CELTICFLUX - Monitoring of Greenhouse Gas Fluxes

Conference – 20th September, 2007 Glenview Hotel, Delgany, Co. Wicklow

The purpose of this conference was to bring together the science of recently funded research projects on Greenhouse gases (GHGs) in Ireland.

In addition to the conference we propose to publish 12 scientific papers in a Special Issue of the journal Agricultural and Forest Meteorology with a publication date before the end of 2007.

The papers will be syntheses, reviews and summaries of the work on greenhouse gas fluxes carried out in Ireland over the past five years.

The conference was heavily subscribed, with researchers from UCC, TCD, UCD, NUI Galway, NUI Maynooth, University of Limerick and Teagasc attending as well as representatives from the EPA and the Department of Agriculture and Food. Prof. Riccardo Valentini of the University of Tuscia, chairman of the CARBOEUROPE flux project and co-ordinator of the EC Environment and Climate programme EUROFLUX was also in attendance.

Posters

We plan to publish papers from the students on their poster topics as a Special Issue of the journal Physics and Chemistry of the Earth.

Projects: CelticFlux, CCFlux & CarbiFor

Project Start Date: December 2001
Project Leaders:

Celticflux: Professor Gerard Kiely, Civil & Environmental Engineering, UCC.

CCFlux & Celticflux: Professor Michael Jones, Botany, TCD.

Research Partners:

  • Dr.Kenneth Byrne, University College, Cork.
  • Dr.Owen Carton, Teagasc, Johnstown Castle, Wexford
  • Dr. Jim Stevens, DARDNI, Northern Ireland.
  • Professor John Albertson, Civil Engineering, Duke University, NC, USA
  • Professor Gabriel Katul, Environmental Sciences, Duke University, NC, USA
  • Professor Ram Oren, Environmental Sciences, Duke University, NC, USA

Funding Agency:

Irish EPA

Project Description:

We have been measuring the CO2 flux from a grassland in County Cork since July, 2001. From May/June 2002, we have been measuring the CO2 flux from a peatland in County Kerry and also from a managed grassland at Johnstown Castle, Co. Wexford. Over the project period, have amassed five years of continuous CO2 fluxes which have given us an understanding of the seasonal and inter annual variation and the factors controlling these variations. N2O fluxes have also been continuously measured using a tunable diode laser absorption spectrometer at the Cork grassland continuously since July 2002, and two years of closed chamber measurements of CH4 have been made at the Kerry peatland. All CO2 and N2O gas concentration measurements are made at 10 Hz. We have applied models at the plot and field scale to model the greenhouse gas fluxes from the two different ecosystems and a water table manipulation experiment has examined the effect of drainage on CO2 fluxes from blanket peat. The goal of the project is to estimate the greenhouse gas balance of different Irish ecosystems.

UCC Flux Sites:

Grassland Site - Donoughmore, Co. Cork
Bog Site - Glencar, Co Kerry
Managed Grassland Site - Johnstown Castle, Co. Wexford

TCD Flux Sites (CCFlux project):
Arable Rotation Site - Oak Park, Co. Carlow
Bioenergy Crop (Miscanthus) Site - Oak Park, Co. Carlow

UCD Flux Sites (CarbiFor project):
Forestry Site - Dooary, Co. Laois

Conference Programme

Each presentation will take 20 minutes (15 minutes plus 5 minutes for questions).
Abstracts: oral presentations & posters

8:15 Registration and coffee
8.50 Opening and welcome

Session 1

Chair: Dr. Frank McGovern, Senior Scientific Officer, Climate Change Programme, Environmental Protection Agency

9.00 Introduction – Greenhouse Gas inventories for Ireland. Phillip O'Brien. EPA.

9:10 Influence of soil type, land use, precipitation, and topography on soil organic carbon in Ireland James Eaton, Nicola McGoff.

9:30 The effects of management practice on the soil organic carbon content of arable soils Lanigan, G., Williams, M.L., Burke, J. & Jones, M.B.

 

9:50 Statistical assessment of the effects of tillage method on NEE at a Spring Barley Crop: replicated eddy covariance measurements Davis, P.A., Clifton Brown, J., Lanigan, G., Saunders, M., Wright, E., Fortune, T., Burke, J., Jones, M.B., Connolly, J. & Osborne, B.

10:10 Comparison of carbon dioxide fluxes and carbon sequestration for three land use types-forest, arable and grassland Bruce Osborne, B., Black, K., Saunders, M., Davis, P., Lanigan, G., Jones, M.B., Burke, J., Williams, Nagy M. & Kumar, S.

10:30–11:10 Coffee & poster session

Session 2

Chair: Prof. Mike Jones, Department of Botany, Trinity College Dublin.

11:10 Variations in annual carbon dioxide exchange over a Sitka spruce stand prior to and following canopy closure Black, K., Tobin, B., Neville P. & Osborne B.

11:30 The contribution of autotrophic respiration to soil respiration in a grazed pasture and cereal field Kumar, S., Jones, M.B. & Williams, M.L.

11:50 Field-testing of the DNDC model for spring barley and pasture fields in Ireland Abdalla, M., Wattenbach, M., Smith, P., Jones, M.B. & Williams, M.L.

12:10 Is carbon being fixed to Irish Soils under existing grassland management practices. Kiely G., Leahy P., Byrne K.

12:30 On the gap in the spectra of atmospheric turbulence. V. Voronovich, G. Kiely.

12.50–14:00 Lunch & poster session

Session 3

Chair: Prof. Bruce Osborne, Department of Botany, University College Dublin.

14:00 Carbon gas fluxes in an Irish lowland blanket bog - effect of changing ecohydrology Laine, A., Byrne, K.A., Wilson, D., Kiely, G. & Tuittila, E.-S.

14:20 Interannual variability of N2O emissions from a grazed grassland Paul Leahy, Ger Kiely.

14:40 Nitrous oxide emissions from a spring barley field under conventional and reduced tillage: Effect of varying nitrogen application M. Abdalla, M., Ambus, P., Burke, J., Jones, M.B. & Williams, M.L.

15:00 Four years Eddy-Covariance CO2 fluxes from an Irish Atlantic blanket bog Matteo Sottocornola and Ger Kiely.

15:20–15:40 Coffee 

Session 4

Chair: Prof. Ger Kiely, Department of Civil and Environmental Engineering, University College Cork.

