Reducing nitrogen and phosphorus levels in surface waters of North Carolina has become a priority, especially in watersheds that drain into nutrient impaired lakes, such as Jordan and Falls Lake. The agricultural community has renewed its efforts to implement best management practices (BMPs) that reduce nitrogen and phosphorus movement from agricultural land to water resources. One such BMP is livestock exclusion fencing.
Livestock exclusion fencing involves constructing a permanent fence along streams in livestock pastures that prevents animals from accessing the stream channel and the land adjacent to the stream (the riparian area). Excluding beef or dairy cattle from the stream channel and area immediately next to the stream has been shown to reduce nitrogen, phosphorus, pathogens, and sediment loads in streams by eliminating direct deposition of animal waste and the trampling of streambanks. This facilitates the growth of herbaceous and woody vegetation that filters runoff from upslope, stabilizes stream channels, and, in some cases, removes nitrate from the groundwater.
In two North Carolina beef cattle pastures with exclusion fencing, comparisons between pre and post-implementation monitoring of streams showed that nitrogen loads were reduced by 33% to 41%, phosphorus loads by 47% to 65%, and sediment loads by 60% to 74% (Line et al. 2016; Line and Doll 2023). Nitrogen was reduced by 78%, phosphorus by 76%, and sediment by 82% in a stream draining a dairy cow pasture with exclusion fencing (Line et al. 2000). Further, Wiseman et al. (2014) documented that nitrate in groundwater was significantly reduced within a riparian area 10 to 15 years after beef cows were excluded and trees planted. These substantial reductions, when multiplied across watersheds, can help achieve the mandated nutrient reduction goals from agricultural land.
These case studies, along with other research, help answer several common questions about the effectiveness of exclusion fencing:
- How far from the stream channel does the fence need to be located?
- Does the length of the whole stream channel need to be fenced?
- What are the effects of limited grazing/vegetation management in the excluded area on water quality?
How far from the stream channel to fence?
Exclusion fencing (see Figure 1) has been shown to be effective in cases where it was implemented 10 ft from the top of the streambank (Line et al. 2016; Meals and Hopkins 2002; Galeone et al. 2006) to 100 ft (Line and Doll 2023; Line et al. 2000). The width, or distance from one side of the stream of the exclusion corridor, depends on the slope of the land, the type and density of the vegetation next to the stream (in the exclusion corridor), the slope and length of the area that drains to the stream, and the amount or intensity of the source of nutrients. In general, the steeper the slope (toward the stream), the less dense the ground vegetation in the exclusion corridor, and the longer and steeper the upslope contributing area, the wider the exclusion corridor must be to maximize the runoff treatment.
For example, the Line et al. 2016 study found that 10 ft from the streambank to the fence was adequate for maximum effectiveness when the land draining to the stream was less than 600 ft from the top of the slope to the stream and its slope was less than 3%. When the slope of the land draining to the stream was 5% to 8% and the length was as much as 600 ft from the top of the slope to the exclusion fence, Line and Doll (2023) found that fencing 50 ft to 90 ft from the streambank was highly effective with greater than 30% reduction in nitrogen loads and greater than 50% reduction in phosphorus and sediment loads. Dense herbaceous vegetation grew quickly in both exclusion corridors creating a vegetated buffer, which dispersed and filtered runoff from the upslope pasture.
There is a combination of slope length and steepness from which runoff can be too great and fast for a narrow exclusion corridor to provide adequate treatment. Runoff from long, steep slopes tends to concentrate before entering the exclusion corridor where it can flatten dense vegetation, which reduces treatment. For a dairy operation with high cow density and an intense source of nutrients, exclusion fence from 80 ft to 100 ft from the stream was found to be highly effective (Line et al. 2000). When biosolids and animal waste are regularly applied to the pasture, a wider exclusion corridor may be required because additional nutrient uptake and filtering by vegetation are needed to protect the stream. State and federal cost sharing programs that support exclusion fencing typically require a minimum of 10 ft from the streambank, although the distance can be greater in specific cases where there is a heavy use area upslope.
