Interstitial water chemistry and soil particles determine vegetation in Ozegahara Mire, Japan

Abstract

The importance of pore water chemistry for the peatland vegetation was closely examined in Ozegahara mire, Japan. Along a transect from a riverside to the center of mire, dominant vegetation changed in an almost decreasing order of plant height: gallery forest, skunk cabbage, reed, sasa-bamboo, Moliniopsis japonica, and sphagnum, with sporadic appearance of cinnamon fern (Osmunda cinnamomea) with heights of around 100 cm along the way. It was found that these vegetations had different (Ca²⁺ + Mg²⁺) concentration in peat interstitial waters and ash content in peat, respectively (p < 0.05), suggesting a close association of the vegetation types with each physicochemical environment. Most of the sites along the transect were found to be ombrotrophic, on the basis of the groundwater tables much higher than the river surface (up to 6.0 m) and SiO₂ concentrations in peat interstitial waters (2.4 ± 0.9 mg/L) that were only around one-tenth of that in the river. Nevertheless, the analysis of ash content in peat demonstrated that soil particles had been transported through river overflows to the mire, especially in the cinnamon fern sites, which had ash contents more than 50% in deeper layers (15–20 cm and 20–25 cm). It was found that SiO₂, Ca²⁺, Mg²⁺, and K⁺ concentrations in peat interstitial waters were significantly correlated with fine-sand contents in peat sampled at 5–10 cm depth (p < 0.05). In addition, plant heights showed significant positive correlations with both K⁺ and Ca²⁺ concentrations (p < 0.05). The results suggest that, in this mire where is mostly ombrotrophic, soil particles derived from flooding would serve as an important mineral source to affect the vegetation type.