Manure Management and Water Quality

Using manure to fertilize crops is a cost-effective way to save money on commercial fertilizer, and can be an environmentally responsible means of manure management. However, while manure is a good fertilizer on land, it can have undesirable effects when it enters nearby streams and lakes. Pathogens in manure can make water unsafe to drink or use for recreation. The nitrogen and phosphorus that make manure so productive on farm fields can create an over-fertilized "soup" when they run off into the water, leading to undesirable algae blooms. These effects are not only unpleasant for recreation and aesthetics, but they also deteriorate the underwater habitat necessary for fish and other aquatic organisms to live.

• How can bacteria and pathogens from manure make water unsafe for recreation?
• How does manure in the water lead to algae blooms and fish kills?
• How does phosphorus from manure affect water quality?
• How can nitrogen from manure affect water quality and human health?
• How can nitrogen and phosphorus levels be reduced?

How can bacteria and pathogens from manure make water unsafe for recreation?

Manure can contain bacteria and other organisms that can be harmful to humans if they get into our waterways or groundwater. Pathogens can become a problem when manure runs off into lakes where people swim or have other direct bodily contact with the water. If a person or animal swallows water from a contaminated source, illness can result. Contamination can also be a concern in drinking water. Generally, municipal drinking water treatment plants do a good job of sanitizing community water supplies, so municipal drinking water supplies are rarely contaminated from manure. However, about 20% of Wisconsin residents have private wells, and these can become contaminated by pathogens from manure.

Fecal coliform is generally used as a water quality measure of bacterial contamination. Coliform is a group of bacteria that, while generally harmless, does have strains such as E. coli (Escherichia coli) that can be harmful. E. coli can cause intestinal disorders, as well as other diseases such as cholera and typhoid fever. Another organism found in manure is Cryptosporidium, a single-celled parasite that causes diarrhea and stomach cramps when ingested. Cryptosporidium was responsible for an outbreak in Milwaukee's drinking water system in 1993.

How does manure in the water lead to algae blooms and fish kills?

Good aquatic habitat has clear
water, letting sunlight reach the
plants below. Fish and other aquatic
organisms need underwater plants
for cover.

After manure enters a waterway, fast-growing algae quickly take up the excess nutrients in the water. This growth can create an algae bloom-a thick mat of algae or "scum" on the water's surface. Many people dislike algae blooms because they make their favorite streams and lakes unsightly and unpleasant for fishing, boating, and swimming. Just as important, however, are the impacts on the other plants, fish, and insects that make up a healthy, functioning stream or lake.

Algae blooms make recreation
unpleasant, as well as lead to fish kills
and unpleasant odors.

As algae blooms grow, the mats that cover the water's surface block out sunlight from the larger plants below. These larger aquatic plants are essential for fish habitat, but can't survive without sunlight and start to die off. Before long, the short-lived algae also start to die, and large masses of dead algae and plant matter begin to decay. As a part of this decomposition process, bacteria are produced that use up oxygen from the water. This has major impacts. Since fish and aquatic insects need the oxygen that is dissolved in water to live, when that oxygen is used up by decaying algae massive fish kills can result, damaging fish populations. All of this decaying material has another unpleasant side effect, too-the odor of rotting algae and fish! All of these effects can turn your favorite stream or swimming hole into a stinking, green mess.

How does phosphorus from manure affect water quality?

Plants need both nitrogen and phosphorus to grow. However, in cool, temperate regions like Wisconsin, it is generally the phosphorus level of a waterbody that determines how much plant and algae growth will occur. In order to keep plant and algae growth at reasonable levels, the amount of phosphorus entering our streams and rivers must be carefully managed. Because many areas of Wisconsin already have an overabundance of phosphorus, reducing phosphorus inputs is often necessary to keep algae growth in check and to keep our streams and rivers healthy.

Direct runoff of manure from fields or manure storage facilities that have been inadequately constructed or maintained are important management concerns. If a rain occurs after manure is spread on crop or hay fields, the phosphorus may run off into nearby waterways instead of sinking into the ground. This is especially problematic during the spring, when manure spread over the winter is washed away by the spring snowmelt. Since this manure is delivered directly into waterways, this can be a major contributor of phosphorus to the streams and lakes. Likewise, manure storage facilities need to be structurally sound and have enough capacity to handle the manure generated at the farm, to avoid leaks or overtopping.

