A critique for current research practices in limnology
Thomaz, SM.1*, Bini, LM.2 and Carvalho, P.1
1
Universidade Estadual de Maringá, Nupelia, PEA-UEM
Av. Colombo, 5790, CEP: 87020-900, Maringá, PR, Brasil.
E-mail: smthomaz@nupelia.uem.br
2
Departamento de Biologia Geral, ICB, Universidade Federal de Goiás
CP: 131, CEP: 74001-970, Goiânia, GO, Goiás, Brasil. E-mail: lmbini@gmail.com
(With 1 figure)
Key words: limnology, criticism, theory
Palavras-chave: limnologia, crítica, teoria
Abbreviated title: A critique for limnology
*
Author for correspondence:
Sidinei Magela Thomaz
Universidade Estadual de Maringá, Nupelia, PEA-UEM,
Av. Colombo, 5790, CEP: 87020-900, Maringá, PR, Brasil.
E-mail: smthomaz@nupelia.uem.br
Abstract
Despite a strong contribution limnologists gave to general ecology in the past, leadership was
lost by limnology and criticism on this science became common place after the 1980s. Here,
we discussed some possible reasons that would explain the current weakness of limnology.
We claimed that the overemphasis on physical and chemical processes of freshwater
ecosystems and the need to solve practical problems were, probably, the main causes of
weakness of this field. The same rationale can be applied for the teaching of limnology, which
in our opinion should be taught focusing mainly upon concepts, but not on limited approaches
focused on specific groups of organisms. Thus, we are advocating that limnologists need to
increase the diversity of approaches, giving the importance that ecological theory deserves.
Resumo: Uma crítica para as atuais pesquisas limnológicas
Apesar da forte contribuição da pesquisa limnológica para a teoria ecológica geral no passado,
sua liderança foi perdida e a partir da década de 80 essa ciência foi freqüentemente criticada.
Nesse artigo, nós discutimos as possíveis razões que explicariam a atual fragilidade da
limnologia. Nós sugerimos que a ênfase exagerada nos estudos que abordam os processos
físicos e químicos dos ecossistemas aquáticos e a necessidade de solucionar alguns problemas
práticos, foram as principais causas da fraqueza dessa área. O mesmo raciocínio pode ser
empregado quando analisamos o ensino da limnologia que em nossa opinião deveria ser
focado, principalmente, em conceitos, e não em abordagens limitadas que focam grupos de
organismos. Portanto, nós sugerimos que os limnólogos necessitam aumentar a diversidade de
abordagens, dando a importância que a teoria ecológica merece.
2
“Since part of the cure for weak sciences is unrelenting
critical reevaluation of its parts, the recognition of weakness
augurs for a return to growth and development, perhaps
even for a scientific revolution. Therefore flourishing
criticism is not negative or damaging to the science. It is
part of rebirth. It is essential to growth.” R. Peters
Introduction
Limnology was considered a branch of ecology since its beginning and its contributions
to concepts and theory for general ecology are well known (e.g., Forbes, 1887; Lindeman,
1942; Hutchinson, 1959). Despite these past contributions, leadership was lost by limnology
and criticism on this science became common place after the 1980s. Several authors
considered the scientific weakness of limnology and proposed a predictive approach in an
attempt to circumvent this weakness (Rigler, 1982; Peters, 1986; Kalff, 1991; Rigler and
Peters, 1995). In general, this approach sustains that limnology should focus mainly on
solving the problems related to water ecosystems faced by society, like eutrophication and
fisheries (Kalff, 1991; Rigler and Peters, 1995).
Although recognizing the importance of a problem-solving approach, others argued that
understanding (not only predicting) was necessary to launch limnology into maturity (e.g.,
Lehman, 1986; Wetzel, 1991; 1992; 2001). It was also claimed that an overemphasis on
applied issues was the main cause for the decline of limnology´ scientific prestige (Reynolds,
1998; Wetzel, 2001). Thus, it is clear that criticism and discussions about the appropriate
approaches in limnology took different, if not, opposite routes (but see Pace, 2001, for a
reconciliation between the predictive and understanding approaches).
