ENERGY BYPRODUCTS: CONTROL AND REMEDIATION TECHNOLOGIES
Impact of Electricity Generation and Transmission
on Ecological Systems
Scott Ferson
Applied Biomathematics, Setauket, NY
Many serious ecological and environmental impacts are by-products of electrical power
generation and delivery systems. In aquatic environments, these include leachate toxicity
from coal mining and combustion residues, and effects of water impoundments and
cooling water intake structures such as entrainment, impingement, thermal impacts,
impediments to fish migration, and alteration of aquatic habitats. There are likewise
many terrestrial impacts, including habitat loss and interference with migration and
dispersal pathways from pipelines and power lines. There are also a variety of incidental
impacts associated with power generation facilities. For instance, avicides intended to
disperse flocks of birds congregating on warm concrete structures of nuclear power plants
enter the food chain and kill hawks and endangered owls.
Engineering minimal-impact designs, as well as planning for mitigation and remediation
strategies, requires clear assessment of the nature, magnitude and consequence of these
impacts. Engineers are beginning to appreciate the need to include ecological processes
in their assessment models. The need arises because ecological systems have an inherent
complexity that can completely erase the effects of an impact or greatly magnify it,
depending on the life histories of the biological species involved. This complexity can
also delay the consequence of an impact or alter its expression in other ways. For
instance, after a lake’s population of bluegills was devastated by the heavy metal
selenium leached from ash settling ponds, a demographic model of the species revealed
that, if selenium poisoning were stopped, the population could recover to pre-impact
abundances within two years. However, the increased abundance would be unevenly
distributed among age groups and, following this temporary recovery, there would a
population crash to levels even lower than those originally caused by the selenium. If
this crash were not forecast in advance, its unanticipated occurrence would have caused
considerable consternation among managers, regulators and the interested public. It is
important to predict the ecological consequences to understand the nature and duration of
biological recovery from toxicological insults. Without the understanding provided by
the ecological analysis, the population decline would probably have been completely
misinterpreted as the failure of the mitigation program.
It is essential that we have a way to synthesize effects from multiple kinds of impacts and
integrate effects from different plants and structures that are distributed across the
environment. Assessments of ecological impacts are complicated by two issues: what
we know about ecology and what we don’t know, i.e., the uncertainty about our models
and their parameters. The state of the art in assessment of ecological impacts from
energy generation has three foci:
Variability versus incertitude. Natural biological systems fluctuate in time and space,
partially due to interactions we understand, but substantially due to various factors that
we cannot foresee. The variability of ecological patterns and processes, and our
incertitude about them, prevent us from making precise, deterministic estimates of the
effects of environmental impacts. Because of this, comprehensive impact assessment
requires a probabilistic language of risk that recognizes variability and incertitude, yet
permits quantitative statements of what can be predicted. The emergence of this risk
language has been an important development in applied ecology over the last decade. A
risk-analytic endpoint is a natural summary that can integrate disparate impacts on a
biological system.
Population-level assessment. In the past, assessments were conducted at the level of the
individual organism, or, in the case of toxicity impacts, even at the level of tissues or
enzyme function. To justify costly decisions about remediation and mitigation, biologists
are often asked “so what?” questions that demand predictions about the consequences of
impacts on higher levels of biological organization. Management plans require
predictions of the consequent effects on ecological populations and communities. Our
scientific understanding of community and ecosystem ecology is very limited, however,
and quantitative predictions, even in terms of risks, for complex systems would require
vastly more data and mechanistic knowledge than are usually available. Extrapolating
the results of individual-level impacts to potential effects on the ecosystem may simply
be beyond the current scientific capacity of ecology, which still lacks wide agreement
about even fundamental equations governing predator-prey interactions. How can we
satisfy the desire for ecological relevance when we are limited by our understanding of
how ecosystems actually work? As a practical matter, focusing on populations and metapopulations (assemblages of distinct local populations) may be a workable compromise
between the organism and ecosystem levels. Risk assessment at the population level
requires the combination of several technical tools including demographic models,
potentially with explicit age, stage or geographic structure, and methods for probabilistic
uncertainty propagation, which are usually implemented with Monte Carlo simulation.
Meta-populations are likely to be at the frontier of what we can address with scientifically
credible models over the next decade.
Cumulative attributable risk. Assessments should focus on the change in risk due to a
particular impact. The risk that a population declines to, say, 50% of its current
abundance in the next 50 years is sometimes substantial whether it is impacted by
anthropogenic activity or not. Only the potential change in risk, not the risk itself, should
be attributed to impact. On the other hand, for environmental protection to be effective,
remediation and mitigation must be designed with reference to the cumulative risks
suffered by an ecological system from impacts and from all the various stresses present
cumulated through time.
The principle of ravnoprochnost (равнопрочность, equi-sturdiness) in engineering holds
that system design should be balanced, rather than an uneven mixture of gold-plated,
hyperdesigned parts with shoddy, unreliable parts. This principle has an analog in
uncertainty analysis: it is wasteful to expend too much effort in estimating some pieces
of an assessment with great precision if the other pieces of the assessment have large
uncertainties that cannot be reduced. The old joke illustrating this principle suggests that
we have “half the solution” to the question of how many angels can dance on the head of
a pin because we can now estimate the surface area of the head of a pin. In the context of
assessing the ecological impacts of electricity generation and transmission, the principle
of ravnoprochnost says we should focus attention on the components of the assessment
where uncertainty has the largest consequence for the reliability of our final predictions.
In complex scenarios of energy by-products causing ecological impacts, the phenomena
needing attention first may be the ecological, toxicological, chemical, or physicomechanical phenomena. In some important situations, ecological phenomena will form
the crucial focus.