Environmental Engineering Reference
In-Depth Information
Table 14.3. Average zooplankton group abundance in Salford Quays for two
selected periods (number L
1
) (APEM unpublished data)
Basin 7
Basin 8
Basin 9
1990-94
2003-07
1990-94
2003-07
1990-94
2003-07
Copepods
5
12
6
11
6
8
Cladocerans
3
16
4
10
4
10
Rotifers
2
2
3
1
7
3
cocooned in fungus at the water surface suggested polluted water to the
general public, although in actuality water quality was improving (Hendry
et al.
1997
).
Recent zooplankton abundance (average 2003 2007) reveals an increase in
both copepod and cladoceran densities throughout all enclosed basins com-
pared to the average in 1990 1994
(
Table 14.3
). Concurrently, rotifer species
showed a decline in Basins 8 and 9. The increase in copepod and cladoceran
densities, particularly in Basin 7, is likely due to the diverse habitat afforded by
the natural colonisation and growth of macrophytes (Irvine et al.
1989
) within
the Quays (see below). The importance of aquatic plants as refuges for cladocer-
ans against predaceous fish has been reported elsewhere (Moss et al.
1994
).
Significantly higher numbers of zooplankton were found in water lily beds
(67 L
1
) compared to open water (6 L
1
) in a shallow lake (Beklioglu & Moss
1996
).
Diversification of the macroinvertebrate community provided a further indi-
cation of the water quality improvements. The invertebrate community in the
enclosed basins in the early years following isolation was dominated by species
characteristic of organically polluted waters, and remained similar to those in
the MSC. Whilst the pollution-tolerant species continued to dominate, species
less tolerant to pollution such as the snail Lymnaea peregra became common
(White et al.
1993
). Various other species also colonised the basins, including
mayfly (Baetis sp.), water bugs (Corixa sp.) and caddis flies (Agraylea sp. and
Phryganea bipunctata). It was suggested that water quality would no longer
restrict the invertebrate community but the homogeneous nature of the basins
and lack of refuges and macrophytes would likely inhibit future diversification
(White et al.
1993
). This issue has subsequently been addressed (see below), and
there has since been a further increase in diversity, with over 50 macroinverte-
brate taxa being recorded in recent years, compared to just nine immediately
following isolation of the dock basins (APEM
2008b
).
The apparent instability in the fish community due to the very limited
diversity, as demonstrated by the 'cocooned' sticklebacks described above,
indicated that there was a need to ascertain whether the Quays could support
a more diverse fish community. A small stocking trial was initiated in 1988,
