Carbon Balance and Offset Potential of the Great Fen Project. Vincent Gauci

Transcription

1 Carbon Balance and Offset Potential of the Great Fen Project Vincent Gauci The Open University and GLCC* Funded by 9th July 2008 *Gauci Land Carbon Consulting 1

2 Contents Summary and recommendations Introduction Aims and objectives Carbon and the Cambridgeshire Fens Estimating Great Fen Project C balance Description of study area and sample methods Quantifying current C losses in the Great Fen Project area Estimating the impact of rewetting on Great Fen GWP Uncertainties and recommendations for long-term monitoring Conclusions...15 References...17 Appendix

3 Summary and recommendations I. GLCC and The Open University were instructed by administrators of the Great Fen Project (GFP), The Wildlife Trust for Bedfordshire, Cambridgeshire, Northamptonshire and Peterborough, to undertake a study of the carbon balance and offset potential of the Great Fen Project. II. A literature study supplemented by a field investigation of the soils within the GFP area was conducted. III. Results of the study suggest that the Great Fen Project represents an important opportunity to prevent the loss of carbon from long-term soil stores. At current rates of peat loss the majority of the peat resource in the area is likely to be mineralised to CO2 in the next 80 years. This rate of loss represents an estimated annual emission of approximately 300,000 tonnes of CO2 to the atmosphere. IV. Rewetting of the GFP area will arrest this emission of CO 2 and lead to reversion of the area from a CO2 source with a positive Global Warming Potential (GWP) (i.e. undesirable) to a carbon sink with a desirable, negative GWP. When including the additional estimated production of N2O for agriculturally converted peatlands, GFP rewetting will result in an annual avoided loss of 325,000 tonnes of CO2 equivalents. V. Over 80 years, each rewetted hectare of GFP land will result in an avoided loss of 10,000 tonnes of CO2 equivalents (averaged across the area of the project comprising peat soil). VI. Where carbon offset is achieved through the maintenance and management of the GFP after the land has been purchased and rewetted, the recommended figure for annual offset is 2,300 kg CO2 (equiv) ha-1 year-1 or, for the entire GFP area 8,350 x 103 kg CO2 (equiv) year-1. VII. Given land prices in July 2008, land purchase funded through a local voluntary carbon offset scheme would represent a good value carbon offset when compared to similar products available on the market. VIII. Income may also be generated in the long-term, after GFP land-purchase, since there is an annual carbon benefit (averaged over 100 years) to actively maintaining and managing the Great Fen Project. IX. A long-term monitoring programme of CO2 and trace gas exchange is required to verify estimates of global warming potential of the GFP area should the project be marketable under the Voluntary Carbon Standard. This data will help to refine estimates of the impact of rewetting on Fenland carbon balance and GWP for the GFP project as well as other planned Fenland rewetting projects. 3

4 1 Introduction 1.1 Aims and objectives The Great Fen Project area of the Cambridgeshire Fens consists of an important yet diminishing resource of carbon (C) in the form of peat. The primary goal of the Great Fen Project is to recreate habitats through the creation of a 3700 hectare landscape for wildlife and people. The project is located within the artificially drained area of the fens in what is one of the largest habitat restoration projects of its type in Europe. Ultimately, the two existing nationally important nature reserves of Holme Fen and Woodwalton Fen will be linked and wet grassland and fen plant communities will be re-established In addition to the benefits for biodiversity in the area and the increased leisure amenity and economic potential for local populations and tourists, there is potential for rewetting to positively influence the carbon balance of the peat soils. This is important as anthropogenic carbon emissions to the atmosphere, are a major and growing contributor to recent climate change (IPCC 2001) The purpose of this report is to estimate the potential impact of rewetting in the Great Fen Project area on the emission of radiatively important gases from restored fenland soil This study comprises two parts: Estimating the current rate of carbon loss to the atmosphere as CO 2 through various processes (including heterotrophic decomposition of drained and cultivated soil carbon) so that avoided losses of C, through Great Fen Project rewetting may be quantified The assessment of the likely response of the Great Fen to re-wetting in terms of enhanced CO2 sequestration, and methane (CH4) and nitrous oxide (N2O) emission (both CH4 and N2O are important greenhouse gases) The estimates of the effect of rewetting are largely driven by values derived from the literature; however soil data from the Great Fen Project area are used to give greater site specificity to the estimates. By combining the study components of avoided-loss and postrewetting sequestration and emissions estimates, the total global warming potential (GWP in CO2 equivalents) of the Great Fen Project will be estimated Given this information, recommendations will be made as to how the Great Fen Project may be used as a carbon offset scheme should the net effect of the project provide a net climate benefit through the reduction of greenhouse gas emissions. 4

