Nonpoint sources of water contamination and their impacts on sustainabimty

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1 Freshwater Contamination (Proceedings of Rabat Symposium S4, April-May 1997). IAHS Publ. no. 243, Nonpoint sources of water contamination and their impacts on sustainabimty RAMESHWAR S. KANWAR Department of Agricultural and Biosystems Engineering, Iowa Sate University, Ames, Iowa 50011, USA Abstract About 20 years ago, it was a popular belief that the goals of economic development and environmental protection were mutually exclusive. Today, it is believed that a better understanding between development and the environment is needed. Contamination of surface and groundwater sources by fertilizer and pesticides has been well documented in the United States. Agriculture is viewed as a significant nonpoint source of groundwater contamination, which presents a difficult problem for the design of governmental methodologies to prevent pollution. About six years ago, the federal government launched an initiative to protect water sources without jeopardizing the economic vitality of U.S. agriculture. The hypothesis was that farmers must change production practices to reduce or avoid contamination of surface and groundwater sources. The present paper summarizes the results of several field-scale studies conducted at Iowa State University to reduce contamination of surface and groundwater sources by developing better tillage and chemical management systems. Results indicate that chemical management practices, such as multiple nitrogen applications at appropriate timing and banding of pesticides, in conjunction with conservation tillage systems can definitely reduce the potential for contamination of water resources. Application of these findings across the nation would save millions of dollars on chemical use, while maintaining the quality of water resources at acceptable levels. INTRODUCTION Recent experience in the developed countries has shown clearly that modern agricultural activities, through the increased use of chemicals, are contaminating surface and groundwater sources of water. Groundwater is a major resource and there is about 67 times more freshwater stored underground within drillable distance than in all the rivers and lakes of the world (Bouwer, 1993). The increased use of agricultural chemicals has contributed significantly to agricultural productivity but has been the source of much controversy recently because of the perceived health risks posed by the presence of nitrate, pesticide, and other compounds in drinking water. This has resulted in groundwater quality legislation by several states in the USA. High concentrations of nitrate-nitrogen (N0 3 -N) in well water was first recognized as a health problem in 1945 when two cases of infant methemoglobinemia (bluebaby syndrome) were reported in Iowa (Comly, 1945). Some evidence exists that high N0 3 -N ingestion is involved in the etiology of human cancer (Fraser et al., 1980; Formant al., 1985).

2 188 Rameshwar S. Kanwar The presence of agricultural chemicals (primarily N0 3 -N and pesticides) in the drinking water sources has raised public concerns about health safety. These concerns have led to regulatory or voluntary action to reduce the transport of these chemicals to surface and groundwater. The U.S. Environmental Protection Agency has established enforceable drinking water standards called Maximum Contaminant Levels (MCLs) for N0 3 -N and several herbicides. Many times, the presence of pesticides in water sources is much below the lifetime health advisories, but even their presence in the water supplies is objectionable to the public. In addition to concern over the acute and chronic toxicity of pesticides, their potential as carcinogens and their presence in groundwater sources have raised questions about their continued use in agriculture. Groundwater is the drinking water source for 50% of the U.S. population, while 80% of the rural population relies on groundwater. Some 86% of the total water resources of the U.S. are contained in groundwater aquifers (CAST, 1985). Because of public concerns, water quality monitoring programs have focused on the presence of N0 3 -N and pesticides in public water supplies. Recent studies in Iowa (Hallberg, 1986; Kross et al., 1993) and in other parts of the U.S. (Fairchild, 1987) have demonstrated that NO a -N and pesticides are present in groundwater as a result of agricultural activities. It is generally presumed that agricultural chemicals found in groundwater are applied to the soil and move through the soil and into the aquifer by mass flow and groundwater recharge. A better understanding of groundwater contamination mechanisms is needed to develop better management systems in order to protect groundwater aquifer systems. Research is needed to develop simple and rapid techniques to demonstrate how agricultural chemicals can move to aquifer systems. The purpose of this paper is to present summaries of various studies initiated at Iowa State University on developing best management practices to minimize the impact of agricultural systems on water quality and to recommend solutions to protect the environment. This paper also summarizes some of the Best Management Practices that should help to protect surface and groundwater sources. METHODS AND MATERIALS Several studies are currently underway and several more have been planned at Iowa State University to develop an understanding of water and chemical transport through the porous media of the soil and their potential on water contamination. Two main ongoing research projects on water quality research are summarized below. In one of the projects, a long-term study was initiated in 1984 at the Iowa State University Agronomy and Agricultural Engineering Research Centre in Boone, Iowa. The site has less than 2% slope and has eight established subsurface drains (each draining an area of c. 0.4 ha) which were intercepted in 1984 to collect drain water samples for N0 3 -N and herbicide analyses. Subsurface drain flow rates were monitored by installing a float-activated continuous water stage recorder and a calibrated V-notch weir on each of the intercepted subsurface drains. Subsurface drainage water samples were collected three times a week for water quality analyses if tiles were flowing. These eight plots were cropped to continuous corn using no-till and conventional tillage systems. Two replications of two tillage systems, comprising

