Planet WGSW-24010 User Manual page 24

· is the river eutrophic, or shortly at risk of becoming eutrophic?
· what is the impact of the QD?
Guidance on sampling strategy and interpretation of MTR results to answer these questions is
given in Sections 3.2.1 and 6.1. The latter includes flow-charts to enable decisions to be made
in a consistent and structured manner. Results are expressed qualitatively in terms of two
standard descriptors, one for trophic status and one for the downstream impacts of the QD.
2.3.3 Post phosphate-r emoval monitor ing
It is anticipated that macrophyte communities previously affected by phosphate eutrophication
will attain higher MTR scores after phosphate removal (phosphate-stripping) is installed at QDs.
Although this response, or the speed at which it occurs, has yet to be demonstrated due to the
early stage of method development, the MTR system should be used to monitor improvements
in the macrophyte community after phosphate-removal has commenced. The information gained
from this monitoring will not only provide direct operational information on the impact of the
P-removal, but will also provide much needed information for the further refinement of the
method. The latter includes information on the speed at which macrophyte communities respond
to a reduction in P concentration; how recovery takes place (which species come back first); and
the effect of P in sediments (how long it takes for phosphate-enriched sediments to cease to have
an effect on the macrophyte community).
The success of biological methods at demonstrating an improvement in the trophic status
of a system is dependent on the availability of a reliable and consistent historical data set.
Lack of such a data set may limit the application of the methods to demonstrate an
improvement in a historical context. For those SA(E)s designated under the 1997 review,
however, post-phosphate-removal monitoring may be able to show measured improvements
using data from the 1996 MTR surveys as the baseline for improvement.
In order to separate the effects of phosphate-removal from natural background variation in
the MTR it may be necessary to carry out an examination of the time series of change to
establish baseline variation in MTR scores. These data may be available by comparison with
MTR scores from previous seasons, but care should be taken to ensure that all factors
relating to the accuracy and comparability of MTR surveys prior to 1996 are satisfactory
before undertaking such comparisons. If you are sure that any change in MTR score prior
to phosphate-removal cannot be accounted for by changes in nutrient concentrations or
other conditions then this variability can be used as a measure of natural background
variation. It is anticipated that any changes due to phosphate-reductions will be
superimposed on this natural change.
R&D Technical Report E38 10