Environmental Engineering Reference
In-Depth Information
the suitability of 'northern hemisphere' ecological
tolerance/preference data for periphytic diatoms in
south-eastern Australian rivers before using particu-
lar bioindicator indices.
presence or absence, is being recorded. In this sit-
uation, comparison of analyses by different ana-
lysts can be carried out on the basis of 'similarity
measures'. The higher the value of the 'measure'
the greater the similarity, rising to a point at which
the two sets of data can be considered derived from
the same population.
Qualityassurance
Althoughtechniquesforstan-
dardised sampling of diatoms (Section 2.10.1), and
different types of indices (Section 3.4.5) are well
defined, the final environmental assessment ulti-
mately depends on the analyst's ability to accurately
record species composition from the environmental
samples. Quality assessment of analyst performance
is important, since regulatory agencies must be confi-
dent that data produced by their staff are relevant and
accurate. In Europe, for example, the requirement of
water companies to install nutrient removal facili-
ties in certain large sewage treatment works (Urban
Wastewater Treatment Directive - European Com-
munity, 1991) is determined by assessment of water
quality and is highly expensive. The use of benthic
diatomsintheimplementationofthisdirective(Kelly,
2002) must be reliable.
In the case of chemical analyses of water qual-
ity (including soluble nitrates and phosphates), the
situation is relatively simple, since chemical param-
eters are relatively few, with comparisons that are
univariate and amenable to conventional parametric
statistics. In contrast to this, biological monitoring
is more complex - based on field samples contain-
ing many species, all of which may contribute to the
assessment. These species counts may be assessed as
presence/absence or in terms of relative abundance.
Kelly (2001) has used the 'Bray-Curtis similarity
measure' to assess analyst performance, with levels
of
60%indicatinggoodagreementbetweenprimary
analyst and auditor. Evaluation of about 60 compar-
isons showed that reliability of assessment varied
with species diversity, and that samples with large
numbers of species had lower levels of similarity
compared to those with low numbers. The use of such
an audit measure, providing an objective approach
to analyst performance, has clear application within
regulatory organisations such as Water Authorities.
>
3.4.7 Nitrogen-fixing blue-green algae
The abundance of benthic nitrogen-fixing blue-green
algae can be used for rapid biomonitoring of nitrate
levels, as demonstrated by Stancheva
et al
. (2013) in
a study on southern Californian streams. This showed
thattherelativeabundanceofN
2
-ixingheterocystous
blue-green algae (
Nostoc
and
Calothrix
) and diatoms
(
Epithemia
and
Rhopalodia
) containing blue-green
algal symbionts decreased with increasing ambient
inorganic N concentrations at the low end of the
N gradient. Response thresholds for these N
2
-ixers
related both to N concentrations (0.075 mg l
−1
NO
3
-
N, 0.04 mg l
−1
NH
4
-N) and the N:P ratio (15:1 by
weight). The NO
3
-N threshold was independently
validated by observing nitrogenase gene expression
using real-time reverse transcriptase PCR.
Presence/absence
. Invertebrate analyses in the
United Kingdom are carried out on this basis,
with water quality being determined in relation to
the presence/absence of key benthic invertebrate
data (Mason, 1996). Reliability of assessment by
individual analysts can be measured as a 'qual-
ity audit', where the number of taxa 'missed' by
an (inexperienced) analyst can be compared to the
sample assessment by an experienced auditor.
3.5
Estuaries
Estuaries are aquatic zones that interface between
freshwater rivers and saline seas. As such, they tend
tobedominatedbysaltwaterconditions,butalsohave
majorfreshwaterinputs.Algaehavebeenwidelyused
Relative abundance
. A more complicated situation
is presented by diatom-based monitoring, where
the relative abundance of taxa, rather than their
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