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View the documentChapter 15:Environmental Impacts

Chapter 15:Environmental Impacts

Chapter 15-
Environmental Impacts

by B.A. Stewart and Wyatte Harman

Abstract

Agricultural activities affect the environment in four general ways: (1) use of chemicals to increase agricultural production, (2) excessive and/or inefficient use of water, (3) injudicious agricultural practices, and (4) conversion of lands to expand cultivated crops. The extent to which the environment will be affected by agriculture in the future will depend on many factors, perhaps the greatest of which will be the degree of pressure placed on soil and water resources to meet demand for food and fiber. It is clearly recognized that the environment will be changed as land use and crop production practices evolve. The impacts will not, however, always be negative because many agricultural practices lead to an enhancement of the environment.

This paper examines trends and projections of future requirements for food and fiber, the likely changes in land use that may be required to meet these demands, and the possible impacts of these land use changes on the environment.


Agriculture in general, and irrigated agriculture in particular, has impacts on the environment, positive or negative. Irrigated crops account for more than 25 percent of the total value of crop production in the United States, but require only 14 percent of the cropland. Irrigated acreage has increased dramatically, growing from about 18 million acres in 1939 to 37 million in 1958 and 58 million in 1977. At the same time, cropland acreage dropped from 531 million acres in 1939 to 449 million in 1958 and 413 million in 1977. A positive impact of the increase in irrigated acreage is that the overall quality of cropland has improved because some erodible cropland has been put to other uses. However, high rates of fertilizers and pesticides sometimes used on irrigated lands can degrade the environment. The conversion of lands into irrigated agriculture may also have diminished wildlife habitats.


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Irrigated acreage is expected to increase in the future, but at a slower rate because of competition for limited water supplies and the depletion of groundwater in several areas. The 1978 National Water Assessment projected that an additional 6.9 million acres would be brought under irrigation by the year 2000.[1]

Considerable attention has been given in recent years to the effect of agriculture on water quality. Stewart et al. (1975), Unger (1979), Bailey and Waddell (1979), and White and Plate (1979) are among those who have assessed the potential for pollution and have suggested appropriate management practices.[2] Environmental effects of agricultural activities arise from four general sources: (1) use of chemicals to increase agricultural production, (2) excessive and/or inefficient use of water, (3) injudicious agricultural practices, and (4) conversion of lands to expand agriculture.

The extent to which the environment will be affected by agriculture in the future will, of course, depend on many factors. Perhaps the greatest single factor will be the degree of pressure placed on the soil and water resources to meet the demand for food and fiber. Therefore, consideration will be given in the following discussion to the trends and projections concerning future requirements for food and fiber, the likely changes in land use that may be required to meet these demands, and the possible impacts of these land use changes on the environment.

Projected Demands for Food and Fiber

World food production is projected to increase 90 percent over the 30 years from 1970 to 2000. During the same period, population will increase about 50 percent. While these projections indicate a per capita increase in food, world distribution problems will remain. The bulk of the increase will continue to go to countries that already have a relatively high level of food consumption. Meanwhile, food will remain scarce or actually decline below present inadequate levels in many of the less developed countries.

Over the next 20 years, USDA projects the demand for U.S. agricultural products to increase by 60 to 85 percent over the 1980 level. The increased demand will be due to growth in exports, increased domestic use for conventional purposes, and for ethanol production. However, these projections are based on the assumption of constant real prices. A significant rise in real cost


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of agricultural products in general, and food in particular, could drastically alter demand. Export demand will have the greatest impact because presently the harvest from one-third of U.S. cropland is exported, and USDA projects the volume of U.S. exports by the year 2000 to grow by 140 to 250 percent above the 1980 level.

The projection that demand for U.S. agricultural products will increase suggests that there will be major changes in land use. Negative impacts on the environment can be minimized or avoided if these changes in land use can be seen in advance and adequately planned.

The production of food and fiber in the United States has increased dramatically during the past 40 years, even while the amount of cropland harvested declined by more than 20 percent. The primary reasons for this remarkable achievement have been the use of fertilizers and pesticides, a vast expansion of irrigated acreage, improved crop cultivars, and improved management practices. During the 1960s crop yields increased nationally at an average annual rate of 1.6 percent, which was sufficient to meet increased demands. However, during the decade of the 1970s, the average annual yield increase dropped to 0.76 percent, and three-fourths of the increased production had to be met by an increased acreage of cropland. After several decades of declining or stable cropland acreage, the 1970s saw an increase of more than 60 million acres in harvested cropland.

The National Agricultural Lands Study (1981) concluded that if the yield increase rate of the 1970s continued until 2000, and projected demands materialize, an additional 140 million acres of land would be required for the production of principal crops, or an increase of about 50 percent.[3] Even at the 1.6 percent yield increase rate of the 1960s, some 85 million acres of additional cropland would be required. While there is little consensus among the agricultural community as to the future rate of increase in yields, a good case can be made for a continued diminishing rate of increase due to rising costs of fuel, fertilizers, and other energy inputs; declining water supplies to sustain the growth in irrigated acreage that occurred during the past few decades; a lowering of the average quality of cropland as fragile lands are used for principal crops; and loss of soil productivity due to erosion and salination. Although there is enough land that could be shifted into cropland to meet the projected demands, even at the low growth rate of increased yields of the 1970s, the cost of food and fiber in real dollars may rise


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significantly since production incentives will be required to develop such an expanded crop acreage. Rising costs may, in turn, reduce demand. In view of these complexities, it is difficult to project with accuracy the additional cropland which will be required by 2000 to meet the demand for U.S. agricultural products. It seems safe to conclude, however, that the acreage requirements will increase.