15:40 Reducing Uncertainties Associated with the Assessment of National Forest Carbon Stock Changes Black, K. & Gallagher, G.

16:00 Improving National Emissions Inventory Estimates from Soils for Ireland Phillip O'Brien.

16:20 Close of meeting

Important dates

Circulation of draft conference programme: 1st August, 2007
Submission of manuscripts for special issue of Agricultural and Forest Meteorology: 19th September 2007

List of Posters

Poster 1. Chamber and flux-tower measurement of N2O flux from Irish grassland. Mishurov, M., Leahy P. and G. Kiely, Centre for Hydrology, Meteorology and Climate Change, UCC.

Poster 2. Water balance, evaporation and energy fluxes in an Atlantic blanket bog in South-western Ireland. Sottocornola M. and Kiely G. Centre for Hydrology, Meteorology and Climate Change, UCC.

Poster 3. Measurement of soil bulk density across differing soil types and land use in Ireland. Nicola McGoff. Centre for Hydrology Meteorology and Climate Change, UCC.

Poster 4. The importance of DOC and POC for the carbon balance of a lowland blanket peatland Ann-Kristin Koehler. Centre for Hydrology, Meteorology and Climate Change, UCC.

Poster 5. Measurement of Soil C Stock and Stock Changes in Irish Forest Soils Christina LaPerle. Centre for Hydrology, Meteorology and Climate Change, UCC.

Poster 6. Nitrous Oxide Flux studies at multiple grassland sites Jimmy Casey . Centre for Hydrology, Meteorology and Climate Change, UCC.

Poster 7. Ecosystem scale CO2 fluxes at a blanket peatland: How detailed must our knowledge be of the topographic microforms in the landscape system? Anna Laine, Matteo Sottocornola, Gerard Kiely, Kenneth Byrne, Centre for Hydrology, Meteorology and Climate Change, UCC. David Wilson, Dept. of Environment Resource Management, University College Dublin, Ireland. Eeva-Stiina Tuittila. Dept. of Forest Ecology, University of Helsinki, Finland.

Poster 8. Field Instrumentation for CO2 flux and related measurements Murphy, K., Leahy P. and Kiely G. Centre for Hydrology, Meteorology and Climate Change, UCC.

Abstracts of Oral Presentations

9.10 Influence of soil type, land use, precipitation and topography on soil organic carbon in Ireland.

J.Eaton and N.McGoff.

Centre for Hydrology, Micrometeorology and Climate Change Civil & Environmental Engineering Dept.,UCC

Soil organic carbon (SOC) is of global importance as it is the largest carbon stock in most terrestrial ecosystems, while also being of local importance as the primary component of soil organic matter. Large scale spatial variation of SOC in Ireland is reflected in the Great Soil Groups (Gardiner and Radford 1980) of Ireland. In order to understand the spatial variability of SOC, we sampled soil at 62 sites throughout Ireland at three depths (0–10 cm, 10–25 cm, and 25–50 cm). We investigated both SOC content (% C) and SOC stocks (Mg ha-1). Of the attributes investigated, we hypothesized that soil type, land use, precipitation, slope, and elevation would affect SOC stocks in the preceding order. We also hypothesized that soil type would be a better predictor of SOC stocks than land use, but only with respect to mineral versus peat soils. We expect SOC stocks to decrease in the following order for land use: bog > rough land > forest > grassland > arable land. SOC stocks are likely to increase with precipitation and elevation and decrease with slope.
Within each land use type, mean SOC content decreased accordingly with depth (from 0–10 cm to 25–50 cm): arable 2.5% to 1.4%, bog 42.1% to 32.0%, forest 20.5% to 10.0%, grassland 7.0% to 4.1%, and rough land 24.5% to 11.6%. High percent carbon values (>15%) are due to the presence of peat soils in the bog, forest, and rough land use classes. The bog class was split between blanket and raised bogs. Percent carbon in blankets bogs decreased with depth (shallow > middle > deep) from 35.0% to 29.3% and then to 25.1%, while the carbon content of raised bogs stayed relatively constant with depth 46.8% to 47.3% to 47.4%. This result is due to mineral soil underlying some blanket bogs. Coniferous forest data indicates that SOC increased from 31.3% in the surface layer to 34.9% for the middle layer before decreasing to 15.1% at depth. A likely explanation for this trend is that afforesting peat soil is leading to increased decomposition in the surface soil layers and a steady state of carbon loss and gain from the soil profile has not been reached.

9.30 The effects of management practice on the Soil Organic Carbon content of arable soils.

G. Lanigan1, M. Williams1, J. Burke2 and M. Jones1.

  1. Botany Department, School of Natural Sciences, Trinity College, Dublin 2
  2. Teagasc, Oak Park Research Centre, Carlow

Increasing soil organic carbon (SOC) sequestration can reduce atmospheric CO2 levels that contribute to climate change. Two-thirds of terrestrial carbon is found below ground, and soil organic carbon generally has slower turnover rates than above-ground carbon. Consequently, carbon storage can be maintained over longer periods of time because it is normally better protected than above-ground carbon, particularly in disturbed ecosystems.
SOC levels from two conventionally-ploughed (CP) Barley plots (area = 2.6 ha each) were compared with those from non-inversion tillage (NIT) plots. The C content and turnover rates of free particulate organic matter (POM), macro- and micro-aggregates, and silt/clay was estimated in order to identify the size and durability of the labile and resilient pools. Overall, SOC was slightly higher in the NIT plots compared with the CP plots, while there was also a higher proportion of macro-aggregates. The rate of micro-aggregate formation was also higher in the NIT plots. These observations are consistent with the hypothesis that micro-aggregate formation occurs within macro-aggregates and that there is less disruption of macro-aggregates associated with eco-tillage.

9.50 Statistical assessment of the effects of tillage method on NEE at a Spring Barley Crop: replicated eddy covariance measurements.

P.A. Davis1, J. Clifton Brown3, G. Lanigan4, M. Saunders4, E. Wright5, T Fortune6, J Burke6, M.B. Jones4 J. Connelly5 and B.Osborne2.

