An Attempt to Assess the Environmental Change in Downstream River of Dams
by Benthic Macroinvertebrate Community
Kunihiko Amano, Yoichi Iwami & Maremi Endoh
National Institute for Land and Infrastructure Management, Tsukuba, Japan
amano-k92ta@nilim.go.jp

Munehiro Igarashi
Ministry of Land, Infrastructure, Transport and Tourism, Japan

Akio Shirai & Satoshi Kashiwabara
Water Resources Environment Technology Center, Japan

ABSTRACT:
Dam construction can significantly alter sediment transport and flow regime at the downstream river. These alterations will induce
channel degradation and/or bed material change, leading to a change in benthic macroinvertebrate community. We have attempted toassess the impact of dam on downstream ecosystems by comparing benthic macroinvertebrate species found at upstream anddownstream of dams, assuming that those at downstream would have been similar to those at upstream without a dam.
For this purpose, we have analysed benthic macroinvertebrate species data obtained at 42 dams nationwide. Macroinvertebrates wereclassified into 166 taxonomic units. TWINSPAN analysis was applied to these assembled data to classify sampling stations according
to the resemblance of the macroinvertebrate communities. The tendency of listed taxon is not similar at upstream and downstream ofdams; implying dams have affected benthic macroinvertebrate community downstream.
Taxa such as Capniidae, Drunella, Epeorus and Glossosoma were typically found at upstream sites, whereas taxa such as Asellidae andMacrostemum were typically found at downstream sites. We have deduced that these biases are led by the downstream environmentthat is characterized by the lack of sand and fine gravel in riverbed, relatively stable and slower current, and abundant organic matter.
Keywords: Benthic macroinvertebrate, environmental impact, flow regime, sediment

1. INTRODUCTION
Construction of dams usually induces enormous
alteration on ambient environment. Fulfilment of theEnvironmental Impact Assessment (EIA) was mandated
for dam construction in Japan in 1997. Avoidance,
reduction, or compensation measures for presumed
environmental impact may be necessary depending on
the result of EIA. Both the accuracy of the EIA andeffectiveness of above mentioned measures are criticallyimportant for the success of remedy of environmental
impact caused by dam constructions.
Aquatic ecosystem is one of the most difficult items toassess in the EIA process since there are many causes bywhich it is affected. These causes include thefragmentation of streams by dam structure, flow regime
shift, water quality change and sediment transport change.
While the fragmentation of streams affects both on up
and downstream of a river on which dam is constructed,
flow regime shift, water quality change and sedimenttransport change mainly happen at the downstream of adam. The fragmentation of streams by dam hinders the
migration of aquatic organisms including fishes. Sincesuch hindrance is thorough, the consequence is relatively
easy to predict (i.e. without remedial measures,migratory fishes obviously can no longer migrate over a
point where dam will be constructed and their habitat
will be shrunk). However; the influences on aquatic
ecosystems caused by the flow regime shift, water
quality change or sediment transport change cannot be soclearly predicted because these changes are different inmagnitude and character among dams and mechanisms
through which their influences propagate on aquatic
ecosystems are not clearly understood.
We have compared benthic macroinvertebrate species
found at upstream and downstream of dams toinvestigate if there is a significant difference. Benthic
macroinvertebrates seem to represent local environmentof a stream since their mobility is limited and depend on
river bed condition which is formulated by water flow,
water quality and sediment transport.

2. METHOD
2.1. Survey Data
The National Survey for River and Riparian Ecosystems
has been conducted since 1990, aiming to collect the listof species found in river system nationwide periodicallyand continuously by the unified formats in Japan. We
have checked these data and picked up dams where
benthic macroinvertebrates have been surveyed at both
upstream and downstream ambient of them.