3 Nonpoint sources of water contamination and their impacts on sustainability 189 no-till (NT) and conventional tillage (CT), and two N fertilizer management practices, comprising a single application of 175 kg ha" 1 (SA, 175 kg ha" 1 ) and three multiple applications of N-fertilizer totalling 125 kg ha" 1 (MA, 125 kg ha" 1 ), were used for this experiment. For multiple N-applications, the first application of 25 kg ha" 1 was made at the time of planting, a second application of 50 kg ha" 1 was made in June, and the last application of 50 kg ha" 1 was made in late June or July. In the second project, long-term tillage experiments were established in 1977 at the Iowa State University Northeast Research Centre, Nashua, Iowa on a 15 ha area with 36 plots, each 0.4-ha in size. Soils at the site are predominantly fine loam. These soils have seasonally high water tables and require subsurface drainage. A tile drainage system was installed in 1979 in all 36 plots to minimize the effect of high water tables on crop growth. A trenchless drain plough was used to install the centre tile line (passing through the middle of the plot), but tile lines between plot boarders were installed with a trencher at a depth of 1.2 cm and were spaced 29 m apart. Tillage treatments included moldboard plough, chisel plough, ridge-tillage and notillage systems. Crop rotation treatments included continuous-corn and corn-soybean rotations. Crop rotations and tillage plots were replicated three times in a split-plot experimental design. Herbicide, insecticide, and fertility treatments have been the same since Continuous corn received 200 kg N ha" 1, and the corn-soybean rotation received 168 kg N ha" 1 in the corn year. No nitrogen was applied in the year soybeans were planted in the soybean-corn rotation. The continuous-corn treatment received Lasso + Atrazine at kg ha" 1 and Counter for rootworm control. Corn in the corn-soybean rotation received Lasso + Bladex at kg ha" 1 and no insecticide. Soybean plots received Lasso + Metribuzin at kg ha" 1. In 1988, the middle tile lines (10 cm in diameter) of all the plots were intercepted at the end of the plot and connected to solid 5 cm diameter pvc pipes. These solid pvc pipes were brought to a central location where they were connected to individual sump pumps for measuring subsurface drainage (tile flow) and collecting water samples for chemical analyses. To monitor tile flow continuously, each tile sump has a 110 V effluent pump, water flow meter, and an orifice tube to collect water samples for water quality analysis. For N0 3 -N sampling, the frequency of sampling averaged three times a week when tile were flowing. During the remaining part of the year, sampling frequency did not exceed more than once a week when tile lines were flowing. Any unusual rainstorm was sampled for both N0 3 -N and pesticide analyses. Pesticide and N0 3 -N analyses were conducted either at the National Soil Tilth Laboratory in Ames or at the University of Iowa Hygienics Laboratory in Iowa City. RESULTS AND DISCUSSION Figures 1 and 2 show N0 3 -N concentrations in the tile water for 1990 and 1991, respectively. These figures reveal that N0 3 -N concentrations in tile water under notill conditions with three multiple applications of N, at a lesser total rate of 125 kg ha" 1, were considerably lower in comparison with plots receiving a single, higher application rate of 175 kg ha" 1. Similar trends were observed in 1986 and Due to severe dry conditions, only a few drainage water samples could be collected in 1985 and 1989 since most of the tiles did not flow. The average N0 3 -N

