Environmental Engineering Reference
In-Depth Information
recession and the consequent closures of large industries together with the
change from coal gas to natural gas that were initially the major factors in
the rapid improvement of water quality in the river. Whether the recession
itself was exacerbated by increasingly stringent pollution controls and their
costs is unknown, but the improvements required were costly and other
countries did not have the constraints. It is also clear that the Tame treatment
lakes were not immediately significant factors in the reduction of ammonia
or invertebrate recolonisation of the lower river, though further investigation
may show that recovery was improved immediately downstream of the lake
outfalls. The treatment would also contribute to the improvement in the
longer term.
Recolonisation rates and succession by invertebrates clearly varied with
location. At both Chetwynd Bridge and Lea Marston, the sites were downstream
of major tributaries, which could contribute cleaner water species. However,
at Lea Marston, despite the potential source of recolonisers from the River
Blythe, no clean-water taxa were recorded, whereas at Chetwynd Bridge at least
four clean-water taxa were recorded. By 2006, ammonia levels were very similar
at both sites but it is likely that episodic pollution from diffuse sources of
proximal urban runoff was more influential at Lea Marston than at the lower
site. At Eagle Lane, Tipton, ammonia levels were not as low as at the other sites
but were well below the threshold at which rapid recolonisation could occur.
Though chemical recovery was slower, a major problem is the lack of any
sources of clean-water fauna within or even near the system to provide a source
of colonisers (Milner
1996
; Langford et al.
2009
). Biological surveys of the
numerous small streams in the upper parts of the catchment show a complete
absence of clean-water fauna (EA BIOSYS and unpublished archive data), and
this is particularly true for the uppermost tributaries of the Oldbury branch
of the Tame on which Eagle Lane is sited. All of the taxa that have recolonised
at Eagle Lane, and many of those at the other sites, are not obligate running
water taxa but are also found in ditches, ponds and pools. Examples are, apart
from the Oligochaeta, snails such as Lymnea sp. and Physa sp. and leeches
such as Erpobdella sp. and Glossiphoniai sp. Leeches, molluscs and oligochaetes
are also likely to be associated because the leeches feed on Oligochaeta and
gastropod molluscs (Elliott & Mann
1998
). Sources of obligate clean river
taxa are remote with the nearest being to the west in the Severn catchment
5 10 km distant.
The significance of the geomorphological condition of the Tame to recovery
is equivocal, though there is some good evidence that more natural, weedy
channels support a slightly more diverse invertebrate fauna than the heavily
engineered channels (Beavan et al.
2001
). In the most channelised reaches with
concrete or bricked margins, there would be, predictably, a restriction of those
clean-water species which require natural marginal habitat such as trailing
