Biological Water Quality Surveys
(from Thomson Ecology webpages, with additional notes in italics)
Biological water quality assessments use standardised indices of invertebrate
biodiversity to assess levels of pollution and other human influences on fresh
water resources. These indices form measures of nature conservation value for
rivers and ponds as part of the assessments required for planning applications.
They are used to monitor freshwater habitat around sensitive developments such
as waste sites and new road schemes, and to assess ecological status of surface
waters for compliance with the Water Framework Directive (WFD). Thomson
Ecology carries out standardised biological water quality surveys for Ecological
Impact Assessments, monitoring existing and new developments, and for
assessing compliance with the WFD.
Standard Biological Indices for Rivers
Organic pollution from diffuse and point sources in rivers can be assessed with
standard surveys of aquatic invertebrate families. The families present in a river are
given scores based on their tolerance to organic pollution. These scores are called
Biological Monitoring Working Party scores (BMWP scores). Similarly, scores
can be calculated for invertebrate tolerance to acid and persistent low flows via the
Acid Water Indicator Community score (AWIC) and the Lotic-invertebrate Index for
Flow Evaluation (LIFE) score. Thomson Ecology conducts these quick, economical
invertebrate surveys for Ecological Impact Assessments, for monitoring the quality of
water resources, and to assess compliance with the Water Framework Directive.
Notes
BMWP index
>150
101–150
51–100
26–50
10–25
0–9
Water quality
Very high
High
Average
Tolerable
Low
Very low
For more accurate calculations, the water BMWP value is divided by the number of
macro-invertebrate groups identified in samples, giving the BMWP biotic score for a
taxonomic group. First used in Great Britiain in 1978.
The biotic score is efficient in highlighting small changes in water quality – based on
the number of macro-invertebrates present. Families have a certain attributed value
between 1 and 10 (see charts) – the more sensitive it is to pollution, the higher the
number. The charts are in order of decreasing attributed value.
Predicting Biological Water Quality
The Environment Agency approved River Invertebrate Prediction and Classification
System (RIVPACS) and the Predictive System for Multimetrics (PSYM) for ponds are
used to compare biological water quality between a survey site and pristine rivers
and ponds. Both systems use standard BMWP scores and similar diversity indices,
such as number of dragonfly/damselfly and beetle families. Thomson Ecology carries
out surveys for use in these comprehensive assessments, which are required for
major development or flood control schemes affecting surface waters.
Aquatic Habitat Surveys
There are several standard methods in the UK for aquatic habitat surveys. They
are used to monitor, classify and map the physical characteristics of river habitats
and floodplain geomorphology. Thomson Ecology offers expertise in lake and
wetland ecology and our consultants have accreditation from the Environment
Agency to carry out these survey techniques to the required standard. Such
surveys are an essential part of the planning process for any works affecting UK
rivers. Thomson Ecology also provides expert ecological input to flood
management and riverside development projects, ecological impact assessments
and mitigation strategies where negative impacts may occur.
River Habitat Survey (RHS)
River Habitat Survey is an Environment Agency approved technique used to assess
the physical character and flora of river habitats that are important to a wide range of
invertebrates and other animals. Based on 500 metre reaches, a series of spot
checks are made at 50 metre intervals to record channel substrate, channel and
bank vegetation structure, and types of modifications made to the channel and
banks. Our team of ecologists are accredited to conduct these surveys and provide
input to flood management and development projects that affect water courses.
Geomorphological River Habitat Survey (GeoRHS)
This new extension of RHS involves detailed characterisation of channel and
floodplain geomorphology over 500 metre reaches, and is used alongside RHS to
help implement River Basin Management Plans under the Water Framework
Directive (WFD). It is also used in flood risk assessments. Thomson Ecology have
accreditation in GeoRHS and were among the first to field test the technique, making
us well placed to provide this component of major flood risk management projects,
and projects relating to WFD implementation.
River Corridor Survey (RCS)
River Corridor Survey is a survey technique required and recognised by planners,
which involves the production of standardised maps of vegetation structure along 500
m stretches of river. This provides a detailed outline of the physical habitat available
for aquatic animals and a botanical survey. Our ecologists use this technique in
Ecological Impact Assessments for riverside developments and for flood
management projects.
Natural England’s Rapid Assessment Technique
This survey technique is used to assess and monitor aquatic plant diversity. It
involves a botanical and physical survey of 500 metre stretches of river, with detailed
spot checks at 50 metre intervals and an overall assessment of management
features along the 500 metre stretch. Thomson Ecology carry out these assessments
for any work that affects river biodiversity.
CHARTS
The charts show all the invertebrate results since 1996 for the site at
Hackney Marshes (TQ 366 865). They suggest poor to moderate water quality, but
there are other issues contributing, such as the poor habitat and flashy flow.
There are very few pollution-sensitive invertebrate species present, with only a
single record of a pollution-sensitive caddis (Leptoceridae) at the site. It is probably
also worth noting that Giant Hogweed is found along this whole stretch, which will
affect the natural bankside vegetation and pose a health risk. [Notes from EA]