Climate Change and Managed Ecosystems - Chapter 18 pdf

Human activities can affect the supplies of water entering wetlands by physically modifying the natural shape and size of the wetland and its surrounding watershed, by drawing water dire

Challenges in Wetlands under Climate Change

in Canada

B.G Warner and T Asada

CONTENTS

18.1 Introduction 355

18.2 Common Misconceptions 356

18.3 Wetland Classification and Inventory 356

18.4 Hydrological Landscape Modifications and Water Budget Fluctuations 360

18.5 Sedimentation and Water Quality Changes 362

18.6 Carbon Cycling and Climate 363

18.7 Invasive Species 363

18.8 Wetland Archival Records 366

18.9 Wetland Ecotechnology: The Way of the Future 367

18.10 Summary and Conclusions 367

References 368

18.1 INTRODUCTION

Wetlands are a characteristic element of the Canadian landscape They occur any-where supplies of water on the land surface sustain waterlogged conditions and anywhere specialized biotic communities are adapted to extreme variations in soil oxygen between periods of wetness and dryness The geomorphologic setting of the land and the buildup of sediments in the wetland itself, especially in the case of peat landforms, are important factors controlling water conditions in wetlands Climate determines the amount of water that enters via precipitation and leaves via evapo-transpiration and, more indirectly, influences the supply of water that may enter via surface runoff and groundwater seepage Human activities can affect the supplies

of water entering wetlands by physically modifying the natural shape and size of the wetland and its surrounding watershed, by drawing water directly from the wetland and the sources supplying it, and by altering the vegetation cover, which,

in turn, affects the inputs from and losses to the atmosphere To understand wetland and climate relationships is to understand relationships between climate and water, but these relationships upset the natural balance when human activities interfere and threaten wetlands and their supplies of water

Several reviews demonstrate Canada’s considerable progress toward understand-ing and managunderstand-ing its wetland resources.1–5 There is a national classification system,

a fundamental first step for defining and recognizing wetlands Regional inventories have been performed based on concepts and terms in the classification system Much has been learned about differences in the character and dynamics of wetlands through scientific research and information gathering, which, in turn, wetland managers have used to develop policies governing wetland protection and wise use These are not small accomplishments considering the extent and great diversity of wetlands in Canada, estimated to be about 18% of the world’s freshwater wetlands.6 Yet there

is a rudimentary appreciation for the delicate linkages among climate, water, and wetlands Wetlands still have not attained the attention they require in assessments

of human impacts on the natural environment This is exemplified by the number

of threats to drinking water supplies, water pollution problems, major floods, droughts, fire, and other environmental disasters in recent years in Canada that revolve around climate, water, wetlands, human health, and economy Wetlands are,

or should be, considered central to these issues

This chapter highlights some topical issues, gaps in our understanding of the role of wetlands in natural and human-dominated landscapes, vulnerability of wet-lands and the environment when climate compounds the problems, and what we need to know to better deal with the wetland and water issues in the future It is by

no means complete but is intended to give a sense of the nature of some problems and the gaps in knowledge Wetland ecotechnology presents the opportunity to direct natural self-organization processes in wetlands to solve problems for the benefit of both the natural environment and society

18.2 COMMON MISCONCEPTIONS

Wetland specialists have met at intervals to review progress and prioritize future directions and information needs Several workshops have addressed knowledge gaps and challenges in the science of wetlands for measuring, predicting, mitigating, and adapting to demands of society including consideration of future changes to climate.7–10 The needs and issues with respect to wetlands identified at these national forums, some more than 10 years ago, still hold to the present This may, in part,

be due to the needs being so diverse and complex that the wetland community is challenged to meet all of them and, in part, from a lack of will owing to a number

of common misconceptions about wetlands in Canada (Table 18.1)

18.3 WETLAND CLASSIFICATION AND INVENTORY

Classification is a fundamental prerequisite for all work on wetlands, because it provides a system for defining and recognizing wetlands in the landscape Two

editions of the Canadian wetland classification have been published, the last of which

is the culmination of nearly 20 years of work.11 The classification system captures the range of both peatland and mineral wetland types, including those that are on land and along freshwater and marine coasts It also includes those influenced by permafrost processes

Classification systems provide the framework for naming and mapping wetlands

in national and regional inventories It provides the standard “taxonomy” used to

TABLE 18.1

Some Common Misconceptions about Wetlands in Canada

Wetlands are abundant in Canada and

are not threatened.

