Chapter 4: Coastal Wetlands

CHAPTER 4

COASTAL WETLANDS

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Chapter 4: Coastal Wetlands

Coordinating Lead Authors
Hilary Kennedy (UK), Daniel M. Alongi (Australia) and Ansarul Karim (Bangladesh)

Lead Authors
Guangcheng Chen (China), Gail L. Chmura (Canada), Stephen Crooks (USA), James G. Kairo (Kenya), Baowen
Liao (China) and Guanghui Lin (China)

Cont ributing Author
Tiffany G. Troxler (IPCC TFI TSU)

Review Editors
Nuria Marba Bordalba (Spain) and Georgi Karl Hiebaum (Bulgaria)

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Chapter 4: Coastal Wetlands

Contents
4

Coastal Wetlands ....................................................................................................................................... 6
4.1

Introduction ...................................................................................................................................... 6

4.2

CO2 emissions and removals ........................................................................................................... 11

4.2.1

Forest management practices in mangroves .................................................................................. 11

4.2.1.1 Biomass ................................................................................................................................. 12
4.2.1.2 Dead organic matter ............................................................................................................... 16
4.2.1.3 Soil carbon ............................................................................................................................. 18
4.2.2

Extraction.................................................................................................................................... 18

4.2.2.1 Biomass ................................................................................................................................. 19
4.2.2.2 Dead organic matter ............................................................................................................... 23
4.2.2.3 Soil carbon ............................................................................................................................. 24
4.2.3

Rewetting, revegetation and creation of mangroves, tidal marshes and seagrass meadows ............. 26

4.2.3.1 Biomass ................................................................................................................................. 26
4.2.3.2 Dead organic matter ............................................................................................................... 27
4.2.3.3 Soil carbon ............................................................................................................................. 27
4.2.4

Drainage in mangroves and tidal marshes ................................................................................. 29

4.2.4.1 Biomass ................................................................................................................................. 30
4.2.4.2 Dead organic matter ............................................................................................................... 30
4.2.4.3 Soil carbon ............................................................................................................................. 30
4.3

Non-CO2 emissions......................................................................................................................... 32

4.3.1

CH4 emissions from rewetted soils and created mangroves and tidal marshes................................ 32

4.3.1.1 Choice of method ................................................................................................................... 33
4.3.1.2 Choice of emission factors...................................................................................................... 33
4.3.1.3 Choice of activity data............................................................................................................ 34
4.3.1.4 Uncertainty assessment .......................................................................................................... 34
4.3.2

N2O emissions during aquaculture use in mangroves, tidal marshes and seagrass meadows ........... 34

4.3.2.1 Choice of method ................................................................................................................... 35
4.3.2.2 Choice of emission factors...................................................................................................... 35
4.3.2.3 Choice of activity data............................................................................................................ 36
4.3.2.4 Uncertainty assessment .......................................................................................................... 36
4.4

Completeness, time series consistency, and Quality Assurance and Quality Control (QA/QC) .......... 36

4.4.1

Completeness .............................................................................................................................. 36

4.4.2

Time series consistency ............................................................................................................... 36

4.4.3

Quality Assurance/Quality Control (QA/QC) ............................................................................... 36

Annex 4A.1 Salinity-based definitions ............................................................................................................ 37
Annex 4A.2 Estimation of above-ground mangrove biomass: higher tier methodology ..................................... 38
Annex 4A.3 Wood density of mangrove species .............................................................................................. 39

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Annex 4A.4 Percent refractory carbon ............................................................................................................. 40
Annex 4A.5 Derivation of N2O emission factor for aquaculture ....................................................................... 41
Appendix 4a.1 Future methodological development for estimating carbon export............................................. 42
References............................................................................................................................................... 43

Equations
Equation 4.1

Estimation of BCEF using BEF and wood densities ...................................................... 12

Equation 4.2

Tier 1 estimation of initial change in carbon stocks with extraction (all C pools) ........... 18

Equation 4.3

Initial change in carbon stocks with excavation (all C pools) ......................................... 18

Equation 4.4

Tier 1 estimation of initial change in biomass carbon stocks due to extraction activities . 20

Equation 4.5

Tier 1 estimation of initial change in dead organic matter carbon stocks due to extraction
activities....................................................................................................................... 23

Equation 4.6

Tier 1 estimation of initial change in soil carbon stocks due to extraction activities ....... 24

Equation 4.7

CO2 emissions from rewetting, revegetation and creation of coastal wetlands ................ 28

Equation 4.8

CO2 emissions on drained organic and mineral soils ...................................................... 30

Equation 4.9

CH4 emissions from rewetted soils and created tidal marshes and mangroves................. 33

Equation 4.10 Direct N2O emissions from Aquaculture use ................................................................. 35

FiguresFigure 4.1

Decision tree to indicate relevant section for Tier 1 estimation of GHG emissions andremovals due to specific management activities in coastal wetlands. ................................ 9

Tables

4.4

Table 4.1

Specific management activities in coastal wetlands ......................................................... 6

Table 4.2

Carbon fraction of above-ground biomass (tonnes C (tonnes d.m.)-1) in mangroves ........ 13

Table 4.3

Above-ground biomass in mangroves (tonnes d.m. ha-1) ................................................ 14

Table 4.4

Above-ground biomass growth in mangroves (tonnes d.m. ha-1 yr-1) .............................. 14

Table 4.5

Ratio of below-ground biomass to above-ground biomass (R) in mangroves .................. 14

Table 4.6

Average density (D; tonnes m-3) of mangrove wood ...................................................... 15

Table 4.7

Tier 1 default values for litter and dead wood carbon stocks in mangroves ..................... 17

Table 4.8

Summary of Tier 1 estimation of initial changes in carbon pools for extraction
activities....................................................................................................................... 19

Table 4.9

Ratio of below-ground biomass to above-ground biomass (R) for tidal marshes ............. 21

Table 4.10

Ratio of below-ground biomass to above-ground biomass (R) for seagrass meadows ..... 21

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Chapter 4: Coastal Wetlands

Table 4.11

Soil carbon stocks for mangroves, tidal marshes and seagrass meadows for extraction
activities....................................................................................................................... 26

Table 4.12

Annual emission factors associated with rewetting (EFRE) on aggregated organic andmineral soils (tonnes C ha-1 yr-1) at initiation of vegetation reestablishment.................... 29

Table 4.13

Annual emission factors associated with drainage (EFDR) on aggregated organic andmineral soils (tonnes C ha-1 yr-1) ................................................................................... 31

Table 4.14

Emission factors for CH4 (EFREWET) for Tier 1 estimation of rewetted land previously
vegetated by tidal marshes and mangroves .................................................................... 34

Table 4.15

Emission factor (EFF) for N2O emission from aquaculture use in mangroves, tidal marshes
and seagrass meadows .................................................................................................. 35

Boxes

Box 4.1

The following examples illustrate different management practices which may result in achange of a land-use category depending on how countries define mangroves and othercoastal wetlands ............................................................................................................. 82013 Supplement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories: Wetlands

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Chapter 4: Coastal Wetlands

4 COASTAL WETLANDS
4.1

INTRODUCTION

This chapter provides guidance on estimating and reporting anthropogenic greenhouse gas (GHG) emissions andremovals from managed coastal wetlands. Coastal wetlands hold large reservoirs of carbon (C) in biomass andespecially soil [global stocks: mangroves, ~8 Pg C (Donato et al., 2011); tidal marshes, ~0.8 Pg C (midrange;
Pendleton et al., 2012); and seagrass meadows, 4.2 – 8.4 Pg C (Fourqurean et al., 2012)]. Soil carbon originates
largely in situ, from root biomass and litter, and can result in a significant pool in coastal wetlands, especiallywhen compared with terrestrial forests (Pidgeon, 2009).
Coastal wetlands generally consist of organic and mineral soils that are covered or saturated, for all or part of theyear, by tidal freshwater, brackish or saline water (Annex 4A.1) and are vegetated by vascular plants. The
boundary of coastal wetlands may extend to the landward extent of tidal inundation and may extend seaward to
the maximum depth of vascular plant vegetation. Countries need to develop a nationally appropriate definition ofcoastal wetland taking into account national circumstances and capabilities. This chapter refers specifically totidal freshwater1 and salt marshes, seagrass meadows, and mangroves. For non-tidal inland mineral wetland soils,
refer to Chapter 5, this supplement.
TABLE 4.1
SPECIFIC MANAGEMENT ACTIVITIES IN COASTAL WETLANDS

Activity

Subactivity

Vegetation types
affected

Activities relevant to CO2 emissions and removals
Forestmanagement
practices inmangroves

Planting, thinning, harvest, wood removal, fuelwood removal, charcoal
production1

Mangrove2

Excavation to enable port, harbour and marina construction and filling or
dredging to facilitate raising the elevation of land

Mangrove, Tidal
marsh, Seagrassmeadow4

Aquaculture (construction)

Mangrove, Tidal
marsh

Salt production (construction)

Mangrove, Tidal
marsh

Drainage

Agriculture, forestry, mosquito control

Mangrove, Tidal
marsh

Rewetting,revegetationand creation3

Conversion from drained to saturated soils by restoring hydrology andreestablishment of vegetation

Mangrove, Tidal
marsh

Reestablishment of vegetation on undrained soils

Seagrass meadow4

Extraction

Activities relevant to non-CO2 emissions

1

Aquaculture(use)

N2O emissions from aquaculture use

Mangrove, Tidal
marsh, Seagrassmeadow

Rewetted soils

CH4 emissions from change to natural vegetation following modifications
to restore hydrology

Mangrove, Tidal
marsh

Including conversion to Forest Land or conversion from Forest Land to other land uses.

2

It is good practice to report mangroves in the appropriate national land-use category according to the national forest definition and to
consider when forest management practices may occur on mangroves classified under land-use categories other than Forest Land(similar types of examples in inventory reporting include wood harvest from orchards or other perennial Cropland or harvest of trees
from Wetlands).
3

The term revegetation is used to refer to practices within the framework of UNFCCC reporting.

4

Countries need to report on emissions from extraction and revegetation only if necessary data are available.

1

At the present time, insufficient data are available to provide generic default data for C pools in tidal freshwater swamps.

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Chapter 4: Coastal Wetlands

It is good practice that inventory compilers determine a country-specific definition of coastal wetlands,
recognizing national circumstances. Having applied the country-specific definition, the specific management
activities (Table 4.1) need to be identified and emissions and removals reported using the methodologies
provided in this chapter. When identifying the nature and location of these activities, inventory compilers need
only report GHG emissions or removals for activities where the anthropogenic contribution dominates overnatural emissions and removals. Management activities resulting in extraction of soils, such as construction of
aquaculture ponds, can result in large carbon dioxide (CO2) emissions in mangroves and tidal marshes. Nitrous
oxide (N2O) emissions can be significant from aquaculture activities. Rewetting increases methane (CH4)emissions from drained freshwater tidal systems and increases carbon accumulation in mangrove biomass, deadwood and soils.
Coastal wetlands can potentially occur in any land-use category defined in Chapter 3, Volume 4 of the 2006
IPCC Guidelines and the management activity may or may not result in a land-use change (see Box 4.1).
Regardless of whether a land-use change occurs, it is good practice to quantify and report significant emissions
and removals (Table 4.1) resulting from management activities on coastal wetlands in line with the countryspecific definition. To cover all potential reporting options, new Wetland subcategories Other Wetlands
Remaining Other Wetlands and Land Converted to Other Wetlands are included. Coastal wetlands can also occur
on areas that are not part of the total land area of the country. Emissions and removals from these areas should bereported separately under the relevant land-use category, however the associated land areas should be excluded
from the total area of the land-use category (refer to Chapter 7, this supplement). In this way, countries need not
be concerned with areas of coastal wetland, with small impacts on carbon stock changes and emissions of nonCO2 gases, which are not included in the total land area.
Readers are referred to Volume 4 of the 2006 IPCC Guidelines for many of the basic equations to estimate GHG
emissions, and new guidance is provided in this chapter, as necessary. The decision tree (Figure 4.1) guides theinventory compiler to the appropriate estimation methodology for each of the specific management activities
covered in this chapter.

COVERAGE OF THIS CHAPTER
This Chapter updates guidance contained in the 2006 IPCC Guidelines to:provide default data for estimation of carbon stock changes in mangrove living biomass and dead woodpools for coastal wetlands at Tier 1.

This Chapter gives new: guidance for CO2 emissions and removals from organic and mineral soils for the management activities
of extraction (including construction of aquaculture and salt production ponds), drainage and rewetting,revegetation and creation;
 default data for estimation of anthropogenic CO2 emissions and removals for soils in mangrove, tidal
marsh and seagrass meadows;
 guidance for N2O emissions during aquaculture use;
 guidance for CH4 emissions for rewetting, revegetation and creation of mangroves, tidal marshes andseagrass meadows.
The Appendix to this Chapter provides the basis for future methodological development to address:
Anthropogenic emissions and removals associated with dissolved or particulate organic carbon (DOC,
POC) loss during drainage as affected by tidal exchange.

For constructed wetlands that occur in coastal zones that are modified to receive and treat wastewater, refer to
Chapter 6 (this supplement). Chapter 6 also covers semi-natural treatment wetlands, which are natural wetlands
where wastewater has been directed for treatment but the wetland is otherwise unmodified.
While countries will follow their own national definitions of coastal wetlands, some general features that may
help in consistent identification can be found throughout this guidance. It is good practice to maintain consistentidentification of lands for the purpose of reporting.

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BOX 4.1
THE FOLLOWING EXAMPLES ILLUSTRATE DIFFERENT MANAGEMENT PRACTICES WHICH MAY RESULT IN A
CHANGE OF A LAND-USE CATEGORY DEPENDING ON HOW COUNTRIES DEFINE MANGROVES AND OTHER
COASTAL WETLANDS

For Land remaining in a Land-use category (i.e. no change in land-use category), when:Seagrass meadows or tidal marshes classified as Wetlands remain reported as Wetlands following
introduction of aquaculture activity.
Mangroves classified as Forest Land according to the national forest definition undergo selective
harvesting or biomass clearing remain reported as Forest Land unless they undergo a land-use
change.
Mangroves, which do not meet all thresholds of a country’s definition of forest, but are coastal
wetlands with trees are classified as Wetlands, and when subject to selective harvesting or biomass
clearing remain reported as Wetlands.
Conversely, management activities may result in a change in reporting category, for example,
when:Seagrass meadows are initially classified as Wetlands, but are considered a Settlement following
introduction of aquaculture activity.
Tidal marshes are classified as Wetlands and are drained for agriculture and subsequently
classified as a Cropland or Grassland.
Mangroves are classified as Forest Land and undergo clearing, or drainage and converted toanother land-use category.

MANAGEMENT ACTIVITIE S IN COASTAL WETLAND S
Coastal wetlands that have been modified by anthropogenic activities are often reduced in area. Globally about
35% of the area of mangroves has disappeared since 1980, with a current global areal rate of loss of between 0.7
and 3% yr-1 (Pendelton et al., 2012). The management activities that have led to the majority of mangrove loss
include forestry activities (26%) and aquaculture, comprising the construction (and extraction of soil) for shrimp
ponds (38%) and fish farms (14%) (Vaiela et al., 2009). Other management activities may lead to the removal ofmangrove biomass without necessarily resulting in mangrove clearance i.e. harvesting for fuelwood, charcoaland construction. The current global areal rate of loss of tidal marsh is estimated to be between 1 and 2% yr -1(Pendelton et al., 2012). Draining for agriculture, diking to isolate marsh from tides, filling (after extraction)with sediment, and the extraction of soil during the construction of ponds for salt production are common
management activities affecting tidal marshes. Seagrass meadows are experiencing a global areal rate of loss
currently of between 0.4 and 2.5% yr-1 (Pendelton et al., 2012). Globally, the main reasons for seagrass loss aremanagement activities such as dredging, leading to the excavation of soil to raise the elevation of land in low
lying areas and contribute to new land areas for settlement and aquaculture.
Revegetation efforts with mangroves, tidal marsh plants and seagrass, have been made worldwide to compensate
or mitigate for coastal wetland loss resulting from management activities (e.g. Bosire et al., 2008; Orth et al.,2011). Recovery of vegetation that characterised the coastal zone generally requires reestablishment of the preexisting environmental setting, such as rewetting (restored hydrology), to maintain saturated soils and facilitate
plant growth. Management activities do not always affect all vegetation types (i.e. mangroves, tidal marsh plants
and seagrasses) or occur in all countries and not all coastal wetlands will be managed. To identify areas affectedrefer to respective sections on Activity Data and throughout this supplement.

