Grazing livestock produce a waste product – manure and urine – containing water, urea (ammonia), organic matter, nitrate, and bacteria. Some of the components of manure inevitably end up in surface water. There are many reasons for adopting good manure management practices: improved animal health, increased pasture productivity, enhanced wildlife habitat, and increased land value.
Dr. Nathan Sayre, professor at the University of California, Berkeley, has stated when speaking about the future of sustainable ranching in the western U.S., “[Ranching] has outlasted beaver trapping and bison hunting. Beaver and bison look like cases where an activity was ecologically unsustainable. But in truth it wasn’t the activities per se that were unsustainable but the way they were practiced in the 19th century, which can be traced to economic forces and property relations rather than ecology . . . The way [ranching] is practiced today is radically different from the way it was practiced then, even if we call it by the same name” (emphasis mine).
Applying this to water quality, the presence or absence of cows in a riparian area is not as important as the way they are managed. This paper addresses the effects of livestock grazing, specifically fecal coliform bacteria and sediment, the pollutants most commonly associated with livestock, and how they behave in the environment. It also addresses temperature and to what extent this can be influenced by livestock. Finally, the paper intends to persuade graziers to practice planned grazing toward a goal of productive pastures/rangelands/forestlands and ecosystem health.
Almost everyone can agree that from an ecological perspective clean water should have: low bacteria levels; a balanced sediment load; no harmful chemicals; a temperature range that supports aquatic life. Water quality is influenced by many human activities, whether agricultural, industrial, or recreational, as well as factors completely beyond our control such as climate events and the activities of wildlife. Livestock grazing is one of the factors over which we have some control. Purposeful water quality change cannot happen without considering the influences of both the vegetation present and the practices employed in managing the land.
Herbivores are animals that derive their sustenance exclusively from plants. Herbivores are the second level in the food chain, taking nutrients built from the sun’s energy by plants and converting it to animal protein. They are the harvesters of solar wealth. Their effects on the landscape are highly variable, even more so under the management of man. The behavior of an herbivore in the absence of any human constraint on their behavior is to “follow the green.” This optimizes consumption of quality forage and the deposition of plant- available nutrients and soil-building organic material. Man has the ability to capitalize on this symbiotic relationship or disrupt it. Well- managed grazing that encourages even utilization of plants and allows time for the plant to fully recover has a number of significant but undervalued benefits to the manager. Forage production is maximized. Animals are much less likely to pick up internal parasites when the grass is left taller than 3-4”, and bare ground is minimized, protecting soil. Stem density is high, serving to slow overland sheet flow. Root growth and sloughing builds soil organic matter which is good for increasing water-holding capacity, nutrient capture, infiltration, and porosity.
The actions of the herbivore – defoliation, hoof action, and manure deposition – affect the plant community at the individual and community level. They also affect soil, including nutrient cycles, compaction or aeration, and water-holding capacity.
Grazing directly affects biomass growth, internal allocation of resources, litter dynamics, recruitment of new plants, and plant stature/longevity. Grazing indirectly affects competitive relationships among species, community composition, percent ground cover, soil development, and successional development of the plant community (Bunting 1998). Understanding specifically how a grazing event will affect the plant community requires knowledge of the species involved. Plants maintain a rough equivalence of above-ground biomass and below-ground root biomass (Fig. 1). When a plant is grazed, there is a die-off of root material proportional to the amount of foliage removed. This root material is rapidly decomposed and stays in the soil as organic matter. This “root sloughing” can be positive or negative. When the plant has time to adequately regrow from clipping, it replaces its root volume so that each defoliation event results in increased organic matter to the soil. In arid regions where decomposition of litter is slow, this may be the primary source of soil organic matter. If the plant is not given adequate time to recover, the successive clippings prohibit root recovery, leaving soil space unoccupied and susceptible to weed invasion.
A diversity of plant species is important to soil health and has implications for water quality. Bunchgrasses provide deeper rooting that accesses deeper nutrients and enhances infiltration, while shallower-rooted rhizomatous species protect the soil surface.
There is never a good excuse for sediment loss from irrigated or dryland pastures. Well- managed pastures will build soil, capturing sediment that is carried by the wind, irrigation water, or run-on water from adjacent areas.
A pasture is essentially a grass filter managed with livestock (Fig. 2); grass filters are one of the most effective solutions to a sediment problem upslope.
Managing for sediment in sheet flow is a matter of simple physics. As water velocity increases, the amount of sediment the water can carry increases. Slowing down the water causes sediment to fall out of suspension.
Therefore, stem density is the most important factor in filtering sediment from overland sheet flow. Infiltration and percolation properties of the soil also aid in preventing sedimentation. If precipitation is able to move into the soil at the point of contact and can move through the soil once absorbed, less water will be prone to move across the surface. Surface roughness is a positive contributor to infiltration.