  1. Biology Department, Indiana University, Bloomington, IN, USA.
  2. Botany Department, UCD, Belfield, Dublin 4, Ireland.
  3. IGER, Aberystwyth, Wales, UK.
  4. Botany Department, TCD, College Green, Dublin 2, Ireland.
  5. Department of statistical and actuarial studies, UCD, Belfield, Dublin 4, Ireland.
  6. Oak park research centre, Teagasc, Carlow, Ireland.

The need for replication when comparing estimates of net ecosystem CO2 exchange (NEE) between two management systems is demonstrated with replicated NEE estimates. NEE was estimated over a spring barley crop sown following conventional ploughing or non-inversion tillage. Measurements were made using mobile eddy covariance towers, which could be moved between plots. Gaps in the NEE measurements caused by the tower movement, were filled using gap-filling models designed to track the changing trajectory of fluxes through time. We use statistical methods to test the comparative NEE responses of the two tillage treatments to environmental factors; to identify when/if treatment effects occur. Variation in NEE between replicates was similar in magnitude to the variation between treatments, demonstrating the need to make replicated NEE estimates in comparisons of NEE between management treatments or ecosystem types that have similar carbon fluxes. During the fallow period of 2003 the non-inversion tillage plots had a dense cover of barley volunteer seedlings that was absent on the conventionally ploughed treatments. This plant cover reduced the winter carbon losses by 37 g C m-2. The greatest variation in the NEE estimates was observed on an inter-annual basis and correlated with water availability. Extended periods of reduced water availability occurred during crop growth during both 2004 and 2005, which resulted in a reduced leaf area index and carbon gain in both treatments compared to 2003. During 2004 the water deficit had a marginally greater impact on carbon gains from the conventionally tilled plots, which gained 64 g C m-2 less than the non-inversion tillage plots during this cropping season.

10.10 Comparison of carbon dioxide fluxes and carbon sequestration for three land use types-forest, arable and grassland

Bruce Osborne1, Kevin Black1, 2, Matt Saunders3, Phil Davis1, Gary Lanigan3, Mike Jones3, James Burke4, Mike Williams3, Miklos Nagy1 & Suresh Kumar3

  1. UCD School of Biology and Environmental Science, University College Dublin, Belfield, Dublin 4
  2. FERS Ltd, Bray
  3. Department of Botany, Trinity College, Dublin 2
  4. Teagasc, Oak Park Carlow

Carbon dioxide fluxes and carbon sequestration was compared for four major land use types in Ireland; a Sitka spruce forest, an arable ecosystem associated with spring barley production and subjected to two management regimes, conventional and reduced tillage, and a Lolium perenne grassland used for grazing and silage. One of our objectives was to identify ways of improving carbon sequestration, particular in arable ecosystems where the land is left fallow for a significant part of the year. Carbon sequestration was highest at the forest site>grassland site>arable site, although there was little evidence that this was associated with differences in soil respiration. At the arable site there was a small increase in carbon sequestration associated with the reduced tillage treatment, although the immediate effects of ploughing were small, indicating that improved carbon sequestration by alterations in these management practices may only be effective in the long-term. Annual gross primary productivity (GPP) was highest for the grassland>forest>arable crop, although maximal values for GPP were similar for both the grassland and arable crops. This reflects the higher proportion of non-photosynthetic tissue associated with forest stands with a consequent reduction in light utilization and/or an increase in respiratory losses. The introduction of a cover crop, or because of volunteer growth of barley seedlings at the arable site, improved annual GPP, largely by reducing daily respiratory losses during the winter. The photosynthetic potential of the cover crop was reduced by exposure to low night time temperatures and this persisted for 2-3 days after the event. These results indicate that differences in carbon sequestration are largely driven by canopy characteristics and may be improved by extending the growing period, by increasing annual green (photosynthetic) leaf area duration and light interception and/or by improving the response to low night temperatures during the winter.

11.10 Variations in annual carbon dioxide exchange over a Sitka spruce stand prior to and following canopy closure.

*Kevin Black1,2, Brian Tobin2, Pat Neville3 and Bruce Osborne2.

  1. Forest Environmental Research & Services (FERS), Ard Brae Court, Vevay Road, Bray, Co Wicklow
  2. School of Biology & Environmental Science, University College Dublin, Belfield, Dublin4
  3. Coillte Teoranta, Research & Development, Newtownmountkennedy, Co. Wicklow

*E-mail: Kevin.Black@ucd.ie

We examined inter-annual and seasonal variability of net ecosystem production (NEP), net primary production (NPP), gross ecosystem photosynthesis (GPP) and ecosystem respiration (R), and their relationship to environmental factors to explain changes in CO2 exchange above a Sitka spruce canopy in the Irish mid-lands (2002-2006). A downward trend in stand NEP (8.9 to 7.6 t C ha-1 a-1) prior to and following canopy closure was primarily associated with a decrease in GPP and an increase in normalised R (R at 10°C) to a smaller extent. The largest decline in NEP (8.9 to 6.6 t C ha-1 yr-1) was observed between 2002 and 2004 following an outbreak of green spruce aphid (Elatobium abietinum) in 2002 and periods of extended water deficits in 2003. However, the decrease in carbon uptake by the canopy was not associated with changes in water use efficiency suggesting that canopy conductance was largely decoupled from vapour pressure deficits (VPD) when these are less than 1.7 kPa (max 2003 VPD). In contrast, reductions in GPP and canopy conductance were associated with a decrease in light capture and leaf area index, particularly in 2004. We suggest that the post-2002 reductions in stand productivity were possibly associated with a 'knock-on effect' of the aphid outbreak. High population densities of spruce aphid in 2002 caused significant browning and subsequent loss of foliage resulting in a 80-90% increase in litter fall in 2003 and 2004. Whilst the reduction in NPP and NEP in 2004 (18-20%) may have been exacerbated by the 2003 drought and self thinning following canopy closure, our results highlight the importance of considering the indirect influence of climate change, such as insect outbreaks, on forest productivity in the future.

11.30 The Contribution of Autotrophic Respiration to Soil Respiration in a Grazed Pasture and Cereal Field

Kumar, S., Jones, M.B. and Williams, M.L.