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Chapter 4: Coastal Wetlands

Figure 4.1

Decision tree to indicate relevant section for Tier 1 estimation of GHG
emissions and removals due to specific management activities in coastal
wetlands 2.
Start

Does this coastal wetland
retain saturated soils and are mangrove forests
managed for wood harvesting or otherpractices?

Yes

Forest management
practices in mangroves
Go to section 4.2.1. for CO2

No

Is biomass, DOM and soil
being extracted from this coastal
wetland?

Yes

Extraction (including
excavation, construction of
aquaculture and salt
production ponds)
Go to section 4.2.2 for CO2

Yes

Aquaculture use
Go to section 4.3.2 for N2O

Yes

Rewetting, revegetation &creation
Go to section 4.2.3 for CO2
OR
Rewetted soils
Go to section 4.3.1 for CH4

Yes

Rewetting, revegetation &creation
Go to section 4.2.3 for CO2

Yes

Drainage
Go to section 4.2.4 for CO2

No

Is the management activity
aquaculture and is it in use?

No
Was thisa drained coastal wetland
and is now being rewetted or managed
to create or reestablish its
natural vegetation?
No
Is this an area being
managed to create or reestablish
seagrass meadows?

No
Has this coastal wetland
been drained?
No
No guidance in this chapter

2

For extraction activities, CO2 emissions and removals are estimated for the initial change in carbon stocks that occur during
the year the extraction activities take place. Once the activity/activities is/are completed, these lands are continually track ed
but CO2 emissions and removals are reported as zero at Tier 1. Forest management practices in mangroves, drainage andrewetting are reported based on the area of land where it occurs, lands are tracked and CO 2 emissions and removals
subsequently are reported in the annual inventory.

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The following sections provide some general information on the specified management activities in coastal
wetlands that result in large anthropogenic emissions and removals.

Fo res t manag eme nt pract ices in ma ngrov es
Removal of wood occurs throughout the tropics where mangrove forests are harvested for fuelwood, charcoal,and construction (Ellison and Farnsworth, 1996; Walters et al., 2008). The wood removal can range fromextensive forest clearing to more moderate, selective harvesting of individual trees, or to minimally invasive
activities such as bark removal. Natural disturbances are another form of biomass carbon stock loss. There may
also be conversion to forest land where mangrove replanting can take place on rewetted, or already saturated,soils.

Ext ract io n
Extraction collectively refers to:(A) Excavation of saturated soils leading to unsaturated (drained) soils and removal of biomass and dead organic
matter. Activities that lead to the excavation of soil often lead to loss of coastal wetlands. The excavated ordredged soil is also commonly used to help develop coastal infrastructure where there is a need to raise theelevation of land in low lying areas and/or contribute to new land areas for settlement.
(B) Excavation during the “construction” phase of aquaculture and salt production ponds in mangroves and tidal
marshes followed by the “use” of these facilities.
Aquaculture and salt production are common activities in the coastal zone and similarly require excavation ofsoil and removal of biomass and dead organic matter for construction. There is a range of aquaculture practices,
but the most important are fish farming and production from shrimp ponds (World Bank, 2006). Salt production,from the evaporation of seawater, is also a widespread activity with sites along tropical and subtropical coasts
worldwide, some of which have been producing salt for centuries (Oren, 2009; Thiery and Puente, 2002). In bothactivities, ponds are constructed in mangroves and tidal marshes by clearing vegetation, levelling the soil andsubsequently excavating the surface soils to build berms where water is held. Depending on the type ofaquaculture (intensive, extensive etc.) and the species stocked in the ponds (shrimp, fish) the soils can be
excavated to make ponds of 0.5 m to 2.5 m depth (Cruz, 1997; Kungvankij et al., 1986; Wang, 1990; Robertsonand Phillips, 1995). In a similar manner the depth of salt production ponds can vary between depths of about 0.5
to 2.5 m (e.g. Ortiz-Milan, 2006; Madkour and Gaballah, 2012).
Construction is only the first phase in aquaculture and salt production. The second phase, termed “use” is whenfish ponds, cages or pens are stocked and fish production occurs. In seagrass meadows, aquaculture ismaintained by housing fish in floating cages or pens that are anchored to the sediment (Alongi et al., 2009) andthese settings are considered during the use phase. N2O is emitted from aquaculture systems primarily as a byproduct of the conversion of ammonia (contained in fish urea) to nitrate through nitrification and nitrate to N 2
gas through denitrification. The N2O emissions are related to the fish production (Hu et al., 2012). When use of
the aquaculture systems has been stopped, often due to disease or declining water clarity (Stevenson et al., 1999),
the systems transition to a final phase i.e. “discontinued”. All three phases (construction, use and discontinued)of aquaculture and salt production are considered together with the other extraction activities, because theactivity data are linked. However, only construction is addressed at Tier 1 for CO2, with higher tiers addressing
use and discontinued phases. For non-CO2, only the use phase is considered at Tier 1.

Rew ett ing, rev eget at io n and creat io n
Rewetting is a pre-requisite for vegetation reestablishment and/or creation of conditions conducive to purposefulplanting of vegetation that is characteristic of coastal wetlands. This activity is also used to describe themanagement activities designed to reestablish vegetation on undrained soils in seagrass meadows. Once thenatural vegetation is established, soil carbon accumulation is initiated at rates commensurate to those found innatural settings (Craft et al., 2002, 2003; Osland et al., 2012).
Rewetting in mangroves and tidal marshes occurs where hydrologic modifications reverse drainage or remove
impoundments or other obstructions to hydrologic flow (e.g. levee breach). Also included in this activity are
mangroves and tidal marshes that have been created, typically by raising soil elevation or removing the upper
layer of upland soil or dredge spoil, and grading the site until the appropriate tidal elevation is reached tofacilitate reestablishment of the original vegetation. Revegetation can occur by natural recolonisation, direct
seeding and purposeful planting. Alternatively, created wetlands with mangroves can be found where highriverine sediment loads lead to rapid sediment accumulation, so that previously sub-aqueous soils can beelevated above tidal influence. This naturally created land can be reseeded or purposefully vegetated.

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The rewetting of tidal marshes and mangroves through reconnection of hydrology may lead to CH4 emissions(Harris, 2010), particularly at low salinities, with an inverse relationship between CH4 emissions and salinity(Purvaja and Ramesh, 2001; Poffenbarger et al., 2011).
In coastal wetlands where seagrass loss has occurred due to anthropogenic activities, soils remain saturated.
Initiatives to allow revegeation can include natural or purposeful dispersal of seed or planting of seagrass
modules (Orth et al., 2011). These same techniques can also be used to create (rather than re-establish) seagrassmeadows (Jones et al., 2012).

Drainage
Mangroves and tidal marshes have been diked and drained to create pastures, croplands and settlements since
before the 11th century (Gedan et al., 2009). The practice continues today on many coastlines. On some diked
coasts, groundwater of reclaimed former wetlands is pumped out to maintain the water table at the required level
below a dry soil surface, while on other coasts drainage is achieved through a system of ditches and tidal gates.
Due to the substantial carbon reservoirs of coastal wetlands, drainage can lead to large CO2 emissions.

4.2

CO 2 EMISSIONS AND REMOVALSThis section provides the methodology to estimate CO2 emissions and removals from human activities in coastal
wetlands comprising forest management practices in mangroves, extraction, drainage and rewetting. The
methodological guidance provided here is consistent with methods for biomass and dead organic matter inVolume 4 of the 2006 IPCC Guidelines and are in large part based on that methodological guidance: (1) forforest management practices in mangroves, methods for biomass and dead organic matter are in large part basedon Chapter 4 of Volume 4; (2) for extraction activities, the methodological guidance is generally consistent withguidance for peat extraction Chapter 7 of Volume 4; and (3) for rewetting and drainage activities, updated
methodological guidance found in other chapters of this supplement is consistent with the methodologies
presented here. Activities covered by this chapter are described in Table 4.1. Separate guidance is provided on
estimation of changes in carbon stock from the five carbon pools.
Depending on circumstances, practices and definitions, specific coastal wetland management activities may or
may not involve a change in land-use category. The guidance in this chapter needs to be applied regardless of thereporting categories. In particular, no recommendation is provided in relation to transition periods between landuse categories; countries can apply the existing transition period of appropriate land-use categories.
Consistent with the 2006 IPCC Guidelines, the Tier 1 default approach assumes that the change in biomass anddead organic matter carbon stocks are zero on all lands except on Forest Land or on Cropland, Grassland andWetlands with perennial woody biomass. On Forest Land and on Cropland, Grassland, or Wetlands with woody
biomass, the woody biomass and woody dead organic matter pools are potentially significant and need to be
estimated in a manner consistent with the guidance provided in Chapters 2 (generic methods), 4 (Forest Land), 5(Cropland), 6 (Grassland) and 7 (Wetlands) in Volume 4 of the 2006 IPCC Guidelines. Guidance provided here
refers to Equations 2.7, 2.8 and the subsequent equations in Chapter 2 of the 2006 IPCC Guidelines which split
the carbon stock changes in the biomass pool or ΔCB into the various possible gains and losses.
If specific management activities in coastal wetlands (Table 4.1) are accompanied by a change in land use thatinvolves Forest Land or Cropland, Grassland or Wetlands with perennial woody biomass, changes in carbon
stocks in biomass, dead wood and litter pools are equal to the difference in carbon stocks in the old and current
land-use categories (see Section 2.3.1.2, Chapter 2, Volume 4 of the 2006 IPCC Guidelines). These changes incarbon stock occur only in the year of the conversion (extraction activities), or are uniformly distributed over thelength of the transition period (e.g. planting, harvesting). In soils the change in carbon stocks for extraction
activities occurs in the year of conversion, while for drainage, emissions persist as long as the soil remains
drained or as long as organic matter remains, following the methodological guidance in this chapter.

4.2.1

Forest management practices in mangroves

This section deals with CO2 emissions and removals associated with forest management practices in mangroves.
It is good practice to follow a country’s national definition of forest, but also to apply the appropriate guidance
when mangrove wetlands have trees, but that do not necessarily satisfy all thresholds of the national definition offorest. Depending on how the land is classified, forest management practices in mangroves may or may not leadto a change in land-use category (examples provided in Box 4.1). For estimation methodologies refer to thegeneric guidance provided in Chapter 2 of Volume 4 and more specific guidance in the relevant chapters of the2006 IPCC Guidelines for reporting CO2 emissions and removals for above-ground biomass, below-groundbiomass and dead organic matter (litter and dead wood).

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4.2.1.1

B IOMASS

Biomass can be stored in mangroves that contain perennial woody vegetation. The default methodology for
estimating carbon stock changes in woody biomass is provided in Section 2.2.1, Chapter 2, Volume 4 of the2006 IPCC Guidelines. The change in biomass is only estimated for perennial woody vegetation of mangroves.
Changes in mangrove biomass may be estimated from either: 1) annual rates of biomass gain and loss (Equation
2.7, Chapter 2) or 2) changes in carbon stocks at two points in time (Equation 2.8, Chapter 2). The first approach(Gain-Loss method) can be used for Tier 1 estimation (with refinements at higher tiers) whereas the second
approach can be used for Tier 2 or 3 estimations. It is good practice for countries to strive to improve inventory
and reporting approaches by advancing to the highest possible tier given national circumstances. For coastal
wetlands with non-woody vegetation (i.e. seagrass meadows and many tidal marshes), increase in biomass stocks
in a single year is assumed equal to biomass losses from mortality in that same year leading to no net change.

CHOICE OF METHOD
Tier 1
If the land (1) satisfies a country’s definition of forest or (2) is a mangrove wetland with trees, that nonetheless
do not meet the national definition of forest, and is managed for forest activities where no land-use change has
occurred, guidance is provided in “Section 2.3.1.1 Land Remaining in a Land-Use Category” and in the specificguidance in Volume 4, of the IPCC 2006 Guidelines. Guidance is applied using the default data provided in thischapter (Table 4.2 – 4.6) and specific guidance below. Examples may include Forest Land to Forest Land,
Wetlands to Wetlands or Other Wetlands to Other Wetlands.
If the land (1) satisfies a country’s definition of forest or (2) is a mangrove wetland with trees, and is managed
for forest activities where land-use change has occurred or trees have been cleared, guidance is provided in“Section 2.3.1.2 Land Converted to a Another Land-Use Category” and in the specific guidance in the relevant
chapters of Volume 4 of the 2006 IPCC Guidelines. Guidance is applied using the default data provided in thischapter (Table 4.2 – 4.6) and specific guidance below.
When either the biomass stock or its change in a category (or sub-category) is significant or a key category, it isgood practice to select a higher tier for estimation. The choice of Tier 2 or 3 methods depends on the types andaccuracy of data and models available, level of spatial disaggregation of activity data and national circumstances.
If using activity data collected via Approach 1 (see Chapter 3 of Volume 4 in the 2006 IPCC Guidelines), and it
is not possible to use supplementary data to identify land converted from and to the respective land category, theinventory compiler needs to estimate carbon stocks in biomass following Section 2.3.1.1 and specific relevant
guidance as indicated above.
Because a biomass conversion and expansion factor (BCEF) is not available for mangroves, when above-groundbiomass is estimated from merchantable growing stock, for conversion of net annual increment, or for
conversion of woody and fuelwood removal volume to above-ground biomass removal, BCEF is derived fromwood density (Table 4.6) and a default value of BEF (Table 3A.1.10- Annex 3A.10 of the Good PracticeGuidance for Land Use, Land-use Change, and Forestry). This formulation follows Equation 4.1 and is
described in Box 4.2 of Chapter 4, Volume 4 of the 2006 IPCC Guidelines.
EQUATION 4.1
ESTIMATION OF BCEF USING BEF AND WOOD DENSITIESBCEF = BEF • D(Section 2.3.1.1, Chapter 2 of the 2006 IPCC Guidelines)
Where:
BCEF = biomass conversion and expansion factor for conversion of growing stock, net annual increment orwood removals into above-ground biomass, above-ground biomass growth or biomass removals; tonnes
d.m. m-3
BEF = biomass expansion factor to expand the dry weight of the merchantable volume of growing stock,
net annual increment or wood removals to account for non-merchantable components; dimensionless
D = wood density; tonnes d.m. m-3

Tier 2
As in Tier 1, the Gain-Loss method can be applied using country-specific data. In addition, the Stock-Difference
method can also be applied using country-specific emission factors. If using the Stock-Difference method,country-specific BEF or BCEF data or species specific wood density values (provided in Annex 4A.3) could beapplied. For Tier 2, countries may also modify the assumption that immediately following conversion to another4.12

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Chapter 4: Coastal Wetlands

land-use category, or after mangrove trees are cleared, biomass is zero. Refer to the relevant sections in Volume
4 of the 2006 IPCC Guidelines for further guidance on Tier 2 methodologies for forest management practices inmangroves.

