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Effects of a Small Hydropower Station Upon Brown Trout Salmo Trutta L. in the River Hoz Seca (Tagus Basin, Spain) One Year after Regulation

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A small hydroelectric power station was built in 1993 on the River Hoz Seca (Tagus basin, central Spain). Pre- and post-regulation studies provided the opportunity to test the early effects of this disturbance on the brown trout Salmo trutta L. population. Before and after comparisons of population density and biomass, age composition, growth and production were made upstream and downstream of the diversion dam. The effects of disturbance on benthic macroinvertebrates were also analysed but no changes in abundance were detected. The downstream estimated population densities and biomass of trout showed a decrease of about 50 and 43%, respectively, following regulation. Examination of length-for-age tables revealed no obvious change in growth but a significant difference in age structure. The main consequence of the imposed fluctuating flow regime was a serious reduction in trout production caused by a loss of suitable habitat and a loss of juveniles. Copyright © 1999 John Wiley & Sons, Ltd.
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REGULATED RIVERS: RESEARCH & MANAGEMENT
Regul. Rivers: Res.Mgmt.
15:
477—484 (1999)
Short Communication
EFFECTS OF A SMALL HYDROPOWER STATION UPON BROWN
TROUT SALMO TRUTTA
L. IN THE RIVER HOZ SECA (TAGUS
BASIN, SPAIN) ONE YEAR AFTER REGULATION
ANA ALMODÓVAR* AND GRACIELA G. NICOLA
Department of Ecology, Agricultura) Research Institute of Madrid (IMIA), El Encín, PO Box 127, E-28800 Alcalá de Henares,
Madrid, Spain
ABSTRACT
A small hydroelectric power station was built in 1993 on the River Hoz Seca (Tagus basin, central Spain). Pre- and
post-regulation studies provided the opportunity to test the early effects of this disturbance on the brown trout
Salmo
trutta
L. population. Before and after comparisons of population density and biomass, age composition, growth and
production were made upstream and downstream of the diversion dam. The effects of disturbance on benthic
macroinvertebrates were also analysed but no changes in abundance were detected. The downstream estimated
population densities and biomass of trout showed a decrease of about 50 and 43%, respectively, following regulation.
Examination of length-for-age tables revealed no obvious change in growth but a significant difference in age
structure. The main consequence of the imposed fluctuating flow regime was a serious reduction in trout production
caused by a loss of suitable habitat and a loss of juveniles. Copyright © 1999 John Wiley & Sons, Ltd.
KEY WORDS:
hydropower;
Salmo trutta; Tagus basin
INTRODUCTION
Flow modification is one of the most widespread human disturbances of stream environments. Discharge
regime and the related physical effects are modified with increasing frequency by catchment management,
especially by activities such as river regulation and transfer, drainage works, afforestation and deforesta-
tion (Milner
et al.,
1981). In general, the most adverse effects of flow regulations are likely to result from
substantial, intermittent flow variations periodically exposing large arcas of the channel bed (Brooker,
1981). Bain
et al.
(1988) and Travnichek
et al.
(1995) identified these artificial flow fluctuations from
hydroelectric dams as a disturbance that can degrade fish habitat and reduce the complexity of the fish
community. It seems obvious that the effects of flow peaking on aquatic systems below dams are
i
mportant considerations in hydropower development and the management of regulated rivers (Heggenes,
1988).
Despite all major rivers in Spain being regulated by more than 1100 dams (Nicola
et al.,
1996), to date
there have been few attempts to study the consequences of river regulation upon fish communities (García
de Jalón
et al.,
1988; Casado
et al.,
1989; Camargo and García de Jalón, 1990; García de Jalón
et al.,
1994). Furthermore, Blanco and González (1992) and Elvira
(1996)
considered dams to be one of the
main negative factors affecting Spanish fishes. Specifically, Almodóvar and Burgaleta (1993) considered
water regulation as an important cause of the decline of brown trout in Spain.
The Hoz Seca is the first tributary of the River Tagus and supplies the greatest proportion of flow to
this upper part of the basin. Since autumn 1993 this stream has been regulated by a small hydropower
station
(700
kW). This paper evaluates the impacts of this recent disturbance on an indigenous brown
trout population. In order to assess changes in the trout population related to alterations in their food
* Correspondence to: Department of Ecology, Agricultural Research Institute of Madrid (IMIA), El Encín, P.O. Box 127, E-28800
Alcalá de Henares, Madrid, Spain.
CCC 0886-9375/99/050477-08$17.50
Received 14 May 1998
Copyright © 1999 John Wiley & Sons, Ltd.
Revised 19 March 1999
Accepted 23 March 1999
478
A. ALMODÓVAR AND G.G. NICOLA
supply, the benthic communities were also analysed, since macroinvertebrates are important food items
for brown trout (Elliott, 1967).
