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Global Change and the Function and Distribution

of Wetlands

Global Change Ecology and Wetlands

Volume 1

Published in collaboration with the Society of Wetland Scientists –

Global Change Ecology Section

The Society of Wetland Scientists’ book series, Global Change Ecology and Wetlands, emerged

from the Society’s Global Change Ecology Section. There is a growing need among wetlands

managers and scientists to address problems of climate change in wetlands, and this series will fi ll

an important literature gap in the fi eld of global change as it relates to wetlands around the world.

The goal is to highlight the latest research from the world leaders researching climate change in

wetlands, to disseminate research fi ndings on global change ecology, and to provide sound science

to the public for decision-making on wetland policy and stewardship. Each volume will address a

topic addressed by the annual symposium of the Society’s Global Change Ecology Section.

For further volumes:

http://www.springer.com/series/8905

Beth A. Middleton

Editor

Global Change and the

Function and Distribution

of Wetlands

Editor

Beth A. Middleton

National Wetlands Research Center

US Geological Survey

Lafayette, LA, USA

ISBN 978-94-007-4493-6 ISBN 978-94-007-4494-3 (eBook)

DOI 10.1007/978-94-007-4494-3

Springer Dordrecht Heidelberg New York London

Library of Congress Control Number: 2012942468

Chapters 2 and 4: © The U.S. Government’s right to retain a non-exclusive, royalty-free licence in and

to any copyright is acknowledged 2012

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v

Contents

Part I Paleoecology and Climate Change

Insights from Paleohistory Illuminate Future Climate Change

Effects on Wetlands ......................................................................................... 3

Ben A. LePage, Bonnie F. Jacobs, and Christopher J. Williams

Part II Sea Level Rise and Coastal Wetlands

Response of Salt Marsh and Mangrove Wetlands to Changes

in Atmospheric CO2

, Climate, and Sea Level ............................................... 63

Karen McKee, Kerrylee Rogers, and Neil Saintilan

Part III Atmospheric Emissions and Wetlands

Key Processes in CH4

Dynamics in Wetlands and Possible Shifts

with Climate Change ...................................................................................... 99

Hojeong Kang, Inyoung Jang, and Sunghyun Kim

Part IV Drought and Climate Change

The Effects of Climate-Change-Induced Drought

and Freshwater Wetlands ............................................................................... 117

Beth A. Middleton and Till Kleinebecker

Index ................................................................................................................. 149

Part I

Paleoecology and Climate Change

B.A. Middleton (ed.), Global Change and the Function and Distribution of Wetlands, 3

Global Change Ecology and Wetlands 1, DOI 10.1007/978-94-007-4494-3_1,

© Springer Science+Business Media Dordrecht 2012

Abstract Climate change could have profound impacts on world wetland

environments, which can be better understood through the examination of ancient

wetlands when the world was warmer. These impacts may directly alter the critical

role of wetlands in ecosystem function and human services. Here we present a

framework for the study of wetland fossils and deposits to understand the potential

effects of future climate change on wetlands. We review the methods and assump￾tions associated with the use of plant macro- and microfossils to reconstruct ancient

wetland ecosystems and their associated paleoenvironments. We then present case

studies of paleo-wetland ecosystems under global climate conditions that were very

different from the present time. Our case study of extinct Arctic forested-wetlands

reveals insights about high-productivity wetlands that fl ourished in the highest lati￾tudes during the ice-free global warmth of the Paleogene (ca. 45 million years ago)

and how these wetlands might have been instrumental in keeping the polar regions

warm. We then evaluate climate-induced changes in tropical wetlands by focusing

on the Pleistocene and Holocene (2.588 Myr ago to the present) of Africa. These past

B. A. LePage (*)

Academy of Natural Sciences , 1900 Benjamin Franklin Parkway , Philadelphia ,

PA 19103 , USA

PECO Energy Company , 2301 Market Street, S7-2 , Philadelphia , PA 19103 , USA

e-mail: [email protected]

B. F. Jacobs

Roy M. Huf fi ngton Department of Earth Sciences , Southern Methodist University ,

P.O. Box 750395 , Dallas , TX 75275-0395 , USA

e-mail: [email protected]

C. J. Williams

Department of Earth and Environment , Franklin and Marshall College ,

P.O. Box 3003 , Lancaster , PA 17604-3003 , USA

e-mail: [email protected]