Wetlands are most abundant in the Boreal Ecozone They are threatened in southern Canada, especially in the most heavily populated and agricultural areas and elsewhere due to dam construction and hydroelectric reservoir development Wetlands quality is high and they are

not degraded.

True for the most pristine and remote regions, but wetlands closest to inhabited regions are in various degrees of deterioration because of incompatible land uses in and around wetlands, long-term degradation from the historical past, urbanization, agriculture, discharge of chemical and biological contaminants, influx of invasive species Wetlands are wastelands and

obstacles to development; human

society and wetlands cannot live

together.

Great progress has been made toward effective management and conservation of wetlands; however, there remains poor appreciation for the value of wetlands, some perceive wetlands as frightening and dangerous places, legislation works against wetlands in some jurisdictions, and there has been a relaxation by groups and organizations to respect the benefits and virtues of wetlands.

Restored and created wetlands are

undesirable and unachievable.

Wrong! Many successful restored and created wetlands exist

in Canada, some of which are recognized as internationally important.

Wetlands are not linked to climate and

are unwanted, because they

contribute greenhouse gases that

warm the climate.

There is a complex linkage between carbon cycling processes

in wetlands and climate Wetlands not only contribute but also remove greenhouse gases from the atmosphere in ways that vary greatly among different wetland types, among similar wetland types, and within the same wetland basin The knowledge base about wetlands

is complete and there is no need for

further work and research on

wetlands.

Wrong! The global scientific community is moving fast to discover new and important attributes about wetlands that need to be explored in Canada For example, we know almost nothing about aspects of wetland biogeochemistry, hydrology, microbial ecology, and biodiversity in Canada, much less the services and values that wetland might contribute to human society.

The peat moss industry is the only

economic value of wetlands.

Wrong! Canada’s wetland industry as a whole, of which the peat moss industry is a part, probably contributes as much

to the economic well-being of Canadians as most of the other natural resource sectors, yet is largely ignored.

name representative wetland types and organize them into groups and subgroups Unfortunately, the classification system has not been universally adopted across all sectors of the federal government even though the Federal Cabinet accepted the national classification system as the standard to follow when it adopted the Federal Wetlands Policy in 1992.12

The 1997 classification system is incomplete and needs refinement Our concepts

of swamp and bog remain confusing as indicated by some discordance between definitions of the classification system and the maps produced by Tarnocai et al.,6,13 largely due to incomplete understanding of the hydrology of wetlands throughout Boreal Canada Consideration should be given to explicitly recognizing the condition

or state of the wetland at probably the form or type level in the classification (Table 18.2) This would recognize restored and created wetlands, which are not included Degraded wetlands are problematic because they have characteristics that do not readily fall into the current classification, which is based largely on pristine wetlands Further work is required in areas such as the following: the classification needs to

be reevaluated and field-tested for redundancies, generalities, and incompleteness, and should be brought up to date with current scientific concepts of bog, swamp, fen, marsh, and shallow open water; restored and created wetlands were largely overlooked in the 1997 classification and need to be included in the classification system; in view of the occurrence of corals in Canada’s offshore areas, consideration

of whether the Canadian definition of wetlands needs to be expanded to be brought

in line with the international definition of the Ramsar Convention, which recognizes coral reefs as components of wetlands; the classification should be used as the basis for more regional classification systems as recognized by the federal government; some consideration needs to be given to developing classifications that are based on both scientific and regulatory needs, such as hydrogeomorphic functional classifi-cations widely used in the U.S.;14 and the Canadian classification should be broad-ened and modified into a classification system for North American wetlands (i.e., with the U.S., Mexico), and perhaps toward a global classification for the Northern Hemisphere.15

Inventories are only as good as the classification system used as the standard reference for naming and differentiating the wetland units The most comprehensive national inventories are those of Tarnocai et al.6,13 Most wetland inventories in Canada exclude large areas of marine, brackish, and freshwater coastal wetlands (both marsh and shallow open water), and overlook many restored and created wetlands The National Wetland Inventory that has been recently launched holds much promise to improve our knowledge of the extent and distribution of wetlands, primarily because it utilizes satellite imagery with modern digital imagery processing techniques.16 This new initiative must build on the Canadian Wetland Classification system, and perhaps can help to resolve outstanding problems, such as accurate

differentiation of Picea swamp vs Picea forest in the Boreal Ecozone, and open

water wetland vs lake and ocean in coastal zones Such challenges can only be confirmed by accurate and supporting field surveys