METHODS
Study area
This study was conducted on the lower reaches of a first-order tributary of the River Tagus. The River
Hoz Seca has a basin area of 175.76 km' and its altitude ranges from 1620 m at the yource to 1250 m at
its confluence with the Tagus. The mean discharge is highest in winter (2 m
3
s -') and decreases in summer
(0.4
m
3
s -'). The river flows over a limestone catchment with an average channel slope of 12.7%. The
water chemistry can be characterised as a non-polluted headstream, with low concentrations of organic
matter and high levels of dissolved salts. The ionic balance shows a dominance of HCO3 (266 mg L -',
534 tS cm' conductivity) and Ca
e
± (40 mg L -'). The water temperature ranges from a low of 8°C in
winter to a high of 14°C in summer, with a pH of 7.6. Stream-bed material was dominated by boulders
and bedrock. Substantial proportions of gravel and sand were also present. The availability of cover for
fish was high, mainly due to boulders. The bank vegetation at the site was dominated by some riparian
deciduous vegetation
(Salix
spp.,
Rosa
spp.,
Prunus spinosa
L.,
Crataegus monogyna
Jacq.,
Rubus
ulmifolius
Schott. and
Berberis hispanica
Boiss.
& Reuter) and pine
(Pinus sylvestris L.).
The aquatic
vegetation consisted primarily of
Chara vulgaris
L.,
Groenlandia densa (L.)
Fourr.,
Zannichellia contorta
(Desf.) Chamisso & Schlech,
Ranunculus peltatus
Schrank and
Cratoneurum commutatum
(Hedw.) Roth.
Brown trout is the only fish species present in this stream, which has never been stocked. Two sampling
sites
were chosen (see Figure 1), with similar sizes and habitat conditions; site 1 was located near the
mouth of the river, about 500 m downstream of the diversion dam; site 2 was a reference sector situated
approximately 3 km upstream of the power plant.
Figure 1.
Map of the study area showing sampling sites and the position of the diversion dam
Copyright © 1999 John Wiley & Sons, Ltd.
Regul. Rivers: Res.
Mgmt.
15:
477—484
(1999)
EFFECTS OF A SMALL HYDROPOWER STATION UPON BROWN TROUT
479
Figure 2.
Mean hourly discharge per day in the downstream section of the River Hoz Seca with minimum (June and September)
and maximum flow periods (November)
The hydroelectric power station in the River Hoz Seca produces frequent and strong daily flow
fluctuations. This effect is especially notorious in autumn when the daily fluctuations range from 0.4 to
1.7
m s -' on average, in spite of being the period of the year with maximum flow (Figure 2). Thus, the
water depth in the downstream site increases 0.3 m on average in a matter of minutes whenever the
discharge from the power station arrives there, continually changing the location of the shoreline.
Benthic macroinvertebrates
Benthic macroinvertebrates were sampled in riffles every two months from January 1993 to November
1994. Three replicate samples per site, taken progressively upstream of each other, were collected on each
sampling date with a Neil cylinder with a 250 µm mesh net. Invertebrate samples were preserved in 10%
formalin for later laboratory identification, sorting and counting. Specimens were dried in an oven at
60°C for 24 h and densities and biomass (dry weight) were determined. Each taxonomic group was
assigned to one of five major functional feeding categories: predators, scrapers, shredders, filterers and
collectors (Cummins, 1973).
Brown trout
Fish were also sampled every 2 months from January 1993 to November 1994 at each site by
electrofishing using a 220
W DC generator. Fish caught were anesthetised with tricaine methane-
sulphonate (MS-222 SANDOZ) and their fork lengths (to within 1 mm) and weights (to within 1 g) were
measured. Scales were taken for age determination. Trout density was estimated by applying the three
catch removal method (Zippin, 1956). Standing crop was calculated following the formula proposed by
Mahon
et al.
(1979). Population estimates were carried out separately for each year class. The mean
instantaneous growth rate (G) was calculated as:
G=1n W
2
—1n
W
1
/t
2
-t
1
,
where
W
1
and
W
2
(in grams) were the mean weight of each year class of fish at times
t
1
and
t
2
(in days).
Production was calculated using Allen's graphic method (Allen, 1951) for each year class. A t-test was
Copyright © 1999 John Wiley & Sons, Ltd.
Regul. Rivers: Res.Mgmt.
15:
477—484
(1999)
480
A. ALMODÓVAR AND G.G. NICOLA
used to compare both total densities and biomass of trout before and after regulation. The same
procedure was also employed to test the mean number of trout caught of each age group.
RESULTS AND DISCUSSION
Benthic macroinvertebrates
In general, the results did not show any drastic change in benthic invertebrate communities below the
dam after the hydroelectric power station was put into operation. Furthermore, the opening of the power
station did not seem to have a negative effect on benthos with regard to total density or biomass (Table
I).
On the contrary, the benthic fauna had a slight increase in spite of the flow disturbances. Similar
results have been found by Armitage (1989) in 50 regulated sites in Great Britain and by Petts
et al.
(1993),
who noted that the regulation did not impoverish the invertebrate fauna but induced subtle
changes in faunal composition. The contribution of each feeding group to community structure was
equivalent in both sampling sites. Collectors were by far the dominant group (around 44%), followed by
predators (around 25%), shredders (15%), scrapers (9%) and filterers (7%). Moreover, frequencies of
functional feeding groups did not differ significantly through the sampling period in either site. On the
whole, the functional organisation of the macroinvertebrate community in the River Hoz Seca corre-
sponds with that predicted for headwater streams by Vannote
et al.
(1980). However, the frequencies did
not seem to follow the hypothetical co-dominance of shredders with collectors in forested headwaters
streams (Cummins, 1974; Vannote
et al.,
1980).