Tier 3Tier 3 approach for biomass carbon stock change estimation allows for a variety of methods including processbased models that simulate the dynamics of biomass carbon stock changes. Country-defined methodology can bebased on estimates of above-ground biomass through use of allometric equations (Annex 4A.2) or include
detailed inventories based on permanent sample plots. Tier 3 could also involve substantial national data on
disaggregation by vegetation type, ecological zone and salinity. Tier 3 approaches can use growth curves
stratified by species, ecological zones, site productivity and management intensity. If developing alternative
methods, these need to be clearly documented. Refer to the relevant sections in Chapter 4, Volume 4 of the 2006
IPCC Guidelines for further guidance on Tier 3 methodologies for forest management practices in mangroves.
Spaceborne optical and radar data can be used for mapping changes in the extent of mangroves and transitions toand from other land covers. Such techniques currently cannot routinely provide estimates of a sufficient level ofaccuracy, although this may become more feasible in the future (refer to this section, “Choice of Activity Data”).

CHOICE OF EMISSION/R EMOVAL FACT ORS
Tier 1For countries using the Gain-Loss method as a Tier 1 approach, the estimation of the annual carbon gains inliving biomass requires the following: carbon fraction of above-ground biomass, average above-ground biomass,mean annual above-ground biomass growth, ratio of below-ground biomass to above-ground biomass andaverage wood density. The default values for these parameters are provided in Tables 4.2-4.6, respectively. It isgood practice to apply annual growth rates that lead neither to over- nor underestimates. Losses due to wood
removals, fuelwood removals and disturbances are also needed (refer to Choice of Activity Data for Tier 1 anduncertainty analysis in this section).

Tier 2National data could include country specific values of any parameter used in the Tier 1 method or values that
permit biomass carbon stock changes using the Stock-Difference method. Refer also to the relevant sections ofVolume 4 of the 2006 IPCC Guidelines for further guidance.

Tier 3Tier 3 methods may employ the use of data that are of higher order spatial disaggregation and that depend on
variation in salinity or further disaggregation of regional differences within a country. Forest growth rates of
specific age ranges could be applied. Refer also to the relevant sections of Volume 4 of the 2006 IPCC
Guidelines for further guidance.

TABLE 4.2
CARBON FRACTION OF ABOVE-GROUND BIOMASS ( TONNES C ( TONNES D.M.)-1) IN MANGROVES 1

1

Component%C

95% CI3

Range

Leaves + wood2

45.1 (n = 47)

42.9, 47.1

42.2-50.2

This Table provides supplementary values to those presented in Table 4.3, Chapter 4, Volume 4 of the 2006 IPCC Guidelines.

2

Sources: Spain and Holt, 1980; Gong and Ong, 1990; Twilley et al., 1992; Bouillon et al., 2007; Saenger, 2002; Alongi et al., 2003, 2004;
Kristensen et al., 20083

95% CI of the geometric mean

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Chapter 4: Coastal Wetlands

TABLE 4.3
ABOVE-GROUND BIOMASS IN MANGROVES ( TONNES D.M. HA-1) 1
DomainTropicalRegionAbove-ground biomass

Range

187, 2048.7-384

n49

Tropical Wet

192

Tropical Dry

923

88, 97

3.2-201

13

754

66, 84

3.9-129

10

Subtropical1

2

95% CI5

This Table provides supplementary values to those presented in Table 4.7-4.9, Chapter 4, Volume 4 of the 2006 IPCC Guidelines.

2

Sources: Golley et al., 1975; Christensen, 1978; Ong et al., 1982; Putz and Chan, 1986; Tamai et al., 1986; Komiyama et al., 1987; 1988,
2000, 2008; Lin et al., 1990; Mall et al., 1991; Amarasinghe and Balasubramaniam, 1992; Kusmana et al., 1992; Slim et al., 1996; Fromard
et al., 1998; Norhayati and Latiff, 2001; Poungparn, 2003; Sherman et al., 2003; Juliana and Nizam, 2004; Kirui et al., 2006; Kairo et al.,2008; Fatoyinbo et al., 2008; Camacho et al., 2011; Kauffman et al., 2011; Thant and Kanzaki, 20113

Sources: Golley et al, 1962; Briggs, 1977; Suzuki and Tagawa, 1983; Steinke et al., 1995; Alongi et al., 2003; Medeiros and Sampoia, 2008;
Khan et al., 2009
4

Sources: Lugo and Snedaker, 1974; Woodroffe, 1984; Lee, 1990; Mackey, 1993; Tam et al., 1995; Saintilan, 1997; Ross et al., 2001;
Coronado-Molina et al., 2004; Simard et al., 2006; Fatoyinbo et al., 2008; Komiyama et al., 2008; Abohassan et al., 2012
595% CI of the geometric mean

TABLE 4.4
ABOVE-GROUND BIOMASS GROWTH IN MANGROVES ( TONNES D.M. HA-1 YR-1)1
DomainTropicalRegionAbove-ground biomass
growth2,3

95% CI4

Range

Tropical Wet

9.9

9.4, 10.4

0.1-27.4

23

Tropical Dry

3.3

3.1, 3.5

0.1-7.5

6

18.1

17.1, 19.1

5.3-29.1

4

Subtropical1

This Table provides supplementary values to those presented in Table 4.10, Chapter 4, Volume 4 of the 2006 IPCC Guidelines.

2

Sources: Ajonina 2008; Kairo et al., 2008; Alongi, 2010n3

Biomass growth rates are from forests of varying age and such default values should only pertain to forests until the carbon biomass stock(Table 4.3) is reached.
4

95% CI of the geometric mean

TABLE 4.5
RATIO OF BELOW- GROUND BIOMASS TO ABOVE-GROUND BIOMASS (R) IN MANGROVES1
DomainRegionR[tonne root d.m.

95% CI5

Rangen(tonne shoot d.m.)-1]
TropicalTropical Wet

0.492

0.47, 0.51

0.04-1.1

18

Tropical Dry

30.28, 0.30

0.09-0.79

9

0.964

0.91, 1.0

0.22-0.27

18

Subtropical

0.29

1

This Table provides supplementary values to those presented in Table 4.4, Chapter 4, Volume 4 of the 2006 IPCC Guidelines.

2

Sources: Golley et al., 1975; Tamai et al., 1986; Komiyama et al., 1987, 1988; Gong and Ong, 1990; Lin et al., 1990; Poungparn, 2003

3

Sources: Golley et al, 1962; Alongi et al., 2003; Hoque et al., 2010

4

Sources: Briggs, 1977; Lin, 1989; Tam et al., 1995; Saintilan, 1997

595% CI of the geometric mean

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Chapter 4: Coastal Wetlands

TABLE 4.6
AVERAGE DENSITY (D; TONNES M-3) OF MANGROVE WOOD1
Wood

D

95% CI2

Range

n

0.71

0.64, 0.74

0.41-0.8785

1

Sources: Global Wood Density Database http://datadryad.org/resource/doi:10.5061/dryad.234/1?show=full; Saenger, 2002; Komiyama etal., 2005; Donato et al., 20122

95% CI of the geometric mean

CHOICE OF ACTIVITY D ATA
All tiers require information on areas of forest management practices in mangroves. Information on mangrove
forest types as well as soil types can be obtained from national wetland and soil type maps (if available) or theInternational Soil Reference and Information Centre (www.isric.org). Mangrove distributions for most countries
can be obtained from the RAMSAR web site (www.ramsar.org). When information is gathered from multiple
sources, it is good practice to conduct crosschecks to ensure complete and consistent representation and avoid
omissions and double-counting.

Tier 1
For Tier 1, these data can be obtained from one of the following sources 3:
FAOSTAT http://faostat.fao.org/
Global Mangrove Database & Information System: http://www.glomis.com/
The UNESCO Mangrove Programme: http://www.unesco.org/csi/intro/mangrove.htm
Mangrove and the Ramsar Convention: http://www.ramsar.org/types_mangroves.htm
USGS Global Mangrove Project http://lca.usgs.gov/lca/globalmangrove/index.php
Mangrove.org: http://mangrove.org/
Mangrove Action Project: http://www.mangroveactionproject.org/
FAO Mangrove Management: http://www.fao.org/forestry/mangrove/en/
USGS National Wetlands Research Center: http://www.nwrc.usgs.gov/index.html
World Atlas of Mangrove: http://data.unep-wcmc.org/datasets/22
World Distribution of Coral Reefs and Mangroves: http://www.unep-wcmc.org
For Tier 1 estimation, FAO data sources can be used to estimate wood removal and fuelwood removal. Further
sources of activity data can be found in the relevant sections of Volume 4 of the 2006 IPCC Guidelines.
Additional resources can be found in IPCC (2010).
Global mangrove cover has been mapped by the United States Geological Service (USGS) for three epochs“1975” (1973-1983), “1990” (1989 – 1993), and “2000” (1997 -2000) and is available for download at
http://edcintl.cr.usgs.gov/ip/mangrove/download.php. Global distribution of Mangroves (V3.0, 1997) has been
compiled by UNEP World Conservation Monitoring Centre (UNEP-WCMC) in collaboration with theInternational Society for Mangrove Ecosystems (ISME).
The Kyoto & Carbon Initiative of the Japan Aerospace Exploration Agency (JAXA) Global Mangrove Watch
project has used Synthetic Aperture Radar mosaics to create maps of global mangrove extent for the years 1995
and 2007-2010 (JAXA 2010a) and maps of annual changes in mangrove areas between the years 1995-2007,
2007-2008, 2008-2009 and 2009-2010. (http://www.eorc.jaxa.jp/ALOS/en/kyoto/mangrovewatch.htm).
Resources providing recent trends in coastal wetland area can help countries understand circumstances of thosetrends and what management activities contribute to them (FAO, 2007; Green and Short, 2003;
http://archive.org/stream/worldatlasofseag03gree#page/n5/mode/2up; JAXA, 2010b; Sifleet et al., 2011;
http://nicholasinstitute.duke.edu/publications?topics=34; Fatoyinbo and Simard, 2013).
Sources providing international data can be verified, validated and updated data with national sources.

3

If these links do not work, either paste into your browser or do a web search for the resources or institution.

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Chapter 4: Coastal Wetlands

Tiers 2 and 3
At Tiers 2 and 3, country-specific activity data is applied, and at Tier 3, at the resolution required for Tier 3
methods. At higher tiers, these data may be obtained from local, state or regional government department
websites as many countries and regional government authorities report this information. Countries also havetheir own remote sensing systems which can be used for land change mapping (Nasciemto et al., 2013) Wooddensity values (Annex 4A.3) of specific species need to be applied at Tiers 2 and 3. Areas of extensive
harvesting of mangroves may be assessed with aerial imagery. When the ALOS-2 satellite is operational,
generation of annual radar mosaics and mangrove extent and change maps is planned(http://www.eorc.jaxa.jp/ALOS/en/kyoto/mangrovewatch.htm).

UNCERTAINTY ASSESSMENT
The major sources of uncertainty for all wetland types, especially mangroves, are dominant species-specificdifferences in carbon content and differences due to forest age, species composition, intertidal location, soil
fertility and community structure. The confidence intervals presented in Tables 4.2 - 4.6, range from about 24%
to 200%. To reduce uncertainty, countries are encouraged to develop country- or region-specific BEFs and
BCEF values. In case country- or region-specific values are unavailable, it is good practice to check the sourcesof default parameters and their correspondence with species present, as well as with the conditions in country.
The causes of variation of annual increment of mangrove growth include climate, site growth conditions, andsoil fertility. Artificially regenerated and managed stands are less variable than natural forests. One of the ways
to improve accuracy of estimates of these wetlands includes the application of country-specific or regional
estimates of growth stratified by the dominant species present. If the default values of growth increments areused, the uncertainty of the estimates need to be clearly indicated and documented.
For mangroves, data on commercial fellings are relatively accurate, although they may be incomplete or biased
due to illegal fellings and under-reported due to tax regulations. Traditional wood that is gathered and useddirectly, without being sold, is not likely to be included in any statistics. Countries must carefully consider theseissues. The amount of wood removed from forests after storms and pest outbreaks varies both in time andvolume. No default data can be provided on these types of losses. The uncertainties associated with these losses
can be estimated from the amount of damaged wood directly withdrawn from the forest or using data on
damaged wood subsequently used for commercial and other purposes. If fuelwood gathering is treated separatelyfrom fellings, the relevant uncertainties might be high, due to the level of uncertainty associated with traditional
gathering.

4.2.1.2

D EAD ORGANIC MATTERThe guidance for changes in the carbon pools in dead organic matter (DOM; dead wood and litter) in mangroves
provided in the 2006 IPCC Guideline remains unchanged. Dead roots ≤2 cm diameter are included in the soil
pool and not considered within the dead organic matter pool. This fraction of dead roots turns over rapidly(Alongi, 2009) with the assumption of approximating steady state. Dead organic matter C stocks can varydepending on tidal inundation and frequency, as well as soil oxidation and vegetation cover. Fine litter can beexported with tidal activity (Alongi, 2009) while a larger fraction of senesced woody biomass is buried or
decomposed in-situ. In wetlands, decomposition of DOM, especially wood, is slow (Robertson and Daniel, 1989)
and accumulates as soil organic matter. Careful consideration of pools is needed in estimating inputs, outputs orchanges of dead organic matter carbon stocks to avoid double-counting. Consistent with the 2006 IPCC
Guidelines, it is good practice to consider dead organic matter carbon stock changes when management
activities in coastal wetlands result in changes in mangrove cover due to human-induced impacts.

CHOICE OF METHOD
Tier 1
If the land (1) satisfies a country’s definition of forest or (2) is a mangrove wetland with trees, that nonethelessdoes not meet the national definition of forest, and is managed for forest activities, where no land-use change has
occurred, guidance is provided in “Section 2.3.1.1 Land Remaining in a Land-Use Category” and in the specificguidance in Volume 4, of the IPCC 2006 Guidelines and applied using the default data provided in this chapter(Table 4.7) and specific guidance below. Examples may include Forest land to Forest land, Wetlands to
Wetlands or Other Wetlands to Other Wetlands.
If the land (1) satisfies a country’s definition of forest or (2) is a mangrove wetland with trees, and is managed
for forest activities where land-use change has occurred or trees have been cleared, guidance is provided in“Section 2.3.1.2 Land Converted to a Another Land-Use Category” and in the specific guidance in the relevant
chapters of Volume 4 of the IPCC 2006 Guidelines and applied using the default data provided in this chapter(Table 4.7) and specific guidance below.

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Chapter 4: Coastal Wetlands

Tier 2Estimation methodologies for Tier 2 can follow Tier 1 methods, but apply country-specific data. The StockDifference method (Chapter 4, Volume 4 of the 2006 IPCC Guidelines) could also be applied if countries havesample plot data from forest inventories for two points in time. Literature data or carbon databases may provide
more feasible and cost-effective data to apply this method.

Tier 3
Loss estimates of dead wood and litter due to tidal movement (export) can also be considered (Appendix 4a.1).
Tier 3 methods may further employ stratification by ecological zone or disturbance regime to reduce
uncertainties. It is good practice to sum changes in both dead wood and litter to report changes in total deadorganic matter. Additional Tier 3 guidance is provided in Chapter 4, Volume 4 of the 2006 IPCC Guidelines.

CHOICE OF EMISSION/R EMOVAL FACT ORS
Tier 1
Default values are provided in Table 4.7 of this supplement for use in Tier 1 assessment of emissions andremovals.

Tier 2Tier 2 methods using country-specific data can be used if such country-specific data can be acquired atreasonable cost.

Tier 3Tier 3 emission factors include model output and validation and disaggregated data sources. Field measurements
can be developed and used to inform and validate model output at Tier 3. For mangroves, Tier 3 methodologies
can employ empirical relationships to provide estimates of canopy litter fall and census of downed wood lying
on the forest floor.