5 1.2 Carbon and the Cambridgeshire Fens Global soil carbon stocks are estimated to be around 1500 Pg (1Pg = 1015g) (Gorham, 1991) with approximately 1/3 of the carbon residing in mid-high latitude Northern Hemisphere peatlands e.g. bogs and fens (Gorham, 1991). In these ecosystems carbon is accumulated as the rate of carbon inputs through primary productivity (i.e. the proportion of photosynthetically fixed carbon that becomes organic material) exceeds that of decomposition. This is because high water-tables (the defining characteristic of peat forming wetlands) mean that oxygen is rapidly consumed in these soils and is then largely absent from the portion of the soil column beneath the water-table. When oxygen has been consumed in these anaerobic soils decomposition proceeds by progressively less energetically efficient means. This results in a slowing of decomposition and carbon loss from the soil and net increase in C inputs, thus peat is produced. It is estimated that peatlands are currently accumulating 1Pg C annually globally (Gorham, 1991) However, peatlands, and the carbon resource within them are vulnerable to natural and human impacts. These include erosion, deleterious impacts of pollution (and so diminished potential for productivity and C sequestration), fire, drainage, cultivation, deforestation, reforestation, afforestation, peat cutting and mining (Maltby and Immirzi, 1993). These can have catastrophic impacts on the carbon content of peat soils turning them from sinks to sources of carbon (Maltby and Immirzi, 1993). Indeed UK peatlands have become a source rather than a sink of carbon over the last 200 years which has resulted in 16-37% loss in their C sequestration capacity (Heathwaite 1993) The Fens have been accumulating C over the duration of the Holocene (i.e. since the end of the Last Ice Age). This was a major period of peatland growth around the world with highly productive fen peat forming in the West Siberian Lowland as well as in other highlatitude locations around the world (Smith et al., 2004). The Fens have been subject to human impacts since the seventeenth century (Darby, 1940) With respect to the area comprising the Great Fen Project area (Figure 1), Fenland has been subject to the effects of, firstly, drainage and then cultivation. In quantifying the effects of drainage and cultivation, it is fortunate that within the Great Fen Project area itself there exists a datum (or fixed point) against which the effects of drainage and cultivation on peat height could be recorded since its installation approximately150 years ago (Hutchinson, 1980). From analysis of soil height relative to the fixed point of the Holme Post (National Grid reference TL203893) in the northern portion of the Great Fen Project area, Hutchinson (1980) identifies 4 stages of drainage associated with successive installations of pumps to drain Whittlesey Mere Cumulatively, there has been a recorded loss of 3.91 m of peat height at the Holme Post between 1850 and 1978, amounting to an average annual loss in peat of 30.5 mm yr -1 (Hutchinson, 1980) While the Holme Post records a substantial loss of peat height not all of this subsidence can be attributed to C loss. Indeed a substantial proportion of this loss is likely to be due to shrinkage and compaction as the peat collapsed under its own weight and was subject to the additional weight of heavy machinery resulting in increased bulk density and carbon density of soils. 5

6 1.2.7 The following sections consider a range of approaches to quantifying the C loss of the Great Fen Project (GFP) area in its current drained, agricultural state followed by estimates of the effect of rewetting on carbon balance and the emission of trace greenhouse gases (i.e. CH4 and N2O). 2 Estimating Great Fen Project C balance 2.1 Description of study area and sample methods. Figure 1: Map showing location of the proposed extent of the Great Fen Project. Yellow filled circles indicate soil sample locations Detailed soil and habitat/eco-hydrological assessments of the study area have taken place by NA Duncan and Associates (2002) and Mountford et al (2004) respectively Mean peat depth across the portion of GFP between Woodwalton Fen and Monk s Lode is 145 cm with a range of cm (NA Duncan and Assoc., 2002) although land east of Holme Fen can be up to 4m deep. These peat soils overly sulfate rich clays (Fen Clay and Oxford Clay) and many of the soil sampling cores taken for their analysis indicate the presence of gypsum crystals (CaSO4) which may mitigate against methane production on rewetting (e.g. Gauci et al., 2002). 6