Maybe shredders were more abundant in other habitats
such as pools (not sampled in this study), where coarse-particulate organic matter (CPOM) could
accumulate (Bunn, 1986).
Brown trout
In relation to trout population, there was a rapid response to regulation in terms of decreasing density
and biomass. From 1993 to 1994, the estimated population density and biomass showed a significant
decrease of about 50%
(t =
6.30,
p
< 0.05) and 43%
(t =
2.69,
p
< 0.05), respectively. However, these two
parameters remained practically unchanged in the upstream section. Thus, the variations in density from
1993 to 1994 were not significant
(t =
1.57,
p
> 0.05) and the biomass did not exhibit significant
(t = 0.11,
p > 0.05) changes across the sampling period aboye the dam. Also, the recruitment of the individual
cohorts showed a progressive fall from 1993 to 1994, which was more evident in 0 + and 1 + year classes.
In Table II the mean number of trout caught by age group in both pre- and post-regulation periods are
compared. There was a significant decrease in the catches of 0 + and 1 + trout at the downstream site
following regulation and a minor but also significant decrease in 2 + and older trout. Accordingly, the
structure of the population became dominated by older fish, probably as a result of flow regulation, since
this was not observed in the non-regulated upstream site. Furthermore, the adverse flow conditions in the
Hoz Seca possibly prevented adult fish from migrating upstream to spawn. These observations agree with
those of Cowx and Gould (1989) for the River Clywedog, where recruitment of brown trout declined over
successive years after extensive regulation began. Hvidsten (1985), working in the regulated river Nidelva,
detected a similar poor recruitment and suggested that the main reason for deficiencies in the number of
0 + trout was that trout usually remain in their river bed habitats and the frequent changes in water level
generated by flow regulation led to increased mortality as a result of stranding.
Since streamflow seems to be the environmental variable likely to exert the greatest influence on
populations of young salmonids (Solomon, 1985; Elliott, 1987), it is worth noting that the loss of
recruitment in the Hoz Seca could be induced by the downstream displacement of 0 + trout as a result
of the violent fluctuations in the water level of the river. Several authors (e.g. Ottaway and Forrest, 1983;
Heggenes and Traaen, 1988; Crisp and Hurley, 1991a,b) have experimentally proved the vulnerability of
salmonid juveniles to downstream removal due to increasing water velocities. In contrast, Heggenes
(1988), testing the response of induced peaking on movement and habitat use of brown trout in a small
Copyright © 1999 John Wiley & Sons, Ltd.
Regul. Rivers: Res.
Mgmt.
15:
477—484 (1999)
EFFECTS OF A SMALL HYDROPOWER STATION UPON BROWN TROUT
481
Norwegian stream, concluded that trout with a mean length of at least 67 mm were not washed out due
to sudden high water flows, provided that coarse substrata supplying cover and low-velocity microhabitat
were present. The area of the Hoz Seca subjected to hydropower operations suffers frequent fluctuations
of water level leading to a repeated drowning and drying up of sections near the riverbanks. This latter
Table I.
Mean density
(D,
individuals
m
-2
)and mean biomass
(B,
g dry weight m-
2
)
of each group of
macroinvertebrates for each section (upstream/downstream) within the pre- (1993) and post-regulation (1994)
periods
Upstream
Downstream
D
B
D
B
1993 1994
1993 1994
1993 1994
1993
1994
Turbellaria
1.785 1.782
0.0019 0.0030
52.595
40.115 0.3462 0.2603
Oligochaeta
5.350
112.772
0.0094 0.0960
11.145
45.465 0.1703 0.1483
Hirudinea
1.785
3.567
0.0009 0.0166 44.575
16.047
0.0339 0.0130
Gastropoda
10.700 14.707
0.0091
0.0650
Crustacea
80.230 52.150 0.1473 0.0575
Insecta
Ephemeroptera
Baetidae
310.225
193.000
0.1389
0.0835
151.100
390.460
0.0715 0.1496
Heptageniidae
67.750 30.310
0.1210
0.0358 60.175 49.475
0.1426
0.0301
Ephemerellidae
258.520
28.525
0.1281
0.0191 67.750
6.687
0.0358
0.0040
Caenidae
7.132
0.0027
58.835
0.0114
Leptophlebiidae
7.130
36.550 0.0007 0.0242 30.755
5.350
0.0313 0.0031
Ephemeridae
12.480 12.927
0.1847
0.0218
8.465 2.675
0.0107 0.0259
Odonata
Calopterigidae
1.335
4.012
0.0001
0.0044
Gomphidae
5.350
0.0030
60.175
5.347
0.0474
0.0191
Aeshnidae
1.785
0.3665
1.335
5.347
0.0001
0.3116
Cordulegasteridae
2.675
0.0001
9.360
0.2959
Plecoptera
Nemouridae
16.045
19.612
0.0051 0.0032
6.685
69.535 0.0013 0.0113
Leuctridae
131.935
168.485
0.0287 0.0563
15.155
29.417
0.0018
0.0072
Perlidae
137.285
67.307
0.5611 0.6755
12.035
0.0275
Coleoptera