Impacts of Land Use Changes on Soil, Water and Air Resources

Many Americans take soil and water resources for granted. There has been sufficient soil, and usually enough water, to grow all the food and fiber needed in the U.S., and then some. Most years, supplies of U.S. agricultural products have been sufficient to export to many foreign nations and still have a worrisome surplus. Soil and water resources are not without limit, however; they are finite and vulnerable to erosion and exploitation. Environmental impacts may vary, depending on physical and economic uses of soil and water resources; consequently, it is difficult to be specific in discussing the impacts of land use changes. Nevertheless, some of the issues can be reviewed.

Irrigated Lands

The 17 western coterminous states have some 49 million acres of irrigated land and account for over 85 percent of all the irrigated land in the United States. The environmental consequences of irrigating this land fall into two broad categories-water pollution and conservation of water and land resources.

Water pollution is a major concern in irrigated crop production because of the generally intensive use of fertilizers. Studies have shown that fertilizers and pesticides can be used very effectively with little or no negative environmental impact. Other studies, however, show that, under some conditions, the environment can be degraded. Nitrate leaching into groundwater supplies has been documented as well as the movement of nutrients and pesticides off the land with sediment. There is, nonetheless, reason to be optimistic; through the use of improved inputs and advanced management practices, environmental quality may be maintained or even enhanced. If the real costs of irrigation water, fertilizers, and pesticides continue to increase in relation to the value of the crops produced, farm operators will utilize inputs much more efficiently. Also, an increased awareness of potential hazards may lead to more careful use of inputs.


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Improved technologies are emerging in irrigated crop production. Of particular significance are irrigation scheduling programs that result in more efficient use of irrigation water. These can reduce leaching of nitrates and also reduce runoff and erosion. Reduced runoff, coupled with improved nutrient application methods, will also reduce losses of plant nutrients from irrigated fields. The use of lasers for more precise land leveling can also greatly improve water management under some conditions.

Nonirrigated Lands

There are about 155 million acres of nonirrigated cropland in the 17 western United States. A large part of this is in areas receiving less than 20 inches of average annual precipitation, where rainfall is often highly variable and sometimes intense. If irrigation becomes restricted either by limited supplies, uneconomic conditions, or by competition with other uses, expansion of dryland acres must increase. As nonirrigated cropland acreage increases, cropland quality will decrease because more and more marginal land will have to be utilized.

Currently, water and wind erosion soil losses average about 5 tons per acre in the United States. In some areas, such as portions of the Palouse Area in Washington, Oregon, and Idaho, the combination of steep slopes and seasonally intense rainfall have resulted in erosion rates of 50 to 100 tons annually. Erosion in excess of topsoil formation is the most critical concern. Even at lower rates of erosion, however, the environment can be negatively affected.

Wind erosion is a major problem for much of the nonirrigated cropland in the 17 western states and particularly in the Great Plains. In the Northern Plains (Kansas, Nebraska, North Dakota, and South Dakota) and Southern Plains (Oklahoma and Texas), annual sheet and rill erosion by water is about 3 tons per acre. Wind erosion amounts in Kansas, North Dakota, South Dakota, and Oklahoma are very similar to water erosion amounts. However, in Texas, wind erosion losses average 15 tons per acre, about five times greater than water erosion. Wind erosion is also high on Colorado and New Mexico croplands. If cropland acreage in these areas is expanded, erosion hazards will increase and improved management practices will be needed. Again, however, new technologies are emerging.

Conservation tillage is very effective in alleviating both wind and water erosion. Conservation tillage is defined as any tillage sequence which reduces soil or water loss compared to conventional tillage. Conservation tillage is synonymous with


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maximum or optimum retention of residues on the soil surface and the utilization of herbicides to control weeds where tillage is not or cannot be performed. In water deficient areas, conservation tillage generally also results in higher yields because of improved water conservation. Conservation tillage will result in increased usage of agricultural chemicals, particularly pesticides. Research and monitoring will be required to insure that the crop production systems developed do not impose a threat to the environment.