Department of Botany, School of Natural Sciences, Trinity College, Dublin 2, Ireland

Soil respiration was measured on a weekly basis for approx. two years in a cut and grazed pasture at the Teagasc Crop Research Centre at Oak Park, Co. Carlow, Ireland. As the site was extensively managed with up to two silage cuts a year and with cattle grazing from July to October, the rate of soil respiration did not follow a standard Q10 relationship with regard to soil temperature. Instead a multiple regression analysis revealed that the rate of soil respiration was best explained in terms of soil temperature, soil moisture, above ground biomass and its interaction with root biomass, the equation accounting for 56% of the variation in the soil respiration data. On its own, root biomass accounted for 35% of the variation in soil respiration. Further to this analysis manipulation experiments were set up in the cut and grazed pasture and also in a spring barley field to determine the relative contribution of autotrophic respiration to soil respiration. Autotrophic respiration followed closely changes in above ground biomass, showed typical diel variation and was a maximum of 60% in both soils before silage cutting in June for the pasture field or crop harvest in late July for the spring barley field. In terms of annual cumulative respiration yields, heterotrophic respiration was the major source of CO2 whilst autotrophic respiration was the most temperature sensitive. This study underlines the critical role of substrate supply in regulating soil respiration and its temperature sensitivity.

11.50 Field-testing of the DNDC model for spring barley and pasture fields in Ireland

  1. M. Abdalla1, M. Wattenbach2, P. Smith2, M. Jones1 and M. Williams1
  2. Department of Botany, School of Natural Sciences, Trinity College Dublin, Dublin 2, Ireland.School of Biological Sciences, University of Aberdeen, Cruickshank Building, St. Machar Drive, UK.

The mechanistic model that describes N fluxes from the soil, DeNitrification DeComposition, or DNDC, was tested against seasonal and annual data sets of nitrous oxide flux from a spring barley field and a cut and grazed pasture at the Teagasc Oak Park Research Centre, Co. Carlow, Ireland. In the case of the arable field, predicted fluxes of N2O agreed with measured values for medium to high fertilizer input values (70 to 160 kg N ha-1) but poorly described the measured fluxes from zero fertilizer plots. In terms of cumulative flux values, the relative deviation of the predicted fluxes from the measured values was a maximum of 6% for the highest N fertilizer inputs but increased to 30% for the medium N and more than 100% for the zero N fertilizer plots. A linear correlation of predicted vs measured flux values for all fertilizer treatments (r2 = 0.85) was produced the equation of which underestimated the seasonal flux by 24%. Incorporation of literature values from a range of different studies on arable and pasture land did not significantly affect the regression slope. DNDC did not describe measured fluxes of N2O from reduced tillage plots of spring barley. Here predicted cumulative fluxes of N2O using the 10cm disc ploughing input option underestimated measured values by up to 55%. This may not be critical for using DNDC to model N2O fluxes from Irish agriculture as reduced cultivation and direct drilling of cereal crops only represents at most 10% of arable land.
For the cut and grazed pasture the relative deviations of predicted to measured fluxes were 150 and 360% for fertilized and unfertilized plots, this poor fit of the modeled data being due to DNDC overestimating the effect of initial soil organic carbon (SOC) on N2O flux, as confirmed by sensitivity analysis of the model. As the arable and grassland soils differed only in SOC content, reducing SOC to the arable field value significantly improved the fit of the modeled data such that the relative deviations decreased to 9 and 5% respectively. Sensitivity analysis also highlighted air temperature as the main determinant of N2O flux, an increase in mean daily temperature of 1.5 °C resulting in almost a doubling in the annual cumulative flux.

12.10 Is carbon being fixed to Irish Soils under existing grassland management practices?

Kiely G., Leahy P., Byrne K.

Centre for Hydrology, Micrometeorology and Climate Change, Civil & Environmental Engineering Dept., UCC

This paper outlines the CO2 flux studies carried out at two grassland sites in Southern Ireland: at Dripsey in County Cork and Johnstown Castle in County Wexford. The measurements were taken over the period, 2003 to 2007 using eddy covariance instrumentation. Both sites were managed for grassland for use beef and dairy cattle with a mix of grazing and silage practices. Fertilisation was applied at both sites with application rates approximately 300 kg N ha-1 a-1. The Net Ecosystem Exchange (NEE) measured by the EC system ranged from ca. 1.0 to 3.0 T C ha-1 yr-1. Precipitation amounts varied during the 5 year period from being wet to dry. We concluded that the NEE for these two humid grassland systems was not sensitive to variation in precipitation amounts. What appeared to impact more on the annual NEE was the timing of herbage harvesting (silage making). More detailed knowledge of the weekly growth rates of grass could lead to the optimum timing of harvesting for optimum NEE. When the farm scale soil carbon budget was evaluated using NEE and all the components of farm inputs and outputs, we found that the amount of carbon fixed to the soil was c 0.5 T C ha-1 a-1. This agrees with recent studies from the EU.

12.30 On the gap in the spectra of atmospheric turbulence

V. Voronovich, G. Kiely

University College Cork, Ireland

Eddy-covariance flux measurements require a researcher to separate the mean and fluctuating parts, i.e. to choose an averaging period ?. The choice is not at all straightforward, as the energy spectra of the turbulence, mesoscale and synoptic structures may overlap. Yet, often enough there exist a gap in the spectra, separating the turbulence proper and mesoscale motions. At the gap scale the spectrum falls almost to zero, and the dependence of the flux on the averaging period becomes especially weak.
This study was concerned with the time scale of the gap in the cospectra of surface fluxes and its dependence on the environmental conditions. The data were collected during March–December 2004 at a grassland site in Co. Cork, Ireland. Gill R3-50 sonic anemometer and LI-7500 open path gas analyzer were mounted on a tower at 3 m height and sampled continuously at 10 Hz. Continuous time series were split into subrecords of 216 points (approximately, 109 min) length and subject to multi-resolution flux decomposition, a wavelet-type processing algorithm based on the Haar, rather than Fourier transform. The 5th order polynomials were fitted to the resulting cospectra, and the gap scale, ?g, identified by the first root or extremum occurring after the turbulence peak. The gap was present in 80-85% of cases, although the scatter in the values of ?g was strong.
During the day ?g was found to fall from circa 16 to 4 min as the wind speed, U, increased from 1 to 7 m s-1, but no dependence on U was present during the night. Increase of stability value, z/L, from -0.3 to 0.3 resulted in the decrease of ?g from 30 to about 4 min. Average (over 10 months) value of ?g is near 7 minutes during the night and 11 minutes during the day, this being about 40% higher for momentum flux. Annual (cumulative) fluxes computed at 27 and 7 min averaging intervals were found to differ by only 1–3% (even less during the day time), which is of the order of instrumentation errors and, most likely, may be neglected in practice. Thus the concern about missing long-term contribution to the total transport may not have serious grounds. Although large at each individual moment, it is negligible due to its erratic nature, when averaged over a very long time interval.