The most significant source of livestock- induced sedimentation is from streambank trampling or heavy grazing which removes the herbaceous and/or woody vegetation (Fig. 3) whose roots hold the bank together.
Streambanks are most susceptible to hoof damage when they are wet, as in early spring. However, this is also the time when upland forage will be greener and more attractive to livestock and the riparian zone is less of an attractant. When the soil is dry, streambanks are much less susceptible to erosion, but cattle may tend to concentrate in riparian areas for the abundant forage and water. Later in the season when herbaceous vegetation has gone dormant or is unavailable livestock may shift their preference to woody species. If use is severe, this can prevent regeneration of woody species that are valuable for anchoring streambanks.
Sediment is perhaps most significant as a carrier of pollutants (bacteria, nutrients, chemicals) rather than as a pollutant itself. It is an indicator that something is wrong.
Fecal bacteria enter streams in two primary ways: direct deposit by animals and overland flow (Larsen 1994). There is a poor correlation between either 1) the numbers of animals in a watershed or 2) the total amount of waste produced, and measured pollutants in-stream. Pollutant yields are much more closely related to hydrogeological and management factors such as flow rate, runoff intensity, animal distribution and frequency of stream disturbance. Bacteria counts are highly dependent on temperature, timing, and distance traveled since deposition (Robbins 1979). A 1985 article by Oregon State University researchers Bohn & Buckhouse speaks to elusive conclusions from bacterial sampling: “Comparisons for research, such as paired watersheds or changes over years, are valid only when all stations are sampled on the same days, at the same times, and under comparable use conditions.” “Use of coliform concentrations as a research procedure . . . may not always be cost- effective or satisfactory because of spatial variability and the need for large sample sizes.”
Coliforms tend to adhere to suspended sediments and settle out once they are in a stream; therefore, bottom sediments are a significant reservoir, subject to resuspension. Bacteria die within 7-14 days in aerobic soil, but may stay alive in the protection of a fecal pat for up to a year (Bohn 1985). This also means that under most circumstances bacteria deposited away from a stream will go into the soil and stay in the soil until they die.
Most fecal contamination is the result of direct deposition in a rangeland situation rather than overland flow. Overland flow can be significant, though, when rainfall or snowmelt rates exceed infiltration capacity (Miner 1992). Nevertheless, manure landing near a stream has a much smaller potential for
impact that manure deposited directly into it. In fact, a study by Larsen found even very narrow filter strips to be highly effective, measuring an 83% reduction in FC in 30 minutes with a 0.61 meter filter of Kentucky bluegrass sod. The same study found a 95% reduction with a filter of 2.13 meters (Larsen 1994). Doyle (1975) found no significant movement of bacteria beyond 3.8 m. However, other studies have found that bacteria can travel long distances overland, such as under circumstances where/when the soil is saturated. Glenne (1984) found that a 50m buffer was required to obtain a 90% reduction of bacteria on a 10% slope. Dickey & Vanderholm (1981) found that vegetative filters were effective at reducing nutrients and solids, but found insignificant reductions of bacterial concentrations. Data from the Kittitas County Water Purveyors indicates that under nutrient-rich conditions, such as in intensively-managed irrigated pastures, bacteria may adsorb to the water molecule instead of a soil particle. In other words, the water may look clear (Fig. 4), as it is free of sediment and even free of the organic material associated with manure, but bacteria levels may remain high.
The source of wildland bacteria is of concern as well. Fecal coliform bacteria are common to the intestinal tracts of warm-blooded animals. Robbins (1979) states “Controlling pollutants from unconfined animal production units may be to no avail unless other pollutant sources that naturally occur in the same watershed are controlled as well . . . Additional information and research on the
form and extent of natural pollutant sources are needed to formulate meaningful water quality management programs.”
Stream temperature is dependent on heat transfer with substances it contacts and incoming solar radiation. Clean water absorbs or transmits most of the visible spectrum as well as the far infrared. If energy is absorbed, it is converted to heat. If transmitted, it is absorbed by underlying soil and absorbed as heat energy.
The most significant factor in stream temperature influenced by livestock management is stream morphology. Narrow, deep streams have less surface area to gain heat from the air than shallow, wide streams. Shallow, wide streams also allow more solar radiation to be absorbed by the streambed, which immediately transmits this to the water through convection. Proper grazing maintains healthy roots of both herbaceous and woody vegetation and prevents trampling, protecting stream function and the mechanisms which moderate temperature.
Riparian forest vegetation intercepts light and reduces incoming solar radiation and contributes to proper stream form.
Management to improve or maintain water quality needs to incorporate practices that reduce the likelihood of direct deposition and discourage overland flow or manure, or conversely, encourage as much precipitation as possible to enter the soil.
