著者

岡田 操

出版者

日本地形学連合

雑誌

地形 (ISSN:03891755)

巻号頁・発行日

vol.31, no.1, pp.17-32, 2010-01-25

参考文献数

19

被引用文献数

1

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String-flark (kermi-schlenke) complex pattern is a characteristic micro-topography in boreal mires. It consists of linear ridges aligned perpendicular to the slope, separated by water zones that are more sparsely vegetated. Various explanations for the formation process of this micro-topography have been proposed, however, the process by which oriented string-flark complex pattern originates is not clear. Nevertheless, as pattern formation occurs very slowly in nature, computer simulation offers useful help in understanding the formation process. In the present study, the formation processes have been defined by classifying the development stages of the string-flark complex pattern. While evaluating the existing theories on origin, a computer program has been coded to simulate using Carex Model, and verified the formation process. Carex Model is based on the growth processes of bog vegetation. Hence it can simulate changes in peat layers and thus predicts the formation of the diverse micro-topographies of mires. The result implies that string-flark complex pattern is generated by the accumulation of additional litter brought by snow-melting flow. Water level changes under the influence of prevailing hydraulic conditions and the patterns are formed with the selective growth of vegetation.

著者

岡田 操

出版者

日本湿地学会

雑誌

湿地研究 (ISSN:21854238)

巻号頁・発行日

vol.2, pp.43-52, 2012 (Released:2019-04-01)

参考文献数

21

著者

岡田 操

出版者

日本地形学連合

雑誌

地形 (ISSN:03891755)

巻号頁・発行日

vol.29, no.3, pp.281-300, 2008-07-25

被引用文献数

2

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In bog mires, peat formation depends largely on plant growth, the amount of which in turn is influenced by rates of primary production, soil pH, sunlight, and ground, air and water temperatures. Plant growth is also affected by soil saturation and thus groundwater, which in turn are influenced by meteorological factors such as precipitation and evapotranspiration as well as hydrological factors such as inflow, outflow and storage. The flow of groundwater is influenced by peat composition, where a lack of water results in plant death, followed by partial decomposition of plant matter. This accumulates contributing to the upper layers of peat. As time progresses, the plant matter undergoes varying degrees of decomposition and consolidation producing peat of variable density, porosity, and permeability. The model proposed in this paper focuses on groundwater table, the most significant factor in peat formation. The characteristic of this model is the determination of the relationship between plant growth and groundwater table under variable conditions. In a given topographical configuration, if boundary conditions such as the inflow and outflow of rainfall and surface soil are manipulated, unsteady flow calculations reveal changes in water level. If this is iterated for an entire season, vegetation grow and peat will accumulate depending on the mean seasonal water level. This relationship is predicted using the growth function of vegetation, which is determined from growth simulations incorporating actual data from the primary production of specific plants. Iterated over the course of several years the thickness of peat layers gradually changes, giving rise to a conspicuous topography. This model demonstrates that causes of topographical formation, which to date could only be determined qualitatively can now be done quantitatively. Based on the growth processes of bog vegetation, this paper proposes a "Carex Model", which simulates changes in peat layers and thus predicts the formation of the diverse micro-topographies of bog mires.

著者

知北 和久 大八木 英夫 山根 志織 相山 忠男 板谷 利久 岡田 操 坂元 秀行

出版者

日本水文科学会

雑誌

日本水文科学会誌 (ISSN:13429612)

巻号頁・発行日

vol.47, no.2, pp.73-86, 2017-08-28 (Released:2017-09-20)

参考文献数

17

被引用文献数

1

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今回の研究対象である北海道・倶多楽湖は,20世紀までは冬季に完全結氷し年によっては湖氷の圧縮・膨張によるお神渡りが観察された。しかし,21世紀に入り,冬季に完全結氷しない年がこれまで4回現れており,今後の温暖化の進行によって倶多楽湖は将来,永年不凍湖になる可能性がある。ここでは,倶多楽湖の貯熱量を2014年6月~2016年5月の2年間にわたり計算し,気象因子の変動に対する熱的応答を感度解析によって検討した。なお,同湖が結氷するのは例年2~3月であるが,2015年は暖冬で部分結氷,2016年は完全結氷し,貯熱量に違いが見られた。ここでは,貯熱量を湖の熱収支に基づく方法と水温の直接測定による方法の二通りで計算し,両者を比較した。その結果,両者の間に決定係数R2=0.903の高い相関があり,熱収支による方法の妥当性が裏付けられた。これを踏まえ,主要な気象因子(気温,日射,降水量,風速)の値を変えて貯熱量に対する感度解析を行った。結果として,倶多楽湖の貯熱量は気温と降水量の増加に対して顕著に増加し,現在の湖周辺での年平均気温の上昇率0.024°C/年を考慮すると,約20年後には永年不凍湖になる可能性がある。