Planet WGSW-24010 User Manual page 33

Box 1 Factor s to consider when deciding whether to use MTR or DQI/TDI
.....continued
8. Distur bance
Neither method should be carried out if conditions at the survey length are not typical
of the survey site (see Box 2).
9. Season
MTR surveys are restricted to the period between mid-June and mid-September
(3.3.1). The DQI method is applicable throughout the year, access permitting,
although it is recommended that studies are performed between spring and autumn
(Kelly 1996b). For comparison purposes it will be necessary to carry out DQI surveys
at roughly the same time of year as MTR surveys.
10. Recover y per iod
When nutrient control measures such as P-stripping are put in place and an assessment
of the subsequent recovery of the biota is required, the relative performance of the
MTR and DQI in detecting improvements in trophic status over time must be
considered. The speed of response of diatom and macrophyte communities to
improvements in trophic status caused by P-stripping, however, is largely unknown at
the present time and more data are required. It is likely that diatom communities will
respond faster as they are entirely dependant on water column nutrients for growth.
The influence of sediment nutrient characteristics on macrophyte recolonisation are as
yet unknown*. The best practice would be to undertake both methods at sites where
nutrient removal is in place, or is likely to be introduced.
11. Har monisation with other sur veys
The DQI is easier and quicker to carry out in the field and, as a result of sample
preservation, allows a greater degree of flexibility in the organisation of survey
programmes than does the MTR. It may thus be more easily added onto an existing
sampling programme, especially invertebrate surveys as the survey area used is
comparable. MTR surveys may, however, be more valuable for comparison with
historic data sets of the same site where only macrophyte data are available. MTR
surveys are also more appropriate if wishing to harmonise with surveys for
classification of river types for conservation purposes.
12. Resour ces
The method used will be dependent on the expertise and equipment available and the
cost of the survey. More time is spent in the field for MTR, but less in the laboratory.
* This is the subject of an ongoing Environment Agency funded PhD project.
R&D Technical Report E38 19