Report 356
Bioindicator and biomonitoring methods for assessing the effects of atmospheric nitrogen on statutory nature conservation sites
Sutton, M.A., Pitcairn, C.E.R. and Whitfield, C.P.
August 2004, Report for contract no. F90-01-535
This project was jointly funded by the Countryside Council for Wales, English Nature, Joint Nature Conservation Committee and the Centre for Ecology and Hydrology

Executive Summary

Bioindicators provide a range of techniques to assess the impacts of air pollution from reactive nitrogen (N) compounds on statutory nature conservation sites. They complement physical monitoring of atmospheric concentrations and deposition and risk assessment based on the critical loads approach by providing site-based information on atmospheric N concentrations, N deposition and/or ecological impacts.
  • Appropriate bioindicators for N may be applied by sampling at one time to compare results between different locations. In particular, local-scale transects can help identify the impacts of a nearby point source of reactive N emissions to the atmosphere.
  • The repeated application of bioindicator methods over time provides the basis for biomonitoring.  In general, biomonitoring reflects changes over periods of several years, although short-term changes can also be monitored (over several weeks and months).
  • This report reviews the wide range of bioindicator and biomonitoring methods for N and incorporates the results of a field test of several of the methods. In addition, datasheets are provided that summarize the key characteristics, advantages and limitations of the different methods.
  • Bioindicator methods can be grouped into several contrasting approaches: Biochemical methods (based on an accumulation of N or a chemical/physiological response to N), Species composition methods (based on previously characterized species preferences) and Transplant methods (based on the response following transplanting of either locally native species or standardized plants). 
  • Nitrogen accumulation methods include measurement of plant tissue N concentration, amino acids, substrate N and foliar ammonium. The accumulation methods provide the closest link to atmospheric N deposition. Results show that the smaller and more available the chemical pool, the larger the magnitude of response, with increasing responses from: total N < substrate N < foliar ammonium.
  • Biochemical response methods include analysis of enzymes such as nitrate reductase and emissions of nitrous oxide from soils.  These methods are useful to demonstrate physiological effects, but tend to be less well correlated with atmospheric N deposition due to interactions with environmental conditions.
  • Species composition methods are of particular interest to the statutory conservation agencies since they relate directly to changes in plant communities due to excess atmospheric N. 'Ellenberg' N preference scores for higher plant and bryophyte species can be used to score the overall community for nitrogen.  The limitation of this approach is that a wide range of other factors may also affect species composition.
  • Lichens are particularly sensitive to atmospheric reactive N, particularly ammonia. Detailed approaches are available to score lichen responses to N, but require more development for UK conditions. There is also the potential to refine simple methods that can be applied by non-experts.
  • The use of standardized grass plants has been shown to provide a robust method for monitoring the deposition and effects of N. The method can be applied in situations of complex terrain where physical estimates of deposition are difficult and as a graphic demonstration of impacts to stakeholders.  It has a key advantage that exposure periods of only a few weeks are necessary.
  • Transplanting native species between sites is useful to demonstrate impacts at polluted sites and conversely the benefits of clean conditions. These methods have been shown to work well for lower plants, and have the benefit of being able to demonstrate recovery following a reduction in deposition where this occurs.
Overall, recognizing the limitations and benefits of the different methods, it is concluded that bioindicators provide a practical site-based approach for assessing N concentrations, deposition and impacts. Each of the above mentioned approaches are have merits, with different techniques matching to the range of questions being addressed. The most robust results are to be obtained by implementing several complementary techniques simultaneously, where possible in combination with low-cost physical monitoring of atmospheric concentrations. 
You will need the free Adobe Acrobat Reader to view this document.
ISSN 0963-8091
Please cite as: Sutton, M.A., Pitcairn, C.E.R. and Whitfield, C.P., (2004), Bioindicator and biomonitoring methods for assessing the effects of atmospheric nitrogen on statutory nature conservation sites, August 2004, Report for contract no. F90-01-535, JNCC Report 356, ISSN 0963-8091