By permission: CRC Press, Inc.
Restoration Ecology: The New Frontier (Chapter 1, pages 1-11)
Rehabilitating Damaged Ecosystems. Volume I
John Cairns, Jr.
CRC Press, Inc. (1988)
Note! Both volumes of this book are on reserve at the University of Idaho Library.
By permission: CRC Press, Inc.
TABLE OF CONTENTS
I. INTRODUCTION
If a natural system is altered, its ecological role is either eliminated or substantially changed. In some cases, such as alteration due to surface mining, some formerly existing ecological characteristics may be replaced relatively quickly and others may take more than a human lifetime to restore. In the worst situation, restoration to the original condition may be impossible. In other cases, such as the construction of condominiums, high-rise buildings, football stadiums, etc., the alteration is permanent from the perspective of the human lifetime. Some artifacts may be demolished after 20 or 30 years, but a high probability exists that they will be replaced with larger more formidable artifacts rather than the original ecosystem. This article focuses on the more tractable problems, namely, restoration or rehabilitation of ecosystems subjected to a disturbance following which remedial measures may be immediately instituted. Even in cases where the intention is to build artifacts that will alter the ecosystem for tens or hundreds of years, consideration should be given to the options for alternative use when the life expectancy of the present artifact has been reached. For example, what should be done with a dam that has filled with silt? Should it be rejuvenated at greater expense by dredging? If so, where will the dredged material be placed? What if the dredged material contains toxic substances? If an alternative ecosystem is more practicable, such as an alluvial plain, what might be done in locating and building the dam to make the conversion easier when the reservoir is no longer functioning as it was originally intended?
Restoration ecology provides an opportunity to establish a new
frontier in both theoretical and applied ecology. Everyone is
agog these days with the opportunities provided by the latest
frontier activity in biology -- biotechnology. Biotechnological
developments have been made possible by some theoretical developments
in the field of genetics that make alterations in the performance
of species practical. These genetically altered organisms can
produce materials that benefit (such as insulin), or they can
reduce hazards that are threatening (e.g., toxic wastes). These
are only single species; however, suppose communities of organisms
are developed that are designed for specific purposes? Of course,
agricultural systems represent a very limited but, nevertheless,
crucial application of environmental management. However, vast
areas of vegetation in power line right-if-ways are controlled
by either periodic applications of chemicals or by cutting vegetation
when it reaches a certain size. Cutting is extremely expensive,
and chemical additions are undesirable even if applications are
carefully monitored. Suppose, however, a community of organisms
could be developed that would never grow above a certain height
and would require no application of hazardous chemicals for control.
Imagine the benefits if communities of organisms could be developed
for hazardous waste sites that would both insure that the waste
is immobilized (and not likely to leave the site through various
routes) and simultaneously transform it to less harmful material.
Alternatively, the waste might be concentrated by this special
community so that it could be better utilized. Both of these
examples are well within the scope of the field of restoration
ecology.
Examples of restoration ecology can now be seen in the production
of both marketable meat and useable energy in Africa. European
cattle use only a small fraction of the vegetation in that continent,
are quite vulnerable to disease, and drop fecal matter that remains
compacted and pretty much unavailable since it is fairly resistant
to recycling. David Hopcraft1,2 has developed a reserve in Africa
in which native organisms, such as giraffe and other native species,
are being raised with far lower management costs and far more
efficient use of the native vegetation than the European cattle.
Not only is the number of pounds of meat per acre greatly increased
and the management cost reduced, but the whole system is environmentally
less damaging and is far closer to the natural system than is
the case when European cattle are raised in large numbers on the
same type of landscape. Although the fecal material of these
native species is much more readily recycled into the natural
system, it can also be collected and used to produce methane that
can then be used to generate electric power or heat. This in
turn may prevent trees from being used as firewood, and may diminish
ecosystem damage.
There is, to my knowledge, no generally accepted definition of
restoration ecology since this a newly emerging field. However,
one might say that restoration ecology is the full or partial
placement of structural or functional characteristics that have
been extinguished or diminished and the substitution of alternative
qualities or characteristics than the ones originally present
with the proviso they have more social, economic, or ecological
value than existed in the disturbed or displaced state.
The roots of ecology are so old that they may well predate recorded
history. However, one might arbitrarily select the first edition
of Fundamentals of Ecology in 1953 by Eugene P. Odum3 as
the emergence of the subdiscipline of ecology. This book presented
ecology as an entity in its own right rather than as a subsection
of another subdiscipline of biology. The book also placed ecology
in perspective in relation to other fields of learning as well.