73.100
48.140
0.2369
0.4930
Dytiscidae
90.930
0.892
0.0349 0.0010
Elmidae
110.540
20.950
0.0089 0.0118
58.390
42.790 0.0212 0.0123
Helodidae
41.005
7.577
0.0107 0.0009
1.785
1.337
0.0002 0.0001
Megaloptera
Sialidae
3.570
8.025
0.0085 0.0045
6.685
0.0084
Diptera
Limoniidae
1.785
1.337
0.0032
0.0011
1.335 1.337
0.0012 0.0001
Simuliidae
281.700 4.905
0.0836 0.0008
14.707
0.0043
Chironomidae
22.730 93.602 0.0013 0.0071
Ceratopogonidae
4.460 4.012
0.0003 0.0001
Stratyomyidae
46.355
8.470
0.1219
0.0151
44.575
13.372
0.1455 0.0556
Trichoptera
1.335 2.675
0.0137 0.0002
Rhyacophilidae
2.675
0.0297
1.785
4.012
0.0002 0.0009
Glossosomatidae
48.140
0.0710
1.785
10.697
0.0012 0.0151
Hydropsychidae
10.695
2.230
0.0324 0.0002
8.025 2.675
0.0291
0.0009
Polycentropodidae
6.685
0.0045
Psychomiidae
8.915
0.0030
2.675
0.0001
Limnephilidae
12.480
62.847
0.0089
0.0802
1.785
2.675
0.0002 0.0005
Sericostomatidae
133.720 109.202
0.2936
0.1952
124.805 141.742
0.1501
0.2467
Total
1790.050 1028.758
2.3167
1.5719
875.860
1131.268
1.5270
2.1410
Copyright © 1999 John Wiley & Sons, Ltd.
Regul. Rivers: Res.
Mgmt.
15:
477-484 (1999)
482
A. ALMODÓVAR AND G.G. NICOLA
Table II.
Mean number of trout caught for 0+, 1+ and 2+ and older age group for each
section (upstream/downstream) within the pre- and post-regulation periods
Site
Period
0+
1
+ 2+ and older
Mean
p
Mean
p
Mean
p
Pre-regulation
18 27
8
Upstream
>0.10 >0.10 >0.10
Post-regulation
20
25 9
Pre-regulation
20
33 55
Downstream <0.001 <0.001
<0.01
Post-regulation
9
9
34
The means were compared through a t-test and the results are shown in the table.
resulted in an important shift within the habitat of 0 + trout, which mostly prefer shallow waters with a
low water velocity (e.g. Heggenes
et al.,
1990; Hubert
et al.,
1994).
Growth was first examined by assessing the mean length of each age class on different sampling
occasions. Growth in length took place throughout the year but was faster between May and September.
Since growth in trout populations virtually ceases by September, the observed lengths-for-age in
November/December were considered as the mean yearly growth. No significant differences (p > 0.05)
were detected in the annual growth increments of trout between sites before and after regulation.
Nevertheless, a more precise examination of changes in the growth rate was made using the mean
instantaneous growth rate in length. A slight but not significant increase in this growth rate was observed
in the downstream site during the year following regulation for 1 + , 2 + and 3 + year classes, whereas
in the upstream site the growth rates remained mostly the same after the disturbance.
The impact of regulation in the River Hoz Seca was also evident in the annual production for trout.
Thus, considerable differences were found in the downstream total production between years, whereas in
the upstream site only a slight difference was detected (Table III). The observed decline in the downstream
site
was probably a function of recruitment loss, since no significant change was noticed in growth rate.
Crisp
et al.
(1983) and Cowx and Gould (1989) obtained comparable results in the annual production
values for salmonids as in growth rate.
In summary, the results suggest that the changes within the downstream trout population were not
induced by a scarcity of food resources. Factors closely linked to water discharge such as water velocity
and habitat modification seem to be responsible for changes in trout population. Water velocity could be
the reason for the observed loss of recruitment by removing of juveniles downstream but alteration to the
habitat involves other changes within physical features of the river like depth, cover or substratum
composition, which could alter the habitat requirements of young trout.
Table III. Percentage of total trout production (kg ha' year-') contributed by each year class and mean biomass
(kg ha-') for each section (upstream and downstream) within the pre- (1993) and post-regulation (1994) periods
Site
Year
1994
1993 1992 1991
1990
1989 1988
Total
production
(kg ha-'
year-')
Mean biomass
(kg ha-')
Upstream
1993
-
6.97
32.75
31.06
23.03
6.13
-
47.334
± 4.8937
68.992
± 6.8628
1994
11.97 19.93
44.65 23.29
-
30.907
± 3.3679
56.3850
± 5.4015
Downstream
1993
-
1.64
7.44
14.62 50.68
22.95
2.65
79.320
+ 4.4533
116.026
+ 9.2063
1994
1.35 6.98
34.23
41.66
15.77
-
-
44.402
± 15.3051
60.226
+ 12.0442
Copyright © 1999 John Wiley & Sons, Ltd.
Regul. Rivers: Res.
Mgmt.
15:
477-484 (1999)
EFFECTS OF A SMALL HYDROPOWER STATION UPON BROWN TROUT
483
ACKNOWLEDGEMENTS
This work was funded by the project SC-95/005 of the Spanish INIA. We are grateful to J. Cubo and J.L.