3
A third group of critics on limnology did not focus on philosophical aspects, but
proposed agendas with specific topics and/or concepts that are not being properly addressed
by limnology but that could contribute to its advance. Wetzel (1992), for example recognized
several important directions poorly approached by limnologists (e.g., microbial, biochemical
and genetic limnology, among others). More recently, Reynolds (1998), showed concern
about the state of limnology, but he also indicated several possible avenues based on concepts
developed by limnologists, trying to integrate them as an organized body of concepts. A more
optimistic view, debating Reynolds’ arguments, was presented by Harris (1999), who based
on the concept that ecosystems “may well be a lot simpler than we think” also offered several
possibilities for the development of limnology.
Finally, comments and criticism of current practices in limnology have also been made
concerning philosophical and methodological problems. For example, Bourget and Fortin
(1995) showed that limnological research was mainly descriptive, rather than experimental,
and instead of testing hypothesis, most studies refined descriptive methods increasing their
precision, believing that by better describing patterns could increase confidence in untested
mechanism. These authors also criticized the excessive databases accumulated by
limnologists, which did not necessarily contribute to scientific advances.
Limnology is a multidisciplinary science, which has been tough in a variety of
departments and, consequently, different definitions and emphases occur (MacDonald, 1996).
At this point, it is important to rescue the original meaning of limnology: “the study of the
structural and functional interrelationships of organisms of inland waters as they are affected
by their dynamic physical, chemical, and biotic environments” (Wetzel, 2001). Thus,
limnology is essentially an ecological, not a chemical, physical or social science (e.g.,
McIntosh, 1985; Lampert and Sommer, 2007; Wetzel, 2001).
4
Unfortunately, as we will try to show here, limnological investigations have been largely
ignoring its ecological roots or, at most, repeating old and obsolete approaches. Still, as
already recognized ten years ago by Reynolds (1998), freshwater ecology (or limnology) is
still dominated by ideas of terrestrial ecologists. Inspired in Rigler and Peters (1995), we will
discuss the evidences of its weakness and the probable causes for such weakness. Then, we
point for some directions toward recovering the importance that this science had in the past.
Most of our arguments are based on our experience as aquatic ecologists, but we always tried
to corroborate our ideas with data obtained with analyses of textbooks, scientific journals or
specific papers.
Symptoms of weakness in limnology
We think that a first and simple way of checking for weakness may be to count how
many papers produced by limnologists were included in the book Foundations of Ecology
(edited by Real and Brown in 1991), which compiles the 40 most influential papers upon
theoretical development of ecology, produced from 1887 to 1974. An inspection of the papers
contained in this book shows that after 1950 (considering that we are more interested in
modern contribution of limnology), only three, out of 26 papers, were produced by
researchers recognized by their contribution in the field of Limnology: Hutchinson (1959),
Brooks and Dodson (1965) and Likens et al. (1970). These papers received 1259, 1612 and
501 citations, respectively (ISI Web of Science, consulted in December 11 2007). These are
certainly important contributions, considering that only 0.01% of all papers published from
1900 to 2005 received more than 1000 citations, and 0.06% received more than 500 citations
(Garfield, 2005). However, three papers are not enough, as 11 contributions published after
1950 in the Foundations were based on typical terrestrial organisms, especially birds,
5
mammals and terrestrial vegetation. This book also has three marine/coastal ecosystems
papers, and thus this field had a similar contribution of limnology.
The leadership of other fields of ecology and their influence on limnology can also be
demonstrated in another way. Some of the most successful and influential ideas permeating
limnological discussions in the last two decades were not first proposed by limnologists, but
they were inspired by ideas from other fields of ecology. We can cite four examples: (i) the
concept of alternative stable states, developed by Scheffer (1990) and Scheffer et al. (1993,
2001), was first proposed by May (1977) and applied to marine communities by Simenstad et
al. (1978); (ii) the concept of functional classification of phytoplankton (Reynolds, 1980), was
inspired on the terrestrial plants relevé method (Tüxen, 1955; Braun-Blanquet, 1964),
according to Reynolds et al. (2002); (iii) the relationship between diversity and ecosystem
functioning (e.g., Engelhardt and Ritchie, 2001) was first applied to terrestrial plant
communities, both in environmental chambers (Naeem et al., 1994) and in the field (Tilman et
al., 1996); (iv) the plant strategy approach, successfully used to classify aquatic macrophytes
(e.g., Murphy et al., 1990) was based on Grime’s studies (1979) on terrestrial vegetation. Of
course, limnologists further developed these concepts and contributed to their advance.
