Water Pollution Continuous Monitoring Technology in Japan
Simplified Measurement

3. Water Quality Evaluation Method Using Biological Indexes

In Japan, river water quality may be evaluated by checking the distribution of benthos living in clean or dirty water, such as larva of dragonfly, and ephmeroptera, etc. The advantage of this method is that an average water pollution level can be understood with less frequent investigations. When simplified water test kit is used in combination with this method, it may be possible to identify the pollution.

The benthos living in water vary from country and country. Therefore, the benthos and water quality of their living environment must be investigated first to select the benthos used as the biological indexes for water quality evaluation. Once the biological indexes and the water quality of their living environment are identified, water quality of target area can be evaluated by checking the distribution of the biological indexes.

In Japan, Beck-Tsuda α and β methods are used for evaluation of water quality by means of visual examination of index organisms. Pantleu Buck method is a method in which the appearance frequency of index organism is taken into account.

(1) Beck-Tsuda-α method and Beck-Tsuda-β method
In the Beck-Tsuda-α method, benthos is classified into those having no resistance against pollution (Group A) and those resistant against pollution (Group B). The value calculated by 2A+B from collected benthos is used as the biological indexes. This method was originally developed by a biologist, Beck, and improved by Professor Tsuda of Japan. Although the Beck-Tsuda-α method analyzes the organisms within an area of 50cm around, the Beck-Tsuda-β method is used for the analysis under any environmental factor of the target area.

The table 6.3.1 below shows the features of Beck-Tsuda-α method and Beck-Tsuda-β method. The Beck-Tsuda-β method is used more frequently than Beck-Tsuda-α method because it can apply to any environmental factor.

Table 6.3.1 Comparison of Beck-Tsuda-α method and Beck-Tsuda-β method(1)


Beck-Tsuda-α method

Beck-Tsuda-β method

Investigation method* Samples are collected from an area of 50cm x 50cm. A frame of 50cm x 50cm is placed on the water bottom and the organisms visually found are collected. Perform sampling twice.

* Organisms are collected from the bottom formed by gravel.

* Locations with many stones the size of a watermelon or orange should be selected for sampling.

* Locations with an average flow rate of 100 to 150cm/sec. should be selected for sampling.

* The number of benthos in the sample is calculated by 2A+B. Compare the sum of the first sample and second sample. Evaluate the water quality based on the sum which is larger of the two.

* Collect organisms in any environment of the target area (slow flow, fast flow, deep area, shoreside, sandy and muddy area, gravel area, water plant, fallen leaves, etc.).

* Samples should be collected for about 30 minutes with 2 to 3 people.

* The number of benthos in the sample is calculated by 2A+B. Compare the sum of the first sample and second sample. Evaluate the water quality based on the sum which is the larger of the two.

Table 6.3.1 Comparison of Beck-Tsuda-α method and Beck-Tsuda-β method(2)


Beck-Tsuda-α method

Beck-Tsuda-β method

Water quality rank

1) Clean water:

Os (Oligosaprobien)

2) Slightly polluted


β m (β methosaprobein)

3) Polluted water

α m (α methosaprobein)

4) strongly polluted water

Ps (Poly-sacrobein)


2A+B >= 20


11 <= 2A+B <= 19



6 <= 2A+B <= 10


0 <= 2A+B <= 5



2A+B >= 30


15 <= 2A+B <= 29



6 <= 2A+B <= 14


0 <= 2A+B <= 5


Notes) A: no resistance species against pollution
B: resistant species against pollution

(2) Pantleu Buck method
The Pantleu Buck method identifies the benthoses in the samples and calculate the pollution index according to the distribution of the benthoses, taking into account the appearance frequency of the index benthoses.

