Rikunomizu（Limnology in Tokai Region of Japan）87 : 53 - 58（2020）

ReportAccumulation of Hydrurus foetidus (Chrysophyceae) in sand ripples of avolcanic inorganic acidified river in the southern part of Mount Ontake,central Japan
Kentaro NOZAKI 1), Yoshitaka MATSUMOTO 2) and Takashi TASHIRO 3)
Abstract
On 28 February 2018, rippled patterns were observed in the riverbed of a volcanic inorganic acidified
river in the southern part of Mount Ontake located in central Japan. The patterns were formed by theaccumulation of colony fragments of a golden alga, Hydrurus foetidus (Villars) Trevisan (Chrysophyceae).
The mean values (±standard deviation) of the areal dry mass, ash free dry mass and chlorophyll-aamounts of H. foetidus deposit were 530±200 g m-2, 170±60 g m-2 and 240±60 mg Chl.a m-2, respectively.
Compared with a previous study, this H. foetidus deposit was observed to be an extremely large biomassat the study site. We considered that H. foetidus does not grow in this river owing to carbon dioxide
limitations, and the accumulated fragments of H. foetidus colonies found in the troughs of sand ripples
flowed from tributaries of neutral or alkaline water.
Key words: ripple, Hydrurus foetidus (Villars) Trevisan, Chrysophyceae, volcanic inorganic acidified
river, Mount Ontake(Received: 22 March 2020; Accepted: 16 April 2020)

Matsumoto et al., 2020). Matsumoto et al. (2020) stated that
the Nigorigawa River is acidified by volcanic sulfuric acid
(H2SO4) from the vents of Mount Ontake, with a mean pH
value of 4.2.
The environmental parameters of the current study site
are shown in Table 1. The water temperature, electricconductivity (EC), pH and turbidity were measured with analcohol thermometer, an EC meter (CM-21P, TOA DKK),a colorimetric method (WAK-pH/WAK-BCG, KyoritsuRikagaku) and a water analyser (WA1, Nippon Denshoku),
respectively. The collected water samples were broughtback to the laboratory. The alkalinity of a 300-mL sample
was measured via titrating until pH 4.8 by 0.2 N H2SO4.
The river water on the sampling dates was not significantly
acidic, with a pH value of 6.5 on 28 February and 6.3 on
1 March. The water temperature, EC, pH and alkalinity

Accumulation of Hydrurus foetidus introughs of sand ripples
Sand ripples are a general pattern on a riverbed caused by
the accumulation of particles less than 0.6 mm (JapaneseSociety of Limnology, 2006; Tashiro, 2014). On 28 February
2018, rippled patterns were observed on the riverbedof the Nigorigawa River in the southern part of Mount
Ontake located in central Japan (N35°48'12", E137°28'54",elevation 1035 m). These ripples had formed on the sandy
bottom of a pool 24-30 cm deep and were filled with theaccumulation of dark brown matter in the troughs (Figs. 1Aand 1B). The Nigorigawa River primarily consists of theNigorizawa River in strong acidic flow from the Jigokudani
Valley (Fig. 2), which has the vent of Mount Ontake, andthe slightly alkaline Denjogawa River (Usami et al., 2019;1)

School of Education, Sugiyama Jogakuen University, Hoshigaoka Moto-machi 17-3, Chikusa-ku, Nagoya, Aichi 464-8662, Japan(E-mail: ken@sugiyama-u.ac.jp)
2)
Department of Civil Engineering, National Institute of Technology, Toyota College, 2-1 Eisei, Toyota, Aichi 471-8525, Japan
3)
Disaster Mitigation Centre, Nagoya University, Furo-cho 1, Chikusa-ku, Nagoya, Aichi 464-8601, Japan53Ⓒ2020

The Tokai Branch of the Japanese Society of Limnology

Kentaro NOZAKI et al.