How much of the stream channel to fence?
For maximum effectiveness, the entire length of the observable stream channel should be fenced because treatment of runoff that becomes concentrated in a stream channel is ineffective. However, some streams begin as shallow intermittent channels, which if they are well-vegetated, may not need to be protected by fencing because the flow will often be shallow and the streambanks low. For example, in the Line et al. 2016 study, the upper 800 ft of the 2500 ft section of stream channel was not fenced because it had only wet-weather flows, was well-vegetated, and had streambanks of less than 1 ft high. The water quality monitoring results indicated that only some of the stream channel needed to be fenced. In the Line and Doll 2023 study, where the entire stream channel was fenced, the effectiveness of nutrient and sediment reduction was generally greater than in the Line et al. 2016 study, although the land slopes in the pasture were steeper. Both studies had similar beef cow grazing densities, soils, and waste applications. Thus, fencing the entire observable stream/waterway channel provided the best treatment. It is important to remember that the effectiveness of exclusion fencing decreases where the stream channel is small (less than 3 ft wide and 2 ft deep) and well-vegetated with intermittent flow.
Fencing even wet-weather waterways can help reduce nutrient, pathogen, and sediment export from a pasture to a stream. In some cases, obtaining cost-share support may require fencing the entire stream channel, as well as the degraded sections of the contributing waterways within the pasture.
What is the cost effectiveness of exclusion fencing?
Exclusion fencing is not a border fence, and can be less sturdy. One or two strands of electric fence are generally sufficient, although many landowners (including those in the three NC case studies) prefer a 4 to 5 strand, barbed wire fence with wooden posts for sturdiness and low maintenance. The Line et al. 2016 study found that the 5-strand barbed wire fence (see Figure 1) cost on average $2.83 per linear ft installed in 2011. In the Line and Doll 2023 study, a 6-strand barbed wire fence cost $2.90 per linear ft installed in 2015. Polywire and high tensile electric fence costs less, and woven wire more, although prices vary by location across the state. In addition to the fence, an alternate watering system (since the stream is inaccessible to the livestock), stream crossings, and gates can increase the cost. In the Line et al. 2016 study, the landowner already had an alternate watering system in the pasture, but needed a culvert stream crossing, which cost an additional $5,000. In the Line and Doll 2023 study, two pipe gates that cost $250 each were installed, along with two watering tanks and piping that cost $4000 each.
Where available, state cost-share programs, such as the North Carolina Agricultural Cost Share Program (ACSP), will pay up to 75% of the cost of the exclusion fencing and the associated costs. When Cost-Share is used, there are technical specifications for the type and extent of fencing and the width of the exclusion corridor.
The Line et al. 2016 study found that annual reductions in total nitrogen (N) and phosphorus (P) loads from the 135-acre pasture were 568 and 233 lb/year. These reductions over 10 years (the typical Cost-Share contract length) as well as the crossing and fence costs yield a cost of $2.55 per lb N and $6.22 per lb of P removed. For the Line and Doll 2023 study, annual reductions were 359 and 62 lb/year for the 48 acres of pasture. These reductions over 10 years plus the costs of the fence, gates, and watering tanks yield a cost of $4.41 per lb N and $25.52 per lb of P removed. These are actual total costs (not the Cost-Share portion), and do not include design, maintenance, or land costs. The higher cost per pound removed in the Line and Doll (2023) study can be attributed to the cost of the alternate watering system and smaller pasture area. As a comparison, current nitrogen and phosphorus offset rates (amount paid to offset export of excessive N and P) for new development in NC range from $11.70 to $120.70 per lb N and from $171.90 to $640.30 per lb of P. Thus, livestock exclusion fencing is a relatively cost-effective strategy when compared to urban stormwater control measures.
Can vegetation inside the exclusion corridor be managed?
