Ground Water Quality and Agricultural Practices

Deborah Fairchild

• Publisher: CRC Press
• Year: 2020
• Print ISBN: 9780873710367
• eBook ISBN: 9781000157437
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Agriculture
• Index: Technology & Engineering

This outstanding reference book deals with effects of various agricultural practices on ground water quality and usage; and ground water management strategies for protection of ground water affected by agriculture.

CHAPTER 1

THE U.S.D.A. AGRICULTURAL RESEARCH SERVICE COMMITMENT TO GROUND WATER RESEARCH

by

Bobby A. Stewart

It is a complicated task—keeping up with the research carried out by a national organization like the Agricultural Research Service (ARS). Therefore, I am going to take a few minutes to make some general comments about our planning strategy in this present climate of increasing fiscal constraint. Then, I will discuss the ARS commitment to ground water research.

As a thumbnail sketch of ARS, we have about 8,200 employees—2,700 of them scientists—working on about 3,000 different projects at a given time. This research to serve the American farmer and rancher is being carried out at 130 different locations in the United States and eight foreign countries.

Our current budget of $478 million has remained relatively constant, when adjusted for inflation, over the past decade. So, our six-year implementation planning strategy has been developed around the concept of constant dollar funding assumptions. By this, I mean that intended increases in funding are equaled by intended decreases in funding. This constant dollar assumption forces some very difficult decisions about which programs expand and which programs receive less support or are drastically cut. This approach is helping us accommodate the constraints imposed by Gramm-Rudman-Hollings. We expect to experience further belt tightening down the road.

The projects in the ARS planning strategy reflect our emphasis on mission-oriented, fundamental, long-range, high-risk research. They also reflect our responsiveness to action agencies, user groups, and the U.S. Congress. The ARS Program Plan includes six objectives that form the strategy: research to improve soil and water conservation; plant production and protection; animal production and protection; commodity conversion and delivery; human nutrition; and integration of systems, using computer technology.

Research on Soil and Water Conservation

There is increasing evidence that the nation’s ground water resources are becoming affected by man’s activities, including those associated with agriculture. Advances in analytical chemistry often allow detection of chemical concentrations at levels so low that information is lacking on toxicological significance. However, monitoring results indicate that agricultural chemicals are present in ground water.

Even if concerted efforts are made, the extent of the problem may not be adequately assessed for several years. Since about one-half the total United States population and 95 percent of rural households depend on ground water for drinking supply, research programs are needed immediately for three objectives:

(1)  to define the extent of the problem;

(2)  to develop procedures for estimating the potential loading of chemicals to ground water systems; and

(3)  to develop alternative management systems to alleviate or minimize the occurrence of agricultural chemicals in ground water.

Movement through the vadose and ground water zones can be very slow, anaerobic conditions exist, and biological and chemical processes that degrade contaminants may be much less effective in ground water than in surface soils. Therefore, strategies that prevent chemical entry into ground water will be much more effective and less costly than ground water clean-up strategies.

Agriculture has a tremendous stake in preventing ground water contamination. Chemicals are indispensable in modern agriculture, but their improper use may lead to serious water quality problems that could impair ground water use for crop and animal production and domestic water supply.

When all agricultural chemicals and quantities used are considered, the creation of water quality problems is probably limited to a relatively few compounds or combinations of conditions. The potential for pesticide leaching appears related to exceeding limits on solubility, volatility, hydrolysis, and photolysis of the pesticide as well as the ground water recharge rate. However, the problems identified arouse public concern for the entire spectrum of chemical use, and this public concern has profound implications for American agricultural practices. This, then, is the crux of the dilemma. It is impossible to meet the rapidly growing world needs for agricultural products without the use of chemicals.

Agricultural chemical usage comes with the responsibility for developing farm systems that have minimum impact on ground water quality. Since agriculture is a major ground water user for irrigation, livestock and drinking water, agriculture has a vested interest in protecting its supply.

Information, technology, and analytical and predictive methods are not sufficient to provide needed strategies for ground water resource protection. Solving the problem requires the development of methods to identify chemical and salt sources, transport routes and control measures. We need to determine the efficacy of these measures in controlling chemical and salt loss to ground water caused by agricultural activities.

Although there has been considerable research on the fate of chemicals in soils, streams, and impounded waters, serious gaps exist in data bases, basic concepts, and the understanding of processes that define ground water quality. Proper implementation of regulatory decisions and the development of alternate management systems require that these gaps be filled.

Models based on sound concepts and validated field data will be needed to predict potential chemical loading to ground water systems under different management and climatic scenarios. These models must also answer questions relative to efficacy and crop production requirements. A proposed management system cannot be considered as a viable alternative unless basic production goals are met.

Only a small fraction of the enormous variety of chemicals used in agriculture is responsible for documented ground water quality problems. The problems identified are serious, and they demand our attention—but they could have been much worse. That they are not more aggravated is due in large part to recent progress made in our knowledge of their environmental reactions and appropriate application rates and techniques.