Sediment, which is clearly recognized as the most undesirable single pollutant, is significantly reduced by conservation tillage. The control of sediment will also, to a large degree, control nutrient and pesticide losses. Thus, conservation tillage offers real promise for enhancing the environment, improving crop yields, and reducing energy inputs. Conservation tillage has increased from about 30 million acres in 1972 to more than 100 million in 1982, but satisfactory cropping systems are still lacking in many areas. Among the 17 western states, the Northern Plains states led with 33 percent adoption of conservation tillage; Southern Plains states were lowest with only 6 percent. The Mountain and Pacific states were intermediate with 28 and 20 percent, respectively. The very low adoption rate in the Southern Plains states is disappointing because both wind and water erosion rates are high in that area and conservation tillage could significantly reduce these losses. Also, water is the main limiting factor in crop production, and conservation tillage can increase soil water storage. Present cropping systems do not lend themselves readily to conservation tillage systems, which is the primary reason for the lower adoption rate. The lack of suitable cropping systems for conservation tillage has been largely due to the limited availability of effective herbicides for the common crop sequences. Satisfactory systems and improved herbicides are now being developed, and there is reason to think that conservation tillage will be widely used in the future. The U.S. Department of Agriculture has projected that conservation tillage will be practiced on about 80 percent of the U.S. crop acreage by 2000. This should have very positive environmental impacts.[4]

Reversion of Irrigated Land to Dryland

Irrigation water will become limited or nonexistent in some areas as groundwater supplies are depleted or become unprofitable to use, and as other sources are partially diverted to other uses. Recreation, energy, municipal, and industrial uses will become increasingly competitive for water supplies. Each of


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these uses has definite impacts on the environment. Consequently, it is important that environmental safeguards be provided.

Declining Groundwater Supplies

Overdraft of groundwater in specific areas, particularly in the western United States, is causing concern because of the impact it has on the future of irrigated agriculture. Examples of overdraft areas are the San Joaquin Valley of California, central Arizona, and the Ogallala Aquifer area of the High Plains. Depletion of groundwater is not the only factor causing reversion of irrigated land to dryland in these areas. The cost of energy for pumping groundwater has risen in recent years much faster than the value of crops produced, and has made irrigation unprofitable in some cases. For example, high pumping lifts and sharp increases in prices for natural gas resulted in a sudden drop in irrigated acreage in the Trans-Pecos areas of Texas.

Significant amounts of irrigated cropland in overdraft areas will revert to dryland in future years. Because of its large size and severity of overdraft, particularly in the southern part, the Ogallala Aquifer area has received considerable attention in recent years. Therefore, it seems appropriate to look specifically at this area as a case study. The detailed studies being made on the area may not only lead to more efficient use of the remaining water in the aquifer, but also lead to better utilization of other aquifers as well.

The Ogallala Aquifer Area

A huge underground layer of sand, gravel, and silt saturated with millions of acre-feet of water, the Ogallala Aquifer underlies some 115 million acres of land, largely in six High Plains states. Before World War II, land in the High Plains was primarily used for producing cattle and dryland crops. Irrigation began in the early 1900s, but did not begin to accelerate until the late 1930s. Following World War II, and particularly during the great drought of 1951-56, irrigated acreage expanded rapidly. The combination of a seemingly unlimited supply of excellent quality water, highly fertile soils, newly developed hybrid grain sorghum and other crops, and a favorable climate resulted in tremendous expansion of agricultural production and associated agribusiness. In a matter of a few years, acreage irrigated from the Ogallala Aquifer accounted for more than 25 percent of all irrigated land in the United States. As irrigation accelerated, however, it


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became apparent that the aquifer was being mined at a rate far in excess of the rate it was being replenished by the sparse snowmelt and rain.

The Ogallala Aquifer has in recent years become of great concern to the nation and world, but particularly to the people whose livelihood is directly affected. The United States Congress initiated the six-state High Plains Study in 1976 to assess the present and future status of the aquifer. Research results and recommendations from the study were to be reported to the Congress in July 1982.

As a part of the High Plains Study, projections through time were made regarding dryland and irrigated acres by crop, value of agricultural output, input costs, employment, and income for each of the six states under a number of alternative development strategies. The baseline analysis was designed to project, from the base year 1977 to 2020, possible changes in the pattern of irrigated and dryland production and water use, by state, under the general assumptions that no new purposeful public action would be initiated to restrict or otherwise regulate irrigation water use in the area. Therefore, the baseline reflects future changes in acreages if no new voluntary or regulatory water management schemes are implemented and if no new water sources are developed. However, interactions between crop yields, water use, improved technology, declining well yields and rising pumping costs, competing crops and cultural practices were considered in the analysis. Mapp (1981) summarized the findings of the analysis and discussed some of the more important of the many assumptions required to perform the study.[5] Space does not allow full discussion of the assumptions, but we report a portion of the results here because of the important environmental implications of the projected changes.

Results from the High Plains Study

Data presented in Figure 15.1 for the High Plains region project a continued increase in irrigated acreage. There is a slight decrease between 1985 and 1990 which results from anticipated deregulation of natural gas prices. After 1990, however, increases in crop yields and real product prices outstrip further increases in energy prices, and irrigated acreage continues to expand. It is especially significant to note in Figure 15.1 that the amount of irrigation water pumped from the aquifer decreases markedly through the 1980s even though irrigated acreage is continuing to increase. After 1990, the water pumped


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image
[Full Size]

Figure 15.1
Projected Acres Irrigated and Acre-Feet Pumped
for the High Plains Ogallala Aquifer Area
Source: Adapted from H.P. Mapp, "The Six-State
Ogallala Aquifer Area Study: Baseline Results
for the Agricultural Sector," 1981.

increases somewhat in proportion to the increase in irrigated acreage. In 1977 about 1.5 acre-feet of irrigation water were pumped for each acre of land irrigated in the region; this is projected to decrease to 1.3 by 1985 and 1.2 by 1990, and then remain fairly constant. Water use will vary greatly between states, however, because of availability. For example, usage in Texas, where underground water supplies are becoming quite limited, is assumed to drop from 1.38 acre-feet per acre in 1977 to about 0.65 acre-feet per acre in 2020. This decreased usage in applied water for each acre of irrigated land is expected to result in marked changes in crops grown, irrigation application methods, and cultural practices.

