Environmental Interactions with Agricultural Production: Background

Environmental Interactions with Agricultural Production Briefing Room Background Animal Agriculture and the Environment Grazing Lands and Environmental Quality Federal Laws Protecting Environmental Quality Policy Instruments for Protecting Environmental Quality

Over 440 million acres (19.5 percent of land) is dedicated to growing crops in the U.S., and another 587 million acres (26 percent) is in pasture and range, largely used for domestic livestock production. Agricultural activities on these lands produce a plentiful, diverse, and relatively inexpensive supply of food and fiber for people here at home and abroad. However, agricultural production practices can degrade the environment. Transformation of undisturbed land to crop production can diminish habitat for wildlife. Soil erosion, nutrient and pesticide runoff, and irrigation can pollute the air and water, degrade soil quality, and diminish water supplies. The extent and degree of the environmental problems associated with agriculture vary widely across the country. Concern over these problems has given rise to local, State, and Federal conservation and environmental policies and programs to address them.

Soil Quality

Soil, as a plant-growing medium, is the key resource in crop production. Soil supports the fundamental physical, chemical, and biological processes that must take place in order for plants to grow; it regulates water flow between infiltration, root-zone storage, deep percolation, and runoff; and it acts as a buffer between production inputs and the environment. Soil can also function as a "degrader" or "immobilizer" of agricultural chemicals, wastes, or other potential pollutants, and can mitigate climate change by sequestering carbon from the atmosphere (when the rate of organic matter production exceeds the rate of oxidation). How well soil performs these functions depends on soil quality. How soil is managed has a major impact on soil quality, and on the potential for various pollutants to leave the field and affect other resources.

Soil quality can be defined as the capacity of a specific kind of soil to function, within natural or managed ecosystem boundaries, to sustain plant and animal productivity, maintain or enhance water and air quality, and support human health and habitation. Soil quality depends on attributes such as the soil's texture, depth, permeability, biological activity, capacity to store water and nutrients, and organic matter content. Soil quality can be maintained or enhanced through the use of appropriate crop production technologies and related resource management systems. Poorly managed fields can lead to soil degradation through three processes: physical degradation, such as via wind and water erosion and soil compaction; chemical degradation, such as toxification, acidification, and salinization; and biological degradation, such as loss of organic matter and decline in the activity of soil fauna. Poor management can also increase runoff of nutrients and pesticides to surface and groundwater systems. Thus, soil degradation can have both direct and indirect negative effects on agricultural productivity and the environment. Even on high-quality soils, overuse of chemical inputs can result in soil toxicity and water pollution.

Water Quality

Agriculture is widely believed to have significant impacts on water quality. While no comprehensive national study of agriculture and water quality has been conducted, the magnitude of the impacts can be inferred from several water quality assessments. A general assessment of water quality is provided by EPA's 2000 Water Quality Inventory. Based on State assessments of 19 percent of river and stream miles, 43 percent of lake acres, and 36 percent of estuarine square miles, EPA concluded that agriculture is the leading source of pollution in 48 percent of river miles, 41 percent of lake acres (excluding the Great Lakes), and 18 percent of estuarine waters found to be water-quality impaired, in that they do not support designated uses. This makes agriculture the leading source of impairment in the Nation's rivers and lakes, and a major source of impairment in estuaries. Agriculture's contribution has remained relatively unchanged over the past decade. (For additional information on agriculture's contribution to water quality problems, see AREI 2.2).

Major Agricultural Pollutants

Sediment is the largest contaminant of surface water by weight and volume, and is identified by States as the second leading pollution problem in rivers and streams and the third leading problem in lakes. Sediment in surface water is largely a result of soil erosion, which is influenced by soil properties and the production practices farmers choose. Sediment buildup reduces the useful life of reservoirs. Sediment can clog roadside ditches and irrigation canals, block navigation channels, and increase dredging costs. By raising streambeds and burying streamside wetlands, sediment increases the probability and severity of floods. Suspended sediment can increase the cost of water treatment for municipal and industrial water uses. Sediment can also destroy or degrade aquatic wildlife habitat, reducing diversity and damaging commercial and recreational fisheries. Regions with the greatest potential to discharge sediment from cropland to surface waters include parts of the Heartland, Mississippi Portal, and Prairie Gateway regions (see ERS Resource Regions for a description of the regions used here).