As is often the case for fields in early stages of development,
much of the earlier work was observational and only more recently
became experimental. The late Robert MacArthur is credited by
many as moving the field into the predictive stage of development.
In addition, since most biologists are oriented to single species,
many ecological studies still focus on that level of biological
organization. Nevertheless, the use of the term ecology
implies studies of higher levels of biological organization than
single species. These studies are now beginning to emerge, as
evidenced by the Hubbard Brook and Coweeta studies, as well as
others.
Although the number of studies of disturbed ecosystems has increased
substantially in the last 30 years (and markedly since the first
earth day made such things academically respectable), the percentage
of ecologists studying pristine or relatively pristine ecosystems
is wildly disproportionate to the percentage of the earth's surface
represented by these ecosystems. To state this more bluntly,
most ecologists drive, fly, or boat past or over enormous territories
in which the ecosystems have been disturbed to arrive at a small
patch of undisturbed ecosystem. Without in any way denigrating
the value of studies of pristine systems that furnish essential
and indispensable information, it is curious that the interesting
information that can be obtained from disturbed ecosystems and
their restoration has only recently been given serious attention
by theoretical ecologists.
Even more curious is the fact that many ecologists are carrying
out research on disturbed ecosystems that have partially recovered.
Sometimes they do this without being aware of the disturbance
and frequently without giving events in the postdisturbance period
the attention they deserve even within the limited scope of the
individual research project. Three of the biological field stations
where I have carried out research are on ecosystems that have
suffered significant disturbance. The University of Michigan
Biological Station on Douglas Lake is located on a tract that
was clear-cut. This was followed by slash fires set to eliminate
branches and other material then considered unmarketable. Figure
1 shows what the area once looked like, and Figure 2 shows its
recent condition. The Rocky Mountain Biological Laboratory near
Crested Butte, Colo., was once the scene of extensive mining and
had a population over an order of magnitude greater than that
resident today. The Bermuda Biological Station is located in
one of the most heavily settled land masses on the face of the
earth. These are not the only biological stations located on
areas that have undergone major disturbance due to human activities.
There are, in fact, many others. These few examples illustrate
that many ecologists are studying stressed ecosystems; however,
this might not be evident from the papers published on the investigations.
Since the publications from these studies are regularly in prestigious,
scholarly, peer-reviewed journals, it is abundantly clear that
valuable information of interest primarily to theoretical ecologists
can be obtained from studying disturbed ecosystems. However,
this discussion shows that much more information can be obtained
than is presently generated.
Almost every field of science requires substantive financial
resources, and restoration ecology is no exception. In these
financially troubled times where more and more scientists (many
in university positions that depend on outside money) are chasing
fewer dollars, one has no difficulty finding acknowledgment of
this situation in the news media, professional journals, etc.
It is surprising that the very substantial amounts of money only
recently available for studies in restoration ecology have been
virtually neglected by universities and colleges but not by consulting
firms and research organizations primarily dependent on contracts
and grants. There is little or not incentive to publish in most
consulting firms; however, many individuals do so anyway. In
some research organizations primarily dependent on outside funding,
the incentives may be present, but they are not as great as the
pressures to keep one's salary intact by obtaining still more
funding before publishing the results of the last study. As a
consequence, much information on restoration ecology does not
appear in scholarly, peer-reviewed journals but appears in limited
distribution reports in the "gray literature" -- usually
not subject to anonymous peer review in the same fashion as it
would be in a scholarly journal. This means that the information
is less readily available, and, that when it is available, one
cannot place as great a trust in it as would be possible had it
been subjected to a rigorous peer-review process by a dispassionate
"outside" anonymous reviewer and editor. Furthermore,
articles published in the peer-reviewed journals are generally
criticized in the same or other journals, and mistakes are corrected
publicly. No standard methods are available in the field of restoration
ecology and, as a consequence, little of restoration ecology is
routine. Therefore, the opportunities for basic research are
enormous and funds are available from nontraditional sources that
are not being exploited by the academic community as they should
be. I understand not only the benefits of involvement with industry
and applied problems but also the dangers, although a discussion
of them is beyond the scope of this article. Also beyond the
scope of this article, but important to the field of restoration
ecology, is the stigma often attached by tenure and promotion
committees to the source of the money obtained by a faculty member
to support his or her research.