Insights from Paleohistory Illuminate Future

Climate Change Effects on Wetlands

Ben A. LePage , Bonnie F. Jacobs , and Christopher J. Williams

4 B.A. LePage et al.

ecosystems demonstrate that subtle changes in the global energy balance had

signi fi cant impacts on global hydrology and climate, which ultimately determine

the composition and function of wetland ecosystems. Moreover, the history of these

regions demonstrates the inter-connectedness of the low and high latitudes, and the

global nature of the Earth’s hydrologic cycle. Our case studies provide glimpses of

wetland ecosystems, which expanded and ultimately declined under a suite of global

climate conditions with which humanity has little if any experience. Thus, these

paleoecology studies paint a picture of future wetland function under projected

global climate change.

1 Introduction

Virtually every aspect of the planet Earth, especially climate, has changed over the

last four billion years. There is no reason to believe that these changes will cease, or

more to the point, that we can stop such changes because they are now impacting

our daily lives. From a geological point of view, global climate change is inevitable,

and we need to ask ourselves whether our efforts to curb such change is likely to

have the desired mitigating effect? While the solution is complicated and certainly

cannot be answered within the context of this chapter, our goal is to help put global

climate change into a geological perspective with respect to wetlands.

When Earth’s history is viewed in a geological context, we see a planet that has

always been in a state of geologic and geomorphologic fl ux. The Earth’s climate has

changed considerably throughout geologic time and ironically, we live at one of the

few times when global climate is cold, or what geologists call “icehouse conditions”.

For most of Earth’s history “hothouse or greenhouse conditions” prevailed, ice caps

were absent, and the average global temperature was considerably warmer than at

present. The consensus among scientists is the anthropogenic input of greenhouse

gases to the atmosphere, particularly carbon dioxide (CO 2

), have triggered a phase of

global warming (Solomon et al . 2007 ; Rosenzweig et al . 2008 ) . The pace and inten￾sity of future warming and the associated signi fi cant environmental changes are

likely to be governed, in part, by anthropogenic greenhouse gas inputs.

What then can the study of ancient wetland communities, some from millions of

years ago, offer to understand better the effects of future climate change on wet￾lands? It is important that we frame our discussion of wetland impacts in the context

of world wetland extent. The current global wetland area is estimated to be approxi￾mately 12.8 million square kilometers (km 2

) or 8.6% of the total land area of the

world (Schuyt and Brander 2004 ) . In an ice-free world, the total wetland area could

double in size to 25 million km 2

(18% of the total land area) if we assume that at

least 50% of the area currently classi fi ed as ice (Greenland and Antarctica) and

tundra would become wetland and the current wetland area of 12.8 million km 2

would be maintained. This assumption seems reasonable judging from the geo￾graphic extent and amount of Cenozoic-age (Fig. 1 ; 65.5 to 2.588 million years old

[Myr]) coals in northern and Arctic Canada, Iceland, Spitsbergen, Alaska, and Russia.

Insights from Paleohistory Illuminate Future Climate Change Effects on Wetlands 5

Berriasian

Valanginian

Hauterivian

Barremian

Aptian

Albian

Lower

Upper

Cenomanian

Turonian

Coniacian

Santonian

Campanian

Maastrichtian

Danian

Selandian

Thanetian

Ypresian

Lutetian

Bartonian

Priabonian

Rupelian

Chattian

Paleocene

Eocene

Oligocene

Miocene

Pliocene

Pleistocene

Holocene

Tarentian

Ionian

Calabrian

Gelasian

Piacenzian

Zanclean

Messinian

Tortonian

Serravallian

Langhian

Burdigalian

Aquitanian

Quaternary Neogene Paleogene

Mesozoic

Cretaceous

Phanerozoic Eonothem Eon

Erathem

Era

System

Period

Series

Epoch Stage Age Calibrated

Age (Myr)

0.0117

0.130

0.781

1.806

2.588

3.600

5.332

7.246

11.608

13.82

15.97

20.43

23.03

28.4

33.9

37.2

40.4

48.6

55.8

58.7

61.1

65.5

70.6

83.5

85.8

88.6

93.6

99.6

112.0

125.0

130.0

133.9

142.2

145.5

Cenozoic

Fig. 1 Stratigraphic chart

showing the ages in millions

of years (Myr) of the geologic

periods and epochs. The ages

follow those adopted by the

International Commission on

Stratigraphy ( 2010 )

6 B.A. LePage et al.

These coal deposits indicate large areas of moderately productive wetlands extended

from 50°N to the pole in the Northern Hemisphere throughout the Paleogene and

Neogene (Bustin 1981 ; Bustin and Miall 1991 ; Kalkreuth et al. 1993 ) . Therefore,

most of the 11.5 million km 2

of area currently classi fi ed as tundra may become

wetland during future climate change so the 50% estimate of the conversion of tun￾dra to wetlands is most likely an underestimate. Nevertheless, global climate change

will considerably increase the area of wetlands on the planet and these wetlands will

undoubtedly have signi fi cant impacts on future climate change, carbon and nutrient

cycling, and biodiversity.