Castañeras for their assistance in the field and to Dr B. Elvira, Dr M. Díaz, Dr D. García de Jalón and
Dr J. Camargo for their helpful advice and comments on the manuscript.
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... Given the paucity of data on primary and secondary production in the streams, we calculated the consequences of four levels of food availability as the basis for bioenergetics simulations, where small RoR hydropower may affect food availability and fish consumption through increases in water temperatures and/or declines in stream flow. Few studies thus far have related fish growth or consumption to flow regulation from hydropower facilities (Almodovar & Nicola, 1999;Petersen & Paukert, 2005). A better understanding of how flow diversion affects water temperature and trout metabolism in bypassed reaches is particularly important given the increasing importance of small-scale hydropower, including small RoR hydropower, worldwide. ...
Article
Full-text available
Over 1 billion USD are devoted annually to rehabilitating freshwater habitats to improve survival for the recovery of endangered salmon populations. Mitigation often requires the creation of new habitat (e.g. habitat offsetting) to compensate population losses from human activities, however offsetting schemes are rarely evaluated. Anadromous Pacific salmon are ecologically, culturally, and economically important in the US and Canada, and face numerous threats from degradation of freshwater habitats. Here we used a matrix population model of coho salmon (Oncorhynchus kisutch) to determine the amount of habitat offsetting needed to compensate mortality (2-20% per year) caused by a range of development activities. We simulated chronic mortality to three different life stages (egg, parr, smolt/adult), individually and simultaneously, to mimic impacts from development, and evaluated if the number of smolts produced from constructed side-channels demographically offset losses. We show that under ideal conditions, the typical size of a constructed side-channel in the Pacific Northwest (PNW) (3405 m 2) is sufficient to compensate for only relatively low levels of chronic mortality to either the parr or smolt/adult stages (2-7% per year), but populations do not recover if mortality is >10% per year. When we assumed lower productivity (e.g.; 25 th percentile), we found that constructed channels would need to be 2.5-4.5 fold larger as compared to the typical size built in the PNW, respectively, to maintain population sizes. Moreover , when we imposed mortality to parr and smolt/adult stages simultaneously, we found that constructed side-channels would need to be between 1.8-and 2.3-fold larger that if the extra chronic mortality was imposed to one life stage only. We conclude that habitat offsetting has the potential to mitigate chronic mortality to early life stages, but that realistic assumptions about productivity of constructed side-channels and cumulative effects of anthropogenic disturbances on multiple life stages need to be considered.
... There are very few published estimates linking records of stranded fish to population-level estimates of fry mortality in streams regulated by RoR dams or larger reservoir-storage systems. For example, Almodόvar and Nicola (1999) attributed rapid declines in density (−50%) of brown trout over one year to drastic daily flow fluctuations (at times, water depth changed by 0.3 m over a few minutes) downstream of a small RoR dam that lead to the loss of suitable habitat. Other studies below larger reservoirstorage dams point to the potential for high mortality of juveniles after flow events. ...
Article
Full-text available
Predicting whether anthropogenic sources of mortality have negative consequences at the level of population dynamics is challenged by mechanisms like density‐dependent survival that can amplify or offset the loss of individuals from anthropogenic disturbances. Run‐of‐river (RoR) hydropower is a growing industry that can cause frequent mortality of salmonid fry through rapid reductions in streamflow, leading to stranding on dewatered shores. However, whether individual‐level impacts reduce population growth rates or increase local extinction risk is difficult to predict. We used a stochastic stage‐structured matrix model to evaluate how the timing and magnitude of anthropogenic flow fluctuations impacted population abundance and extinction risk of coho salmon (Oncorhynchus kisutch), which spend up to 1.5 yr in many streams regulated by RoR hydropower. We additionally assessed how the timing (spring, winter) and strength (weak, moderate, high) of natural density‐dependent bottlenecks experienced by salmon in freshwaters tempers or amplifies the potential for RoR‐induced mortality to scale to emergent population dynamics. We compared population sizes and the 45‐yr probability of quasi‐extinction under 12 scenarios that varied the frequency (0–20 events per year) and magnitude (1–10% mortality per event) of RoR‐induced flow fluctuations, as well as the timing and strength of density‐dependent bottlenecks occurring during the first year in freshwater. We found that even mild flow fluctuations by RoR hydropower can impact coho salmon population dynamics, especially if density dependence is weak or occurs early in freshwater residency (spring). When density dependence was strong and during winter, the potential for population‐level impact was lessened, but populations still declined by 13–42% when RoR‐induced mortality was severe (5–10%) or frequent (10–20 events/yr). We conclude that strong density‐dependent survival bottlenecks could partially mitigate the loss of fry from anthropogenic flow fluctuations, especially if bottlenecks occur late in freshwater residency, but not for all intensities of flow fluctuations. Even with strong density dependence in winter, our models predict declining populations by up to 70% under strong and very frequent flow fluctuations, which should serve to caution those tasked with regulating flows in streams affected by RoR hydropower.
... Dams disrupt longitudinal connectivity, which especially affects migratory fish, including both short and long distance migrating species, such as salmonids [23]. Accordingly, significant declines in the numbers of salmonids have been observed since the construction of micro-hydropower plants in small mountain rivers in Spain and Belgium [24,25]. Fish populations remaining in upstream river reaches separated by dams from the lower river reaches are often characterised by lower genetic diversity and a lower effective population size compared to populations below dams [26]. ...
