Whim Bog: long-term nitrogen experiments

Scientific importance

The Whim experimental bog is a globally unique study of how peatland ecosystems respond to different levels and forms of nitrogen (N) deposition. In operation since 2002, the field manipulation experiment provides a quantified ammonia (NH3) concentration / deposition gradient to an ombrotrophic bog, plus separate wet treatments comparing different levels of oxidized (NaNO3) and reduced (NH4Cl) N deposition. The site also includes treatments with phosphorus and potassium (K2HPO4) at two N doses to compare N effects with and without limitations of other nutrients. 

About the site

Whim is a typical Calluna vulgaris-Eriophorum vaginatum blanket bog (UK national vegetation classification NVC M19a) with deep acidic peat (pH ~3.5, peat depth 3-6m). Hummocks are dominated by Calluna (heather) and the bog moss Sphagnum capillifolium, hollows include S. fallax and S. papillosum. The site is located in the Scottish Borders (3°16′W, 55°46′N) at 282 metres above sea level. Annual rainfall is approximately 900mm and mean annual temperature is 10.7°C.

The field manipulation experiment covers 2ha, with a 60m long × 10m wide NH3 transect and 44 wet N deposition plots, each with an area of 13m2.

Nitrogen treatments

The dry NH3 treatment is controlled with an NH3 release system which is determined by wind direction measured every five seconds by a sonic anemometer. An automated free air release creates a gradient of NH3 concentration along the transect, with average annual concentrations ranging from ambient (c. 0.5 µg NH3 m-3) to up to 100 µg NH3 m-3. Peak concentrations during fumigation events can reach 1600 µg NH3 m-3. Annual NH3-N deposition along the transect in 2003–2006 was calculated as 3.0 kg NH3-N ha-1 y-1 in ambient air and 50–70 kg NH3-N ha-1 y-1 at annual average air concentrations of 70–90 µg NH3 m-3 (Cape et al 2008: Atmospheric Environment, 4: 6637-6646).

Wet treatments are supplied when meteorological conditions are appropriate. Rainfall is collected on site and stored in a reservoir; when the reservoir is full, rainwater is pumped through a network of pipes, dosed with the appropriate N form and concentration, and sprayed onto the experimental plots. Spraying only occurs when the wind speed is below 5m s-1. Wet deposition plots are large (13m2), each with four replicates. Nitrogen deposition treatments in the wet plots are 8, 24, and 56 kg N ha−1 y−1 above ambient (8-11 kg N ha-1 y-1). The additional PK treatments are supplied at two N doses (8 and 56 kg N ha-1 yr-1) by addition of K2HPO4, with P at a 1:14 ratio to N (16 plots).

Wet treatments are closed down during freezing conditions and re-activated when night temperatures rise above 0°C. Dry treatment continues throughout the year, with the exception of routine maintenance times.

After one year, deleterious effects of high concentrations of dry-deposited NH3 could be measured on several key species. Over time, damage has been detected further down the transect at lower concentrations and with accumulated N dose, and is linked to secondary environmental stresses such as cold winters or dry summers. Calluna and species of Cladonia lichen and the bog moss Sphagnum have now disappeared from parts of the dry NH3 transect where inputs exceed 10 kg N ha-1y-1. Similar levels of wet N deposition have not caused the same degree of direct vegetation damage or species loss, and may be associated with longer-term ecological and ecosystem change. Measurements of key ecosystem functions have identified a range of ecosystem services that respond in different ways to different N forms, particularly carbon sequestration and greenhouse gas (GHG) emissions.

Summary of scientific objectives

  • Long-term exposure to N-deposition treatments on a typical bog community, allowing separate assessment of the impacts of dry-deposited NH3 versus wet-deposited ammonium (NH4+) and nitrate (NO3-).
  • Real-world treatment doses and frequencies, coupled to meteorology.
  • Numerous international collaborations (see below).
  • Large 13m2 replicated (4) wet-deposition plots; 60m long × 10m wide NH3 gradient
  • Large data banks (NitroEurope, ÉCLAIRE, ExpeER) of above- and below-ground chemistry, species composition and cover (held in a Microsoft Access database), greenhouse gas emissions.

