Environmental Engineering Reference
In-Depth Information
It should be stressed that the reference condition as defined by the WFD does
not represent a desire to revert to pre-industrial conditions by removing
human influence from the catchment, but a desire to achieve high quality
and sustainable water resources for use by both humans and other organisms
that persist within the catchment. Importantly, by inference, the WFD defines
reference conditions as having to be statistically comparable to the test sites.
Thus, the measures of the biological community used to produce the required
observed and expected scores must be derived without any differences in the
measure at either reference or test sites arising from unaccounted differences
in sampling methodology. There must be an equal probability of taxa being
recorded in the data used to derive the reference conditions as in a test site
that does not suffer any stress, or if there is bias between the sampling
methodologies, any effect must be quantified and included in the calculated
O/E. Historic data rarely achieve these requirements, which precludes long
distance hind-casting of reference conditions to some pre-industrial utopia.
For some biological quality elements, it is possible to produce a description of
historic communities using palaeolimnological techniques (identifying sub-fossil
remains from sediments) or other historic data. However, if different techniques
are used to define reference condition from those used to assess sites, any
methodological bias (due to sampling, preservation or technique differences)
between the representation of taxa in samples used to define reference condition
and those derived from sampling test sites must be taken into account. Any
difference in uncertainty will also have to be accounted for (see below).
This strict definition of reference condition also differs markedly from a
target condition as would be applied to the restoration of an impacted site.
Whilst the target of restoration may be to achieve reference condition, a
restoration target is more likely to include other characteristics of the commu-
nity, either as individual species or other aspects of community composition,
which would be required at a site to indicate that a restoration had been
successful (e.g., presence of a Biodiversity Action Plan species). Furthermore,
the methods used to derive these requirements do not have to be comparable to
those used to assess the level of success. Hence, an anecdotal historic record of a
rare species may be sufficient to include its recovery as a target. Having said
this, the WFD does aim to restore all water bodies to 'good' ecological status,
where there is little impact upon the structure and function of the biological
community. This is an admirable aim and one that will bring considerable
conservation benefit. If a functionally equivalent community is restored to a
site, it is likely that the appropriate niches for species of conservation value will
be present, and there is a high probability of them being able to persist, even if
not initially present. Conversely, if the community is not functioning in the
appropriate way, species of conservation value are unlikely to persist, even if
present, as their niches are lacking.
