The Iowa Department of Natural Resources, Geological Survey Bureau (GSB); the University of Iowa Hygienic Laboratory (UHL); and the U.S. Geological Survey (USGS) have been working together to address this question. As part of the Iowa Ground Water Monitoring (IGWM) Program, water samples have been collected from selected Iowa municipal wells since 1982. An examination of this data identified two trends: 1) concentrations of atrazine were generally decreasing over time, and 2) concentrations of metolachlor were generally were increasing. Continuing ground-water sampling can determine if these trends represent long-term changes in chemical concentrations.
Iowa has some of the most productive farmland in the world. Agricultural chemicals (pesticides and nitrogen fertilizers) have become an integral part of farming in Iowa, where some of the most intensive applications are used (Battaglin and Goolsby, 1995). Intensive chemical use has focused investigations on Iowa to determine the occurrence of agricultural chemicals in ground water (Libra and others, 1987; Detroy and others, 1988; Hallberg, 1989; Kross and others, 1990). Research has documented that alachlor, atrazine, cyanazine, and metolachlor historically have been the most frequently detected pesticides in Iowa's ground water. This research has increased public awareness of the occurrence of agricultural chemicals in ground water. A public concern has been whether concentrations of agricultural chemicals have changed over time. Few studies, however, have provided the consistency and longevity to adequately address this issue on a regional scale (Barbash and Resek, 1996). In response to this concern, the Geological Survey Bureau, the University of Iowa Hygienic Laboratory, and the USGS formed the IGWM in 1982 to monitor agricultural chemicals in Iowa's ground water. From 1982-95, 2,041 nitrate samples from 1,024 municipal wells and 1,375 pesticide samples from 730 municipal wells were collected for the IGWM (fig. 1).
Figure 1. Location of the municipal wells repeatedly sampled from 1982-1995 for the IGWM.
Figure 2. Concentration differential for selected agricultural chemicals. This concentration differential was calculated by subtracting the median 1987-91 concentration from the 1992-95 concentration for the 89 wells having the longest record of agricultural-chemical data. The nitrate data is in parts-per-million and the herbicide data is in parts-per-billion.
Average chemical use Compound (1000 pounds/year of Average intensity of use active ingredient) (pounds/acre) ------------------------------------------------------------------------------------------------ 1982-85 1987-91 1992-95 1982-85 1987-91 1992-95 ------------------------------------------------------------------------------------------------ Nitrogen fertilizer(1) 1,931,824 1,844,520 1,839,168 138 129 118 Alachlor(2) 13,800 8,246 5,180 2.01 2.25 2.28 Atrazine(2) 8,179 7,451 7,195 1.46 0.96 0.90 Cyanazine(2) 9,440 5,852 6,988 2.06 2.06 2.32 Metolachlor(2) 6,744 10,910 10,378 2.40 2.05 2.09
1. Vroomen, 1989; U.S. Department of Agriculture, 1995
2. Hartzler and Wintersteen, 1991; U.S. Department of Agriculture, 1995; Hallberg and others, 1996 Agricultural Chemicals in Iowa's Ground Water -- Are Things Changing?
Figure 3. Concentration differential for selected agricultural chemicals by well depth. This concentration differential was calculated by subtracting the median 1987-91 concentration from the 1992-95 concentration for the 89 wells having the longest record of agricultural-chemical data.
Figure 4. Generalized ground-water movement and pesticide transport in the subsurface (modified from Roberts and Jones, 1996).
Figure 5. Concentration differential for selected agricultural chemicals by aquifer type. This concentration differential was calculated by subtracting the median 1987-91 concentration from the 1992-95 concentration for the 89 wells having the longest record of agricultural-chemical data.
Figure 6. Conceptual geologic ross-section and aerial view of typical alluvial aquifers in Iowa (Prior, 1991).
Figure 7. Aerial view of an alluvial aquifer in northeast Iowa (Prior, 1991).