14.00 Carbon gas fluxes in an Irish lowland blanket bog - effect of changing ecohydrology

Anna Laine1,2, Kenneth A. Byrne1, David Wilson3, Ger Kiely1, Eeva-Stiina Tuittila2

  1. Department of Civil and Environmental Engineering, UCC
  2. Peatland Ecology Group, Department of Forest Ecology, University of Helsinki, Helsinki,
  3. School of Biology and Environmental Science, UCD

Peatlands have a joint effect on atmospheric greenhouse gas balances. On the one hand they have removed large amounts of carbon dioxide (CO2) from atmosphere into peat as a result of photosynthesis and incomplete decomposition of dead organic matter due to the high water table and anoxic conditions. On the other hand peatlands release CO2 back into atmosphere in plant and soil respiration and are also a source of high methane (CH4) emissions. The changing climate, in return, affects peatland functioning and C dynamics. Climate change is presumed to increase summer temperatures, which results in higher evapotranspiration and together with reduced summer precipitation may cause changes in peatland water levels. Climate change affects peatlands mainly through their ecohydrology. The estimated water level draw down may cause increase in decomposition, reduction in peat production and changes in species composition. Large spatial variation has been observed in the flux rates within and between peatlands, which is linked to water level and vegetation characteristics. Strong temporal variation has also been observed, with the annual C balance oscillating from positive to negative according to weather conditions. While a number of C exchange studies have been carried out in boreal and continental peatlands, maritime blanket bogs have received less attention. In this study, CO2 and CH4 exchange were studied in an Irish lowland blanket bog from July 2003 to September 2005. Chamber method was used to measure fluxes and non-linear regression models combined with environmental data were used to integrate the fluxes over the study period. Fluxes were measured in four different vegetation communities along a water level gradient, namely hummocks, high lawns, low lawns and hollows. An experimental set up with water level draw down and flooding experiments was established during the second year of the study. Strong spatial and seasonal variation was observed in gas fluxes. The annual net ecosystem CO2 exchange was 99, 60, -16 and -14 g C m-2 in hummocks, high lawns, low lawns and hollows, in respect. The annual CH4 flux was 2, 3, 4 and 9 g C m-2 in hummocks, high lawns, low lawns and hollows, in respect. A 5 to 10 cm drop in water level increased respiration and decreased photosynthesis and CH4 efflux, while flooding decreased respiration and increased CH4 efflux.

14.20 Interannual variability of N2O emissions from a grazed grassland

Paul Leahy and Ger Kiely

Department of Civil and Environmental Engineering, UCC

Nitrous oxide emissions from soils are extremely variable in both space and time. Past measurements with closed chambers in Scotland have observed local CVs of up to 120%. Flux magnitudes from a chamber plot (<1 m2) may vary by a factor of 100 over a period of a week. Micrometeorological flux measurement techniques such as eddy covariance provide a continuous, area-integrated measurement of trace gas fluxes at typically 30 minute resolution. The area of integration depends on the local land cover, topography, wind conditions and the height of the measurement. This integration is at once a strength and weakness of the technique, as it allows for landscape-scale measurements but loses the underlying spatial heterogeneity of the source field.
N2O fluxes have been measured by eddy covariance at a grassland of c. 1 km2 near Cork, Ireland continuously from 2002. This large dataset offers a unique opportunity to explore temporal variability at annual and sub-annual timescales. The dominant land cover of the measurement area is grassland. The study site is partially grazed and partially harvested. In early 2005 part of the site was afforested.
High interannual variability of N2O fluxes was observed, with the highest net emission of 8.5 kg N2O–N ha-1 occurring in 2003. This is believed to have been caused by high soil N availability combined with low soil moisture during the warm summer/autumn season, interspersed with several heavy soil wettings due to intense rainfall events. Overall N inputs to the site from animal and synthetic fertilisers have been decreasing for several years, and there has been a resulting reduction in N2O emissions to 4.2, 4.5 kg and 3.3 kg N2O–N ha-1 for 2004, 2005 and 2006. Arriving at area-integrated annual emission factors is complicated by the heterogeneous management regime at the site, but an annual EF of 3.0% has been calculated for 2003 and less than 2% for subsequent years. The observed high interannual variability of N2O fluxes emphasises the role of weather in N2O production from agricultural soils and the necessity of multi-year observations in order to accurately treat climate- and secondary management-induced variability.

14.40 Nitrous oxide emissions from a spring barley field under conventional and reduced tillage: Effect of varying N application

M. Abdalla1, P. Ambus2, J. Burke3, M. Jones1 and M. Williams1

  1. Department of Botany, School of Natural Sciences, Trinity College Dublin, Dublin 2, Ireland
  2. Riso Research Centre, Technical University of Denmark, Frederikborgvej 399, DK-4000, Roskilde
  3. Teagasc Oak Park Research Centre, Carlow, Ireland

Key words: Nitrous oxide, conventional tillage, reduced tillage, spring barley, N application
Nitrous oxide (N2O) flux measurements from an Irish arable field managed under conventional and reduced tillage and different N fertilizer application at the Teagasc Oak Park Research Centre were made for two consecutive seasons. The aim was to investigate the efficacy of reduced tillage and reduced N fertilizer on seasonal fluxes and emission factors of N2O and to study the relationship between crop yield and N-induced fluxes of N2O. The soil is classified as a sandy loam to loam with a pH of 7 and a mean organic carbon and nitrogen content at 15 cm of 19.4 and 1.9 g kg-1 dry soil respectively. Reduced tillage had no significant effect on N2O fluxes from soils or crop grain yield. Emission factors were ranged from 0.42±0.41 to 0.65±0.14%, approximately 50% of the IPCC default EF of 1.25% of applied N fertilizer. By reducing the applied nitrogen fertilizer by 50 % compared to the normal field rate, N2O emissions could be reduced by 57% with no significant decrease on grain yield. This was consistent over the two years of measurements. Best fit multiple regressions revealed soil moisture and interaction between soil moisture and soil nitrate to be the main significant factors affecting N2O flux from soils.