Inventory work such as that of Snell17,18 for southern Ontario needs to be updated and expanded to other regions of the country, where a significant extent of wetland has been converted to alternative land uses since European settlement Such inventories

serve to identify priority regions and sites where wetlands are especially vulnerable and where conservation efforts and protection should take precedence (Figure 18.1) Regions where wetlands may not be especially widespread anymore but existed in the

TABLE 18.2

Classification Considering State of Wetland Condition

Wetland

Type Wetland Condition

Degree of Human Intervention

Degree of Direction by Humans to Organize Wetland Ecosystem

Degraded

(a) Minor Degradation: partly

influenced by humans retaining same

wetland form and type as before

human contact

(b) Moderate Degradation: a viable

wetland is retained but some parts and

forms of the wetland have changed

and the wetland is in a state of

transformation from one wetland type

to another

(c) Major Degradation: the wetland

form and type have been severely

influenced by humans and there is a

general trend of species

impoverishment or replacement of

dominant species by others

Restored Passively restored

Returned to some preexisting state by

one-time human action and remaining

in the new state

Actively restored

Returned to some preexisting state by

ongoing human action

Created Human-initiated

Bringing wetland into existence by

intentional or unintentional action

where none existed previously; able

to persist thereafter

Artificial

Bringing wetland into existence by

deliberate action where none existed

previously; without ongoing human

actions it would revert to its original

condition

Small

Great

Greatly directed

Not directed

on purpose

Slightly directed

historical past reflect areas of high probability of success and should be targeted for restoration The problem is compounded, because regions where wetlands are most vulnerable due to historical reasons are also regions where climate-warming scenarios predict extreme warming and drought.19

18.4 HYDROLOGICAL LANDSCAPE MODIFICATIONS

AND WATER BUDGET FLUCTUATIONS

Our unwise use and poor management of water resources has created problems for wetlands that, if they continue, will only pose more serious threats to wetlands under climate change scenarios Humans have disrupted the magnitude and timing of natural river flows through land clearance, dam and reservoir construction, diversion and transfer of water across watersheds, exploitation of groundwater aquifers, channeliza-tion of streams, and reconfigurachanneliza-tion of coastlines in Canada These activities allow control of water resources to generate electricity, supply water for agriculture and industry, mitigate flooding, navigate rivers and lakes, and use the land and near shore for purposes incompatible with natural conditions.20,21 Canada ranks third next to the

FIGURE 18.1 Map of Canada showing regions where wetlands are most threatened

(Mod-ified after Rubec 76 )

0 500 1000

kilometers

N

High Moderate Low to None

U.S and Russia in having the greatest number of major dams.21 Innumerable wetlands and aquatic habitats have been lost and altered as a result of these landscape changes Land clearance by early settlers changed the land from being forest, wetland, and water-dominated to one that is open, drier, and largely devoid of wetlands Smaller water bodies and streams were obliterated and larger ones became larger,

so large that rivers overflowed and changed their channels and water levels rose

in the receiving water bodies Land-use history necessitated the creation of the Conservation Authorities system in the 1940s in Ontario to monitor floods.22 The loss of wetlands and water bodies on the Prairies prompted the formation of Ducks Unlimited Canada in 1938 to reverse the historical trends and restore wetlands.22

Large to small dam construction has increased fivefold since the 1950s This has resulted in major changes in the volume of water flowing in rivers by water being impounded in upper reaches and significant decreases in volumes reaching lower reaches and the river mouth Extent of dam construction on a single water-shed can be substantial For example, the Columbia River Basin in Canada and the U.S has 19 dams on its 2000-km length; only 70 km of the river remains free flowing and natural.21 What has this kind of control of natural water flow done to wetlands in the watershed? Another serious problem is the change to natural seasonal patterns of river discharge This has led to an increase in the age of waters reaching the river mouth because it may take water more than a year to reach the mouth compared to days and weeks under natural conditions The hydroperiods

of wetlands in riparian zones have changed, the influx and/or efflux of nutrients have increased, and water and/or nutrients in downstream areas are diminished The reservoirs themselves have altered natural habitats Source and sink strength for greenhouse gases have been affected by the reservoirs that can emit large quantities of greenhouse gases.24 Hydroelectric reservoirs are particularly a prob-lem because not only are they sources of greenhouse gases, but also of methyl-mercury, which accumulates and biomagnifies in the aquatic food chain.25,26 Hydro-electric development is the primary threat to wetlands in central parts of Manitoba, Ontario, and Quebec (Figure 18.1)

