habit estuaries—a special type of aquatic
environment at the months of rivers
l
that is subject
to constant uctuations between fresh water and sea water.
Taking into account these limitations to biological adaptability, especially
the ability to regulate internal salt concentrations, the Federal Water Pollu—
tion Control Administration of the US. Department of the Interior recom—
mended standards [27]: For estuaries, no changes should be made in channels,
basin geometry, or freshwater inow that will create more than a 10 percent
change from natural variation in salinity. In order to maintain a diversied
freshwater animal population,
the salt concentration should not exceed 1500
mg/l. Also, total dissolved solids should not increase to more than one—third of
the water’s natural concentration in order to maintain local conditions. These
Î
standards are important because salts from a number of human activities nd
their way
into surface and ground water. Some of the sources of excess salin—
ity are efuents from desalination plants, brine from deep-well injections, and
;
salt from the winter deicing of streets in urban areas.
While the desalination of salt water for drinking purposes
is not a com'
mon practice, it is now carried out in approximately 25 communities around
the world. The process involves separating salt from water and results in two
streams of water—one which is less saline than the original and a waste stream
which is more saline than the original. An additional waste stream contains
heated cooling water. Some plants have been planned which will have conversion capacities of 50 million gallons per day. A study of a government—
sponsored sali'ne conversion plant at Point Lorna, near San Diego in California, pointed out some of the deleterious effects this type of efuent can have
*
on the environment. The concentration of the brine discharged was 1.5 to
two times that of sea water. The temperaüne of the cooling water efuent
was also high. Sea water temperatures varied from 52°F (winter) to 72°F
(summer); water temperatures in the efuent stream ranged from 83°F (win—
ter) to 110°F (summer).
Examination of aquatic life showed a signicant drop in the numbers of
plant and animal species, particularly at the conversion plant outfall. The
mean number of species in two sample areas near the plant outfall was 4.2
and 5.0; in three adjacent areas more distant from the source of eluent, the
average number of species was 7.7, 8.0, and 12.0. Thus, only the more hardy
species could survive the combined effects of increased salinity and temper—
ature [28].
Since 1947, the use of salts for the winter deicing of roads and streets has
‘
increased 1800 percent, from a half—million tons in 1947 to nine million tons
in 1970. A study of the salt concentration in efuent from the Kennedy EXpressway in Chicago by a member of the American Public Works Association
revealed that, assuming 1.5 tons of salt are applied for each mile of a two-lane
h1ghVÿay,_there
would be 1300 mg/l of chloride ion in the runot£ Thus, the
chloride
ron alone in highway runoË may be close to the 1500 mg/l salinity
Ë3ît
recommended in the previously cited FWPCA standards for fresh water
50
An Uncommon Friend
'
environment at the months of rivers
l
that is subject
to constant uctuations between fresh water and sea water.
Taking into account these limitations to biological adaptability, especially
the ability to regulate internal salt concentrations, the Federal Water Pollu—
tion Control Administration of the US. Department of the Interior recom—
mended standards [27]: For estuaries, no changes should be made in channels,
basin geometry, or freshwater inow that will create more than a 10 percent
change from natural variation in salinity. In order to maintain a diversied
freshwater animal population,
the salt concentration should not exceed 1500
mg/l. Also, total dissolved solids should not increase to more than one—third of
the water’s natural concentration in order to maintain local conditions. These
Î
standards are important because salts from a number of human activities nd
their way
into surface and ground water. Some of the sources of excess salin—
ity are efuents from desalination plants, brine from deep-well injections, and
;
salt from the winter deicing of streets in urban areas.
While the desalination of salt water for drinking purposes
is not a com'
mon practice, it is now carried out in approximately 25 communities around
the world. The process involves separating salt from water and results in two
streams of water—one which is less saline than the original and a waste stream
which is more saline than the original. An additional waste stream contains
heated cooling water. Some plants have been planned which will have conversion capacities of 50 million gallons per day. A study of a government—
sponsored sali'ne conversion plant at Point Lorna, near San Diego in California, pointed out some of the deleterious effects this type of efuent can have
*
on the environment. The concentration of the brine discharged was 1.5 to
two times that of sea water. The temperaüne of the cooling water efuent
was also high. Sea water temperatures varied from 52°F (winter) to 72°F
(summer); water temperatures in the efuent stream ranged from 83°F (win—
ter) to 110°F (summer).
Examination of aquatic life showed a signicant drop in the numbers of
plant and animal species, particularly at the conversion plant outfall. The
mean number of species in two sample areas near the plant outfall was 4.2
and 5.0; in three adjacent areas more distant from the source of eluent, the
average number of species was 7.7, 8.0, and 12.0. Thus, only the more hardy
species could survive the combined effects of increased salinity and temper—
ature [28].
Since 1947, the use of salts for the winter deicing of roads and streets has
‘
increased 1800 percent, from a half—million tons in 1947 to nine million tons
in 1970. A study of the salt concentration in efuent from the Kennedy EXpressway in Chicago by a member of the American Public Works Association
revealed that, assuming 1.5 tons of salt are applied for each mile of a two-lane
h1ghVÿay,_there
would be 1300 mg/l of chloride ion in the runot£ Thus, the
chloride
ron alone in highway runoË may be close to the 1500 mg/l salinity
Ë3ît
recommended in the previously cited FWPCA standards for fresh water
50
An Uncommon Friend
'