.
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Agricultural runoff carries nutrients added to the soil to increase crops into rivers
and lakes where they increase crops of algue instead.
further study will resolve some of the interpretive dierences. The sources of
the nutrients in the studies, however, were predominantly human activities.
Two of the more readin identiable man—made sources of nutrients are
the inorganic nitrogen fertilizers used extensively in agriculture and the phos—
phates from sewage efuents, a large part of which are from detergents.
Much of the nitrates in surface water have been attributed by some scientists
to the increasing use of inorganic nitrogen fertilizers. Studies carried out- in
the Sangamon Biver Watershed in central Illinois in the spring of 1970
showed that at least 55—60 percent of the nitrate found in surface waters
there came from fertilizer nitrogen rather than from natural sources [25].
Limiting the amount of nitrate entering the water is important not only
because it may contribute to eutrophication but because of a health hazard,
methemoglobinemia, to be discussed later. For these reasons, regulation of
fertilizer is now being considered. Robert Harmeson of the Illinois State Wa—
’
ter Survey pointed out at state hearings on the subject that the nitrate con—
centration of the Illinois River and most of the watersheds studied has been
steadily increasing from 1897 to 1971 [26]. Since phosphates are also used in
fertilizers (in the United States, 80 percent of phosphate supplies are used in
.
fertilizers [27]), this factor also was discussed at the hearings. It was reported
that the amount of phosphates from fertilizers which may increase the phos—
Limiiing Factors
135
‘
……
“.
…
'
,_,
…
.…
.
“MMM—__
___—_
_‘
..
5
"‘
«,
«
°
'.
_
:
\‘
'
.;
…
î
Agricultural runoff carries nutrients added to the soil to increase crops into rivers
and lakes where they increase crops of algue instead.
further study will resolve some of the interpretive dierences. The sources of
the nutrients in the studies, however, were predominantly human activities.
Two of the more readin identiable man—made sources of nutrients are
the inorganic nitrogen fertilizers used extensively in agriculture and the phos—
phates from sewage efuents, a large part of which are from detergents.
Much of the nitrates in surface water have been attributed by some scientists
to the increasing use of inorganic nitrogen fertilizers. Studies carried out- in
the Sangamon Biver Watershed in central Illinois in the spring of 1970
showed that at least 55—60 percent of the nitrate found in surface waters
there came from fertilizer nitrogen rather than from natural sources [25].
Limiting the amount of nitrate entering the water is important not only
because it may contribute to eutrophication but because of a health hazard,
methemoglobinemia, to be discussed later. For these reasons, regulation of
fertilizer is now being considered. Robert Harmeson of the Illinois State Wa—
’
ter Survey pointed out at state hearings on the subject that the nitrate con—
centration of the Illinois River and most of the watersheds studied has been
steadily increasing from 1897 to 1971 [26]. Since phosphates are also used in
fertilizers (in the United States, 80 percent of phosphate supplies are used in
.
fertilizers [27]), this factor also was discussed at the hearings. It was reported
that the amount of phosphates from fertilizers which may increase the phos—
Limiiing Factors
135