Article
Hydropower is currently experiencing a boom in southeast Europe. For Romania, the number of hydropower plants is estimated to be between 545 and 674, but little has been published about their environmental impact. We provide the first overview of the geographical distribution of hydropower plants in Romania, supplemented by a review of current knowledge about their environmental impact, and present case study evidence on the effects of small hydropower plants on fish in headwater streams of the Carpathian Mountains. We show that 49% of the documented 545 hydropower plants in Romania are located in Natura 2000 or other protected areas, 5% are located in water bodies with ‘very good’ ecological status, and another 12% in water bodies with ‘good’ ecological status and ‘very good’ hydromorphological status according to the EU Water Framework Directive. Second, we demonstrate that hydropower plants significantly impact fish populations in several ways, both in upstream and downstream reaches, e.g. by water abstraction, dam construction and other hydromorphological alterations. Following the construction of hydropower plants in headwater streams, trout (Salmo trutta fario) and bullhead (Cottus gobio) populations often disappeared completely, and only remained in 38% of the stream reaches either upstream or downstream of the respective hydropower plants. In conclusion, the significant environmental impacts of each individual hydropower plant combined with the large number of them as well as the relative lack of effort to mitigate environmental impacts together represent a significant threat to aquatic biodiversity in Romania. The impacts exerted by hydropower plants are often unjustifiable by public interest according to EU directives, as small hydropower plants account for only around 3% of Romania's total electricity production. Better availability and access to environmental monitoring data are needed, as this would greatly support the development of more integrative management approaches to Romanian rivers.
... As a result, aquatic habitat gets fragmented in small hydromorphologic units such as riffles and pools [44,141,144]. For instance, brown trout (Salmo trutta) demonstrates high sensitivity to altered flow regime; degradation of habitat influences notably the community composition of juvenile fish and may decrease their densities and biomass up to 50 % [145][146][147][148][149]. ...
Article
Full-text available
The general perception of small run-of-river hydropower plants as renewable energy sources with little or no environmental impacts has led to a global proliferation of this hydropower technology. However, such hydropower schemes may alter the natural flow regime and impair the fluvial ecosystem at different trophic levels. This paper presents a global-scale analysis of the major ecological impacts of three main small run-of-river hydropower types: dam-toe, diversion weir, and pondage schemes. This review's main objective is to provide an extensive overview of how changing the natural flow regime due to hydropower operation may affect various aspects of the fluvial ecosystem. Ultimately, it will inform decision-makers in water resources and ecosystem conservation for better planning and management. This review analyses data on ecological impacts from 33 countries in five regions, considering the last forty years' most relevant publications, a total of 146 peer-reviewed publications. The analysis was focused on impacts in biota, water quality, hydrologic alteration, and geomorphology. The results show, notably, the diversion weir and the pondage hydropower schemes are less eco-friendly; the opposite was concluded for the dam-toe hydropower scheme. Although there was conflicting information from different countries and sources, the most common impacts are: water depletion downstream of the diversion, water quality deterioration, loss of longitudinal connectivity, habitat degradation, and simplification of the biota community composition. A set of potential non-structural and structural mitigation measures was recommended to mitigate several ecological impacts such as connectivity loss, fish injuries, and aquatic habitat degradation. Among mitigation measures, environmental flows are fundamental for fluvial ecosystem conservation. The main research gaps and some of the pressing future research needs were highlighted, as well. Finally, interdisciplinary research progress involving different stakeholders is crucial to harmonize conflicting interests and enable the sustainable development of small run-of-river hydropower plants.
... Given the paucity of data on primary and secondary production in the streams, we calculated the consequences of four levels of food availability as the basis for bioenergetics simulations, where small RoR hydropower may affect food availability and fish consumption through increases in water temperatures and/or declines in stream flow. Few studies thus far have related fish growth or consumption to flow regulation from hydropower facilities (Almodovar & Nicola, 1999;Petersen & Paukert, 2005). A better understanding of how flow diversion affects water temperature and trout metabolism in bypassed reaches is particularly important given the increasing importance of small-scale hydropower, including small RoR hydropower, worldwide. ...
Article
Full-text available
Many anthropogenic disturbances impact stream ecosystems by changing flow and temperature regimes. The emerging industry of small Run‐of‐River (RoR) hydropower reduces streamflow in bypassed reaches, with largely unknown consequences for water temperatures and fish growth. We used empirical and simulated data from two small RoR regulated streams in British Columbia (Canada) to quantify changes in water temperatures in bypassed reaches and assess the potential impacts to resident rainbow trout (Oncorhynchus mykiss) growth using bioenergetics models under a range of consumption scenarios. We found increases in mean monthly water temperature in bypassed reaches due to flow diversion of 0.5–0.8°C (0.17–0.19°C/km). Bioenergetics models using those temperatures predicted increases in annual O. mykiss growth (compared to natural temperatures) if consumption was unlimited (+200–450%), increases (+15–42%) if consumption was scaled with higher metabolic demand, and small reductions (−5 to 7%) if consumption remained constant. If food availability was reduced by 25%, annual growth was predicted to decline by 45%. Empirical estimates of annual growth of fish sampled indicate modest reductions in annual growth less severe than those modelled by our Scenario 2. Our results highlight that increases in water temperature induced by flow diversion for small RoR hydropower could be large enough to have consequences for O. mykiss growth, but the impacts depend on how and when RoR hydropower affects food supply and consumption.
