Geoscience Reference
In-Depth Information
for over 150 years (Spicer, 1950; Lord, 1968;
Lester, 1975). As late as the 1970s a division
between murky polluted and clear unpolluted
water was clearly visible for several hundred
metres downstream of confluences where mixing
of the water was weak (Lord, 1968). As with
many polluted rivers in the UK, improved water
quality in the early 1960s resulted from better
sewage treatment and reduced industrial discharges
(Martin, 1994). Despite reductions in several
pollutants, nitrate and phosphate concentrations
have continued to increase, most probably linked to
the intensification of farming methods and sewage
treatment works where ammonia is oxidized (Jose,
1989).
From the 1920s, electricity generating power
stations were constructed along parts of the river.
These abstracted and discharged large amounts of
cooling water, in some cases involving volumes
that were more than half the dry-weather flow of
the river. The Trent was unique in that it supported
the largest concentrations of power stations in the
world by the 1960s, producing over 15 000MW
of electricity in total (Langford, 1983, 1990). As
a consequence, water temperatures could exceed
30
◦
C in summer and 15
◦
C in winter in some
reaches, while temperature rises of 8-10
◦
Cwere
typical. The chemical and biological effects have
been well studied, but
that the biological effects of raised temperatures
were often obscured by the amount of background
organic and inorganic pollution (Langford, 1972).
Closure of the older power stations and the
introduction of cooling towers resulted in a
decrease in river temperatures from the 1980s.
Methods and data sources
The overall aim of the River Trent study is to
quantify long-term changes in the biology and
chemistry of the river, using data from as many
sampling sites as possible and applying the results
for future environmental planning and control.
Data from a small number of sites are illustrated in
this chapter to test the potential uses of the more
extensive databases. The historical trend analysis
is based on information derived from a variety
of sources (Table 21.1). The varied nature of the
data, and in particular the variation in quality
and sampling frequency, mean that interpretations
must be treated with caution, despite considerable
efforts to ensure comparability both spatially and
temporally. Consequently, it is not always possible
to show variability for some years or sites, so only
broad trends can be deduced.
For
the purposes of
this chapter, chemical
pollution is
indicated by minimum dissolved
the main problem was
oxygen (DO)
concentrations to determine the
Table 21.1
Summary of data sources used for the River Trent study.
Data
Period
Data sources
Chemical data
1923-1990 National and Parliamentary archives; mostly in Ministry of Agriculture Fisheries
and Food (MAFF), Standing Committee on River Pollution (SCORP) reports.
1988-2010
Records from the Environment Agency Water Information Management
System (WIMS).
Summarized chemical data
1938-1990
Reports produced by the Trent Fishery Board, Trent River Board, Trent River
Authority, Severn Trent Regional Water Authority, and the National Rivers
Authority.
1946-2010
Peer reviewed research papers.
Biological data (benthic
macroinvertebrate records)
1956-1987 Historic River Data Archive at the University of Southampton (dated 1950s
onwards), plus more recent records (1970s and early 1980s) donated by the
Environment Agency.
1988-2010
Records from the Environment Agency National Biological Systems Database
(BioSys).