TABLE 4.7
TIER 1 DEFAULT VALUES FOR LITTER AND DEAD WOOD CARBON STOCKS IN MANGROVES
DomainEcosystem
type

Litter C stocks of mature stands(tonnes C ha-1) with 95% CI1

Dead wood C stocks of mature stands(tonnes C ha-1) with 95% CI1

Tropical/Subtropicalmangroves

0.7 (0-1.3)

10.7 (6.5-14.8)

Litter: Utrera-Lopez and Moreno-Casasola, 2008; Liao et al., 1990; Chen et al., 2008; Richards et al., 2011; Ramose-Silva et al., 2007;
Twilley et al., 1986
Dead Wood: Kauffman et al., 2011; Donato et al., 2012; Allen et al., 2000; Steinke et al., 1995; Robertson et al., 1989; Tam et al., 1995;
Krauss et al., 2005
1

95% CI of the geometric mean

CHOICE OF ACTIVITY D ATA
Tier 1
Carbon stock changes in dead organic matter are generally not reported at Tier 1 when management activities incoastal wetlands do not result in changes in mangrove cover due to human-induced impacts (following guidancein Section 4.2.2.3 of Chapter 4, Volume 4 of the 2006 IPCC Guidelines), and thus no activity data are required.
If a land-use change has occurred resulting from an increase in woody biomass stock, it is good practice toreport the change in dead organic matter carbon stock. For a Tier 1 method, the annual rate of conversion to
Forest Land or other land-use categories with woody mangrove biomass is required, following Section 4.3.2.3 ofChapter 4, Volume 4 of the 2006 IPCC Guidelines. Activity data should be consistent with those used for
estimating changes in carbon stock.

Tier 2 and T ier 3
Inventories using higher tiers will require more comprehensive information on the establishment of new forests,
using climate, for example, as a disaggregating factor and at higher spatial and temporal resolution. Additional
resources can be found in IPCC (2010).

UNCERTAINTY ASSESSMENT
The uncertainty assessment given in section 4.2.2.5 in Chapter 4, Volume 4 of the 2006 IPCC Guidelines
identifies sources of uncertainty in estimates of carbon stock changes in the dead organic matter pool of2013 Supplement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories: Wetlands

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Chapter 4: Coastal Wetlands

mangroves. Other sources of uncertainty include output of dead organic matter due to decomposition or tidal
export.

4.2.1.3

S OIL CARBONThe Tier 1 default assumption is that soil CO2 emissions and removals are zero (EF=0) for forest management
practices in mangroves. This assumption can be modified at higher tiers. At higher tiers, it is recommended toconsider CO2 emissions from soils due to forest clearing in carbon stock estimations (Alongi et al., 1998). It
should also be considered that at Tier 1, rewetting (section 4.2.3) and drainage activities (section 4.2.4) can occur
as a result of forest management practices. In this case, follow the guidance for estimating CO2 emissions andremovals from soil carbon stock changes (Sections 4.2.3.3 and 4.2.4.3, respectively).

4.2.2

Extraction

Extraction refers collectively to the following activities: (A) excavation (associated with dredging used toprovide soil for raising the elevation of land, or excavation to enable port, harbour and marina construction andfilling), (B) construction of aquaculture ponds and (C) construction of salt production ponds (where soil is
excavated to build berms where water is held in ponds). Each of these extraction activities is associated with theremoval of biomass, dead organic matter and soil, which results in significant emissions when their removal isfrom saturated (water-logged) to unsaturated (aerobic) conditions (World Bank, 2006). The Tier 1 methodology
assumes that the biomass, dead organic matter and soil are all removed and disposed of under aerobic conditions
where all carbon in these pools is emitted as CO2 during the year of the extraction with no subsequent changes.
Tier 1 guidance is given here for reporting the intial changes in carbon (Table 4.1). Regardless of whether the
extraction activities result in a change in land-use category, CO2 emissions and removals associated withextraction are the same, following Equation 4.2 below. This approach follows the methodology applied for peat
extraction in Chapter 7, Volume 4 of the 2006 IPCC Guidelines.

EQUATION 4.2
TIER 1 ESTIMATION OF INITIAL CHANGE IN CARBON STOCKS WITH EXTRACTION(ALL C POOLS)ΔCEXT = ΔCexcav + ΔCaq-constr + ΔCsp-constr
Where:ΔCEXT = Changes in carbon stocks from all extraction activities; tonnes C
ΔCexcav = Initial change in biomass, dead organic matter and soil carbon stocks from extraction due to
excavation; tonnes C
ΔCaq-constr = Initial change in biomass, dead organic matter and soil carbon stocks from extraction during
construction of aquaculture ponds; tonnes C
ΔCsp-constr = Initial change in biomass, dead organic matter and soil carbon stocks from extraction during
construction of salt production ponds; tonnes C
Equation 4.2 is applied to the total area of coastal wetland where extraction activities take place. The terms
ΔCexcav, ΔCaq-constr, and ΔCsp-constr are estimated as ΔCCONVERSION (Equations 4.4 - 4.6) for intial change in carbon
stocks of each of the C pools for each of the respective activities comprising extraction. Equation 4.3 is applied
for each of the extraction activities (and A-C as described above) to estimate the intial change in stocks of eachof the C pools.
EQUATION 4.3
INITIAL CHANGE IN CARBON STOCKS WITH EXCAVATION (ALL C POOLS)
ΔCexcav = ΔCexcav-AB + ΔCexcav-BB + ΔCexcav-DOM + ΔCexcav-SO
Where:
ΔCexcav = Initial change in biomass, dead organic matter and soil carbon stocks with excavation; tonnes C
ΔCexcav-AB = Initial change in above-ground biomass carbon stock changes with excavation; tonnes C
ΔCexcav-BB = Initial change in below-ground biomass carbon stock changes with excavation; tonnes C
ΔCexcav-DOM = Initial change in dead organic matter carbon stock changes with excavation; tonnes C

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Chapter 4: Coastal Wetlands

ΔCexcav-SO = Initial change in soil carbon stock changes with excavation as annual CO2 emissions andremovals; tonnes C
At Tier 1,
ΔCexcav-AB + ΔCexcav-BB= ΔCB-CONVERSION (Equation 4.4, Section 4.2.2.1)
ΔCexcav-DOM = ΔCDOM-CONVERSION (Equation 4.5, Section 4.2.2.2)
ΔCexcav-SO = ΔCSO-CONVERSION (Equation 4.6, Section 4.2.2.3)
Equation 4.3 provides the formulation to estimate the initial change in carbon stock in each C pool for the
specific extraction activity, excavation. To estimate the initial changes in intial carbon stock change for thesepools for construction of aquaculture and salt production ponds, replace ΔC excav with ΔCaq-constr and ΔCsp-constr inEquation 4.3, respectively.
The Tier 1 methodology assumes that the biomass, dead organic matter and soil are all removed and disposed ofunder aerobic conditions where all carbon in these pools is emitted as CO2 during the year of extraction(consistent with the assumption applied for peat extraction in Section 7.2.1.1, Chapter 7, Volume 4 of the 2006
IPCC Guidelines) and that no subsequent changes occur.
Table 4.8 summarises the Tier level guidance provided for extraction activities, which deals with excavation in
general and excavation during the construction phase of aquaculture and salt production, in particular. Estimates
are not made at Tier 1 for CO2 emissions and removals while (1) fish ponds are stocked and salt production is
occuring (use phase of aquaculture and salt production) or (2) when the activity has ceased (discontinued phase),although they are considered together with other extraction activities because the activity data are linked.
TABLE 4.8
SUMMARY OF TIER 1 ESTIMATION OF INITIAL CHANGES IN CARBON POOLS FOR EXTRACTION ACTIVITIESC pools

Extraction
activities

Mangrovebiomass,dead woodand litter1
Excavation
Aquaculture
Construction
and
Use
Salt
Discontinued
Production

Tier 1
Tier 1

Soils
Mangrove and Tidal Marsh

Seagrass
Meadow

Organic

Mineral2

Tier 1
Tier 1

MineralTier 1
Tier 1
No guidance4
No guidance4

1

Removal of biomass resulting from extraction activities is estimated at Tier 1 level in mangroves only.

2

Tier 1 assumption is that all seagrass soils are mineral.

3

Extraction activity of aquaculture pond construction, is not applicable for seagrass meadows.

4

No suitable Tier 1 methodologies are available for C pools during these phases/activities.

4.2.2.1

Tier 1NA3B IOMASS

This section addresses estimation of changes in living (above and below-ground) biomass pools associated withextraction activities comprising excavation, and construction of aquaculture and salt production ponds in coastal
wetlands. For extraction in coastal wetlands with tidal marshes and seagrass meadows, changes in biomass
carbon stocks are reported at only Tier 2 or higher estimations. It is good practice to report the conversion ofabove-ground and below-ground biomass that occurs with extraction of mangroves.

CHOICE OF METHOD
Following Box 4.1 extraction may or may not result in a change in land-use category, however the same
methodologies apply for mangrove wetlands with forest regardless of how the land is classified.

Tier 1
Changes in carbon stock of living biomass during extraction are associated with clearing and removal ofvegetation. The area applied is that of a certain year in which the conversion occurs. Regardless of the land-use
category, the loss in biomass associated with extraction activities is estimated as ∆Cconversion following the2013 Supplement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories: Wetlands

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Chapter 4: Coastal Wetlands

methodology for peat extraction (Chapter 7, Volume 4 of the 2006 IPCC Guidelines), modified here as Equation
4.4.
EQUATION 4.4
TIER 1 ESTIMATION OF INITIAL CHANGE IN BIOMASS CARBON STOCKS DUE TO EXTRACTION
ACTIVITIESΔCB-CONVERSION = ∑v,c{BAFTER • (1+R) − BBEFORE * (1+R)} • CF • ACONVERTEDv,cWhere:ΔCB-CONVERSION = Changes in biomass carbon stock from conversion due to extraction activities; tonnes C
BAFTER = Carbon stock in above-ground biomass per unit of area immediately after the conversion byvegetation type (v) and climate (c); tonnes d.m. ha-1; default value = 0
BBEFORE = Carbon stock in above-ground biomass per unit of area immediately before the conversion;
tonnes d.m. ha-1
R = ratio of below-ground biomass to above-ground biomass by vegetation type (v) and climate (c); tonnes
d.m. below-ground biomass (tonnes d.m. above ground biomass)-1
CF = carbon fraction of dry matter; tonnes C (tonnes d.m.)-1
ACONVERTED = Area of conversion by vegetation type (v) and climate (c); ha
The Tier 1 methodology assumes that the biomass is removed and disposed of under aerobic conditions where all
carbon is emitted as CO2 during the year of the extraction and that no subsequent changes occur. At Tier 1,
initial change in carbon stocks of biomass {BAFTER • (1+R) − BBEFORE • (1+R)} is assumed to be zero for coastal
wetlands without perennial biomass or trees. For mangrove wetlands with perennial biomass or trees, the stock
after the conversion (BAFTER) at Tier 1 is taken to be zero.

Tier 2
At Tier 2, changes of carbon stock in living above-ground biomass of tidal marsh and seagrass meadow
vegetation can be estimated and reported for the specified activities employing the equation for ΔCB-CONVERSION,
using country-specific emission factors and default values for R given in Tables 4.9 and 4.10, in conjunction
with country-specific data on above-ground biomass. At Tier 2, the Gain-Loss or Stock-Difference methods canbe applied to estimate biomass carbon stock changes of mangrove in lands where extraction activities(aquaculture and salt production) are discontinued (i.e. regrowth). Tier 2 approaches could also include
evaluation of the assumption of instantaneous oxidation of the converted biomass pool.

Tier 3
In Tier 3, estimation could include methods to incorporate data on the fraction of biomass carbon stock that is
retained under saturated conditions to improve estimation of proportion of carbon that is oxidized.

CHOICE OF EMISSION/R EMOVAL FACT ORS
Tier 1
Default data for Tier 1 method is provided for mangroves in Tables 4.2-4.6, Section 4.2.1, including aboveground biomass carbon stock, carbon fraction and below-ground to above-ground ratio, for the different climate
domains and regions, where applicable.

Tier 2
Under Tier 2, countries apply country-specific data to estimate changes in carbon stock in above-ground biomass.
The conversion of above-ground and below-ground biomass that occurs with extraction activities in tidal marshand seagrass meadows may be estimated using Tables 4.9 and 4.10 for tidal marshes and seagrass meadowsrespectively. These data are to be used in conjunction with the carbon fraction of dry matter alongside countryspecific data on above-ground biomass carbon stock.

Tier 3
Field measurements can be developed and used to inform and validate model output at Tier 3. It is expected thatdata improvements for excavation activities such as ground-truth estimates of overall area impacted, the depth atwhich removal of biomass has occurred, or the fraction of biomass removal, could be used to develop and verify
models.

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Chapter 4: Coastal Wetlands

TABLE 4.9
RATIO OF BELOW- GROUND BIOMASS TO ABOVE-GROUND BIOMASS (R) FOR TIDAL MARSHES
DomainR[tonne root d.m.
(tonne shoot d.m.)-1]

95% CI5

Rangen

Mediterranean

3.631

3.56, 3.70

1.09-7.15

5Subtropical

3.65

2

3.56, 3.74

2.23-9.41

5

Temperate
freshwater tidal

1.153

1.12, 1.18

0.36-3.85

7Temperate

2.114

2.07, 2.15

0.33-10.15

17

1

Sources: Scarton et al., 2002; Neves et al., 2007; Boyer et al., 2000

2

Sources: Lichacz et al., 1984; da Cunha Lana et al., 1991

3

Sources: Birch and Cooley, 1982; Whigham et al., 1978

4

Sources: Kistritz et al., 1983; Hussey and Long, 1982; Smith et al., 1979; Dunn, 1981; Connor and Chmura, 2000; Gross et al.,
1991; Whigham et al., 1978; Elsey-Quirk et al., 2011; Adams et al., 2012
595% CI of the geometric mean

TABLE 4.10
RATIO OF BELOW- GROUND BIOMASS TO ABOVE-GROUND BIOMASS (R) FOR SEAGRASS MEADOWS
DomainR[tonne root d.m.
(tonne shoot d.m.)-1]

95% CI4

Rangen

Tropical

1.71

1.5, 1.9

0.05-25.62

396

2.4

2

2.3, 2.6

0.07-16.8

391

1.3

3

1.1, 1.5

0.14-13.8

91

Subtropical
Temperate
1

Sources: Aioi and Pollard, 1993; Brouns, 1985; Brouns, 1987; Coles et al., 1993; Daby, 2003; Devereux et al., 2011; Fourqurean
et al., 2012; Halun et al., 2002; Holmer et al., 2001; Ismail, 1993; Lee, 1997; Lindeboom and Sandee, 1989; McKenzie, 1994;
Mellors et al., 2002; Moriarty et al., 1990; Nienhuis et al., 1989; Ogden and Ogden, 1982; Paynter et al., 2001; Poovachiranon
and Chansang, 1994; Povidisa et al., 2009; Rasheed, 1999; Udy et al., 1999; van Lent et al., 1991; van Tussenbroek, 1998;
Vermaat et al., 1993; Vermaat et al., 1995; Williams, 1987
2

Sources: Aioi, 1980; Aioi et al., 1981; Asmus et al., 2000; Bandeira, 2002; Boon, 1986; Brun et al., 2009; Collier et al., 2009; deBoer, 2000; Devereux et al., 2011; Dixon and Leverone, 1995; Dos Santos et al., 2012; Dunton, 1996; Fourqurean et al., 2012;
Hackney, 2003; Herbert and Fourqurean, 2008; Herbert and Fourqurean, 2009; Holmer and Kendrick, 2012; Jensen and Bell,2001; Kim et al., 2012; Kirkman and Reid, 1979; Kowalski et al., 2009; Larkum et al., 1984; Lee et al., 2005; Lee et al., 2005b;
Lipkin, 1979; Longstaff et al.,1999; Masini et al., 2001; McGlathery et al., 2012; McMahan, 1968; Meling-Lopez and IbarraObando, 1999; Mukai et al., 1979; Paling and McComb, 2000; Park et al., 2011; Powell, 1989; Preen, 1995; Schwarz et al., 2006;
Stevensen, 1988; Townsend and Fonseca, 1998; Udy and Dennison, 1997; van Houte-Howes et al., 2004; van Lent et al., 1991;
van Tussenbroek, 1998; Walker, 1985; West and Larkum, 1979; Yarbro and Carlson, 2008
3

