Relationship between habitat environments of aquatic organisms and
physical conditions of river channels
Hiroki Yabe、Makoto Nakatsugawa
Civil Engineering Research Institute of Hokkaido, Japan
ABSTRACT: It is becoming important for river improvement and maintenance works to conserve and restore rivers while maintaining diverse
habitats and growing environments for the animals and plants there. This paper focuses on aquatic organisms (specifically, benthic animals) as indicators of river conditions, toward clarifying the relationship between inhabitation by these animals and physical conditions of river channels
such as flow velocity, water depth and bottom materials, as well as the food environment (i.e., periphyton and particulate organic matter). Pools
and riffles are significant in understanding the river environment; thus, the relationship between the populations of benthic animals and their
physical environment was examined by comparing pools and riffles in various types of river channels, such as those with and without river improvement works.
1.Introduction
River topography and water flow regimes are complex
and diverse. It has been reported that changes in river
environment throughout the river, including a decrease in
the number of pools and riffles caused by river improvement works and changes in river basin conditions, have
led to changes in organic matter in a river and thus affect
populations of fish, benthic animals and other organisms.
Populations of benthic animals reflect the microenvironment, which is an important factor in the soundness of the river ecosystem, on a scale smaller than riverbeds of pools and riffles. Populations of benthic animals
also reflect the topographic features of rivers and the effects of improvement works on the river environment.
Benthic animals can be used to assess ecosystems. However, there are few studies clarifying the relationships between physical conditions of rivers, features of river
channels such as pools and riffles, river improvement
works and the food environment.
This study investigates two rivers in Hokkaido for
the purpose of comparing populations of benthic animals,
the physical environment (flow velocity, water depth,
riverbed material and loose rock) and the food environment (periphyton and particulate organic matter) between
the sections with and without river improvement in the
same river and between the sections with no river improvement in two different rivers. The habitat conditions
for benthic animals are analyzed to examine the relationship between the populations of benthic animals and the
structural features of pools and riffles. In other words,
this study focuses on using benthic animals to elucidate
river improvement and nature restoration measures appropriate to ensuring diverse habitats and growing environments for animals.
2. Methods and survey sites
The Atsubetsu River, which runs through Sapporo,
has sections with and without river improvement works.
The section without improvement works is 3 to 5 m in
surface width and is surrounded by riparian forest of
broadleaf and coniferous trees. In the section with improvement works, about 5 km downstream from the unimproved section, interlocking blocks are placed from the
bank to the riverbed. Drops of about 1 m high are constructed at intervals of several hundreds of meters, and 20
to 30 years has passed since improvement works were
conducted. The width of water surface is about 8 m. It
includes the riverbed with rocks in the center (2 m) and
the riverbed along the bank, which is covered by the interlocking-block lining extending from the bank slope (3
m each on the both banks). The riparian woods are
sparse. Willows predominate.
The Gunbetsu River, which runs through Hamamasu,
is in its natural state. The surface width of the Gunbetsu
is 5 to 7 m at the upper reaches and 5 to 10 m at the lower
reaches. The river is classified as Aa to Bb, and there are
steps, slow-flowing pools, and deep pools created by meandering flow. The riparian forest, which covers the
wide area from the stream edge to the land some distance
from the bank contains willow and broadleaved tress
(e.g., white oak and Japanese elm).
In October 2003 in these rivers, benthic animals were
collected and the physical conditions and organic matter
quantities were measured. Classification of riffles, mudflats and pools was based on the method of Bisson et al.
A hand net (25 cm × 25 cm) was used to collect 4 to 6
samples of benthic animals per river unit, excluding certain places such as nooks under large rocks or where an
unusually large number of fallen leaves were trapped.
