In “Riparian Regulations Threaten Livestock” we describe how new riparian regulations were threatening livestock grazing in Maryland, providing an example from one grazier trying to find ways to cope with the new rules. The theory behind keeping animals out of streams and waterways is simple: to improve water quality. But that simple goal may not take into account the ways that pasture-based agriculture contributes to watershed protection. Since these kinds of regulations are periodically considered all across the country, it’s important for graziers to understand what science tells us about problems and contributions that livestock make to water quality.
There are three main pathways for animal-based nutrient pollution to cause problems: 1) run-off from manure on pastures or fields; 2)
leaching of nutrients from manure through the soil to ground water; and 3) poop deposited right into water.
Path 1: Run-off
Contributions from run-off are nominal, and we’ve known this for a long time. For example, research done in south Nebraska more than 30 years ago found that while there is more fecal coliform in runoff from grazed pasture than from ungrazed pasture, both concentrations were similar to the numbers coming off urban land and cropped fields. To muddy that water a bit, the researchers also think that the bacteriological inputs from the grazed and ungrazed pasture were likely a result of wildlife deposits. As for nutrient pollution, runoff from the grazed pasture was typically much less than that coming from cropped land.
For decades, we’ve known that there is much less runoff overall from pasture than from cropped fields. Mature pasture acts like a sponge. Its vegetation keeps soil in place, and slows water, allowing more of it to infiltrate. In fact, the USDA’s soil-loss calculations say pastures lose 80-90% less soil than the several tons per acre average from traditionally managed row crops. You can see this difference for yourself in this video from grass-based farmer, Eric Noel showing run-off from a grain farm, a grain and dairy farm and his own grass pasture as they come together at the base of the watershed.
While there isn’t much runoff to worry about on grazed pastures to begin with, a concerned grazer can add buffer strips along their waterway. Buffer strips are 10 to 50 ft of vegetation planted between fields and waterways to slow the flow of water coming off a field. By slowing the water, sediment settles into the buffer strip rather than flowing right into the surface water. Experts vary on how wide these strips need to be, so if you’re interested, talk to your local extension agent about what they recommend for your specific location.
Path 2: Leaching
Leaching is an interesting concept for how livestock contribute to water pollution, and it has incited some strong opinions on both sides. The basis for thinking that livestock cause nutrient leaching may be due to research some scientists have done using columns filled with soil, called lysimeters, measuring urine flow through them. Their results show significant amounts of nitrogen leaching through the lysimeter, and they have concluded that livestock on pasture can cause nutrient pollution to groundwater by peeing on pasture.
If you think the lysimeters provide an accurate representation of what is happening in pasture, you will think that leaching could be an issue. However, many scientists aren’t sure that lysimeters give a good picture of what is going on, and doubt that grazing causes nutrient pollution via leaching.
These scientists point out that construction of the lysimeters doesn’t mimic the typical pasture or the conditions under which urine hits it. For example, one study used a 70 cm deep lysimeter with a diameter of 50 cm (1 foot 8 inches across) filled with rocky soil. It likely had plenty of cracks and crevices. So when the urine was poured on top, it wended its way through the column quickly along those larger channels. Meanwhile, we know from experience watching cows pee on pasture, that if there’s any sort of slope, the pee spills downhill, spreading out along the pasture surface. The slower movement through the vegetation and the soil profile would allow soil to act like the natural filter it is, attracting nutrients and allowing them to be taken up by plants.
Given the problems with the research methods, and other research that counters the lysimeter results, it’s safe to say that leaching is not an important, livestock-caused problem.
Path 3: In the stream
If a cow poops in the stream and a neighbor sees it, there’s nutrient pollution. If no one saw it, it’s hardly going to make a ripple.
The problem lies in the frequency and scale of livestock’s use of a waterway. Given no options and only one water source, livestock can cause stream bank erosion and cause nutrient pollution in a stream. But given other water sources, or when managed with rotational grazing, waterway issues can be easily reduced.
For example, given a choice between stream water and troughs of clean water, cows will spend most of their time (92% in a West Virginia study) drinking from the troughs, so stream bank erosion was reduced. When Dr. Ron Sheffield and his colleagues measured the effects of providing grazing animals off-stream water, they found stream banks had 77% less erosion, and streams carried less sediment in the water (90%), and less nitrogen and phosphorus (54 and 81%, respectively).
This all goes to say that IF grazing management is good, it’s not going to harm stream water quality. Good grazing management means the herd moves frequently, not spending too much time on any section of stream. Ideally, it means water is available outside of the stream, too.
While we promote good grazing management, including not allowing much time along stream banks, an Iowa study found no difference in stream bank erosion when cows were kept off stream banks than when they had unrestricted access to stream banks.
Can we legislate water quality?
While good grazing management is important, and providing off-stream water sources to drink from seems to help stream water quality, the challenge in this debate is that it’s all predicated on hugely variable factors- weather, animals, streams and farmers. If farmers manage their pastures and streams carefully, livestock access shouldn’t be bad for water quality
This gets us back to where we started with in the first article. If we end up legislating livestock exclusion, farmers might choose to stop grazing rather than try to comply with inordinately onerous laws. Then we are likely going to end up with row crops where pasture stood. And that may be two steps in the wrong direction by anyone’s count. We all want clean water. A better solution might be to consider the problems and benefits of pasture-based livestock and how we can work together to ensure we get what we want. Well-managed pastures can provide food and watershed protection. We’re going to begin discussing these “ecosystem services” that farmers and ranchers provide and what that might mean to your bottom line.