Ecological recovery in a river polluted to its sources: the River Tame in the English Midlands - Ecology of Industrial Pollution - page 263

(e.g., Alabaster & Lloyd 1980 ). Relationships between selected chemical indica-
tors were analysed using Pearson correlation analysis. Biological recovery is
indicated by taxon richness (Ntaxa), using identification to the BMWP 'family'
level (Wright et al. 2000 ). As the weighted indicators of ecological quality, e.g.,
ASPT and BMWP (Wright et al. 2000 ), are based on the tolerance of selected taxa
to chemical determinands such as ammonia and Biochemical Oxygen Demand
(BOD), using these would not give as clear an indication of the biological
processes of recolonisation and succession as taxon richness. Successional
changes in the invertebrate fauna are summarised by chronological analysis of
the raw data. 'Clean-water' taxa include all those which score 8 10 in the BMWP
pollution scoring system (Wright et al. 2000 ). The presence and absence of fish
is also indicated from survey results supplied by the Environment Agency.

Results
Chronological changes
Chemistry and taxon richness
The responses of all three sites are similar chronologically in that, from the
mid 1960s to the present, there has been a reduction in average annual
ammonia concentrations from in excess of 15mg L 1 to less than 2mg L 1 .At
Chetwynd Bridge ( Fig. 13.4 ) and Lea Marston ( Fig. 13.4 ) , average concentrations
were below 1mg L 1 from the mid 1990s. At Eagle Lane ( Fig. 13.4 ), ammonia
concentrations from the 1990s were slightly higher than at the other two sites,
averaging between 1 and 2mg L 1 . Also, at Eagle Lane, there was a sharp fall in
ammonia to an average of c. 5mgL 1 in the late 1960s (coinciding with the
closure of two large coal-based gasworks), but a subsequent increase to between
5 and 10mg L 1 (reasons unknown to date) which was maintained until the mid
1980s when a second decline began. BOD values did not increase at Eagle Lane
in the late 1960s, though as with the ammonia concentrations, there was a
period from 1970 to 1990 when there was no decline (Environment Agency
WIMS database). Increases in taxon richness also followed similar upward
trends though the increases began in 1975 1977 at Chetwynd Bridge and Lea
Marston but as late as the early 1990s at Eagle Lane. The increases in taxon
richness coincided with periods when the ammonia concentrations fell below
5mgL 1 with accelerated increases below 2.5mg L 1 . The 2.5mg L 1 threshold is
shown as dotted lines on Fig. 13.4 .
The changes in ammonia concentrations were significantly correlated with
BOD (F

¼ < ¼

24) and, as a result of improved oxidation, nega-
tively with nitrate (NO 3 ) concentrations (F

0.965, p 0.001, n

24). Correl-
ations between other determinands were not investigated for this univariate
analysis, though further work will include multivariate analyses using other
determinands. The variation in ammonia levels was greater before 1990 than
in more recent years at all three sites with maxima declining from about
10mg L 1 to 2mg L 1 or less.

¼ 0.756, p < 0.01, n ¼