The primary advantage of restoration ecology research is that
the investigator is forced to study the entire system rather than
components of the system in isolation from each other. It is
simply impossible to restore an ecosystem one species at a time,
and one is thus forced to consider both the structural and the
functional aspects of the ecosystem, including spatial relationships,
species interactions, predator-prey relationships, nutrient and
energy cycling, relationships between the physical, chemical,
and biological components, etc. One of the most compelling reasons
for the failure of theoretical ecologists to spend more time on
restoration ecology is the exposure of serious weaknesses in many
of the widely accepted theories and concepts of today. If the
outcome of a prediction is highly uncertain, the underlying theoretical
constructs are probably not sound. On the other hand, if the
development and function of ecosystems are to be understood, predictive
capabilities necessary for the foundation of restoration ecology
must also be developed.
IV. WHY DO SOME PROFESSIONAL ECOLOGISTS RESIST INVOLVEMENT IN THE RESTORATION PROCESS?
1. Some fear that admission of even partial effectiveness in restoration
will be viewed as a license for further ecological destruction
in the name of progress and growth. They further fear that some
of the wilderness areas, national parks, and other ecosystems
that now have exceptional protection will have this protection
reduced as a consequence of the feasibility of repairing damage
following exploitation of various resources in these systems.
Some attempts will almost certainly be made to intrude on previously
protected areas on the grounds that the restoration process is
now sufficiently advanced to make this possible. However, if
the true cost and difficulties of restoration are made abundantly
clear and responsibility for them correctly assigned, these costs
will probably be a major deterrent to disturbing ecosystems of
any kind. In addition, once costs become a major factor, great
care will be taken during the period of disturbance to minimize
the cost of restoration. As usual, the situation is one of balanced
risks and benefits.
2. Many ecologists wish to be considered theoretical ecologists
and disdain the term "applied ecology". This is true
even in land grant universities and other academic institutions
where service to society is part of the mission of the institution.
Even ecologists now working for consulting firms entirely on
applied problems frequently hasten to tell anyone who will listen
that this is merely a stop gap job until a "real position"
in theoretical ecology materializes. The fears of these individuals
are not without foundation. Tenure and promotion committees regularly
make distinctions on the source of research funding, and a dollar
from the National Science Foundation carries more weight with
such committees than a dollar from a mining company. Unfortunately,
traditional positions are unavailable for all the theoretical
ecologists now in the marketplace, and no substantial number of
new positions in the customary institutions is likely to materialize
in the foreseeable future. On the other hand, the prospect for
positions in applied ecology is very heartening. It is quite
possible that an ecologist doing applied research might have more
opportunity to carry out theoretical work than in some of the
positions with heavy teaching loads that theoretical ecologists
are now accepting.
3. Ecology is a relatively new field and its predictive capabilities
vary enormously. In some situations, the probability of predictions
being accurate approach 100%. In other cases, predictions may
be correct <10% of the time. Precise predictions of the outcome
or restoration practices will be, for some time, an area in which
the outcome is highly uncertain. Naturally, ecologists are apprehensive
about venturing into a field where they have less confidence in
their pronouncements than they do in many other areas of ecology.
V. WHY ARE ENVIRONMENTALISTS FREQUENTLY AGAINST DEVELOPMENTS IN RESTORATION ECOLOGY?
1. The environmental movement that expanded enormously during
the earth day periods has been confrontational for many years.
Environmentalists have won some of their most significant victories
in courts of law. Restoration ecology, if it is to be successful,
requires close collaboration between the academic community, the
environmental groups, regulatory agencies, and industry. The
three latter groups have regularly confronted each other in court
for more than a decade. Members of the academic community collaborate
with each of the other three groups, often simultaneously, although
individual ecologists of the academic community are mostly more
or less in one "camp" (i.e., environmental group).
Because the outcome of any course of action in restoration ecology
is uncertain at this early stage in the development of the field,
the best results will only be obtained with an attitude of mutual
trust. This is difficult to ensure with the history of confrontation
that has been characteristic of the group interactions for many
years and is still continuing.
2. Environmentalists have been strongly protection-oriented regarding
use of the environment. There are excellent historical reasons
for this, as well as present ones. Restoration of damaged ecosystems
focuses on multiple use, environmental management, and a variety
of other practices that are alien to the protectionist point of
view. However, if decision analysis is used in reaching management
goals and if all major contending parties have a say about desirable
environmental quality and condition, this public discussion will
do more for the environment as a whole than any course of action
that could be taken. At present, the environment is being protected
in fragments when protecting a whole system would be better.