The registration process now administered by the U.S. Environmental Protection Agency prevents most pesticide impacts before they occur. Persistence, mobility, and other environmental effects are all limited—or at least defined—by current registration procedures. The pesticide registration process has, in general, accomplished its goal of keeping chemicals with potentially serious environmental impacts out of the marketplace.

The ARS has been engaged in research on the linkage between agriculture and environmental quality for more than a quarter of a century. Contributions to environmental improvement have come both from research on natural resource management and from advances in crop production and protection technologies.

Current ARS research continues to focus on improved soil and water management and on more effective and efficient use of agricultural chemicals. A substantial component of the ARS program contributes indirectly to the development of technologies for improving ground water quality. Ongoing research will provide a sound scientific basis for evaluating the effect of changes in cropping, culture, tillage, and water management on ground water quality. It will also provide better guidelines for improving the formulation and application of agricultural chemicals.

The current ARS commitment to soil and water conservation research represents about 13 percent of the total agency budget—or a little over 60 million dollars. The ARS planning strategy calls for an increase to 14 percent of the budget for this research over the next 6 years. The present ARS commitment to ground water quality research is about 12 million dollars, or about 20 percent of the funds reserved for soil and water research. The ARS planning strategy calls for increased emphasis on ground water quality research in the years ahead.

Research on Nutrients, Pesticides, Salinity, and Modeling

Nutrient research at a number of ARS locations relates indirectly to ground water quality. For example, at some locations scientists are discovering ways to more efficiently use plant nutrients. This research increases the producer’s profit and improves ground water quality by minimizing excess nutrient content in the root zone. Results of current irrigation and drainage research will better define the effect of water management techniques on nutrient movement in the soil. At some locations, scientists are conducting research on nitrogen transformations in the root zone, near-stream zone, wetlands and impoundments. Such nitrogen transformations are crucial to the movement and impact of nutrients in ground water systems.

Research is also underway to determine the effect of nutrient transport and reactions in ground water systems on the nutrient content of streams and down-gradient aquifers. ARS is beginning to explore the geochemistry of deep ground water as affected by land use. Also, models are being developed to describe nutrient movement in saturated and unsaturated flow systems and to better define mass balances.

ARS has a basic research program on the detection, movement, sorption, binding, plant uptake, microbial metabolism, and volatility of pesticides in soils and related systems. Unique pesticide problems exist at certain specific geographic locations. At several locations, ARS is conducting limited research directly related to pesticide movement in the vadose zone and underlying aquifers. This research provides soil-water partition coefficients useful for predicting pesticide leaching into the root zone and eventually into ground water.

Herbicide persistence, leaching, and possible ground water contamination are being investigated under conservation tillage conditions. The possible transmission of pesticides via ground water into the Chesapeake Bay is being investigated. Public water supplies and reservoirs in central Maryland are being monitored for the presence of herbicides.

Control of salts in the root zones of irrigated lands is necessary if the productivity of these lands is to be maintained. Leaching is the only practical method of removing excess salt. The leachate or deep percolation water necessary to remove these salts moves and returns to the river as subsurface return flow, or it moves down to the underlying ground water. The ARS program on ground water salinity is directed toward improved understanding and modeling of water and chemical transport. The objective is to more accurately assess and control the contribution of irrigated agriculture to the total salt loading of aquifers.

The principal processes under investigation include the kinetics of salt precipitation and dissolution in soils, ion exchange, carbonate kinetics, and the dispersion and diffusion of salts in the soil profile. Techniques are being developed to use isotope ratios to trace the origin of leachates from natural or man-made sources. In addition, the potential for reducing the “leaching fraction” of applied irrigation water is being evaluated.

ARS is involved in analytically simulating most of the physical and chemical processes affecting chemical movement in the environment. Many of these models are related to ground water quality, even though not specifically developed for that purpose. Major models such as EPIC (Erosion Productivity Impact Calculator), SWRRB (Simulation for Water Resources in Rural Basins), SPUR (Simulation of Production and Utilization of Rangelands), CREAMS (Chemicals, Runoff, and Erosion from Agricultural Management Systems), and SWAM (Small Watershed Model) all have components that relate to ground water quality. All of them simulate the movement of water in the root zone; and the SWAM model includes a complete ground water quality submodel.

Most ARS scientists include models of the system they are studying as part of their research programs. The models related to ground water quality include pesticide models that simulate adsorption-desorption, volatilization, microbial decomposition, and related processes. Transport in both the vadose and ground water zones has been simulated. The movement and concentration of salts in both natural and irrigated lands have been modeled.

The transport processes of these subsystems are dependent upon accurate representation of water movement since it is the transporting medium. The movement of water is well described in most mediums and subsystems; infiltration, unsaturated and saturated flow, in two and three dimensional format and in stochastic as well as deterministic settings. Many of the models have been developed principally as descriptions of the physical processes, but others are being developed with the planner or manager in mind.

