Planet WGSW-24010 User Manual page 32

Box 1 Factor s to consider when deciding whether to use MTR or DQI/TDI
1. River type
MTR may be more applicable to slow-flowing lowland silty rivers than the DQI
because of lack of suitable substrates for diatom growth. Use of artificial substrates
extends the range of situations where DQI is applicable, although suitable positions to
leave the artificial substrates are still required (Kelly 1996b). Water depth may limit
the use of both methods.
2. Shade
Both macrophyte and diatom communities, and particularly their biomass, may be
influenced by shading, such as that caused by bankside trees, suspended sediments or
surface floating vegetation.
3. Flow
Neither method should be used after spates. For both methods, careful consideration
should be given before undertaking surveys in circumstances where the flow from a
point-discharge maintains river flows greater than would be expected (Boxes 2 & 3).
4. Or ganic pollution
If the effect of organic pollution is suspected then it is strongly recommended that the
DQI method be used (in addition to the MTR, if appropriate), as this has a component
to establish the extent of pollution integral within the method. If it is not possible to
use the DQI method but an MTR macrophyte survey can be used, it may be necessary
to do an invertebrate survey in conjunction with the MTR to establish the extent of
pollution. The most comprehensive assessment could be provided if all three methods
can be used: diatom, macrophyte and invertebrate. It should be noted that the effects
of organic pollution on the MTR are unquantified at this time and information from
invertebrate surveys carried out at the same time will be useful for refining the MTR
method in future. Gross indications of organic pollution, such as the presence of
sewage fungus, should be noted when using any of these methods.
5. River management
Macrophyte communities may be affected by weed cutting and other associated
maintenance activities.
6. Navigation
The impact of navigation on the applicability of survey methods is varied. MTR
surveys rely on clear water, but watercourses with boat traffic tend to more turbid than
un-navigable reaches. Water clarity does not affect the DQI (TDI) to such an extent
but makes finding suitable substrates difficult (Kelly 1996c).
7. Nuisance value
In some circumstances both diatoms and/or macrophytes can cause a nuisance with
respect to intended water use. Diatom scums are particularly prevalent in spring and
excessive growth of macrophytic algae late in summer may require management to
eliminate the nuisance. In circumstances where there is a recognised nuisance from
either diatom and/or macrophyte growths, it may be prudent to ensure that the
assessment method(s) chosen includes the 'nuisance' element of the biota (ie DQI
and/or MTR respectively).
R&D Technical Report E38 18
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