Sources: Agostini et al., 2003; Cebrian et al., 2000; Fourqurean et al., 2012; Hebert et al., 2007; Holmer and Kendrick, 2012;
Larned, 2003; Lebreton et al., 2009; Lillebo et al., 2006; Marba and Duarte, 2001; McRoy, 1974; Olesen and Sand-Jensen, 1994;
Rismondo et al., 1997; Sand-Jensen and Borum, 1983; Terrados et al., 2006
4

95% CI of the geometric mean

CHOICE OF ACTIVITY D ATA
Extraction: Submissions of licenses for prospecting and exploitation and associated environmental impact
assessments (EIAs) can be used to obtain areas under extraction activities. Relevant regulation for extraction canbe found at international and national levels. International regulation is covered by the UN Convention on the
Law of the Sea (UNCLOS) 1982 (www.un/org/Depts/los/index.htm). Contracting Parties are under the
obligation to publish/communicate reports on monitoring and assessment of potential harmful effects ofextraction. The OSPAR Convention 1992 (www.ospar.org) provides guidance for programmes and measures forthe control of the human activities in the North-East Atlantic region. The “Agreement on Sand and Gravel
Extraction” provides that authorisation for extraction of marine soils from any ecologically sensitive site should
be granted after consideration of an EIA. The Helsinki Convention 1992 (www.helcom.fi) covers the Baltic Sea
Area and requires EIAs to be carried out as part of the extraction process and that “monitoring data” and “resultsof EIA’s………be made available for scientific evaluation”. The Barcelona Convention 1995

2013 Supplement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories: Wetlands

4.21

Chapter 4: Coastal Wetlands(www.unepmap.org), covers the regulatory framework for the Mediterranean. The ICES Convention 1964
(www.ices.dk) provides data handling services to OSPAT and Helsinki Commissions. An overview of theregulation of marine aggregate operations in some European Union Member States is reported in Radzevicius etal. (2010) and includes relevant EC Directives and national legislation/regulation. Other such sources of activity
data include, for example, statistics on sand and gravel extraction for the OSPAR martime area (e.g.
www.ospar.org/documents/dbase/publications/p0043) as well as information on sand and gravel activities andrelated statistics for North Sea Continental Shelfs and UK waters (http://www.sandandgravel.com/).
If time series data back to 1990 are unavailable, it is suggested that surrogate data be used, derived fromstatistical reports/databases containing information on temporal changes in proxy factors such as humanpopulation density, port or marina development, port revenue, shipping tonnage, and commodity exports. Suchdata can be obtained from the internet e.g. for the Asia-Pacific region from the UN ESCAP Commission(http://www.
unescap.org/stat/)
and
for
the
Balticfrom
http://epp.eurostat.ec.europa.eu/portal/page/portal/statistics/themes. Data on shipping indices can be obtained
from http://www.worldshipping.org/about-the-industry/global trade/trade-statistics. Such data for most countries
can also be obtained from http://datacatalog.worldbank.org.
Aquaculture and salt production: Annual data (1950 – present) providing statistics on aquaculture production
is collated by the FAO Fisheries and Aquaculture Department. Additional data on type aquaculture (e.g.
freshwater or brackish) and area under aquaculture production is summarised in country profiles enablingstratificationofaquaculture
into
those
occurringincoastalwetlands(http://www.fao.org/fishery/countryprofiles/search/en). As local regulations typically apply for developing new
aquaculture activites (i.e licensing, permitting), regulations also typically apply to report such activities to the
Ministry of Fisheries and Marine Affairs (or country equivalent). For example an aquaculture farm needs to get alicense (or permission) to operate. Depending on the country, it is given by the regional (e.g. in Spain it is theautonomic, e.g. Balearic- government, who approves it) or local (e.g. at Bolinao, The Philipines) and maybe inothers the national government. For example, in Indonesia local government must be consulted on land-use
change including aquaculture pond construction and are obliged to report activities to the Ministry of Fisheries
and Marine Affairs.
Similar project information for salt production activities can be obtained from the Salt Institute atwww.saltinstitute.org.
Literature sources can also provide national area change statistics from aerial photographs of ponds or structures
used for aquaculture and salt production.
A map of available tidal marsh distribution (with area data) is in production by the World Conservation andMonitoring Center (WCMC; http://data.unep-wcmc.org/) currently holding layers for Europe, the United States,
Australia and China. It is the intent to expand mapping of tidal marsh to global coverage.
A map of global distribution of seagrasses (V2.0, 2005) is also available at the WCMC (http://data.unepwcmc.org/) and prepared in collaboration with Dr. Frederick T. Short. Other regional and national maps are alsoavailable (e.g. http://www.ospar.org/documents/dbase/publications/p00426_zostera_beds). A tabulated list of
web sites for existing seagrass monitoring programmes is given in Borum et al., (2000;
http://www.seagrasses.org/handbook/european_seagrasses_high.pdf).
These data sources, and those provided in Section 4.2.1.1, can be used in conjunction with activity data
described above to improve estimations of areas of mangroves, tidal marsh and seagrass meadow undergoing
extraction activities.

UNCERTAINTY ASSESSME NT
For uncertainty assessment for mangroves, see Section 4.2.1 (this chapter). The uncertainties involved in
extraction in mangroves also follow those outlined in Section 4.3.1.5 of Chapter 4, Volume 4 of the 2006 IPCC
Guidelines. Variability in tidal marsh biomass will be due to differences in dominant species and competition
between species, as well as salinity of flood waters, frequency of tidal flooding and climate. For example, thehigh biomass in mediterranean climates is due to the frequent dominance of perennial shrubs. For all vegetation
there can be considerable interannual variability in production of biomass and seasonal variability in standing
biomass that contributes to uncertainty in ratios of below-ground to above-ground biomass. Most empirical data
are available from temperate regions and North America and there are limited data available for tidal freshwaterand boreal and subtropical tidal marshes. The average ratio of below-ground to above-ground biomass forseagrass is variable depending on the dominant species, and fertility of the soil. The data are mainly derived
from observations along the coasts of North America, Western Europe and Australia. Data were scarce fromSouth America and Africa.

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Chapter 4: Coastal Wetlands

4.2.2.2

D EAD ORGANIC MATTER

Previously saturated dead organic matter (DOM), which is exposed to aerobic conditions, can contribute to large
sources of CO2 emissions from extraction activities. Consistent with the 2006 IPCC Guidelines for Forest Land,in coastal wetlands, it is good practice to consider dead organic matter carbon stock changes when extraction
activities result in changes in mangrove cover due to these human-induced impacts.

CHOICE OF METHOD
Tier 1
During extraction activities, existing dead organic matter pools may be reduced to zero as vegetation is cleared
and removed while at the same time no new carbon enters the dead organic matter pool. At Tier 1, changes incarbon stock in dead organic matter in tidal marshes and seagrass meadows are assumed to be zero. It is noted,
however, that extraction activities that result in vegetation or soil disturbance in tidal marsh with perennial
woody biomass may have significant impacts on CO2 emissions and removals. It is good practice for countryspecific methods to be developed to cover these cases, if feasible. Regardless of the land-use category, the loss indead organic matter associated with extraction activities is estimated as ∆C conversion following the methodology
applied for peat extraction (Chapter 7, Volume 4 of the 2006 IPCC Guidelines), modified here as Equation 4.5:

EQUATION 4.5
TIER 1 ESTIMATION OF INITIAL CHANGE IN DEAD ORGANIC MATTER CARBON STOCKS DUE TO
EXTRACTION ACTIVITIESΔCDOM-CONVERSION = ∑v(DOMAFTER − DOMBEFORE)v • ACONVERTEDv
Where:ΔCDOM-CONVERSION = Initial changes in dead organic matter carbon stock from conversion due to extraction
activities by vegetation type (v); tonnes C
DOMAFTER = Carbon stock in dead organic matter per unit of area immediately after the conversion byvegetation type (v); tonnes d.m. ha-1; default value = 0
DOMBEFORE = Carbon stock in dead organic matter per unit of area immediately before the conversion byvegetation type (v); tonnes d.m. ha-1
ACONVERTED = Area of conversion by vegetation type (v); ha
The Tier 1 methodology assumes that the dead organic matter is removed and disposed of under aerobic
conditions where all carbon is emitted as CO2 during the year of the extraction and that no subsequent changes
occur. The choice of method follows that in Section 4.2.2.

Tiers 2 and 3
The choice of method follows that in Section 4.2.2. For these management activities that impact dead organic
matter pools in tidal marshes with perennial or woody biomass, Tier 2 and higher estimation methods arerecommended.

CHOICE OF EMISSION/R EMOVAL FACT ORS
Tier 1
Default values of dead organic matter carbon stock (for dead wood and litter) for mangroves are provided inTable 4.7 of this supplement for use in Tier 1 estimations. In tidal marsh and seagrass meadows the Tier 1
assumption is that carbon stocks in the dead organic matter pools resulting from extraction activities are zero.

Tier 2
At Tier 2, the assumption that all dead organic matter lost in the year of conversion is oxidized can be reassessed.
Tier 2 assumption of zero for dead organic matter pools in tidal marsh can also be assessed. It is good practicefor countries, in such cases, to use national estimates for dead organic matter carbon stocks for mangroves andtidal marshes with perennial biomass, if such country-specific data can be acquired at reasonable cost.

Tier 3Tier 3 emission factors include model output and validation and disaggregated data sources.

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Chapter 4: Coastal Wetlands

CHOICE OF ACTIVITY D ATA
Choice of activity data follows from guidance provided in Section 4.2.2.1. The area in which the extraction
activities occur will be the same area applied for each carbon pool, especially forest biomass.

UNCERTAINTY ASSESSME NT
The discussion on uncertainty outlined in Section 4.3.2.5 of Chapter 4, Volume 4 of the 2006 IPCC Guidelines isalso relevant for extraction of mangroves.

4.2.2.3

S OIL CARBON

Extraction activities that occur within coastal wetlands can influence organic and mineral stocks of carbon insoils and both soil types are covered at Tier 1 (Table 4.11). During extraction activities, the stock of soil carbon
that is removed depends on the soil type (i.e. carbon stock is higher in organic soils). For Tier 1 estimation, in theabsence of soil map data or other resources to differentiate soil type, the following assumptions can be applied.
i. Assume that soils in which seagrass grow are mineral.
ii. Assume all soils, regardless of dominant vegetation in or at the mouth of estuaries or adjacent to any river
characterised by a large and/or mountainous catchment and high flow, are mineral. For all othermangroves and tidal marshes the soils are organic. See Durr et al. (2011) for additional national levelguidance.
iii. If soils cannot be dissagregated into organic and mineral, use the aggregated default data given in Table
4.11.

CHOICE OF METHOD - ORGANIC AND MINERAL SOILS
Tier 1
Regardless of the land-use category, the loss in soil carbon associated with extraction activities is estimated as∆Cconversion following the methodology applied for peat extraction (Chapter 7, Volume 4 of the 2006 IPCC
Guidelines), modified here as Equation 4.6.
EQUATION 4.6
TIER 1 ESTIMATION OF INITIAL CHANGE IN SOIL CARBON STOCKSDUE TO EXTRACTION ACTIVITIESΔCSO-CONVERSION = ∑v,s(SOAFTER − SOBEFORE)v,s • ACONVERTEDv,s
Where,
ΔCSO-CONVERSION = Initial changes in soil carbon stock from conversion due to extraction activities byvegetation type (v) and soil type (s); tonnes C
SOAFTER = Soil carbon stock per unit of area, immediately after the conversion, by vegetation type (v) andsoil type (s); tonnes C ha-1; default value = 0
SOBEFORE = Soil carbon stock per unit of area, immediately before the conversion, by vegetation type (v)and soil type (s); tonnes C ha-1
ACONVERTED = Area of conversion by vegetation type (v) and soil type (s); haAt Tier 1, soil extraction depth to 1 m approximates the mid-range of the extraction depth for construction of
aquaculture and salt production ponds (see extraction activities in section 4.1). Countries may modify theassumption of 1 m extraction depth at higher tiers.
The Tier 1 methodology assumes that the soil is removed and disposed of under aerobic conditions where thecarbon stock is emitted as CO2 (oxidised) during the year of the extraction. The carbon stock is taken as all soil
carbon except any refractory (unoxidisable) carbon. In mangrove soils, 4% of the carbon stock is refractory(Annex 4A.4) and this is taken to be representative of the refractory carbon in tidal marshes and seagrassmeadows as well. Therefore, after the initial conversion of the soil pool in the year in which the activity occurs,
CO2 emissions are reported as zero. It is good practice to track these lands to consider management activities
that may occur on those lands in the future and for higher tier estimations. The choice of method follows that in
Section 4.2.2. For Tier 1, CO2 emissions are reported as the conversion in soil carbon where this activity occurs;
the type of vegetation and the available activity data to distinguish between organic and mineral soils determines
which data are applied from Table 4.11.

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Chapter 4: Coastal Wetlands

Tier 2
At Tier 2, methodology can be applied to disaggregate by vegetation type and soil type. For the specificextraction activity, countries may use national data to determine their particular extraction processes and thevolume of soil removed, if sufficient data are available. Because tidal marshes can occur in a range of climates,
disaggregating by climate may also be applied to improve estimates if those country-specific data are available.
Tier 2 may also refine the estimate for the soil carbon stock that is excavated to construct the aquaculture or salt
production ponds by including country-specific information on the depth excavated during the construction
phase.

Tier 3Tier 3 methods can employ models to estimate CO2 emissions based on the effect of temperature and salinity on
soil oxidation both seasonally and with climate and vegetation type. At Tier 3, it is good practice for countries tovalidate models with field measurements. Tier 3 methods may also include site-specific measurements of, forexample, carbon content, bulk density, clay content, salinity, redox potential, etc., to determine the underlying
processes of emissions.

CHOICE OF EMISSION FACTORS - ORGANIC AND MINER AL SOILS
Tier 1
Default Tier 1 soil carbon stocks (to 1 m depth) for mangrove, tidal marsh and seagrass meadows for the
calculation of CO2 emissions are given in Table 4.11. These values are to be used in conjunction with Equation
4.6 to estimate emissions. If soil type is not known, a generic default value for aggregated organic and mineralsoils can be applied (Table 4.11).

Tier 2Tier 2 includes the use of country-specific emission factors that can be applied to disaggregate by soil type andvegetation type to improve on Tier 1 estimates. Country-specific data may include excavation depth to improveon the default estimation of soil extracted.

Tier 3
A Tier 3 approach could use models that take into account the time-dependent nature of the CO2 fluxes over arange of timescales. For example, during the construction phase, a pulse of CO2 efflux from soil directly after
mangrove clearing and prior to excavation, followed by a logarithmic decline in CO 2 fluxes over time, has beenshown to occur (Lovelock et al., 2011). For fish and shrimp ponds, the actual area excavated and the depth towhich soil is excavated, could be taken into account as this varies with aquaculture and salt production practices.

CHOICE OF ACTIVITY D ATA
Choice of activity data follows from guidance above provided in Section 4.2.2.1 as the area in which theextraction activities occur will be the same area applied for each C pool.

UNCERTAINTY ASSESSME NT
Variability in soil carbon stocks will derive from a number of sources. The soil stock represents global averages
and may therefore under or over-estimate emissions and removals when applied to specific countries. Deriving
country-specific carbon stocks can reduce uncertainties using Tier 2 methodology. There may also be significant
within country differences due to: (1) the dominant species present in mangroves, tidal marshes or seagrassmeadows, (2) climatic conditions and (3) general environmental setting in which the vegetation is found, all ofwhich may influence the carbon stock. When deriving global emission factors, uncertainties can also be
introduced by areas where there is greater prevalence of data from specific regions of the globe. The change incarbon stock on extraction is dependent on the value assigned to the percent refractory organic carbon. The value
applied is taken from soil in mangroves and may not be fully representative of the value for tidal marshes andseagrass meadows.