Experimental facilities

  • Small cabin with workspace and room for equipment. Mains electricity (3-phase) available within the cabin and at various outside locations.
  • Span decks to access plots.
  • Track access to the main site hut, with access to treatment plots via boardwalks. Approximately 2km of boardwalks for access around site.

Boardwalks at Whim Bog nitrogen experiment monitoring siteEquipment and instruments available on site

  • Automatic weather station comprising 2D sonic for wind speed and direction, temperature/relative humidity sensors, photosynthetically active radiation (PAR), total solar radiation and soil temperature probe.
  • Hydrology: 200 manual dipwells (44 measured monthly), tipping bucket rain gauge, soil moisture probes and pressure transducers for water table depth.
  • Radiative gases: Flux tower: LI-COR for CH4/H2O/CO2 fluxes plus 3D sonic for wind speed, direction and turbulence, static chambers for soil/vegetation CH4/ H2O/ CO2/ N2O fluxes, ADC LcPro for portable gas exchange with light and temperature control, PP systems respirometer.
  • Vegetation: Hansatech handy PEA chlorophyll fluorescence meter and a Porometer for stomatal conductance.

Routine measurements

Meteorology and Radiative Gases

  • Precipitation, wind direction, wind speed, temperature (15 minute averages)
  • CH4/H2O/CO2 fluxes from tower (continuous)

NH3 transect and wet deposition plots

  • NH3 air concentrations along the transect (monthly, by passive sampler)
  • Soil water table (monthly)
  • Soil water composition (anions: Cl-, NO3-, SO42; cations: Na+, NH4+, K+, Ca2+, Mg2+), total N, total C (monthly)
  • Vegetation cover (every 2 years)

Recent and current site research

  • The Whim site was set up as part of the Defra-funded NERC Global Nitrogen Enrichment (GANE) thematic programme. It then became part of a large network of manipulation site experiments for the five-year NitroEurope and the four-year ÉCLAIRE projects, contributing long-term time series data to both databases. NitroEurope data are freely available; ÉCLAIRE data are available to co-authoring collaborators.
  • It is an ExpeER site, hosting trans-national access visitors (until May 2015).
  • It has hosted many international scientific collaborators as well as MSc and PhD students from countries including the Netherlands, Spain, Finland, Japan, Portugal and the US.
  • Whim is part of the Burnsmuir site proposed for the H2020 Infrastructure eLTER bid.
  • A new experiment on the response of vegetation to the combined effects of ozone and NH3 will start in spring 2015. This will involve adding an O3 fumigation system into an area of the bog exposed to different levels of NH3 but which is not along the main transect.

Work with us

If you wish to discuss specific opportunities to work at Whim please contact: Netty van Dijk, Whim site scientific coordinator.

Recent publications

2014

Sheppard, L J, Leith, I D,  Kivimaki, S K, Gaiawyn, J. 2014. The form of reactive nitrogen deposition affects the capacity of peatland vegetation to immobilise nitrogen: implications for the provision of ecosystem services. In: Nitrogen Deposition, Critical Loads and Biodiversity (Eds. Sutton M A et al) Springer, ISBN 97809400779389

Sheppard, Lucy J; Leith, Ian D; Mizunuma, Toshie; Leeson, Sarah; Kivimaki, Sanna; Cape, J Neil; van Dijk, Netty; Leaver, David; Sutton, Mark A; Fowler, David; van den Berg, Leon J L; Crossley, Alan; Field, Chris; Smart, Simon. 2014 Inertia in an ombrotrophic bog ecosystem in response to 9 years' realistic perturbation by wet deposition of nitrogen, separated by form. Global Change Biology, 20 (2). 566-580. 10.1111/gcb.12357

Jones, L; Provins, A; Holland, M; Mills, G; Hayes, F; Emmett, B; Hall, J; Sheppard, L; Smith, R; Sutton, M; Hicks, K; Ashmore, M; Haines-Young, R; Harper-Simmonds, L. 2014 A review and application of the evidence for nitrogen impacts on ecosystem services. Ecosystem Services, 7. 76-88. 10.1016/j.ecoser.2013.09.001

Munzi, S; Cruz, C; Branquinho, C; Pinho, P; Leith, I D; Sheppard, L J 2014 Can ammonia tolerance amongst lichen functional groups be explained by physiological responses?  Environmental Pollution, 187. 206-209.