Group 1
G01

G10

G11

G1000

G1010

G1100

G1110

G1111

**
**

*
*

*

G0010

**

* A dam, of which samples taken at

G0011

**
**
**

* upstream and downstream were* divided at the first division (Level 1)
*

G0101

**

*

*

*

G0110

**

*

*

*

G0111

**

*

*

*

G1000

Level 4G000 G001

G0000
G0001 A dam

G010

G0100

B dam
B dam

U or D
Up

Up
Down

G1001
G1010 A dam

G1101

G0110

YZ

…

Dam

G1011

G0100

… … X

AB C

sample

G1001

G111

G0111

G110

G0101

G101

G0011

G100

G0010

G011

G0001

G010

G100 G101 G110 G111

G001

G011

G000
G0000

Level 3taxa

Level 3

Group 1
G11

Flow regime change caused by dams is various
depending of the operation of dams. We have categorized
flow regime change by dams into three patterns (Fig. 2).
First pattern is characterized by the decrease of ordinary
flow which is often found in dams of which main
purpose is power generation. Second pattern ischaracterized by the significant decrease of the peak offlood discharge which is found in large dams with large

G10

2.3. Classification of Flow Regime Change by Dams

G01

Dams of which up and downstream samples are divided
at the first division (Level 1) can be considered to havesignificantly different benthic macroinvertebrate
community at up and downstream of them. On thecontrary, dams of which up and downstream samples are
not divided even at the fourth division (Level 4) can beconsidered to have similar benthic macroinvertebrate
community at up and downstream of them (Fig. 1). Suchtwo groups of dams are extracted and compared with theflow regime change at downstream of them.

Group 0A divisive classification method named TWINSPAN(Two-way Indicator Species Analysis) is employed toclassify data samples and macroinvertebrate taxa.
TWINSPAN is a program to classify species and samples,
producing an ordered two-way table of their occurrence(Hill 1979, Kobayashi 1995). The process ofclassification is hierarchical. Analysed samples are
successively divided into categories, and taxa are thendivided into categories on the basis of the sample
classification (McCune and Mefford 1999). Division was
conducted four times (Levels); classifying samples andtaxa into 16 categories for each of 56 pairs of dataset
independently (i.e. 112 samples).

G00

2.2. Data Analysis

G00

Level 2

Level 4
Level 2

Macroinvertebrates were classified into 166 taxonomic
units. Mayflies, stoneflies and caddisflies were classified
into a genus or family level and others were classified
above a family level. It was difficult to classify thesemacroinvertebrate data into species level because of thelimitation of information.

Group 0Level 1
Conceptual tableof TWINSPAN

Level 1

Such datasets were available at 42 dams nationwide fromthe data of the National Survey for River and Riparian
Ecosystems which were obtained from 1996 to 2002.
Macroinvertebrate
data
which
were
collected
simultaneously at upstream and downstream of a dam in
winter were chosen for analysis, since benthic
macroinvertebrates are usually abundant during winter.
Since some dams have data pairs of up and downstream
for more than two years, total number of chosen dataset
pairs is 56 out of 42 dams.

flood control capacity. Third pattern is characterized by
the small flow regime change found in smaller dams. Ourclassification method for flow regime change isqualitative. Patterns of flow regime change at thedownstream of dams are classified by method above andcompared with the implied environmental change byindex macroinvertebrate taxa to check the conformity.

Down

G1011

**

*
*

*
*

*

*

*

*

*

*

*

*

*

*

*

B dam, of which samples taken at
upstream and downstream were notdivided even at the fourth
division* * * * *(Level 4)

*

*

G1100
G1101
G1110

*

*
*

*
*

*

G1111

*
*

*

*
*

*

*

*

*
*

*

*

*

**
*

*
*
*

*
*

*
*

*
*

**
*

*

*

**

*

*

**

Figure 1. Conceptual Table of TWINSPAN analysis(1) Decrease in ordinaryflow(2) Peak cut of flood
discharge(3) Small change
Inflow
Outflow

Figure 2. Three Categorized Patterns of Flow Regime Change
by dams

2.4. Environmental Comparison by Index Taxa
Classification results by TWINSPAN analysis show justan array of dataset ordered by similarity of the list of taxa
found in samples and they do not explain theenvironmental character of sampling stations. Thus; wehave chosen several index taxa of which habitat
preference is clear to explain environmental character ofsampling stations. Index taxa we have chosen are as
follows;a) Taxa representing very slow flow; Asellidae, Speridae,
Lymnaeidae, Ephacerella, Tubificina and Uracanthella,b) Net spinning caddisflies representing stable river bed;
Macrostemum,
Stenospyche,
Hydropsyche
andChaumatopsyche,c) Taxa representing the abundance of sand; Ephemera,
Glossosoma, Lepidostoma, Goera and Hydroptila.
The logarithm of the number of index taxon per 1 square
meter is ranked following a criterion in Table 1. The rankof each index taxon is evaluated both at upstream sample
and downstream sample of each dams. Then, the rank of
upstream sample and downstream sample are summed toSlowflow
flow* * Slow
Stablebed
bed**** Stable
Sand****** Sand

