EFFECTS OF CLIMATE CHANGE ON WETLANDS
Current state of knowledge regarding the world’s wetlands
and their future under global climate change: a synthesis
Wolfgang J. Junk
•
Shuqing An
•
C. M. Finlayson
•
Brij Gopal
•
Jan Kve
ˇ
t
•
Stephen A. Mitchell
•
William J. Mitsch
•
Richard D. Robarts
Received: 21 February 2012 / Accepted: 24 September 2012 / Published online: 30 October 2012
Ó Springer Basel 2012
Abstract Wetlands cover at least 6 % of the Earth’s
surface. They play a key role in hydrological and biogeo-
chemical cycles, harbour a large part of the world’s
biodiversity, and provide multiple services to humankind.
However, pressure in the form of land reclamation, intense
resource exploitation, changes in hydrology, and pollution
threaten wetlands on all continents. Depending on the
region, 30–90 % of the world’s wetlands have already been
destroyed or strongly modified in many countries with no
sign of abatement. Climate change scenarios predict addi-
tional stresses on wetlands, mainly because of changes in
hydrology, temperature increases, and a rise in sea level.
Yet, intact wetlands play a key role as buffers in the
hydrological cycle and as sinks for organic carbon, coun-
teracting the effects of the increase in atmospheric CO
2
.
Eight chapters comprising this volume of Aquatic Sciences
analyze the current ecological situation and the use of the
wetlands in major regions of the world in the context of
global climate change. This final chapter provides a syn-
thesis of the findings and recommendations for the
sustainable use and protection of these important
ecosystems.
W. J. Junk (&)
National Institute for Science and Technology in Wetlands
(INCT-INAU), Federal University of Mato Grosso (UFMT),
Av. Fernando Corre
ˆ
a da Costa 2367, Bairro Boa Esperanc¸a,
Cuiaba
´
MT, Brazil
e-mail: wjj@evolbio.mpg.de
S. An
The Institute of Wetland Ecology, The State Key Laboratory
of Pollution Control and Resource Reuse,
School of Life Science, Nanjing University,
210093 Nanjing, China
e-mail: anshq@nju.edu.cn
C. M. Finlayson
Institute for Land, Water and Society, Charles Sturt University,
PO Box 789, Albury, NSW 2640, Australia
e-mail: mfinlayson@csu.edu.au
B. Gopal
Centre for Inland Waters in South Asia, National Institute
of Ecology, 41 B Shiv Shakti Nagar, 302017 Jaipur, India
e-mail: brij44@gmail.com
J. Kve
ˇ
t
Faculty of Science, University of South Bohemia,
Branis
ˇ
ovska
´
31, 37005 C
ˇ
eske
´
Bude
ˇ
jovice, Czech Republic
e-mail: Jan.Kvet@seznam.cz
J. Kve
ˇ
t
Institute of Systems Biology and Ecology,
Academy of Sciences of the Czech Republic,
Dukelska
´
145, 379 01 Tr
ˇ
ebon
ˇ
,
Czech Republic
S. A. Mitchell
Water Research Commission, Private Bag X03,
Gezina 0031, Pretoria, South Africa
e-mail: smitch2503@gmail.com
W. J. Mitsch
W. H. Schiermeier Olentangy River Wetland Research Park,
The Ohio State University, 352 W. Dodridge Street,
43202 Columbus, Ohio, USA
e-mail: mitsch.1@osu.edu
R. D. Robarts
UNEP GEMS/WATER Programme,
c/o NWRI, 11 Innovation Blvd,
Saskatoon S7N 3H5, Canada
e-mail: Richard.Robarts@EC.GC.CA
Aquat Sci (2013) 75:151–167
DOI 10.1007/s00027-012-0278-z
Aquatic Sciences
123
Keywords Wetlands Distribution Threats
Management Climate change
Introduction
Although wetlands cover only about 6 % of the earth’s
surface, they play a key role in biogeochemical cycles, are
sources or sinks for carbon, are important buffers in the
landscape’s hydrology, and harbour a large part of the
earth’s biodiversity, including many endemic species. They
provide many services for humans, such as food, water,
recreation and space for living; all large tropical and sub-
tropical wetlands still harbour traditional societies which
have sustainably managed these systems often for centuries
or even millennia.
