SMALL-SCALE HYDRO: HOW DOES THE ENVIRONMENTAL
IMPACT COMPARE WITH OTHER RENEWABLE ENERGY? [1]
Björn S.
SVENSSON
ABSTRACT
To
judge from the arguments put forth by NGOs, hydropower constitutes a larger threat
to biodiversity than any other extraction of renewable energy. Life Cycle
Analyses (LCA) provide one method of comparing the environmental performance of
different kinds of electricity production. Biodiversity is not easily included
in LCAs. However, most interest centres on the protection of species. So
analyses of different energy systems could at least include the fate of species
as a variable when characterising the environmental impacts. I have used
information from the literature to get realistic estimates of the abundance and
richness of species in different habitats. By combining this information with
the amount of land required to supply a certain amount of energy, I have
attempted to estimate the loss of individuals per unit electricity produced
when either water or biomass is used as fuel.
I. INTRODUCTION
Life
Cycle Analyses (LCA) provide one method of comparing the environmental
performance of different kinds of electricity production. The method is
particularly well suited to characterise these complex systems, where the
amount of service varies considerably between different options and where the
use of natural resources or emissions of pollutants have a strong coupling to
the geographical setting. So far, it has been customary to stop the LCA when
the inventory phase has been completed, i.e. making a Life Cycle Inventory
(LCI). Thus, results of such LCIs are usually given as lists, where the total
appropriation of a particular resource or emission of a particular pollutant
are summed up over the entire life-time of the system and divided by the total
output of electricity during the same period. Consequently, the contribution to
global warming is, for example, given as amount of carbon-dioxide equivalents
per unit electricity generated, i.e. g CO2-equiv. per kWh-1.
A
compilation of LCIs made on hydropower reveals that large projects tend to be
more efficient in terms of resource use compared to small projects; at least as
far as hydropower with reservoirs are concerned (International Energy Agency
2000). The last decades’ debate on hydropower clearly shows that few
environmentalists accept this conclusion, and in some countries, like for
example
To
judge from arguments frequently put forth, there is a widespread contention
that hydropower with reservoirs constitutes a larger threat to biodiversity
than any other extraction of renewable energy (McAllister et al. 2001).
However, statements or quantifications of impacts of hydroelectric power plants
as a basis for decisions about future energy development are not meaningful
unless comparisons are made between different options on an equal base.
Biodiversity
is not easily included in LCAs and, besides, there is still a lack of consensus
about the practical meaning of the concept (Schenck 2001). However, most
interest centres on the protection of species (May 1994). So analyses of
different energy systems should at least include the fate of species as an
additional variable when characterising the environmental impacts.
Unfortunately, very few studies provide data that are sufficient for such
analyses to be carried out. I have used information from the literature to get
realistic estimates of the abundance and richness of species in different
habitats. By combining this information with the amount of land required to
supply a certain amount of energy, I have attempted to estimate the loss of
individuals and/or species per unit electricity produced when either water or
biomass is used as fuel.
II. THE IMPACT
OF HYDROPOWER ON BIODIVERSITY
The
ecological consequences of river regulation, i.e. damming, flow alterations,
and perhaps diversion of water, are complex and comprehensive. They involve
direct impacts related to habitat alterations and obstruction to dispersal as
well as indirect impacts that are coupled to physico-chemical and ecological
changes. General compilations of these effects include Ward & Stanford
(1983 & 1995), and World Commission on Dams (2000). Life cycle analyses on hydropower have, so far, only treated these
kind of impacts qualitatively and descriptively, while providing detailed
quantitative estimates of the flow of material and matter, including emissions
(Vattenfall 1999; Vold et al. 1996; Frischknecht & Müller-Lemans 1996;
Beals & Hutchinson 1993; International Energy Agency 2000). In addition, most studies of impacts of hydropower relate to power
plants with reservoirs. Hydroelectric plants of run-of-river type are dealt
with only exceptionally (Hildebrand et al. 1980; Turbak et al. 1981; Loar &
Sale 1981; Olson et al. 1985; Hildebrand et al. 1980; Loar et al. 1980).
While
opponents to large-scale hydropower have long lists of potential negative
impacts to support their standpoints, only aesthetics and the potential effects
on biodiversity and fishery seem to be valid arguments against small-scale
hydropower development. There are numerous success stories that describe how
stocks of fish are maintained following the construction of low-head dams (e.g.