However, we have to admit that despite the seminal papers produced in the first half of the
20th century by limnologists, which inspired generations of ecologists (e.g., “The trophic
dynamic aspect of ecology” by Lindenan, 1942 and “Homage to Santa Rosalia” by
Hutchinson, 1959), the breakthrough concepts in the last two decades were not proposed by
limnologists, but by terrestrial, marine or theoretical ecologists.
The weakness in limnology can be also verified by comparing the impact factors (IFs) of
ecological journals of recognized prestige with those of limnology and how they changed over
time (Peters, 1991). Although it must be taken with caution (e.g., Amin and Mabe, 2000;
Rossner et al., 2007), IF is considered nowadays one of the most important ways to measure
6
impact of individual journals (Amin and Mabe, 2000; Garfield, 2005). We did this search by
using exactly the same leading journals considered by Peters (1991: page 9). It was clear that
the IFs of four, out of five journals of ecology considered in his book (namely Annual Review
of Ecology and Systematics, The American Naturalist, Evolution and Ecology) increased (50%
to 73%) between 1985 and 2006, while the IFs of the limnological journals quoted by him
(Limnology and Oceanography and Canadian Journal of Fisheries and Aquatic Sciences)
remained almost constant (increases of 3 and 5%, respectively). Still, since Peters’ book,
journals in ecology with high IFs were created (e.g., Ecology Letters, IF = 7.5, and Frontiers
in Ecology and the Environment, IF = 4.8), but none with such high IFs appeared in
Limnology. Thus, also by using the same approach and journals quoted by Peters (1991), the
relative weakness of limnology, compared to general ecology, remained apparent in the last
two decades.
We applied the same procedure to a wider data set, taking IFs of journals of general
ecology, limnology and marine sciences / oceanography, obtained at the Journal Citation
Reports (ISI Web of Knowledge, 2006). By ranking the IFs (as the well known Whittaker
plot, used by ecologists), it was clear that journals in ecology have higher IFs than those in
limnology and marine sciences (Figure 1). It is also intriguing that three, out of the top five
limnological journals, can not be considered traditionally concerned with theoretical or
conceptual aspects of this science, since they deal mainly with paleolimnology (Journal of
Paleolimnology) or applied issues (Aquatic Toxicology and Limnology and OceanographyMethods). Thus, also by using this criterion the limnological journals are near the marine
ones, but both are positioned behind the general ecology journals.
>>> Figure 1
7
Thus, it seems that limnologists are not producing new concepts or theories appealing to
a broader public in ecology. We interpret these results as signs of weakness of limnology, and
will discuss below possible causes for it.
Possible causes of limnology weakness
Overemphasis on applied issues and on old concepts
The emphasis on physical and chemical processes of freshwater ecosystems was clear
since the beginning of limnology and it is comprehensive given the importance these
processes on aquatic biota and ecosystems functioning (McIntosh, 1985; Wetzel, 2001).
Although this emphasis obviously brought important contributions to ecology, in particular
with regard to advances about nutrient cycling and about the human impacts upon ecosystems
(e.g., Likens et al., 1970), this over-emphasis probably contributed to one of the reasons of its
weakness: the search of solutions for immediate problems caused by pollution and
contamination.
For instance, limnologists are profoundly interested in eutrophication. There is nothing
wrong about studying eutrophication, given this is still (and sadly will remain) one of the
greatest problems regarding water quality worldwide (Carpenter, 2005). However, the
mechanisms behind eutrohication were long understood and achieved (Vollenweider, 1968;
Schindler, 1977). Techniques to solve eutrofication (e.g., effluent treatment, good agricultural
practices – GAP) also became common place all over the world, although costs associate with
them can be impeditive in developing countries. In addition, and after Richard A.
Vollenweider seminal contribution, considered by some as one of the greatest practical and
theoretical contributions of limnology (Kalff, 1991; Righer and Peters, 1995), solving
problems of eutrophication became common place for several other professionals (e.g.,
8
engineerings, applied chemists etc.). If these water problems persist, we cannot blame the lack
of scientific knowledge. They persist due to lack of political actions that would overtake the
causes of eutrophication. To fight in this arena, we can only use, as citizens, our scientific
reputation to persuade politics, but it is not science.
