Appendix 3: CH4 Emissions from Flooded Land: Basis for Future Methodological Development

Appendix 3

CH4 Emissions from Flooded Land: Basis for
Future Methodological Development

This Appendix provides a basis for future methodological development rather than complete guidance.
Flooded Land may emit CH4 in significant quantities, depending on a variety of characteristic such as age anddepth of reservoirs, land-use prior to flooding, climate, and management practices. In contrast with CO2emissions, CH4 emissions are highly variable spatially and temporally. Current measurements of CH4 fluxes
from Flooded Land are not sufficiently comprehensive to support the development of accurate default emission
factors (especially for bubbles emissions and degassing emissions). In addition, data are not available forcountries with substantial surface area cover by reservoirs, as India, China, and Russia.
Measurement studies do not indicate that the time elapsed since flooding has a significant influence on CH4fluxes from boreal and temperate reservoirs. The opposite is true in tropical regions where time elapsed since
flooding may have a significant influence on both diffusive, bubbles CH4 and degassing emissions. This trend
was observed only on Petit-Saut reservoir in French Guiana (Abril et al., 2005); however, some old tropicalreservoirs show high bubbles emissions (Duchemin et al., 2000; Stallard and Keller, 1994). The model
developed on Petit-Saut reservoir predicted very well the dissolved CH4 concentrations in an Ivory Coast
reservoir (Galy-Lacaux et al., 1998).
Evidence suggests that in Flooded Land, CH4 was generally produced exclusively from flooded soils; theproduction of this gas could sustain measured fluxes at the water-air interface (Houel, 2003; Duchemin, 2000;
Abril et al., 2005).

3a.1

Flooded Land Remaining Flooded Land

This section provides information on how to estimate CH4 emissions from Flooded Land Remaining Flooded
Land. This information is drawn from available literature and is intended to be useful to countries that wish todevelop preliminary estimates of CH4 emissions from this source. Countries with potentially significant CH4
emissions from Flooded Land seeking to report these emissions should consider the development of countryspecific emission factors to reduce overall uncertainty. Guidance on the development of such factors is provided
in Box 2a.1 in Appendix 2.

3 A .1.1

CH 4 EMISSIONS FROM F LOODED L AND R EMAININGF LOODED L AND

METHODOLOGICAL ISSUES
Post-flooded CH4 emissions can occur via the following pathways:•

Diffusive emissions, due to molecular diffusion across the air-water interface;•

Bubble emissions, or gas emissions from the sediment through the water column via bubbles; this is a very
important pathway for CH4 emissions, especially in temperate and tropical regions;•

Degassing emissions, or emissions resulting from a sudden change in hydrostatic pressure, as well as theincreased air/water exchange surface after reservoir waters flow through a turbine and/or a spillway (Hélie,2004; Soumis et al., 2004; Delmas et al., 2005); this is a very important pathway for CH4 emissions fromyoung tropical reservoirs.

The Tier 1 approach only covers diffusive emissions. Tier 2 includes a term for estimating CH4 bubble emissions,and if applicable, separate consideration of ice-free and ice-covered periods. Tier 3 methods refer to any detailed
measurement-based approach that includes an estimate of all relevant CH4 fluxes from Flooded Land, which also
includes degassing emissions, and considers the depth, the geographical localization and water temperature of
the reservoir for its entire life-time. Tier 3 methods are not outlined further in this chapter, but countries shouldrefer to Box 2a.1 in Appendix 2 on the derivation of country-specific emission factors as a resource for
implementing a Tier 3 approach. Table 3a.1 summarizes the coverage of the three tiers and CH4 emission
pathway.

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TABLE 3A.1
SUMMARY OF METHODS AND EMISSIONS COVERAGE

CH4
Tier 1•

Diffusive emissions

Tier 2••

Diffusive emissions
Bubble emissions

Tier 3•All emissions

The following section describes the Tier 2 and Tier 1 approaches for CH4 emissions.