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Chapter 4: Coastal Wetlands

TABLE 4.11
SOIL CARBON STOCKS FOR MANGROVES, TIDAL MARSHES AND SEAGRASS MEADOWS FOR EXTRACTION ACTIVITIESORGANIC SOILS ( TONNES C HA-1)
Vegetation type

95% CI1

range

n

471

2

436, 510

216-93543

3315, 366

221-579

35

SOBEFORE

MangroveTidal marsh

340

4

Seagrass meadow

NA
MINERAL SOILS ( TONNES C HA-1)
95% CI1

rangen

Mangrove286

5247, 330

55-1376

77

Tidal marsh

2266

202, 252

15.6-623

82

8

84, 139

9.1-82989

Vegetation type

SOBEFORE

108

7

Seagrass meadow

AGGREGATED ORGANIC AND MINERAL SOILS ( TONNES C HA-1)

Mangrove

SOBEFORE
386

95% CI1
351, 424

range
55-1376n
119

Tidal marsh

255

254, 297

15.6-623

117

Vegetation type1

95% CI of the geometric mean

2

Sources: Adame et al., 2012; Breithaupt et al., 2012; Chmura et al., 2003; Donato et al., 2011; Kauffman et al., 2011; Osborne
et al., 2011; Vegas-Vilarrúbia et al., 2010
3

Sources: Anisfeld et al., 1999; Callaway et al., 1996; Callaway et al., 2012; Chmura and Hung, 2004; Craft et al., 1988; Craft,
2007; Hussein et al., 2004; Kearney and Stevenson, 1991; Orson et al., 1998; Markewich et al., 1998; McCaffrey and Thomson,
1980
4

Seagrass meadows are assumed to be on mineral soils.

5

Sources: Donato et al., 2011; Chmura et al., 2003; Breithaupt et al., 2012; Fujimoto et al., 1999; Adame et al., 2012; Perry and
Mendelssohn, 2009; Ren et al., 2010; Kauffman et al., 2011; Ray et al., 2011; Zhang et al., 2012; Khan et al., 2007; Matsui,
1998
6

Sources: Cahoon et al., 1996; Callaway et al., 2012; Chmura and Hung, 2004; Connor et al., 2001; Craft et al., 1988; Craft,
2007; Hatton, 1981; Kearney and Stevenson, 1991; Livesley and Andrusiak, 2012; Loomis and Craft, 2010; Morris and Jensen,
2003; Oenema and DeLaune, 1988; Patrick and DeLaune, 1990; Roman et al., 1997; Yu and Chmura, 20097

For extraction only

8

Source: Fourqurean et al., 2012

4.2.3

Rewetting, revegetation 4 and creation of mangroves,tidal marshes and seagrass meadowsThis section addresses the carbon stock changes and CO2 emissions and removals for the rewetting, revegetationand creation activities relating to mangroves, tidal marshes and seagrass meadows.
The rewetting and revegetation activity refers collectively to the following (1) rewetting, which saturates the soilof drained sites previously colonised by mangrove and tidal marshes and is a prerequisite for, and thus facilitates,
reestablishment of the original vegetation by natural recolonisation, direct seeding and/or purposeful planting, (2)raising or lowering the soil elevation to facilitate reestablishment of the original vegetation by natural
recolonisation, direct seeding and/or purposeful planting, (3) creation of coastal wetlands where it may bedifficult to identify where they previously occurred and are in proximity to the coastal margin, and (4)reestablishment of seagrass on undrained soils by natural recolonisation, direct seeding and/or purposefulplanting.

4.2.3.1

B IOMASS

The initiation of soil carbon accumulation is only possible with the presence of vegetation, which is introducedby purposeful seeding/planting or natural recolonisation For mangroves, methodological guidance for estimating
4

The term revegetation is used to refer to practices within the framework of UNFCCC reporting.

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Chapter 4: Coastal Wetlands

carbon stock changes in the biomass pool, including choice of method and choice of emission and removal
factors, follows Section 4.2.1.1 of this Chapter. For tidal marshes and seagrass meadows, changes in biomass
carbon stocks, are reported only for Tier 2 or higher estimations. Guidance for estimating biomass carbon stockchanges for tidal marshes and seagrass meadows follow those presented in Volume 4, Section 6.2.1.1 of the 2006
IPCC Guidelines (Grassland Remaining Grassland) for Gain-Loss and Stock-Difference methods. These areused with country-specific data on above-ground biomass stocks and ratios of below-ground to above-groundbiomass provided in Tables 4.9 and 4.10. Refer to Volume 4, Section 6.2.1.4 of the 2006 IPCC Guidelines forcalculation steps useful in applying these methods.

4.2.3.2

D EAD ORGANIC MATTER

For mangroves, methodological guidance for estimating carbon stock changes in the dead organic matter pool,including choice of method and choice of emission and removal factors, follows Section 4.2.1.2 of this Chapter.
For tidal marshes and seagrass meadows, changes in biomass carbon stocks, are reported only for Tier 2 orhigher estimations. Guidance for estimating dead organic matter carbon stock changes for tidal marshes andseagrass meadows follows that presented in Volume 4, Section 6.2.2.1 of the 2006 IPCC Guidelines (Grassland
Remaining Grassland) for Gain-Loss and Stock-Difference methods. These are used with country-specific data.
Refer to Volume 4, Section 6.2.2.4 of the 2006 IPCC Guidelines for calculation steps useful in applying thesemethods.

4.2.3.3

S OIL CARBON

The guidance provided in this section on soils differs from that in Chapter 3 (this supplement) because, on
coastal wetland soils, revegetation leads to the accumulation of soil organic carbon when vegetation isreestablished and a CO2 sink is then developed. The CO2 emission factor is approximated as zero whenresaturated soils are devoid of vegetation. This is consistent with the default EFs for rewetted soils for temperate
and tropical regions (but not the boreal region) presented in Chapter 3 of this supplement. Based on information
for natural fluxes from rewetted organic soils, it is consistent with data illustrating that rewetting effectively
stops soil organic matter oxidation but does not necessarily reestablish the soil carbon sink function.
Guidance for inventories of rewetting and revegetation activities of coastal wetlands follows the assumptions at
Tier 1 level of estimation that:i. upon rewetting and revegetation of previously drained soil, creation of a mangrove or tidal marsh or on
restablishment of a seagrass meadow, soil carbon accumulation is initiated when natural vegetation
becomes established andii. the rate of soil carbon accumulation is instantaneously equivalent to that in natural settings.
Craft et al. (2003) found that (a) soil carbon accumulation, developed almost instantaneously with theestablishment of vegetation along a chronosequence of 1- to 28-yr old constructed marshes and (b) a similar soil
carbon accumulation rate over 10 years in a natural and created marsh (Craft et al., 2002) and over 20 years in acreated mangrove (Osland et al., 2012). Given this equivalence, estimates of soil carbon accumulation rates inmangroves, tidal marshes and seagrass meadows (Chmura et al., 2003; Breithaupt et al., 2012; Duarte et al.,2013) make it possible to quantify carbon gains at sites characterised by rewetting and revegetation activities. A
transition time for soil carbon stocks to become equivalent to those in natural/undrained settings with vegetation(Table 4.11) will exceed the default land-use transition time of the typically used land-use category conversions(i.e. 20 years). Instead it is suggested to apply the EF for soil carbon accumulation as long as the soil remains
rewetted and vegetated, until such time as stocks are equivalent to soil carbon stocks in natural/undrained
settings with vegetation (Table 4.11) or there is a change in management practice.

CHOICE OF METHOD
Changes in soil carbon resulting from rewetting, revegetation and creation activities for mangroves, tidal
marshes and seagrass meadows are estimated because they represent potentially large carbon removals from theatmosphere.

Tier 1
At Tier 1, the default method, EFRE values are to be used in conjunction with Equation 4.7 to estimate CO2
emissions.

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Chapter 4: Coastal Wetlands

EQUATION 4.7
CO2 EMISSIONS FROM REWETTING, REVEGETATION AND CREATION OF COASTAL WETLANDS
CO2SO-RE = ∑v,s,c(ARE • EFRE)v,s,cWhere:
CO2SO-RE = CO2 emissions associated with rewetting, revegetation and creation activities by vegetation
type (v), soil type (s) and climate (c); tonnes C yr-1
ARE = Area of soil that has been influenced by rewetting, revegetation and creation activities byvegetation type (v), soil type (s) and climate (c); ha
EFRE = CO2 emissions from aggregated mineral and organic soils that have been influenced by rewetting
and revegetation activities by vegetation type (v), soil type (s) and climate (c); tonnes C ha-1 yr-1
EFRE = 0 for rewetted and naturally saturated soils where no vegetation has been re-estabished or where reestablishment is expected to occur by recolonization.
At Tier 1, EFRE is applied (Table 4.12) when vegetation has been established through replanting or reseeding. If,
however, re-establishment of vegetation is expected to occur by recolonization, EFRE = 0 is applied at Tier 1. It isgood practice to document the basis on which the EFRE is applied. When vegetation has been established the
EFRE is disaggregated with respect to vegetation type. Organic and mineral soils are not differentiated at Tier 1
within any particular vegetation type, as the organic carbon inputs mainly derive from the production of aboveground and below-ground biomass under similar conditions of soil saturation. Land area estimates should bebased on land classification within the new land-use category (if applicable) to apply Tier 1 EFRE.

Tier 2
Under the Tier 2 method, country-specific carbon accumulation rates could be dissagregated with respect to areaof organic and mineral soils. Where such country-specific data can be acquired and used to improve estimations,disaggregation by climate zone could also be applied.

Tier 3
Under the Tier 3 method, the land use prior to rewetting, its climate and vegetation type could be taken into
account. A comprehensive understanding and representation of the dynamics of CO 2 gas emission factors, basedon field measurements of, for example, carbon content, bulk density, clay content, salinity, redox potential, etc.,
could be employed at Tier 3. A Tier 3 approach could also use empirical measurements and models that take into
account the time-dependent nature of the CO2 fluxes over a range of timescales (Morris et al., 2012), location
relative to the low to high intertidal zone (Alongi, 2010) or other dynamics (Craft, 2007).

CHOICE OF EMISSION/R EMOVAL FACT ORS
Tier 1
The choice of EFs at Tier 1 is applied based on the coastal wetland vegetation type being established through therewetting, revegetation or creation activity. It is assumed that within each vegetation type, CO2 emissions are thesame regardless of how the suitable conditions for revegetation are facilitated. If vegetation is reestablishedthrough direct reseeding or purposeful planting, apply EFRE in Table 4.12. If the rewetting, revegetation or
creation activity is associated with recolonization (no direct replanting or reseeding), apply EF RE = 0. It is goodpractice to evaluate and document these activities (See Choice of Activity Data below) and modify what EF isapplied, as appropriate. If the rewetting and revegetation activity results in patches of biomass (if coverage data
are available), EFRE >0 should only be applied when the mangrove, tidal marsh plant or seagrass canopy covers
at least 10% of the overall area. This consideration follows the definition of forest (Table 4.2, Chapter 4, Volume
4, 2006 IPCC Guidelines).

Tier 2
In a Tier 2 approach, country-specific emission factors for rewetting, revegetation or creation activities could beapplied. The assumption of EFRE=0 in areas where vegetation had not been established could also be reassessed.
Country-specific emission factors could be applied based on disaggregation of organic and mineral soils andclimate.

Tier 3
In a Tier 3 approach, field measurement of soil organic carbon content and CO2 emissions from areas whererewetting and revegetation activities occur could be used to develop an empirical relationship (for example, asimple regression equation) that can be used across other sites where rewetting and revegetation activities occur
within a particular area or country. Country-specific values can be developed to model possible time-dependentchanges in CO2 emissions. Soil carbon accumulation rates will likely change, as vegetation grows and biomass

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Chapter 4: Coastal Wetlands

matures. Increased inundation and soil saturation, as a result of intertidal location in tidal marshes andmangroves, will accelerate development of soil characteristics of revegetated soils. Thus, rates of CO2 emissions
in these tidal wetlands will vary in relation to a combination of these factors and consideration of them would
result in more accurate estimation of CO2 emissions.

TABLE 4.12
ANNUAL EMISSION FACTORS ASSOCIATED WITH REWETTING (EFRE) ON AGGREGATED ORGANIC AND MINERAL-1-1
SOILS ( TONNES C HA YR ) AT INITIATION OF VEGETATION REESTABLISHMENT
Ecosystem

EFREWET1

95% CI5

rangen

Mangrove-1.622

1.3, 2.0

0.10-10.2

69

Tidal marsh-0.9130.7, 1.1

0.05-4.65

66

Seagrass meadow-0.4340.2, 0.7

0.09-1.12

6

1

Negative values indicate removal (i.e. accumulation) of C

2

Sources: Breithaupt et al., 2012; Chmura et al., 2003; Fujimoto et al., 1999; Ren et al., 2010

3

Sources: Anisfeld et al., 1999; Cahoon et al., 1996; Callaway et al., 1996; Callaway et al., 1997; Callaway et al., 1998;
Callaway et al., 1999; Callaway et al., 2012; Chmura and Hung, 2003; Hatton, 1981; Craft, 2007; Kearney and Stevenson,
1991; Markewich et al., 1998; Oenema and DeLaune, 1988; Orson et al., 1998; Patrick and DeLaune,1990; Roman et al.,1997
4

Sources: Mateo and Romero, 1997; Serrano et al., 2012

595% CI of the geometric mean

CHOICE OF ACTIVITY D ATA
Historical photos and coastal wetland maps, if available at the appropriate spatial resolution, may be used toestimate the pre-restored wetland area. Information on regional wetland restoration and creation projects
worldwide can be obtained from the Global Gateway to Geographic Information Systems of the FAO(www.fao.org) as well as from the websites, www.wetlands.org and www.globalrestorationnetwork.org. Withina given country, government agencies responsible for issuance of permits for restoration/creation/alteration of
wetland are to be consulted for information of area data on the wetlands being considered. In addition, many
countries may have a process for reporting rewetting and revegetation activities as permission is often required.
For example, in Australia, the Environmental Protection Agency in Western Australia approves revegetation
projects as part of their Ministerial Conditions. The Australian Government Department of Sustainability,
Environment, Water, Population and Communities also directs the Federal Minister to approve or reject
revegetation programs. The establishment of vegetation and/or change in areal extent can be reviewed on a five
year period and assessed for accurate implementation of the appropriate soil EF. If data are lacking, expert
judgement about success rates of projects implemented under similar conditions could be used for initialassessments (examples are size of project, vegetation type, tidal range, proximity to coast, climate). In general,
for rewetting activities that include purposeful planting or direct reseeding, an EFRE (using Table 4.12) isappropriate for Tier 1 estimation. Information on which the choice in EF is based should be documented.

UNCERTAINTY ASSESSME NT
Uncertainties in estimating CO2 emissions and removals from rewetting, revegetation and creation of mangroves,tidal marshes and seagrass meadows largely lie in the underlying assumptions and area to which the EFs areapplied. The values for EFREWET in Table 4.12 represent global averages and have large uncertainties due tovariability in soil carbon accumulation rate with 1) depth of the intertidal zone, 2) the dominant species type, its
morphology and rate of growth, and 3) climate. The underlying assumption of EFRE=0 for rewetted/saturated
soils where vegetation has not been re-established may introduce uncertainty into estimates. Also, theassumption of complete areas with or without vegetation cover could introduce under- or overestimates.