Taxon

GroupNumberof Taxaofd

Noof
Downstream Evaluation
Upstream
Upstream
Downstream(b)biasedbiasedbias No bias
bias
biased (a)biased (c)
00
0
∞
0 5
5
00
3
1
0.33
3
1
44
0
4.00
0 1
1

c

Number of Taxa

Taxon represening the existence of sand***b

Net spinning caddisfly to represent stable river bed**aTaxon representing very slow flow

Upstream biased

Evaluation
Evaluationofbias (d)Equationd=c/(a+b)∞d=c/(a+b)0.33
d=a/(b+c)
4.00

No bias

=
>
>
>
>

5 :
6 :
7 :
8 :
9 :

>
>
>
>
>

54.6
148.41403.431096.632980.96

Criterion
for Judgment
Criterion
for Judgment

0
0
2.72
7.39
20.09

downstream
if d>2 if d>2
d=c/(a+b) Slow flow
Slowatflow
at downstream
bed at bed
downstream
if d>2 if d>2
d=c/(a+b) StableStable
at downstream
downstream
if d>2 if d>2
d=a/(b+c) Less sandLessatsandat downstream

Evaluation
Equation

0 :
1 :
2 :
3 :
4 :

The logarithm of the number of individuals per 1
square meter is ranked by following threshold.

Downstream biased

0%
0%
0%
0%
0%
0%
0%
0%
0%
0%
0%
0%
14%
20%
42%
44%
45%
50%
50%
50%
53%
53%
64%
100%
100%
100%
100%
100%
100%
100%
100%
100%
100%
100%
100%
100%
100%
100%
100%

*

Ratio in upstream in
total rank

7 5 5 5 5 5 5 5 3 3 3 2 1 1 1 1 11 15 17 16 8 4 11 16 12 5 7 1 1 2 3 3 3 3 4 5 5 6 7 8 8

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 4 7 8 8 4 2 6 9 7 4 6 1 1 2 3 3 3 3 4 5 5 6 7 8 8

7 5 5 5 5 5 5 5 3 3 3 2 1 1 1 1 7 8 9 8 4 2 5 7 5 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0

Macrostemum **Lumbriculidae
Psephenidae
Baetiella
Ephemera ***Ephacerella *Asellidae *Pleuroceridae
Lymnaeidae *Kamimurai
Crambidae
DipteraUracanthella *Athericidae
Ceratopogonidae
Gibosia
Corydalidae
Stenopsyche **Rhyacophila
Hydropsyche **Cheumatopsyche **Tipulidae
Chironomidae
Glossosoma ***Amphinemura
Paraleptophlebia
Lepidostoma ***Apsilochorema
Simuliidae
Goera ***
Perlodidae
Cincticostella
Cinygmula
Hydroptila ***Caroperla
Chloroperlidae
Capniidae
Rhithrogena
Epeorus

Upstream
Rank ofDownstream
number
Total

Taxon

Table 1. An example of the check of Bias in the Emergence of Index Taxa of Macroinvertebrate for a dam

obtain total rank of numbers for each taxon. The ratio of
the rank at upstreamSpheridae
to the total* rank is calculated and0%if
this ratio is more thanTurbellaria
60%,0%obtain total rank of numbers for each taxon. The ratio of
the rank at upstream to the total rank is calculated and if
this ratio is more than 60%, then this taxon is considered
to be biased to emerge at upstream. If this ratio is
between 40 to 60%, this taxon is considered not to bebiased. If this is less than 40%, then this taxon isconsidered to be biased to emerge at downstream (Table
1).
The number of taxa which are considered to be upstream
biased, no biased, and downstream biased is summarized
and the bias is evaluated by evaluation equation which isshown in Table 1. The evaluation of the bias is referredto the criterion for judgment for three index taxon groups
and the implied environmental difference between
upstream and downstream of each dam by the bias of theemergence of index macroinvertebrate taxa is evaluated.