CHOICE OF METHOD
Methane can be emitted from flooded lands through release of bubbles, by diffusion and by degassing. The
decision tree in Figure 3a.1 guides inventory compilers through the processes of selecting an appropriate
approach for CH4 emissions from Flooded Land. Tier selection and the level of spatial and temporaldisaggregation implemented by inventory compilers will depend upon the availability of activity data andemission factors, as well as the importance of reservoirs as contributors to national greenhouse gas emissions.
Country-specific scientific evidence and data are always preferable to Tier 1 default data.
Tier 1The Tier 1 method for estimating CH4 emissions from Flooded Land includes only diffusion emissions during
ice-free period. Emissions during the ice-cover period are assumed to be zero. Equation 3a.1 can be used withmeasured emissions provided in Table 3a.2 and country-specific total area of flooded land:

EQUATION 3A.1
CH4 EMISSIONS FROM FLOODED LANDS (TIER 1)
CH 4 EmissionWWflood = P • E (CH 4 ) diff • A flood _ total _ surface • 10 −6

Where:
CH4 emissionsWW flood = total CH4 emissions from Flooded Land, Gg CH4 yr-1
P = ice-free period, days yr-1 (usually 365 for annual inventory estimates, or less in country with ice-coverperiod))E(CH4)diff = averaged daily diffusive emissions, kg CH4 ha-1 day-1
Aflood, total surface = total flooded surface area, including flooded land, lakes and rivers, ha

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Appendix 3: CH4 Emissions from Flooded Land: Basis for Future Methodological Development

Figure 3a.1

Decision Tree for CH 4 Emissions from Flooded Land Remaining Flooded
Land

Start

Are
country-specificseasonally integrated emission factors
available for major
type of reservoirs?

Estimate emissions from all
relevant emission pathways
using country-specificemission factors (Tier 3).

Yes

Box 4: Tier 3NoAre
country-specific CH4
diffusive and bubble emissions
data available for major
type of reservoirs?

NoAre
flooded lands
a key category1 and is
CH4 significant2?

No

Estimate emissions
using default
emission factors(Tier 1).
Box 1: Tier 1

Yes

Yes

Are
country-specific CH4
degassing data available
for major type ofreservoirs?

Determine seasonally integrated
CH4 emission factors for diffusive
and bubble emissions for major
type of reservoirs.

No

Yes
Estimate diffusive, bubble
and degassing using
country-specific emission
factors (Tier 2).
Box 2: Tier 2

Estimate diffusive andbubble emissions only,
using country-specificemission factors(Tier 2).
Box 3: Tier 1/2

Note:
1: See Volume 1 Chapter 4, "Methodological Choice and Identification of Key Categories" (noting Section 4.1.2 on limited resources), for
discussion of key categories and use of decision trees.
2: A subcategory is significant if it accounts for 25-30% of emissions/removals for the overall category.

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Tier 2
A Tier 2 approach for CH4 emissions requires country-specific emission factors for diffusive and bubble
emissions, and if applicable, accounts for different rates of diffusion and bubble emissions during the ice-free
and ice-covered periods. Flooded land area may also be disaggregated by climatic zone, or any relevant
parameter listed in Box 2a.1 in Appendix 2. This approach is described in Equation 3a.2.

EQUATION 3A.2
CH4 EMISSIONS FROM FLOODED LANDS (TIER 2)(()⎡ P f • Ef (CH 4 ) diff • A flood , surface +⎤⎢⎥CH 4 EmissionsWWflood = ⎢ P f • Ef (CH 4 ) bubble • A flood , surface +⎥⎢⎥⎣⎢ Pi • E i (CH 4 ) diff + E i (CH 4 ) bubble • A flood , surface ⎦⎥())