This chapter is focused on insights that can be garnered from the past that help

us understand the impact of global climate change on wetlands. Paleobotanical

research can illuminate past climate and other environmental conditions through the

plant macrofossil (leaves, seeds, fl owers, seed cones, wood) and palynomorph (pol￾len and spores) records. After the composition and relative abundances of species in

the paleo fl ora are known, climate and paleoecology can be reconstructed based on

comparisons with nearest living relatives and the morphological (the study of form

and structure) attributes of fossil leaves. Paleobotany can also be integrated with

physical geological studies to understand better such physical processes as moun￾tain building, relative sea-level change, and sediment transport, deposition, and ero￾sion involved in development of the regional landscape through time. The relatively

new discipline of geochemistry is focused on the study of elements that were part of

these ancient environments and ultimately incorporated into plant tissues. When

applied in a multidisciplinary framework, the tools employed by geologists, paleon￾tologists, and geochemists to reconstruct past climate and environments provide a

better understanding of how plant communities functioned in the past and how they

could respond to changing climate and environment in the future.

2 The Study of Fossil Plants and Ancient Environments

Most fossil plant assemblages are the remnants of ancient wetland communities,

and by virtue of their topographically low position on the landscape, wetlands are

the most likely communities to be preserved because low-lying areas are often

fl ooded or saturated with water. In water or under saturated conditions, the soil and

organic matter become acidic and low in oxygen (anaerobic), and these conditions

restrict the saprotrophs (decomposers) that break down organic matter. As a result,

the rate of organic matter accumulation is greater than the rate of decomposition.

Therefore, the nature of the accumulated organic matter can then be used as a proxy

to represent the composition of the former wetland communities at the site.

Considerable insight into how ancient wetland communities responded to regional

and global climate change can be gained from both temporal (time) and spatial

(geographic) studies of their composition, structure, and function. Paleobotanical

and paleoecological studies are usually based on more fragmentary components of

whole communities than their modern counterparts. Fossil plant assemblages are

Insights from Paleohistory Illuminate Future Climate Change Effects on Wetlands 7

best viewed as snapshots in geological time that represent days to years (sometimes

hundreds of years) of organic matter accumulation over varying spatial scales. It is

rare to fi nd entire plant communities preserved in situ (in place) and in those

instances, the preserved plant species are generally herbaceous (Kidston and Lang

1917 ; Rothwell and Stockey 1991 ; Wing et al . 1993 ; Stockey et al . 1997 ) , or some￾times woody (Francis 1987, 1988, 1991 ; Jacobs and Winkler 1992 ; Basinger 1991 ;

Williams 2007 ; DiMichele and Gastaldo 2008 ) .

While we are cognizant of the fragmentary nature of the plant fossil record and

the limitations that various plant parts provide for interpreting and reconstructing

past and future environments and climate, fossil plant remains provide proxies from

which reasonably robust paleoenvironmental interpretations can be made using sys￾tematic assessments. As such, we discuss the major groups of plant organs that are

commonly recovered from sedimentary deposits and the types of interpretations

that are possible based on recover of these fossil tissues. Nevertheless, before we

begin, it is important that the reader understand the concepts of space and time and

the limitations that each imparts on interpreting the plant fossil record.

3 Spatial and Temporal Resolution

When working with data generated from fossil materials, one needs to be aware of

the spatial and temporal scales represented and the limitations that these data place

on paleoecological interpretations. Bennington et al. ( 2009 ) identi fi ed temporal and

spatial components, which must be considered when working with fossils including

time averaging and source area (related to transport distance), respectively. Both trans￾port distance and time averaging are addressed by the fi eld of taphonomy; the

study of how organisms become fossils (i.e., their transition from the biosphere

to the lithosphere). Taphonomic studies provide a mechanistic understanding of the

processes of transport, burial, and preservation, which are factors that may bias

the paleoecological interpretation of a fossil deposit. Depending on the nature of the

deposit, plant fossil assemblages generally provide a good indication of the amount

of transport endured by the plant remains and these deposits can be classi fi ed as

autochthonous, allochthonous, and/or parautochthonous. Autochthonous deposits

are those where there has been no transport and the fossils are effectively buried in situ .