The overemphasis on solving practical problems was also recognized by Wetzel (2001),
for whom “Limnology is currently experiencing a period of introspection. ...Many problems
have arisen, however, in part because of the purported necessity to respond rapidly to
governmental and societal demands without an in-depth scientific underpinning.” Lampert
(2007) argues the same concern and in a recent article commenting about the end of the
traditional Max Planck Institute for Limnology at Plön, Germany, affirms that “at least in
Europe, limnology as a whole did not lose importance, but curiosity-driven, fundamental
research with potential for discoveries and the development of new paradigms is declining”.
This rationale leads naturally to a comparison with physics, considered the model of
hard sciences. It is clear that theoretical physicists still find place all over the world, even in
small universities, and they study issues which are not always immediately applied (see
Pigliucci, 2002 for a similar content about ecology and evolution). However, many times their
theories are used by a variety of more “applied” fields, especially in engineering. Again, why
should we limnologists attribute lower value to theory, compared to practical problems, and
justify our proposals to obtain funds always on solving problems of pollution, contamination,
eutrophication and fisheries? The obvious answer seems to be that if we do not do that we will
not get funds. Although partially true (we will discuss this later), we should ask why we are so
weak in convincing society, managers and funding agencies about the importance of
producing concepts and theories, a task that physicists do very well.
The tendency of paying less attention to emergent issues in ecology can be illustrated
taking into account a hot theme: biodiversity and conservation. Fundamentals about
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biodiversity and its relationship to community stability and ecosystem functions were
primarily developed in terrestrial ecosystems (McNaughton, 1977; Tilman and Downing,
1994; Tilman et al., 1996), but tests of these theoretical advancements in aquatic ecosystems
are still infrequent (Harris, 1999). The paucity of research on the design and management of
freshwater protected areas has also been a serious obstacle to establish conservation goals
(Saunders et al., 2002). In general, freshwater habitats are usually protected as an appendix of
terrestrial ones and frequently their protection follows designs addressed for terrestrial
ecosystems (Saunders et al., 2002; Agostinho et al., 2005). In fact, in 2007 only 3% of the
papers published in Conservation Biology concerned freshwater habitats, while 8.3%
concerned marine, 36.1% were theoretical or miscellaneous, and 46.3% were developed in
terrestrial habitats. Again, it suggests that limnologists are not producing papers on this issue,
despite the fact that aquatic ecosystems are experiencing the highest rates of species
extinction (Jenkins, 2003; Saunders et al., 2002). One of the most influential papers in
ecology and conservation in the last decade is about the concept and identification of hotspots
(Myers et al., 2000). All rationale behind hotspots came from terrestrial ecology. Much work
has also been done, but few investigations address the concept of hotspots to freshwater
ecosystems (e.g., Chernoff et al., 2000; McCullgh et al., 2002). We should ask: it is not the
time to identify and amplify this concept for freshwater ecosystems?
Overemphasis on species or groups of organisms
Freshwater ecosystems offer excellent opportunities to test general hypotheses and
propose new concepts. For example, they are relatively easy of conceptualizing, physically
bounded, their biota’s ecology is subject to tangible properties of the environment readily
comprehended and easy to manipulate, and still the responses of aquatic species and
communities are compatible with the time scales of the human observer (Reynolds, 1998, but
10
see Bourget and Fortin, 1995, for a different opinion). In addition, size spectra, trophic
structures, stoichiometric ratios and empirical relationships are particularly easy to measure in
pelagic ecosystems because of the small scale of many of the organisms (Harris, 1998).
It seems that limnologists do not take the opportunity of using these advantages to
propose and test general ecological concepts. Differently from terrestrial ecologists,
limnologists devote excessive emphasis on specific groups of organisms (or, “aquatic
communities”). For instance, textbooks in general ecology usually are divided in chapters
dealing with “habitats”, “populations”, “communities” and “ecosystems” with their related
sub-topics (e.g., succession and diversity in community ecology). Differently, textbooks in
limnology prioritize specific aquatic communities (“plankton”, “nekton”, “macrophytes”,
etc.), in addition to the physical and chemical aspects (chapters are usually titled as
“temperature”, “oxygen”, “phosphorus”, etc.), as discussed previously (but see Limnoecology,
by Lampert and Sommer, 2007, which is an excellent exception). This tendency shows clearly
that textbooks in general ecology are more interested in theories and concepts, which can be
applied to all organisms, populations, communities or ecosystems, while textbooks in
limnology are more interested in specific variables related to the abiotic environment or to
specific aquatic communities sharing the same habitat. Such historical differences in
textbooks certainly influenced how we learned and strongly affect how we teach limnology.