4.2.4

Drainage in mangroves and tidal marshes

This section addresses the changes in carbon stock and CO2 emissions and removals for drainage in mangroves
and tidal marshes. Drainage may be accompanied by land clearing, also resulting in changes in biomass and deadorganic matter pools. If burning accompanies drainage, it is good practice to report emissions from changes inthose C pools. For methods to estimate changes in carbon stock in biomass, and for default data, refer to Section
4.2.1 of this report for guidance on mangroves and Section 4.2.2 for guidance on tidal marshes. It is important toretain information about drained coastal wetlands so that guidance in this supplement can be applied if a reversalof drainage conditions occurs.

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Chapter 4: Coastal Wetlands

Drainage causes soils to dry and ordinarily increases rates of organic matter decomposition, resulting in loss ofsoil carbon via CO2 release (Armentano and Menges, 1986). This response varies with climate (Pozo and Colino,1992) and locally with soil salinity and texture, and the quantity of labile organic matter available (Setia et al.,2011). Activities associated with extensive lowering of the water table are often linked to the construction ofdrainage channels leading to CO2 fluxes due to oxidation of DOC and POC in the water carried by drainage
channels. However, there is currently not enough information to provide emission factors for DOC and POC
export (see Appendix 4a.1, “Future methodological development for estimating carbon export”).

4.2.4.1

B IOMASS

Methodological guidance for estimating carbon stock changes in the biomass pool, including choice of method
and choice of emission and removal factors, follows Section 4.2.3.1 of this chapter. For tidal marshes, increase inbiomass stocks in a single year is assumed equal to biomass losses from mortality in that same year at Tier 1.

4.2.4.2

D EAD ORGANIC MATTER

Methodological guidance for estimating carbon stock changes in the dead organic matter pool, including choiceof method and choice of emission and removal factors, follows Section 4.2.3.2 of this chapter. For tidal marshes,
CO2 emissions and removals from change in biomass and dead organic matter pools are reported as zero at Tier
1.

4.2.4.3

S OIL CARBON

Annual carbon losses from drained mineral and organic soils are applied similarly for mangroves and tidal
marshes (but not applicable to seagrass meadows) at Tier 1 level of estimation (Table 4.13). Data on CO2emissions from drainage in mangroves is limited, however, the CO2 emission rate from drainage in tidal marshes
was considered to provide an appropriate Tier 1 default emission factor. This value is also consistent withdrained forest default EF presented in Chapter 2 of this supplement.

CHOICE OF METHOD
Tier 1
Guidance for inventories on drainage in coastal wetlands follows the assumptions at Tier 1 level of estimation
that:
i.

emissions persist as long as the soil remains drained or as long as it takes for soil carbon stocks
equivalent to those in natural/undrained settings with vegetation (Table 4.11) to be oxidised andii.

the drainage condition is characterized by full drainage (i.e. the water table has been changed to 1 m
below the soil surface for organic and mineral soils), consistent with the Tier 1 approach in Chapter 2 ofthis supplement.

Emissions from drained coastal wetland soils are estimated at Tier 1 for mangrove forests and tidal marshes
using Equation 4.8.
EQUATION 4.8
CO2 EMISSIONS ON DRAINED ORGANIC AND MINERAL SOILS
CO2-SO-DR = (ADR • EFDR)
Where:
CO2-SO-DR = CO2 emissions from aggregated organic and mineral soil carbon associated with drainage;
tonnes C yr-1
ADR = land area under drainage; ha
EFDR, = CO2 emissions from organic or mineral soil carbon associated with drainage; tonnes C ha-1 yr-1
As described above, the Tier 1 emission factor is applied until the soil carbon stock (Table 4.11) is depleted anddetermines the time frame for emissions due to drainage regardless of whether a land-use change occurs. Once
depleted, guidance from the 2006 IPCC Guidelines applies.

Tier 2The Tier 2 estimation method is the same as the Tier 1 method, but national data can be used to additionallydisaggregate by vegetation, soil type and regional climatic factors, if such data are available at reasonable cost.

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Chapter 4: Coastal Wetlands

Tier 3Tier 3 methods could take account of differences in the management of the drained wetland. Empiricalmeasurements of gas flux based on site-specific measurements of, for example, carbon content, bulk density,
clay content, salinity, redox potential, etc., to determine the underlying processes of emissions could be included.
Site differences in frequency of drainage activity could also be considered at Tier 3 methods. Other factors that
could be used to apply disaggregated data include salinity and tidal export of DOC and POC (Appendix 4a.1).

CHOICE OF EMISSION/R EMOVAL FACT ORS
Tier 1
At Tier 1, a generic default emission factor is applied for drainage, regardless of vegetation or soil type (Table
4.13). That is, the same EF is applied regardless of the management activity involving soil drainage.

TABLE 4.13
ANNUAL EMISSION FACTORS ASSOCIATED WITH DRAINAGE (EFDR) ON AGGREGATED ORGANIC AND MINERAL SOILS(TONNES C HA-1 YR-1)
Ecosystem

EFDR

95%
CI2

Range

N

Tidal marshes and mangroves

7.91

5.2, 11.8

1.2-43.9

22

1

Sources: Camporese et al., 2008; Deverel and Leighton, 2010; Hatala et al., 2012; Howe et al., 2009; Rojstaczer and Deverel,1993

2

95% CI of the geometric mean

Tier 2Tier 2 emission factors apply country-specific data disaggregated by soil type, vegetation type, and climate,
where feasible. Data to address any change in emissions since initiation of drainage could additionally be
implemented.

Tier 3
In a Tier 3 approach, field measurements of soil organic carbon content and CO2 emissions from the drained sitewould be useful to develop an empirical relationship (for example, a simple regression equation of soil carbon
content versus rate of carbon removal) that can be used across other drained sites within a particular area orcountry. Country-specific values can thus be developed to model possible time-dependent changes in CO2emissions such as changes in relation to timing and rate of soil drainage, depth of drainage and additional
national information about mean annual water table and land-use type or intensity. A comprehensive
understanding and representation of the dynamics of CO2 emission factors, based on field measurements of, forexample, carbon content, bulk density, clay content, salinity, redox potential, etc., could be employed at Tier 3.

CHOICE OF ACTIVITY D ATA
Tier 1The Tier 1 approach requires area data of drained land for each land-use category that have been identified incoastal wetlands. Classification systems for activity data that form the basis for a Tier 1 inventory are provided
in the respective chapters of the 2006 IPCC Guidelines. For coastal wetlands, the predominant land-use category
conversion is to Cropland and Grassland.

Tier 2 and 3
Activity data for higher tier estimates are generally derived following the methods presented in Chapter 3 of the2006 IPCC Guidelines. To disaggregate by soil type and vegetation type, several institutions, including ISRIC
and
FAO
have
country-specificandglobalmaps
thatincludeorganicsoils(http://www.fao.org/geonetwork/srv/en/main.home or http://www.isric.org/). A global consortium has been
formed to make a new digital soil map of the world at fine resolution (http://www.globalsoilmap.net/).
Drainage is assumed to result in persistent emissions from soils as long as the management system remains inplace. Activity data may be spatially explicit and could be disaggregated by type of management, if appropriate
emissions factors are available.
The combination of land-use databases and soil maps or spatially-explicit data allow delineation of combinationsof land-use categories, climate domains, and management systems and their changes over time on organic soils.
Information sources about drainage with adequate disaggregation may include that listed below.

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Chapter 4: Coastal Wetlands

National land-use statistics. Land-use maps and soil maps, maps of water and nature conservation zones
with restrictions for water management, wetlands.



National water management statistics. In most countries, the agricultural land base including croplands is
usually surveyed regularly, providing data on distribution of different land-uses and other aspects ofmanagement, often at sub-national, regional level. These statistics may originate, in part, from remotesensing methods, from which additional information about wetness or periods with seasonal flooding could
be extracted.

Inventory data from a statistically based, plot-sampling system of water table wells, ditches and surface
waters on organic soils. Water table is monitored at specific permanent sample plots either continuously oron plots that are revisited on a regular basis. It has to be documented that the water data represent the watertable in the organic soil and for what land-use and drainage stratum and that the data cover a representative
period, which represents a multi-year mean annual water table.



Water management plans and documentation from water management installations.



Drainage maps.

UNCERTAINTY ASSESSME NT
Three broad sources of uncertainty exist in estimating emissions and removals from drainage: 1) uncertainties inland-use and environmental data; 2) uncertainties in the emission/removal factors for Tier 1 or 2 approaches; and3) model structure/parameter error for Tier 3 model-based approaches, or measurement error/sampling
variability associated with Tier 3 measurement-based inventories. In general, precision of an inventory is
increased and confidence ranges are smaller with more sampling to estimate values for these categories, while
accuracy is more likely to be increased through implementation of higher Tier methods that incorporate countryspecific information.
For Tier 1, the default uncertainty level of emissions/removal factors is the 95% confidence interval in Table
4.13. Countries developing specific emission factors for their inventories at higher tiers should assess theuncertainty of these factors.
If using aggregate land-use area statistics for activity data (e.g. FAO data), the inventory agency may have toapply a default level of uncertainty for the land area estimates, for example. It is good practice for the inventory
compiler to derive uncertainties from country-specific activity data instead of using a default level of
uncertainty. Uncertainties in activity data may be reduced through a better national system, such as developing
or extending a ground-based survey with additional sample locations and/or incorporating remote sensing toprovide additional coverage. Uncertainties in activity data and emission/removal factors need to be combinedusing an appropriate method, such as simple error propagation equations. Details are given in Chapter 3, Volume
1 of the 2006 IPCC Guidelines and in Chapter 5 of the GPG-LULUCF.

4.3

NON-CO 2 EMISSIONSThis section provides methods for estimating the emissions of CH4 emissions from rewetted mangroves and tidal
marshes and N2O from aquaculture use.

4.3.1

CH4 emissions from rewetted soils and createdmangroves and tidal marshes

Rewetting of drained soils, through reconnection of hydrology, shifts microbial decomposition from aerobic toanaerobic conditions, increasing the potential for CH4 emissions (Harris et al., 2010). In environments where low
salinity also occurs (especially <5 ppt), microbial decomposition of organic matter may result in production of
CH4. However, in soils saturated with seawater, microbial reduction of sulfate to sulfide will generally occur
before methanogens produce CH4 regardless of the organic matter content. A strong inverse relationship between
CH4 emissions and salinity of mangrove soils exists (Purvaja and Ramesh, 2001). A review by Poffenbarger et al.
(2011) showed that CH4 emissions decrease as salinity in tidal marshes increases.
Guidance for estimating CH4 emissions associated with rewetting land previously characterised by mangrove
and tidal marsh vegetation differs from that for estimation of CO2 emissions in that, at Tier 1 level of estimation,
the EF remains the same for CH4, regardless of extant vegetation.

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4.3.1.1

C HOICE OF METHODTIER 1In the case of rewetting of lands that had been previously in an agricultural (or any other drained) land-use
category, the Tier 1 method estimates CH4 emissions without considering the land-use prior to rewetting.

EQUATION 4.9
CH4 EMISSIONS FROM REWETTED SOILS AND CREATED TIDAL MARSHES AND MANGROVES
CH4-SO-REWET = ∑v(AREWET • EFREWET)v
Where:
CH4-SO-REWET = CH4 emissions associated with rewetted and created coastal wetlands by vegetation type(v); kg CH4 yr-1
AREWET = Area of soil that has been rewetted (including tidal marsh or mangrove wetland creation), byvegetation type (v); ha
EFREWET = CH4 emissions from mineral and organic soils that have been rewetted by vegetation type (v);kg CH4 ha-1 yr-1

TIER 2
At Tier 2, country-specific data can be applied. Improved estimates can be produced if country-specific data
could include more disaggregation by salinity and vegetation type.

TIER 3
At Tier 3, country-specific values can be used and developed to model possible time-dependent changes in CH4emissions. Tier 3 methods may also consider vegetation composition and density, as plants can act as a conduit
for gas exchange between the soil and atmosphere (e.g. Burdick, 1989; Purvaja and Ramesh, 2001; Kristensen etal., 2008).

4.3.1.2

C HOICE OF EMISSION FA CTORSTIER 1
Tier 1 CH4 emission factors are found in Table 4.14 and should be used in conjunction with Equation 4.9 toestimate emissions taking into account vegetation type (and associated salinity level). The choice of emission
factor at Tier 1 is differentiated between rewetting by freshwater and brackish water (<18ppt) and saline water(>18ppt, Annex 4A.1). Rates of CH4 emissions approximate 0 in saline water marshes and mangroves but are
greater than zero in freshwater tidal and brackish marshes and mangroves (Table 4.14). For rewetting that resultsin salinities >18 ppt), the Tier 1 assumption is to apply an annual CH4 emission rate = 0. Within each vegetation
type, CH4 emissions are the same regardless of the management activity involving rewetting at Tier 1.

TIER 2
In a Tier 2 approach, country-specific CH4 emissions are encouraged to be used and will provide better estimates
based on the salinity of water used to rewet the mangrove or tidal marsh, particularly to determine CH4 emissions
from tidal brackish marshes.

TIER 3
In a Tier 3 approach, field measurements of soil salinity and CH4 emissions from the rewetted site could be used
to develop an empirical relationship (for example, a simple regression equation of salinity versus rate of methane
emission) and applied across other rewetted sites within a particular area or country. Country-specific values canthus be developed to model possible time-dependent changes in CH4 emissions such as changes in relation tofrequency of tidal inundation, frequency of the rewetting activity and elevation from the water’s edge. Suchconsiderations would result in more accurate estimation of CH4 emissions.

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TABLE 4.14
EMISSION FACTORS FOR CH4 (EFREWET) FOR TIER 1 ESTIMATION OF REWETTED LAND PREVIOUSLY VEGETATEDBY TIDAL MARSHES AND MANGROVES

Vegetation Type

Salinity (ppt)

Tidal freshwater andbrackish marsh andmangrove1
Tidal saline water marsh andmangrove1<18

EFREWET(kg CH4 ha-1 y-1)
193.72>1803

95% CI4

Range

99.8, 358

10.95-5392

1

See Annex 4A.1 for salinity-based definitions

2

Sources: Keller et al., 2013; Ma et al., 2012; Poffenbarger et al., 2011; Sotomayor et al., 1994; Tong et al., 2010

0-40

3

Marshes and mangroves with salinities >1 ppt approximate an order of magnitude lower rates than from tidal freshwater andbrackish marsh (as defined here, salinity <18ppt), so a Tier 1 assumption is to apply 0.
4

95% CI of the geometric mean

4.3.1.3

C HOICE OF ACTIVITY DATA

To estimate emissions using CH4 emission factors refer, in part, to the guidance for rewetting in Section 4.2.3
above. The EF should be applied to the specific type of vegetation that will be reestablished, which is associatedwith salinity. When salinity data are not available the type and location of rewetting may be used as a proxy forsalinity. For example, breaching of sea walls and rewetting in an estuarine setting will result in rewetting withsaline waters. If rewetting occurs with freshwater, a salinity of <18ppt is likely. When applying guidance fortidal freshwater marsh, it is good practice to determine the inland boundary for rewetting of tidal freshwater
wetlands as based on national circumstances, and to consistently apply these conditions to identifying theserewetted lands. If more information is available on salinity concentrations associated with the area being
rewetted, better estimates of CH4 emissions can be determined. Information used for these assessments should be
documented.

4.3.1.4

U NCERTAINTY ASSESSMEN T

There have been few empirical measurements of emissions disaggregated by factors such as temperature, tidal
frequency or duration of inundation, which introduce uncertainty in global default emission factors. However,higher tier approaches can take these factors into account to improve estimations. Few reports are available togive specifics of the types of rewetting activities that may vary geographically. Because activity data may belimited in terms of delineating salinity boundaries to apply more constrained CH4 emission factors, aggregationof data to produce Tier 1 emission factors was based upon expert knowledge. There is also uncertainty in thetime, depth of soil affected, and the contribution of vegetation to rate of CH4 loss.