Wetlands are often considered as wastelands, which
should be transformed to ‘‘useful’’ systems, e.g., by tradi-
tional agricultural, forestry, husbandry and aquaculture, or
for the construction of houses, and infrastructure. Wetland
destruction is advanced in densely populated regions, such
as Western Europe and parts of China, or in countries with
shortages of water, such as Australia, and also in countries
with powerful agro-industries, such as the USA. However,
a global value for ecosystem goods, services, biodiversity,
and cultural considerations of US$ 6,579 9 10
9
year
-1
has
been estimated for all inland waters and wetlands in
comparison to US$ 5,740 9 10
9
year
-1
for all other non-
marine ecosystems combined. The average values per unit
area of rivers (US$ 8,498 ha
-1
year
-1
) and wetlands (US$
14,785 ha
-1
year
-1
) are higher than those of the most
valuable terrestrial ecosystems, such as forests (US$
969 ha
-1
year
-1
) and grasslands (US$ 232 ha
-1
year
-1
)
(Costanza et al. 1997). The numbers of this estimate have
been challenged, especially in relation to the accuracy of
the scaling-out that was done, but there is still no doubt
about the ecological and socio-economic importance of
intact wetland areas (MEA 2005).
The predicted changes in global climate will, among
other impacts, increase temperature, modify the precipita-
tion regime, raise the sea level and increase extreme
climate events. All these changes will have a large impact
on wetlands. But wetlands are not considered adequately in
many climate change scenarios. For instance, predictions
about the future of the Amazon rain forest do not consider
that 30 % of the Amazon basin is composed of wetlands
(Junk et al. 2011).
In response to this situation, we have assembled in this
volume of Aquatic Sciences an overview of the available
information on wetlands from around the world. We
summarize this information in this synthesis chapter and
provide a general global view on wetlands and their role in
a changing world. Specific literature citations are given in
the chapters by Mitchell (2012) for Africa, An et al. (2012)
for East Asia and High Asia, C
ˇ
ı
´
z
ˇ
kova
´
et al. (2012) for
Europe, Finlayson et al. (2012) for Australia, Gopal (2012)
for tropical Asia, Junk (2012) for South America, Mitsch
and Hernandez (2012) for North an Central America, and
Robarts et al. (2012) for Russia.
Wetland extent and classifications
The current distribution and extent of wetlands no longer
coincides closely with that which previously existed; the
conversion and loss of wetlands has seen major changes in
the area and ecological condition of many wetlands. Huge
areas of wetlands have been destroyed in most countries.
On the other hand, wetland restoration and man-made
wetlands are becoming increasingly important. In the USA,
during recent years, wetland restoration has increased the
total area of wetlands. In China, 47 % of the wetlands are
human-made (rice paddy plantations and fish ponds). A
similar situation is found in many tropical and subtropical
SE Asian countries. But wetland destruction continues in
most parts of the world, sometimes at an increasing rate,
because of wetland-unfriendly land-use planning. How-
ever, the exact data about losses are not widely available.
The extent of wetlands is not known for several major
regions, e.g., South America, Africa and Russia, because
detailed inventories do not exist, and the definition of
wetlands is not uniform. Small riparian wetlands along low
order streams, as well as small depression or temporary
wetlands, are often not considered, but may add up to large
areas. For example, in the Amazon basin, these areas may
cover up to 1 million km
2
. Table 1 indicates the order of
magnitude of total wetland area in the regions described in
this volume.
North and Central America cover an area of about
24.9 km
2
and has a population of 529 million inhabitants
(USA 9.83 million km
2
, 308 million inhabitants, Canada
9.98 million km
2
31.6 million inhabitants, Mexico 1.97
million km
2
, 110 million inhabitants). Large parts of
Alaska and Canada have a very low human population
density and are covered by boreal peatlands and permafrost
soils with a high storage capacity for organic carbon. The
central drier part contains the prairie potholes and large
river floodplains of the Mississippi, Missouri and Ohio
Rivers, which join to form a large subtropical delta in the
Gulf of Mexico. Several large wetlands have traditionally
elicited specific attention based on their size, their biodi-
versity, their landscape beauty, and/or their potential for
agriculture, such as the Everglades in Florida. The wetland
area in Mexico and Central America is much smaller than
152 W. J. Junk et al.
123
in the USA and Canada, with most found at or near the
coastlines.
Europe covers an area of 10.5 million km
2
and harbours
733 million inhabitants. The population density is very
high in some West-European countries, e.g., in The Neth-
erlands (380 persons km
-2
) and in Germany (231 persons
km
-2
). This high population density has created heavy
pressure on many wetlands. The abundant peat bogs in
Western Europe have been mined and freshwater marshes
have been reclaimed as valuable arable land. Coastal
marshes and parts of the periodically flooded Wadden Sea
in the North Sea were converted to polders and used for
pastures. Flood protection has eliminated most large river
floodplains; along the Rhine River and on the upper Dan-
ube River only small remnants of the formerly extended
floodplains are left and are now under protection. Major
floodplains exist on the lower Danube and in the Danube
Delta and along Russian rivers. In the European part of
Russia large peat bogs still exist.