This separation amongst groups of organisms sharing similar characteristics in freshwater
ecosystems is also reproduced in laboratories, which are excellent in training specialists in
taxonomy or specific ecological features of a certain group, but usually fail in training
students to understanding ecological theories.
Overemphasis on concepts exclusive of aquatic ecosystems
11
It is obvious that limnology, as a science, has to deal with aquatic ecosystems. However,
there are several concepts and theories produced by terrestrial ecologists that are relevant to
aquatic ecologists. Why is the opposite so rare? Again it seems that in addition of being
focused on specific groups of organisms, limnologists also overemphasize processes and
mechanisms found exclusively in aquatic ecosystems, loosing the chance of testing and
producing more general concepts and theories. The seminal contribution of Forbes (1887),
“The lake as a microcosm”, is an example showing that it is possible to produce general
ecological theory using an aquatic ecosystem. Differently, some of the most influential papers
produced in limnology in the last three decades (e.g., the River Continuum Concept, Vannotte
et al., 1980, and the Flood Pulse Concept, Junk et al., 1989) are restrict to aquatic ecosystems.
Despite overemphasizing problems restricted to water ecosystems, some concepts
developed by limnologists have the potential of being widely applied. For example, Wiens
(2002) stressed that riverine ecosystems may provide excellent opportunities for developing
and testing landscape ecological theory. However, as discussed by Reynolds (1998), when
ideas have developed mainly within aquatic ecology (e.g., trophic cascades – Hrbáčzek et al.,
1961; Carpenter et al., 1985) they remain restricted to the limnological realm. Maybe the
mistake here is that limnologists do not know (or know poorly) how to demonstrate and
convince general ecologists about the generality of their concepts. This failure may also be
due to lack of consensus in limnology about the major scientific problems to be solved (Kalff,
1991), leading to lack of discussions and more theoretical based papers.
Concluding remarks and perspectives
We regret to repeat what was written ten years ago by Reynolds (1998): “In short, basic
freshwater science is in a poor state of health”. Partially, we think this may be attributable to
12
the fact that we abdicated from prioritizing theory and focus much more on immediate
application of the limnological knowledge.
After presenting such deep criticism on the way we limnologists are conducting our
research, certain pessimism may merge and an obvious question is asked: how can we
overcome these weaknesses and promote progress in our science? Some have a philosophical
way to do so, as for example, advocating for a complete change in the approach used in
limnology (Rigler and Peters, 1995). Others offer agendas with specific topics that should be
investigated by limnologists (e.g., Reynolds, 1998; Harris, 1999). We do not have magical
answers, neither do we intend to compete with suggestions offered by these authors.
However, as a corollary of some of the points advocated by us, we can offer some alternatives
to overcome the limnology weakness.
Firstly, the emphasis on groups of organisms (or “aquatic communities”) should be
changed towards emphasis on concepts and theories. We forecast that great advances would
be reached if aquatic communities were considered as models to test concepts and theories,
and not the main aim of investigations per se. It does not make much sense to divide
limnology in areas like “fish ecology”, “plankton ecology” or “macrophyte ecology”. General
ecological concepts can be tested with any of these particular communities and thus, the
concepts should become the central focus of limnological studies. Aquatic communities can
diverge concerning specific aspects, such as methods of sampling, environmental optima,
tolerances or dispersal ability, but general theories or concepts should be tested considering
any group and this should be the focus of limnological studies. Along this line, and trying to
establish the elements of a linkage between terrestrial and aquatic ecology, Wiens (2002)
pointed out that the traditional distinction in ecology between if something is happening on
land or in water is of minor importance in the context of landscape ecology and he concludes
13
that the spatial patterns, relationships and processes are what matter, not the substrate or the
medium.
The same rationale can be applied for the teaching of limnology, which should be taught
focusing mainly upon concepts. Wetzel (1991; 1996) also recognized that limnology was not
taught adequately (at least in the US), but his point of view was based much more on lack of
integration among different fields (e.g., physical, chemical and biological facets). He even
presented a proposal with disciplines necessary to form well trained limnologists. Although
agreeing with Wetzel, we think that in addition to the need of being more integrated, advances
will be reached only if teaching limnology was driven mostly on concepts and theories, not on
specific groups or organisms or physical and chemical variables.