7 Figure 2. Modelled distribution of Great Fen habitats after rewetting (from Mountford et al., 2004) Water-table depth averaged approximately 75 cm beneath the soil surface with a range of 14 cm to >240 cm (NA Duncan and Assoc., 2002). These values were recorded from November 2001 to January Given that water-tables normally peak in the winter, it is likely that the water table is normally far lower than these recorded values during the growing season Mountford et al., (2004) provided a habitat scenario for the GFP area based on high resolution topographical information obtained through remote sensing methods (LIDAR) (Figure 2). Based on their modeled hydrology of the GFP area, they subdivided the area of the GFP into four habitat potential vegetation cover classes with distinct hydrological regimes based on the remotely sensed altitude data: 1) Open Water: <1m altitude 2) Reed: 1-2m altitude 3) Wet grassland: 2-3m altitude 4) Dry grassland: >3m altitude (Mountford et al., 2004) Under GFP rewetting scenario 2 it is estimated that 1053 ha of the GFP area will become fen (i.e. a combination of reed bed (s4) tall herb fen (s24) and fen meadow (m24)); 1100 ha will turn to wet grassland (mg8) with the remainder, 1480 ha being dry grassland (mg5). These values shall be used when calculating the impact of post GFP rewetting on C balance in the area. Soils were collected from a representative selection of soils spanning the northern and southern sections of the Great Fen Project area in October These included soils 7

8 within the Adventurers, Prickwillow and Ridley soil series south of New Dyke and Ridley, Padney and Turbary Moor soil series north of New Dyke. This sampling therefore covered a broad area of the Great Fen Project and included soils from main soil series in the area and so can be considered representative of the soils within the GFP Pits were dug to a depth of 50cm with intact cores collected at 15cm depth intervals for bulk density analysis. Bulk soil ( g) was also collected at each depth interval for analysis of soil content. At three locations in the sampling (all at Middle farm) soils had recently been ploughed so no reliable surface bulk density measurement could not be made. At two locations (Middle Farm 3 and New Decoy Farm) woody deposits at the lower most depths prevented reliable sampling Bulk soils were air-dried and sieved through a 2 mm sieve. 10g of soil were shaken with 40ml of KPO4 for 16 hours at 120 RPM filtered through Watman No. 42 filters and stored frozen until analysis via ion chromatography (Dionex) for extractable sulfate and nitrate. Total percentages of carbon, sulfur and nitrogen were assessed via LECO Element Analyzer Results are summarized in Table 3 of the Appendix. 2.2 Quantifying current C losses in the Great Fen Project area There are three possible ways by which Carbon losses may be calculated: 1) through estimates derived from subsidence rates, 2) via estimates of peat depth loss due to carbon mineralization rates (i.e. conversion of organic carbon to CO2) as modeled using the input variables of mean annual temperature (MAT) and annual precipitation rates and 3) by measuring CO2 fluxes directly (Kasimir-Klemedtsson et al., 1997). Given that the last of these methods requires a site specific monitoring programme, estimates of C loss will be derived using the first two methods Calculations are complicated for arable soils, especially for those where the growing of potatoes, sugar beet and onions is the norm (as is the case in the GFP area), since loss will result from the export of soil that is attached to the crops when harvested. To this author s knowledge this component of soil loss has not been quantified for other studies so, for our purposes, it is assumed that the carbon component of this soil will ultimately be oxidized to CO As previously discussed the subsidence of drained and farmed peatlands can be the result of a combination of physical processes (e.g. settlement and consolidation, shrinkage and compaction) and the biological processes of heterotrophic microbial decomposition (i.e. oxidation of organic matter to CO2) (Kasimir-Klemedtsson et al., 1997) as well as by direct removal through crop harvest and wind blown erosion (where the majority is mineralized to CO2; Lal, (2004)). 8