Periphyton samples were collected from rocks (5 cm × 5
cm) in the same places. Benthic animals 0.5 mm or larger were identified at the level of genus or species. Or-
Table１ Physical conditions and benthic animals　(Atsubetsu)
no improvement(Atsubetsu　river)
riffles
n=3
mudflats
n=3
pools
n=3
factors
23.4 (3.1)
29.0 (3.2)
42.7 (4.4)
water depth(cm)
64.2 (4.9)
50.9 (6.5)
45.9 (1.5)
flow velocity(cm)
5.8 (0.2)
5.0 (0.7)
5.3 (0.1)
riverbed material
2.2 (0.2)
2.5 (0.3)
3.3 (0.3)
loose rock
1704.0 (474.6)
2038.7 (495.8)
1438.2 (293.0)
populations(/㎡)
19.2 (2.0)
23.5 (0.8)
18.9 (2.6)
number
2.2(0.04)
2.4(0.10)
2.1(0.19)
diversity(shannon)
0.46 (0.08)
0.54 (0.09)
0.43 (0.11)
FPOM
3.86 (2.00)
4.23 (1.42)
2.87 (0.83)
CPOM
0.50 (0.10)
0.77 (0.03)
0.45 (0.23)
chlorophyl-a
32% Rhithrogena(cg/sc)
23% Rhithrogena(cg/sc) 27%
dominant species Rhithrogena(cg/sc)
9%
14% Amphinemura(sh)
9%
Amphinemura(sh)
Amphinemura(sh)
7%
9%
9%
Baetis(cg/sc)
Epeorus(cg/sc)
Apatania(cg/sc)
Relationship between benthic animal populations and the factors
1
0.8
0.6
0.4
0.2
ma
te
ri
al
-s
d
ma
te
ri
al
ri
ve
rb
ed
ve
lo
ci
ty
-0.8
ri
ve
rb
ed
ro
ck
de
pt
h
fl
ow
wa
te
r
-0.6
lo
os
e
-0.4
CP
OM
ch
lo
ro
ph
yl
-a
0
-0.2
FP
OM
correlation cofficient
factors
Relationship between number of benthic animal and the factors
1
0.8
0.6
0.4
0.2
ma
te
ri
al
-s
d
ma
te
ri
al
factors
ri
ve
rb
ed
ve
lo
ci
ty
-0.8
ri
ve
rb
ed
ro
ck
de
pt
h
fl
ow
wa
te
r
-0.6
lo
os
e
-0.4
CP
OM
ch
lo
ro
ph
yl
-a
FP
OM
0
-0.2
Relationship between diversity and the factors
1
0.5
ma
te
ri
al
-s
d
ve
lo
ci
ty
ma
te
ri
al
ri
ve
rb
ed
factors
①unitscale(riffeles・pools)
③sub-no improvement
⑤sub-improvement
⑦sub-no improvement(mudflats)
⑨sub-improvement(riffeles)
ri
ve
rb
ed
ro
ck
de
pt
h
fl
ow
wa
te
r
-1
lo
os
e
-0.5
CP
OM
ch
lo
ro
ph
yl
-a
0
FP
OM
3.1 Comparison of benthic animal populations, river
channels and river bed units
Comparison was done between the sections with
and without improvement works on the Atsubetsu River.
The physical conditions such as water depth and flow velocity by riverbed unit are shown in Table 1(no improvement). In the improved section, the point immediately downstream of the drop work is considered a pool.
Table 1 shows the number of benthic animals, the number of taxa, and the dominant species. The dominant
species were divided, according to feeding pattern, into
“collector-gatherers” (cg, cf), i.e., those that feed on
small organic matter:FPOM), “shredders” (sh), i.e., those
that feed on large organic matter:CPOM, and “scrapers”
(sc),predator(pr).
To examine how the benthic animal populations
(number of individuals, number of taxa, and diversity index) differed between river channels (i.e., sections with
and without improvement works) and between different
riverbed units (i.e., riffles and pools), two-way analysis
of variance was conducted. Mean values were used for
populations and physical environment (i.e., flow velocity,
water depth, riverbed material and organic matter quantities). To allow the assumption of homoscedasticity, all
variables were logarithmically transformed and compared
between different riverbed units. Consequently, there
were more benthic animals in riffles than in pools for
both sections (p < 0.05). In the analysis of the number of
taxa and diversity, an interaction effect was observed for
the river channels and riverbed units. Significantly small
3.2 Analysis of the relationship between benthic animal populations and physical conditions
Correlation analysis was done to clarify the relationship between the benthic animal populations and the
physical conditions that affect them(Figure1). In the
analysis of riverbed units excluding those in the mudflats
correlation coefficient
3. The results of study on river sections with and
without improvement works
values were obtained in one-way analysis of variance,Tukey’s HSD test for the pool of the improved section.
