Nutrients and Water Quality: The Basics
Agriculture is a significant source of nutrients in many degraded waters, including the Chesapeake Bay, the Gulf of Mexico, and major water bodies worldwide. Agriculture becomes a source of nutrients when fertilizers for crops and manure from livestock are moved through runoff and other processes into water resources -- groundwater, streams, rivers, and lakes.
Agriculture is generally considered a "nonpoint source" of nutrient pollution. A municipal wastewater treatment plant is considered a point source of nutrient pollution since it discharges treated sewage by a pipe into the receiving waters. Nonpoint sources follow complex pathways compared with a point source. For example, nitrogen applied to farm fields can:
- Leach into groundwater and gradually move into a stream as base flow
- Run off across land during a storm or snow melt event into surface water
- Volatilize into the atmosphere, where it would mix with rain and eventually run off to ground- and surface waters.
Each of these pathways contributes to surface water impairments. The complexities of the pathways make measuring and managing nutrients from agriculture a challenge.
Why Does the Problem Exist? Structure of Agriculture and the Nutrient Cycle
The economics of the agricultural sector reward cost efficiency and specialization. This drives much of Pennsylvania toward intensive production of animal products such as milk and eggs, particularly given its proximity to large consumer markets.
Some of the material that is fed to Pennsylvania farm animals is grown on Pennsylvania farms. But farmers also import feed from farms in other areas like the Midwest, where economics favor specialization in the production of grains. The result is a large-scale movement of grain and the nutrients contained therein from the Midwest to Pennsylvania.
A portion of the nutrients consumed by farm animals becomes part of the animal products that are sold to consumers in milk, meat, and eggs. Animals turn about one-quarter of the initial nutrients consumed into usable animal products. The remaining three-quarters of nutrients are excreted in manure. Farmers conventionally apply manure to their land to fertilize crops.
Like animals, crops cannot extract all of the nutrients applied to the land. Nutrients in excess on the farm can become nutrient pollution. The nutrient pollution problem is essentially an outcome of imbalance. In a balanced system, nutrients would cycle from soils to crops to livestock and then back to soils. Under the current agriculture structure in Pennsylvania, in which large quantities of feed are imported, this balance is broken.
Nutrients that are contained in grain grown in other geographic regions are imported into Pennsylvania and fed to livestock. Some of the nutrients are then excreted from the animal and land applied for crop utilization. The result is an overall importation of nutrients to croplands. Source: Doug Beegle.
Nutrients in animal agriculture have two costs. One is an internal cost borne by farmers and ultimately by consumers. This is the market cost to farmers for the resources they use to produce or purchase feed. Farmers have market-based incentives to conserve nutrients to minimize these internal costs.
The second cost of nutrients is the loss of ecosystem services caused by the degradation of ecosystems. This cost is an external cost of food production not borne by the farmer but by others.
Unlike feed, fuel, and other conventional inputs, no markets or market prices translate the costs of environmental degradation to the source. Consequently, farmers have no market-based incentive to limit nutrient pollution.
Flow diagram of economic and social forces that affect farm processes such as nutrient application. There are economic forces for nutrient costs that encourage crop farmers to apply nutrients that maximize yield, but paying for nutrient application beyond crop utilization may be economically unfavorable. Social forces of excess nutrient application, such as downstream water pollution impacts, typically do not affect farm-level nutrient application decisions. These forces are external to farm-level decisions. Source: Les Lanyon and Doug Beegle.
What Are the Solutions?
Farm Scale Solutions to the nutrient problem can be viewed from various angles. The first angle is to evaluate options at the farm level for reducing nutrient losses to the environment.
Solutions at this scale focus on technologies and management practices within the farm system:
- Improving nutrient uptake in animals to reduce nutrient losses to manures
- Managing manure in crop production to maximize the nutrients taken up by crops and minimize nutrients that can be lost to the environment
- Using practices to reduce runoff and the delivery of nutrients to water
Restructuring of Food Systems
As described earlier, the structure of the agricultural system is fundamental to the nutrient pollution problem. Actions taken by individual farmers within the context of the existing food system may not be adequate to address the nutrient imbalance created by the system. It is likely that policy change is needed to address the problem at the food-system level.
Internalizing Environmental Costs of Agriculture
One policy approach worth considering is the internalization of pollution costs. If pollution costs are reflected in farm production costs and ultimately in the prices paid by consumers, market incentives will exist to steer the system toward balance. Finding methods for internalizing costs that are politically and socially acceptable is a major challenge.
Achieving balance by internalizing the environmental costs of food production. Source: Doug Beegle.