NUTRIENTS
DISCHARGED TO THE MISSISSIPPI RIVER
FROM
EASTERN IOWA WATERSHEDS, 1996-1997
From Journal of the American Water Resources Association,
vol. 36, no. 1, pp. 161-173
By Kent D. Becher, Douglas J. Schnoebelen, and
Kimberlee, K.B. Akers
U.S. Geological Survey, Iowa City, IA
Abstract
The
introduction of nutrients from chemical fertilizer, animal manure, wastewater,
and atmospheric deposition to the eastern Iowa environment creates a large
potential for nutrient transport in watersheds. Agriculture constitutes 93
percent of all land use in eastern Iowa. As part of the U.S. Geological Survey
National Water Quality Assessment Program, water samples were collected
(typically monthly) from six small and six large watersheds in eastern Iowa
between March 1996 and September 1997. A
Geographic Information System (GIS) was used to determine land use and quantify
inputs of nitrogen and phosphorus within the study area. Streamflow from the
watersheds is to the Mississippi River. Chemical fertilizer and animal manure
account for 92 percent of the
estimated total nitrogen and 99.9 percent
of the estimated total phosphorus input in the study area. Total nitrogen and
total phosphorus loads for 1996 were
estimated for nine of the 12 rivers
and creeks using a minimum variance unbiased estimator model. A seasonal pattern
of concentrations and loads was observed. The greatest concentrations and loads
occur in the late spring to early summer in conjunction with row-crop fertilizer
applications and spring runoff and again in the late fall to early winter as
vegetation goes into dormancy and additional fertilizer is applied to row-crop
fields. The three largest rivers in eastern Iowa transported an estimated total
of 79,000 metric tons of total
nitrogen and 6,800 metric tons of
total phosphorus to the Mississippi River in 1996. The estimated mass of total nitrogen and total phosphorus
transported to the Mississippi River represents about 19 percent of all estimated nitrogen and 9 percent of all estimated phosphorus input to the study area.
AVAILABILITY
Limited number of reprints of this report are available upon request
from
Project Chief
Eastern Iowa Basins
U.S. Geological Survey
PO Box 1230
Iowa City, IA 52244
Phone: (319) 358-3611
email: sjkalkho@usgs.gov