4.3.2

N2O emissions during aquaculture use in mangroves,tidal marshes and seagrass meadows

The most significant activity contributing to N2O emissions from managed coastal wetlands is aquaculture. Onethird of global anthropogenic N2O emissions are from aquatic ecosystems, and nearly 6% of anthropogenic
N2O−N emission is anticipated to result from aquaculture by 2030 at its current annual rate of growth (Hu et al.,2012). Shrimp and fish cultivation increases nutrient loads in culture ponds. As opposed to indirect N2Oemissions originating from activities on terrestrial lands or as wastewater treatment, coastal wetland aquaculture
occurs as a direct source of N2O from coastal wetlands, including mangroves and tidal marshes from aquaculture
pond use. In seagrass meadows, this direct N2O source arises from N added to fish cages (e.g. off-shore
installations). While this differentiation should assure no double-counting, it is good practice to evaluate thisassessment considering national circumstances. As such, this new activity fills a gap in the current reporting on
direct and indirect sources of N2O emissions. A country can exclude N2O emissions from estimation that occur
during aquaculture activities where no mangroves, tidal marsh or seagrass meadows exist (i.e. outside of coastal
wetland areas).
N2O is emitted as a by-product of the conversion of ammonia (contained in fish urea) to nitrate throughnitrification and nitrate to N2 gas through denitrification (Hu et al., 2012; Annex 4A.5). N2O emissions canreadily be estimated from fish production data.

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4.3.2.1

C HOICE OF METHODTIER 1N2O emissions from aquaculture ponds can be estimated based on fish/shrimp production of the aquaculture
activity. N2O emission estimation follows a modified form of Equation 11.1 from Chapter 11, Volume 4 of the2006 IPCC Guidelines and is presented in Equation 4.10.

EQUATION 4.10
DIRECT N2O EMISSIONS FROM AQUACULTURE USE
N2O-NAQ = FF • EFF (based on fish production)
Where:
N2O-NAQ = annual direct N2O-N emissions from aquaculture use; kg N2O-N yr-1
FF = annual fish production; kg fish yr-1
EFF = emission factor for N2O emissions from fish produced; kg N2O-N (kg fish produced)-1

TIER 2Tier 2 estimation methodology follows that of Tier 1 with the added information provided by country-specific
data.

TIER 3Tier 3 estimation methodology could include the consideration of fish/shrimp type, type of feed and stocking
density, category of aquaculture (fish/shrimp species or feed stuff), aquaculture use intensity, and impact ofenvironmental factors (e.g. climate zone, season, and salinity).

4.3.2.2

C HOICE OF EMISSION FA CTORSTIER 1
Hu et al. (2012) used the relationship between in-coming nitrogen loads and N2O emissions from wastewater
plants to estimate that 1.8% of the N is emitted as N2O (0.00169 kg N2O-N is emitted per kg fish produced). The
EFF is applied during the ‘in use’ phase of aquaculture (Table 4.15). In the construction and discontinued phases,
non-CO2 emissions are assumed negligible with EF=0. At Tier 1, countries could consider applying this EF toother species groups under aquaculture production. Because the EF is developed for fish, wider application may
introduce additional uncertainty.

TIERS 2 AND 3
Under the Tier 2 method, country specific emission factors for N2O are applied. At Tier 2, these country-specificemission factors could incorporate a different value for the proportion of N emitted as N2O. For Tier 3 emission
factors, comprehensive understanding and representation of the dynamics based on direct field measurements ormodels is involved, which estimates emission factors considering the category of aquaculture (fish/shrimp
species or feed stuff), aquaculture use intensity, and impact of environmental factors e.g. climate zone, season,and salinity.

TABLE 4.15
EMISSION FACTOR (EFF) FOR N2O EMISSION FROM AQUACULTURE USE IN MANGROVES, TIDAL MARSHES AND
SEAGRASS MEADOWS

1

Default EF(kg N2O-N per kg fish produced)

95% CI1

Reference

0.00169 kg N2O-N per kg fish produced

0, 0.0038

Hu et al., 2012

95% CI of the geometric mean.

Note: Approach used by Hu et al. (2012) using N in feed to fish biomass: Hargreaves, 1998; Protein content of fish biomass:
USDA nutrient database for Standard Reference Nutrient Data Laboratory; N content of protein: Nelson and Cox, 2013; N to
N2O conversion: Hu et al., 2013; Kong et al., 2013; Kampschrew et al., 2008; Ahn et al., 2010 (refer to Annex 4A.5)

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Chapter 4: Coastal Wetlands

4.3.2.3

C HOICE OF ACTIVITY DA TA

Data for fish and shrimp production are needed. These data can be obtained from FAO(http://www.fao.org/fishery/statistics/global-aquaculture-production/en). For additional guidance, see Section
4.2.1.

4.3.2.4

U NCERTAINTY ASSESSMEN T

Emission factors for N2O emissions from aquaculture systems are based on protein content of fish, relationships
between total nitrogen content and wet weight of fish and the percent of nitrogen load emitted as N 2O. There areno such data for shrimp production so using fish data as a proxy adds a high level of uncertainty. The fish-related
factors can vary greatly, and in part on environmental conditions, so high variation can occur among fish
aquaculture systems. Decreased uncertainty can be achieved at Tier 2 and 3 to reflect variability in N2Oemissions based on shrimp and fish species and type of food (pellets vs. trash fish). Uncertainties in N2Oemissions associated with stocking of aquaculture facilities can be reduced greatly by better estimation of shrimp
and fish production.

4.4

COMPLETENESS, TIME SERIESCONSISTENCY, AND QUALITY ASSURANCEAND QUALITY CONTROL (QA/QC)

4.4.1

Completeness

General guidance on completeness is provided in Chapter 7 of this supplement.

4.4.2

Time series consistency

It is good practice that countries clearly define coastal wetlands and use this definition consistently over time.
Consistent time series require that the same methodology is used for the entire time series. Whenever new
methodologies are used previous estimates should be recalculated using the new methods for all years in the timeseries. It is also good practice to report why the new estimates are regarded as more accurate or less uncertain.
One potential problem in recalculating previous estimates is that certain data sets may not be available for theearlier years. There are several ways of overcoming this limitation and they are explained in detail in Chapter 5,
Volume 1 of the 2006 IPCC Guidelines. Time series consistency is discussed further in Chapter 7.6 of the
Wetlands Supplement and Chapter 5 (Time series consistency and recalculations), Volume 1 of the 2006 IPCC
Guidelines.

4.4.3

Quality Assurance/Quality Control (QA/QC)

Quality assurance/quality control (QA/QC) procedures should be developed and implemented as outlined in
Chapter 7 of this supplement.

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Chapter 4: Coastal Wetlands

Annex 4A.1 Salinity-based definitions
SALINITY-BASED DEFINTIONS
Commondescription

Salinity (ppt)1

Tidal fresh water<0.5

Brackish water

0.5 - 18

Saline water>18

1

ppt is parts per thousand (‰) and is roughly
equivalent to grams of salt per litre of water2013 Supplement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories: Wetlands

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Chapter 4: Coastal Wetlands

Annex 4A.2 Estimation of above-ground mangrove biomass:
higher tier methodology
Because of field conditions and heavy weight of wood, an accurate survey of a mangrove forest is difficult andtime-consuming. Allometric methods (Soares and Schaeffer-Novelli, 2005; Komiyama et al., 2008) estimate thewhole or partial weight of a tree from measurable tree dimensions, notably trunk diameter and height, using
allometric relations developed from empirical measurement of weight of individual tree components (leaves,branches, stem). Use of allometric equations is favored because it is non-destructive and is therefore useful for
estimating temporal changes in forest biomass by means of subsequent stem diameter measurements oversubsequent years.
Up until recently, the major drawback of this method has been the site- and species-specific differences inallometric relations, necessitating the use of different allometric equations for different sites (e.g. Smith andWhelan, 2005) and, at a minimum, different species. However, a number of workers, using global datasets, havedeveloped a common allometric equation applicable for all tropical tree species, with the most applicable
equations for above-ground biomass being those developed for all tropical trees by Chave et al. (2005) and forall mangrove species by Komiyama et al. (2005):
Wtop = 0.168pDBH2.47 (Chave et al. 2005)
Wtop = 0.251pD2.46 (Komiyama et al. 2005)
where Wtop = above-ground tree weight in kg dry weight, p = wood specific gravity, D = tree diameter, and DBH= diameter-at-breast height. The relative error of each equation varies among species, but is typically within therange of -10% to +10%. There are, of course, arguments to be made that empirical measurements should bemade in all mangrove forests, considering the significant allometric differences between species and for the same
species at different locations (Smith and Whelan, 2005; Soares and Schaeffler-Novelli, 2005). However, thisidea is impractical for inventory compliers; a relative error of ± 10% is acceptable being within the range of error
for allometric relations within a forest where biomass has been weighted.
Comparing the two equations, the Chave estimation gives lower above-ground weight estimates than that of the
Komiyama equation. Presuming that a complete census of all trees, with species identified, and their diameter
have been undertaken from replicate plots within a given forest, these numbers can then be used in either
equation to derive individual tree weight.

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Chapter 4: Coastal Wetlands

Annex 4A.3 Wood density of mangrove species
WOOD DENSITY OF MANGROVE SPECIESSpeciesn

Average density(tonnes m-3)

Standarderror

Brugueria gymnorrhiza
Xylocarpus granatum

8
7

0.81
0.61

0.07
0.04

Sonneratia apetala
Sonneratia alba
Rhizophora mucronata
Rhizophora mangle

2
6
9
7

0.50
0.47
0.83
0.87

0.01
0.12
0.05
0.02

Rhizophora apiculata
Laguncularia racemosa
Heritiera littoralis

4
3
6

0.87
0.60
0.84

0.06
0.01
0.05

Heritiera fomes
Excoecaria agallocha
Ceriops tagal

3
7
7

0.86
0.41
0.85

0.14
0.02
0.04

Ceriops decandra

2

0.87

0.10

Avicennia officinalis

3

0.63

0.02

Avicennia marina
Avicennia germinans

6
5

0.62
0.72

0.06
0.04

0.71

0.02

Average

Source: Global Wood Density Database
http://datadryad.org/resource/doi:10.5061/dryad.234/1?show=full; Saenger, 2002; Komiyama et al., 2005;
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Chapter 4: Coastal Wetlands

Annex 4A.4 Percent refractory carbon
Percent refractory carbon in organic/mineral soils were estimated for mangrove soils based on either the amountof phenolic compounds/lignins in soils or % TOC in mangrove soils deeper than 1 m if there was no further
decline in TOC concentration.
PERCENT REFRACTORY CARBON APPLIED TO
ESTIMATE % C OXIDATION FOR MANGROVESOILS (% BY SOIL DRY WEIGHT)
Mean

3.98

Median3.4

N

16

Source: Prasad and Ramanathan, 2009; Marchand et al.,
2003; Dittmar and Lara, 2001; Koch et al., 2011;
Ranjan et al., 2010; Marchand et al., 2005, which issimilar to that in tidal marshes (Filip et al., 1988;
Alberts et al., 1988; Reddy and DeLaune, 2008).

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Chapter 4: Coastal Wetlands

Annex 4A.5 Derivation of N2O emission factor for aquaculture
The emission factor of 0.00169 kg N20-N per kg fish produced in Table 4.15 is based on the following. Firstly,
the protein content of fish is estimated from 80 values in various cultured fish species as 17.72 ± 2.97% (USDA
nutrient database for Standard Reference Nutrient Data Laboratory). Using the protein content of fish and theaverage N content of protein (16%; Nelson and Cox, 2013) implies an N content of 2.84 ± 1.33% of fish biomass;
i.e. one metric tonne of fish contains 2.84 x 104 g N. Secondly, the % N in aquaculture fish feed that isincorporated into fish biomass averages 23.22 ± 5.88% (Hargreaves, 1998). This value is based on results fromfour aquaculture production methods in which 18 individual estimates for the conversion of fish biomass to fish
N were obtained from 11 different cultured fish species.
Following Hu et al. (2012; and references therein), it is assumed that all the feed is ingested by fish and the N
input as ammonia to the aqueous phase to produce 1 metric tonne of fish is 12.23 x 104 g - 2.84 x 104 g = 9.39 ±4.69 x 104 g. Given that on average, during N transformation in the aqueous phase, 1.8 ± 0.7% of the N isconverted to N2O (Kong et al., 2013; Kampschreur et al., 2008; Ahn et al., 2010; Hu et al., 2013), the amount of
N emitted to the atmosphere as N2O-N is 1.69 x 103 g. Thus the average N2O emission factor of an aquaculture
system is 1.69 g N2O-N per kg fish or 0.00169 kg N2O-N per kg fish produced. The uncertainty range isestimated using standard error propagation through the calculations indicated.

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Chapter 4: Coastal Wetlands

Appendix 4a.1 Future methodological development for estimating
carbon export
The amount of dissolved and particulate carbon potentially available for export is highly variable among coastal
wetlands, depending on a large number of factors such as: net primary productivity, tidal range, the ratio of
wetland to watershed area, lateral trapping of tidal water, the presence of high salinity plugs in the tropical dry
season, total wetland area, frequency of storms, amount of precipitation, and volume of water exchange. Eachecosystem is unique; some wetlands export DOC but import POC, others import DOC and POC but export DIC,
while other systems import or export all forms of dissolved and particulate C. The direction of net exchange also
usually varies within the same estuary with change in season. Emerging evidence indicates that DIC (derived
from CO2 by heterotrophic organisms and/or carbonate dissolution) is exported from coastal wetlands by thephysical processes of tidal drainage of soils and subsequent advection to adjacent waterways (Alongi, 2009;
Perillo et al., 2009). For instance, in mangroves, tidal export of respiratory-derived DIC may equate to as muchas one-third of carbon fixed by the forests. However, available data are still too few to allow for generalization,and the scant data are highly variable with tidal amplitude being a major driver of soil DIC drainage.
Estimation of tidal exchange in a particular wetland is not a straightforward process. Many workers haveprovided rough estimates by multiplying carbon concentrations suspended in wetland creeks and waterways by
the tidal range multiplied by the creek/waterway cross-sectional area. Estimates derived from such simple
calculations are invalid and misleading for a number of reasons, including the inherent assumption that there aredifferences in carbon concentrations between ebb and flood tide stages and that the tidal prism is symmetrical. In
fact, carbon concentrations in many wetland waters do not show significant differences between tides. Further,tides in most wetlands are characterized by a pronounced asymmetry between ebb and flood tides with the ebb
most often being of shorter duration but with stronger current velocity than the flood tide. Also, tidal velocities
vary across a waterway with faster surface current velocities mid-stream than those just above the creekbed or
proximal to the wetland.
For these reasons, it is not possible to make simple generalizations regarding dissolved and particulate organicand inorganic total carbon export from mangroves, seagrasses or tidal marshes and, in fact, comparatively few
such measurements have been made properly. The correct method would be to measure water volume andvelocity over entire tidal cycles over several seasons in relation to position in the water-column to derive an
overall annual estimate of average water flow by volume. This involves fairly complex instrument measurements
and sophisticated mathematical modelling as well as extensive and expensive repetitive measurements ofdissolved and particulate carbon concentrations. For mangroves, net exchange of carbon has been properly
measured in only twelve systems (DIC has only been measured in four systems), with no clear exchange patterns
among locations, although it does appear that most mangroves export POC as litter but with rates ranging widelyfrom 0.1-27.7 mol C m-2 yr-1 (Alongi, 2009). This export equates globally to only about 10% of total carbon fixedby trees; respiration to the atmosphere is by far the largest loss of carbon to the atmosphere. Such appears to be
the case for tidal marshes (Chmura et al., 2003) and subtidal seagrass beds (Fourqurean et al., 2012). Some
recent syntheses and literature do hold promise for future development of model relationships that can be used
for estimating carbon export (Adame and Lovelock 2011; Maher et al., 2013).

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Chapter 4: Coastal Wetlands

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