Environmental Engineering Reference
In-Depth Information
composition of the flora and fauna will depend mainly on the physico-chemical
condition of the water unless the structure of the channel is extremely modi-
fied physically, for example, as a concrete channel or culvert with no natural
or semi-natural structure (Langford & Frissell
2009
). Ecological recovery from
gross pollution can therefore be expected to be a progress toward the unpol-
luted state, with a flora and fauna intolerant of the polluted conditions. Such
recovery is also dependent upon recolonisation and subsequent succession by
species from relevant sources (Yount & Niemi
1990
; Milner
1996
). The rate of
recovery is dependent upon the severity of the disturbance, the proximity
of a potential source of species, the mechanism of recolonisation and the
mobility of the relevant species. Ultimate recovery to the unpolluted ecological
condition will depend on the availability of the original species assemblage,
though knowledge of this is unlikely in streams polluted to their sources over
hundreds of years (e.g., Holland & Harding
1984
). Excellent predictive systems
of the potential composition of unpolluted communities have been developed
based on reference conditions. In the UK, the River Invertebrate Prediction and
Classification System (RIVPACS) (e.g., Wright et al.
2000
and
Chapter 6
) has been
developed over some 30 years based on data from over 600 sites. However, the
sites used for the predictions are on cleaner rivers which may or may not have
been subjected to marked historical chemical and physical disturbances and
such reference sites are often viewed with caution.
Where gross pollution occurs to the absolute sources of a river system,
ecological classification may be misleading once chemical quality has
improved, in that the absence of potential colonisers does not allow ecological
recovery to follow chemical recovery closely (Langford et al.
2009
). This could be
important for industry or municipal authorities in that ecological classifica-
tion of the river may suggest that further treatment of discharges entailing
further costs are necessary, whereas the real problem is in the biological
recovery processes and not the chemical quality of the water. Limitations on
recolonisation may also stem from some extreme physical factors such as
absence of natural margins or substrates in culverted or heavily engineered
channels (Davenport et al.
2004
).
In this present account, long-term data originate from three sites on the
River Tame, but further studies are using more extensive data from the catch-
ment. The main source of material is a 50-year sequence of biological data from
the 1950s to the present day originating from records of the Trent River Board
and its successors (Woodiwiss
1964
). Other material has been extracted from
published data (e.g., Hawkes
1956
,
1962
,
1975
) and from local archives. These
extensive datasets were used to develop the Trent Biotic Index (Woodiwiss
1964
), one of the earliest biological indices for monitoring ecological effects
of river pollution, variations of which are still in use in Europe (e.g., De Pauw &
Vanhooren
1983
; Metcalf-Smith
1996
; Sweeting
1996
).
