浄かっ栄養塩（total inorganic N, Phosphate-P, Silicate-Si）が豊富で鉄濃度が低い富山湾深層水を用い，屋内100L 透明水槽4 基（施肥と遮光の有無）と屋外2000 L, FRP 水槽2 基（施肥の有無）でバッチ培養を行った． 施肥水槽では鉄と栄 養塩の濃度が上昇し，無遮光では主に珪藻が増えた．珪藻は遮光・施肥水槽でも増え，従属栄養が 示唆された．無遮光水槽に入れたマコンブの未成熟配偶体はすべて成熟し幼胞子体が出現した．そ の体色が濃く密度が高かったのは，屋内では施肥，屋外では非施肥水槽で，後者は珪藻の繁茂によ る光不足が原因と考えられた． 海域の施肥投入地点でも施肥材による微細藻と大型藻の増殖効果が 期待できるが，両者の競合も懸念された．
The deficiency of iron in seawater has been considered as a factor of the reduction of kelp beds. In vitro culture has demonstrated the requirement of iron in maturation of kelp gametophyte; in situ fertilization, i.e., deployment of iron-enriched fertilizer (mixture of con-verter-derived steelmaking slag and mixed with humus) has suggested their positive effects on restoration of kelp beds. However, the gap between the former simplified and the latter complicated conditions have made it difficult to evaluate the results of fertilization. In the present study, a closed fertilization experiments in indoor and outdoor tanks using Toyama Bay deep seawater (known as clean, stable and enriched seawater with less iron concentra-tion than surface seawater) to detect any positive effects on algae caused by the iron-enriched fertilizer. Four 100 L translucent tanks (with or without fertilizer and blackout cover) and two 2000 L FRP tanks (with or without fertilizer) were used for batch cultures in the indoor and outdoor experiments, respectively. In both experiments, elevation of iron and macronutrients (total inorganic N, Phosphate-P, Silicate-Si) were detected and diatom (and green microalgae in one tank) increased to higher concentrations in open fertilized tanks. Diatom also increased in dark and fertilized tanks presumably because of hetero-- trophy. All of the immature gametophyte ofぬccharinaルponica deployed in the open tanks could produce young sporophytes; the color of sporophyte was deeper and its density was higher in the fertilized tank in the indoor experiment and unfertilized tank in the outdoor experiment. The latter unexpected result might be caused by short of light with vigorous coverage of diatom. These experiments suggest the positive micro- and macroalgal response to iron-enriched fertilizer as well as the competition between them near the fertilized spot at sea.
The deficiency of iron in seawater has been considered as a factor of the reduction of kelp beds. In vitro culture has demonstrated the requirement of iron in maturation of kelp gametophyte; in situ fertilization, i.e., deployment of iron-enriched fertilizer (mixture of con-verter-derived steelmaking slag and mixed with humus) has suggested their positive effects on restoration of kelp beds. However, the gap between the former simplified and the latter complicated conditions have made it difficult to evaluate the results of fertilization. In the present study, a closed fertilization experiments in indoor and outdoor tanks using Toyama Bay deep seawater (known as clean, stable and enriched seawater with less iron concentra-tion than surface seawater) to detect any positive effects on algae caused by the iron-enriched fertilizer. Four 100 L translucent tanks (with or without fertilizer and blackout cover) and two 2000 L FRP tanks (with or without fertilizer) were used for batch cultures in the indoor and outdoor experiments, respectively. In both experiments, elevation of iron and macronutrients (total inorganic N, Phosphate-P, Silicate-Si) were detected and diatom (and green microalgae in one tank) increased to higher concentrations in open fertilized tanks. Diatom also increased in dark and fertilized tanks presumably because of hetero-- trophy. All of the immature gametophyte ofぬccharinaルponica deployed in the open tanks could produce young sporophytes; the color of sporophyte was deeper and its density was higher in the fertilized tank in the indoor experiment and unfertilized tank in the outdoor experiment. The latter unexpected result might be caused by short of light with vigorous coverage of diatom. These experiments suggest the positive micro- and macroalgal response to iron-enriched fertilizer as well as the competition between them near the fertilized spot at sea.