Eutrophication and hypoxia (low oxygen levels) in the northern Gulf of Mexico have been linked to nitrogen loadings from the Mississippi River. Agricultural sources (fertilizer, soil inorganic nitrogen, and manure) are estimated to contribute about 65 percent of the nitrogen loads entering the Gulf from the Mississippi Basin. As much as 15 percent of the nitrogen fertilizer applied to cropland in the Mississippi River Basin makes its way to the Gulf of Mexico. The Gulf of Mexico is not the only coastal area affected by nutrients. Recent research by the National Oceanographic and Atmospheric Administrations has found that 44 estuaries (40 percent of major U.S. estuaries) exhibit highly eutrophic conditions, caused primarily by nitrogen enrichment. Farmers apply a wide variety of pesticides to control insects (insecticides), weeds (herbicides), fungus (fungicides), and other problems. Well over 500 million pounds (active ingredient) of pesticides have been applied annually on farmland since the 1980s, and certain chemicals can travel far from where they are applied. Pesticide residues reaching surface-water systems may harm freshwater and marine organisms, damaging recreational and commercial fisheries. Pesticides in drinking water supplies may also pose risks to human health. Pesticide concentrations exceeded one or more human-health benchmarks in about 10 percent of agricultural streams examined by USGS as part of the National Water Quality Assessment Program, and in about 1 percent of sampled wells used for drinking water in agricultural areas.

Watersheds with a high propensity to discharge pesticides to surface water are located primarily in the Heartland and Mississippi Portal regions. Watersheds with a high propensity to discharge pesticides to ground water are primarily in the Heartland, Prairie Gateway, and Southern Seaboard regions.

Some irrigation water applied to cropland may run off the field into ditches and receiving waters. These irrigation return flows often carry dissolved salts as well as nutrients and pesticides into surface or ground water. Increased salinity levels in irrigation water can reduce crop yields or damage soils such that some crops can no longer be grown. Increased concentrations of naturally occurring toxic minerals—such as selenium, molybdenum, and boron—can harm aquatic wildlife and impair water-based recreation. Increased levels of dissolved solids in public drinking water supplies can increase water treatment costs, force the development of alternative water supplies, and reduce the lifespans of water-using household appliances. The possibility of pathogens contaminating water supplies and recreation waters is a continuing concern. Bacteria are the largest source of impairment in rivers and streams, according to EPA's water quality inventory. Potential sources include inadequately treated human waste, wildlife, unconfined livestock, and animal operations. Diseases from micro-organisms in livestock waste can be contracted through direct contact with contaminated water, consumption of contaminated drinking water, consumption of crops irrigated with contaminated water, or consumption of contaminated shellfish. Bacterial, rickettsial, viral, fungal, and parasitic diseases are potentially transmissible from livestock to humans. Fortunately, proper animal waste management practices and water treatment minimize this risk. However, protozoan parasites, especially Cryptosporidium and Giardia, are important sources of waterborne disease outbreaks. Cryptosporidium and Giardia may cause gastrointestinal illness, and Cryptosporidium may lead to death in persons with compromised immune systems. These parasites have been commonly found in beef herds and Cryptosporidium is widespread on dairy operations.

Air Quality

Ever since farmers began raising animals and cultivating crops, agricultural production practices have generated a variety of substances that enter the atmosphere with the potential of creating health and environmental problems. The relationship between agriculture and air quality became a national issue in the 1930s with the severe dust storms of the Dust Bowl. Although dust storms of this magnitude no longer occur in the U.S., soil particulates, farm chemicals, and odor from livestock are still carried in the air we breathe. These emissions can harm human health and pollute the environment. Air quality in most rural areas is not a cause for concern, but there are some farming communities where ozone and particulates have impaired air quality to the same extent as in urban areas.