Russia covers an area of 17,075,400 km
2
and harbours
143 million people. Large areas support a population
density of \2 persons km
-2
and large near-pristine wet-
lands. About two-thirds of Russia’s land area is covered by
flat lands (lowlands, plains and low hills with average
heights of not greater than 600 m), which contributes to the
development of conditions favouring wetland formation.
Wetlands cover [1.8 10
6
km
2
and are most prevalent in
the north. Some wetlands are expanding, such as in the
West Siberian Plains. Most common are peat bogs that
cover 1.6–1.8 million km
2
corresponding to 1/3 of the
worlds peat lands. In the Russian Arctic 0.75 9 10
6
km
2
of
permafrost wetlands exist. The large Russian rivers are
accompanied by extended river floodplains and large
deltas.
China covers an area of 9.6 million km
2
and harbours a
population of 1.34 billion people. Large areas of the
country, however, have a very low population density
because of an adverse climate, e.g., steppes and deserts and
the Himalayan mountains. For millennia, Chinese wetlands
have been intensively managed by the local population for
rice and fish culture. Near natural wetlands cover an area of
about 362,000 km
2
and correspond to 53 % of the total
wetland area. Human pressure on wetlands is rising, mainly
in the coastal regions. The extended river floodplains along
the large Chinese rivers are heavily affected by reservoir
construction.
South America covers an area of 17.8 million km
2
and
contains a population of 381 million inhabitants. But this
population is concentrated along the coastline and in some
cities along the large rivers. Large areas of South America
have a human population of \2 persons km
-2
and many
near pristine wetlands. South America is a wet sub-conti-
nent. About one-third of its area is covered by tropical
rainforest (biomes of Amazon Rain Forest and tropical and
subtropical Atlantic Forest). It is dominated by large river
systems. The Amazon, Orinoco, and Parana
´
/Paraguay
Rivers have the highest, third, and tenth highest discharge
among the largest rivers in the world and are accompanied
by extended fringing floodplains. Flat interfluvial areas are
periodically flooded during the rainy season and form
extended wetlands. Therefore, most South American wet-
lands belong to the floodplain category with a pulsing
water-level and pronounced dry and wet periods. Perma-
nently waterlogged areas occur mostly under boreal
climatic conditions in Patagonia and in the Andean high
plains. Mangroves cover 45,400 km
2
mostly along the
Atlantic coast, corresponding to 27 % of the world’s total
mangrove area (Lacerda 2002).
Africa covers an area of 30.3 million km
2
and harbours a
population of about 944 million people, Large areas,
however, have a very low population density because of
adverse climatic conditions. The central part around the
equator is covered by the tropical rain forest in the Zaire
River basin. Adjacent to the North and South savannas,
deserts prevail including the Sahara Desert, the largest
desert on the globe. Several rivers, such as the Nile, Zaire,
Niger, Zambesi, and Okavango with fringing floodplains
and internal deltas, dominate the scenario of African wet-
lands. Most of them have a pronounced wet and dry period
and are subject to a flood pulse. Mangroves cover
Table 1 Total wetland area,
area of artificial wetlands, and
percentage wetland area of the
respective land area, where this
is known
? not known
a
Conservative estimate without
Algeria, Egypt, Libya,
Mauritania, Morocco, Tunisia
and Western Sahara, and
without wetlands along low
order rivers and coastal
wetlands
Region Land area (km
2
) Wetlands (tot.) (km
2
) Wetlands (art.) (km
2
) Wetland (%)
N. & C. America 24,900,000 2,490,000 ? 10
Europe 10,000,000 500,000 ? 5
Russia 17,075,400 [1,800,000 ? [10
China 9,600,000 684,900 322,900 7
South America 17,850,000 [3,000,000 ? [20
Africa
a
30,065,000 2,129,285 ? 7
Sub-Saharan A. 23,003,885 2,072,775 ? 9
Tropical Asia 14,536,000 686,570 ? 2.8
Australia 7,692,024 230,077 6,657 3
Current state of knowledge regarding the world’s wetlands 153
123
32,600 km
2
, comprising 19 % of the world’s total. Most
African wetlands have been colonized by humans for
millennia and make an important contribution to the live-
lihoods of the local populations. Increasing conflicts for
water and land threaten African wetlands.