15.00 Four years Eddy-Covariance CO2 fluxes from an Irish Atlantic blanket bog

Matteo Sottocornola and Gerard Kiely

Dept. of Civil & Environmental Engineering, University College Cork, Ireland

Northern peatlands contain about 30% of the world's soil carbon pool. In Ireland, peatlands cover about 16% of the landscape, of which 240,000 ha are blanket bogs. Blanket bogs are peatlands that occur in maritime regions where precipitation is much greater than evapotranspiration. The role of blanket bogs in C dynamics has not been quantified. We describe an investigation of CO2 fluxes using an eddy covariance (EC) system in a pristine Atlantic blanket bog in Glencar, Co. Kerry between the 1st October 2002 and the 30th September 2006. This is the first multiyear study using EC techniques in a blanket bog.
We found that the bog ecosystem was a CO2 sink for five months in each year. The annual CO2 flux had a sink magnitude of about 0.6 ± 0.3 T C–CO2 ha-2. The CO2 fluxes measured in the Glencar peatland are similar to those found in boreal raised bogs, despite the occurrence in the Atlantic blanket bog of a perennial high water table, that reduce decomposition. The reason for this similarity may be due to the lower plant cover and the higher litter decomposition rate of the plant species occurring in the blanket bog, both factors reducing the CO2 uptake compared with the boreal bog.

15.40 Reducing Uncertainties Associated with the Assessment of National Forest Carbon Stock Changes

Kevin Black1, 2, * and Gerhardt Gallagher2

  1. Forest Environmental Research & Services (FERS), Ard Brae Court, Vevay Road, Bray, Co Wicklow.
  2. Council for Forest Research and Development (COFORD), Arena House, Arena Road, Sandyford, Dublin 18.

*E-mail: Kevin.Black@ucd.ie

Under the agreed terms of the Kyoto protocol, Ireland is committed to reduce green house gas (GHG) emissions by 13% above the 1990-base year level. This posses a tremendous challenge, given the rapid growth of the Irish economy in the past decade, since current green house gas (GHG) emission levels are 23% above the 1990 level. Assuming a business as usual scenario, it is estimated that the contribution of national forests, under Article 3.3, may offset ca. 16 % of the required GHG emissions for the first commitment period (2008 to 2012). However, estimation of the extent to which forests sequester carbon in the mid to long-term is hindered is by a high degree uncertainty due to spatial heterogeneity and temporal variability. Sensitivity analysis on the national forest sink model (CARBWARE) suggests that the largest degree of uncertainty (ca. 30%) was associated with the estimation of vegetation carbon sink. Uncertainty of the vegetation sink was affected most by assumptions on forest management (i.e. forest stocking input data) and biomass algorithm errors. CARBWARE was re-parameterised and improved using permanent plot data to better reflect changes stand structure over the entire rotation in the Irish forest estate. This implies that stand management assumptions used in the model can significantly influence the uncertainty associated with the estimation of national forest sink capacity.

16.00 Improving National Emissions Inventory estimates from Soils for Ireland

P.O'Brien

EPA, McCumisky House, Richview, Clonskeagh, Dublin

At present, Ireland employs the Tier 1 default IPCC methodologies to estimate nitrous oxide emissions from agricultural soils. In recent review of National Inventory Reporting, it was may clear that there was "room for improvement" in the estimate of N2O emissions. Specifically, it was suggested that results from N2O measurement studies (typical range of N inputs, soil types, rainfall & temperature) should be incorporated into the procedures, It was also suggested that the modelling of N2O emissions, both empirical and process modelling, be investigated in order to improve the estimates.
In this presentation, we discuss progress towards improving estimates of N2O. This includes a strategy for making estimates at an intermediate regional scale as a solution to the problems of upscaling local field measurements to the national scale.
Data limitations, such as information on farming practice, are also discussed.

Abstracts of Posters

Poster 1 Chamber and flux-tower measurement of N2O flux from Irish grassland

Mishurov, M., Leahy P. and G. Kiely

Centre for Hydrology, Meteorology and Climate Chnage, UCC.

Nitrous oxide (N2O) is a powerful greenhouse gas (GHG), having warming potential almost 300 times that of carbon dioxide. One of the main sources of N2O emission in Ireland is agriculture, which uses high amounts of mineral nitrogen fertilizers and disposes of organic nitrogen in forms of dung and slurry. Furthermore, denitrification processes convert these into gaseous forms, such as N2O, N2, NO and others. These emissions are highly variable in space and time and are known to be controlled by nitrogen availability, soil organic carbon and moisture and temperature conditions. Two techniques, closed chambers and eddy covariance, were employed to estimate N2O flux from Irish grasslands. Seven field sites were established across the Munster province in south-western Ireland for chamber measurements. All sites were located at active dairy or beef farms, and had basic meteorological stations, recording soil temperature, moisture and rainfall at thirty minute intervals, installed. Soil samples taken at the field sites were analysed for common chemical parameters with emphasis on various nitrogen forms. The general NitroEurope methodology was used for sampling. Chamber- and ambient-air samples collected weekly were stored in air-tight pre-evacuated containers and their analysis was performed on a gas chromatograph within 48 hours of collection. One of the sites near Donoughmore, Co. Cork, has eddy covariance tower producing 10 Hz wind direction and speed data, along with a trace gas analyser system for N2O concentrations. The preliminary measurements of N2O fluxes between mid-April and mid-July 2007 amounted to emission of 970 g N ha-1.

Poster 2. Water balance, evaporation and energy fluxes in an Atlantic blanket bog in South-western Ireland

Matteo Sottocornola and Gerard Kiely.

Centre for Hydrology, Meteorology and Climate Chnage, UCC.

