standardization of environmental data and information - International ...

3. What did we learn from DISCOL?
3.1. Restrictions, number of samples and processing efforts
A critical point of a proposed experimental design is that the
samples will be segregated in different physical locations and that it is
impossible to randomise and intersperse samples receiving different
treatment. Disregard of randomisation and interspersion results in
uncontrolled conditions in an experimental design because differences
between the localities of two samples may already have existed before the
experiment. This may result in unrecognised locality effects that would bias
the treatment effects. Such a design can lead to misinterpretation of the
results and would be regarded as pseudoreplication 27 .
Although interspersion in both impacted and unimpacted areas
certainly would be preferred, this feature is difficult to achieve in the type of
large-scale experiments we propose. The DISCOL experiment demonstrated
that true replication could not be achieved within the experimental field
because it was impossible to designate sub-areas not affected by
resettlement of resuspended material that could serve as truly unimpacted
control sites. Reliable interspersion of treatments would thus require a
number of spatially well-separated experimental locations (at least four 28 )
plus a corresponding number of reference areas. The resultant effort, both
at sea and during data analyses over the entire programme, would be many
times greater than under the proposed scheme and would go far beyond
any reasonable or practical limits.
In the present case, there is only a limited risk of biasing effects due
to the pre-existence or later intrusion of differences between locations,
because of the relative homogeneity of deep ocean basin environments.
The proposed treatment area of approximately 2 nmi² is relatively large, and
dispersion of samples over that area should compensate for the potential of
pseudoreplication. Accordingly, care should also be taken to have similar
inter-sample distances at the two reference sites. However, a certain
environmental variability within the entire proposed target area cannot be
excluded a priori and should be properly evaluated in the pre-baseline and
baseline studies. It is obvious that data analyses and interpretations of
these studies must be completed before the start of the experiment,
because they constitute the basis for selection of the three experimental
and reference localities (out of five baseline localities), which should be as
similar as possible.
INTERNATIONAL SEABED AUTHORITY 343