These types of deposits provide the most complete record of the plant composition

in the immediate burial area. Allochthonous assemblages are comprised of fossils

that have been transported and buried up to a few kilometers from where they grew.

Parautochthonous remains were transported a smaller distance. Nevertheless, from

a taphonomic standpoint, even autochthonous deposits are likely to possess a percent￾age of non-local parautochthonous and allochthonous plant elements.

When sampling and interpreting fossil assemblages, it is important to consider

the spatial scale with regard to each type of deposit. Fossil plant assemblages pre￾served in a particular stratum across a region represent snapshots in time of the

dominant species and in some cases changes in the dominant species can be recognized

8 B.A. LePage et al.

if the bedding plane within which the plants are contained is preserved laterally.

If one were to examine the fossil plants at various locations within a single deposit

there would likely be many similarities in plant composition within this stratum,

which would then be a re fl ection of the dominant plant species for the time and

region. But depending on the distance between the sampling locations, subtle

changes in the composition and relative abundance (dominance) of the vegetation

would be expected throughout this local landscape. These changes could be due to

changes in soil conditions, aspect, micro-topography, or hydrology (Fig. 2 ). For

example, assuming that there were suf fi cient depositional environments within each

zone (Fig. 2 ), the aquatic zone would be biased towards species growing in the

aquatic and riparian zones with some elements from bottomland forests or more

rarely from the uplands. Sampling in the bottomland forest would provide an excel￾lent proxy of the species composition growing in this zone within this stratum.

Riparian and upland elements would be represented in low numbers, and aquatic

species would not be expected. Similarly, if we were to collect samples in the

uplands, we would not likely encounter any aquatic, riparian, and bottomland forest

elements. Furthermore, lateral sampling along a single fossiliferous deposit can pro￾vide paleoecological information about heterogeneity in species composition due to

the biotic factors themselves.

To test these well-accepted paleobotanical assumptions Burnham ( 1989, 1997 )

sampled the forest fl oor litter in a number of fl oodplain forest sub-environments in

a Mexican paratropical forest and Costa Rican dry forest. A variety of sub-environments

in the same stratigraphic level was necessary to increase the accuracy of regional

reconstructions (Burnham 1989 ) . Moreover, certain sub-environments such as channel

deposits consistently misrepresented the source fl ora. Sample size was crucial

for reliably reconstructing local and regional vegetation communities. The leaf

litter study in the dry forest indicated that 70% of the tree species per hectare were

Aquatic

Riparian

Bottomland

Upland

Riparian

Fig. 2 The relationship between local topography and spatial changes in the vegetation. The

macro- and microfossils collected in the fi eld across these vegetation types would be analyzed to

determine species composition and relative abundance. The sampling location and frequency

determines the accuracy of vegetation and climate reconstruction for the local and regional areas

of the study

Insights from Paleohistory Illuminate Future Climate Change Effects on Wetlands 9

represented in the leaf collecting baskets, which were placed over the forest fl oor.

From these data, the dominant and co-dominant species could be determined

(Burnham 1997 ) . Studies such as these illustrate the importance of understanding

the relationships between the ecology and dynamics of modern forested ecosys￾tems, geomorphology, and taphonomy.

The second component identi fi ed by Bennington et al. ( 2009 ) is that of temporal

mixing or so-called “time averaging”, whereby events that happened at different times

appear to be synchronous in the geologic record (Kowalewski 1996 ) . For example, a

stratigraphic horizon could contain the remains of several generations of plant com￾munities that were never contemporaries. This situation is inherent to most sedimen￾tary deposits, even if sediment accumulation is continuous. Even with precise age

controls, such as those provided by annual laminations (varves) or materials amenable

to radioisotope dating (e.g., 14 C, 210 Pb), it is sometimes dif fi cult to know exactly how

much time is represented by a speci fi c stratigraphic interval at a locality.

