Habitats Directive Meeting

1. Ecological Assessment: Need for
Guidance?
Dr James Riley, Associate Director
July 2015

2. Available guidance
– Main guidance focusses on calculations relative to high-level
thresholds: PC exceeds 1% critical load/level, PEC exceeds 70% of CL
etc.
– Some habitats don’t have Critical Loads on APIS (e.g. freshwater)
– Public guidance (e.g. DRMB) often then states ‘consult an ecologist’
– Most ecologists not trained in air quality. Often this results in a very
conservative conclusion.
– Guidance dispersed. Almost no guidance on some issues e.g. acid
deposition.
July 21, 2015
Ecological Assessment: Need for
Guidance?
Page 2

3. Examples of common misconceptions leading to very conservative
assessments
– That ‘1% of CL’ and ‘70% of CL’ are damage thresholds rather than an
initial sieve to remove the smallest contributors.
– That a deposition rate above 1% of the CL is a high rate of deposition.
Generally actually a low rate.
– That the Critical Load is a ‘set in stone’ figure which applies in all
circumstances.
– Failure to appreciate extent to which other activities can over-ride air
quality impacts
– Effects can be greater when exceedence is very small than when it is
much larger
July 21, 2015
Ecological Assessment: Need for
Guidance?
Page 3

4. Other things an ecologist needs to consider
– Reliability of the critical load for the relevant habitat - consult APIS
– Other considerations that may override air quality effects (e.g.
management regime) - Professional judgment
– ‘Shape’ of habitat response graph e.g. linear or curvilinear - published
research for some habitats e.g. acid grassland and species e.g. lichen
– How much additional deposition will result in how much change? -
Some published research e.g. acid grassland and heathland
– Guidance on all these issues would be very valuable
July 21, 2015
Ecological Assessment: Need for
Guidance?
Page 4

5. Example 1 – nitrogen deposition exceedence on acid grassland
from road traffic
• Level 1 text 24pt Arial
– Level 2 bullet 20pt Arial
• Level 1 text 24pt Arial
– Level 2 bullet 20pt Arial
• PC = 2.5% of CL
• Consult DMRB: ‘Small’ change (i.e. not
exceeding 5% of CL)
• Consider background: High background rate
(22 kgha-1yr-1)
• Consult research: at deposition rates over 20
kgha-1yr-1, an increase in deposition rate of 3
kgha-1yr-1 in acid grassland required to reduce
species-richness by 1 species.
• Consider management: Area closely mown as
firebreak
• Conclusion: No Adverse Effect
July 21, 2015
Ecological Assessment: Need for
Guidance?
Page 5

6. Example 2 – NOx and nitrogen deposition exceedence on coastal
saltmarsh from power station
• Level 1 text 24pt Arial
– Level 2 bullet 20pt Arial
• Level 1 text 24pt Arial
– Level 2 bullet 20pt Arial
• PC = over 20% of CL; exceedence of both
24hr NOx and annual NOx
• Consider research: Study on NOx and
saltmarsh concluded N deposition rates
were of greater importance
• Research reliability of critical load: APIS
website indicated CL for nitrogen on
saltmarsh less reliable than other habitats
• Consider circumstances: Marine nitrogen
inputs very high at this site, coupled with
regular tidal flushing
• Conclusion: No Adverse Effect
July 21, 2015
Ecological Assessment: Need for
Guidance?
Page 6

7. Thank You
James.d.riley@aecom.com
July 2015