In the comparison of the number of dominant species among the sections, shredders were identified as
dominant in the unimproved section. This suggests that
the differences in the supply of fallen leaves as well as
the physical environment of the river channel are the
main contributors to the significantly larger number of
CPOM in the unimproved section than in the improved
section.
correlation coefficient
ganic matter was divided into coarse particulate organic
matter (CPOM: 1 mm or larger) and fine particulate organic matter (FPOM: smaller than 1 mm) for measurement of ignition loss.
For the purpose of measuring physical conditions,
five transects were set per river unit, and four survey
spots were set per transect. Flow velocity and water
depth were measured at 5 points per survey spot, and riverbed material and the percentage of loose rock were
measured at 25 points and 5 points respectively. For the
measurement of riverbed materials, the Wentworth system of size classification was extended and eight categories (1. bedrock, 2. less than φ2 mm, 3. φ2 to 16 mm, 4.
φ16 to 32 mm, 5. φ32 to 64 mm, 6. φ64 to 128 mm, 7.
φ128 to 256 mm, 8. greater than φ256 mm) were visually
determined. Four categories of loose rock rates (1. less
than or equal to 25%, 2. 25% to 50%, 3. 50% to 75%, 4.
75% to 100%) were visually determined on the basis of
the colors of the collected rocks. Flow velocity was
measured for 5 seconds per survey spot, at the water
depth of 20% and 80%, or at 60% when measurement
was difficult because of shallowness or the like. The
mean value of the measured 5-second flow velocity was
obtained. In addition to these, water level, water temperature, air temperature and water quality were investigated.
②subunit scale
④sub-no improvement(riffeles・pools)
⑥sub-no improvement(riffles)
⑧sub-no improvement(pools)
⑩sub-improvement(pools)
Figure１Relationship between benthic animals and physical conditions
of the unimproved section, the size of riverbed material
correlates positively with the number of both benthic
animals and taxa, and the loose rock rate correlates negatively with the number of benthic animals. CPOM correlates positively with diversity. Furthermore, the sampling
data of benthic animals were directly used for correlation
analysis of populations and physical conditions and also
for assessing the microenvironment (at the subunit scale).
This analysis more clearly indicated that the number of
benthic animals and the number of taxa correlated positively with FPOM, CPOM and chlorophyll-a and negatively with the percentage of loose rock and water depth.
The results of subunit scale analysis done per riverbed unit are as follows. In the unimproved section, the
number of benthic animals and taxa correlated only
weakly with the physical conditions in riffles and pools.
In the riffles of the improved section, however, they correlated negatively with the percentage of loose rock and
flow velocity and correlated positively with the size of
riverbed material. Food environment correlated positively with FPOM and CPOM in almost all riverbed units
of the unimproved section. Such correlations were not
recognized in the improved section, except for the positive correlation with CPOM in the pools. A positive correlation with chlorophyll-a was found in the riffles of the
improved section, but there was no such correlation in the
unimproved section. When the number of both benthic
animals and taxa were compared between the two sections, diversity did not correlate with FPOM in the unimproved section and nor with chlorophyll-a in the improved section. Regarding the physical conditions, flow
velocity correlated positively with diversity in the riffles
and mudflats of the unimproved section.
As described above, the populations of benthic
animals may be affected by FPOM and CPOM, an effect
that is more obvious in the section without improvement
works. CPOM has a particularly great affect on diversity
and, thus, is regarded as an important factor. In the riffles of the improved section, however, the populations
correlate with chlorophyll-a and physical conditions such
as the percentage of loose rock, the size of riverbed material and the flow velocity.
4. Results of study based on artificial changes in
the physical and food environments
iron pins, ② pile works section (rapid flow), where iron
pins change the accumulation of fallen leaves so that water flows rapidly or the flow velocity does not decrease
away from the groin works, ③ pile works section (slow
flow), where iron pins change the accumulation of fallen
leaves so that water flows slowly near the groin works,
and ④ energy-dissipated section, where groin works
change the physical environment (the flow velocity).
