IJERD – International Journal of Environmental and Rural Development (2012) 3-1

Research articleerd

Growth Situation of Phragmites australis (Cav.) Trin. Usedin Artificial Floating Islands for Water Purification in ColdRegions
MASATO KIMURA*
Obihiro University of Agriculture and Veterinary Medicine, Hokkaido, Japan
Email: masa-k@obihiro.ac.jp

OSAMU TSUJI
Obihiro University of Agriculture and Veterinary Medicine, Hokkaido, JapanTOSHIMI MUNEOKA
Obihiro University of Agriculture and Veterinary Medicine, Hokkaido, JapanHIROTO OTE
Obihiro University of Agriculture and Veterinary Medicine, Hokkaido, Japan
Received 15 December 2011Accepted 18 April 2012(*: Corresponding Author)

Abstract In this study, growth experiments of Phragmites australis (Cav.) Trin., used aspart of artificial floating islands for water purification, were conducted. The Lake
Mizusawa, which is the study area, is located in Biei Town, Hokkaido. The area aroundthis lake is hilly and mostly comprises farm fields . Due to the topography and land use,soil particles and fertilizer flow into the lake after heavy rains. This is the most importantcause of lake eutrophication. One way to clear up this eutrophied lake is to place artificial
floating islands using the Phragmites on the lake surface. The Phragmites used for theartificial floating islands absorb nitrogen, including the contained in lake’s water, topromote lateral buds sprouting. After that, grown lateral buds are cut and hence thepollution is carried away outside the system. However, this method has been little tested incold regions such as Hokkaido. Thus, on July 2010, we put artificial floating islands in thebiotope which was developed on a drained paddy close to the lake. The Phragmites grewsteadily. There were about four hundreds lateral buds sprouting by October 2010, and themaximum plant length of lateral buds was 0.74 meters. Observed artificial floating islands
were left in the biotope during winter. In 2011, the lateral buds sprouted and grew in ashorter period of time compared to 2010. Similarly, maximum plant length of lateral buds
was 1.86 meters. Ear emergence was also observed, although it was not observed in 2010.
Therefore, it is considered that there was no damage to the Phragmites due to the cold.
From these results, it was found that the Phragmites used for the artificial floating island
were able to grow in cold region. Thus, this method is a promising way to improve water
quality of Lake Mizusawa.
Keywords water purification, Phragmites australis (Cav.) Trin., lake eutrophication,
cold region

INTRODUCTION
Biei-cho, Hokkaido, is one of the areas with the most beautiful scenery in Japan. Lake,Mizusawa arepresentative scenic spot, is known as a stopover for migratory birds and is familiar to people as aprecious waterside space. Conservation activities are therefore undertaken in this area to protect thebeautiful landscape and local environment.
However, Lake Mizusawa suffers from a significant eutrophication problem arising from thetopography and land use of this area. The terrain around this lake is hilly and mostly comprisesⒸ ISERD

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farm fields. During periods of agricultural production, large amounts of fertilizer are applied to thefields to increase yield. However, following heavy rains, soil and fertilizer flow into the lake. Thisis the most important cause of lake eutrophication, which negatively affects the ecosystem andlandscape around the lake and leads to occurrence of blue-green algae and generation of an
unpleasant smell. Therefore, to preserve this beautiful landscape and local environment, it isnecessary to improve water quality.
One way to clear up eutrophied lakes is to place artificial floating islands of Phragmites
australis (Cav.) Trin. on the lake surface. However, this method, which was suggested by Uchida etal. (1999, 2001), Uchida and Maruyama (1998), and Tazaki et al. (2002), has been little tested incold regions such as Hokkaido. Tsuji et al. (2009) studied the artificial floating islands ofPhragmites and confirmed sprouting of lateral buds. However, they were unable to fully examine
the subsequent growth because most Phragmites plants could not adapt to the changing water leveland died as a result of dehydration.
In the present study, we observed the growth of Phragmites for 2 successive years. In the firstyear, the artificial floating islands of Phragmites were placed in the biotope in July, and the growthof Phragmites was examined. The artificial floating islands were left in the biotope during thesubsequent winter to examine the winter hardiness of Phragmites. In the second year, the growth
was examined from July to September. The results were used to assess the possibility of using theartificial floating islands of Phragmites for water purification.
METHODOLOGY
Study area
The study area was at Lake Mizusawa (Fig. 1), a man-made lake at  latitude  43°32′14′′  north  and  longitude   142°29′41′′   east located at Biei-cho in the central part of Hokkaido. The area
(approximately 2 × 106 m2) around this lake comprises hillside farms. Most farms in this area growpotatoes, beet, and corn, which require large amounts of fertilizer. According to Ote et al. (2011),
the amount of nitrogen applied on these hillside farms was 1.8 × 103 kg in 2010. Because the rateof nitrogen runoff from farms was 11%, the nitrogen loading into Lake Mizusawa was estimated tobe 2 × 103 kg (Ote et al., 2011).
The biotope on which the artificial floating islands were placed adjoined Lake Mizusawa. Thisbiotope was developed on a drained paddy.