4 190 Rameshwar S. Kanwar CTSA, 175Kg-N/ha NTSA, 175Kg-N/ha CTMA, 125Kg-N/ha NTMA, 125Kg-N/ha Fig. 1 N0 3 -N concentration in subsurface drainage water for 1990 as a function of tillage and N-fertilizer. concentrations in tile water for 1990 (a wet year) were 51.4, , and 11.6 mg l" 1 under CTSA, NTSA, CTMA, and NTMA, respectively. This shows that N management systems have a definite impact on the quality of shallow groundwater. Table 1 shows that N0 3 -N concentrations in the drain water were significantly higher under continuous corn in comparison with the corn-soybean rotation for all tillages. Three year ( ) average N0 3 -N concentrations in drain water from moldboard plough plots were significantly higher in comparison to the no-till and ridge-till plots. Of concern, was the fact that yearly N0 3 -N concentrations of 10 mg l" 1 (a drinking water standard in the United States) in tile flow was exceeded by nearly all the samples for each tillage system and crop rotation. The yearly total NO3-N losses in drain water ranged from 9.1 kg ha" 1 in 1992 to kg ha" 1 in Three year average ( ) N0 3 -N losses in drain water were much higher under continuous corn in comparison with the corn-soybean rotation. Although N0 3 -N concentrations were greater under conventional tillage than under a no-till system, total N0 3 -N losses in subsurface drain flow were higher under the notill and chisel plough systems because of the greater volume of water moving through the soil. Best management practices for environmental enhancement Best management practices (BMPs) are practices that can be used to control nonpoint source pollution and are economically, socially, and environmentally acceptable. Nonpoint source BMPs can be divided into two groups: (a) Chemical selection and rates of application for efficient chemical use:

5 Nonpoint sources of water contamination and their impacts on sustainability o GTSA, 175 Kg-N/ha m NTSA, 175 Kg-N/ha A CTMA, 125 Kg-N/ha + NTMA, 125 Kg-N/ha S Time in Julian Days I. -I 1. l.l li, it.1 It. I J L Fig. 2 N0 3 -N concentration in subsurface drainage water for 1991 as a function of tillage and N-fertilizer management practice formulation of chemical, - rates of application; reduced application rates, - placement of chemicals (banding, broadcast, incorporation), - timing of applications; split-n application. (b) Tillage, crop, land, and water management: - conservation tillage systems, cropping systems with legume crops in rotations, contour farming, terracing, strip cropping, Table 1 Average N0 3 -N concentration and annual N0 3 -N loss in the water flowing into the subsurface drainage system. Crop rotation and tillage Continuous corn Chisel plough Moldboard plough Ridge-till No-till NO3-N concentration (mg ') NO3-N loss (kg ha- 1 ) Rotation corn Chisel plough Moldboard plough Ridge-till No-till

6 192 Rameshwar S. Kanwar - filter strips, drainage and water table management, - irrigation systems with better chemical use, sludge and manure application. These BMPs could be used for site specific conditions to reduce the contamination problem from nonpoint source. SUMMARY Studies have been conducted recently to understand the effects of Best Management Practices on the environmental fate of chemicals and their impacts on the contamination of water resources. However, the complex chemistry of agricultural chemicals and the variations in time and space of soil-water-plant-weather systems make it very difficult to apply these studies on a large scale. Therefore, there is a strong need for conducting large scale, basin-type studies with various combinations of BMPs for local conditions. These kinds of studies should help to demonstrate that practices that are known to be effective on a small scale in reducing contamination of water resources can be beneficial at a watershed scale. The water quality initiative taken at Iowa State University should help in developing and evaluating new BMPs in protecting our water resources. Ongoing research efforts in the USA will result in developing new and innovative practices which should be economical, socially acceptable, and environmentally sustainable. REFERENCES Bouwer, H. (1993) Sustainable irrigated agriculture: Water resources management in the future. Irrigation J. 43, Comly, H. H. (1945) Cyanosis in infants caused by nitrates in wellwater. J. Am. Med. Assoc. 129, Council for Agricultural Science and Technology (CAST) (1985) Agriculture and groundwater quality. CAST Report no. 103, Ames, Iowa. Fairchild, D. M. (1987) A national assessment of groundwater contamination from pesticides and fertilizers. In: Groundwater Quality and Agricultural Practices, Lewis Publishers, Inc., Chelsea, Michigan, USA. Forman, D., Al-Dabbagh, S. & Doll, R. (1985) Nitrates, nitrifies, and gastric, cancer in Great Britain. Nature 313, Fraser, P., Chilvers, C, Beral, V. & Hill, M. J. (1980) Nitrate and human cancer: a review of the evidence. Int. J. Epidemiol. 9, 3-9. Hall, J. K., Pawlus, M. & Higgins, E. R. (1972) Losses of atrazine in runoff water and soil sediment. J. Environ. Qual. 1, Hallberg, G. R. (1986) Overview of agricultural chemicals in groundwater. In: Agricultural Impacts on Ground Water, National Water Well Association, Worthington, Ohio, USA. Kross, B. C, Hallberg, G. R., Bruner, D. R., Cherryholmes, K. & Johnson, J. K. (1993) The nitrate contamination of private well water in Iowa. Am. J. Pub. Health 83(2),