Environmental Engineering Reference
In-Depth Information
Table 14.2. Mean and range (parentheses) for selected water
quality parameters measured monthly from
a
- April 1989 to May
1990 at seven equidistant sites or
b
- August 1990 to July 1991 at
two equidistant sites between Pomona Docks and Mode Wheel
Locks (adapted from Hendry et al.
1993
)
Parameter
Mean (range)
Dissolved oxygen (mg L
1
)
a
6.4 (0.0-13.1)
BOD (mg L
1
)
a
9.6 (2.5-36.0)
Ammonia (mg L
1
)
a
4.2 (0.1-9.3)
Suspended solids (mg L
1
)
b
16.3 (4.0-68.0)
Fish were absent from the MSC until the 1950s and only returned to some
areas during the 1980s. Even then, only roach (Rutilus rutilus) and stickleback
(Gasterosteus aculeatus) were found in the upper MSC (Hendry
1991
). These species
are able to withstand a high degree of pollution stress and are typical of
eutrophic conditions ( Jones
1964
). Fish were absent during the summer
months however presumably having migrated into the lower River Irwell to
avoid asphyxia.
Indirect effects of bottom water anoxia include an alteration of the redox
potential at the water-sediment interface which, in turn, can lead to mobilisa-
tion of phosphorus and some metals (Mortimer
1941
). However there is little
evidence of impacts of heavy-metal water and sediment contamination on fish
condition through bioaccumulation up the food chain or direct toxicity. In a
study of metal accumulation in biota in the lower Irwell (Critchley
1998
),
sediment bound metals appeared to be passed onto the invertebrate community.
Accumulation of higher quantities of copper and zinc by A. aquaticus and Erpob-
della octoculata, respectively, were attributed to different feeding habits resulting
from differences in trophic level, metal detoxification strategy and the secretion
of extracellular polysaccharides by E. octoculata. Results from analysis of stickle-
backs found no evidence of biomagnification of metals through the food chain.
Findings from a similar recent study of the lower Irwell and upper MSC sup-
ported this conclusion as sediments contained significantly more metals than
macroinvertebrates, whilst macroinvertebrates such as A. aquaticus and E. octocu-
lata contained higher levels than gudgeon (Gobio gobio) (Bassett
2005
).
Notwithstanding periodic poor water quality influxes, principally due to CSO
operation exacerbated by warmweather, gradual improvements to water quality
and subsequently to ecology have occurred in the upper MSC during recent years.
The improvements result from investments inWwTW infrastructure via the AMP
3
3
Asset Management Plan (AMP): a five yearly investment cycle of maintenance, infrastructure,
quality and environmental improvements undertaken by UK water companies.
