Effects of a raised water table on greenhouse gas emissions and celery yield from agricultural

peats under climate warming conditions

Magdalena Matysek (University of Sheffield)

Steven Banwart (University of Leeds) Jonathan Leake (University of Sheffield)Donatella Zona (University of Sheffield)

GSOC17 - Global Symposium on Soil Organic Carbon, 21-23 March 2017FAO, Rome

Agricultural use of peat soils

Farming on peat requires drainage: crops intolerant of waterlogged conditions agricultural machinery sinks when the water table is high

Upon drainage peat: is exposed to aerobic conditions and is lost via oxidation thickness decreases due to shrinkage and compression

Drained peat becomes a source of CO2

• 40% of UK peatlands have been drained for agricultural use• Vast majority of peatlands in England are now carbon sources

rather than sinks

Lack of studies on peatlands used for horticultural production

(Dixon et al., 2014; Natural England, 2015)

The Fens• East Anglian Fenlands (the Fens): one

of the most important regions for crop production on lowland peats in the UK

• 88% of the Fens area is cultivated• 89% of agricultural land is grade 1

or 2• 37% of vegetable production in

England comes from the Fens• Fenland peats contain 41 Tg of

carbon• Shrinkage, compaction and oxidation

cause peat wastage of 2.1 cm/yr

(Darby, 1956; Holman, 2009; Natural England, 2015; NFU, 2008)

Why is the water table level important? Greenhouse gases: CO2, CH4, N2O CO2 is produced in aerobic conditions CH4 is produced in anaerobic conditions A higher water table should decrease mineralisation and CO2

loss And increase CH4 emissions How would raising the water table influence the total warming

potential budget?

Raising the water table would prolong the lifespan of agricultural peat

But how would it affect crop yield?

Conservation interests Commercial interests

Can they be reconciled?

Renger et al. (2002) say YES:

Keeping the water table at -30 cm allows for 90% of the maximum grassland productivity

Mineralisation is lowered by 30-40% of the maximal value

What about horticulture on peat?

Moreover…

• Predicted global temperature increase is within the range of 0.3-4.8°C• RCP 8.5 – 'business as usual'; CO2-eq > 1000 ppm; temperature increase: 2.6-4.8°C• Higher temperatures should increase the rate of organic matter decomposition• But will they increase crop growth? (IPCC, 2014)

HypothesesYield CO2 flux CH4 flux

Water table: -30 cm vs -50 cm

Increasing the water table from -50 cm to -30 cm will

not affect yield

Lower emissions when the water table is higher

(-30 cm)Higher emissions at -30

cm

Temperature:ambient vs +5°C

Higher yield at the increased temperature

Higher emissions at the increased temperature No effect

Experimental design• Peat collected from Rosedene Farm, Methwold Hythe, Norfolk

• 64 peat cores made from 50 cm x 11 cm PVC pipes

• Water table maintained via the drainage pipe

• Two environmental chamber rooms to maintain temperature

• CO2 and CH4 fluxes measured weekly

• Crop: celery (Apium graveolens) marshland plant, adapted to high water table conditions (Seale, 1975)

most profitable for the farmer

Experimental design

-50 cm is the water level on the field -30 cm is the water table recommended by Renger et al. (2002) for grassland + 5°C is the RCP 8.5 warming scenario value (IPCC, 2014) Fertiliser: CHAFER 6-6-12 (liquid ammonium polyphosphate), at a rate 800 l/ha

Ambient +5°C

-30 cm -50 cm

Planted Not planted Planted Not planted

-30 cm -50 cm -30 cm -50 cm -30 cm -50 cm

Four treatments

Temperature:

Planting:

Water table:

Fertilisation: Yes No Yes NoYes No Yes No Yes No Yes No Yes No Yes No

Celery yieldTemperature

No effect of increased temperature on wet aboveground celery biomass

Dry biomass was higher from elevated temperature: higher transpiration with temperature increase?

Celery did not acclimate

Water table

A higher water table significantly decreased both dry and wet shoot biomass

Mean wet yield was 19% lower Constrained root expansion at -30 cm Nutrient limitation

*

* *

CO2 emissions Temperature

Mean emissions from the elevated (+5°C) temperature treatment were significantly higher by 25%

Increased oxidation of organic matter and greater peat loss with more warming

Water table

Significantly higher (by 31%) mean CO2 emission from the -50 cm water table

A significant portion of CO2 emissions originated in the zone between -30 cm and -50 cm

Significantly higher soil water content in the oxic zone Raising the water table would be a viable option for peat

preservation

Fertiliser use

Significantly higher emissions from fertilised cores N addition may stimulate microbial activity

No significant interactions found

*

*

*

CH4 fluxesNo effect of temperature, fertiliser and water table

Consumption of CH4 dominates

Temperature

Methanotrophic and methanogenic microbial communities affected to the same extent?