Significant differences in water supply exist among the High Plains states that overlie the Ogallala Aquifer. The aquifer contains an estimated 21.8 billion acre-feet of water, which if evenly


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distributed would be about 190 acre-feet of water under each acre of land. Texas, Oklahoma, and New Mexico, however, contain approximately 30 percent of the aquifer area but only about 15 percent of the water, whereas Nebraska contains 36 percent of the aquifer area but 64 percent of the volume.

The baseline projections for the six states studied are shown in Figure 15.2. Nebraska is expected to continue to rapidly expand its irrigated acreage while other states show fairly sharp decreases, or remain constant. The projections for Nebraska also show that irrigated acreage will expand much more than dryland acreage will decrease. Consequently, large acreages of land presently used for purposes other than cropland will be brought under cultivation, much of it undoubtedly in sandy areas presently in grass. The large expansion of irrigated land in these areas, particularly on sandy soils, will present pollution potentials because of the marked increase in fertilizer and pesticide usage that will be associated with intensive crop production. Natural recharge of the aquifer is higher in this area than any other area in the region, and with added irrigation, the possibilities of leaching nutrients and salts into the aquifer will be greater. Good management systems which address pollution hazards will be needed.

Projections for Kansas and Texas show substantial decreases in irrigated acreage and corresponding increases in dryland acreage. The dryland acreage in Kansas is projected to increase even more than irrigated acreage will decline, which again indicates that total cropland acreage will have to come from somewhat marginal lands with perhaps higher than average erosion potential.

The data for Colorado and New Mexico (Figure 15.2), and Colorado in particular, suggest that irrigated acreage will decrease without an accompanying increase in dryland acreage. Therefore, much of the irrigated land in these areas is expected to go out of cultivation. In some areas within other states this will also happen; in many cases these will be sandy areas that were not in cropland until center-pivot sprinkler irrigation systems were installed. Much of this land will not be suitable for dryland farming, and unless special care is given, serious environmental consequences could be encountered. Wind erosion will be a major problem and revegetation of the areas will be very difficult, unless it is done before irrigation is stopped. A bill was introduced in the Nebraska legislature that would have required center-pivot irrigators to revegetate wind erosion-prone


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image
[Full Size]

Figure 15.2
Projected Acreage of Irrigated and Dryland Cropland
in Six States of the Ogallala Aquifer Area.
Source: Mapp, 1981.


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land before irrigation systems could be removed. Although it is unlikely a bill of such nature will be passed, its introduction recognized the potential environmental hazard of irrigated lands reverting to dryland.

In areas where cropland was primarily dryland-farmed prior to the time it was irrigated, the land can generally be returned to its former use without serious environmental impacts. The production from dryland areas will be extremely variable, ranging from fairly high yields in above average rainfall years to very low yields or even crop failures in drought years. There is very little likelihood, however, that widespread dust storms such as those that occurred during the "Dirty Thirties" will reoccur. For example, recently improved cropping methods and cultural practices result in more efficient storage of soil water during fallow periods. Large farming equipment developments allow more timely and effective cultivation. Better crop varieties are less prone to complete failure. Other technologies are also emerging that, when coupled together into integrated farming systems, are very effective in controlling erosion. This is not to say that there will not be localized areas where environmental hazards are acute, but the region as a whole is not expected to be seriously damaged.

The conversion of irrigated land to dryland in the High Plains states will result from either a declining supply of water, the inability to realize enough profit from irrigated farming to pay for the associated energy costs, or a combination of the two. If water availability is the primary constraint, the conversion of irrigated land to dryland will be gradual and will generally move from fully-irrigated to limited-irrigated to dryland. Limited irrigation will involve only one or two irrigations, or perhaps only preplant irrigations during the winter to reduce evaporation losses. This orderly conversion to dryland presents little environmental hazard.

The most serious environmental threat would result from a situation in which energy costs, or some other economic condition, causes a sudden abandonment of large areas of irrigated land. The most environmentally-critical areas, as already mentioned, would probably be sandy areas presently irrigated with center-pivot systems. These lands were broken out of native range due to economic incentives and generally have low dryland production potential. Unless some orderly plan is developed to revegetate these lands with permanent cover, serious environmental hazards will result. The most serious hazard, of course,


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would be wind erosion. Figure 15.3 shows the principal soils overlying the Ogallala Aquifer. The sandy soils that present the greatest environmental hazard are illustrated by crosshatched areas. The double crosshatched soil areas represent the most severe environmental hazard potential. Irrigated acreage has expanded substantially in some sandy areas in recent years. It is evident that if irrigated acreage expands further, as projected in the High Plains Study (Figure 15.2), much of the increase will likely occur on soils having a severe environmental hazard potential.