Ammonia is a gas and one of the most abundant nitrogen-containing compounds emitted to the atmosphere. Animal farming systems contribute about 50 percent of the total anthropogenic emissions of ammonia into the atmosphere in the U.S. Ammonia is a health hazard to humans and animals in high concentrations. Once in the atmosphere, ammonia is rapidly converted to ammonium particles by reactions with acidic compounds such as nitric acid and sulfuric acid found in ambient aerosols. These ammonium particles can be carried long distances in the atmosphere and contribute to fine particulate pollution and haze. Ammonium is redeposited to the earth's surface by both wet and dry deposition, contributing to eutrophication of water resources.

Nitrous oxide is another nitrogen compound of concern. It is a greenhouse gas and contributes to ozone depletion. Nitrous oxide forms primarily in the soil during the microbial processes of nitrification and denitrification. Agricultural sources include manure from livestock farming and commercial fertilizer. Agriculture contributes about 70 percent of total anthropogenic emissions of nitrous oxide in the U.S., mostly from the fertilization of cropland. About 25 percent of the anthropogenic sources of nitrous oxide in the U.S. is from animal waste.

Wind erosion can produce short-term levels of particulate pollution in rural areas that exceed urban levels. Particulates from wind erosion can impose costs on those living in affected areas, including cleaning and maintenance of businesses and households, damage to nonfarm machinery, and adverse effects on health. Another source of particulates is open-field burning. Open-field burning is used as a means of removing crop residue after harvest and controlling disease, weeds, and pests. Diesel engines from farm equipment and irrigation pumps are also a source of particulates.

A source of fine particulates (particles smaller than 2.5 microns, also known as PM2.5) is gaseous emissions of ammonia and nitrogen oxides (NOx, or nitric oxide, and nitrogen dioxide). Ammonia and NOx in the atmosphere react with other compounds to form fine particulates, such as ammonium. Fine particulates pose a health risk because they can be inhaled deep into lungs. Fine particulates are also a source of haze, which detracts from views in many popular national parks. The atmosphere is now recognized as a major pathway by which pesticides can be transported and deposited far from their point of use. Pesticides can enter the atmosphere directly from the spray cloud during application, from evaporation after application, and attached to windborne soil particles. As much as 80 percent of some pesticide applications evaporate. And many of these pesticides across different chemical groups have been detected in the atmosphere. The U.S. Geological Survey found that the most frequently detected pesticides in the atmosphere are DDT, methidathion, diazinon, heptachlor, malathion, and dieldrin. Even though some of these have been banned for years, they continue to be detected.

Deposition of airborne pesticides will also affect water quality, but an understanding of the extent to which airborne deposition of pesticides contributes to water quality impairments requires additional monitoring. The highest concentrations of pesticides detected in air and rain occur in those areas where they are applied most frequently and in the highest amounts. Atmospheric concentrations of pesticides also vary seasonally, and not surprisingly, the highest concentrations in air and rain usually occur in the spring and summer months, when most pesticides are applied and temperatures are warmest.

Odor is a major nuisance associated with animal production facilities. The expansion of urban and suburban development into rural areas has brought more people into contact with animal operations. People who are agricultural novices living near farms often object to the traditional "smells" of farming. However, farmers too are objecting to odors from large animal feeding operations, particularly hog operations with large lagoons. Odorous gases consist of a host of compounds (over 300) that originate from animal housing, manure storage units, and land application of manure. USDA's Agricultural Research Service is currently conducting research on interactions between agricultural production practices and air quality, and new approaches for addressing air quality problems.

Wildlife Habitat

Habitat is a combination of environmental factors that provides the food, water, cover, and space that a living organism needs to survive and reproduce. Agricultural land use can benefit some species, harm others, and sometimes do both. Potentially harmful effects of farming include plowing up habitat, farming riparian buffers, fragmenting habitat, diverting water for irrigation, and diffusing agricultural chemicals into the environment. In addition, specialization in agriculture reduces landscape diversity by creating more of a monoculture. This reduces the presence of ecological niches, which can limit wildlife populations and biodiversity on farms. Historically, the conversion of native forests, prairies, and wetlands to cropland has dinimished wildlife. Habitat loss associated with agricultural practices on over 400 million acres of cropland has been identified as a primary factor depressing wildlife populations in North America. Agriculture is thought to affect the survival of 380 of the 663 species listed by the Federal Government as threatened or endangered in the conterminous 48 States.