Water table

Increases in methane flux with a water table rise are often attributed to increased water-filled pore space in the oxic zone (Juszczak et al., 2012)

However, studies on agricultural peat (grassland/pasture) often show that a water table of -20 cm or lower is enough for complete oxidation of methane (Regina et al., 2015; Karki et al., 2016; Poyda et al., 2016; Renou-Wiloson et al., 2016)

Increasing the water table to -30 cm would reduce C loss from temperate peat used for horticulture

Planting

A possible effect of planting (χ2(1)=4.8773, P=0.027) Celery could potentially increase CH4 flux by the means of:• Tissue conductance • Root exudates which stimulate and/or supress microbial

activity

Conclusion

Raising the water table from -50 cm to -30 cm would depress celery yields by 19%

But the rate of peat oxidation into CO2 would be 31% lower-30 cm would not be high enough to result in higher CH4

emissionsIs the yield loss acceptable to the farmer?

Global warming is likely to increase summer peat CO2 emissions by 25%

And unlikely to improve celery yields

Future work• Winter emissions of CO2 and CH4 at different water table levels• Impact of an elevated water table on another crop

Acknowledgements• Simon Benson, University of Leicester

• Mark Burrell, University of Sheffield

• Alexander Cumming, University of Leicester

• Grantham Centre for Sustainable Futures

• Martin Hammond, farm manager

• Owen Hayman, University of Sheffield

• Irene Johnson, University of Sheffield

• Dr Jörg Kaduk, University of Leicester

• Felix Lim, University of Sheffield

• Samuel Musarika

• Prof Susan Page, University of Leicester

• Alan Smalley, University of Sheffield

• Anthony Turner, University of Sheffield

Research funded by:

References• Darby, H. C., 1956. The draining of the Fens. Cambridge University Press.• Dixon, S. D., Qassim, S. M., Rowson, J. G., Worrall, F., Evans, M. G., Boothroyd, I. M. and Bonn, A., 2014. Restoration effects on water table depths and

CO2 fluxes from climatically marginal blanket bog. Biogeochemistry, 118, 159–176.• Holman, I.P., 2009. An estimate of peat reserves and loss in the East Anglian Fens Commissioned by the RSPB.• IPCC, 2014: Summary for policymakers. In: Climate Change 2014: Impacts, Adaptation, and Vulnerability. Part A: Global and Sectoral Aspects.

Contribution of Working Group II to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Field, C.B., V.R. Barros, D.J. Dokken, K.J. Mach, M.D. Mastrandrea, T.E. Bilir, M. Chatterjee, K.L. Ebi, Y.O. Estrada, R.C. Genova, B. Girma, E.S. Kissel, A.N. Levy, S. MacCracken, P.R. Mastrandrea, and L.L.White (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, pp. 1-32.

• Juszczak, R., Humphreys, E., Acosta, M., Michalak-Galczewska, M., Kayzer, D. and Olejnik, J., 2013. Ecosystem respiration in a heterogeneous temperate peatland and its sensitivity to peat temperature and water table depth. Plant and Soil, 366 (1-2), 505-520.

• Karki, S., Elsgaard, L., Kandel, T. P. and Lærke, P. E., 2016. Carbon balance of rewetted and drained peat soils used for biomass production: a mesocosm study. GCB Bioenergy, 8, 969–980.

• Natural England., 2015. Summary of evidence: Soils EIN012. http://publications.naturalengland.org.uk/publication/6432069183864832.• Poyda, A., Reinsch, T., Kluß, C., Loges, R. and Taube, F., (2016) Greenhouse gas emissions from fen soils used for forage production in northern Germany,

Biogeosciences, 13, 5221-5244.• Regina, K., Sheehy, J. and Myllys, M., 2015. Mitigating greenhouse gas fluxes from cultivated organic soils with raised water table. Mitigation and

Adaptation Strategies for Global Change, 20 (8), 1529–1544.• Renger, M., Wessolek, G., Schwarzel, K., Sauerbrey, R. and Siewert, C., 2002. Aspects of peat conservation and water management. Journal of Plant

Nutrition and Soil Science, 165 (4), 487–493.• Renou-Wilson, F., Barry, C., Müller, C. and Wilson, D., 2014. The impacts of drainage, nutrient status and management practice on the full carbon

balance of grasslands on organic soils in a maritime temperate zone. Biogeosciences, p.4361.• Seale, R., 1975. Soils of the Ely district (sheet 173) (Soil Survey of Great Britain (England and Wales). Memoirs). Harpenden (Rothamsted Experimental

Station, Harpenden, Herts.): Soil Survey.

Wet celery yield: means +/- SE

Fertilised

+5°C

Soil respiration: means +/- SE

Fertilised

+5°C

Dissolved Organic Carbon

Temperature

Higher concentration from the +5°C temperature

Planting

Lower concentration from planted cores

NEENo efect of any of the treatments on the Net Ecosystem Exchange