9 Figure 3. Predicted subsidence rates attributable to oxidation after agricultural drainage of fen peat soils (adapted from Eggelsman, 1976). The ratio of annual mean precipitation to annual mean temperature for the GFP area is indicate via the vertical perpendicular line from which the annual subsidence rate is estimated (horizontal line). The dotted line is a modeled extrapolation An initial consolidation phase occurs immediately after drainage and results in the highest rates of subsidence as records of Holme Post observations demonstrate (Hutchinson, 1980). Thereafter, subsequent rates of subsidence diminish at a progressively slower rate (Figure 3). It is therefore recommended that rates of subsidence should only be used to calculate oxidative loss several years after drainage has commenced (KasimirKlemedtsson et al., 1997). Given that the GFP area has been subject to the effects of drainage for >150 years, it is valid to use annual height loss data, together with measures of carbon density to estimate rates of C loss AN Duncan and Associates (2002), in comparing their own peat depth data with that reported by Burton and Seal (1981), calculate a loss in peat height averaging 1.8 cm yr-1 over the last 30 years. Using an average value for bulk density of 0.54 g/cm3 and an average %C content in fen peat soil of 33% (see appendix) results in an average loss of 32 x 103 kg C ha-1 yr-1 or for the whole GFP area (minus Woodwalton and Holme Fens, and 660 ha of mineral soil = 2600 ha) equates to an annual loss of 834 x 10 6 kg C yr-1 or 306,000 tonnes CO2 to the atmosphere annually. However the avoided loss figure, in global warming potential (GWP) equivalents is likely to be higher when the likely contribution of N2O emission to GWP is considered. See section 2.3 below One can verify whether the depth of annual peat subsidence is the result of oxidation (or the result of other, physical processes) by employing the statistical modeling approach of Eggelsman (1976) where the annual depth of peat soil lost through oxidation is a function of climate (i.e. an index of annual mean precipitation divided by mean annual temperature). Using local climate data reported in Kecharvarzi et al., (2007) and Mountford et al., (2004) this approach indicates that oxidation may be responsible for up-to 24 mm of peat height loss from the GFP area (Figure 3) Given that the estimated annual rate of peat loss calculated by AN Duncan and Associates (2002) is less than this value, for the purpose of estimating C loss from the GFP area, it is considered valid to attribute all 1.8 cm of loss they calculate to oxidation of C to CO2. 9

10 2.3 Estimating the impact of rewetting on Great Fen GWP Rewetting represents a shift away from aerobic decomposition under drained conditions towards a far greater proportion of anaerobic decomposition as the water table nears the soil surface While anaerobic decomposition is a far slower process than aerobic decomposition (and so C mineralization rates are reduced substantially so that C accumulation may occur), the processes of denitrification (occurring when the water table is fluctuating) and methanogenesis (occurring under strictly anaerobic conditions) lead to the formation of powerful greenhouse gases, namely N2O and CH In principle, anaerobic decomposition is subject to the same physical and environmental controls as aerobic decomposition, principally soil moisture and temperature. For decomposition in soils to follow an anaerobic path soil moisture levels must be saturating and, given that ecosystems with an anaerobic component also include microbes with varying temperature optima, temperature will also be a factor Anaerobic decomposition tends to be far slower at mineralizing C to the atmosphere than aerobic decomposition chiefly due to the lack of oxygen in these soils. For this reason, although decomposition still takes place albeit at a slower rate, predominantly wet ecosystems such as peatlands tend to be very carbon rich. Even if net primary productivity may be low it will not be as restricted by the waterlogged conditions as would decomposition (Chapin et al., 2001). This therefore leads to net accumulation of carbon and to very high carbon content in peat relative to other soil types When oxygen isn t available, microorganisms must use other ions in order to get energy from organic matter. This is a sequential process, with the most energy yielding alternative ions to oxygen utilized first. When this has been depleted the next electron accepting ion is used and so on until only those electron acceptors that yield the least amount of energy remain (equation 1). O2 > NO32- > Mn4+ > Fe3+ > SO42- > CO2 > H+ (Equ.1) In practice this sequential usage of alternate electron acceptors such as (nitrate and sulfate) follows the ecological principles of competitive exclusion. Following the sequence in equation 1, once residual oxygen in flooded soils is consumed, denitrifying bacteria start to use the nitrate and, because the denitrifying bacteria will gain more energy from performing this process than microorganisms using manganese or iron, they gain a competitive advantage over available substrates which leads to decomposition and, as waste products, the production of nitrous oxide (N2O) and nitrogen gas (N2) As with the depletion of oxygen preceding it, when the nitrate supply gets consumed other bacteria take over having taken a competitive advantage over the general microbial population. The processes of decomposition then progresses along a process known as 10

