Submitted to: First Interagency Conference on Research in the Watersheds
Publication Type: Proceedings
Publication Acceptance Date: September 25, 2003
Publication Date: October 27, 2003
Citation: ALBERTS, E.E., JAYNES, D.B., LERCH, R.N. NUTRIENT AND HERBICIDE MOVEMENT IN STREAMFLOW FROM TWO MIDWESTERN WATERSHEDS. PROCEEDINGS OF FIRST INTERAGENCY CONFERENCE ON RESEARCH IN THE WATERSHEDS. 2003. UNITED STATES DEPARTMENT OF AGRICULTURE. AGRICULTURAL RESEARCH SERVICE. WASHINGTON, D.C. P. 385-390 CDROM. Interpretive Summary: Nutrients and herbicides applied to improve crop production can move from their point of application causing downstream surface water contamination. Watersheds of various sizes can be instrumented to better understand differences in climates, crops, soils, and landscapes on nutrient and herbicide movement to determine if present agricultural management practices are degrading surface water quality. We collected precipitation, streamflow, nitrate-nitrogen (NO3-N), and atrazine data for ten years (1992-2001) from the outlet of the 7,280-ha Goodwater Creek watershed located in north-central Missouri and the 5,130-ha Walnut Creek watershed in central Iowa. Each watershed was intensively cropped, but corn was more prevalent in the Walnut Creek watershed. We found that each watershed had a major water quality problem. Annual water-weighted atrazine concentrations from the Goodwater Creek watershed exceeded the EPA's maximum contaminant level (MCL) of 3 ppb for 7 of the 10 years, while NO3-N concentrations from the Walnut Creek watershed exceeded the EPA's MCL of 10 ppm for 6 of the 10 years. The results can be primarily attributed to differences in how water moves within the watersheds. About 90% of the streamflow discharged from Goodwater Creek was associated with surface runoff events, with high atrazine concentrations in the runoff for the 60- to 90-day period following application. About 74% of the streamflow discharged from Walnut Creek over the 10-year period was tile drainage. NO3-N, being much more mobile in the soil than atrazine, readily entered the tile drain system and moved rapidly from upland areas of the watershed to Walnut Creek. These results will be useful to national and regional planners to better understand the sources of nutrient and herbicide contamination within the Mississippi River Basin. Results will also be useful to scientists, extension/education personnel, and to farmers that must understand and solve water contamination problems at the watershed level.
Technical Abstract: Watersheds in different geographic areas offer many opportunities to study how differences in climate, crops, soils, and landscapes affect the off-site movement of nutrients, herbicides, and other environmental contaminants. The objective of this research was to compare differences in nitrate-nitrogen (NO3-N) and atrazine concentrations and discharges in streamflow from two watersheds in the Midwest for a 10-yr period, 1992 through 2001. One watershed was the 7,280-ha Goodwater Creek watershed located in north-central Missouri, the other, the 5,130-ha Walnut Creek watershed in central Iowa. Over 80% of the area within each watershed is cropped, but the fraction of corn cropping is higher in the Walnut Creek watershed. The drainage outlet of each watershed is instrumented with a concrete v-notch weir, water stage recorder, and refrigerated automatic pumping sampler. Mean annual NO3-N discharges from the Goodwater and Walnut Creek watersheds were 6.9 and 20.4 kg ha**-1. Flow-weighted NO33-N concentrations (10 yrs) from the Goodwater and Walnut Creek watersheds were 1.8 and 9.2 mg L**-1, with flow-weighted annual concentrations ranging from 1.2 to 2.7 mg L**-1 for Goodwater Creek and 6.3 to 13.1 mg L**-1 for Walnut Creek. Mean annual atrazine discharges from the Goodwater and Walnut Creek watersheds were 18.1 and 1.7 g ha**-1. Flow-weighted atrazine concentrations from the Goodwater and Walnut Creek watersheds for the 10-yr period were 4.6 and 0.8 ug L**-1, with flow-weighted annual concentrations ranging from 0.8 to 19.3 ug L**-1 for Goodwater Creek and 0.1 to 1.9 ug L**-1 for Walnut Creek. Our results show that water quality problems associated with crop production are dependent on how water moves within and through the watershed topography because of soil and anthropogenic factors. In the Goodwater Creek watershed, streamflow is comprised of about 90% surface runoff and 10% ground water recharge making atrazine more susceptible to movement. About 74% of the streamflow discharge from Walnut Creek over the 10-yr period was tile drainage, with NO3-N readily moving in the drainage water.