Tropical and subtropical South-East Asia cover an area
of about 24.5 million km
2
and has approximately 2.8 bil-
lion inhabitants. Most areas are densely populated, e.g.,
India with a population of 1.21 billion people and a density
of 350 persons km
-2
. The monsoonal climate favours the
occurrence of intermittent wetlands and river floodplains.
But a large variety of local climatic conditions leads to a
large variety in wetland types and total wetland extent. The
large SE-Asian rivers, such as the Mekong, Ganges,
Brahmaputra, Irrawaddy, Indus, Euphrates and Tigris are
accompanied by extended fringing floodplains and form
large deltas. Tonle Sap is connected to the Mekong River
and provides the highest catch of an inland fishery world-
wide. High population density and millennia of wetland
cultivation have dramatically reduced the size of natural
wetlands as a result of conversion to artificial wetlands,
mainly for rice paddy plantations, fish ponds and small
reservoirs. With 75,100 km
2
, tropical and subtropical
South-East Asia contains about 44 % of the world’s man-
grove area. Of special interest are the peat swamp forests in
Indonesia, which represent the most important tropical
wetlands with a high carbon store and which are under
severe human pressure.
Australia covers about 7.69 million km
2
and has a popu-
lation of 22.6 million persons. Large areas have a population
density\2 persons km
2
. It is a very dry continent, with a low
percentage of wetland area. Many wetlands are intermittent,
often with multiannual dry periods because of variable and
unpredictable rainfall events. Exceptions include the man-
groves that cover about 17,200 km
2
, corresponding to 10 %
of the global total. Extensive coastal floodplain wetlands
occur along the tropical, northern and north-eastern coasts,
including those within Kakadu National Park. Despite a very
low population density, the continent struggles with water
shortages. Water abstraction strongly affects river discharge
and connected floodplains, e.g., in the Murray-Darling Basin.
In response there has been a large investment in water-use-
efficiencies and environmental flow allocations. The area of
wetland as derived from official mapping products comprises
3 % of the landmass, although there are also significant areas
of marine wetlands not included in this figure.
Wetland classification
Countries with a well developed wetland policy, such as
the USA, Europe and Australia have wetland classifications
corresponding to legal or jurisdictional requirements.
Others, such as Russia, apply the wetland classification
scheme of the USA with some modifications to take into
account specific features of their wetlands. For some major
world regions general classification systems exist, e.g., for
South Asia. Many countries without a national wetland
classification have separate habitat classifications for spe-
cific wetlands or wetland types, such as Argentina and
Brazil, but they have little impact on local policy. For the
purposes of supporting legislation dealing with the man-
agement and protection of wetlands, politicians and
planners would benefit from a convergence in approaches
and the adoption of a unified classification.
State of knowledge, research efforts and research
infrastructure
Wetland research and management during the past few
decades has become increasingly important, however, to
different ways around the world. At the global level, the
International Union for the Conservation of Nature and
Natural Resources (IUCN), the Ramsar Convention, and
Wetlands International have dealt extensively with differ-
ent aspects of wetland protection. Since 1980, the Wetland
Working Group of the International Association of Ecology
(INTECOL) has held an international conference some-
where in the world every 4 years. The journals Wetlands
and Wetlands Ecology and Management deal specifically
with wetlands, but there are many other scientific journals
that also publish articles on wetland-related topics. Non-
governmental agencies, such as The Nature Conservancy
and Worldwide Fund for Nature also deal with wetland-
related problems.
At the regional level, the picture is heterogeneous. The
status of knowledge about wetlands is relatively high in
Europe, North America and Australia, partly because past
large-scale wetland destruction has led to increasing
awareness by the public about the value of wetlands. An
increasing amount of data is becoming available about the
wetlands of China and most countries of tropical South-
East Asia, Africa and Central America, as high human
pressure on wetlands and an increasing need for water
requires political actions by national governments. In South
America, some key wetlands, such as the Pantanal, parts of
the floodplains of the Parana
´
, Magdalena, Orinoco and
Amazon Rivers, and some boreal swamps of Patagonia are
reasonably well known, while others are very poorly
studied. Least known are the wetlands of Russia.
In North America, many institutions deal with wetlands.
The Canadian Rivers Institute at the University of New
Brunswick, Wetland and Waterfowl Research (IWWR) the
scientific research arm of Ducks Unlimited, and Wetlands
Research Center, University of Waterloo, should be men-
tioned among others. Several research centers in the United
154 W. J. Junk et al.
123
States concentrate on wetlands, such as the Sapelo Island
Marine Institute in Georgia, the School of Coast and
Environment at Louisiana State University, the H.T. Odum
Center for Wetlands at the University of Florida, the Duke
Wetland Center at Duke University, and the Wilma H.