11 fermentation, where biologically available compounds are broken down into simple organic compounds such as acetate and hydrogen. These simple products of fermentation (including CO2) may then be used in the final and lowest energy yielding steps of anaerobic decomposition, sulfate reduction and then finally, methane production by a specialist group of Archaea known as methanogens For the GFP area nitrate concentrations were highest across Middle and New Decoy Farms. Sulfate concentrations generally increased with depth being particularly high in lower portions of Middle Farm profiles. (Appendix Table 3) When sulfate is present, sulfate reduction by sulfate reducing bacteria is the competitively superior process. This is commonly the process occurring in oceanic sediments or in freshwater wetland soils exposed to sulfate in acid deposition or from underlying sulfate rich clays (as in the GFP soils). Normally in low sulfate, freshwater wetlands sulfate consumption by sulfate reduction processes is a transitory step in the redox sequence shown in Equation 1, with the terminal step being methanogenesis or methane production. However in sulfate rich wetlands such as the Hudson Bay Lowland (Reeve et al., 1996) CH4 emissions are far lower than in comparable, low-sulfate, wetlands. Gauci et al., (2004) estimate that when sulfate isn t limiting in wetland ecosystems CH4 emissions are approximately 40% lower than an emissions from an equivalent, low-sulfate freshwater peatland Whiting and Chanton (2001) report that pristine fens have a positive (i.e. undesirable), warming impact on the atmosphere over a 100 yr time horizon and exert a net negative, i.e. desirable, cooling effect over the atmosphere over a 500 yr horizon. However, fens do lie close the GWP compensation point (Net GWP of zero) and it is likely that the high sulfate concentration status of the GFP soils (see appendix) will have decreased potential CH4 emissions (e.g. Gauci et al., 2004) without any accompanying effect on total C mineralization (Vile et al., 2003). If this is the case then it is likely that the project will have a negative i.e. desirable global warming impact in the shorter term. Table 1: Estimated changes in the global warming potential of Great Fen Project area following rewetting (kg CO2 equivalents ha-1yr-1) Drained Rewetted Phase 1 N2O N2O CH4 CO2 Fen 62 16, Grassland (wet and dry) Fen (high) CH4-27 CO2 117,682 GWP Phase 2 GWP N2O CH , CO2 Phase 3 GWP N2O CH4 CO2 GWP -3, , , These and other data were reviewed to estimate the global warming potential impact of rewetting in the GFP area. The methodology of Joosten and Augustin (2006) was applied with modified emissions factors to reflect the specifics of the GFP area. Emissions factors 11

12 for N2O and CH4 were considered and multiplied by the GWP of each gas over a 100-year time horizon i.e. the standard time horizon used. For the business-as-usual (BAU), drained state of the GFP N2O and CH4 values reported for the Fen high category were used (given the high C mineralization estimated for the site; (Joosten and Augustin 2006). A negative CH4 value is used since the soil column in the drained state is predominantly oxidizing atmospheric CH4 and thus is a sink of CH On rewetting, 3 phases, each with individual emissions characteristics, as detailed by Joosten and Augustin (2006), were modified to reflect soils in the GFP and the habitats in the scenario 2 provided by Mountford et al., (2004) being fen, wet grassland and dry grassland. Areas of wet grassland, being inundated for only a short period in each year, albeit generally during the coolest and least productive period of the year, were combined with dry grassland and given a negative CH4 emission value equivalent to the dry grassland value in Joosten and Augustin (2006). This is because any CH4 produced lower down the soil profile throughout the dominant aerated period of the year, is rapidly oxidized by a group of aerobic microorganisms known and methanotrophs in oxic soils higher up the profile. Further, during short periods of inundation it can take a considerable period of time for the O2 supply (and other alternate electron accepting ions such as nitrate and sulfate) to become sufficiently depleted for methanogenesis to take place. The fen habitat had a 40% reduction in CH4 emission imposed to reflect the high sulfate content of GFP soils. This may be an underestimate given that wetland ecosystems exposed to very high inputs of sulfate can have CH4 emission reduced by up to 70% (van der Gon et al., 2002). Grassland ( wet and dry) is a CH4 sink and CO2 sequestration values were derived from the review conducted by Dawson and Smith (2007) where they report an enhanced CO2 sink for the first 20 years following rewetting. In the second phase emissions of CH4 are reduced and the CO2 sink term is largest and in the third phase, both N2O and CH4 emissions are reduced, as is the CO2 sink term. In constructing the GWP for each land cover type, 100 year time horizons were used giving trace gas GWP s of 21 for CH4 and 310 for N2O (i.e. 21 and 310 x the global warming potential of CO2: Table 1). * Value is over 80 years as there will be no further peat beyond this time frame at current rates of loss Scenario BAU (no rewetting) Rewetting Scenario 1 Rewetting Scenario 2 Rewetting Scenario 3 Great Fen, GWP (kt CO2 x 100 yr1) 26,020* -1, Table 2: Total cumulative global warming potentials of 4 different emission/ sequestration scenarios for the entire Great Fen Project area. Where BAU is Businessas-usual, and then in order of increasingly pessimistic scenario: Scenario 1 = 5 yrs at Phase 1, 15 years at Phase 2 and 80 years at Phase 3. Scenario 2 = 20 yrs at Phase 1, 15 years at Phase 2 and 65 years at Phase 3. Scenario 3 = 50 yrs at Phase 1, 1 year at Phase 2 and 49 years at Phase 3. 12