Similar problems occurred during the 1930s when many farmers abandoned sandyland farms near Dalhart, Texas. To alleviate the vast erosion from the area, the federal government bought the farms and charged the USDA Soil Conservation Service with the task of revegetating the land. These lands now are part of the National Grasslands managed by the U.S. Forest Service. Similar projects occurred in other parts of the Great Plains.

The discussion above points out some of the complexities of the High Plains region. It is clear that there will be a gradual decrease in irrigated acres for all states in the region except for Nebraska, where the water-to-land ratio is high. The decline in acres irrigated will likely be much slower than the actual decline in acre-feet pumped from the aquifer. Improved irrigation techniques and equipment are being developed which allow more efficient use and distribution of irrigation water. Also, cropping systems are being developed that emphasize utilizing limited amounts of irrigation water; fully irrigated systems of the past were designed for maximum yields rather than efficient use of water. The primary benefit of limited irrigation in this region is that it allows for much more efficient use of the natural precipitation. The average amount of irrigation water pumped for each acre of irrigated land in the region is about 20 inches. The addition of just 8 inches of irrigation water to the natural precipitation of the region could have a very beneficial effect on crop yields and would help stabilize production and reduce risks.

Groundwater pumped from other major aquifers in the western United States will also likely decrease in future years as a result of overdraft or uneconomic conditions. Unlike the High Plains region, much of the irrigated land in other areas of the western United States is in arid areas. In general, 14 inches or more of annual rainfall are required to sustain dryland agriculture. However, water harvesting technologies and more drought tolerant crop varieties are emerging that may extend dryland crop production in areas previously considered too dry.


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image
[Full Size]

Figure 15.3
Principal Soils Overlying the High Plains Ogallala Aquifer
Areas of sandy loam and loam soils are cross-hatched, and sandy soils are
double cross-hatched. Soils in other areas are primarily loams and clay loams.
Source: Fred Pringle and Gerald Ledyard, USDA Soil Conservation Service.

Loss of Irrigation Water to Domestic and Commercial Uses

Although domestic and commercial use of water represents only a small percentage of total withdrawals and consumption, these uses have a high priority which makes resource management critical. In 1975, these uses accounted for 8.5 percent of total fresh-water withdrawals and 6.9 percent of consumption. In contrast, irrigation accounted for 47 percent of withdrawals and 81 percent of consumption. By the year 2000, domestic and commercial uses are expected to increase by about 30 percent-and by as much as 50 percent or more in some of the western regions. Much of this increase will come from water presently used for irrigation, and the transfer of this water will likely result in decreased acreage of irrigated land. This is particularly true when groundwater rights are sold for domestic uses. In areas where dryland agriculture is not feasible, the diversion of water should be accompanied by revegetation of the land.

In areas where increased use of domestic and commercial water is diverted from rivers or sources other than groundwater supplies, there will not necessarily be a decline in irrigated acreage. Developing technologies are making agriculture more water-efficient, and some diversion to other uses can be made without seriously affecting the acreage of irrigated land.

Loss of Irrigation Water for Mining Fuels

Minerals production or mining has relatively minor water needs compared to irrigation. The National Water Assessment (1978) stated that the mineral industry accounted for only 2 percent of fresh water withdrawals in 1975, and projected that this would increase only to 3 percent in 2000. However, because quantities and qualities of minerals vary by regions, water demands vary accordingly. Even in the western regions where minerals are abundant and water supplies are short, the National Water Assessment does not project water needs for mining to represent a substantial portion of total water consumption. The 1975 and projected 2000 withdrawals of fresh water for fuels production, as compared to irrigation, are shown in Table 15.1. These data illustrate that the projected requirements for water for mining fuels are relatively small in relation to irrigation, and even though water demands for mining fuels will increase dramatically on a percentage basis in some regions, irrigated acreage will not be greatly reduced. Localized impacts, however, may be severe, because in most cases the increased water for mining will have to be taken from agriculture. The diversion


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Table 15.1
Fresh Water Withdrawals for Irrigation and Fuels Production, Selected Regions
Water Resources Region Irrigation Fuels Production
  (million gallons per day)
  1975 2000 1975 2000
Missouri1 31,636 39,376 144 236
Arkansas-White-Red2 9,980 9,776 172 185
Texas-Gulf3 11,538 7,427 837 930
Upper Colorado4 6,400 6,672   68 171
1 Missouri (Nebraska, South Dakota, most of North Dakota, Montana, and Wyoming, and northeastern Colorado and northern Kansas)
2 Arkansas-White-Red (southeastern Colorado, southern Kansas, Oklahoma, Texas Panhandle, and western Arkansas
3 Texas-Gulf (Texas except for the Panhandle and Trans-Pecos)
4 Upper Colorado (western Colorado, eastern Utah, southwest Wyoming, and portions of Arizona and New Mexico)

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will have political, social, and environmental impacts. In most western states, the diversion of irrigation water will result in a loss of cropland because rainfall in these areas is too low to sustain dryland crop production. Consequently, the lands taken from production should be revegetated to ensure that environmental hazards are minimized.