2013

Sheppard, L J; Leith, I D; Leeson, S R; van Dijk, N; Field, C; Levy, P. 2013 Fate of N in a peatland, Whim bog: immobilisation in the vegetation and peat, leakage into pore water and losses as N2O depend on the form of N. Biogeosciences, 10 (1). 149-160. 10.5194/bg-10-149-2013

Gray, A; Levy, P E; Cooper, M D A; Jones, T; Gaiawyn, J; Leeson, S R; Ward, S E; Dinsmore, K J; Drewer, J; Sheppard, L J; Ostle, N J; Evans, C D; Burden, A and Zieliński, P. 2013 Methane indicator values for peatlands: a comparison of species and functional groups. Global Change Biology, 19 (4). 1141-1150. 10.1111/gcb.12120

Sheppard, L J; Leith, I D; Leeson, S; Mizunuma, T; de Bakker, R; Elustondo, D and Garcia-Gomez, H. 2013 PK additions modify the effects of N dose and form on species composition, species litter chemistry and peat chemistry in a Scottish peatland. Biogeochemistry, 116 (1-3). 39-53. 10.1007/s10533-013-9880-y

Kivimaeki, Sanna K; Sheppard, Lucy J; Leith, Ian D; Grace, John. Long-term enhanced nitrogen deposition increases ecosystem respiration and carbon loss from a Sphagnum bog in the Scottish Borders. Environmental and Experimental Botany, 90. 53-61. 10.1016/j.envexpbot.2012.09.003

Payne, Richard J; Jassey, Vincent E J; Leith, Ian D; Sheppard, Lucy J; Dise, Nancy B; Gilbert, Daniel. 2013 Ammonia exposure promotes algal biomass in an ombrotrophic peatland. Soil Biology & Biochemistry, 57. 936-938

2012

Carter, M S; Larsen, K S; Emmett, B; Estiarte, M; Field, C; Leith, I D; Lund, M; Meijide, A; Mills, R T E; Niinemets, Ü; Peñuelas, J; Portillo-Estrada, M; Schmidt, I K; Selsted, M B; Sheppard, L J; Sowerby, A; Tietema, A; Beier, C. 2012 Synthesizing greenhouse gas fluxes across nine European peatlands and shrublands: responses to climatic and environmental changes. Biogeosciences, 9 (10). 3739-3755. 10.5194/bg-9-3739-2012

Phoenix, Gareth K; Emmett, Bridget A; Britton, Andrea J; Caporn, Simon J M; Dise, Nancy B; Helliwell, Rachel; Jones, Laurence; Leake, Jonathan R; Leith, Ian D; Sheppard, Lucy J; Sowerby, Alwyn; Pilkington, Michael G; Rowe, Edwin C; Ashmorek, Mike R; Power, Sally A. 2012 Impacts of atmospheric nitrogen deposition: responses of multiple plant and soil parameters across contrasting ecosystems in long-term field experiments. Global Change Biology, 18 (4). 1197-1215. 10.1111/j.1365-2486.2011.02590.x

Limpens, J; Granath, G; Aerts, R; Heijmans, M M P D; Sheppard, L J; Bragazza, L; Williams, B L; Rydin, H; Bubier, J; Moore, T; Rochefort, L; Mitchell, E A D; Buttler, A; van den Berg, L J L; Gunnarsson, U; Francez, A-J; Gerdol, R; Thormann, M; Grosvernier, P; Wiedermann, M M; Nilsson, M B; Hoosbeek, M R; Bayley, S; Nordbakken, J-F; Paulissen, M P C P.; Hotes, S; Breeuwer, A; Ilomets, M; Tomassen, H B M; Leith, I; Xu, B. 2012 Glasshouse vs field experiments: do they yield ecologically similar results for assessing N impacts on peat mosses? New Phytologist, 195 (2). 408-418. 10.1111/j.1469-8137.2012.04157.x

Millett, Jonathan; Leith, Ian D; Sheppard, Lucy J; Newton, Jason; 2012 Response of Sphagnum papillosum and Drosera rotundifolia to Reduced and Oxidized Wet Nitrogen Deposition. Folia Geobotanica, 47 (2). 179-191.

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Facility Type: 

  • Monitoring Site

Science areas: 

Issues: