OR/14/047 Research needs

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Farr, G, and Hall J. 2014. Atmospheric deposition and groundwater dependent wetlands: implications for effective catchment management and future Water Framework Directive groundwater classification in England and Wales. British Geological Survey Internal Report, OR/14/047.


The site level assessment of nitrogen deposition impacts present a range of difficulties. Emmett et al. (2011)[1] list the following shortfalls in understanding;

  • Time scale of responses to background N deposition in the UK are poorly documented
  • Long term monitoring is available only from very few locations
  • Historic data for vegetation composition, plant and soil chemistry are rare thus we do not know how many habitats have changed already
  • It is very difficult to separate the effects of other sources of nutrient input (e.g agricultural run off, site management) from atmospheric deposition

In addition (Bobbink & Hettelingh 2011)[2]:

  • The combined nitrogen load from groundwater and atmospheric sources may exceed biological thresholds even where separately the critical load or GWDTE threshold are not exceeded

Emmet et al. (2011)[1] also suggest that Common Standards Monitoring is not suitable to detect N deposition impacts on individual sites due to the lack of repeat monitoring at permanent quadrats over time meaning changes in vegetation are not likely to be recorded. Stevens et al. (2009)[3] make suggestions for how the assessment of atmospheric deposition and critical loads can be taken into account during SSSI condition assessments.

Adams (2003)[4] lists the following research needs relating to atmospheric nitrogen deposition:

  • improved understanding and quantification of the N cycle, particularly relatively unstudied processes such as dry deposition, N fixation and decomposition/rnineralisation
  • carbon cycling as affected by increased N deposition

Critical loads[edit]

Critical loads do not exist for all habitat types in the UK and the digital maps of interest feature locations and areas are not currently available. Thus to improve the use and application of critical loads;

  • Further data and evidence of nitrogen impacts on sensitive habitats is needed to enable new critical loads to be derived and current values to be improved (Bobbink & Hettelingh, 2011)[2]
  • Spatial digital data on the location of and areas occupied by designated feature habitats (e.g. NVC mapping) within designated sites needs to be improved to enable the area of sensitive habitats at risk from atmospheric deposition to be better quantified
  • Critical loads do not currently take account of inputs of N from non-atmospheric sources, although this knowledge gap is noted (Bobbink & Hettelingh 2011)[2], there are currently no recommendations on how to address this

Source apportionment and nitrogen budgets[edit]

Quantifying a nitrogen budget for a GWDTE will require information on the sources, pathways and receptors for nitrogen from both atmospheric and terrestrial sources. Furthermore the fate of nitrogen within the GWDTE in terms of retention, fixation, attenuation, accumulation of N in peat, uptake by plants and loss via processes such as denitrification needs to be better understood (e.g. Drewer et al. 2010)[5]. Recharge mechanisms and bypass flow mechanisms, for example in karst terrains, should also be considered as these may offer direct pathways to groundwater bypassing the soil and unsaturated zones where attenuation of nitrogen could take place. Härdtle et al. (2009)[6] also show that management schemes (grazing and mowing), in conjunction with atmospheric deposition, can have effects upon the N and P budgets of Heathland Ecosystems. Very few studies have assessed impacts from atmospheric and surface or groundwater inputs at the same site. This is a major knowledge gap.

Source apportionment studies would need to distinguish between atmospheric and terrestrial sources of nitrogen perhaps using nitrogen and oxygen stable isotopes (e.g. Saccon et al. 2013)[7] and each site would require a preexisting hydrogeological conceptual model. It should be noted that by the term ‘source apportionment’ we are hoping to define the relative sources of pollution e.g. agriculture 60% road traffic 40% and we are NOT trying to identify specific locations, e.g. Mr Smiths Farm. Existing source apportionment tools such as the Environment Agency N&P spreadsheet calculator (AMEC, 2010) could benefit catchment wide source apportionment studies, it has been applied in recent studies in the Linconshire Chalk (AMEC, 2012)[8].

Recommendations from EEA (2005)[9] are applicable to such studies and include the need for:

  • Data to quantify annual discharges from point sources (e.g sewage systems)
  • Data to quantify annual retention within the wider hydrological cycle
  • Information on groundwater residence time and degradation of nitrogen within aquifers
  • Information on agricultural practices to allow development of models for nutrient loss


  1. 1.0 1.1 EMMET, B A, ROWE, E C, STEVENS, C J, GOWING, D J, HENRYS, P A, MASKELL, L C, and SMART, S M. 2011. Interpretation of evidence of nitrogen impacts on vitiation in relation to UK biodiversity objectives. JNCC Report No. 449.
  2. 2.0 2.1 2.2 BOBBINK, R, HETTELINGH, J P (Eds.), 2011. Review and revision of empirical critical loads and dose-response relationships. Proceedings of an expert workshop, Noordwijkerhout, 23e25 June 2010, ISBN 978-90-6960-251-6. http://www.rivm.nl/bibliotheek/rapporten/680359002.pdf.
  3. STEVENS, C J, CAPORN, S J M, MASKELL, L C, SMART, S M, DISE, N B, and GOWING, D J. 2009. Detecting and attributing air pollution impacts during SSSI condition assessment. JNCC Report No. 426.
  4. ADAMS, M. 2003. Ecological issues related to N deposition to natural ecosystems: research needs. Environment International, JUN, Vol. 29, No. 2–3, pp.189–199 ISSN 0160-4120.
  5. DREWER, J, LOHILA, A, AURELA, M, LAURILA, T, MINKKINEN, K, PENTTILÄ, T, DINSMORE, K J, MCKENZIE, R M, HELFTER, C, FLECHARD, C, SUTTON, M A, and SKIBA, U M.. 2010. Comparison of greenhouse gas fluxes and nitrogen budgets from an ombotrophic bog in Scotland and a minerotrophic sedge fen in Finland. European Journal of Soil Science, 10, Vol.  61, No. 5, pp.640–650 ISSN 13510754. DOI 10.1111/j.1365-2389.2010.01267.x.
  6. HÄRDTLE, W, VON OHEIMB, G, GERKE, A, NIEMEYER, M, NIEMEYER, T, ASSMANN, T, DREES, C, MATERN, A, and MEYER, H. 2009. Shifts in N and P Budgets of Heathland Ecosystems: Effects of Management and Atmospheric Inputs. Ecosystems, 02, Vol. 12, No. 2, pp.298–310 ISSN 14329840. DOI 10.1007/s10021-008-9223-3.
  7. SACCON, P, LEIS, A, MARCA, A, KAISER, J, CAMPISI, L, BÖTTCHER, M E, SAVARINO, J, ESCHER, P, EISENHAUER, A, and ERBLAND, J. (2013) Multi-isotope approach for the identification and characterisation of nitrate pollution sources in the Marano lagoon (Italy) and parts of its catchment area. Applied Geochemistry, 34. pp.75–89. ISSN 08832927
  8. AMEC. 2012. Nitrate porewater modeling — Lincolnshire Chalk. For Environment Agency.
  9. EUROPEAN ENVIRONMENT AGECNY. 2005. Source apportionment of nitrogen and phosphorus inputs into the aquatic environment. ISBN 92-9167-777-9