There are 12 dams with 17 datasets of which samples
taken at upstream and downstream were divided at thefirst division (Level 1). Macroinvertebrates communities
at the upstream and downstream of these dams aredifferently composed. The number of dams of whichsamples taken at upstream and downstream were notdivided even at the fourth division is 6 with 7 datasets.
Table 2. Number of samples at the first division by
TWINSPAN

Group 0Group 1
Total

2.5. Extraction of Biased Taxa by IndVal Method
Macroinvertebrate taxa sampled at dams of which up anddownstream samples are divided at the first division in
TWINSPAN analysis (Level 1) are analyzed by IndVal
method to extract indicator taxa. IndVal is a method tofind indicator taxa and taxa assemblages characterizing
groups of samples (Dufrêne and Legendre 1997). For
each taxon i in each site group j, we computed the
product of Aij, the mean abundance of taxon i in group jcompared to the mean abundance of taxon i in all groups
in the study, by Bij, the relative frequency of occurrenceof taxon i in group j, as follows:
Aij = Nindividualsij / Nindividualsi
Bij = Nsitesij / Nsitesj
IndValij = Aij × Bij × 100

typically found at downstream sites. We have deduced
that these biases are led by the downstream environmentthat is characterized by the lack of sand and fine gravel inriverbed, relatively stable and slower current, andabundant organic matter.

(1)
(2)
(3)

IndVal values for upstream and downstream arecalculated for each taxon and if there is a significant
difference from these values with randomly arranged
sites, such taxon is extracted as an indicator taxon.

3. RESULTS
3.1. Classification by TWINSPAN
There was a bias in the emergence of taxa depending onwhether the sample was obtained at upstream or
downstream of dams. All samples were divided to Group
0 or Group 1 at the first division. 47 samples out of 69
samples which are divided to Group 0 are from upstreamsites. 34 samples out of 43 samples which are divided toGroup 1 are from downstream sites (Table 2). These
results imply that the tendency of the emergence ofbenthic macroinvertebrate taxa is different between sites
at upstream and downstream of dams.
Taxa such as Capniidae, Drunella, Epeorus andGlossosoma were typically found at upstream sites,
whereas taxa such as Asellidae and Macrostemum were

Upstream47
956

Downstream
22
34
56

Total
69
43
112

3.2. Classification of Flow Regime Change by Dams
12 dams with 17 datasets of which samples taken at
upstream and downstream were divided at the firstdivision (Level 1) are classified into “decrease inordinary flow”, “peak cut of flood discharge”, and “smallchange” patterns in terms of flow regime change by 5, 5,
and 7 datasets, respectively. 6 dams with 7 datasets ofwhich samples taken at upstream and downstream were
not divided even at the fourth division (Level 4) areclassified into “decrease in ordinary flow”, “peak cut offlood discharge”, and “small change” patterns in terms offlow regime change by 1, 2, and 4 datasets, respectively.
3.3. Environmental Comparison by Index Taxa
Environmental change at the downstream for 12 dams
with 17 datasets of which samples taken at upstream anddownstream were divided at the first division (Level 1) in
TWINSPAN analysis is presumed by the evaluation
procedure in Table 1. The number of datasets which aresuggested to have slow flow at the downstream is 4, 3,
and 4 for flow regime change patterns of (1) decrease inordinary flow, (2) peak cut of flood discharge, and (3)small change, respectively (Table 3, Fig. 3). The numberof datasets which are suggested to have stable river bed
at the downstream is 0, 3, and 1 for flow regime change
patterns of (1), (2) and (3), respectively (Table 3, Fig. 3).
The number of datasets which are suggested to have sandshortage at downstream is 2, 1, and 4 for flow regimechange patterns of (1), (2) and (3), respectively (Table 3,
Fig. 3).
Percentage of datasets which are implied to have slow
flow at downstream by biased emergence of taxa such as
Asellidae, shellfish, Tubificina and Uracanthella is highin dams of which flow regime change pattern is classified
to “decrease of ordinary flow”. Dams of which flow
regime change pattern is classified to “significant

Table 3. Number of datasets for flow regime change patterns

decrease of the peak of flood discharge” occupy most ofdatasets which are implied to have stable riverbed bybiased emergence of net spinning caddisfly such as
Macrostemum and Stenospyche at downstream. Ratio ofdatasets which are implied to have less sand indownstream riverbed by biased emergence of taxon
Ephemera and Glossosoma at upstream is high in dams ofwhich flow regime change pattern is classified as “smallchange”.

