factor of 3. Nutrients, such as nitrogen and phosphorus, may be expected to
show somewhat the same growth pattern.
Also, the future of eutrophication in the lake depends in large part on
whether inorganic nutrients continue to accumulate. Lake Michigan is a huge
cul—de—sac which is ushed out very slowly through the Straits of Mackinac
into Lake Huron. So slow is the flushing that an estimated 95 percent of the
am1ual input of phosphates into the lake are retained there, according to A. F.
Bartsch (FWPCA). As an essential element in plant and animal growth, phos—
phorus tends to be retained in the natural aquatic cycle—now in living tissue,
now in decaying organic matter, now in inorganic phosphates excreted by
various organisms. Its retention time in the lake therefore is even greater than
that of a stable dissolved pollutant that follows the main ow of the lake water. Because of the factors of wind, current, shoreline barriers, and thermal
stratication, and the man-induced factor of intensied pollution in shallow
waters, it might take 1000 years for the lake to ush itself of 90 percent of the
general pollution load even with very effective pollution controls, according
to an estimate made at the February 1, 1968, session by Donald ]. Baumgart—
ner, Chief of Oceanography at the Pacic Northwest Water Research Labo—
ratory, Corvallis, Oregon. Wastes like phosphorus that build up
in the aquatic
system may follow a ushing pattern that covers an even longer span of time.
Furthermore, although phosphorus in the form of inorganic phosphates
appears to be the most critical nutrient in eutrophication, other nutrients—
particularly nitrogen—also contribute to the problem. Phosphates are more
easily removed in the waste treatment process and nitrogen is naturally more
abundant, so phosphorus reduction in treatment plants more effectively re—
duces eutrophication. Nevertheless, very large amounts of nitrogen in inorganic nitrates are released in water due to human activities. In Lake Mich—
igan, A. F. Bartsch estimated the annual input of nitrogen from all sources to
be about 166 million pounds, of which 81 percent is retained in the basin
each year.
Other trends in lake chemistry point to Lake Michigan’s deterioration,
trends which go hand in hand With the decline in water quality in rivers and
lakes elsewhere. From 1870 to 1967, concentrations of sulfates, chlorides, and
total dissolved solids (total content of dissolved car‘bonates, bicarbonates,
chlorides, sulfates, phosphates, and other substances) rose steadily, as depicted
in the following graphs.
These trends were reported by W
.
F. Carbine, then
Great Lakes—Central Region, U.S. Bureau of Commercial Fisheries, who said
these three substances were the only ones for which reliable, standardized
measurements could be obtained over a long period of time. Nevertheless,
Carbine- saw these trends as broadly representative of what is happening to
the concentrations of many (though by no means all) other chemical sub—
stances and similar to the steady increases that took place in Lake Erie prior
to the more recent sharp increases there.
The rising curve for chlorides was singled out as particularly signicant.
Chloride concentration increased only 2 ppm during 1905—1955, a period of
Problems Accumulote
21
show somewhat the same growth pattern.
Also, the future of eutrophication in the lake depends in large part on
whether inorganic nutrients continue to accumulate. Lake Michigan is a huge
cul—de—sac which is ushed out very slowly through the Straits of Mackinac
into Lake Huron. So slow is the flushing that an estimated 95 percent of the
am1ual input of phosphates into the lake are retained there, according to A. F.
Bartsch (FWPCA). As an essential element in plant and animal growth, phos—
phorus tends to be retained in the natural aquatic cycle—now in living tissue,
now in decaying organic matter, now in inorganic phosphates excreted by
various organisms. Its retention time in the lake therefore is even greater than
that of a stable dissolved pollutant that follows the main ow of the lake water. Because of the factors of wind, current, shoreline barriers, and thermal
stratication, and the man-induced factor of intensied pollution in shallow
waters, it might take 1000 years for the lake to ush itself of 90 percent of the
general pollution load even with very effective pollution controls, according
to an estimate made at the February 1, 1968, session by Donald ]. Baumgart—
ner, Chief of Oceanography at the Pacic Northwest Water Research Labo—
ratory, Corvallis, Oregon. Wastes like phosphorus that build up
in the aquatic
system may follow a ushing pattern that covers an even longer span of time.
Furthermore, although phosphorus in the form of inorganic phosphates
appears to be the most critical nutrient in eutrophication, other nutrients—
particularly nitrogen—also contribute to the problem. Phosphates are more
easily removed in the waste treatment process and nitrogen is naturally more
abundant, so phosphorus reduction in treatment plants more effectively re—
duces eutrophication. Nevertheless, very large amounts of nitrogen in inorganic nitrates are released in water due to human activities. In Lake Mich—
igan, A. F. Bartsch estimated the annual input of nitrogen from all sources to
be about 166 million pounds, of which 81 percent is retained in the basin
each year.
Other trends in lake chemistry point to Lake Michigan’s deterioration,
trends which go hand in hand With the decline in water quality in rivers and
lakes elsewhere. From 1870 to 1967, concentrations of sulfates, chlorides, and
total dissolved solids (total content of dissolved car‘bonates, bicarbonates,
chlorides, sulfates, phosphates, and other substances) rose steadily, as depicted
in the following graphs.
These trends were reported by W
.
F. Carbine, then
Great Lakes—Central Region, U.S. Bureau of Commercial Fisheries, who said
these three substances were the only ones for which reliable, standardized
measurements could be obtained over a long period of time. Nevertheless,
Carbine- saw these trends as broadly representative of what is happening to
the concentrations of many (though by no means all) other chemical sub—
stances and similar to the steady increases that took place in Lake Erie prior
to the more recent sharp increases there.
The rising curve for chlorides was singled out as particularly signicant.
Chloride concentration increased only 2 ppm during 1905—1955, a period of
Problems Accumulote
21