Summary

In summing up, I would remind you that the complexity of the area of ground water quality research means that there are a large number of topics that must be resolved. Among agriculturally related ground water quality problems, I believe three stand out as most important. They are:

(1)  occurrence of pesticides in ground water;

(2)  occurrence of nutrients in ground water; and

(3)  irrigation driven salt-water migration.

Major efforts are needed to ensure long-term good ground water quality. The ARS will play a major role in future ground water quality research and is well qualified to conduct multidisciplinary research, to identify ground water quality issues and develop economical viable management systems to alleviate present concerns and prevent the development of future problems.

CHAPTER 2

NATIONAL SURVEY OF PESTICIDES IN DRINKING WATER WELLS

by

Jerry Kotas

The U.S. Environmental Protection Agency (EPA) is planning to conduct a nationwide survey of pesticides in drinking water wells over the next two years. This project summary explains the reasons for conducting the survey, how the survey will be designed and conducted, and the current status of the survey planning effort as of July 1, 1986.

Why is a Survey Needed?

Pesticides present in drinking water can pose dangers to human health if ingested. Current indications are that some pesticide contamination of drinking water wells does exist. However, no one knows exactly which pesticides are present in wells, how high their concentrations are, and which wells are contaminated. To date, some analyses of pesticides in ground water have been undertaken, but they were limited to a small number of pesticides and specific geographic areas. For example, the State of California completed a ground water monitoring program in 1983. Four pesticides, EDB, DBCP, Simazine, and Carbofuran, were monitored in the San Joaquin Valley and Riverside County.

Since 1975 urban water systems have been required to monitor for six pesticides: endrin, lindane, methoxychlor, toxaphene, 2,4-D, and 2,4,5-T. Recent evidence indicates a larger problem of pesticides in ground water; for example, EPA found that 17 pesticides were detectable in the ground water of 23 states as a result of normal land application (Office of Ground Water Protection, 1986).

The National Survey of Pesticides in Drinking Water Wells is a major component of the agency’s overall effort to understand and characterize the problem of agricultural chemicals in ground wa...

Table of contents

• Cover
• Title Page
• Copyright Page
• Dedication
• Preface
• Table of Contents
• Contributors
• List of Table
• List of Figure
• 1 The U.S.D.A. Agricultural Research Service Commitment to Ground Water Research
• 2 National Survey of Pesticides in Drinking Water Wells
• 3 Water Conservation for More Crop Production in the Great Plains
• 4 Ground Water Conservation Techniques: Potential Impacts on Water Usage and Quality
• 5 Conjunctive Use of Surface and Ground Water in the South Platte River Basin: A Case Study of the Central Colorado Water Conservancy District
• 6 Ground Water Recharge for Oklahoma—An Analysis of Past and Future Methodology—
• 7 Effects of Irrigation Practices on Stream-Connected Phreatic Aquifer Systems
• 8 Ground Water Contamination from Saltwater Intrusion and Limitations on Agricultural Activities
• 9 Economic and Environmental Impacts of Using Municipal Sewage Effluent for Agricultural Production
• 10 Soil Testing as a Guide to Prudent Use of Nitrogen Fertilizers in Oklahoma Agriculture
• 11 Efficient Nitrogen Fertilization in Agricultural Production Systems
• 12 Nitrates and Pesticides in Ground Water: An Analysis of a Computer-based Literature Search
• 13 Behavior and Subsurface Transport of Agrochemicals in Conservation Systems
• 14 Impacts of Agricultural Chemicals on Ground Water Quality in Iowa
• 15 Assessing Some Potentials for Changing Agronomic Practices and Improving Ground Water Quality—Implications from a 1984 Iowa Survey—
• 16 Assessment of Empirical Methodologies for Predicting Ground Water Pollution from Agricultural Chemicals
• 17 Investigation of Nitrate Contamination in Shallow Ground Waters Near Woodward, Oklahoma
• 18 Saline Seep on Wheatland in Northwest Oklahoma
• 19 A National Assessment of Ground Water Contamination from Pesticides and Fertilizers
• 20 Quantitative Studies of Biodégradation of Petroleum and Some Model Hydrocarbons in Ground Water and Sediment Environments
• 21 Interactive Simulation of Chemical Movement in Soil
• 22 Regulation of the Agricultural Utilization of Sewage Sludge in New Jersey
• 23 Incentives and Institutions to Reduce Pesticide Contamination of Ground Water
• 24 Poultry Manure Management and Ground Water Quality: The Delaware Solution
• 25 Nitrogen and Ground Water Protection
• 26 Ground Water and Agriculture: Addressing the Information Needs of Pennsylvania’s Chesapeake Bay Program
• 27 Developing a State Ground Water Policy in the Corn Belt: The Iowa Case
• INDEX