Geoscience Reference
In-Depth Information
River monitoring in England
and Wales
and the presence of non-native riparian plants are
also recorded to assess impact on physical structure
and native wildlife. Full details are provided in a
survey manual (Environment Agency, 2003). From
a monitoring perspective, the key datasets are the
national RHS baseline surveys of 1995-1996 and
2007-2008. For both surveys, nearly 5000 sites
were sampled across England and Wales, using
three randomly located sites within each 10 km
square of the Ordnance Survey national grid. This
approach provides a geographically representative
and unbiased picture of river habitats in England
and Wales, while permitting detailed mapping of
rivers at regional and national scales (Environment
Agency, 2010b; Seager
et al
., this volume).
River monitoring in England and Wales is carried
out predominantly by the Environment Agency
(http://www.environment-agency.gov.uk). A wide
variety of biological (e.g. epilithon, macrophytes,
benthic macroinvertebrates, fish populations),
water chemistry, discharge and habitat data are
collected. Two of the most extensive datasets
derived during the last 20 years have been
associated with the General Quality Assessment
(GQA) scheme and two baseline surveys using
River Habitat Survey (RHS).
The GQA scheme was introduced in 1990 by the
National Rivers Authority; it used chemical and
biological (benthic macroinvertebrates) parameters
to assess river water quality (Environment
Agency, 2010c). Benthic macroinvertebrates
were sampled using 3-minute kick samples,
taken in the spring (March-May) and autumn
(September-November), with field sampling,
sorting and identification following a standard
protocol (Murray-Bligh, 1999). Water samples
were collected from the same, or nearby, locations
at monthly intervals, and analysed primarily for
those determinands that indicate organic pollution
(e.g. Biochemical Oxygen Demand (BOD),
dissolved oxygen and ammonia). Several thousand
sites across England and Wales were sampled for
GQA purposes, with national surveys completed
in 1990, 1995 and 2002. These were followed by
a smaller rolling 3-year programme, which has
now been superseded by sampling protocols for
the WFD (Environment Agency, 2010c). Rivers
were categorized by GQA into quality classes for
both chemistry and biology, ranging from A ('very
good') to F ('bad').
RHS was developed in the mid-1990s to provide
a method for assessing the physical character of
river channels to assist with site management
and provide a basis for habitat quality assessment
(Raven
et al
., 1997). Sampling is based on a
500 m length of watercourse, with a wide range
of attributes recorded; these include river-bed
substratum, flow-types, erosion and deposition
features, vegetation structure on the banks and
adjacent land-use. Modifications to the channel
Water quality changes since 1990
The GQA classification of rivers indicated
substantial improvements in water quality
during 1990-2010 (Environment Agency, 2010a).
Impairments to both chemical and biological water
quality showed a similar reduction in geographical
extent and severity (Plate 12). In England, the
proportion of rivers at 'good' or 'very good'
chemical quality increased from 55% to 79%,
while the equivalent increase for biology was
from 55% to 72% (Environment Agency, 2010a).
Quality improvements in Wales were smaller, but
started at a higher level: 86 to 95% for chemistry
and 79 to 88% for biology (Environment Agency,
2010a).
These improvements probably reflect a
combination of improved regulation and treatment
of wastewater discharges and reduced pressure
from industrial effluents, the latter reflecting a
decline in heavy industry during the final decades
of the twentieth century (Langford
et al
., this
volume). The relative contributions of these factors
are the subject of ongoing research (T. Langford,
pers. comm.; I.P. Vaughan and S.J. Ormerod,
unpublished data). Analyses are helped by the
large size of the GQA dataset, which allows
changes to be tracked in detail (Plate 12).
Changes in physical habitat
The primary purpose of the RHS baseline surveys
was to obtain a representative picture of
the