1ANorth

1BSampling station
1.0 kmFig. 2. Map of the study area.
Table 1. Environmental parameters in the sampling site of theNigorigawa River.

Fig. 1. Ripples in riverbed of a pool (1A) in a volcanic
inorganic acidified river, Nigorigawa, at the southern part ofMount Ontake on 28 February 2018. Dark areas consist ofbrown particles found at troughs of ripples (1B). White arrow
indicates the flow direction.

The Tokai Branch of the Japanese Society of Limnology

1 MarchCloudySampling time

12:20

11:10

Water temperature (℃）
Electric conductivity (mS m-1)
pHAlkalinity (mgCaCO3 L-1)
Turbidity (mg L-1)

6.3
40.0
6.5
6.1
5.2

3.5
32.5
6.3
2.4
25.3

Weatherdecreased, whereas the turbidity increased after 24.5 mm ofrainfall occurred from 0:00 to 11:00 on 1 March. As the pH
decreased within this short period, the alkalinity markedly
reduced from 6.1 mgCaCO 3 L -1 to 2.4 mgCaCO 3 L -1.
Furthermore, the Shimokurosawa, a neutral river adjacent tothe Nigorigawa, had an alkalinity of 16.3 mgCaCO3 L-1 on
28 February. From these results, the Nigorigawa River wasjudged to be in a volcanic inorganic acidified state.
The deposited matter in the ripple troughs was gently
collected with a glass pipette from a 3×3-cm area. When thesamples were observed with an optical microscope (BX-51,Olympus Company) with a digital camera (DP 27, Olympus
Company), they were observed to be colony fragmentsof golden alga Hydrurus foetidus (Villars) Trevisan (Figs.
3A-D). This freshwater alga is distributed worldwide(Kristiansen and Preisig, 2011; Klaveness, 2019) and formsⒸ2020

28 FebruaryFinebushy thalli up to 30 cm long on stones; it is known as a
typical cold water species on the Japanese islands (Kobayasi,1961; Fukushima, 1962; Kobayasi, 1972; Takahashi, 1977;
Iyama et al., 1984). Klaveness et al. (2011) found that H.
foetidus is positioned at the Chrysophyceae clade in thephylogenetical tree based on 18S and 28S rRNA sequences.
However, the position within the Chrysophyceae is still
unclear, because of the limited numbers of sequences for
Chrysophyceae taxa.
The dry mass, ash-free dry mass (AFDM) and
chlorophyll-a amounts (UNESCO method) of the H.
foetidus deposit are shown in Table 2. These factors were54

Accumulation of Hydrurus foetidus (Chrysophyceae) in a volcanic inorganic acidified river

3A

3B

3C

3D

Fig. 3. Microscopic photos of a golden alga Hydrurus foetidus (Villars) Trevisan (Chrysophyceae) collected from the deposit ina pool of the Nigorigawa River on 28 February 2018. 3A: ×40, 3B: ×100, 3C: ×200, 3D: ×400.
Table 2. Dry mass and chlorophyll-a amount of Hydrurus
foetidus deposit in 28 February 2018.

measured according to Matsumoto and Nozaki's (2014)
procedure. The mean values (±standard deviation）of theareal dry mass, AFDM and chlorophyll-a amounts were
530±200 g m-2, 170±60 g m-2 and 240±60 mg Chl.a m-2,respectively. Nozaki (2016) reported that the epilithic algal
biomass in the Nigorigawa River was low at 0.02-0.06 mg
Chl.a m-2 between September 2015 and February 2016.
Therefore, this H. foetidus deposit at this study site wasproven to be an extremely large biomass.
The growth potential and accumulation processes ofH. foetidus at the sampling site were estimated using
environmental factors. Normally, the alga is firmly attachedto stone, and the colonies (20-30 cm long) form a slimy
covering on riverbed materials (Takahashi, 1977; Kristiansenand Preisig, 2011). However, here, these collected H.
foetidus deposits were colony fragments. Regarding its ecophysiological features, sufficient light (30-100 μmol m-2