Water and energy fluxes control the development of northern peatlands and influence their carbon budget. Atlantic blanket bogs are peatlands that occur in maritime regions where precipitation is much greater than evapotranspiration. In this poster we examine four hydrological years (October 2002 to September 2006) of evapotranspiration and energy fluxes in the context of the predicted climate change for South-western Ireland. We also analyse the full water balance (precipitation, evapotranspiration, stream flow and water table change) for the hydrological year 2002/2003. Over the four years, annual precipitation ranged from 2428 to 2742 mm a-1 and evapotranspiration ranged from 357 to 406 mm a-1. The stream discharge measured over one hydrological year was 1852 mm. The water balance was dominated by stream discharge while evapotranspiration was lower and Bowen ratio higher than in other peatland types, despite higher precipitation and higher water table. Evapotranspiration was limited by the low occurrence of both vascular plants and mosses, more so than by the low vapour pressure deficit and cool summer air temperature. A comparison between the four years suggests that the predicted climate change will probably increase winter evapotranspiration and lead to an earlier start of the growing season. The expected decrease in summer precipitation will probably not affect radically the major evapotranspiration patterns of the bog. However, if the frequency of summer rain events should diminish, the moss component of these ecosystems may become water-stressed, ultimately leading to lower evapotranspiration, and possibly to a decrease in CO2 uptake by the ecosystem.

Poster 3. Measurement of soil bulk density across differing soil types and land use in Ireland.

Nicola McGoff

Centre for Hydrology Meteorology and Climate Change, UCC.

Bulk density estimates add a valuable and missing dimension to understanding Irish soils on the national scale. These estimates are required for calculating stocks of carbon and other nutrients found in soils. Current national estimates of soil organic carbon rely upon bulk density estimates generated from soil properties, such as organic matter, clay content and silt content. Little is known about the accuracy and suitability of applying mathematical estimates of bulk density to Irish soils. Without better knowledge of bulk density and other factors (i.e. the spatial extent of land use classes and soil types) affecting estimates of carbon and nutrient stocks in soils, we can understand nothing of the changes in these stocks over time.
We collected soils at 62 locations (46 mineral soils and 16 peat soils) throughout Ireland to 50 cm depth. Soils sampled included five land use types (arable land, bog, forest, grassland, and rough land) and eight soil types (Acid Brown Earth, Brown Podzolic, Gleys, Grey Brown Podzolic, Lithosols, Podzol, Shallow Brown Earth, and Peat). The bulk density of Irish soils is principally affected by land use. The bulk density of arable lands varies the least, ranging from 0.92-1.47 g cm-3 for top 10 cm of soil and 1.11-1.71 g cm-3 for 40-50 cm depth. The variation of bulk density for grassland soils is the largest with estimates of 0.21-1.52 g cm-3 for the top 10 cm and 0.19-1.56 g cm-3 for 40-50 cm depth. The bulk density of forested sites depends on whether the forest is coniferous or broadleaf. Coniferous forest, often planted on marginal land, have highly organic/peaty soils with low bulk densities. Broadleaf forest, found primarily on mineral soils, have higher bulk densities. Sites with peat soils, such as raised bog, blanket bog and rough lands, have low bulk densities ranging from 0.07-0.37 g cm-3 for the top 10 cm and 0.07-1.18 g cm-3 for 40-50 cm depth. The high bulk density estimates at depth are due to the influence of mineral soils.

Poster 4 The importance of DOC and POC for the carbon balance of a lowland blanket peatland

Ann-Kristin Koehler

Centre for Hydrology, Meteorology and Climate Change, UCC.

Northern peatlands store about 1/3 of the global soil C but the predicted long-term global warming may threaten this storage capacity (Gorham 1991).Our study site is a lowland blanket bog located near Glencar in County Kerry, Southwest Ireland. Measurements of carbon dioxide (CO2) and methane (CH4) were carried out over a 26 months period in the years 2003-2005 with annual estimates of NEE (net ecosystem CO2 exchange) of 242 g CO2 m-2 and CH4 of 6.2 g CH4 m-2 (Laine 2006). Because this does not include the riverine export of dissolved organic carbon (DOC) which was shown to be an important component of the peatland C cycle (Moore, Roulet et al. 1998) my work is focused on this component.
Up till now most of the long term studies concentrate solely on the flux of DOC and are based on weekly or more seldom sampling of the river of interest. This will miss peak losses of DOC and POC that were shown to occur during storm events (Crisp and Robson 1979). For this reason we started in 2007 continuous measurements with the s::can spectro::lyer which gives half-hourly estimates of the concentration of DOC and TOC in the stream draining our catchment using spectro-photometrical measurements.
The goal is to estimate the importance of the leaching of DOC and POC for the annual carbon balance of the studied peatland and to determine if there are major changes of the ratio of DOC to POC during events of heavy rainfall. Because up to now studies of DOC flux are based on lab-analysis of 'grap' samples we used several 24-hour bottlesampler results (samples taken hourly) which were analyzed for DOC and TOC to compare the two kinds of methods and to establish a relationship between them. Furthermore for the annual carbon balance it is important to calculate the flux of DOC and POC beside their concentrations. This was done by using continuous stream height and manual water velocity measurements so that the discharge could be calculated. To get a general idea about the hydrologic behaviour of the catchment the unit hydrograph for the stream is estimated and compared to those investigated for other streams in Ireland. The fast response of the stream height after a rain event shows that most precipitation does not reach deeper soil layers but overland flow is dominant.
The results will be used to estimate the DOC and POC flux from the mid of January 2007 up to now and to compare them with the gaseous C exchange data of earlier studies to get a general idea of the importance of DOC and POC for our study site and to interpret the values in regard to their global warming potential (GWP).
Crisp, D. T. and S. Robson (1979). "Some Effects of Discharge Upon the Transport of Animals and Peat in a North Pennine Headstream." The Journal of Applied Ecology 16(3): 721-736.
Gorham, E. (1991). "Northern peatlands: role in the carbon cycle and probable responses to climatic warming." Ecological Applications 1(2): 182-195.
Laine, A. M. (2006). Carbon Gas Fluxes in an Irish Lowland Blanket Bog. Department of Civil and Environmental Engineering. Cork, University College Cork.
Moore, T. R., N. T. Roulet, et al. (1998). "Uncertainity in predicting the effect of climatic change on the carbon cycling of canadian peatlands." Climatic change 40: 229-245.

Poster 5 Measurement of Soil C Stock and Stock Changes in Irish Forest Soils

Christina LaPerle

Centre for Hydrology, Meteorology and Climate Change, UCC.