Agriculture's negative effects on wildlife need not be permanent. U.S. agriculture is in a unique position with respect to the Nation's wildlife resources. The management of land now controlled by U.S. farms and ranches can play a major role in protecting and enhancing the Nation's wildlife. In 2002, private farms accounted for 41 percent of all U.S. land, including 434 million acres of cropland and 395 million acres of pasture and range. Farms also account for 76 million acres of forest and woodland, and 92 million acres of nonfederal wetlands. Different types of habitat can be restored or improved through conservation on agricultural lands.

Grassland Habitat

Grasslands constitute the largest land cover on America's private lands. Privately owned grasslands and shrub lands (including tribal) cover more than 395 million acres in the United States. These lands contribute significantly to the economies of many regions, provide biodiversity of plant and animal populations, and play a key role in environmental quality. Grasslands directly support the livestock industry. They also provide habitat for many wildlife species, reduce the potential for flooding, control sediment loadings in streams and other water bodies, and provide ecological benefits such as nutrient cycling, storage of atmospheric carbon, and water conservation. Grasslands also improve the aesthetic character of the landscape, provide scenic vistas and open space, provide recreational opportunities, and protect the soil from water and wind erosion.

Large expanses of grassland acreage are annually threatened by conversion to other land uses such as cropland and urban development. About half of all grasslands in the U.S. have been lost since settlement, much due to conversion to agricultural uses.

Wetland Habitat

Wetlands are complex ecosystems that provide many ecological functions that are valued by society. They take many forms, including prairie potholes, bottomland hardwood swamps, coastal salt marshes, and playa wetlands. Wetlands are known to be the most biologically productive landscapes in temperate regions. More than one-third of the United States' threatened and endangered species live only in wetlands, and nearly half use wetlands at some point in their lives. Most freshwater fish depend on wetlands at some stage of their lives. Many bird species are dependent on wetlands for either resting places during migration, nesting or feeding grounds, or cover from predators. Wetlands are also critical habitat for many amphibians and fur bearing mammals. Besides supporting wildlife, wetlands also control water pollution and flooding, protect the water supply, and provide recreation.

When the country was first settled there were 221-224 million acres of wetlands in the continental U.S. Since then, about half have been drained and converted to other uses, nearly 85 percent for agricultural uses. Currently, there are about 111 million acres of wetlands on nonfederal lands. About 15 percent are on agricultural lands (cropland, pastureland, and rangeland). For more information on wetlands and their value to society, see EPA's Wetlands Homepage.

Riparian Habitat

Riparian areas are the zones along water bodies that serve as interfaces between terrestrial and aquatic ecosystems. Riparian ecosystems generally compose a minor proportion of the landscape, but they are typically more structurally diverse and more productive from a wildlife perspective than adjacent upland areas. This is especially true in the arid West. Studies in the Southwest show that riparian areas support a higher breeding diversity of birds than all other western habitats combined. In Arizona and New Mexico, at least 80 percent of all animals use riparian areas at some stage of their lives. Western riparian habitats contain the highest noncolonial avian breeding densities in North America.

Riparian zones also support productive aquatic habitat. They stabilize streambanks, thus reducing streambank erosion and sedimentation. Detritus from streamside vegetation provides energy to the stream ecosystem. Vegetation also provides shade, preventing extreme temperature swings that are detrimental to healthy stream ecosystems. Riparian areas also filter out sediment, nutrients, and pesticides in runoff, thereby protecting water quality.

No comprehensive national inventory has been completed on the status and trends of riparian areas. However, NRCS estimates that the conterminous U.S. originally contained 75-100 million acres of riparian habitats, and that between 25 and 35 million acres remain.

Implications for Policy

Agriculture has wide ranging impacts on environmental resources. Because of this, it also has the capacity to provide a wide range of environmental services. Understanding the links between agriculture and environmental quality enhances our ability to design programs that best meet the needs of producers and those who value the services the environment can provide.