Spring-fed marshes in Oomori-okuyama, Kani City, Gifu Prefecture, Central Japan: Landform, water characteristics, and aquatic flora and fauna

Abstract

　The term “spring-fed marshes” characterizes wetlands without peat accumulation on the bottom gravel layer, contrasting with “peat mire”. Because this type of wetland is usually small and has a very short lifespan as an isolated habitat, it received little attention until the 1990s; even now information is quite limited. We herein describe the limnological features of spring-fed marshes distributed in Oomori-okuyama (Kani City, Gifu Prefecture, Tokai Region, Japan). These marshes develop on hill slopes, in gradients of 5-20°. They receive oozing waters at their upper margins, and typically lack inflowing waterways. The water flows over hill surfaces or as ground water in a shallow layer over an impermeable ground layer composed of Oniita (plate-like limonite). The volume of water decreases as it flows downstream. As a result, the wetland develops a fan-like shape. The water is characterized by low pH and low conductivity, and the small algal communities are dominated by filamentous Tribonema affine (Xanthophyceae) and desmids. These features are common in dystrophic environments distributed in high and cool regions in Japan. In contrast, the aquatic insect communities are composed of taxa that also inhabit ponds and swamps from lower altitudes.