13 Three different scenarios were constructed to represent the likely outcome of trace gas emissions from GFP rewetting on total GWP for the area. Each scenario was constructed from a combination of phases of trace gas emission response to rewetting with scenario 1 the most optimistic (in terms of GWP) and scenario 3 the most pessimistic (i.e. highest trace gas emissions and so least negative GWP)(Table 2). These were constructed over a 100-year time period (only an 80 year time period was used for the business as usual calculation as it is estimated that at current rates of peat loss, the majority of peat resource of the GFP would be lost in that time frame, although peat in portions of GFP east of Holme Fen would take longer to diminish) The estimates presented here demonstrate that full implementation of the GFP has a high potential for C conservation with an annual avoided loss of 325,000 t CO2 equivalents. While trace gas emissions after re-wetting mitigate against active C negative GWP brought about though increased CO2 uptake, the difference between potential C loss under business-as-usual and post rewetting GWP is large, amounting to approximately 24 million tonnes negative GWP over the next 100 years For the purposes of land purchase through the sale of the C offset potential on rewetting of land within the GFP, a figure that includes the avoided carbon losses (in GWP equivalents) over the remaining 80 year lifetime of the diminishing peat resource should be used. i.e. 10,000 x103 kg CO2(equiv) ha Where carbon offset is achieved through the maintenance and management of the GFP after the land has been purchased and rewetted, a figure based on annual carbon storage potential through net ecosystem production should be used. It is recommended that the negative GWP (i.e. offset) under rewetting scenario 2 (table 2) should be used as a best estimate of CO2 equivalent sequestration The recommended figure for this annual offset is 230 kg CO2 (equiv) ha-1 year-1 or, for the entire GFP area 8,350 x 103 kg CO2 (equiv) year Although there is no current market for peatland carbon credits it is possible to estimate the potential value of the GFP should such a trading scheme be introduced. The May 30th European Emissions Trading Scheme price of a tonne of CO2 is Euro 25 (approximately 20 GBP). Based on this value and assuming a constant price for CO 2 (when in reality it will fluctuate) the GFP could generate an income of 167,000 annually through carbon offsetting alone Any land within the project area that is yet to be purchased would generate 200,000 per ha when turned over to the GFP, rewetted and the carbon losses avoided. A figure that far exceeds agricultural land values in the region In the absence of carbon trading in peatland carbon credits a voluntary market for carbon offsetting has developed with a much lower price per tonne of CO2 conserved. For example the current Climate Care cost to individuals to offset 1 tonne of CO2 is 8.80 (May 30th 2008). At this price the GFP could generate an income of 73,500 per year through carbon offsetting while land purchase for offsetting would generate 88,000 ha-1. 13

