[MIS06-05] Effects of various vegetation factors on sand saltation from the viewpoint of roughness
キーワード：サルテーション、臨界摩擦速度、生態系機能、植被率、粗度、植生の空間分布
Vegetation factors such as coverage, height, spatial arrangement and species composition have a combined effect on sand saltation. Several studies reported about vegetation mitigating wind erosion with high coverage. The impact of vegetation coverage has already been incorporated into the aerosol model of Japan Meteorological Agency in the form of the Leaf Area Index. On the other hand, there is not enough research on community height, species composition, and spatial arrangement. Vegetation also suppresses sand saltation by declining the wind speed near the ground surface. It is well known that the vertical wind profile is affected by the community height and the shape of the structures (species composition), however there are few studies on sand saltation considering these factors. In addition, it is pointed out that the vegetation coverage only represents the average coverage of the site, and that the spatial arrangement of plants cannot be considered. It has been proposed that sand saltation causes dust emission with saltation bombardment. Elucidating relationship between sand saltation and vegetation is important to estimate dust emission. Therefore, this study was performed to clarify the effectiveness of several vegetation factors on sand saltation. Sand saltation is important to estimate dust emission.
Our study site is Tsogt-Ovoo sum, Mongolia, which is arid area in Northeast Asia and known as a dust source. In this area, there is a gradient in vegetation from the hilly area to the lowland. We selected two type shrub land (dominated with Salsola passerine, Anabasis brevifolia and Nitraria sibirica) and almost bare land for observation site. Vegetation survey, saltation and meteorological observation were conducted. 9 quadrats were placed at each site and we recorded species composition, coverage and community height. In 4 sites dominated with N. sibirica, spatial arrangement and height of every shrubs were recorded. As saltation observation, piezoelectric particle counters (ud-101) was used to count saltation particle numbers and we introduced 3 instruments for each site to identify variance of saltation number in microscale. We also determined wind profile with portable weather meters (Kestrel weather meter 5500). Roughness, zero-plane displacement and friction velocity were calculated from wind profile with maximum correlation method, and threshold friction velocity was estimated with a method of Owen (1964).
Saltation flux were decreased with increasing of coverage. However, threshold friction velocity was not explained with coverage or community height. Roughness length explained threshold friction velocity well. Although it is a well-known fact that vegetation effects on roughness length, it is suggested that each vegetation factor is not enough to explain roughness and also saltation occurrence by itself. In a heterogenous site dominated with N. sibirica, 3 instruments showed deferent trends slightly in spite of similar trends in other homogenous sites. Further studies that consider effect of spatial arrangement and its interaction to other factors are needed in order to clarify combined effects of vegetation to sand saltation.
Our study site is Tsogt-Ovoo sum, Mongolia, which is arid area in Northeast Asia and known as a dust source. In this area, there is a gradient in vegetation from the hilly area to the lowland. We selected two type shrub land (dominated with Salsola passerine, Anabasis brevifolia and Nitraria sibirica) and almost bare land for observation site. Vegetation survey, saltation and meteorological observation were conducted. 9 quadrats were placed at each site and we recorded species composition, coverage and community height. In 4 sites dominated with N. sibirica, spatial arrangement and height of every shrubs were recorded. As saltation observation, piezoelectric particle counters (ud-101) was used to count saltation particle numbers and we introduced 3 instruments for each site to identify variance of saltation number in microscale. We also determined wind profile with portable weather meters (Kestrel weather meter 5500). Roughness, zero-plane displacement and friction velocity were calculated from wind profile with maximum correlation method, and threshold friction velocity was estimated with a method of Owen (1964).
Saltation flux were decreased with increasing of coverage. However, threshold friction velocity was not explained with coverage or community height. Roughness length explained threshold friction velocity well. Although it is a well-known fact that vegetation effects on roughness length, it is suggested that each vegetation factor is not enough to explain roughness and also saltation occurrence by itself. In a heterogenous site dominated with N. sibirica, 3 instruments showed deferent trends slightly in spite of similar trends in other homogenous sites. Further studies that consider effect of spatial arrangement and its interaction to other factors are needed in order to clarify combined effects of vegetation to sand saltation.