The results of comparison between the preliminary
study and the posteriori study in each section are as follows(Table2). In the refference section, the number of
benthic animals decreased, the number of taxa did not
change, and the diversity increased. With regard to
dominant species, scrapers eating attached algae and collectors decreased in number.
Shredders increased
slightly in overall number and number of taxa. In the section with dissipated flow, the benthic animals decreased
in number and in number of taxa but the diversity increased. As for dominant species, scrapers decreased
marginally in number of taxa but sharply in number of
individuals, and collectors decreased in number of taxa.
In the pile works (slow flow) and pile works (rapid flow)
sections, benthic animals increased in number of animals,
taxa and diversity. With regard to dominant species,
shredders sharply increased in the number of individuals
and taxa, and collectors and predators (preying on other
insects) increased in number of individuals and taxa.
Thus, the difference in flow velocity did not result in any
differences between the two sections. In improving the
food environment of benthic animals and thereby increasing their populations, it seems to be important that the
structure of riffles traps fallen leaves.
5. Results of comparison of unimproved sections
in two rivers
The results of survey on the Atsubetsu River show
that physical conditions such as flow velocity and water
depth correlate less strongly with benthic animal populations than with FPOM and CPOM. Thus, analysis, comparison and examination at the unit scale and subunit
scale were also done in the unimproved Gunbetsu River.
Table 3 shows the water depths of riffles, mudflats and pools as well as the physical conditions of the
river channel such as the flow velocity. The number of
both benthic animals and taxa and the dominant species
are shown .
The dominant species differed between riffles and
pools. For pools, there were three species of shredder,
versus just one species for pools. From the viewpoint of
Between late October and mid-November 2003, experiments were conducted and sampling was done Atsubetsu river(improvement). The experiments were done at
these sites: ① refference section, affected by neither
groin works nor
T ab le２
R esults o f artificial chang es in p hy sical env iro nm ent
e x p e rim e n ts
fa c to rs
w a te r d e p th (c m )
flo w v e lo c ity (c m )
riv e rb e d m a te ria l
lo o se ro c k
p o p u la tio n s(/ ㎡ )
num ber
d iv e rsity (sh a n n o n )
FPO M
CPOM
c h lo ro p h y l- a
d o m in a n t s p e cie s
re ffe re n c e s e ctio n
n=3
a fte r
1 7 .9
2 0 .7 (2 .9 )
6 2 .2 (1 1 .5 )
5 6 .8
5 .1 (0 .2 )
4 .6
4 .0 (0 .0 )
4 .0
5 5 9 5 (3 2 7 2 )
2912
2 2 .0 (8 .5 )
2 2 .3
1 .3 (0 .4 )
2 .1
0 .4 5 (0 .0 8 )
1 .2 7
3 .2 1 (2 .8 0 )
7 .0 8
0 .0 3 (0 .0 1 )
0 .8 4
b e fo re
n=3
(4 .0 )
(1 0 .0 )
(0 .3 )
(0 .0 )
(1 8 4 1 )
(1 2 .1 )
(0 .6 )
(0 .9 4 )
(7 .6 9 )
(0 .2 6 )
p ile w o rk s s e ctio n (ra p id flo w ）
b e fo re
n=3
a fte r
2 0 .7 (3 .3 )
1 4 .3
6 0 .3 (1 0 .0 )
3 9 .1
4 .8 (0 .1 )
4 .5
4 .0 (0 .0 )
3 .7
5 3 6 0 (1 4 5 1 )
12453
2 5 .7 (2 .1 )
4 6 .3
1 .4 (0 .3 )
2 .6
0 .3 2 (0 .1 2 )
5 .1 1
3 .5 3 (1 .8 0 )
1 8 .7 9
0 .0 7 (0 .0 4 )
2 .4 6
R h ith ro ge n a (c g / sc )
6 5 % R h ith ro g e n a (c g / s c)
2 7 % R h ith ro g e n a (c g / s c)