14 The purchase price for land under vacant possession in the GFP area is approximately 14,800 ha-1 (David Goodson pers. comm.) which represents a cost per tonne of CO 2 equivalent saved through avoided loss of approximately 1.48 making land acquisition under the GFP an extremely good value carbon offset project when compared with those available on the voluntary carbon market. 2.4 Uncertainties and recommendations for long-term monitoring It is important to stress the limitations in estimating annual carbon offset potential through the use of literature values. The laboratory based data on current carbon loss has the greatest certainty while the annual GWP of the GFP after rewetting (the smallest component in terms of overall GWP of the project) carries the greatest uncertainty. This is because the terrestrial atmosphere exchange of greenhouse gases can have high spatial variability with many factors contributing to overall flux and there are a limited number of long-term studies of terrestrial atmosphere exchange following fenland restoration, with no known studies that extend to the duration of the post-rewetting scenarios identified in Table 2. In addition, a figure of 660 ha of land within the GFP is considered to be primarily a mineral soil. This figure may underestimate the total area of peat soil within the GFP by, at most, a few 10s of hectares. Inclusion of this figure is consistent with the cautious approach employed throughout for the purpose of calculating carbon offset potential of the GFP. Verification of the estimates detailed here will be required (to meet the Voluntary Carbon Standard) through the monitoring of CO 2 exchange, CH4 and N2O fluxes on project land undergoing various stages of rewetting ranging from land within the area that is still being used agriculturally (to establish baseline values for fluxes), to recently rewetted areas (e.g. Darlow s Farm) to newly acquired land that is undergoing the first stages of transition to rewetted fen (e.g. Middle Farm). An initial 3-year monitoring programme is recommended followed by return field measurement monitoring campaigns at 5-year (x2) and then decadal intervals (comprising a 2-year monitoring programme for each of these subsequent campaigns) It is recommended that such a monitoring programme be introduced at the earliest opportunity since changes associated with a transition to rewetting may result in shortterm yet large pulses in emissions of trace gases such as N2O. 3 Conclusions 3.1 The Great Fen Project represents an important opportunity to prevent the loss of carbon from long-term soil stores. At current rates of peat loss the majority of the peat resource in the area is likely to be mineralised to CO2 in the next 80 years. This rate of loss represents an estimated annual emission of approximately 300,000 tonnes of CO2 to the atmosphere. 3.2 Rewetting of the GFP area will arrest this emission of CO2 and lead to reversion of the area from a CO2 source with a positive GWP (i.e. undesirable) to a carbon sink with a desirable, negative GWP. When including the additional estimated production of N2O for agriculturally converted peatlands, GFP rewetting will result in an annual avoided loss of 325,000 tonnes of CO2 equivalents. 14

15 3.3 Over 80 years, each rewetted ha of GFP land (averaged across the area of the project comprising peat soil), will result in an avoided loss of 10,000 tonnes of CO2 equivalents. 3.4 Where carbon offset is achieved through the maintenance and management of the GFP after the land has been purchased and rewetted it is recommended that the negative GWP (i.e. offset) under rewetting scenario 2 (table 2) should be used as a best estimate of CO 2 equivalent sequestration. 3.5 The recommended figure for this annual offset is 2,300 kg CO2 (equiv) ha-1 year-1 or, for the entire GFP area 8,350 x 103 kg CO2 (equiv) year Given land prices in July 2008, land purchase funded through a local voluntary carbon offset scheme would represent a good value carbon offset when compared to similar products available on the market. 3.7 Although on a smaller scale, income may also be generated in the long-term, after GFP landpurchase, since there is an annual carbon benefit (3.5 above; averaged over 100 years) to actively maintaining and managing the Great Fen Project. 3.8 A long-term monitoring programme of CO2 and trace gas (CH4 and N2O) exchange, as outlined in (above) is required to verify estimates of global warming potential of the GFP area should the project be marketed under the Voluntary Carbon Standard. This data will help to refine estimates of the impact of rewetting on Fenland carbon balance and GWP for the GFP project as well as other planned Fenland rewetting projects. 15

