No.307 研究課題 / Project
多摩川上流に位置する奥多摩湖の富栄養化に及ぼす釣りレジャーの影響に関する調査研究Study on the impact of leisure fishing on eutrophication of Lake Okutama| 学術研究 Academic Research |
No.307 |
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| 代表研究者 Principal Investigator |
牧野 育代 Ikuyo Makino |
| 所属（採択当時） Affiliation |
東北大学環境保全センター 助教 Assistant Professor, Environment Conservation Center Tohoku University |
| 研究内容要約 Research Summary |
奥多摩湖の富栄養化に，奥多摩湖および2本の流入河川においてされている釣りレジャーが及ぼす影響を調査した．調査の方法としては，現地調査，水質分析，底泥分析，釣り餌の成分分析，生物試験，DNA試験，および統計解析を用いた．そのうち，生物試験では，主に奥多摩湖への釣り餌の投入の影響を検討した．複数の種類の釣り餌を添加物として，アオコ形成種であるMicrocystis属および奥多摩湖で捕集した野生種の増殖試験を行った．複数の種類の釣り餌に対してMicrocystis属と野生種は増加を見せた．また，DNA試験では，奥多摩湖のアオコ形成種藻類は釣りレジャー施設のある河川由来であるかについて検討した．Microcystis属は奥多摩湖と2本のうちの1河川の全ての調査地点から検出された．一方，Anabaena属は，2本のうちの1河川の釣りスポットのみで検出された．これらの結果と水質分析等の結果を用いて，統計解析による奥多摩湖の富栄養化の原因を検討した．土地利用形態として釣りスポットは特にリン供給の場となりうる可能性が示唆されたが，それに対する釣り行為にそのものによる関与は低いと考えられた． 近年のレジャーブームを背景に，河川敷や湖沼での釣りレジャーが全国的に普及している．本研究で明らかになった釣りレジャーの奥多摩湖への影響は，釣り行為を規制していない全国の水源地帯におけるレジャーのあり方を検討する資料となりうると考えられる．奥多摩湖で捕獲したアオコ形成種藻類は，複数の種類の釣り餌において増殖反応を見せた．つまり，奥多摩湖への釣り餌の投入量によっては富栄養化に基づく現象を引き起こす主要な原因となるため，釣り餌の選定が重要となる．また，流入河川の釣りスポットにおいては奥多摩湖へのリン供給源となる可能性が高いことを示したが，それが釣り行為によるものとは考えられにくかった．釣り人による釣り餌投入以外の関与が十分に考えられ，特に，河川の流水を占用する河川敷の土地利用に注目したところ，そこからの排水がリンを含む栄養塩類の供給に関与していることがわかった．排水は釣りレジャーとは直接的な関係はないものの，観光資源となる水産場からの放流水であった．今後は本研究で明らかになった釣レジャーの現状を考慮した奥多摩湖の水質保全を考えていきたい． We investigated the impact of leisure fishing done on Lake Okutama and its two f eeding rivers on the eutrophication of Lake Okutama. As the methods of our investigation, we used field surveys, water quality and sludge analyses, component analyses of fishing baits, water biological analyses, DNA tests and statistical analyses. In the water biological analysis, we mainly studied the impact of fishing baits that had been thrown into Lake Okutama. Considering multiple kinds of fishing baits as "additives", we conducted the proliferation test on Microcystis genus which were Microcystis, as well as on the wild species scavenged from Lake Okutama. Vis-a-vis the multiple kinds of fishing baits, Microcystis genus and the wild species showed an increase. Moreover, in the DNA test, we investigated whether the microcystis seaweeds of Lake Okutama, had their origin in the rivers with leisure fishing facilities. The Microcystis genus was detected in all the investigation spots of Lake Okutama and one of the two rivers. On the other hand, Anabaena genus was detected only in the fishing spots of one of the two rivers. Using these findings and those from the water quality analysis, etc, we investigated the cause of eutrophication of Lake Okutama, based on statistical analysis. The results suggested that, as the pattern of land use, fishing spots in particular had the potential of becoming fields of phosphorus supply. Given the leisure boom of recent years, leisure fishing on river beds and lake shores has become widespread throughout Japan. It is conceivable that the impact of leisure fishing on Lake Okutama which this research has elucidated could constitute the materials for the investigation of how leisure ought to be pursued along the headwaters of this country where fishing activities have not been regulated. The microcystis seaweeds which had been scavenged from Lake Okutama indicated that they had elicited proliferation effect on multiple kinds of fishing baits. In other words, the fishing baits which had been thrown into Lake Okutama, depending on their quantity, constituted the major factor of the phenomenon based on eutrophication. For that reason, the selection of fishing baits came to be considered to be of great importance. Moreover, the fishing spots of the feeding rivers indicated its high potential of becoming the supply source of phosphorous, but it was difficult to determine whether that was caused by fishing activities themselves. It is amply conceivable that causes other than the fishing baits which the fishermen had thrown into the lake were responsible for this situation. When we focused our attention, in particular, on the utilization of the land of the river beds that relied exclusively on the flowing water of the rivers, our findings suggested that drainage from those rivers had played a part in the supply of nutrient salts that contained phosphorous. Even though it was not directly related to leisure fishing, the drainage was the discharge from the fishery grounds that constituted tourism resources. In the future, we wish to continue to give careful thought to the water quality safety of Lake Okutama, the existing condition of whose leisure fishing has been elucidated by this research. |
| 共同研究者 Collaborators |
矢作 裕司 大村 達夫 真砂 佳史 風間 聡 Yuji Yahagi Tatsuo Omura Yoshifumi Masago So Kazama |
| 研究全文 Full Text |
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