G lo s so so m a (sc )
1 2 % G lo s s o s o m a (s c)
1 6 % G lo s so s o m a (s c)
O rth o c la d iin a e (c g/ s c )
5 % C in ctico s te lla (cg )
8 % O rth o cla d iin a e (c g / s c)
7 0 % P a ra le p to p h le b ia (cg )
n=3
(2 .5 )
(9 .3 )
(0 .1 )
(0 .6 )
(4 7 3 9 )
(4 .5 )
(0 .1 )
(2 .1 4 )
(2 .9 2 )
(1 .7 9 )
(A tsub etsu)
p ile w o rk s s e c tio n (slo w flo w ）
b e fo re
n=3
a fte r
1 7 .0 (1 .5 )
1 2 .9
4 6 .5 (8 .0 )
1 9 .2
4 .9 (0 .1 )
4 .0
4 .0 (0 .0 )
3 .3
3 9 0 4 (7 1 9 )
9584
2 3 .7 (3 .5 )
3 9 .0
1 .7 (0 .4 )
2 .4
0 .3 1 (0 .2 0 )
5 .1 5
3 .4 9 (2 .3 1 )
3 2 .7 8
0 .1 4 (0 .0 9 )
1 .0 5
2 0 % R h ith ro g e n a (cg / s c )
5 4 % G o e ro d e s (s h )
6 % R h ith ro g e n a (c g / s c)
1 4 % G lo s s o s o m a (s c )
1 8 % P a ra le p to p h le b ia (cg )
5 % G o e ro d e s (s h )
1 4 % O rth o c la d iin a e (cg / s c)
8 % A p a ta n ia (c g / s c)
n=3
b e fo re
(3 .1 )
(1 0 .8 )
(0 .4 )
(0 .6 )
(4 0 6 7 )
(7 .2 )
(0 .1 )
(1 .0 4 )
(1 3 .4 9 )
(0 .8 2 )
e n e rg y - d is si
n=3
1 6 .8 (2 .4 )
5 7 .7 (4 .7 )
4 .9 (0 .3 )
4 .0 (0 .0 )
7 2 6 4 (1 4 5 6 )
2 7 .3 (4 .6 )
1 .7 (0 .1 )
0 .8 4 (0 .3 5 )
6 .2 7 (2 .6 6 )
0 .4 6 (0 .2 6 )
2 4 % G lo s s o s o m a (s c)
51%
1 5 % R h ith ro g e n a (c g / s c)
22%
1 1 % O rth o cla d iin a e (cg / s c )
6%
Table3 Physical conditions and benthic animals
factors
water depth(cm)
flow velocity(cm)
riverbed material
loose rock
populations(/㎡)
number
diversity(shannon)
FPOM
CPOM
chlorophyl-a
dominant species
riffles
25.1
64.7
6.6
3.3
2846.7
22.6
2.3
0.63
7.95
1.00
Epeorus(cg/sc)
Glossosoma(sc)
Goerodes(sh)
(Gunbetsu)
no improvement(Gunbetsu　river)
n=3
mudflats
n=3
pools
n=3
(3.5)
35.2 (4.6)
41.8 (10.6)
(11.6)
38.3 (4.8)
33.2 (14.8)
(0.0)
6.3 (0.2)
6.2 (0.4)
(0.5)
3.2 (0.4)
3.2 (0.1)
(918.5)
1974.7 (499.2)
867.6 (190.5)
(1.4)
21.8 (3.5)
13.4 (1.0)
(0.1)
2.3 (0.2)
2.0 (0.1)
(0.21)
0.30 (0.03)
0.32 (0.10)
(3.19)
2.60 (0.35)
3.97 (0.96)
(0.38)
0.90 (0.28)
1.22 (0.70)
18% Epeorus(cg/sc)
22% Glossosoma(sc)
21%
16% Glossosoma(sc)
22% Epeorus(cg/sc)
15%
10% Rhithrogena(cg/sc)
6% Rhithrogena(cg/sc)
13%
Relationship between benthic animal populations and the factors
0.8
0.4
0.2
ma
te
ri
al
-s
d
ma
te
ri
al
ri
ve
rb
ed
-0.8
ri
ve
rb
ed
ve
lo
ci
ty
de
pt
h
ro
ck
wa
te
r
fl
ow
-0.6
lo
os
e
-0.4
CP
OM
ch
lo
ro
ph
yl
-a
0
-0.2
FP
OM
correlation coefficient
0.6
-1
factors
Relationship between number of benthic animal and the factors
0.8
0.4
0.2
-0.6
ma
te
ri
al
-s
d
ma
te
ri
al
-0.8
ri
ve
rb
ed
ve
lo
ci
ty
ri
ve
rb
ed
fl
ow
wa
te
r
de
pt
h
ro
ck
lo
os
e
-0.4
CP
OM
ch
lo
ro
ph
yl
-a
0
-0.2
FP
OM
correlation coefficient
0.6
factors
Relationship between diversity and the factors
0.8
0.6
0.4
0.2
ma
te
ria
l-s
d
ma
te
ria
l
riv
er
be
d
-0.6
riv
er
be
d
flo
w
ve
lo
ci
ty
de
pt
h
wa
te
r
se
ro
ck
a
ph
yl-
loo
-0.4
ch
lo
ro
CP
OM
0
-0.2
FP
OM
correlation coefficient
component percentages, there tend to be more shredder
individuals and taxa, and scrapers are present at high
rates in mudflats and pools. In the unimproved section of
the Atsubetsu River, almost the same number of shredder
species was found in riffles, mudflats and pools. In terms
of component percentages, the number of taxa is more or
less the same in riffles, mudflats and pools, but the number of shredders are large and the percentage of scrapers
are small respectively in mudflats.