Environment
Number of Datasets
implied by taxa
(1)
(2)
(3)
a) Slow flow
434b) Stable bed
031c) Sand
2
1
4
Total
5
5
7
(1) decrease in ordinary flow, (2) peak cut of flood
discharge, and (3) small change, respectively

100%

100%

100%

80%

80%

80%

60%

60%

60%

40%

40%

40%

20%

20%

20%

0%

0%

0%

(1)

(2)

(3)

(1)

(2)

(3)

(1)

(2)

(3)

Figure 3. Correspondence to Implied Environmental Change by Index Taxa among dams with different flow regime change pattern(Left: Percentage of datasets which are implied to have slow flow at downstream, Middle: Percentage of datasets which are implied tohave stable riverbed at downstream, Right: Percentage of datasets which are implied shortage of sand at downstream. Circled digit
represents group of different flow regime change pattern at downstream. (1) Decrease of ordinary flow, (2) Significant decrease of thepeak of flood discharge, (3) Small change.)
IndVal value

upstream

downstream

Drunella
Cincticostella
Glossosoma

91.64
84.5
78.38

1330./ 163947./ 171026./ 14

36./ 1724./ 852./ 4significance(p≦0.01)******

Epeorus
Chloroperlidae
Rhithrogena
Perlodidae
Capniidae
Taeniopterygidae
Paraleptophlebia
Blephariceridae
Lepidostoma
Cinygmula

77.17
76.47
64.64
61.56
58.67
58.13
49.26
40.56
39.77
35.29

5346./ 16463./ 131905./ 111228./ 121534./ 10
1857./ 10
1178./ 9265. /7
282./ 7
1924./ 6

1174./ 7
0./ 0
2./ 1
180./ 44./ 2
22./ 288./ 34./ 2
10./ 1
0./ 0

**
**
**
**
**
**
*
*
*
*

Perlodidae
Asellidae
Macrostemum
Lumbriculidae
Ceraclea

29.41
64.71
58.45
35.29
23.53

78./ 50./ 050./ 1
0./ 0
0./ 0

0./ 0
498./ 117828./ 10324./ 626./ 4

*
**
**
*
*

Taxon

Ameletus

5.79
A./ B
Significance84./ 65310. /1*
A: Toal number of individuals
B: Total of points of emergence (max. 17)**: Significant for both A and B*: significant for either A or B

Epeorus

Glossosoma

Plecoptera

Typical at upstream

Macrostemum
Asellidae
Typical at downstream

Figure 4. Indictor taxa emerging biased at upstream or downstream

3.3. Extraction of Biased Taxa by IndVal Method

5. CONCLUSION

Indicator taxa which can be considered to emerge at
upstream or downstream are listed in Fig. 4. These taxa
are similar to presumed index taxa, suggesting that our
presumed index taxa can imply representing environment
such as slow flow, stable riverbed, or abundance of sand.

We have shown several macroinvertebrate index taxa
which represent typical environmental changes caused byflow regime change at the downstream of dams.
Comparison of macroinvertebrate community at
upstream and downstream of dams can be used to plan
effective remedial measures for the impact of dams.

4. DISCUSSION
REFERENCES

While Tanida and Takemon (1999) summarized thepresumed mechanisms by which dams affect on benthic
macroinvertebrates at downstream of them as changes offlow regime, river morphology, water temperature,
turbidity, and organic matter flux and fragmentation of
stream continuity, we have compared benthic
macroinvertebrates with only flow regime change. Flowregime change is one of the important factors which
affect physical environment of rivers. Since threepatterns of flow regime change we have classified seemto have their typical effects on macroinvertebrates
through different environmental impact, effective
remedial measures should be also different. Increase ofdischarge variation to cause appropriate disturbance canbe effective for dams with low ordinary flow discharge
and/or high peak cut of flood. If the flow regime is not
modified largely, supply of fine sediment like sand may
be effective.

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Ecology and Systematics, Cornell University, Ithaca, NY.
Kobayashi, S. (1995): Multi-variate analysis of biologicalgroups, Aoki Shobo, Tokyo (in Japanese).
McCune, B. and Mefford, M.J. (1999): PC-ORD. Multivariate
Analysis of Ecological Data. Version 4.25. MjM Software,
Gleneden Beach, Oregon, USA.
Tanida, K and Takemon, Y. (1999): Effects of dams on benthic
animals in streams and rivers, Ecology and Civil Engineering,2(2), pp. 153-164 (in Japanese with English abstract).