For maximum effectiveness, management of vegetation inside the excluded corridor should be minimal. Natural revegetation has been shown to provide a fast, effective way to stabilize the stream channel and adjacent land. Trees or shrubs can be planted in the exclusion corridor to create a wooded riparian buffer, which can enhance nitrogen removal (Wiseman et al. 2014), shade the stream, stabilize the streambanks, and provide wildlife habitat. However, some landowners, such as in the Line et al. 2016 study, do not allow any woody vegetation in the exclusion corridor and will cut it down. This did not appear to significantly reduce the water quality effectiveness of the exclusion. However, flash grazing, which allows livestock in the exclusion corridor for a day or week to manage vegetation, does have a significant, albeit short term, effect on the water quality effectiveness of the exclusion. In the Line and Doll 2023 study, cattle roamed unintentionally in the excluded corridor for several days in December, 2021. This resulted in a 5-fold increase in ammonia nitrogen concentrations during the corresponding two-week period. With a few exceptions, livestock are not allowed at any time in the exclusion corridor when NC Agricultural Cost Share program funds are used.
Are there other benefits to livestock exclusion?
One benefit of exclusion fencing is that it forces livestock to drink from the cleaner alternative watering sources upslope from the stream. Another benefit is that the fencing reduces the likelihood of livestock injury on the steep, unstable banks of stream channels. Young livestock are also prevented from accessing the muddy stream bottom where they can become stuck or fall down while navigating the streambanks. One final benefit is that livestock can be more easily observed when not in a stream channel.
Agricultural production practices such as allowing livestock unlimited access to streams in pastures can sometimes threaten water quality. The threat can be reduced by installing fencing that excludes livestock from direct access to stream channels. Research has shown that, in general, a relatively narrow (10 ft minimum from streambank) exclusion corridor is effective for more flat, more narrow pastures, while a wider exclusion corridor (50 to 90 ft from the streambank) for wider and steeper pastures is effective. Other factors such as animal density and waste application to the pasture may also affect the width of the corridor. Cost-share programs may be available to off-set the costs of livestock exclusion, which include fencing, alternative water sources, gates, and stream crossings. Livestock health and well-being may also be improved by blocking access to the stream.
Livestock exclusion fencing is a great example of a BMP that allows producers to maintain a high level of agricultural production while also preserving water quality.
Galeone, Daniel G., Robin A. Brightbill, Dennis J. Low, and David L. O’Brien. 2006. “Effects of Streambank Fencing of Pasture Land on Benthic Macroinvertebrates and Quality of Surface Water and Shallow Ground Water in the Big Spring Run Basin of Mill Creek Watershed, Lancaster County, Pennsylvania, 1993-2001.” USGS Scientific Investigations Report 2006-5141.
Line, D.E. and B.A. Doll. 2023. “Effects of Livestock Exclusion on Pollutant Export from a North Carolina Beef Cow Pasture.” TRANS ASABE (in press).
Line, Daniel E., Deanna L. Osmond, and Wesley Childres. 2016. “Effectiveness of Livestock Exclusion in a Pasture of Central North Carolina.” Journal of Environmental Quality 45, no. 6: 1926-1932.
Line, D.E., W.A. Harman, G.D. Jennings, E.J. Thompson, and D.L. Osmond. 2000. “Nonpoint-Source Pollutant Load Reductions Associated with Livestock Exclusion.” Journal of Environmental Quality 29, no. 6:1882-1890.
Meals, D.W. and R.B. Hopkins. 2002. “Phosphorus Reductions Following Riparian Restoration in Two Agricultural Watersheds in Vermont, USA.” Water Science and Technology 45, no.9: 51-60.
Wiseman, Jacob D., Michael R. Burchell, Gary L. Grabow, Deanna L. Osmond, and Tiffany L. Messer. 2014. “Groundwater Nitrate Concentration Reductions in a Riparian Buffer Enrolled in the NC Conservation Reserve Enhancement Program.” Journal of American Water Resources Association 50, no. 3: 653-664.
Publication date: May 17, 2023
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