Direct access of livestock to streams and ponds can also be a problem if the streambank is not well vegetated. Not only do cattle and hogs "direct deposit" manure into the water, they can also overgraze and trample streambanks, leading to erosion problems. Trampled banks also damage fish habitat, destroying overhangs used for shelter and compacting stream bottoms that are used for spawning and feeding.

An important characteristic of phosphorus that has significant implications for water quality is its tendency to bind to soil particles. Because of this, when phosphorus is applied to fields it stays relatively immobilized and stable on land as long as the soil remains intact. However, when land suffers from erosion, soil is washed into waterways and the phosphorus attached to it is then released into the water. Once phosphorus enters the water, the algae bloom cycle begins. Because of this process, erosion and runoff are key issues that need to be addressed for good phosphorus management.

How can nitrogen from manure affect water quality and human health?

Nitrogen is an essential nutrient for plant growth, and is one of the primary components of manure and commercial fertilizers. However, although nitrogen is very productive when applied to crops, excess nitrogen can have negative impacts in our lakes, rivers, and groundwater.

• Because of its fertilizing properties, nitrogen is a key contributing factor to algae growth in streams and lakes.
• Excess nitrogen in rivers and streams can be toxic to aquatic animals at high levels. This toxicity is due to ammonium hydroxide (NH4OH), which is produced at greater rates under conditions that are common where waste spills have occurred (such as low oxygen levels, high pH, and high temperature). Toxic levels of ammonium hydroxide are usually due to pollution from manure and sewage spills, and can result in fish kills and loss of other aquatic organisms.
• Nitrogen pollution also leads to human health concerns about groundwater contamination. Unlike phosphorus, which binds to the soil's surface, nitrogen filters down through the soil easily and can enter drinking wells. Infants less than six months are most susceptible to nitrate poisoning. High nitrate levels in groundwater can reduce the blood's capacity to carry oxygen, causing a fatal condition in infants called "blue baby syndrome." For this same reason, deaths can also occur in livestock that drink from a water supply high in nitrates. Pregnant or nursing women are advised to avoid water with high nitrate levels. Adults with heart or lung disease, certain inherited enzyme defects, or cancer may have increased sensitivity to the toxic effects, and adults with lifetime exposures to high nitrate levels may experience related health issues. The federal safety standard for nitrate is 10 mg/L, and 6.5% of Wisconsin's private wells exceed this safety standard.

How can nitrogen and phosphorus levels be reduced?

For farmers, nutrient management is an integral part of business, and there are important steps that can be taken to reduce their nutrient loss to streams and lakes. The two main ways of reducing the nutrients that enter our waterways from agriculture are 1) decreasing the amount of nutrients applied to the landscape, and 2) preventing spills, runoff, and erosion from transporting those nutrients to our waterways.

Decreasing excess nutrients applied to the landscape is the first step necessary for maintaining good water quality.

• Careful nutrient management planning can help farmers determine how much nitrogen and phosphorus is in their manure and how much the crops on each field require to be productive. This planning can help farmers apply only as much nitrogen and phosphorus as their crops will use, preventing excess runoff. In areas that already have phosphorus buildup in the soil or impacted waterways, farmers may need to manage specifically to reduce phosphorus levels.
• One way livestock operators can reduce unnecessary phosphorus in manure is by changing their feed supplements. Phosphorus is typically fed to cattle to ensure reproductive success. However, new research is showing that lower phosphorus levels in feed can be optimal for both maintaining herd health and for cost-effectiveness.
  
  See How Much Phosphorus Do Dairy Cows Need? [exit DNR] by Larry Satter, USDFRC for more information.
  
  Another option under development is the use of feed additives to help animals use more of the phosphorus that they are fed. Both of these methods help reduce the phosphorus levels in the resulting manure.

The second important step is to prevent the nutrients that are stored or applied to the land from getting into waterways.

• In many cases, manure should be stored over the winter while the ground is frozen. Because of this, manure storage facilities are a management option often chosen for operations that handle large quantities of manure. Sound construction and maintenance of these storage structures is essential to preventing leaks to groundwater and overflows that can damage nearby streams and lakes.
• Prevention of erosion and runoff is essential for keeping nutrients out of our lakes and streams. Maintaining good plant cover is one of the most effective ways to reduce the amount of soil and phosphorus that runs off into the water. Plant roots stabilize the soil and help reduce erosion. Buffer strips of grasses or trees along stream banks catch runoff and sediments flowing from upland fields and trap them before they enter waterways. Well-vegetated uplands and buffers are critical for water quality.

Contact Thomas S. Bauman with feedback about this page.