Ideally, restoration ecology would force examination of the larger
system if only because the organisms for recolonizing damaged
areas must frequently come from outside the damaged system. Also,
determining what kind of restoration is possible necessitates
looking at the larger system into which the restored area must
fit. As a consequence, public attention must necessarily expand
to geographic areas it might not otherwise consider.
VI. IS RESTORATION THE ANSWER TO ALL THE PROBLEMS?
Restoration is an admission that environmental quality was not
protected? It is in many ways analogous to the relationship between
preventative medicine and surgery -- when damage has occurred,
a method of quick repair whenever possible is reassuring, but
avoiding the damage in the first place would have been better.
In some cases, mismanagement, accidental spills due to faulty
equipment or operator error, or deliberate damage to an environment
while extracting fossil fuels or minerals will leave an ecosystem
so seriously damaged that normal recuperative processes will not
suffice, and management intervention is mandatory. Knowing when
to intervene requires more skill and judgment than one might suppose.
For example, following the wreck of the oil tanker Torrey
Canyon, some cleanup methods appear to have caused more damage
to the indigenous biota than the oil itself. In addition, an
equilibrium was restored more readily to the natural systems where
no intervention occurred than those with intervention. Careless
use of suction devices, scrapers, dispersants, and the like may
cause more stress to the ecosystem if improperly used than the
material of the spill itself.
Damaged ecosystems can often be used for partially replacing
systems lost elsewhere. In Wetlands and Water Management on
Mined Lands,4 abundant evidence is given that surface mined
land can be used to create wetlands where none existed before.
Since natural wetlands are being lost to agriculture (~ 80% of
the loss) and for building construction and other purposes (20%)
at a frightening rate, the replacement of many of their functions
elsewhere has positive features. The book is quite readable,
although some technical knowledge is required for some passages.
The basic message of the book -- highly productive artificial
wetlands are used by water fowl, deer, and other organisms --
is reassuring. Furthermore, artificial wetlands are extremely
useful, at least in the short term, for improving water quality
by acting as a trap for heavy metals and other toxicants and for
adjusting the pH of the water and making other water quality improvements.
There is also evidence in the same volume that overloading the
systems will impair their ability to function effectively, a statement
that would be platitudinous were it not for the fact that people
are regularly overloading natural systems and are probably likely
to do so for artificial systems. The possibility of replacing
wetlands on systems where other types of ecosystems formerly existed
should not diminish the efforts to protect the remaining valuable
wetlands in the contiguous U.S.
VII. CLOSURE OF HAZARDOUS WASTE SITES
Although the precise number of hazardous waste sites in this
country is controversial, the number is unquestionably exceedingly
large. They represent a particular challenge in the restoration
of damaged ecosystems -- they must be restored without further
hazard to human health and the environment. Several major options
are available.
Option 1 -- Detoxify the site and restore to original
condition or some alternative ecologically stable condition.
Option 1, though highly desirable, is probably possible only in
areas where the hazard is minimal and the original ecological
condition well known.
Option 2 -- Option 1 may be technologically impossible,
or the cost may be prohibitive. In some cases, collecting the
waste is difficult because of leakage and other problems, and,
even when it is collected, detoxification through incineration
or and some other means such as chemical treatment may not be
either economically or technologically feasible. On these sites,
the primary objectives would be to exclude the general public,
migratory water fowl, and so no to reduce or eliminate the changes
of inadvertent exposure to hazardous materials and to immobilize
the waste so that adjacent areas are not contaminated. Avoiding
contamination of groundwater is particularly important in this
regard. Site restoration can be carried out so that evapotranspiration
of water is enhanced, thereby reducing contamination of groundwater
supplies. In addition, it may be possible to utilize some form
of treatment. The rehabilitation processes in ecological terms
for Option 2 are not well designed to date, but they offer a particular
challenge in restoration ecology. Some of the management measures
that may be taken in structuring soil profiles and the like can
be adapted from those already proven effective for reclamation
of surface mined areas.5
Option 3 -- A third and economically more palatable option
is to remove and treat those portions of the hazardous waste still
in a relatively concentrated form (i.e., in storage containers
and the soil immediately surrounding containers if there has been
leakage) and to leave the partially dispersed and transformed
wastes that are difficult to collect and treat on the site until
natural transformations continue. Certain types of radioactive
wastes with a known decay time might be particularly appropriate
test cases for this strategy. In this particular situation, it
will be important to determine what rehabilitation processes to
use to immobilize the hazardous material on the site and to determine
whether limited use is possible after the initial rehabilitation
is completed. An additional requirement for this option would
be to develop an ecosystem that would be compatible with the surrounding
ecosystem and merge with it eventually. In Option 2, a case could
be made for a totally different ecosystem than the surrounding
ecosystem due to more limited access, a higher degree of hazard
and risk, and the pressing need to contain or immobilize hazardous
wastes. In Option 3, all these strategies might be done initially,
perhaps with revegetation and associated other biota that would
gradually be replaced as the hazard diminished since the transition
time would be markedly less than that for Option 2.