The differences in the number of individuals and taxa
as well as in the diversity index according to riverbed
units of riffles, mudflats and pools were identified by
one-way analysis of variance. In the Gunbetsu River,
there were differences in the number of individuals and
taxa between riffles/mudflats and pools, but not in the diversity. FPOM and CPOM were different between riffles
and mudflats/pools. In the Atsubetsu River, no differences in the populations ,number,diversity were recognized between different units. Neither FPOM nor CPOM
shows difference between riffles and mudflats/pools.
Analysis at the scale of unit shows that the number
of individuals correlates negatively with water depth and
variations in the size of riverbed material, and positively
with flow velocity. Such correlations were not found
with food environment. Factors contributing to the number of taxa and diversity were not clearly identified.
At the subunit scale, factors such as FPOM,
CPOM, flow velocity and the size of riverbed material
were obviously relevant with regard to the number of individuals. In riffles, the number of individuals correlates
positively with CPOM and FPOM, and the number of
taxa correlates positively with CPOM. The size of riverbed material correlates negatively in mudflats and positively in pools with the number of individuals. The number of taxa correlates positively with FPOM and CPOM
in mudflats and riffles, respectively. Diversity correlates
negatively with FPOM and CPOM and positively with
loose rock rate in pools. It is clear that there are some
other affecting factors. From the viewpoint of subunits
overall, the effects of physical conditions are reflected in
the number of taxa and diversity. No correlations were
found with chlorophyll-a.
In the Gunbetsu River, the populations of benthic
animals are affected by physical conditions as well as by
FPOM and CPOM.
-0.8
-1
factors
unit scale
subunit scale
sub-riffles
sub-mudflats
sub-pools
Figure２Relationship between benthic animals and physical conditions
6. Conclusion
The improved section of the Atsubetsu River is at
the upper reaches. But this study revealed that the quantities of CPOM and chlorophyll-a, as well as the quantity
and the percentage of shredders that feed on CPOM, indicate that the upper reaches section with improvement
works showed the features typical of the middle and
lower reaches of a river. In the experiment in which the
features of riffles in the improved section were artificially
modified, the identified quantities of CPOM and FPOM
helped confirm that the structures that trap fallen leaves
and organic matter affect populations of benthic animals
The situation is different in the Gunbetsu River,
where the populations of benthic animals related more
closely with physical conditions, although they are also
affected by FPOM and CPOM. The reason for this difference will be analyzed more specifically in connection
with feeding patterns and life forms under various river
channel conditions, including the channel structures of
riffles and pools.
Further survey with the same focus as this paper also
will be done in spring, because the composition of benthic animal populations and the quantities of organic matter and chlorophyll-a change by season. These data will
be accumulated for analysis and used as indexes of the
river environment.