Biei-cho

Biei-cho

Mizusawa LakeFig. 1 Study area in Lake Mizusawa located at Biei-cho, Hokkaido
Construction of artificial floating islands
Figure 2 shows the drain mat (Yoshiharakakou Co., Ltd.) used to form the artificial floating islandsof Phragmites. The mat measured 0.50 m × 0.50 m × 0.02 m (length × width × height). The
completed island comprised a drain mat and stems of Phragmites plants that were growing wildaround Lake Mizusawa. As shown in Fig. 2, 5 stems cut to about 0.50 m were inserted into holes inthe mat. Twenty-one artificial floating islands were constructed in this way and they were wiredⒸ ISERD

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each other (Fig. 3). As shown in Fig. 3, the mats were arranged in two rows and were placed in thebiotope.

Five stems of Phragmites inserted
into a mat.

Fig. 2 Drain mat used to make artificial floating islands for water purification

Fig. 3 Artificial floating islands wired each other and placed on biotope surface
Growth of Phragmites andabsorption of nitrogen
Lateral buds sprouting

Nitrogen in the water
Outside the system

Phragmites inserted intoa matFig. 4 Outline of the water purification scheme using artificial floating islands of Phragmites
Figure 4 shows the outline of the water purification scheme using the artificial floating islandsof Phragmites. The scheme comprises the following 3 steps: First, the artificial floating islands areplaced on the surface of eutrophied water, and lateral buds sprouting from nods of Phragmites
plants are inserted into the drain mat. Second, after lateral buds have sprouted, they grow andⒸ ISERD170

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absorb large amounts of nitrogen, including nitrogen from the eutrophied water. This is an
important step in water purification using Phragmites. Finally, in autumn, Phragmites plants,
which accumulate nitrogen, are cut and transported outside the system. The artificial floatingislands are left in place during winter and reused next year.
Growth of Phragmites
The stem length and sprouting rate of the plants were recorded every 2 weeks in 2010 and 2011.
The sprouting rate is the ratio of the total number of sprouts to the total number of nods. Because
more than 2 lateral buds sprout from a nod, the sprouting rate generally exceeds 100%.
In 2010, growth was assessed from July 4 to October 31. After the last assessment in 2010, theartificial floating islands were left in the biotope to evaluate their winter hardiness. The growth ofthe overwintered Phragmites plants was assessed between July 7 and September 21 in 2011. Inaddition, to check the growth of rhizomes, the mats that were fixed to the ground surface in thebiotope were dug up on October 21, 2011.
RESULTSGrowth of Phragmites in 2010

0.8

1800.71600.6140

1200.51000.4

800.3

600.2

400.1

200Average stem lengthMaximum stem length
Sprouting rate

Sprouting Rate (%)

Length (m)Figure 5 shows changes in the sprouting rate and maximum and average stem length during 2010.
The artificial floating islands were placed in the biotope on July 4. After 2 weeks, sprouting oflateral buds was observed. At this time, the sprouting rate and maximum stem length were 4% and0.15 m, respectively. From late July to mid-September, both the sprouting rate and maximum stem
length increased steadily with increasing air temperature. However, the maximum stem length
stopped increasing on September 8. In contrast, the sprouting rate increased moderately after thatdate because lateral buds continued sprouting. On October 31, 419 lateral buds sprouted and thesprouting rate was 153%.The maximum stem length was 0.74 m. After examination in 2010, theartificial floating islands were left in the biotope during winter to examine the winter hardiness ofPhragmites.