Where:
CH4 emissionsWW flood = total CH4 emissions from Flooded Land per year, kg CH4 yr-1
Pf = ice-free period, days yr-1
Pi = period with ice cover, days yr-1
Ef(CH4)diff = averaged daily diffusive emissions from air water-interface during the ice-free period, kg
CH4 ha-1 day-1
Ef(CH4)bubble = averaged daily bubbles emissions from air water-interface during the ice-free period, kg
CH4 ha-1 day-1
Ei(CH4)diff = diffusive emissions related to the ice-cover period, kg CH4 ha-1 day-1
Ei(CH4)bubble = bubbles emissions related to the ice-cover period, kg CH4 ha-1 day-1
Aflood, surface = total flooded surface area, including flooded land, lakes and rivers, ha

CHOICE OF EMISSION FACTORS
Tier 1The key default values for Tier 1 are emission factors for CH4 via the diffusion pathway. Table 3a.2 provides
measured emissions for various climate zones. To the extent possible given available research, these measured
emissions integrate spatial (intra reservoir and regional variations) and temporal variations (dry/rainy and otherseasonal, inter-annual variations) in the emissions from reservoirs. Default emission factors should be used inTier 1 for the ice-free period only. During complete ice-cover period, CH4 emissions are assumed to be zero.
When default data are not available, countries should use the closest default emission factors value (emissions of
the most similar climatic region).
Tier 2
Under Tier 2, country-specific emission factors should be used instead of default factors to the extent possible.
Additional estimates of winter emissions and CH4 bubble emissions are also needed, which will require thedevelopment of country-specific emission factors. It is anticipated that a mix of default values and countryspecific emission factors will be used when the latter do not cover the full range of environmental andmanagement conditions. The development of country-specific emission factors is discussed in Box 2a.1 inAppendix 2. The derivation of country-specific factors should be clearly documented, and published in peer
reviewed literature.

CHOICE OF ACTIVITY DATA
Several different types of activity data may be needed to estimate flooded land emissions, depending on the tierbeing implemented and the known sources of spatial and temporal variability within the national territory. These
activity data types correspond to the same data required for CO2 emissions as described in Section 7.3.2.

Flooded land area
Country-specific data on flooded land area are required for all tiers to estimate diffusive and bubble emissions.
Alternatively, countries can obtain an estimate of their flooded land area from a drainage basin cover analysis,
from a national dam database, from the International Commission on Large Dams (ICOLD, 1998) or from theAp3.4

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Appendix 3: CH4 Emissions from Flooded Land: Basis for Future Methodological Development

World Commission on Dams report (WCD, 2000). Since flooded land area could change rapidly, countries
should use updated and recent data. Tier 2 and Tier 3 approaches preferably rely on a national database to trackreservoirs surface area. This database should also include other parameters as reservoir depth, year of flooding,reservoir localization (see Box 2a.1 in Appendix 2).

Period of ice-free cover/Period of ice-cover
Under Tiers 2 and 3, the periods during which the reservoirs are ice-free or ice-covered are required to estimate
emissions of CH4 emissions. These data can be obtained from national meteorological services.

Outflow/Spillway volume
Under Tier 3, flooded land outflow and spillway volume are required to estimate degassing emissions of CH4.

CH 4 concentrations upstream and downstream of dams
Under Tier 3, CH4 concentrations upstream and downstream of dams would be needed for estimating degassing
emissions. Information on how to measure these data can be obtained from the references cited in Box 2a.1 inAppendix 2.

TABLE 3A.2
CH4 MEASURED EMISSIONS FOR FLOODED LAND
Diffusive Emissions (ice-free period)
Ef(CH4)diff (kg CH4 ha-1 day-1)

ClimateReferences

Median

Min

Max

Nm

Nres

Polar/Boreal, wet

0.086

0.011

0.3

253

13

Blais 2005; Tremblay et al. 2005;
Therrien, 2004; Therrien, 2005;
Huttunen et al., 2002; Lambert,
2002; Duchemin, 2000

Cold temperate,
moist

0.061

0.001

0.2

233

10

Tremblay et al., 2005; Therrien,
2004; Blais, 2005; Lambert, 2002;
Duchemin et al., 1999