A hypothetical stratigraphic column can illustrate this point (Fig. 3 ). If we assume

that sediment and plant accumulation are continuous throughout the section and we

Fig. 3 In sedimentology the relationship between time and sediment accumulation rates can be

illustrated using a hypothetical stratigraphic column. The ages can be determined using 14 C or

another radioactive isotope that has a half-life suitable for the geologic age of the deposits. The

sediment accumulation rates are calculated on the basis of the amount of sediment that accumu￾lated during the time represented between the 14 C levels. This illustrates the point that although

sediment accumulation may have been constant, the rate of sediment accumulation can vary

through time. Single point accumulation rates are based on the use of a single age date . Compared

to a stratigraphic section that has multiple age dates, the same stratigraphic section that is cali￾brated with one age date can over- or under-estimate the rate of sediment accumulation. The arrows

at 300 and 350 cm indicate the location of a 50-cm thick sediment package that was deposited

instantaneously, probably during a fl ood event

0

50

100

150

200

250

300

350

400

9,060 +/- 130

5,280 +/- 100

18,600 +/- 150

Depth in

cm

14C age Time represented

by the sequence

1 cm = 25 years

1 cm = 11 years

Accumulation

rates (multiple are dates)

1 cm = 106 years

0 +/- 100

20,200 +/- 150

1 cm = 191 years

1 cm = 51 years

1 cm = 74 years

1 cm = 45 years

1 cm = 106 years

Single point

accumulation rates

10 B.A. LePage et al.

have only one radiometric age of 20,200 years at the bottom of the section, then the

average rate of sediment accumulation over the 4 m section would be 1 cm every

51 years. Although this assumption is reasonable, the example illustrates that

although sediment accumulation may have been continuous, the rate of accumula￾tion can be variable. Similarly, if only one radiometric age date of 18,600 years at a

depth of 250 cm is available, then the sediment accumulation rate for the 250 cm

thick sedimentary unit would be 1 cm every 74 years. Again, assuming that only one

radiometric age (9,060 or 5,280 years) was available, the sediment accumulation

rates would be very different (45 and 106 years per centimeter) from the other radio￾metric ages. There are many instances where a sediment core or outcrop (also called

a geologic section) contains a limited amount of material suitable for radiometric

dating (in this case 14 C) and it is only possible to obtain a single radiometric age. In

these cases, the sediment accumulation rate can only be calculated from the location

where the sample was collected to the top of the core or section and the accumula￾tion rate of the sediment located below the sample location is unknown.

The example also illustrates that change in sediment accumulation rates are not

identi fi ed by single age calibration points. Multiple calibration points increase the

accuracy for reconstructing the local vegetation community and physical setting,

especially when interpretations require higher temporal resolution. Moreover, the

study of the sediments between radiometric dates provides constraints on the depo￾sitional environment and questions such as basin stability (as it relates to tectonics),

cyclicity/periodicity of the deposit, and the position of the sampling locations over

the landscape can be determined. In this example, four radiometric dates calibrate

the section. Between 20,200 and 18,600 years 150 cm of sediment accumulated

over 1,600 years and between 18,600 and 9,060 years only 50 cm of sediment accu￾mulated over 9,540 years. From 9,060 to 5,280 years 150 cm of sediment accumu￾lated over 3,780 years and the uppermost 50 cm of sediment accumulated between

5,280 years and the present. Thus each centimeter of sediment between 20,200 and

16,060 years represents 11 years, between 18,600 and 9,060 years represents

191 years, between 9,060 and 5,280 years each centimeter represents 25 years, and

between 5,280 years and the present each centimeter represents 106 years . In this

example, the sediment accumulation rates are highly variable. The reconstruction of

forest structure, composition, and dynamics would not be accurate if only the single

point accumulations rates were used. Use of any of the single point values alone

would have either over- or under-estimated the time it took for the sediment to accu￾mulate as well as the biological and physical processes represented during that

interval of time. The accumulation rates as based on the multiple point accumula￾tion approach provide better estimates of the time it took for the sediment to accu￾mulate within a depositional basin (Fig. 3 ).

Sediment accumulation rates are nothing more than averages that are based on

modern processes and calibration points. The concept of averaging the time taken

for a package of sediment to accumulate is then applied to the vegetation preserved

in the sediment package. Thus, using the example of the single radiometric age date

of 20,200 years (Fig. 3 ), changes in the macro- and micro- fl ora throughout the 4 m

section would be interpreted using a 51-year baseline with the assumption that

deposition was continuous. By virtue of the averaging process, instances of erosion