Conversion of Lands to Expand Agriculture

In 1977 there were nearly one billion acres of nonfederal rural land not used for cropland in the United States. Of this total, 127 million acres have high or medium potential for cropland.[6] Consequently, there is ample land available for expanding our cropland base. Converting this land to cropland would result in both losses and gains. Wind and water erosion problems could be substantial, and special care would be necessary. If large acreages of rangeland and forest land were converted to cropland, this would reduce production of forage and wood products. Loss of forest and rangelands would also affect water runoff and streamflows in some areas. If wetlands were also drained and converted to cropland, wildlife habitat would be changed. The conversion of these lands to cropland could, however, significantly increase the nation's ability to produce food and fiber for use at home and for export.

The rate of conversion and the extent of environmental impact are difficult to assess. Technologies are presently available and others are emerging which could expand agricultural production even while maintaining or enhancing the environment. Adoption of these technologies, however, is not sufficient; analysis of the political, social, and economic factors associated with the adoption of these technologies is also needed.

Impacts of Land Use Changes on Other Resources

Fish and Wildlife

Fish and wildlife are extremely sensitive to environmental change. Land use changes nearly always affect them, as a result of one or more of the following-stream temperature, amount of runoff, draining of wetlands, clearing of forests, cultivation of rangelands, and sedimentation. Land use changes are imperative, however, if the anticipated needs for food and fiber are to be met.


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Declining water supplies and rising costs associated with irrigation will have pronounced effects on the use of water, the most significant of which will be the reduced quantity of water applied per acre for irrigation. Water conservation and irrigation efficiences will have direct effects on environmental, social, and economic conditions as changes in streamflow and quality occur.

Although change in land use is inevitable, it is important to realize that change sometimes enhances the environment. A well managed farm is an ideal habitat for many kinds of wildlife. By 2000, conservation tillage will be utilized on about 80 percent of the cropland, and this will greatly increase cover for wildlife. In the Texas High Plains, dramatic increases in the populations of dove and pheasants have already been noted with the increased use of conservation tillage systems.

Responsible agencies should monitor the effects of agricultural activities on fish and wildlife resources closely; at the same time, they should try to dispel the beliefs of many who assume that only negative impacts occur.

Natural, Historic, and Wilderness Areas

Natural, historic, and wilderness areas require water of ample quantity and quality, or the esthetic values of these areas will suffer. Although the amount of the nation's water resources that is consumed by such uses is minute with respect to the total, it is appropriate that some areas be preserved. While all groups generally agree with this principle, they can seldom agree on the specifics. Though only relatively small quantities of water are at stake, particular locations will be crucially affected. Natural areas are particularly sensitive to irrigation projects. Considerable interest in recent years has pertained to wetlands, as vast acreages have been drained to expand cropland areas.

Society will have to decide the proper balance between national economic development and historic and cultural values. As the pressure on our natural resources becomes greater, water and land resource assessment and planning will take on an ever increasing importance.

Summary and Conclusions

Irrigated acreage is expected to continue to expand, but at a much slower rate than during the past few decades. Acreage will decrease in some regions because of overdraft of groundwater, uneconomic conditions, and loss of water supplies to other uses.


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As water supplies decline and the costs of applying the water increase, technologies will emerge to increase conservation, which may provide water for alternative purposes such as fuel production. Even with improved conservation, however, streamflows in the semiarid West are likely to continue to decrease. The relationship between quantity and quality of water is clear; water quality problems become more acute with reduced streamflows, and this affects fish and wildlife maintenance as well as recreational activities. All impacts, however, need not be negative. Improved water technologies will also allow better control of fertilizers and pesticides, and lesser amounts of these reaching surface or groundwater supplies. Conservation tillage systems result in substantially more plant residue remaining on the surface, and this encourages some forms of wildlife by providing better habitat.

Marked changes in irrigation practices and land use will have environmental impacts. While it is impossible to foresee perfectly, we can see trends and make some projections about the implications of certain developments. Careful assessment at this time should help us to better utilize our natural resources in the future.

Discussion:
Thomas L. Kimball

Stewart and Harman have presented a good discussion of the impact of agricultural activities on the environment. I would like to add some further comments. Water manipulation has some serious adverse impacts on the environment. Dams, diversions from streams, and a lowered water table from overpumping are cases in point. Increasing series of dams and impoundments has greatly impaired and in some cases destroyed the anadromous fish runs along both coasts. Hatcheries have had to replace much of the natural spawning lost, but most of the hatchery production is near the coast which is no help to the production lost in stream courses inland.

The diversion of smaller streams has a disastrous effect on the aquatic ecosystem. The problem is further exacerbated by the fact that greater demands for water usually come when streamflows are at the lowest ebb. The fisheries values in the Blue River of Colorado will be greatly impaired unless minimum streamflows can be guaranteed below the Dillon diversion when most of the water is diverted across the Continental Divide to Denver. In the Central Utah Project there will be seven small trout streams in the high Uinta Mountains whose water flow will be completely diverted to serve the agricultural interests of central Utah, with no mitigation for the loss of the fisheries resource.

The lowering of water tables by overpumping underground reservoirs can have a serious adverse effect on wildlife. The mesquite bosques of the lower Santa Cruz River in Arizona were destroyed by a lowered water table. These large trees served as the principal nesting area of the white-winged dove, and their destruction brought about a marked decline in dove numbers.

Irrigation canals, particularly those lined with concrete, pose some serious problems. Unless they are fenced, many of the terrestrial forms of wildlife may drown; wide canals often interfere with the migrations of many of the ungulates. Fencing and natural looking bridges can solve most of these difficulties.