07/4 7/20 8/5 8/21 9/6 9/22 10/8 10/24

DateFig. 5 Seasonal changes in sprouting rate and average and maximum stem length in 2010
Growth of Phragmites in 2011
The growth of Phragmites plants that had overwintered on the floating artificial islands wasassessed in 2011. Figure 6 shows changes in the sprouting rate and maximum and average stem
length. As shown in Fig. 6, the overwintered plants grew more steadily in 2011 than in 2010. WhenⒸ ISERD

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1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
0.20850

Average stem length
Maximum stem length
Sprouting rate

800750700
650600Sprouting Rate (%)

Length(m)Length(m)the first evaluation was made on July 7, 2011, the sprouting rate was already 578% and themaximum stem length was 1.35 m. However, although the sprouting rate increased steadily untillate September, the maximum stem length showed little increase after August. In contrast, ear
emergence was observed in 2011, although it was not observed in 2010. Figure 7 shows a
Phragmites rhizome photographed during growth examination on October 21. This figure showsthat Phragmites took root in the biotope.

550

500
7/7

7/21

8/4

8/18
Date

9/1

9/15

Fig. 6 Seasonal changes in the sprouting rate and average and maximum stem length in 2011

Fig. 7 Phragmites rhizome on October 21, 2011DISCUSSIONOn October 31, 2010, the sprouting rate and maximum stem length were 153% and 0.74 m,
respectively (Fig. 5). In summer, both these values increased rapidly with increasing air
temperature, indicating that Phragmites plants used to form the artificial floating islands were able
to grow in the warm season in a cold region such as Hokkaido. However, the artificial floatingislands were left in the biotope during the subsequent winter to evaluate the growth of Phragmites
plants that had overwintered.
The Phragmites plants on the artificial floating islands grew more steadily in 2011 than in
2010, and on September 21, 2011, the sprouting rate and maximum stem length were 788% and1.89 m, respectively (Fig. 6). Two factors were considered to cause the difference in growthincrement: first, the Phragmites plants were not damaged by cold and second, the plants could
absorb nutrient salts more effectively because their rhizomes had grown steadily (Fig. 7).

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These results show that Phragmites used in the artificial floating islands for water purification
can grow for multiple years without difficulty. Thus, this method could be put to practical use forwater purification of the eutrophied Lake Mizusawa.
CONCLUSION
The use of the artificial floating islands of Phragmites was suggested to improve water quality ofthe eutrophied Lake Mizusawa. However, because this method has been little tested in cold regions,we placed the artificial floating islands in the biotope near Lake Mizusawa and examined thegrowth of Phragmites plants on these islands in 2010 and 2011. The plants grew steadily both in2010 and 2011. From the results obtained in 2011, we observed that the Phragmites plants were notdamaged by cold during the preceding winter. These results indicate that Phragmites plants on theartificial floating islands can grow in cold regions. Thus, it could be possible to improve water
quality by use of the artificial floating islands of Phragmites.
REFERENCES
Ote, H., Tsuji, O., Muneoka, T. and Kimura, M. 2011. Purification of water quality of Lake Mizusawa by
artificial floating island used Phragmites australis (Cav.) Trin. Biei-cho. Proceed. 60th Annu Conf. Jpn.
Soc. Irrigation, Drainage and Rural Eng., Hokkaido Branch, 98-101.
Tazaki, F., Uchida, T. and Maruyama, J. 2002. Elongation of lateral buds in segments of each organ and nodeorder of Phragmites australis (Cav.) Trin. J. Jpn. Soc. Reveget. Tech., 28, 49-54. Tsuji, O., Murakami,N.and Tokura, Y. 2009. Purification of water quality of Mizusawa Lake by artificial floating island inBiei town. 58th Annu. Conf. Jpn. Soc. Irrigation, Drainage and Rural Eng., Hokkaido Branch, 114-115.
Uchida, T. and Maruyama, J. 1998. A new attempt to seedling production of common reed (Phragmitesaustralis (Cav.) Trin.). J. Jpn. Soc. Reveget. Tech., 24, 104-108.
Uchida, T., Andoh, Y.and Maruyama, J. 1999. Studies on the efficiency of shoot production using lateral budof Culm and Rhizome of common reed (Phragmites australis (Cav.) Trin.). J. Jpn. Soc. Reveget. Tech.,25, 13-24.
Uchida, T., Tazaki, F.and Maruyama, J. 2001. A new method on waterfront revegetation using Phragmites
australis (Cav.) Trin. Culm. J. Jpn. Inst. Landsc. Architect., 64, 507-512.

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