Forests are estimated to store 77% of the global carbon (C) stored in vegetation and 39% of the C stored in soil (Bolin et al., 2000). Consequently, this has led to the inclusion of Article 3.3 in the Kyoto Protocol. Article 3.3 allows changes in C stocks due to afforestation, reforestation, and deforestation since 1990 to be used to offset emissions. Due to Ireland's high level of afforestation since 1990 Article 3.3 offers considerable potential to offset emissions. To meet the requirements of Article 3.3 and more precisely estimate the soil C stock and stock changes in Ireland the collection of nationally specific data is required.

Previously, Tomlinson (2005) has estimated the soil C stock and stock changes in Irish soils but emphasized the need for field measurements, particularly bulk density, for different soil types and land covers. This project will address these needs by developing a quantitative assessment of C stocks and stock changes in Irish forest soils using the paired plot approach. The paired plot approach has been in used in New Zealand (Scott et al. 1999).
To accomplish this task, we will visit 30 of the National Forest Inventory (NFI) sites. The 30 sites will cover the major forest types in the country. At each site we will sample mineral soils to 30 cm depth and determine the C content, bulk density and texture. We will also sample the litter layer at each site. At the sites with peat soils we will determine peat depth as well as take peat samples for bulk density and C content. Each site will have a paired site which will have the same soil type and be representative of the pre-afforestation land use. The same sampling method will be used at the paired site. By comparing the forested and non-forested sites we will be able to access C stock changes due to afforestation. From this information we will develop new default estimates for soil C stock changes in Irish forest soils (including the litter layer) which will substantiate reporting to the United Nations Framework Convention on Climate Change (UNFCCC). We will also be able to estimate total soil C stock in Irish forest soils. All soil samples will be archived for possible further analysis.

Poster 6. Nitrous Oxide Flux studies at multiple grassland sites

Jimmy Casey

Centre for Hydrology, Meteorology and Climate Change, UCC.

This DAF funded project is being undertaken to estimate the Greenhouse Gas (GHG) emissions of N2O from the grassland agricultural sector of Ireland. The Intergovernmental Panel on Climate Change (IPCC) has prescribed limits on national GHG emissions and provides methods for their estimation. It is currently estimated that N2O emissions are responsible for ~15% of the national GHG emissions. This estimate is currently obtained through the IPCC 'Tier I' method which assumes that 3% of nitrogen in fertilisers is returned to the atmosphere as N-N2O. The Irish agricultural sector therefore requires: (i) an accurate nationally, representative N2O emissions inventory avoiding possible overestimation by Tier I method; (ii) environmental and agronomically sound mitigation options for N2O emissions; (iii) an examination of the effects of possible future changes in land use and management practices on N2O emissions.
Emissions from 8 agricultural sites in the south west of Ireland will be analysed. On one site N2O emissions are detected using the eddy covariance technique and on all eight agricultural sites gas samples are taken at 1 hr periods by means of gas flux monitoring chambers. Placement grooves for the gas chambers are cut weeks in advance of the sampling-taking place. This is done to allow the soil to return to emission equilibrium, as cutting the grooves may cause soil emissions, which would not be an accurate representation. Soil temperature, moisture content and rainfall are continuously recorded at all 8 sites. Soil samples are also taken at various depths to determine and classify the soil with regards to bulk density, total carbon/nitrogen content and other parameters. The gas chamber samples are returned to the laboratory and analysed using a gas chromatograph for N2O concentrations. Natural and artificial fertilisers applications are also monitored and the emissions from the different soil types will be examined to determine if a relationship exits between the amount and type of fertiliser applied to the soil, the soil conditions and the N2O emissions from the soil.

Poster 7. Ecosystem scale CO2 fluxes at a blanket peatland: How detailed must our knowledge be of the topographic microforms in the landscape system?

  1. Anna Laine, Civil & Environmental Engineering, University College Cork, Ireland
  2. Matteo Sottocornola, Civil & Environmental Engineering, University College Cork, Ireland
  3. Gerard Kiely, Civil & Environmental Engineering, University College Cork, Ireland
  4. Kenneth Byrne, Civil & Environmental Engineering, University College Cork, Ireland
  5. David Wilson, Dept. of Environment Resource Management, University College Dublin, Ireland
  6. Eeva-Stiina Tuittila. Dept.of Forest Ecology, University of Helsinki, Finland

Blanket peatlands are ombrotrophic bogs which distribution is restricted to maritime climatic conditions. Their surface is a mosaic of microforms: hummocks, lawns and hollows. The water level and vegetation composition varies between the microforms, which cause differences in their carbon dynamics. In an ongoing study at a blanket peatland in County Kerry, Ireland, we use both chamber and eddy covariance (EC) techniques over a four months (July–October) period to determine the ecosystem scale fluxes of CO2. In this study we aim to determine the level of detail required of microform spatial distribution for optimum ecosystem flux estimation. In determining chamber fluxes, simulations were done using microform specific CO2 exchange models that were based on chamber measurements. We upscale the chamber measurements, firstly using the microform distribution over the whole area and secondly using the moving footprint area, defined for each single measurement period. We then compare chamber fluxes with the EC estimated fluxes and test two contrasting hypotheses:
(1) Distribution of the microforms inside the blanket peatland is homogenous enough that with a moving footprint it is possible to make ecological interpretation of peatlands CO2 dynamics.
(2) In order to make ecological interpretation of peatlands CO2 dynamics from the varying landscape of the blanket peatland, the composition inside the momentarily footprint must be known. Results show high spatial variation in the proportion of different microforms. The cover of hollows, lawn, and hummocks varied between 0 and 42 %, 52 and 99 %, and 0 and 11.2 %, respectively in the 16 transects extending to different wind directions from eddy covariance tower.

Poster 8. Field Instrumentation for CO2 flux and related measurements

Murphy, K., Leahy P. and Kiely G.

Centre for Hydrology, Meteorology and Climate Change, UCC.

Reliable instrumentation is crucial in many areas of environmental investigation. For a number of years now our centre has maintained continuous CO2 flux measurements at two grassland sites located in County Cork and County Wexford, and a peatland site in County Kerry. In addition, extensive metrological, hydrological and other environmental measurements have been collected at these sites. The sites are fully automated and data is recorded at regular intervals. The data is used in studies such as net ecosystem exchange (NEE), energy balance (EB) and water balance.
Some of the instrumentation is complex, having a number of hardware components and requiring a number of calculations. The principles and methods for a selection of systems are described, in particular the CO2 eddy-covariance flux systems.

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