Page 287 - Freshwater-Biology-and-Ecology-Handbook

9

INVESTIGATIVE MONITORING –

UK EXAMPLE

The impacts of pollution or other incidents may need to be 45% (Defra 2016). (147) Although low oxygen saturation had
investigated by investigative monitoring. Such information been recorded in the past, it was accompanied by a very high
should not be used for classification because the intensity concentration of ammoniacal nitrogen of more than 7.5 mg/l
of sampling may distort the long-term picture. However, – the Bad status boundary in this type of river is 2.5mg/l N –
the surveillance monitoring data provides the baseline which is indicative of untreated organic waste. (145) Although
information, so changes from this may indicate that a an invertebrate survey was not undertaken until about 4
pollution event has damaged the biota. months after the event, its impact on the invertebrate fauna
was still clear.
An example of the impact of a series of organic pollution
events, together with the scale of impact on the biota, The delayed recovery of biota enables biological
is shown in Figure 6.12. It also demonstrates that the assessments to detect pollution long after the pollution has
combination of chemical and biological monitoring ceased. Although WHPT ASPT and WHPT NTaxa were
information provides evidence of the cause and effect not particularly high before the incident, both dropped
of the pollution incidents. substantially after it: WHPT ASPT fell from 5.1 to 3.3 and
WHPT Ntaxa from 23 to 11. Similar changes were seen in
This figure shows results from a monitoring site on a lowland other invertebrate indices.
river in southern England, the River Thame, a tributary of the
River Thames. This monitoring site was downstream from This information was used in enforcement action by the
a sewage treatment works that was allowed to discharge Environment Agency, in the courts, against a privatised
a very poorly treated effluent. When the major incident water company. The water utility company received a £20M
occurred is clear from the monthly chemical monitoring fine because of its poor management at both this and other
results. The oxygen concentration fell to less than 10% wastewater treatment plants.
saturation – the Bad status boundary for this type of river is

Oxygen (% saturation)

PSI
WHPT NTaxa
SPEARpesticidesFam
LIFE
WHPT ASPT
Ammoniacal nitrogen (mg/l)

Figure 6.12
Chemical and invertebrate impacts from untreated wastewater discharges to a lowland river

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