(Swales 1989; Olson et al. 1985; Trussart et al. 2002). Measures that maintain or restore the habitats for plants and
invertebrates, i.e. which enhance biodiversity in general, usually require less
efforts (Gore 1985). Consequently, there are reasons to assume that
run-of-river hydropower plants, when properly managed, have insignificant
impacts on biodiversity. Yet, in order to provide input to comparisons with
other means of electricity production, quantifications of impacts are needed.
In the absence of actual measurements and as a starting point for such
comparisons it is perhaps reasonable to assume a total loss of animals and
plants within the area that was directly influenced when the power plant was
constructed. In a LCA perspective, this means that a measure of impact on
biodiversity reduces to a function of specific land use, i.e. area reclaimed
per unit electricity produced, and some expression of the content of
biodiversity, e.g. average abundance or species richness, within the same area
before it became exploited.
After
this simplification, one major problem still exists, namely the quantification
of biodiversity. Very few ecosystems have been completely surveyed with respect
to their content of organisms. Birds, mammals, groups of insects and plants are
usually well known, but inconspicuous groups of minute and taxonomically
difficult invertebrates are not. In the absence of complete sets of data,
ecologists therefore commonly use indicators to characterise biodiversity.
Indicators are groups of easily sampled and easily identified organisms, such
as birds, butterflies and vascular plants. In this context, indicators must
also reflect the overall biodiversity or richness of species in an area.
Correlations between different groups of potential indicators show that this
latter requirement is sometimes, but not always, met (Malmqvist & Hoffsten 2000;
Heino et al. 2003; Lawler et al. 2003; Paavola et al. 2003). For the time being, I have chosen to use insects as indicators of
biodiversity because insects are the most numerous multi-cellular organisms in
terrestrial (Stork 1988) as well as freshwater environments (Illies 1978). In
addition, there are many field studies that provide data on the abundance of
insects in different environments. Hence, it is possible to obtain information
about the richness of insects with enough confidence to calculate the magnitude
of maximal losses due to different land use practices, including hydropower
development. A compilation of data from numerous published surveys reveals that
insect abundance in aquatic as well as riparian environments is in the order of
5 x 103 x m-2 on average (Svensson, unpubl.).
The appropriation of land and water for the
operation of two Swedish hydroelectric power systems has been estimated (Table 1).
One system consists of a run-of-river plant, Hornsö, located in Alsterån, a
South Swedish river (Klercq in press). The other system is Luleälven in
northernmost
|
Name |
Annual average energy production (GWh) |
Land appropriation (km2) |
Specific loss of insects (inds x kWh-1) |
|
Hornsö |
10 |
0.15 |
75 |
|
Luleälven |
13600 |
328 |
120 |
Table 1. Data on two Swedish hydroelectric power systems.
Hornsö is a run-of-river plant located in southern
The difference between the two options in terms of specific loss of
insects is probably larger than indicated because the simplistic approach used
here exaggerates the negative impact on biodiversity caused by run-of-river
hydropower vs. hydropower with reservoirs. Although the riparian and aquatic
habitat in the immediate surrounding of the run-of-river plant is altered,
there is no reason to think that these alterations are transplanted downstream
as long as the natural discharge is maintained. When most water that runs the
turbine is intermittently abstracted from a natural river channel, the impact
on the aquatic biodiversity depends on the frequency and magnitude of the flow
changes (Fig. 1).
Also, the impact on biodiversity of hydropower with reservoirs as
quantified by the method used above is too large. Even if the draw-down zone
loses most of its set-up of flora and fauna, it is invaded by species that can
cope with the harsh conditions and make use of this new environment (Fisher
& LaVoy 1972; Friden 1984; Shafigullina 2000; Greenwood et al. 1995). The net effect is,
however, still comprehensive and always negative as regards the number of
species.
The construction of dams is often said to cause fragmentation of
affected rivers. By this one means that the river system is cut into more or
less isolated pieces. According to ecological theory, habitat fragmentation
will always bring about reductions in the richness of species. The use of
“fragmentation” to describe the ecological effect of dam construction is,
however, erroneous. When the flow is still maintained, be it for various
periods of time, the aquatic habitat is basically kept uninterrupted. A dam
that prevents migrating species such as salmons and sea trout to reach their
spawning grounds is not causing “fragmentation” but “loss of habitat”, which is
something completely different. It is unfortunate that ecologists frequently tend
to mix up these two phenomena because the interpretation in terms of potential
ecological impacts then also tends to be biased (Fahrig 2003).
