5:15 PM - 7:15 PM
[MIS22-P06] Diatoms in highly acidic and strongly alkaline hot springs in Yamagata Prefecture, Japan
Keywords:diatom, hot spring, strongly acidic , strongly alkaline
Diatoms are siliceous microalgae that inhabit all water bodies, including strongly acidic and strongly alkaline waters. In the case of diatoms, the concentration of available silica is usually low in strong acid lakes, on the other hand in strong alkaline lakes, the valves were easily decomposed (Watanabe 1985). There are many studies on the effect of pH on diatoms (e.g., Hustedt 1937-1939), with species classified into five categories; acidobiontic, acidophilous, circumneutral, alkaliphilous and alkalibiontic (Watanabe 2005).
In this study, diatoms from two spas in Yamagata Prefecture were investigated; Zao Spa (pH= 1.52~1.93), a strongly acidic, sulfur-containing-aluminum-sulfate-chloride hot spring, and Yubunezawa Spa (pH = 9.35~9.93), a strongly alkaline, simple sulfur cold mineral spring. Sampling surveys were conducted seasonally in February (winter), May (spring), August and September (summer) and October (autumn) 2024, with Yubunezawa Spa sampled twice in summer because its pH was neutral due to heavy rain. The collected samples were observed using an optical microscope to quantify the seasonal ecological changes. The results for Zao Spa were compared with those of a previous study (Jordan 2001). As there were no previous studies on Yubunezawa Spa, comparisons were made with previous studies on other highly alkaline springs from around Japan.
Jordan (2001) reported three diatom species from two genera in Zao Spa, with Pinnularia acidojaponica as the dominant species, followed by Pinnularia acoricola, and then Fragilaria sp. ( Fragilaria sp. was not identified in this survey.)
However, the present survey identified four additional species (Eunotia exigua, Aulacoseira sp., Pinnularia borealis, Nitzschia amplectens, and Melosira sp.) in three genera, resulting in a total of seven species in five genera from this spa.
On the other hand, 28 diatom species belonging to 19 genera were identified in the strongly alkaline waters of the Yubunezawa Spa, with Achnanthes minutissima as the dominant species at high pH except in summer, with Navicula veneta appearing as the second dominant species, and Meridion circulare appearing less commonly at high pH. In contrast, M. circulare was the dominant species when the summer pH was neutral and A. minutissima was rare. Most of the diatoms that appeared at high pH in Yubunezawa Spa also appeared at neutral pH in summer, however, the species that appeared in summer disappeared in autumn. Comparing our results with those in the literature, Osoushi Spa with a pH of 10.0~10.4 (Tsuji 1995), is similar to Yubunezawa Spa, and appeared to have more common species (N. veneta and M. circulare) than Nebuta Spa with a pH of 10.1 (Watanabe & Asai 1995).
The results of the present study suggest that the new additions to the Zao Spa diatom flora may be due to the increased water volume in the hot spring at the time of sampling compared to Jordan (2001). Both P. acidojaponica and P. acoricola appear to be dominant species in highly acidic waters below pH 4.0, although P. acidojaponica was found to be more tolerant of hydrothermal water and pH than P. acoricola. The unidentified Melosira sp. may be a new species and should be investigated by scanning electron microscopy in the future.
On the other hand, the results from the Yubunezawa Spa suggest that diatoms that are highly tolerant to strong alkalinity can tolerate temporary neutrality and that even temporary changes in pH can have a significant impact on diatom community changes.
In this study, diatoms from two spas in Yamagata Prefecture were investigated; Zao Spa (pH= 1.52~1.93), a strongly acidic, sulfur-containing-aluminum-sulfate-chloride hot spring, and Yubunezawa Spa (pH = 9.35~9.93), a strongly alkaline, simple sulfur cold mineral spring. Sampling surveys were conducted seasonally in February (winter), May (spring), August and September (summer) and October (autumn) 2024, with Yubunezawa Spa sampled twice in summer because its pH was neutral due to heavy rain. The collected samples were observed using an optical microscope to quantify the seasonal ecological changes. The results for Zao Spa were compared with those of a previous study (Jordan 2001). As there were no previous studies on Yubunezawa Spa, comparisons were made with previous studies on other highly alkaline springs from around Japan.
Jordan (2001) reported three diatom species from two genera in Zao Spa, with Pinnularia acidojaponica as the dominant species, followed by Pinnularia acoricola, and then Fragilaria sp. ( Fragilaria sp. was not identified in this survey.)
However, the present survey identified four additional species (Eunotia exigua, Aulacoseira sp., Pinnularia borealis, Nitzschia amplectens, and Melosira sp.) in three genera, resulting in a total of seven species in five genera from this spa.
On the other hand, 28 diatom species belonging to 19 genera were identified in the strongly alkaline waters of the Yubunezawa Spa, with Achnanthes minutissima as the dominant species at high pH except in summer, with Navicula veneta appearing as the second dominant species, and Meridion circulare appearing less commonly at high pH. In contrast, M. circulare was the dominant species when the summer pH was neutral and A. minutissima was rare. Most of the diatoms that appeared at high pH in Yubunezawa Spa also appeared at neutral pH in summer, however, the species that appeared in summer disappeared in autumn. Comparing our results with those in the literature, Osoushi Spa with a pH of 10.0~10.4 (Tsuji 1995), is similar to Yubunezawa Spa, and appeared to have more common species (N. veneta and M. circulare) than Nebuta Spa with a pH of 10.1 (Watanabe & Asai 1995).
The results of the present study suggest that the new additions to the Zao Spa diatom flora may be due to the increased water volume in the hot spring at the time of sampling compared to Jordan (2001). Both P. acidojaponica and P. acoricola appear to be dominant species in highly acidic waters below pH 4.0, although P. acidojaponica was found to be more tolerant of hydrothermal water and pH than P. acoricola. The unidentified Melosira sp. may be a new species and should be investigated by scanning electron microscopy in the future.
On the other hand, the results from the Yubunezawa Spa suggest that diatoms that are highly tolerant to strong alkalinity can tolerate temporary neutrality and that even temporary changes in pH can have a significant impact on diatom community changes.