Report 356
Bioindicator and biomonitoring methods for assessing the effects of atmospheric nitrogen on statutory nature conservation sites
(2004)
Sutton, M.A., Pitcairn, C.E.R. and Whitfield, C.P.
This project was jointly funded by the Countryside Council for Wales, English Nature, Joint Nature Conservation Committee and the Centre for Ecology and Hydrology
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.
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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