Figure 1. Relationship between the largest daily flow
increase observed and the effect on species richness of macro invertebrates
(positive or negative). The effect is the difference between observed and
predicted number of species (modified from Englund & Malmqvist 1996).
III. THE IMPACT OF BIOMASS EXTRACTION ON
BIODIVERSITY
Biomass for energy purposes derives from many
sources. In
Although use of FR is encouraged in
There is also an allocation problem when
attempting to quantify the specific burden of FR removal. Since logging of saw
timber and pulpwood, activities that cause the major impact on biodiversity,
has priority, one generally views the possible extra impact of fuel extraction
as insignificant. However, if we accept that the change of habitats following
logging is entirely attributed to those prioritized activities, we still need
to know if and how much the FR would support biodiversity if being left to
decompose naturally. Unfortunately, few studies deal with this question. So
far, I have not been able to find any data in the scientific literature that
integrate the content of insects and other animals in woody debris over its
entire cycle. Since the life span of woody debris extends over years and
decades, depending of size and origin (Lundborg 1994), studies of its life
support potential are not easily carried out.
I have anticipated that the
number insects that would make use of 1 kg of woody debris from its deposition
until fully decomposed amounts to at least 500; in reality this number is
probably considerably higher. The information I have used to arrive at this
figure derives from many sources, e.g. Abbott & Crossley 1982; Schiegg
2000; Irmler et al. 1996; Schiegg 2001; Dajoz 2000; Marshall et al. 1998; Elton
1966; Hövemeyer & Schauermann 2003.
The heat content of 1 kgdw
of FR reaches 5 kWh at most (AB Svensk Energiförsörjning 1998). This means that
the extraction of 1 kWhheat brings about a
net loss of at least 100 insects, i.e. similar to the two Swedish hydropower systems
described above. However, the loss of insects from biomass use is actually
larger, because of the adjustment for energy conversion losses when burning
biomass.
The average yield of biomass
in Swedish forests is estimated at 0.5 kg x m-2 x yr-1 (Johansson 2001; Parikka 1997). About 20% of the annual
growth is available as FR.
IV. DISCUSSION AND CONCLUSION
Clearly, there are many uncertainties that need
being considered and evaluated when the impact of renewable energy utilization
on biodiversity is estimated. Moreover, the above attempt to do so provides
only one of many possibilities. Opponents to the approach used here could for
example claim that insects are not the most important biodiversity indicators
and that the threat to red-listed or endangered species would be more relevant[2].
However, the intention with the above reasoning is not to advocate an immediate
shift in the political attitude to different energy sources but merely to
introduce a necessary complement to the description of different energy supply
options and consequently a better decision support system.
Nevertheless, the result may seem surprising
given the massive information about the damaging impact of hydropower on river
ecology. This is partly a result of the reluctance to understand the need of
considering the degree of service provided by a particular power plant.
Hydroelectric power makes a more efficient use of the reclaimed land compared
to extraction of biomass energy. Therefore, especially small-scale
hydroelectric power will always be a better option compared to energy
production based on forest residues. When energy crops are used instead,
considering that agriculture is the prioritised land-use, the picture is less
clear. Using willow planted on arable land as the source of biomass energy will
probably bring about a net gain in biodiversity compared to traditional
production of cereals (Göransson 1994; Berg 2002), not the least because of the need to use pesticides to keep number of
weeds and insects low in modern agriculture.
It is, however, not only necessary to divide
the total environmental burden with the amount of electricity produced. One
must also consider when the capacity to provide electricity is available. In
countries with a high share of hydroelectric power this energy source not only
constitute a stand-alone option, but also provides the necessary back-up that
makes the entire energy mix match the demand. Hydroelectric power with
reservoirs is a firm energy source as opposed to most other sources of
electricity. A fair comparison between different options in terms of their
environmental characteristics should also look at the possible need to use
complementary power from sources that are partly or fully operated for
peaking-power production. Unfortunately, the allocation of impacts that takes
this aspect into account is a complicated matter and good studies are still
awaited.
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