Sampling depth (cm)Mean value(n = 3)27SD
3-2

Dry mass ( g m )

530

200

Ash-free dry mass ( g m-2)
Ratio of ash-free dry mass (%)
Chlorophyll-a (mg Chl.a m-2)

170
3324060
560s-1), a low water temperature (2-3 ℃ ), and turbulence areimportant for growth (Klaveness and Lindstrøm, 2011).
Current ripples are formed at a wavelength 600-800 times
the mean diameter of sand particles under a steady flow (e.g.
Charuru et al., 2013; Tashiro, 2014), and circulatory flow
formed behind each lee slope of ripples, wherein the shear
flow is separated from the crests and reattached to the stoss

55

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Kentaro NOZAKI et al.
Table 3. Dry mass and chlorophyll-a amount of epilithic
materials in the main channel of the Nigorigawa River in 28
February 2018.
Mean value(n = 3)SD

135383
36
9.5
1.0

10
1
0.2
1.5

25
11
1.4
15.8
0.2

8
6
0.6
10.0
0.1

5A

Stagnation
Sampling depth (cm)-2

Dry mass ( g m )Ash-free dry mass ( g m-2)
Ratio of ash-free dry mass (%)
Chlorophyll-a (mg Chl.a m-2)
RiffleSampling depth (cm)Dry mass ( g m-2)
Ash-free dry mass ( g m-2)
Ratio of ash-free dry mass (%)
Chlorophyll-a (mg Chl.a m-2)

5B

Fig. 5. Colony of H. foetidus growing on a cobble surface in ariffle of the Denjogawa River with the slightly alkaline water ofa tributary of the Nigorigawa River on 9 November 2018. 5A:
The white arrows indicate colonies. 5B: Microscopic photo of H.
foetidus (×100).
Fig. 4. Microscopic photo of epilithic materials collected from acobble surface in a riffle of the Nigorigawa on 28 February 2018(×200).

channel were extremely low (Table 3). The alga could not
be seen even when observing the epilithic materials with an
optical microscope (Fig. 4). Certain factors seemed to be
inhabiting the growth of the epilithic algae in this river. We
assumed that the most influential factor was the depletionof carbon dioxide (CO 2), a source of photosynthesis.
CO2 concentration as dissolved inorganic carbon (DIC)
is generally decreased in acidified freshwaters (Satake etal., 1972; Satake and Saijo, 1974). In Experimental Lakes
Area, Canada, a lake was artificially acidified with H2SO4,decreasing the pH from 6.8 to 4.5 over seven years. As
the pH decreased, the alkalinity and DIC concentration
also declined, and the net photosynthesis of the epilithic
algal community was significantly attenuated (Turner etal., 1991; 1995). Therefore, we considered that the H.
foetidus in this study did not grow due to the CO2 limitation

slopes (e.g. Sekine and Kikkawa, 1987; Raudkivi, 1996).
Here, as the substrate was not stable enough to be attached
to and the eddies were large enough to trap the fragments,
we considered that the H. foetidus accumulated in the ripples
had not grown there but drifted from the upper reaches.

Source of the H. foetidus deposit
The colony fragments of the H. foetidus might have been
supplied from epilithic materials on stone surfaces in theNigorigawa River and accumulated in the pool. However,the dry mass, AFDM and chlorophyll-a amount in theepilithic materials at the stagnation and riffle in the main

