EFFECTS OF HEATED EFFLUENTS
83
" day degrees ", where " day degrees ') are defined as mean temperatures
xdays (Boetius, 1962). Reish (1964), also, has demonstrated a direct
relationship between the number of species in a Mytilus edulis community and the temperature of the water, such that in higher temperatures a greater diversity of organisms was observed. Furthermore in
heated areas there is evidence of more protracted periods of colonization of new timber, as well as of breeding, by the wood-boring isopod
Limnoria (Eltringham and Hockley, 1961 ; Pannell, 1962; Jones, 1963;
Hockley, 1963; Naylor, 1965), and by Teredo (Pannell et al., 1962).
There is too some evidence that heating resulted in increased depredation by Teredo in docks at Swansea (Bell, 1949), such that it became
necessary to replace wooden jetties with structures of reinforced concrete.
It seems, also, that after the early 1930's when the docks were first
used as cooling ponds it soon became uneconomical to use the small
timber boats which carried mooring ropes of docking vessels owing to
increased depredation by wood borers. At any rate, at that time the
timber boats were replaced by metal punts and many dock timbers
were replaced by concrete piles. Not all the effects of heating are
detrimental since, for the River Thames (Ministry of Housing and Local
Government, 1961), it has been concluded that there are only localized
effects from even the largest heated effluents, and that some miles downstream some benefit might be felt. The beneficial aspects of heated
effluents have also been stressed by Markowski (1960) on the basis
of higher densities of organisms nearer outfalls than intakes. In addition
Iles (1963) and Markowski (1965) have reported increased rates of
growth of fish in the cooling ponds of power stations, which clearly have
beneficial implications (but see p. 70).
Apart from the direct effects of heated effluents several possible
indirect effects should be considered, since temperature also influences
the effects of other environmental factors such as oxygen concentration,
CO,,pH,dissolved solids and toxins (PennsylvaniaDept. of Health, 1962).
The fact that high temperatures may be associated with low concentrations of dissolved oxygen, particularly in areas receiving oxidizable
effluents as well as heat, has been confirmed by Alabaster and Wellcomme (1962). This occurs despite the fact that high temperatures
increase the rate of oxygen uptake by water at any particular level of
oxygen deficiency, owing to the facts that solubility is reduced and rates
of oxygen utilization by bacteria are increased (Ministry of Housing,
1961). Thus even though Swain and Newman (1962) report that oxygen
variations in a heated tidal river were related to variations in freshwater flow and pollution, not to heating, nevertheless it has been recommended (Ministry of Housing and Local Government, 1961) that
83
" day degrees ", where " day degrees ') are defined as mean temperatures
xdays (Boetius, 1962). Reish (1964), also, has demonstrated a direct
relationship between the number of species in a Mytilus edulis community and the temperature of the water, such that in higher temperatures a greater diversity of organisms was observed. Furthermore in
heated areas there is evidence of more protracted periods of colonization of new timber, as well as of breeding, by the wood-boring isopod
Limnoria (Eltringham and Hockley, 1961 ; Pannell, 1962; Jones, 1963;
Hockley, 1963; Naylor, 1965), and by Teredo (Pannell et al., 1962).
There is too some evidence that heating resulted in increased depredation by Teredo in docks at Swansea (Bell, 1949), such that it became
necessary to replace wooden jetties with structures of reinforced concrete.
It seems, also, that after the early 1930's when the docks were first
used as cooling ponds it soon became uneconomical to use the small
timber boats which carried mooring ropes of docking vessels owing to
increased depredation by wood borers. At any rate, at that time the
timber boats were replaced by metal punts and many dock timbers
were replaced by concrete piles. Not all the effects of heating are
detrimental since, for the River Thames (Ministry of Housing and Local
Government, 1961), it has been concluded that there are only localized
effects from even the largest heated effluents, and that some miles downstream some benefit might be felt. The beneficial aspects of heated
effluents have also been stressed by Markowski (1960) on the basis
of higher densities of organisms nearer outfalls than intakes. In addition
Iles (1963) and Markowski (1965) have reported increased rates of
growth of fish in the cooling ponds of power stations, which clearly have
beneficial implications (but see p. 70).
Apart from the direct effects of heated effluents several possible
indirect effects should be considered, since temperature also influences
the effects of other environmental factors such as oxygen concentration,
CO,,pH,dissolved solids and toxins (PennsylvaniaDept. of Health, 1962).
The fact that high temperatures may be associated with low concentrations of dissolved oxygen, particularly in areas receiving oxidizable
effluents as well as heat, has been confirmed by Alabaster and Wellcomme (1962). This occurs despite the fact that high temperatures
increase the rate of oxygen uptake by water at any particular level of
oxygen deficiency, owing to the facts that solubility is reduced and rates
of oxygen utilization by bacteria are increased (Ministry of Housing,
1961). Thus even though Swain and Newman (1962) report that oxygen
variations in a heated tidal river were related to variations in freshwater flow and pollution, not to heating, nevertheless it has been recommended (Ministry of Housing and Local Government, 1961) that