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Ecosystem-scale trade-offs between impacts of ozone and reactive nitrogen Ed Rowe, Felicity Hayes, Kasia Sawicka, Gina Mills, Laurence Jones, Filip Moldan, Sereina Bassin, Netty van Dijk & Chris Evans EGU, Vienna, 13th April 2015 Nitrogen is an acidifying pollutant • Many systems are recovering from ‘acid rain’ UK SO2 emissions • But reductions in reactive-nitrogen (NOx, NHy) emissions have been small, compared to reductions in S emissions UK NOx emissions Giant Mountains, Czech Republic, 2005 UK NH3 emissions RoTAP report, CEH, 2012 Temporal deposition sequence from GANE project (Fowler et al 2004 WASP:Focus 4: 9-23) Nitrogen is also a fertiliser Ammonium nitrate delivery, Gwynedd, UK, 2006 End of the fertiliser bag, Mutare, Zimbabwe, 2002 ‘Current Legislated [N] Emissions’ ‘Maximum Feasible [N] Reduction’ Additional European C sequestration due to N pollution de Vries & Posch (2011) Env Poll 159: 2289-2299 not good for species that need ground-level light d Canopy Height Class 4.0 3.8 c 3.6 3.4 bc 3.2 3.0 ab a 2.8 2.6 2.4 Drosera rotundifolia Threatened Rare Uncommon Decreasing Increasing Conservation status Hodgson et al. (2014) Functional Ecology 28: 1284-1291. more N --> increasing • productivity • ground-level shade • litterfall Lotus corniculatus Urtica dioica Heathland, UK Number of species Acid grassland, UK Number of species N deposition reduces species-richness 30 5 45 0 0 kg N ha-1 y-1 Stevens et al. (2004) Science 303: 1876-1879 Maskell et al. (2010) Global Change Biol.16: 671–679 40 Global reactive-N deposition 60 20 5 1 “For terrestrial ecosystems, land-use change probably will have the largest effect [on biodiversity], followed by climate change, nitrogen deposition, biotic exchange, and elevated carbon dioxide concentration.” Sala et al 2000, Science 287: 1770-1774 0.1 mg N m-2 yr-1 kg N ha-1 yr-1 Dentener et al. 2006 Global Biogeochem Cycles 20: GB4003 Predicting effects of N and S (MADOC) N14C: vegetation growth and soil organic matter development VSD: cation exchange and pH DyDOC: dissolution of organic matter MADOC: dynamic integration, allowing feedback between pH and DOC N14C: Tipping et al. 2012 Ecological Modelling 247:11-26 VSD: Posch & Reinds 2009 Env Modelling and Software 24: 329-340 DyDOC: Michalzik et al. 2003 Biogeochemistry 66, 241-264 MADOC passes some plausibility tests Calibration dataset (EHFI acidification / alkalisation experiment) Independent dataset (Acid Waters Monitoring Network sites) Rowe et al. 2014 Environmental Pollution 184, 271-282. Predicting effects on plant species and biodiversity Total N deposition Biogeochemistry Other drivers Vegetation and soil biogeochemistry MADOC Key: Indicators of environmental conditions e.g. pH, mineral N, light Model Quantity Plant ecology Rhynchospora alba Floristic response MultiMOVE Other drivers Habitat suitability for individual species Smart et al. 2010 J Veg Sci 21: 643:656 Henrys et al. New J Bot in prep. Summarising effects on ‘biodiversity’ Rowe et al. (submitted) Ecological Indicators How will ozone pollution interact? Ozone in the stratosphere protects the planet from ultraviolet radiation …but tropospheric i.e. ‘ground-level’ ozone is a problem. • Formed in reactions involving nitrogen oxides and Volatile Organic Compounds • European NOx and VOC emissions controls decreasing peak concentrations • Hemispheric transport increasing background concentrations • Effects on human health • Damage to plants increasing crop losses Photo: Gina Mills Tropospheric ozone formation diagram: http://keutsch.chem.wisc.edu/ Ozone effects supported by evidence 1. Decreasing plant C Flows productivity Timing of flowering (NPP) at greater Fruit/seeds ozone concs. reduced productivity, reduced carbon inputs CO2 Stomatal opening CO2 Photosynthesis Respiration Above ground biomass Litterfall CO2 From soil New C turnover Below ground biomass Mycorrhyzae more potential for N loss e.g. leaching, N2 O ? Exudation Old C turnover 2. Reduced translocation of N out of senescing leaves at greater ozone concs. ? ? Ozone effects added into MADOC 1. Reduction in NPP with increasing ozone concentration Ozone effects added into MADOC 2. Reduced translocation of N out of senescing leaves with increasing ozone conc. Sites Sitessimulated modelled in ECLAIRE Whim Gårdsjøn Sourhope Grizedale Brandbjerg Clocaenog LlynBrianne Oldebroek Klausen Alpflix Montseny Kiskunsag Responses to N treatments Whim Moss Scotland heath exposed to dry NH3 or wet NaNO3 or wet NH4Cl Symbols = Modelled Lines = observed Responses to N treatments Gårdsjön Sweden coniferous forest subcatchments Treatments: Control; +40 kg N ha-1 yr-1 (wet NH4NO3) Symbols = Modelled Lines = observed Responses to N x O3 treatments AlpFlix Switzerland Alpine grassland, extremely low N deposition, but chronically exposed to ozone O3++_N4 O3++_N54 O3control_N4 O3control_N54 300 2 NPP [g C/m /y] 250 Experimental responses (circles): • Strong productivity response to N • No significant productivity response to ozone 200 o o 150 100 50 0 1990 2000 2010 2020 Modelled responses (lines): • responses to N and ozone • negative interaction (ozone limits response to N, and vice versa) Bassin et al (2007) New Phytologist 175, 523-534. Symbols = Modelled Lines = observed Sensitivity of productivity to N and Ozone NPP [gC/m2/y] 100 550 80 450 400 60 350 300 250 40 10 45 150 20 30 40 0 35 0 100 300 200 0 250 20 0 200 150 Ambient ozone [ppb] 500 40 N deposition [kg/ha] 50 50 i.e. ozone reduces plant productivity by a greater proportion at greater N deposition Could it be said that ozone pollution moderates the effects of N pollution? Direct ozone effects on biodiversity Cover (relative units) Effect of ozone exposure on cover of Campanula rotundifolia in calcareous grassland 6 5 R² = 0.2625 4 3 2 1 0 0 5 10 15 POD1 mmol m-2 Hayes et al. (unpublished) 20 25 Conclusions • We need more ecosystem-level experiments on N-ozone interactions • Simulations are the best available basis for assessing ecosystem effects of O3 and N • N is likely to increase productivity benefits for agriculture and forestry, C storage disbenefits for biodiversity • Ozone is likely to decrease productivity benefits for biodiversity? likely to be outweighed by direct adverse effects of O3 • N and ozone together are likely to increase soil N cycling rates disbenefits due to N leaching and NOx emissions Acknowledgements This work was funded by the UK Government (Defra) and by the European Union (FP7 ECLAIRE project)