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Accumulation of Hydrurus foetidus (Chrysophyceae) in a volcanic inorganic acidified rivercommunity of Japanese mountain river. BotanicalMagazine, Tokyo, 74: 228-235.
Kobayasi, H. (1972): Chlorophyll content and primary
production of the sessile algal community in the mountainstream Chigono-zawa running close to the Kiso Biological
Station of the Kyoto University. Memoirs of the Facultyof Science, Kyoto University. Series of biology, 5: 89-107.
Kristiansen, J. and H. R. Preisig (2011): Order Hydrurales.
In The Freshwater Algal Flora of the British Isles - An
Identification Guide to Freshwater and Terrestrial Algae(Second Edition), John, D. M., B. A. Whitton and A.
J. Brook (eds.): 308-310, Cambridge University Press,Cambridge.
Matsumoto, Y. and K. Nozaki (2014): 3. Mizu No Kagakubunseki (Analysis of water chemistry). In Mijika Na Mizu
No Kankyo Kagaku, Jisshu Sokutei Hen (Methods forEnvironmental Studies of Inland Waters), Tokai Branchof Japanese Society of Limnology (ed.): 81-124, Asakura
Publishing, Tokyo (in Japanese).
Matsumoto, Y., K. Nozaki and A. Usami (2020): Spatialand short-term water quality variation in Otaki watershedlocated at the southern side of Mt. Ontake. Rikunomizu(Limnology in Tokai Region of Japan), 87: 11-22 (inJapanese with English abstract).
Nozaki, K. (2016): Autumn and winter periphyton biomassin the Ohtakigawa River watershed 1 year after the 2014
eruption of Mount Ontake, central Japan. Rikunomizu(Limnology in Tokai Region of Japan), 74: 13-21.
Rudkivi, A.J. (1966): Bed forms in alluvial channels.
Journal of Fluid Mechanics, 26(3): 507-514.
Satake, K., Y. Saijo and H. Tominaga (1972): Determinationof small quantities of carbon dioxide in natural waters.
Japanese Journal of Limnology, 33: 16-20.
Satake, K. and Y. Saijo (1974): Carbon dioxide content andmetabolic activity of microorganisms in some acid lakes
in Japan. Limnology and Oceanography, 19: 331-338.
Sekine, M. and H. Kikkawa (1987): Experimental study
on the suspended-load over a rippled bed. Proceedingsof the Japan Society of Civil Engineers, 387: 95-103 (inJapanese).
Takahashi, E. (1977): Family Hydruraceae. In Illustrationsof the Japanese Fresh-water Algae, Hirose, H and T.
Yamagishi (eds.): 188-189, Uchida Rokakuho Publishing,Tokyo (in Japanese).
Tashiro, T. (2014): Kashokeitai To Kashogata (Form andtype of riverbed), In Mijika Na Mizu No Kankyo Kagaku,Jisshu Sokutei Hen (Methods for Environmental Studies

in the Nigorigawa River, but that the colony fragments
accumulated in the sand ripple troughs flowed in fromtributaries of neutral or alkaline water. For example, on 9
November 2018, we observed the growth of H. foetidus on acobble surfaces in the slightly alkaline Denjogawa River (pH7.3), a tributary of the Nigorigawa River (Fig. 5A and 5B).

Acknowledgments
We are grateful to our colleagues participating in this study,
Drs. Tomomasa TANIGUCHI, Yukio ONODA, Akiko USAMI andAkihiko YAGI for their help in field surveys and for providing
suggestions. This research was supported by a Grant-in-Aidfor Scientific Research (B) from the Japan Society for thePromotion of Science (No. 19H04318) to Takashi TASHIROand a Grant from the Water Resource Environmental Centre(No. 2017-05) to Yoshitaka MATSUMOTO.