Warm temperate,
moist

0.150

- 0.05

1.1

416

16

Tremblay et al., 2005; Soumis et al.,
2004; Duchemin, 2000; Smith andLewis, 1992

Warm temperate, dry

0.044

0.032

0.09

135

5

Therrien et al., 2005; Therrien,
2004; Soumis et al., 2004

Tropical, wet

0.630

0.067

1.3

303

6

Tavares de lima, 2005; Abril et al.,2005; Therrien, 2004; Rosa et al.,
2002; Tavares de lima et al., 2002;
Duchemin et al., 2000; Galy-Lacaux
et al., 1997; Galy-Lacaux, 1996;
Keller and Stallard, 1994

Tropical, dry

0.295

0.070

1.1

230

5

Rosa et al., 2002; Dos Santos, 2000

The values in the second column represent the medians of CH4 emissions reported in the literature, which themselves are arithmetic
means of flux measured above individual reservoirs. The medians are used because the frequency distributions of underlying flux
measurements are not normal, and their arithmetic means are already skewed by extreme values. Min and Max values are, respectively,
the lowest and highest of all individual measurements within a given climate region; these are provided as an indication of variability
only. Nm = number of measurements; Nres = number of reservoirs sampled.
These measurements may include non-anthropogenic emissions (e.g., emissions from carbon in the upstream basin) and possible double
counting of anthropogenic emissions (e.g., waste water from urban areas in the region of the reservoir) and so may overestimate theemissions.

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UNCERTAINTY ASSESSMENT
The two largest sources of uncertainty in the estimation of CH4 emissions from Flooded Land are the quality ofemission factors for the various pathways (diffusive, bubble and degassing) and estimates of the flooded land
areas.

Emission factors
As shown in Table 3a.2, average diffusive emissions can vary by an order of magnitude in boreal and temperateregions, and by one to three orders of magnitude in tropical regions. The same variability in bubble emissions isobserved in all regions (about one order of magnitude). Therefore, the use of any default emission factor will
result in high uncertainty.
CH4 degasssing emissions are also an important source of uncertainty. Degassing emissions are importantcomponent of GHG emissions from flooded tropical lands (Galy-lacaux et al., 1997), accounting for more than
40% of the total GHG emissions from a nine year old reservoir (Delmas et al., 2005). However, for many
reservoirs degassing emissions are small or negligible (Duchemin, 2000; Soumis et al., 2004). Hence, until
additional knowledge becomes available on the dynamics of CH4 degassing emissions, estimation should be
conducted on a case-by-case basis.
To reduce the uncertainties on emissions factors, countries should develop appropriate, statistically-valid
sampling strategies that take into account natural variability of the ecosystem under study (Box 2a.1 in Appendix
2). When applicable, the distinction between ice-free and ice-covered periods may be a significant improvementin accuracy (Duchemin et al., 2005). Those sampling strategy should include enough sampling stations per
reservoir, enough reservoirs and sampling periods. The number of sampling stations should be determined using
recognized statistical approach. Moreover, countries should consider factors included in Box 2a.1 in Appendix 2.

Flooded land surface area
Information on the flooded area retained behind larger dams (>100 km2) should be available and will probably
be uncertain by approximately 10%, especially in countries with large dams and hydroelectric reservoirs. For
countries with many flooded lands and where national databases are not available, flooded area retained behinddams will probably be uncertain by more than 50%. Detailed information on the location, type and function ofsmaller dams may be also difficult to obtain, though statistical inference may be possible based on the size
distribution of reservoirs for which data are available. In addition, reservoirs are created for variety of reasonsthat influence the availability of data, and, consequently, the uncertainty on surface area is dependent on countryspecific conditions.

3a.2

Land Converted to Flooded Land

With the actual knowledge, for Land Converted to Flooded Land, it is suggested to use measured emissions inTable 3a.2. Inventory compilers should use Tier 1, Tier 2, and Tier 3 methods described in Section 3a.1 toestimate CH4 emissions from Land Converted to Flooded Land.