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World food production is projected to increase 90 percent over the thirty years from 1970 to 2000. An additional 140 million acres of land would be required for the production of principal crops. Stewart and Harman conclude that such a shift in land use will impact the environment, but not all those impacts will be negative. Negative environmental impact, however, is difficult if not impossible to define-the definition is, like beauty, in the eye of the beholder. For example, if we view environmental quality as maintaining the integrity of our natural ecosystems, then it follows that whenever we alter those systems a negative impact occurs. On the other hand, if we define maintaining environmental quality as mitigation where possible, or the substitution of a modified ecosystem that produces benefits that are acceptable to landowners, the public, and public policy makers, then we can say that many impacts are not negative. We could have fifty million buffalo again in the United States, but we would have to take out the fences in the midsection of the country, restore the prairie, and eliminate the competition from domestic livestock for the grass. The transformation of the prairie into farmland also extirpated the grouse and prairie chicken. The grain farm ecosystem, however, created a suitable environment for the Chinese ring-necked pheasant, and for some this has been an acceptable substitute for the indigenous species lost. Nevertheless, all is not well for the ring-necked pheasant. Monoculture, clean farming, and the use of chemicals, pesticides, herbicides, and fertilizers have increased crop yields but taken away winter and nesting cover to the detriment of the birds.

The problem is that generally we have single use concepts of land and water management. What is really needed is to develop multiple use objectives for every land and water project. We should encourage every private landowner to consider the many values and objectives that are inherent in land and water management, and provide him with as much information as is available to make intelligent decisions. Multiple use objectives should be required on all major projects where public tax money is utilized. Although there are many laws designed to accomplish this purpose, many of our public servants have to be pushed into efforts to achieve that objective.

Water pollution is a much greater problem than recognized by Stewart and Harman. While great strides have been made in cleaning up our nation's water supply from known sources of pollution, nonpoint sources continue to be a real and increasing threat. Pesticides and residue nutrients continue to play havoc


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with aquatic ecosystems. One of the consequences of the tremendous quantity of added nutrients is the accelerated eutrophication of our lakes. Lake Okeechobee in Florida, one of the nation's largest fresh water lakes, is rapidly losing its premium water quality by pesticide and fertilizer runoff and pumpback from agricultural lands irrigated from the lake.

Salt water intrusions into fresh water aquifers and estuaries is also a major problem. The quality of water in the brackish water zones in our estuaries is becoming more difficult to maintain. These waters are critical to the well-being of many pelagic fishes and, biologically speaking, are the most valuable and productive. Diversion of the principal flow of large rivers, such as the Sacramento, could allow salt water intrusions that could impair the entire Delta and San Francisco Bay ecosystems.

Waste of irrigation water is one of the most critical environmental problems of proper water and agricultural management. The competition for available water grows daily in the semiarid western states. While food production will always enjoy a high priority in water use, that priority should not extend beyond the actual amounts of water necessary to grow crops to maturity under the best available technology. Western water law is based upon beneficial use of water; waste can never be construed as a beneficial use. The time will come when water right owners will lose water that is wasted.

The authors project that nonirrigated farmland will increase substantially in the future as underground supplies are depleted and the need for food increases. Let us hope to avoid the mistakes of the "Dirty Thirties." Those lands whose soil texture is subject to severe wind erosion, particularly national grasslands, should be purchased by the federal government to protect them from serious and continuing erosion under cultivation. Those lands should never be put to the plow unless proven technologies demonstrate adequate wind erosion protection.

In the minds of most naturalists, variety and abundance of wildlife is the litmus paper of environmental quality. It is true that changes in habitat are not always negative to all species of wildlife, but such changes will adversely affect some or many species. Many of our wildlife species are adaptable to environmental change. For example, the ubiquitous coyote is now as much at home in the garbage cans of Los Angeles as he is in the Sierra wilderness. On the other hand, the prairie chicken is usually extirpated from areas where the strutting grounds are plowed and planted with crops. The mountain lion and grizzly


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bear are true wilderness animals; when humans move in, they move out.

Once priorities of land and water use are determined, the solution to many environmental difficulties is to collect enough knowledge and information about the established objectives to minimize adverse impacts and maximize the enhancement of environmental quality. Such effort will preserve adequate habitat for variety and adequate numbers of wildlife. In order to minimize adverse environmental impacts created by a diminishing water supply, the following suggestions and recommendations are made.

1) Devise a program to eliminate water waste in irrigated agriculture. If such a program could be developed and successfully executed, nothing could provide more benefits to all interests.

2) Develop multiple use objectives on all land and water development projects. When concern is shown for the many and varied interests in land and water management, there may be increasing support for the project.

3) Take a close look at impacts on fish and wildlife resources. These are indicators of environmental quality.

4) Include economic and social factors in long range planning, because these will probably have greater impact on the future of agriculture in America than any other. With two-thirds of the world hungry today, the United States still cannot sell its bumper crops of grain for an amount sufficient to cover the cost of production. Even if the grain could be sold at a profit, the means of transporting foodstuffs to those who need it most is completely antiquated and inadequate.

