Cultivation System and Conservation of Wetland from the Viewpoint of Ground Water Quality Succession Process from Lake to Bog.

Recently, wetlands are gradually shrinking in Japan and many other countries due to human activities. Especially, the bog-mire system is valuable, because it was formed over a span of thousand years and a unique ecosystem is maintained there. However, the bog-mire ecosystem is delicate to external impact. We investigated the quality of ground water and the chemical properties of accumulated peat in lakes and wetlands at different succession stages at Wakasakanai costal dune located in northern Hokkaido, Japan, and studied the change of water quality and water cultivation system in the succession process. The results are summarized as follows. We proved chemically in situ that the surface ground water of wetland changes from minerotrophic to ombrotrophic, with peat accumulation. This change was caused by the inversion of ground water flow. These tendencies were clarified by Principal Component Analysis of water quality. Carbon content was about 50% in peat soil. This percentage composition did not differ much at different depths. Nitrogen content was 3-4% in lake mud, and humic soil, but in peat soil the content became lower, being about 1% in sphagnum peat soil. On the surface of sphagnum peat soil, it became slightly high because living plants seem to take in nitrogen. From the point of view of soil composition, the nutrient content must be low to form sphagnum peat. To conserve the bog-mire system or the sphagnum area, surface ground water must be kept ombrotrophic. To this end, ground water flowing downstream is necessary.