References
Abril, G., Guérin, F., Richard, S., Delmas, R., Galy-Lacaux, C., Gosse, P., Tremblay, A., Varfalvy, L., dosSantos, M.A. and Matvienko, B. (2005). Carbon dioxide and methane emissions and the carbon budget of
a 10-years old tropical reservoir (Petit-Saut, French Guiana), Global Biogeochemical Cycle, 19,
doi:10292005GB002457.
Blais, A.-M. (2005). Étude des gaz à effet de serre en milieux aquatiques Relevés de terrain 2005. Rapportd'Environnement Illimité à Hydro-Québec Production. 30 p. and annexes.
Delmas, R., Richard, S., Guérin, F., Abril, G., Galy-Lacaux, C., Delon, C. and Grégoire, A. (2005). Long Term
Greenhouse Gas Emissions from the Hydroelectric Reservoir of Petit Saut (French Guiana) and Potential
Impacts. In Tremblay, A., L. Varfalvy, C. Roehm and M. Garneau (Eds.). Greenhouse gas Emissions:
Fluxes and Processes, Hydroelectric Reservoirs and Natural Environments. Environmental Science Series,
Springer, Berlin, Heidelberg, New York, pp. 293-312.
dos Santos, M.A. (2000). Inventário emissões de gases de efeito estufa derivadas de Hidréletricas, PhD.
Dissertation, University of Rio de Janeiro, Rio de Janeiro, Brazil, 154p.
Duchemin, E., Lucotte, M., Canuel, R. and Soumis, N. (2006). First assessment of CH4 and CO2 emissions fromshallow and deep zones of boreal reservoirs upon ice break-up, Lakes and Reservoirs: Research andManagement, 11:9-19.

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Appendix 3: CH4 Emissions from Flooded Land: Basis for Future Methodological Development