The pollution index (S) is calculated using the equation below:

    S = Σ(s x h) / Σh
S: pollution index s: pollution class index h: appearance frequency

Pollution level exponent (s)
-Organism living in clean water (Oligosaprobien): Point 1
-Organism living in slightly polluted water (β methosaprobein): Point 2
-Organism living in polluted water (α methosaprobein): Point 3
-Organism living in strongly polluted water (Poly-sacrobein): Point 4

After identifying the benthoses collected, each benthos is separated into the categories above. Then, the number of benthoses of each category is counted and applies the appearance frequency (h) rank below. The number of each rank is determined according to the specific conditions of each target area and the number shown below is one of the examples.

Appearance frequency (h)
-Rare (ex. 30 or less): Point 1
-Many (ex. 31- 60): Point 2
-Extremely large number (ex. 61 or more): Point 3

The pollution index (S) calculated is compared with the water pollution level classification in the table below and the water quality of the target area is evaluated.

Table 6.3.2 Water quality rank using the pollution index (S)

Water quality rank

Pollution index (S)

1) Clean water:

Os (Oligosaprobien)

2) Slightly polluted water:

β m (β methosaprobein)

3) Polluted water

4) strongly polluted water

Ps (Poly-sacrobein)

1.0 < S < 1.5


1.5 < S < 2.5


2.5 < S < 3.5


3.5 < S < 4.0

(3) Other methods
The above-mentioned Beck-Tsuda-α, Beck-Tsuda-Β and Pantleu Buck methods require detailed identification of index benthos into species such as "Paragnetina tinctipennis (species name) of Perlodidae (family name) of Plecoptera (order name)". Therefore, staff having experience in benthos identification is necessary.

In the case of simple water quality evaluation performed by ordinal residents or non-specialists, only typical biological indexes should be used for ease of measurement. With this purpose, the Environmental Agency of Japan developed a method which allows easy evaluation of water quality through identification of typical biological indexes. The examples of investigation form and biological index designated by the Environmental Agency are shown in Table 6.3.3 and Fig.6.3.1, respectively.

-Investigation should be performed by groups consisting of 3 to 5 people.

-Select a location where the water depth is approx. 30cm, the flow rate is approx. 30 to 40cm / sec. and there are stones of sizes from fist to head on the riverbed. (If there are no stones with the size of a head, select a location with gravel, sand or pebbles.)

-Remove stone or gravel, stir the river bottom under the stone or grave with a shovel or foot, and catch the benthos flowing with a colandar.

-Move stones and gravel onto the shore-side and collect all the benthos on them.

-Record the collected benthos on the recording sheet.

-After recording, return the stones, gravel and benthos into the river.

Table 6.3.3 Example of Investigation Form Based on Water Quality Evaluation Method by the Environment Agency of Japan


Organization Name                              

River Name                              

Chief Stuff Name                              

Location of investigation (No. )

( 1 )

(       )


May 5, 1995








Water temperature (°C)



Width of river (m)



Spot of sampling benthos

Center of river


Depth of water in sampling benthos(cm)



Flow rate



State of bottom in river

Many head-size


Turbidity, Odor, Others

Clear water


Rank of

Water quality

Index benthos

Enter "O" for confirmed index benthos and
"l " for the largest number of index benthos



I Clean

1 Dudesia japonica


2 Geothelphusa dehaani  

3 Simulium sp


4 Plecoptera



5 Rhyacophilidae / Glossosomatidae



6 Heptageniidae



7 Magaloptera


I • II

8 Trichoptera except No.5

 9 Ephemeroptera except
No.6, No.11

"l "


II Slightly

10 Mataeopsephus




11 Baetis sahoensis


12 Erpobdellidae


13 Asellus hilgendorfii



14 Physa (Physella) acuta


IV Serious pollution

15 Chironomus yoshimatsui  

16 Tubifex hattai


Rank of water quality









Evaluation of water


1 The Number of species in index benthos confirmed





2 Number of species in the largest number index benthos confirmed






3 Total (1+2)






Rank of water quality of
the location



Fig 6.3.1 Biological Indexes designated by the Environment Agency

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