Other Applications - Planet WGSW-24010 User Manual

2.4

Other applications

2.4.1 Non-qualifying point-sour ce dischar ges
In many river systems in the UK, a significant proportion of the phosphate-loading comes from
WWTWs of less than 10,000 pe although surface water run-off and storm sewer overflow may
also be significant sources of phosphorus in urban areas. These discharges do not qualify under
the UWWTD for statutory improvement works to remove P from the effluent discharge. This
means that eutrophication can be primarily caused by phosphate-loading from sources other than
QDs and hence outside the legislative framework of the UWWTD. It also means that rivers are
frequently degraded upstream of the QD, making the demonstration of an impact of a QD
difficult to achieve in absolute terms. The MTR can be used to identify non-QDs which are
having a significant impact on the macrophyte community in order to target these for future
nutrient control measures where possible. Sampling protocol and interpretation of results is as
for assessment of QDs (3.2.1 and 6.2.1).
2.4.2 Non-point sour ce dischar ges
The phosphate-loading of many agricultural catchments may arise mainly from non-point
sources, such as soil run-off and diluted slurry effluent. The use of the MTR is these
circumstances is largely untried, but provisional guidance on sampling strategy and interpretation
of result is given in 3.2.2 and 6.2.2. The information gained from such studies will help
determine if the MTR system is capable of detecting the effects of non-point source discharges.
2.4.3 Catchment studies
Studies of the MTR over a whole catchment or sub-catchment may be considered for three
purposes.
To impr ove the inter pr etation of MTR values, by placing them in a catchment context
The main inherent limitation of the MTR is that it is influenced to some extent by factors other
than nutrient levels; in particular, by the substrate, underlying geology of the river and to some
extent the flow regime. This means that to interpret the MTR in terms of trophic status it is
necessary to compare results with values expected in a relatively un-impacted reach of a similar
type. Such reaches, or at least similar reaches with less nutrient enrichment, may be found
elsewhere in the catchment being surveyed.
A second limitation relates to the sensitivity of the MTR in detecting the impact of individual
nutrient sources. In a complex environment, the impact of a nutrient discharge may not be
manifest by the MTR for some distance downstream due to impact by other polluting factor(s)
in the same discharge or by another discharge close by. In either case, interpretation of MTR
results may be improved if the sampling programme includes surveys at regular intervals down
the catchment to assess the varying influences on the macrophyte community (3.2.3).
R&D Technical Report E38 11