Sampling Strategy - Planet WGSW-24010 User Manual

3.2 Sampling str ategy
3.2.1 Assessing the impact of point-sour ces of nutr ients
The general sampling strategy for assessing all point-sources of nutrients, whether UWWTD
qualifying discharges or not, is very similar to other biological assessment methods. An MTR
survey should be undertaken from a site upstream of the discharge and compared with an MTR
survey downstream of the discharge. More than one survey downstream will be required to
assess the geographical extent of any impact. More than one survey upstream of the discharge,
or in other physically-similar parts of the catchment, may be required to help determine whether
the MTR is suppressed by factors other than nutrient enrichment. In cases where it is suspected
that the downstream change in MTR is being influenced by factors other than trophic status (by
increased turbidity, for example), there is justification for using information from other biological
assessment methods, such as the DQI and the River Invertebrate Prediction and Classification
System (RIVPACS), to give a more refined picture of the impact of the discharge.
3.2.2 Non-point sour ce dischar ges
It may be difficult to pinpoint specific areas where degradation of the aquatic macrophyte
community structure occurs unless a comprehensive study of the whole catchment is undertaken.
However, surveys may be targeted around the areas where the potential for non-point source
pollution is highest. Examples include: areas where the nature of the land use means that there
is a high potential for sediment erosion; areas where the potential for farm effluents entering the
river system is highest; and areas where run-off from hard surfaces in urban areas is occurring.
3.2.3 Catchment studies
To improve the interpretation of MTR values by placing them in a catchment context (2.4.3),
surveys should be undertaken at regular intervals down the catchment to assess the varying
influences on the macrophyte community.
To undertake a 'eutrophication audit' of an individual catchment, to determine where nutrient
control measures would be targeted most effectively, surveys should be undertaken at intervals
over the whole catchment. However, the inherent limitations of the method must be taken into
account when selecting sites and interpreting data. Results must only be compared between
physically similar sites (6.2.3).
To provide an overview of the trophic status of a catchment to compare with other catchments
on an area, regional or national basis, the survey strategy is as outlined in the paragraph above.
However, the limitations on comparison between catchments (2.4.3 and 6.2.3) must be taken into
account when planning the surveys and interpreting results.
3.2.4 Eutr ophication management str ategies
To assess and prioritise problems on a large (eg national) scale, surveys of whole catchments or
sub-catchments will be of most use. More restrictive surveys targeted at specific discharges (eg
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