Sources and Contributions of Nitrogen and
Phosphorus to an Iowa Stream
E. ROBERT BAUMANN, Professor
SHELDON KELMAN, Assistant Professor
Sanitary Engineering Section
Engineering Research Institute
Iowa State University
Ames, Iowa
SOURCES OF NUTRIENTS
Several potential sources of the nitrogen and phosphorus which enter the
surface waters of Iowa are readily recognized. For years, industrial and municipal
wastes have been considered to be the major contributors of N and P. Before we
install tertiary treatment to remove N and P from these sources, we must consider
whether tertiary treatment will cause any significant changes to be observed in the
rivers. In recent years, attention has been focused on the potential contributions
from surface runoff. Corey (1) has listed the following available nitrogen sources for
plant growth: soil organic matter, animal manure, legume fixation, commercial
fertilizer and that naturally present in precipitation. The same sources, of course, are
potential contributors of nitrogen to runoff.
The average daily N and P contribution of each person connected to a sewer is
well established. Given sewered population data, the quantities of nitrogen and
phosphorus discharge in domestic wastewater can readily be approximated (an
example will be discussed later in this paper). Other sources of these nutrients may
equal or even exceed the quantities in domestic wastewater. Industrial wastes from
packing houses contain large quantities of nitrogen and phosphorus since meat is a
protein containing high concentrations of both nutrients.
Animal wastes form an increasing source of such nutrients. Both wild and
domestic animals are significant sources of fertilizer elements. When storm runoff
occurs, large quantities of animal wastes are washed into streams. Iowa, for example,
has a domestic population of 2.75 million. This state is noted, however, for its
production of pork and beef. Approximately 6,100,000 swine and 3,300,000 beef
animals are on feed at any one time. Nearly 46,000 animal feed lots are recorded in
Iowa. The daily waste from these animals is equivalent to the daily waste from a
human population of 65—90 million people. Naturally, not all this waste finds its
way into our streams. But when it rains—as it does in Iowa 20 to 30 times per year
with intensities of 1 inch/hour or more—several days accumulation of these wastes
may find their way into our surface waters. Feedlot regulations are now designed to
control runoff from the 100-200 feedlots that feed over 1000 head of cattle.
However, no such control to prevent surface water pollution is now envisioned for
the 45,000 feedlots feeding less than this number. Such animal wastes, together with
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