Changes in riparian forests in the Kushiro Mire, Japan, associated with stream channelization

Abstract

The Kushiro Mire, the largest mire in Japan, presently faces the serious problem of turbid water flooding. Shortening of stream channels associated with agricultural development is a major cause of streambed aggradation. This aggradation reduces the carrying capacity of the channel, resulting in sediment laden water spilling over the wetlands in a flood event. Sedimentation progresses with repeated inundation by turbid water, which significantly alters the edaphic conditions, and thereby the composition and structure of marsh forests. Aggradation of the geomorphic surfaces with sedimentation lowers the water level, and increases soil particle size and nutrient status. This situation was clearly displayed in an ordination of canonical correspondence analysis. Among the environmental variables, water level was related most strongly to the pattern of a forest community. Salix species dominated the flood areas, which were characterized by a low water level, coarse sediment, and high electrical conductivity. Alnus japonica, the most common tree species in the Kushiro Mire, favors soil conditions represented by high water table and organic content. A. japonica adapts to a higher water level by developing lenticels with hypertrophied and adventitious roots, multiple sprouting and regenerates vegetatively. Basal areas (BAs) of A. japonica, however, seem to be limited by high fluctuations in water levels, which are amplified by channelization. This raises serious concerns for the integrity of the Kushiro Mire. It is important to implement a conservation plan from a watershed perspective because most problems originate in upper basins. Creating riparian buffer strips, sediment-filtering wetlands, and restoring the original meandering course may slow down sedimentation in the mire, and thus help to restore the natural hydrological regime.

Simulation of hydrologic and geomorphic changes affecting a shrinking mire

“…An extension of the model to include vegetation growth (tree regeneration and succession, etc.) (Glenn-Lewin et al, 1992), which would also include clarification of water-heat-sediment-nutrient-vegetation interactions using statistical approaches such as canonical correspondence analysis and cluster analysis (Nakamura et al, 2002), would also be very attractive for evaluating more ideal environmental conditions for the mire, for reproducing alder invasion into the mire and for forecasting the possibility of future mire-ecosystem recovery. Evaluation of the survival range for submerged depth in this study (Figure 9), in comparison with previous work (Yabe and Onimaru, 1997;Hotes et al, 2001;Ohmi Environment Preservation Foundation, 2001), would be very important for simulation of vegetation succession from mire vegetation (reeds etc.)…”

Recent Changes of Sedimentation Rate in Lake Takkobu, Northern Japan, Determined210Pb Dating

“…인간 활동이 활발해지면서 농업, 하천공사 및 산림벌채 등의 개발이 급속도로 증가하고 있으며, 이로 인해 강우 시 다량의 토사가 유출되고 있다 (Nakamura et al, 1997(Nakamura et al, , 2002Walling et al, 2003;Mizugaki et al, 2006;Ahn et al, 2006;2009;2010). 토지이용 변화로 인해 산림에서 생산된 토사는 바다까지 유출·퇴적되고 있어 토사의 이 동 범위는 매우 광범위하다고 할 수 있다.…”

Variation in microbial function through soil depth profiles in the Kushiro Wetland, northeastern Hokkaido, Japan

“…In 1980, the wetland was registered under the Ramsar Convention on Wetlands, and in 1987 it officially became a national park in Japan. However, there have recently been reports of increased sedimentation and nutrient loading into the Kushiro Wetland in response to changes in land use, such as an increase in agricultural land and timber harvesting, and river channelization (Nakamura et al 2002(Nakamura et al , 2004Ahn et al 2008). Increased sedimentation and nutrient loading affect all living organisms in a wetland and can cause drastic changes in wetland structure and function.…”