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The high plains aquifer system, which underlies nearly 85 percent of the state of Nebraska, supplies about 95 percent of all groundwater used in Nebraska. Agricultural activities in the state use most of the groundwater (94 percent), while domestic and commercial users also depend heavily on this groundwater source. About 84 percent of the state's public drinking water supplies are from groundwater (Comfort, Shea, and Roeth 1994; Exner and Spalding 1990). With such high dependence on groundwater preserving groundwater quality is of crucial importance.
Intensive agriculture characterizes this region, especially in the Central Nebraska Basin (CNB), in part because of the good irrigation supplies provided by the Middle Platte alluvial aquifer system. Nearly one-third of the cropland in the CNB is irrigated and 50 percent of all cropland is planted to corn. About 729,000 tons of nitrogen, 184,000 tons of phosphorus, and 33 million pounds of pesticides (45 percent of which is atrazine) are applied annually on Nebraska's cropland. The intensive application of nutrients and chemicals every year creates the potential for nonpoint source contamination, which is a major concern for communities. Exner and Spalding (1990) analyzed 5,826 groundwater samples from the Nebraska basins for nitrates and 2,260 samples for pesticides, and found that about 20 percent of the samples had nitrate-nitrogen concentrations exceeding the drinking water Maximum Contaminant Level (MCL) of 10 parts per million (ppm) and 12.4 percent of the samples had detectable levels of atrazine.
The U.S. Environmental Protection Agency, Region VII, is working with the Nebraska Department of Environmental Quality, Nebraska's Natural Resource Districts (NRDs), and other partners to develop a comprehensive ecosystem approach to manage the Platte River Basin, which is one of the five national case study sites for multiple stressor-based ecological risk assessments. One of the objectives of the Platte River Basin program is to evaluate agricultural economic and environmental tradeoffs resulting from commonly adopted crop production systems and their contributions ton nonpoint source nutrient and chemical pollution.
The research team at the Center for Agricultural and Rural Development (CARD), Iowa State University, initiated an effort to develop a comprehensive economic and environmental modeling system to study the effects of alternative crop production systems on edge-or-field nonpoint source loadings of agricultural nutrients and chemicals using the field-level survey data collected under the (NB Area Study project . The CNB is also one of the US Geological Survey's National Water Quality Assessment Program (NAWQA) sites NAWQA is designed to assess historical current, and future water quality conditions in representative river basins and aquifers nationwide.
This report describes the integrated modeling system that addresses the economic and environmental tradeoffs associated with agricultural nonpoint source pollution management in the CNB study area and provides a brief description and summary of the field-level Area Study survey data that will operationalize this system A brief description of policy, economic, and environmental models that make up the integrated system is also provided Use of an integrated modeling system for evaluating the environmental effects of alternative agricultural production systems, fer a given set of resource and other sitespecific environmental conditions, is a widely used procedure. Studies by Wossink et al (1992) and Teague, Bernardo, and Mapp (1995) at the farm level by Gardner and Young (1988), Setia and Piper (1992), and Lakshmmarayan, Johnson, and Bouzaher (1995) at the watershed level; and by Bouzaher et al. (1995), Lakshminarayan, Bouzaher, and Shogren (1996). and Lakshminarayan and Babcock (1995) at the regional level have used integrated modeling systems to assess such tradeoffs resulting from agricultural practices.