Duchemin, É. (2000). Hydroelectricity and greenhouse gases: Emission evaluation and identification ofbiogeochemical processes responsible for their production, PhD. Dissertation, Université du Québec àMontréal, Montréal (Québec), Canada, 321 p (available on CD-ROM).
Duchemin, É., Lucotte, M., Canuel, R. and Chamberland, A. (1995). Production of the greenhouse gases CH4
and CO2 by hydroelectric reservoirs of the boreal region, Global Biogeochemical Cycles, 9, 4, 529-540.
Duchemin, É., Lucotte, M., Canuel, R., Almeida Cruz, D., Pereira, H.C., Dezincourt, J. and Queiroz, A.G.
(2000). Comparison of greenhouse gas emissions from an old tropical reservoir and from other reservoirs
worldwide, Verh. Internat. Verein. Limnol., 27, 3, 1391-1395.
Duchemin, É., Canuel, R., Ferland, P. and Lucotte, M. (1999). Étude sur la production et l’émission de gaz àeffet de serre par les réservoirs hydroélectriques d’Hydro-Québec et des lacs naturels (Volet 2), Scientificreport, Direction principal Planification Stratégique - Hydro-Québec, 21046-99027c, 48p.
Galy-Lacaux, C. (1996). Modifications des échanges de constituants mineurs atmosphériques liées à la créationd'une retenue hydroélectrique. Impact des barrages sur le bilan du méthane dans l'atmosphère, PhD
dissertation, Université Paul Sabatier, Toulouse (France), 200 p.
Galy-Lacaux, C., Delmas, R., Jambert, C., Dumestre, J.-F., Labroue, L., Richard, S. and Gosse, P. (1997).
Gaseous emissions and oxygen consumption in hydroelectric dams: a case study in French Guyana,
Global Biogeochemical Cycles, 11, 4, 471-483.
Galy-Lacaux, C., Delmas, R., Kouadio, G., Richard, S. and Gosse, P. (1998). Long-term greenhouse gas
emissions from hydroelectric reservoirs in tropical forest regions, Global Biogeochemical Cycles, 13, 2,
503-517.
Hélie, J.F. (2004). Geochemistry and fluxes of organic and inorganic in aquatic systems of eastern Canada:
examples of the St-Lawrence River and Robert-Bourassa reservoir: Isotopic approach, PhD. Dissertation,
Université du Québec à Montréal, Montréal (Québec), Canada, 205p.
Houel, S. (2003). Dynamique de la matière organique terrigène dans les réservoirs boréaux, PhD. Dissertation,
Université du Québec à Montréal, Montréal (Québec), Canada, 121p.
Huttunen, J.T., Väisänen, T.S., Hellsten, S.K., Heikkinen, M., Nykänen, H., Jungner, H., Niskanen, A., Virtanen,
M.O., Lindqvist, O.V., Nenonen, O.S. and Martikainen, P.J. (2002). Fluxes of CH4, CO2, and N2O inhydroelectric reservoir Lokka and Porttipahta in the northern boreal zone in Finland, Global
Biogeochemical Cycles, 16, 1, doi:10.1029/2000GB001316.
International Commission on Large Dams (ICOLD) (1998). World Register of Dams 1998. Paris. International
Comittee on large Dams (Ed.). Metadatabase.
Keller, M. and Stallard, R.F. (1994). Methane emission by bubbling from Gatun lake, Panama, J. Geophys. Res.,99, D4, 8307-8319.
Lambert, M. (2002). Campagne d'échantillonnage sur les émissions de gaz à effet de serre des réservoirs et deslacs environnants - Rapport de terrain 2001. Rapport présenté à la Direction Barrage et environnement par
la Direction Environnement, Hydro-Québec, 108 p and appendix.
Rosa, L.P., Matvienko Sikar, B., dos Santos, M.A., and Matvienko Sikar, E. (2002). Emissoes de dioxido decarbono e de metano pelos reservatorios hydroelectricos brasileiros, Relatorio de referencia – Inventorio
brasileiro de emissoes antropicas de gase de efeito de estufa, Ministerio da Ciencia e tecnologia, Brazil,
199p.
Smith, L.K. and Lewis, W.M. (1992). Seasonality of methane emissions from five lakes and associated wetlandsof the Colorado Rockies, Global Biogeochemical Cycles, 6, 4, 323-338
Soumis, N., Duchemin, É., Canuel, R. and Lucotte, M. (2004). Greenhouse gas emissions from reservoirs of thewestern United States, Global Biogeochem. Cycles, 18, GB3022, doi:10.1029/2003GB002197.
Tavares de Lima, I. (2005). Biogeochemical distinction of methane releases from two Amazon hydroreservoirs,
Chemosphere, (in press)
Tavares de Lima, I. (2002). Emissoa de metano em reservatorio hidreletricos amazonicos atraves de leis depotencia (Methane emission from Amazonian hydroelectric reservoirs through power laws), PhD
Dissertation, Universidade de Sao Paulo, Sao Paulo, Brazil, 119 p.
Therrien, J. (2004). Flux de gaz à effet de serre en milieux aquatiques - Suivi 2003. Rapport de GENIVAR
Groupe Conseil Inc. présenté à Hydro-Québec. 52 p. et annexes.

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Therrien, J., Tremblay, A. and Jacques, R. (2005). CO2 Emissions from Semi-arid Reservoirs and Natural
Aquatic Ecosystems. In Tremblay, A., L. Varfalvy, C. Roehm et M. Garneau (Eds.). Greenhouse Gas
Emissions: Fluxes and Processes, Hydroelectric Reservoirs and Natural Environments. Environmental
Science Series, Springer, Berlin, Heidelberg, New York, pp. 233-250.
Tremblay, A., Therrien, J., Hamlin, B., Wichmann, E. and LeDrew, L. (2005). GHG Emissions from Boreal
Reservoirs and Natural Aquatic Ecosystems. In Tremblay, A., L. Varfalvy, C. Roehm and M. Garneau(Eds.). Greenhouse gas Emissions: Fluxes and Processes, Hydroelectric Reservoirs and Natural
Environments. Environmental Science Series, Springer, Berlin, Heidelberg, New York, pp. 209-231.
WCD (2000). Dams and Development a New Framework for Decision-Making, The report of the World
Commission on Dams, Earthscan Publications Ltd, London and Sterling, VA, 356 p.

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