EFFECTS OF HEATED EFFLUENTS
77
For freshwater organisms in general the normal population structure
is maintained only up to a tolerance limit of about 32°C and extensive
loss in numbers and diversity of organisms occurs above that temperature (Coutant, 1962). Some genera were shown to be more tolerant than
others of temperatures higher than 32"C, but all species were limited
by temperatures of 40-43°C (Coutant, 1962). Cairns (1956) concluded
that to maintain survival in temperate streams large areas should not
be heated above about 30°C for long periods. This conclusion is also
supported by results of work by Alabaster (1963) who showed that
t,hough coarse fish are attracted into water heated to about 26"C,
temperatures of above 30°C were avoided.
All this work, including some in Poland (Stangenberg and Pawlaczyk, 1961) and in the U.S.S.R. (Luferova, 1960; Mikheev, 1962;
Rutkovskiy, 1962) has been concerned with freshwater localities. In
strictly marine or estuarine localities effects are less striking since
effluents are usually immediately diluted in larger volumes of cooler
water. However, Chadwick et al. (1950) have pointed out that whereas
the intake tunnels of power stations are often choked with fouling
organisms, no serious fouling occurs in discharge tubes. The elimination
of fouling species was attributed by these authors to differences in temperature of the water in the two conduits, and indeed they, like Ritchie
(1927), describe a system for controlling troublesome growths of sessile
marine organisms by periodically reversing the flow of discharged water
down alternative intake tunnels. Experimental work on the thermal
tolerance of fouling organisms, particularly Mytilus, coupled with trials
at the Westbank Electricity Station, Portobello (Ritchie, 1927) and at
the Redondo Power Station (Chadwick et al., 1950 ; Fox and Corcoran,
1957) showed that fouling by Mytilus edulis and M . californianus could
be completely controlled in this way. Thus in Southern California,
where these species normally breed and settle from mid-March to midOctober when sea temperatures are about 16°C and above, mussel
fouling was prevented by tri-weekly reversals of discharge water either
for periods of 1 h at 38-41°C or for 7 h a t 346°C (Fox and Corcoran,
1957). In Scotland Ritchie (1927) showed that Mytilus edulis could be
controlled by flushing the intake ducts with effluent water at a minimum
temperature of about 43°C once every 4 weeks during the spatting season
from March to October.
In the vicinity of ocean outfalls off SouthernCalifornia, Resig (1960)
has shown that heating effects are apparent up to a few thousand feet
away from discharge areas and that in the heated areas species of Foraminifera with calcareous tests are less abundant than those with arenaceous tests. However, though it is known that Foraminifera are
77
For freshwater organisms in general the normal population structure
is maintained only up to a tolerance limit of about 32°C and extensive
loss in numbers and diversity of organisms occurs above that temperature (Coutant, 1962). Some genera were shown to be more tolerant than
others of temperatures higher than 32"C, but all species were limited
by temperatures of 40-43°C (Coutant, 1962). Cairns (1956) concluded
that to maintain survival in temperate streams large areas should not
be heated above about 30°C for long periods. This conclusion is also
supported by results of work by Alabaster (1963) who showed that
t,hough coarse fish are attracted into water heated to about 26"C,
temperatures of above 30°C were avoided.
All this work, including some in Poland (Stangenberg and Pawlaczyk, 1961) and in the U.S.S.R. (Luferova, 1960; Mikheev, 1962;
Rutkovskiy, 1962) has been concerned with freshwater localities. In
strictly marine or estuarine localities effects are less striking since
effluents are usually immediately diluted in larger volumes of cooler
water. However, Chadwick et al. (1950) have pointed out that whereas
the intake tunnels of power stations are often choked with fouling
organisms, no serious fouling occurs in discharge tubes. The elimination
of fouling species was attributed by these authors to differences in temperature of the water in the two conduits, and indeed they, like Ritchie
(1927), describe a system for controlling troublesome growths of sessile
marine organisms by periodically reversing the flow of discharged water
down alternative intake tunnels. Experimental work on the thermal
tolerance of fouling organisms, particularly Mytilus, coupled with trials
at the Westbank Electricity Station, Portobello (Ritchie, 1927) and at
the Redondo Power Station (Chadwick et al., 1950 ; Fox and Corcoran,
1957) showed that fouling by Mytilus edulis and M . californianus could
be completely controlled in this way. Thus in Southern California,
where these species normally breed and settle from mid-March to midOctober when sea temperatures are about 16°C and above, mussel
fouling was prevented by tri-weekly reversals of discharge water either
for periods of 1 h at 38-41°C or for 7 h a t 346°C (Fox and Corcoran,
1957). In Scotland Ritchie (1927) showed that Mytilus edulis could be
controlled by flushing the intake ducts with effluent water at a minimum
temperature of about 43°C once every 4 weeks during the spatting season
from March to October.
In the vicinity of ocean outfalls off SouthernCalifornia, Resig (1960)
has shown that heating effects are apparent up to a few thousand feet
away from discharge areas and that in the heated areas species of Foraminifera with calcareous tests are less abundant than those with arenaceous tests. However, though it is known that Foraminifera are