Schiermeier Oletangy River Wetland Research Park (OR-
WRP) at Ohio State University. The U.S. Fish and Wildlife
Service, U.S. Environmental Protection Agency, the U.S.
Army Corps of Engineers, U.S. Environmental Protection
Agency, the U.S. EPA, especially through its Office of
Wetlands, Oceans, and Watersheds (OWOW), and the
Natural Resources Conservation Service are the primary
wetland management agencies in the United States (Mitsch
and Gosselink 2007). The Association of State Wetland
Managers and the Society of Wetland Scientists (SWS)
disseminate information on wetlands, particularly in North
America, with SWS having recently established chapters in
several other regions. The INTECOL Wetland Conference
has been held three times in North America: Columbus,
Ohio, USA (1992), Quebec City, Quebec, Canada (2000),
and Orlando, Florida, USA (2012).
In most European countries, wetland research centers
undertaking basic and applied research projects are found.
A number of universities offer courses on wetland ecology
and management and the state of knowledge about wet-
lands is rather good. Research concentrates mostly on
wetland management, protection and restoration. In 2004,
the Society of Wetland Scientists established a European
chapter whose annual meetings are becoming a represen-
tative forum for European wetland scientists (Zak et al.
2011). The Wetlands Working Group of INTECOL has a
broad base of collaborating wetland scientists who gather
at International Conferences on Wetlands every 4 years
with three out of eight of these conferences held so far at
the European wetland research centers at Tr
ˇ
ebon
ˇ
(Czechoslovakia), Rennes (France) and Utrecht (The
Netherlands).
In Russia, wetlands were recognized only in 1989 as a
separate type of ecosystem. Knowledge on wetlands and
appreciation of their value has steadily increased during the
last decade, but is dispersed in many different reports and
journals and is far from being satisfactory. Currently in
Russia there is no research team or group that focuses
primarily on wetlands as a specific ecosystem type. There
is no equivalent in Russia of the Society of Wetland Sci-
entists in North America. The influence of scientists on
Russian policy is small.
In China, the central government started the national
research on wetlands in 1997 under help of UNDP, GEF
and WB, and published the first guideline book of China’s
national wetland conservation action plan. The first
national inventory of wetlands was undertaken during 1997
and 2003, and all information about China’s wetlands was
taken from this inventory. The second inventory with more
detailed information begun in 2010 and will be completed
in 2015. There are a few institutes focusing on wetland
research, such as Nanjing University, Nanjing Institute of
Geography and Limnology of Chinese Academy of Science,
East China Normal University, Northeast Institute of
Geography and Agricultural Resource of Chinas Academy
of Science. The number of wetland scientists in China is
too small to meet the requirements of national wetland
management.
Most South-American countries have wetland research
activities going on in various universities and research
institutions. Research infrastructure is improving but
insufficient for a modern research and development policy
of the countries. The different research groups are not in-
terlinked and their political influence is small. The
INTECOL-wetland conference, held in 2007 in Cuiaba
´
,
Brazil, has called attention to South America and has given
a positive signal to the research community.
In Africa, international NGOs and various donor agen-
cies have been active in researching the role of wetlands in
the livelihoods of the local populations and this has con-
tributed to the substantial knowledge of certain of the
larger and more prominent systems. Uganda leads the way
in incorporating this knowledge into policy and manage-
ment in a way that aims to provide sustainable wetland
management while providing sustainable livelihoods for
people living adjacent to the wetlands. In southern and
eastern Africa there has been ongoing research into the
implementation of environmental water requirements of
rivers, wetlands and estuaries based on the understanding
that without sufficient water, these systems will be unable
to provide the benefits required of them by the people who
use these benefits.
In tropical and sub-tropical Asia, research on wetlands
has progressed well though the countries differ consider-
ably among themselves. Inventorisation and management
issues have received considerable attention. Most of the
research is lead by the universities though several research
institutes such as the Wildlife Institute of India, Salim Ali
Centre of Ornithology and Natural History and NGOs like
the Bombay Natural History Society, WWF, IUCN and
Wetlands International with their offices in several coun-
tries of the region contribute extensively to the knowledge
of wetlands. Much interest in recent years has emerged in
using the tools of ecological economics for valuation and
management of wetlands.
In Australia, the status and knowledge of wetlands has
increased in recent years with greater understanding of
their distribution and extent, biota and ecological condi-
tion. Research capacity is spread across many separately
operating units, although there have been significant efforts
to establish collaborative research efforts. A number of
Current state of knowledge regarding the world’s wetlands 155
123