Option 4 -- The fourth option is to reduce the hazard
or risk to a level considered acceptable to society and then to
restore the site to either original condition or to some alternative
ecosystem (such as a wetland) that would be acceptable to society.
Although this may appear to be the most costly in the short term,
in the long term it may prove to be the least expensive. A hazardous
waste site where the chemicals are merely stored must be constantly
monitored to determine that no groundwater is being contaminated
or other movement is occurring in the toxic material from the
site. If this is done properly for air, ground-, and surface
water, and soil, the annual cost might be very great indeed.
Such monitoring quite likely would be needed for a number of years.
In addition, keeping humans and animals off the site is a problem.
This would require physical barriers at the very least and, probably
for the very hazardous sites, some type of security force. Finally,
it is difficult to give absolute assurance that some natural disaster,
such as an earthquake or hundred-year flood, will not render the
safety measures ineffective.
Closure of hazardous waste sites represents a great opportunity
and challenge for restoration ecologists. A glance at a map of
the sites identified in the contiguous U.S. will show that they
occur in a wide variety of climatic regions where the temperatures,
rainfall, soil profiles, and biota are quite different. The types
of problems posed by the hazardous wastes themselves are equally
diverse. Although much remains to be done, a considerable body
of information is available on the physical and chemical constraints
of site closure. Ecological prerequisites and constraints are
not nearly as advanced. Without in any way denigrating the complexity
and difficulty of solving the physical and chemical problems,
it is fair to assert that the ecological problems are at least
as complex and, quite likely, more so. Given the rather high
cost of chemical analyses these days, particularly for exotic
chemicals in low concentrations, and the cost of boring sampling
wells to plot the extent of groundwater contamination, the cost
of getting suitable ecological information is almost certainly
no greater than these costs and may well be less. As a consequence,
it seems unfortunate that funds for the development of the ecological
information base have not been available as they have for the
chemical and physical information bases. Part of the responsibility
for this lack of funding should be assigned to the community of
ecologists who have not made as good a case for the generation
of the necessary information as have the other professions.
Every site will be considered experimental for the near future
in regard to the ecological component of closure of hazardous
waste sites. Therefore, legislation that is too prescriptive
will hamper the generation of necessary research information to
improve the ecological capabilities and the rehabilitation and
site closure process. Unfortunately, many industrial organizations
are unwilling to spend significant amounts of money on the ecological
component of hazardous site closure unless regulatory requirements
demand it. In order to ensure minimal performance levels in this
activity, regulations tend to be quite prescriptive. From an
industrial standpoint, this position is acceptable. Industries
wish to know that their competitors are incurring the same costs,
and, equally important, they wish to be able to predict accurately
the cost of every component of their operations. Treating the
closure of each hazardous waste site as an experimental or research
project almost ensures that the cost will not be identical for
each site and that the precise cost of achieving the ecological
objectives cannot be estimated with precision. One possible solution
to this dilemma is to allow industries to accept one of three
alternatives. (1) A certain set of objectives must be met (i.e.,
the closed site will not be hazardous to human health and the
environment) and the company will be left to meet these requirements
in its own way. If this can be done in a cost-effective manner
that produces acceptable results at a lower cost than the other
options, those companies with enough integrity to achieve this
should be encouraged to do so. Of course, the criteria would
have to be more explicit than those just give for illustrative
purposes, but the strategy of placing the burden of reaching the
objectives on the industry that created the problem is not without
precedent. For example, Section 316A of Public Law 92-500 permits
steam electric power plants to exceed national and state standards
for thermal discharges if they can demonstrate no harm to the
indigenous biota. This has proven to be ecologically successful
and cost effective for industry and has generated much useful
information. (2) A second option is to have highly prescriptive
regulations using the best available methodology with an appreciable
safety factor added for hazardous waste concentration due to the
inadequacy of available information. These regulatory requirements
would be updated periodically as new information becomes available,
just as they have been with toxic substances. (3) The industry
could agree to the site being used as an experimental site with
the understanding that it would pay a sum comparable to the sum
required for prescriptive Option 2 and that cost beyond that would
be borne by some governmental agency, research foundation, or
a consortium with a common interest in resolving this problem.
