The problem
Clean water is a resource that is required for all living things, and horses are no exception. With increased land use, including urban development and agricultural activities, there is increased pollution. This pollution often moves through water as storm runoff, eventually making its way into surface waters such as lakes and streams, and into groundwater.
While there are many sources of water pollution, one commonly associated with agricultural activities is the use of fertilizer, which contains high levels of nitrogen and phosphorus. Increased levels of these two elements can result in a range of environmental effects, including algal blooms that can result in fish kills, and in extreme causes can make our drinking water toxic. Animal manure, including horse manure, is another source of these nutrients.
Additionally, manure can contain harmful bacteria and parasites that can negatively impact water quality. It can be tempting to say, “It’s not just my animals doing this, what about all the wildlife that deposits waste in streams and water ways?” Indeed, there are many pollutant inputs from a range of sources, including wildlife. However, these two scenarios are not completely comparable. In a natural setting, many different species are moving across the landscape, unconfined and unhindered. This results in waste being deposited across a large area, typically on the order of square miles, with a greater amount of land available to utilize and process this waste. Livestock farming is the opposite, with one or two species in large numbers being confined to the same area of land. For example, a horse will produce an average of 35 to 50 pounds of manure a day, where a deer only produces 1.7 pounds. The larger the horse herd, the larger the waste input, A herd of 10 horses, for example, is equivalent to having ~250 deer confined to an area of land much smaller than they would normally use.
Hence, land used for livestock is under constant pressure to utilize the waste inputs of a much larger population of animals, and this may result in the land and water being overwhelmed with these pollutants. This impact can be even greater if a single stream or pond is the only water source in the field. The horses will spend a greater amount of time near the water, resulting in erosion and sediment pollution entering the water, in addition to any waste the animals deposit while spending more time in the area.
The solution
The good news is that there are natural methods of reducing water pollution from our horse farms. One of the most effective of these methods is the use of well-designed and maintained riparian buffers. Riparian buffers, defined generally, are vegetated areas near water resources that protect water quality while providing bank stabilization and habitat for aquatic and terrestrial species. They often include stream banks, wetlands, and vegetated floodplains such as fields and forests that exist along the length of bodies of water, such as streams and lakes. These riparian buffers work in several different ways to reduce pollutant runoff.
The vegetation in a riparian buffer works to first slow down the flow of surface water. This gives time for any sediment and other particles to settle out of the flowing water. Additionally, the plants utilize the nutrients and water for their own growth, absorbing nitrogen and phosphorus so it cannot enter water sources and instead becomes a part of the plant. Soil bacteria are another incredibly important component to riparian buffers. Certain soil bacteria utilize nitrogen as their energy source. Once planted, riparian buffers need little maintenance—you simply let nature take its course.
Careful considerations must be made to ensure that a riparian buffer will be effective before one is placed on the landscape. Key questions include:
What factors impact the effectiveness of a riparian buffer?
How wide should the riparian buffer be?
What plants should be used in the riparian buffer?
Does my state have any laws pertaining to riparian buffers?
The overall effectiveness of a riparian buffer is tied to hydrology, or how water moves across the landscape. Riparian buffers should be located adjacent to any surface waters where they can intercept water flowing off of pastures or manure piles. The flow of water must be slowed enough to allow sediments to settle out and prevent channels from being formed. Channels will effectively act as pipes that let the water pass through the buffer without being treated, so steps must be taken to prevent their formation. Be aware that most nitrogen reaches surface waters from water that has infiltrated the soil and become groundwater. Hence, the plants used in a riparian buffer must have deep roots to utilize nitrogen below the ground.
Width is the most important controllable variable that is considered when designing a buffer. While the slope of the land and existing vegetation are already dictated, width can be adjusted. In general, the wider the buffer, the more effective the buffer will be at removing pollutants. The wider the buffer, the more time water has to travel through it, slow down, and allow sediments to fall out of it; one source suggests buffers could be anywhere from 98 to 328 feet wide depending on the soil, slope, and nutrient input levels. The buffer width should increase if other factors are present that impact buffer effectiveness, including:
Steeper slopes that speed up water flow.
Less permeable soils that prevent water from infiltrating and becoming available to plants and bacteria.
The larger the animal population, the wider the buffer should be.
Areas with higher erosion rates.
In a comprehensive review of riparian buffer studies, some general guidelines on width have been established and can be used to help plan an effective riparian buffer. The most common suggestion is the use of a 3-zone buffer system, with specific plants and minimum widths. Zone 1, closest to the stream, should be undisturbed native trees to help stabilize the lake or stream bank, and it should ideally be at least 15 feet wide. Trees have the benefit of a deep root system, which brings carbon down to bacteria, stimulating the bacteria that will be necessary to remove nitrogen. Trees also provide long-term storage of nitrogen, since trees have longer lifespans than grasses. Zone 2, should be a combination of native trees and shrubs, which can be harvested occasionally to remove nitrogen, and should be the widest of the three zones. Zone 3 should be grass, at least 20 feet wide, to filter and slow water. Ideally, this grass zone should be fenced out of the pastures (Figure 2).
On many small-acreage horse farms, a large buffer area might not be feasible. However, just because a buffer might be smaller does not mean it is ineffective. Indeed, a balance must be found between the amount of property available for the horses and for the buffer, the number of horses on the property, the landscape (slope, ecosystem, proximity to water), and costs of implementing a buffer.
When selecting plants to include in a riparian buffer, choose species that 1) are native to the area to prevent the introduction of invasive species, 2) are not toxic to horses, and 3) are not nitrogen-fixing species, such as clover. Nitrogen-fixing plants have bacteria in their roots that provide nitrogen to the plant, so they are less likely to remove nitrogen from the environment.
It is important to realize and account for the impacts that horses may have on that landscape. With water quality impaired in many places across the U.S., reducing the impact of one’s animals can assist in making waters cleaner on both your property and to downstream users and aquatic habitats. Riparian buffers provide a natural, effective solution to the question of horse-related nutrient pollution. With a little planning, they can be implemented on many properties as a cost-effective best management practice.
Where to find more help?
Your local Natural Resource Conservation Service office or Soil Conservation District office can help with riparian buffer guidelines and practical advice specific to your area, and can help determine if your farm is eligible for grant funds to help offset the costs of riparian buffer restoration. They can also assist you should your particular state have any laws regarding riparian buffers that need to be met, as such laws are becoming more prevalent across the U.S.
A handful of representative states and their riparian buffer programs are listed below:
-Utah
コメント