Wetlands must be a central concern in understanding the impact of hydrological alterations The obvious impacts are complete displacement and destruction of wet-lands, but less known are the less obvious subtle changes to wetland water budgets and the responses by wetland biota Detailed information needs include the follow-ing: undertake detailed evaluation of the state of existing knowledge base and prioritize information needs on impact to wetlands of hydrological alterations; assess impacts of seasonal changes to river runoff cycles on water budgets and hydroperiods

of associated wetlands, especially wetlands in riparian and floodplain zones; identify linkages between large-scale hydrological alterations, regional water cycles, wet-lands, and climate; determine changes to hydrological conditions, nutrient cycles, and biota in wetlands in upstream vs downstream reaches; undertake historical comparisons between pre-disturbance and present-day landscapes, wetland ecosys-tems, and climate, which can be readily done using paleoecological techniques, and long-term monitoring sites need to be established to assess future impacts; and consider conversion to wetland for reservoirs and impoundments when they are

decommissioned and taken off-line Gorham et al.27 have reviewed the merits of the longer time frames and spatial scales offered by paleoecological approaches in dealing with environmental problems that directly and indirectly affect peatlands There needs to be much greater use and recognition of the archival record in peatlands as an important management tool for climate change

18.5 SEDIMENTATION AND WATER QUALITY

CHANGES

Overloading of sediments and nutrients due to poor land-use practices is a major threat to wetlands The gaps and needs in this area with respect to wetlands are complex and have been addressed by the workshops referred to earlier They are also closely related to issues surrounding hydrological alterations discussed previ-ously This area has received little attention in the context of wetlands, but likely is

a large problem in the vicinity of the mouths of many streams and rivers and along the associated lake shores and ocean coasts of Canada just as it is in other parts of the world It has likely escaped the attention of Canadians because the problems have not yet reached catastrophic proportions although there may well be accidents waiting to happen There have been intermittent reports in the Canadian popular press in recent years that report fish kills in our water bodies that are usually attributed to natural cyclic phenomena There needs to be discussions of nutrients and overall water quality when such fish kills do occur to ensure that poor land-use practices are not contributing to “natural phenomena.” Lessons learned from the Mississippi basin issue can help in Canada

The Gulf of Mexico hypoxia problem in the U.S serves as a good example for Canadians to illustrate the magnitude of problems of poor land-use management and the catastrophic environmental and economic consequences exacerbated by warm climate Nutrient loading and sedimentation throughout the Mississippi River basin has been shown to increase significantly in recent decades A zone of low oxygen levels less than 2 mg l–1 has been noted on the continental shelf of the northern part of the Gulf of Mexico.28–30 Transport of excess nutrients by the Mis-sissippi River has contributed to increased primary production along with warm summers and regional water circulation processes has been found to be responsible Nitrate concentrations from the Mississippi River show major increases in the 1950s after nitrogen fertilizer came into widespread use and after expansion in other activities such as artificial drainage and hydrological alterations in the basin, such

as increased runoff, wastewater discharge from urban settlements, and intensification

of agriculture contributed to the problem.29 Hypoxia is exacerbated by warm climate Restoration of wetlands is viewed as ways by which nutrients and sediments can be controlled from entering the river and transported downstream to the river mouth.28 Sedimentation and a decline in water quality in the Great Lakes have been attributed

to agriculture and urbanization in adjacent watersheds and efforts are under way to restore wetlands to correct the problem.31