This would enable society and the industry to share research
costs, would enable the industry to predict the amount to be expended,
would ensure equitable treatment with those industries following
the prescriptive regulations, and would ensure a lower cost for
the research information needed by society since only a portion,
not the entire cost, would be borne by the government.
I favor Options 1 and 3 because either would generate useful
research information. Even some useful information can be generated
by Option 2, if performance monitoring and quality assurance information
are generated during the closure process. Probably a mixture
of all four options would provide the ideal information base at
the lowest cost to society. Another major advantage of following
this course of action is that the research will, in all cases,
be carried out on already damaged sites. If industry is not involved,
it may be necessary to damage additional sites to obtain the necessary
research information -- a course of action that should not be
palatable to very many people.
VIII. FUTURE NEEDS
Effective ecosystem restoration or rehabilitation cannot be accomplished
without good science. Among the many prerequisites for good science
is the willingness to share existing information, to construct
and test hypotheses and models, to validate predictions made from
present information and make the necessary corrections when the
predictions prove unsatisfactory, and to develop quality assurance
programs so that errors can be corrected. Ecosystem rehabilitation
and restoration, particularly when alternative ecosystems are
used to replace the damaged ecosystem, require a close collaboration
of industry, regulatory agencies, scientists and engineers, and
the general public or its representatives. In order to accomplish
the necessary tasks, a greater degree of mutual trust is necessary
than now exists. Although this sounds utopian, the restoration
of Lake Washington in the U.S., the Thames River and Estuary in
the U.K., and numerous other examples show that this is possible.
Although much of the early success in protecting the environment
was the result of litigation, examples are now emerging of more
funds being expended in litigation than it would cost to resolve
the problem with existing methodology. Possibly equally important
is the prescriptive way that laws and regulations are written.
They are frequently so detailed and specific that they discourage
innovative, creative approaches to solving problems, One consequence
of this is that the regulated and the regulators are pitted against
each other in such as way that simple solutions to obvious problems
are often hampered or ignored because of legal technicalities.
Courts of law are not conducive to good scientific judgments.
In order to accomplish the objectives outlined in this discussion,
industrial support for research projects will be essential since
the traditional sources have less money than they once did and
because most of the existing funds in many of the major foundations
supporting biological research go to purely theoretical, as opposed
to applied, problems. Some of the money now spent in litigation
will have to be diverted to generating a good scientific base
that should then reduce the legal battles further. A whole generation
is accustomed to taking environmental problems to a court of law
instead of a science court, and much effort, mutual understanding,
and tolerance will be required to change direction. I am persuaded
that there is no other way to address some of the problems briefly
presented here.
REFERENCES
1. Hopcraft, D., Productivity Comparison Between Thomson's
Gazelle and Cattle, and Their Relation to the Ecosystem in Kenya,
Ph.D. thesis, Cornell University, Ithaca, N.Y., 1975.
2. Arman, P. and Hopcraft D., Nutritional studies on East
African heriboves. I. Digestibilities of dry matter, crude fibre,
and crude protein in antelope, cattle and sheep. Br. J. Nutr.
, 33, 255,1975.
3. Odum, E.P., Fundamentals of Ecology, W.B. Saunders,
Philadelphia, 1953.
4. Brooks, R.P., Samuel, D.E., and Hill, J.B., Eds. Wetlands
and Water Management on Mined Lands, Pennsylvania State University
Press, University Park, Pa., 1985.
5. Parizek, R.R., Exploitation of hydrogeologic systems
for abatement of acidic drainages and wetland protection, in
Wetlands and Water Management on Mined Lands, Brooks, R.P.,
Samuel, D.E., and Hill, J.B., Eds., Pennsylvania State University
Press, University Park, Pa., 1985, 19.
By permission: CRC Press, Inc.