Limnological features of small pools in the Tarobe-daira Wetland, Hida mountain range, Toyama Prefecture, Japan

Abstract

　The morphological, chemical and biological features of small pools located in the high mountain region of the Hida Mountains in Toyama Prefecture, Japan, were redescribed for the first time in 50 years. Although these pools are in an interesting limnetic environment and they are noteworthy monitoring sites for long-term changes in regional temperature and precipitations, there is limited limnological information. The pools are called ‘Ta (paddy fields)’ or ‘Gaki-ta (paddy fields for hungry ghosts)’ in Japanese based on their resemblance to subdivided paddy fields. The pools were classified into two types based on morphology and topography: irregular-shaped pools on steep slopes and isolated round-shaped pools on gentle slopes or flat ground. Although both pool types are fed by snowmelt, the former develops through erosion along the temporal current to form irregular basins, while the shores of the latter are eroded by wind and develop into round basins.
　The pH in the water of the six pools was around 4.5, irrespective of the shape and size of the pool: the pH was about 0.7 lower than 50 years ago, perhaps due to recent acidic precipitation. Dissolved oxygen was undersaturated at midday in pools without submerged vegetation due to oxygen consumption of the sediment mud. Conversely, dissolved oxygen was oversaturated at midday in the pools with submerged Sphagnum. The rate of oxygen production by Sphagnum is dependent on water temperature; for example, at 17℃ it is 0.26±0.13 mgO₂ wet g^-1 h^-1 and at 27℃ it is 0.72±0.29 mgO₂ wet g^-1 h^-1.
　Filamentous Tribonema affinis (Xanthophyceae) and members of the acidophilous taxon of Diatomaceae, such as Frustulia rhomboides and Pinnularia spp. were dominant in the epipelic algal communities of the pools that were studied.