5) Develop a program to preserve the "Class I" farmlands in the United States. Robert Frost once said, "What makes a great nation in the beginning is a good chunk of real estate." In the United States we have a great chunk of real estate. Whether we remain a great nation will depend upon how wisely we develop and use it. The most dramatic success story in the United States is our agricultural production. We can stay a super power only insofar as


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we maintain that agricultural success. The world cannot march ahead on an empty stomach.

6) The United States Department of Agriculture should review its priorities, and do so frequently in the future. The Soil Conservation Service was created to protect our nation's farmland from soil and water erosion. Now we should enlarge and expand research and extension efforts to achieve better land and water management. Technologies must be developed and brought to the landowner and applied on the land.

7) Agricultural as well as all other special interests should wean themselves from the public treasury. The nation's current economic condition is due in part to all segments of society running to the taxpayer for help. Government can no longer afford to expend more money than it takes in. Water projects and programs must bear their true costs-those who benefit must pay. Such a principle applied to all interests subsidized by the taxpayer would go a long way towards solving our nation's current economic ills as well as its environmental problems.

Discussion:
George H. Wallen

Stewart and Harman do a good job in discussing how reductions of irrigated agriculture will likely result in the use of more marginal lands for production. Intensive farming practices, where chemicals are used to enhance production and all available space is tilled, limit environmental amenities, whether or not the fields are irrigated.

Such generalizations are useful from a theoretical viewpoint. However, more specific information on the relationships between irrigated agriculture and environmental quality is necessary if irrigation farmers and project managers are to maintain desirable environmental amenities.

The addition or withdrawal of water may have significantly different environmental impacts in different parts of the country. Effects on fish and wildlife illustrate the point that environmental values vary with farming practices and with regional climatic conditions.


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Fish and wildlife and other environmental resources are significantly affected when irrigation systems are installed and operated on lands previously dryfarmed or idle. The species composition and populations of wild animals and native plant species change significantly. Native species are not always lost; however, their numbers may be greatly depressed, while species that can adapt to the new water regime and cropping pattern may expand. For example, in the Texas Panhandle, species such as prairie chicken, prairie dog, and antelope decline with more intensive farming and improved water delivery. On the other hand, populations of pheasant, whitetailed deer, and waterfowl increase in response to the increase in available food and the additional permanent water areas provided to store and deliver irrigation water to the fields.

In some parts of the country, the principal effect on wildlife resources from the installation of irrigation facilities may be the drying out of wetlands so that crops can be produced with the regulated application of the irrigation water. This type of change augurs against wetland-dependent species in favor of upland varieties. In these areas it is the drainage rather than water delivery facilities that has the most significant effect.

Irrigation projects may also be attractive recreation areas. Data for reclamation projects show that, in 1980, approximately 67 million visitor-days were spent at the almost 6 million acres of land and water available for recreation at 214 operating reclamation projects or units. Sightseeing was reported to be the most popular activity, followed by fishing and camping. Most of the use was at multipurpose projects, where water is stored for power production, flood control, and municipal water supply in addition to irrigation. However, visitor use of smaller irrigation reservoirs and conveyance facilities was also substantial.

When water that has been available for irrigation is reduced or diverted to other uses, a change in environmental quality occurs that is just as dramatic as the first application of the irrigation system. In most of the West, the most common reason for halting irrigation in any given area is the expansion of urban growth. In those instances, fields become roads, parking lots, buildings, and lawns. Water formerly used in agriculture is used for municipal and industrial purposes.

Irrigated fields are seldom abandoned because of lack of water. The more likely scenario has been reversion to nonirrigation, or the temporary return to dryland crops until new arrangements were made for water. In these cases, the environmental attributes of an area change little.


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Under unusual circumstances, fields may be left idle or abandoned with the loss of irrigation water. Such lands return to natural conditions with a dominance of native vegetation at a rate that can be correlated to the amount of natural precipitation available. In the central Washington area, where the Columbia Basin Project is located, fields return to natural conditions after three to five years. In the much dryer central part of Arizona, perennial plants such as greasewood may be established in wetter areas after 8 to 10 years, but many native species never return to former densities.

The speed with which lands formerly irrigated return to desirable quality is affected by the measures taken by land managers, whether private landowners or public agencies. Fish and game species can be encouraged to return to formerly irrigated areas by proper food and cover plantings and by the provision of suitable watering areas. Careful use of pesticides and fertilizers also may encourage reestablishment of desirable plant and animal species. An abandoned field that is surrounded by cropland may provide an island of cover and sanctuary for many wildlife species. Abandoned ditches and canals may also provide desirable food and cover if properly managed. Native species may be encouraged if that is a desirable goal. As irrigation facilities are reduced, public use of such facilities will also decline unless positive steps are taken to manage the areas to provide desirable recreation resources.

If one holds a more utilitarian view, it is easy to rationalize that most of the changes caused by irrigation are highly valued by people living in the last 20 years of the 20th century. For the most part, environmental amenities have been piggybacked either by accident or design onto existing projects. Obvious examples are permanent wetlands in desert climates, high quality recreation lakes resulting from overdesign of supply facilities, and vegetation at the edge of fields that results from overapplication of water. If water becomes limited, however, these amenities may be hard to keep.


 

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