The results presented in this report were summarized from a previously published research paper. Additional information on the results of this study is available in this paper:
Kolpin, D.W., Sneck-Fahrer, D.A., Hallberg, G.R., and Libra, R.D, 1996, Temporal trends of selected agricultural chemicals in Iowa's groundwater, 1982-95: Are things getting better?: Journal of Environmental Quality, v 26, n. 4, p.1007-1017.Barbash, J.E., and Resek, E.A., 1996, Pesticides in Ground Water: Distribution, Trends, and Governing Factors: Ann Arbor Press, Inc., Chelsea, MI, 588 p.
Battaglin, W.A., and Goolsby, D.A., 1995, Spatial data in geographic information system format on agricultural chemical use, land use, and cropping practices in the United States: U.S. Geological Survey Water-Resources Investigations Report 94-4176, 87 p.
Detroy, M.G., Hunt P.K.B., and Holub, M.A., 1988, Ground-water-quality- monitoring program in Iowa: Nitrate and pesticides in shallow aquifers: U.S. Geological Survey Water-Resources Investigations Report 88-4123, 32 p.
Hallberg, G.R., 1989, Pesticide pollution of groundwater in the humid United States. Agriculture Ecosystems & Environment, v. 26, p. 299-367.
Hallberg, G.R., Riley, D.G., Kantamneni, J.R., Weyer, P.J., and Kelley, R.D., 1996, Assessment of Iowa Safe Drinking Water Act monitoring data: 1988-1995: The University of Iowa Hygienic Laboratory Research Report No. 97-1, 132 p.
Hartzler, R., and W.K. Wintersteen, 1991, A survey of pesticides used in Iowa crop production in 1990. Iowa State University Extension Service Publication Pamphlet 1441, 11 p.
Kolpin, D.W., Burkart, M.R., and Thurman, E.M, 1994, Herbicides and nitrate in near-surface aquifers in the midcontinental United States, 1991: U.S. Geological Survey Water-Supply Paper 2413, 34 p.
Kolpin, D.W., Thurman, E.M., and Goolsby, D.A., 1996, Occurrence of selected pesticides and their metabolites in near-surface aquifers of the midwestern United States: Environmental Science & Technology, v. 30, p. 335-340.
Kolpin, D.W., Kalkhoff, S.J., Goolsby, D.A., Sneck-Fahrer, D.A., and Thurman, E.M., 1997, Occurrence of selected herbicides and herbicide degradation products in Iowa's ground water, 1995: Ground Water, v. 35, n. 4, p. 679-688.
Kross, B.C., and others, 1990, The Iowa State-wide rural well-water survey -- Water-quality data, initial analysis: Iowa Geological Survey Technical Information Series Report 19, 142 p.
Libra, R.D., Hallberg, G.R., and Hoyer, B.E., 1987, Impacts of agricultural chemicals on groundwater in Iowa: in Fairchild, D.M., ed., Ground water quality and agricultural practices: Lewis Publisher, Inc., Chelsea, MI, p. 185-217.
Potter, T.L., and Carpenter, T.L., 1995, Occurrence of alachlor environmental degradation products in groundwater: Environmental Science & Technology, v. 29, p. 1557-1563.
Prior, J.C., 1991, Landforms of Iowa: Iowa City, University of Iowa Press, 153 p.
Roberts, L.M., Jones, J.L., 1996, Pesticides found in ground water below orchards in the Quincy and Pasco Basins: U.S. Geological Survey Fact Sheet 171-96, 4 p.
U.S. Department of Agriculture, 1995, Agricultural chemical usage: 1994 field crops summary. National Agricultural Statistics Service and Economic Research Service. U.S. Dept. of Agric., Report Ag CH 1 (95).
Vroomen, H., 1989. Fertilizer use and price statistics, 1960-1988. Economic Research Service, U.S. Department of Agriculture, ERS Statistics Bulletin 780, 56 p.