... Macroinvertebrates are often utilized as an indicator to evaluate the changes in a water environment [7][8][9]. Although many studies have investigated the impact of hydropower stations on macroinvertebrates [10][11][12][13][14][15][16][17], their results have been inconsistent. Different types of hydropower stations have different interception effects as well as ecological effects [18]. ...
Article
Full-text available
Many studies have investigated the influence of hydropower stations on macroinvertebrate communities, but few have clarified the influence of different types of hydropower stations. A total of 133 samples obtained from seven rivers, on which 45 hydropower stations are located, with the rivers distributed across four provinces (Yunnan, Jiangxi, Fujian, and Hubei) were investigated to study the influence of different types of small hydropower stations on macroinvertebrate communities. Samples were collected during 2011–2012. Results showed that 126 taxa of macroinvertebrates were collected, of which 68.3% were insects. The average macroinvertebrate density and biomass were 966 ± 112 ind/m2 and 17.31 ± 1.54 g/m2, respectively. For dam-type hydropower stations, the intercepting effect of the dam was the main factor affecting macroinvertebrate populations, whereas the influence of hydrological period was nonsignificant. Macroinvertebrate taxa richness exhibited a gradual increase from reservoir reaches to down-dam reaches and then to natural reaches (4.4, 6.5, and 9.5, respectively). The Shannon–Wiener index showed a similar increasing trend (1.06, 1.48, and 1.58, respectively), whereas biomass levels exhibited a decreasing trend (56.3, 25.2, and 6.0 g/m2, respectively). For the diversion-type hydropower stations, hydrological period was the main influential factor, whereas the intercepting effect of the dam was nonsignificant. From wet to dry seasons, increases were observed in macroinvertebrate abundance (5.2 to 8.3), density (322.2 to 1170.5 ind/m2), biomass (24.6 to 40.1 g/m2), and Shannon–Wiener index (1.23 to 2.08).
... Effects on the aquatic environment (55%) Aquatic species (e.g. lamprey, eels, trout) and assemblages Water flow Water quality and sediment Benthic ecosystem Macroinvertebrates [4,66,53,130,145,81] Economic effects (6%) Regional economic effects Effects on property [69]; Aras [161] Public and stakeholder perception (4%) Local attitudes Landscape preferences conflict [88]; Lazdane [162]; [70] Noise The synthesis revealed several underexplored, high level research gaps and research opportunities-some of which are specific to certain energy sources, and others that are cross-cutting. The literature on the environmental effects of low carbon power development specific to Canada is sparse. ...
Article
This study provides a portrait of the state of impact assessment (IA) research for four types of low carbon power production (wind, solar, small-scale hydro and small modular nuclear reactors). The emphasis is on IA research that has relevance to the Canadian policy setting. The method involved a systematized scan of the academic literature (peer reviewed publications, conference proceedings and book chapters) and reports and studies produced by government and other organizations. The literature was categorized according to a framework adapted from transition theory. The results indicate that the literature addressing wind power is comprehensive, but there is a relative scarcity of research (in both quantity and breadth) on the impacts of solar, small-scale hydro, and small modular reactors (SMRs). In each of these three energy areas there is a lack of available work addressing the social, political and cultural impacts accompanied by more specialized gaps in the biophysical research. Drawing on a transition theory typology, the majority of the literature can be characterized as reflexive , with less than 20% of research exploring primarily operational, tactical, or strategic themes. But there are many sources where the research contains overlapping categories. The research for SMR impacts is distinct from the other three alternative power sources; this literature is largely strategic. Priorities for further analysis in the short-term include applying lessons from the international literature to the Canadian context and developing a better understanding of the specific impacts of alternative energy sources on Indigenous communities. In the longer term, there is a need for more research in the field, with a particular emphasis on understanding the operational and strategic qualities of low carbon power production.
... Por otra parte, este deterioro del medio intersticial puede aliarse con otros problemas comunes en estas zonas altas de los ríos en perjuicio de los peces, como la fragmentación y/o alteración de la continuidad ecológica por presas y minicentrales hidroeléctricas que limitan sus movimientos y migraciones. Además, ocasionan otros impactos sobre sus poblaciones, como son la reducción de la productividad en los tramos explotados, tanto por la escasez de caudal circulante como por la brusca variación diaria del régimen aguas abajo de tomas y socaces (Almodóvar y Nicola, 1999). De hecho, las presas de las tres minicentrales instaladas en el Alto Tajo son barreras infranqueables para la ictiofauna que fragmentan la población truchera e impiden el acceso de los adultos reproductores a las mejores zonas de desove, particularmente al río Hozseca. ...
Book
Full-text available
Este libro es fruto de las jornadas organizadas por el CIREF y Wetlands International en colaboración con la Agencia Vasca del Agua URA, COBE, AIL, Diputación Foral de Gipuzkoa, Gobierno Vasco y Ayuntamiento de Donostia-San Sebastian en septiembre de 2017 en Urdaibai. El libro ha sido publicado por el Servicio Central de Publicaciones del Gobierno Vasco gracias a la Agencia Vasca del Agua.