18.6 CARBON CYCLING AND CLIMATE

Wetlands contain the largest quantities of carbon in both their living biomass and

in their deep peat and sediments in the terrestrial biosphere Canada contains around one third of the global peatland carbon although uncertainties exist on extent of peatland and carbon in the world.32 Wetlands in Ontario are estimated to contain about 19% of Canada’s wetland carbon and about 6.6% of the wetland carbon in the world.33 The recent review of McLaughlin32 presents a good summary of the current state of knowledge of wetland carbon cycling that, despite a focus on Ontario, applies to much of Boreal Canada Large-scale assessments of general climate change effects on carbon cycling processes are reasonably clear.33–39 Specific topics that have received considerable attention include the following: net primary produc-tion and litter decomposiproduc-tion,40–42 peat carbon accumulation,39,43–46 and methane and carbon dioxide production and emission.47,48 Different models are being developed

to scale up peatland carbon to landscape, regional, and global scales.19,49,50 There are several important areas that require further research to refine our understanding of carbon pools, fluxes, and cycling processes at different temporal and spatial scales.32,51 Considerable effort has been directed at quantifying the various carbon pools but gaps still exist For example, belowground carbon in litter and roots

is thought to be large in peatlands covered by vascular plants, yet real estimates are poor at best There remains incomplete understanding of variability in the nature of temporal and spatial variability of carbon sink and source strength at microtopo-graphic scales Plant community composition differs markedly and climate is expected to exhibit enough influence to cause vegetation composition to shift both peatland structure and community type For example, fens are expected to shift into bogs and swamps Such vegetation changes will vary the nature of carbon being added to the litter and long-term storage Little is known about how climate will interact with the new litter quality, oxidation–reduction processes, and microbial communities Recent studies show that smaller-scale intrinsic factors such as water tables, vegetation composition, and litter governed by peatland microtopography and peat formation may be stronger forces in carbon cycling processes than larger scales and longer-term responses to changes in climate.52,53 Climate is expected to enhance effects of ultraviolet-B (UV-B) radiation on production and decay rates.54 How will radiation affect carbon cycling and sequestration processes in peatlands?

Much of the attention on wetland carbon cycling and climate has focused on peatlands Mineral wetlands contain significant quantities of carbon, albeit much less than in peatlands, but in quantities that should not be ignored.33,55

18.7 INVASIVE SPECIES

Wetlands seem to be particularly favorable habitats for invasive species and warmer climate may be compounding the problem by allowing more species to survive the winter period than would otherwise under more severe conditions Invasive species are both non-native species and native species that become harmful to the ecosystem and, in turn, likely cause harm to the economy and humans The list includes animals (insects, mollusks, fishes, birds, herpitiles, mammals), plants (algae, bryophytes,

vascular plants), fungi, and microbes Unfortunately, there is no complete list of what these species are in Canadian wetlands and aquatic habitats To compare, a total of 334 non-native aquatic species have been introduced into wetlands in the U.S.56 The Global Invasive Species Database (http:// www.issg.org) lists 18 taxa (Table 18.3) in Canadian wetlands, but this is only a small fraction of invasive species actually known to affect fresh, brackish, and marine wetlands This list does not

include well-known examples such as Dreissena polymorpha (zebra mussel), Tinca

tinca (tench fish), or Cabomba caroliniana (fanwort macrophyte), which are having

major impacts on freshwater wetlands.57 There are at least 150 non-native invasive species in the Great Lakes basin that have been introduced in the 1900s.57 The vast majority of these live in or close to wetlands A comparable number of invasive species are associated with marine and estuarine wetlands of the Strait of Georgia

in southwest British Columbia Included are such species as Sargassum muticum (brown seaweed), Zostera japonica (dwarf eelgrass), Venerupis philippinarum (Manila clam), and Branta canadensis (Canada goose).57

The status of many alien invasives is poorly understood A good example is

Phragmites australis, a common wetland plant widely distributed across Canada It

has become a nuisance in the eastern U.S., and is expanding its dominance throughout

TABLE 18.3

Invasive Species Reported in Wetlands in Canada from the Global Invasive Species Database ( http://www.issg.org/database )

Scientific Name Common Name Alien or Native Status

Plants

Elaeagnus angustifolia Russian olive (tall shrub) Alien

Myriophyllum spicatum Eurasian water- milfoil (herb) Alien

Animals

Micropterus salmoides American black bass (fish) Alien, uncertain, and/or native

Mustela erminea Short-tailed ermine (mammal) Uncertain and/or native

Orconectes virilus Northern crayfish (crustacean) Native

Microbes