The Urabandai Lake Group consisting of about 80 lakes and ponds was formed by the eruption of the Volcano Bandai in 1888. The waters of these lakes are similar in nature in having sulphuric or hydrochloric acid in high concentrations. Lake Tatsu-numa is one of such lakes. Lake Tatsu-numa was selected as the IBP water area for two reasons : (1) all trophic levels from primary producers to higher consumers are present, and (2) the lake is comparatively small and is convenient for censuring by a few researchers.
As a part of the studies on the biological productivity in the disharmonic waters in the JIBP-PF The Urabandai Lake Group consisting of about 80 lakes and ponds was formed by the eruption of the Volcano Bandai in 1888. The waters of these lakes are similar in nature in having sulphuric or hydrochloric acid in high concentrations. Lake Tatsu-numa is one of such lakes. Lake Tatsu-numa was selected as the IBP water area for two reasons : (1) all trophic levels from primary producers to higher consumers are present, and (2) the lake is comparatively small and is convenient for censuring by a few researchers.
As a part of the studies on the biological productivity in the disharmonic waters in the JIBP-PF section, the author has engaged in research on the primary production since 1967, especially the plankton production in Lake Tatsu-numa.
(1) Lake Tatsu-numa is situated at the central portion of the Goshiki-numa Lake Group (Fig. 1). Its water contains such ions in high concentrations as SO4-- (237mg/l), Ca++ (61.6mg/l), and Na+ (67.5mg/l), and has a pH of 6.4 (5.9-6.9) (KATO & AITA, 1970) (Fig. 2). Under such environmental conditions, there were found in this lake about 43 species of phytoplankton, among which, the following 9 species were selected by ADACHI (1970) as the important phytoplanktonic species in Lake Tatsu-numa. They are : Oscillatoria pseudogeminata, Melosira granulata, M. italica, Nitzschia obtusa var. scalpeiiiformis, Surireiia sp., Gymnodinium ordinatum, Peridinium inconspicuum, Scourfieldia cordiformis, and Tracheiomonas volvocina.
(2) The standing crop of the phytoplankton in Lake Tatsu-numa varied from 40.5 to 557.4 in the number of cells per 1 millilitre during these five years. The chlorophyll-a content showed the value from 0.136 to 2.5mg/m3 and from 0.5 to 9.1 mg/m2, and the energy efficiency in the gross production ranged from 0.0042 to 0.036% throughout the year. The carbon uptake obtained by 14C-experiments was 19.97 mg/m2/day in November, 1971. On the basis of these results, Lake Tatsu-numa is classified into an oligotrophic type (Figs. 4-6, Table 1).
(3) In the marginal shrub zone of Lake Tatsu-numa, there were found abundantly Oedogonium sp. and diatoms (Fig.8), which grew to a large biomass by autumn. The standing crop of these littoral sessile algae was estimated to be 10.77 kg in dry weight in November, 1971 for the lake as a whole. Moreover, the algal mat consisting of Vaucheria hamata, Niteiia sp., and diatoms developed over the bottom surface of the lake (Fig. 9). The standing crop of such benthic algae was estimated by SHOJI and SHISHIDO (1972) to be 65 kg in dry weight and about 500 kg in fresh weight in November, 1971.
The standing crops of phytoplankton, sessile algae in the marginal shrub zone, and of benthic algae on the lake bottom were estimated to be 4.2kg, 10.77kg, and 65kg in dry weight, respectively in the late autumn. Their percentages to the whole were 5.25%, 13.5%, and 81.3%, respectively, their ratios to the phytoplankton being 1 : 2.6 : 15.5, respectively.