Secondly, by attaining the importance of theory, limnologists should be aware of new
frontiers and hot topics appearing in the most influential journals of ecology and rapidly
testing these new concepts in aquatic ecosystems – timing is everything. There are excellent
examples of such advances in limnological research when this is done (e.g., alternative stable
states by Scheffer, 1990 and phytoplankton functional classification by Reynolds, 1980;
Reynolds et al., 2002). We should be concerned about remaining so behind the new issues
appearing every day in the literature. In addition to keeping us behind developments in
general ecology, it still delays development of concepts useful for applied issues. However,
we emphasize that only applying concepts and testing theories generated by other fields is not
enough and leadership will only be achieved again if new, more general, concepts and
theories are produced by limnologists. As we commented earlier, examples by Forbes,
Lindeman and Hutchinson should always serve as inspiration for new generations.
Thirdly, and probably most difficult, is how to address the overemphasis on applied
issues. It is apparently a dead-end, since most advocate that if we do not do applied science,
we do not get funds. We think that this reasoning is only partially true. Firstly, we have to
14
convince ourselves about the importance of formulating and testing ecological theories. Many
of us judge grant applications or review manuscripts for scientific journals and ask the
investigators where that work will be applied. Two of us are Associate Editor of
Hydrobiologia and it is noticeable the high frequency of submitted manuscripts in which the
authors call the attention of the potential usefulness of their results in applied issues, even
when these potentialities are clearly tangential. We too often forget that scientific curiosity
should be enough for publication. Thus, if many of us act this way, what can we expect from
our agency decision makers?
Also, good science does not necessarily need too much money (Wetzel, 2001; Harris,
1999) neither too much data (Bourget and Fortin, 1995). This is especially true for theoretical
work and it would release us from relying on great amounts of money given by financial
agencies. Along this direction, it is inspiring to think on the elegance and simplicity of some
classical experiments in ecology. For example, what can be simpler than avoid predation by
starfish in a small area of rock shore and count the number of invertebrates after a short period
of time? Or cut and weight grasses inside quadrats before and after a drought in prairies?
Nevertheless, the first experiment launched the key-stone species concept (Paine, 1966) while
the second, served as one of the first tests in the field of the diversity-stability hypothesis
(Tilman and Downing, 1994), which had been debated since the 1950ths. Both became
classical contributions to general ecology and are obligatory in any ecological textbook
nowadays.
Finally, we are not advocating that all limnologists give up working with applied issues
and move toward theory. We understand that limnology was and will ever continue to be an
important branch of ecology, with interdisciplinary characteristics and the duty of helping to
solve a variety of problems occurring in aquatic ecosystems, not only related to direct use by
man but also to biodiversity conservation. We just claim that we will not reach these aims
15
without developing new concepts and theories. Thus, increasing the diversity of approaches
and giving again the importance that theory deserves, will certainly help solving
environmental problems and also allow limnologists to contribute to the production of
ecological theory.
Acknowledgements
We are grateful to K. Martens (Royal Belgian Institute of Natural Sciences, Belgium) for his
constructive comments and encouragement. S. M. Thomaz and L.M. Bini are especially
thankful to the Brazilian Council of Research (CNPq), for continuous funding through a
Research Productivity Grant. P. Carvalho is supported by the PDTA program (Fundação
Parque Tecnológico Itaipu – FPTI-BR).
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Legends of figures
Figure 1. Whitaker plot of the impact factors of journals (Journal Citation Reports – ISI Web
of Knowledge 2006) in general ecology, limnology and marine ecology. The five top journals
are TREE, Annual Review of Ecology and Evolution, Ecology Letters, Ecological
Monographs and Frontiers in Ecology and the Environment (general ecology), Limnology
and Oceanography, Journal of Paleolimnology, Aquatic Toxicology, Freshwater Biology and
Limnology and Oceanography – Methods (limnology) and Oceanography and Marine
Biology, Limnology and Oceanography, Paleoceanography, Marine Biotechnology and
Limnology and Oceanography – Methods (marine ecology / oceanography).
22
16
ecology
limnology
marine ecology / oceanography
14
Impact Factor
12
10
8
6
4
2
0
0
10
20
30
40
50
60
Rank
Figure 1
23