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.
The spatial distribution of submerged macrophytes, in terms of dry weight and species composition, was surveyed in the southern Lake Biwa basin in September 2017, using SCUBA. Submerged macrophytes were observed at 40 out of 52 sampling stations. The average total biomass of submerged macrophytes per site was 54 g dry wt. m-2. During study period, the area covered by vegetation in the basin was estimated to be 39.7 km2 and the total biomass was estmated to be 2761 t. Thirteen species of submerged macrophytes were observed in this study, and the average number of species per site and its standard deviation was 4.5±3.0. Hydrilla verticillat and Elodea nuttallii dominated the observed submerged macrophytes, with biomass of 777 t and 776 t, respectively. Potamogeton maackianus (556 t), Egeria densa (283 t), and Myriophyllum spicatum (257 t) followed. Biomasses of other species were each less than 100 t. We also observed that a substantial amount of filamentous algae existed in the south basin, and its biomass (1161 t) is equivalent to about 40% of the total biomass of submerged macrophytes in the basin.