16 References Burton R.G.O & Seale R.S (1981) Soils in Cambridgeshire 1, Sheet TL18E/28W (Stilton). Soil Survey of England and Wales, Record No 65. Harpenden. Chapin FS, Matson PA and Mooney HA (2001) Principles of Terrestrial Ecosystem Ecology Springer. Darby HC (1940) The Drainage of the Fens, Cambridge University Press, Cambridge. Dawson J.J.C and Smith P (2007) Carbon losses from soil and its consequences for land-use management Science of the Total Environment 382: Duncan, N.A. (2002). Great Fen Project: Soil and Agricultural Land Classification Survey. Report to the Wildlife Trusts. Over: N.A. Duncan and Associates. Eggelsman, R. (1976). Peat consumption under influence of climate, soil condition and utilization. Proceedings of the Fifth International Peat Congress, I, pp Poznan. Poland. Gauci, V., Dise, N.B. and Fowler, D., Controls on suppression of methane flux from a peat bog subjected to simulated acid rain sulfate deposition. Global Biogeochemical Cycles, 16 (1): Art. No Gauci, V., Matthews, E., Dise, N., Walter, B., Koch, D., Granberg, G., Vile, M., (2004). Sulfate suppression of the wetland methane source in the 20th and 21st centuries. Proceedings of the National Academy of Sciences USA, 101, Gorham E. (1991) Northern Peatlands: Role in the Carbon Cycle and Probable Responses to Climatic Warming Ecological Applications, Vol. 1, No. 2 pp Heathwaite A. L. (1993) Disappearing Peat-Regenerating Peat? The Impact of Climate Change on British Peatlands The Geographical Journal, Vol. 159, No. 2. pp Hutchinson J.N. (1980) The record of peat wastage in the East Anglian Fenlands at Holme Post Journal of Ecology. 68, Joosten, H. & Augustin, J. (2006). Peatland restoration and climate: on possible fluxes of gases and money. In: Bambalov, N.N. (ed.): Peat in solution of energy, agriculture and ecology problems. Proceedings of the International Conference Minsk, May 29 June 2, Tonpik, Minsk, Kasimir Klemedtsson, A., Klemedtsson, L., Berglund, K., Martikainen, P., Silvola, J., Oenema, O., (1997). Greenhouse gas emissions from farmed organic soils: a review. Soil Use Manage. 13, 1 6. Kechavarzi C., Q. Dawson, P. B. Leeds-Harrison, J. SzatyŁowicz & T. Gnatowski (2007) Watertable management in lowland UK peat soils and its potential impact on CO2 emission Soil Use and Management, 23,

17 Lal R. (2004) Climate Change and Food Security Soil Carbon Sequestration Impacts on Global Science 304, 1623 Maltby, E & Immirzi, C.P. (1993) Carbon dynamics in peatlands and other wetland soils - regional and global perspectives. Chemosphere, 27 (6), pp Mountford, J.O., M.P. Mccartney, S.J. Manchester and R.A. Wadsworth (2004) Wildlife Habitats and Their Requirements Within The Great Fen Project. Report to the Great Fen Project Steering Group. Reeve, AS. Siegel, DI. and Glaser, PH (1996) Geochemical controls on peatland pore water from the Hudson Bay Lowland: A multivariate statistical approach Journal of Hydrology Volume: 181: 1-4 Pages: Smith, LC; MacDonald, GM; Velichko, AA, et al. (2004) Siberian peatlands a net carbon sink and global methane source since the early Holocene Science Volume: 303 Issue: 5656 Pages: Vile, M.A., Bridgham, S.D., Wieder, R.K., Novak, M., (2003). Atmospheric sulfur deposition alters pathways of gaseous carbon production in peatlands. Global Biogeochemical Cycles 17 Art. No Whiting GJ and Chanton JP (2001), Greenhouse carbon balance of wetlands: methane emission versus carbon sequestration Tellus 53B,

18 Appendix: Table 3: Summary of laboratory data from GFP Field sampling Location Sample pit Sample Depth/cm Nitrate (mg/kg) Sulfate (mg/kg) Carbon % Sulfur % Nitrogen % Bulk density (g/cm3) 52o N 00o W Middle Farm 1 Middle Farm 1 Middle Farm 1 Middle Farm o N 00o W Middle Farm 2 Middle Farm 2 Middle Farm 2 Middle Farm o N 00o W Middle Farm 3 Middle Farm 3 Middle Farm o N 00o W Darlows Farm Darlows Farm Darlows Farm Darlows Farm o N 00o W New Decoy Farm New Decoy Farm New Decoy Farm o N 00o W Ladyseat Farm Ladyseat Farm Ladyseat Farm Ladyseat Farm o N 00o W Holme Lode Farm Holme Lode Farm Holme Lode Farm Holme Lode Farm