References
Charuru, F., B. Andreotti and P. Claudin (2013): Sand
Ripples and Dunes. Annual Review of Fluid Mechanics,
45: 469-493.
Japanese Society of Limnology (2006): Rikusui No Jiten(Dictionary of Limnology): 184, Kodansya Publishing,Tokyo (in Japanese).
Fukushima, H. (1962): Preliminary report on the life
history of Hydrurus foetidus. Acta Phytotaxonomica etGeobotanica, 20: 290-295 (in Japanese with Englishsummary).
Iyama, Y., N. Takayanagi, T. Ohura and I. Yasuda (1984):
The Relation between Biological Assessment and BODof the River Water. Japanese Journal of Water Treatment
Biology, 20(2): 7-12 (in Japanese).
Klaveness, D. (2019): Hydrurus foetidus (Chrysophyceae):
an update and request for observations. Algae, 34(1): 1-5.
Klaveness, D. and E.-A. Lindstrøm (2011): Hydrurusfoetidus (Chromista, Chrysophyceae): A large freshwater
chromophyte alga in laboratory culture. PhycologicalResearch, 59(2): 105-112.
Klaveness, D., J. Brate, V. Patil, K. Shalchian-Tabrizi, R.
Kluge, H. Ragnar Gislerød and K. S. Jakobseni (2011):
The 18S and 28S rDNA identity and phylogeny of thecommon lotic chrysophyte Hydrurus foetidus. European
Journal of Phycology, 46(3): 282-291.
Kobayasi, H. (1961): Chlorophyll content in sessile algal

57

Ⓒ2020

The Tokai Branch of the Japanese Society of Limnology

Kentaro NOZAKI et al.

of Inland Waters), Tokai Branch of Japanese Society ofLimnology (ed.): 26-28, Asakura Publishing, Tokyo (inJapanese).
Turner, M. A., E. T. Howell, M. Summerby, R. H.
Hesslein, D. L. Findlay and M. A. Jackson (1991):
Changes in epilithon and epiphyton associated withexperimental acidification of a lake to pH. Limnology andOceanography, 36: 1390-1405.
Turner, M. A., D. W. Schindler, D. L. Findlay, M. B. Jacksonand G. G. C. Robinson (1995): Disruption of littoral algal
associations by experimental lake acidification. Canadian
Journal of Fisheries and Aquatic Sciences, 52: 22382250.
Usami, A., Y. Matsumoto, A. Yagi and E. Iwatsuki(2019): Role Difference among rivers affected byvolcanic activities of Mt. Ontake for water quality of theNigorigawa River. International Journal of GEOMATE,
16: 76-81.

黄金色藻ミズオ（Hydrurus foetidus）の堆積
喬3)

2018年2月28日に，御嶽山南麓の火山性無機酸性河川の河床において砂漣上に紋様が観察された。この紋様は，黄金色藻ミズオ Hydrurus foetidus (Villars) Trevisan の群体の断片が窪みに堆積することで形成されていた。ミズオ堆積物の単位
面積あたりの乾燥重量，強熱減量およびクロロフィル a 量の平均値±標準偏差は，それぞれ，530±200 g m-2，170±60 g m-2，240±60 mg Chl.a m-2であった。先行研究と比較すると，このミズオ堆積物は，本調査地において大変に大きな生物量であることがわかった。ミズオは，二酸化炭素律速によって，この川では成長できず，砂漣上に堆積していた群体の断片は，中性もしくはアルカリ性の支流から流入してきたと推察された。
，黄金色藻，
キーワード：砂漣，ミズオ（Hydrurus foetidus）
火山性無機酸性河川，御嶽山

The Tokai Branch of the Japanese Society of Limnology〒471-8525愛知県豊田市栄生町2-1国立豊田工業高等専門学3)〒464-8601名古屋市千種区不老町 名古屋大学減災連携研究センター

御嶽山南麓の火山性無機酸性河川における砂漣へのⒸ2020

2)

校都市環境工学科

要野崎健太郎1)・松本嘉孝2)・田代〒464-8662名古屋市千種区星が丘元町17-3椙山女学園大学
教育学部（E-mail: ken@sugiyama-u.ac.jp）(Editor: Dr. Ryota TSUBAKI, Graduate School of Engineering,
Nagoya University; Guest Editor: Dr. Akihiro T UJI ,Department of Botany, National Museum of Nature andScience)

摘1)58