... Por otra parte, este deterioro del medio intersticial puede aliarse con otros problemas comunes en estas zonas altas de los ríos en perjuicio de los peces, como la fragmentación y/o alteración de la continuidad ecológica por presas y minicentrales hidroeléctricas que limitan sus movimientos y migraciones. Además, ocasionan otros impactos sobre sus poblaciones, como son la reducción de la productividad en los tramos explotados, tanto por la escasez de caudal circulante como por la brusca variación diaria del régimen aguas abajo de tomas y socaces (Almodóvar y Nicola, 1999). De hecho, las presas de las tres minicentrales instaladas en el Alto Tajo son barreras infranqueables para la ictiofauna que fragmentan la población truchera e impiden el acceso de los adultos reproductores a las mejores zonas de desove, particularmente al río Hozseca. ...
Article
The Cernadilla reservoir, located on the River Tera (northwest Spain, Duero Basin) is an oligotrophic reservoir with a capacity of more than 250 × 106m3 and a depth of 70 m. The regulated flow pattern is characterized by higher summer flows, higher day flows than night ones, and lower weekend flows. The effects of this artificial flow regime on the stream ecosystem were evaluated by comparing the aquatic communities of an upstream station with those of three downstream stations, located at 1, 8, and 24 km from the dam. Physiocochemical characteristics of the water, fish and macrobenthic communities, and macrophytes were studied at each station. Summer water temperatures were significantly lower downstream of the reservoir. Macrophyte biomass, macrobenthic diversity, and richness were reduced below the dam. The trophic structure was changed by an increase of shredders and grazers. Fishery total biomass greatly fluctuated seasonally, but was higher above the reservoir than below it. However, in spring the trout populations were higher upstream because large numbers of spawning cyprinids from the reservoir invaded upstream reaches of the River Tera and displayed resident trout populations.
Article
1. The food of trout (Salmo trutta) was investigated in relation to the invertebrate drift and the benthos. 2. Using an electrical stunning machine, fish samples were taken from June 1963 to October 1964 in the day and from April to October 1964 at night. 3. Nearly all the common members of the benthos and drift occurred in the trout stomachs, but only the 1 + and 2+ trout contained the larger members of the benthos and drift. The biomass and numbers of most items in the stomachs increased with the size of the trout, and showed no definite pattern when compared on a monthly basis. 4. The principal day foods were nymphs of Baetis spp. for 0 + trout, terrestrial invertebrates and oligochaetes for 1 + trout, and large larvae of Limnephilidae for 2 + trout. It is suggested that this marked difference in the principal foods reduced the competition for food between the fish classes. 5. Most of the animals taken exclusively from the drift were only important as constituents of the diet in summer, and those taken chiefly from the benthos were important in both winter and summer. Some animals were taken from both drift and benthos in large numbers, especially in winter. 6. The fish samples taken at night indicated that the trout were feeding in the early hours of the night during the summer months. It is concluded that the availability of many benthic animals increased at night and that the trout were utilizing this readily available food either as drift or from the tops of stones.
Article
(1) The population density, growth, biomass, fecundity and production of bullhead (Cottus gobio L.) and brown trout (Salmo trutta L.) were estimated in the River Tees below the regulating reservoir at Cow Green. Comparisons were made with estimates obtained for the same site before impoundment, and with data from Maize Beck, an unregulated tributary of the Tees below the reservoir. (2) Changes in the growth of trout were negligible, but there was an apparent decrease in the observed lengths of O group bullheads in the regulated Tees. This may reflect a shorter growing season because bullheads spawned later in the Tees after impoundment, possibly in response to the delay in the increase in water temperature during the spring. (3) There were marked annual variations in the numbers of brown trout and bullhead, but population densities of both species increased in the Tees following regulation. The numbers of trout (excluding the O group) increased from 3.5 to 4.9 100 m-2 For bullheads the largest increases occurred in the I and II age-groups: 9.5 to 81 5 100 m-2 and 5.2 to 24.4 100 m-2 respectively. The numbers of both species were significantly higher (P 0.05). (6) Only very approximate values were obtained for annual production of trout. Estimated bullhead production increased slightly at Maize Beck and by a factor of three in the Tees, largely as a result of increases in O and I group production. Annual production by older fish changed little. (7) The results suggest that the combination of environmental changes caused by regulation has improved conditions for the downstream fish populations. This has been exploited by the bullheads and trout mainly through increased population density and population biomass, rather than through any marked increase in the growth rate of individual fish. This would be expected because growth rate appears to be limited mainly by water temperature.
Article
We propose that the Concept provides a framework for integrating predictable and observable biological features of lotic systems. Implications of the concept in the areas of structure, function, and stability of riverine ecosystems are discussed. -from Authors
Article
Induced peaking flows that increased discharge 4–100 times (up to 350 L·s) in a small stream did not displace brown trout Salmo trutta (mean total length ≥ 67 mm) downstream. Coarse substrate was thought to be essential by creating low-water-velocity microniches. In the available habitat, brown trout were significantly associated with certain depths, water velocities, substrate, and cover. Larger fish occupied areas with deeper water and more cover than did yearling brown trout. Short-term changes in flow did not influence habitat use. Fluctuating flows increased emigration slightly, especially at night.