open access

https://hdl.handle.net/2115/58415

Numerical Study of the Formation of Microtopography of Peat Bogs

日本語

2013-10-30

北海道大学大学院農学研究院

Memories of the Research Faculty of Agriculture, Hokkaido University

33(1)

1-44

This study describes the development of a model for the microtopographic formation of peat bogs, which is named 'Carex Model'. Basically, this model has been built on the well-known fact that peat formation is the result of accumulation of dead plants without decomposition under excess water and low temperature conditions. Therefore, the scenario assumed in this model is that the primary production of wetland plants may control the amount of peat accumulation, and uneven peat accumulation will influence the microtopography. This study provides a solution to realize this process and represents the volume of peat formed. According to several researches regarding plant ecology, the amount of primary production of bog plants depends upon the condition of the groundwater table. From this relation, the question of the amount of peat accumulation and the topographical transformation of a bog can be both transposed and treated as a matter of groundwater flow, which is purely a physical phenomenon. As a result, it is comparatively easy to model mathematically. The core of the model is how to represent the relationship between primary plant production and the groundwater table. It is expressed as a function of a logarithmic normal distribution, including the restriction for high water table conditions. The prototype of the Carex Model sufficiently reproduced the typical microtopographies seen in bogs. These are the ridges of the banks of a bog pool, the distribution of numerous pools in the stair-like slope of bogs and the concentric arrangement of Picea glehnii on the flat peak of domed bogs. Bog rill is a relatively large channel that is formed in the gentle slope of a bog. In the case of the simulation of the bog rills in Sarobetsu Mire, the rills were clearly simulated with the Carex Model by involving the high permeability portion of the bog matrix in the initial conditions of the simulation. The 'string-flark complex' of the bog comprises a set of parallel ridges aligned perpendicular to the slope and separated by narrow pools that are more sparsely vegetated. The results of simulation by the Carex Model suggested that this microtopographic pattern was generated by the accumulation of additional litter deposited by snow-melting flow. Consequently, the changes in water level under the influence of the prevailing hydraulic conditions will facilitate the selective growth of vegetation, thus developing this unique bog microtopography. The proposed Carex model enables the reproduction and estimation of both the past-to-present and present-to-future forms of bog topography. In addition, it facilitates the quantitative evaluation of the conditions of existing bogs.

紀要論文

Version of Record

1881-8064

AA12190860