Water tanks – Water tanks are an extremely valuable management tool. Miner, Buckhouse, and Moore (1992) found that the presence of a watering tank reduced the time that livestock spent drinking or loafing in the stream by more than 90%. Logically, there is a corresponding decrease in direct deposition of manure into that stream. Where animals are dispersed, i.e., not concentrated on or near the stream, there is little documentable effect on a stream’s chemical composition or bacterial loading (Milne 1976).
Not only is there significant benefit to water quality, but water tanks are one of the most effective strategies for improving pasture/rangeland distribution to make better use of upland forage and have been legitimately credited with improvements to animal health. Early spring conditions are tough on young calves. Wet and cold and coated in manure is a recipe for disaster. Animals with a wet coat in the cold are burning up their caloric intake trying to maintain body temperature, leaving little nutrition for growth. These conditions weaken the immature immune system, worsening the already high bacteria challenge present in manure-covered wintering areas. Decreasing animal contact with animal waste and decreasing the stress levels associated with wet and cold significantly reduces the costly risk of scours, navel ill, mastitis, internal parasites, and reproductive diseases (Smith 2005).
Tanks are also one of the cheapest solutions for confinement lots where access to surface water may be a concern. Milne (1976) found that where livestock activity is concentrated, bacterial concentration increases dramatically, although this increase tends to be short-lived.
Water gaps – An on-stream alternative to a tank is a hardened crossing or water gap. Specifications for crossings and water gaps are widely available; an ideal design makes the animal uncomfortable while obtaining water so that the time spent in direct contact with surface water is restricted what is necessary for drinking. Relatively steep
access roughened with large cobble effectively discourages loafing.
Riparian paddock – Riparian enclosures are an effective management strategy, especially in locations or during seasons in which the difference in forage quality and quantity between the riparian zone and the adjacent upland is pronounced. It is always a good idea to fence “like” areas – fences should follow soil types, topography, water tables, aspect change, slope breaks, etc. On western rangelands and forests, vegetation differences tend to be very pronounced. Fencing like areas simplifies management by reducing the variability within a paddock so that utilization is more uniform and areas of either sacrifice or underuse are avoided. Exclosures certainly work to prohibit direct deposition of manure but may develop other problems, such as weed infestation, excessive shrub or tree growth.
Supplementation – Grazing livestock are not always able to meet their nutrient requirements from available forage, especially during times of high nutrient demand, such as when lactation and pregnancy overlap, or during periods of low forage quality, such as during late gestation, often in winter. Where available crude protein and energy are less than the animal’s
need, supplementation is required to maintain body condition and animal performance. As most commercial supplements are highly palatable, animals will actively seek supplement locations and travel significant distances to consume it. Research conducted by Bailey & Welling in 1999 showed low-moisture blocks affected grazing patterns up to 600 meters from the supplement. Supplement placement has great potential to positively influence livestock distribution in rangeland settings toward benefits such as improved manure distribution for even nutrient application and increased distance of manure deposition from surface water. For more information on livestock distribution, go to http://animalag.wsu.edu/forages/index.html.
Herding – Herding is often misunderstood as “chasing”. Chasing has been found to have little long-term benefit to either livestock distribution or water quality. Herding, however, has proven to be an effective method for planning and directing livestock forage use. Herding properly means low- stress stock movement from here to there and giving animals a reason to stay “there”. Herding in combination with supplementation is more effective than either alone. For more information on herding, go to http://managingwholes.com/–low-stress-livestock.htm.
Planned grazing – Perhaps the most overlooked solution in the search for quick fixes is smarter grazing management. In the end, water quality is related to watershed health. Watershed health is driven by the health of the individual ecological sites that comprise it. Those ecological sites are characterized by specific plant communities that are responding to all of the biotic (animal use, plant-plant relationships, plant-soil interactions) and abiotic factors (precipitation, wind, parent material/soil fertility, etc.) present. Grazing livestock are one significant influence that we can control. It is worth restating that the most important factor in successful grazing, i.e., grazing that promotes ecosystem health, is allowing
adequate time for plant recovery. This is not restricted to leaving enough residual or staying off long enough to allow replacement of the photosynthetic leaf tissue but also includes timing grazing in order to facilitate the long-term health and reproduction of the dominant or desired forage plants. Poor grazing management is just like weeding your garden in reverse – removing the most desirable plants and leaving the least desirable to take advantage of nutrients, moisture, sunlight, and soil space. Pictures are often more effective to describe the cumulative effects of the loss of desirable perennial vegetation on an ecosystem.
Compare this photograph (courtesy of the National Riparian Service Team) of the Crooked River, Oregon in 1979 to the follow- up photograph taken seven years later.
The plant community and stream morphology in the first picture is the result of decades of continuous, season-long grazing. Riparian- type vegetation has been lost, causing the stream to become shallower and wider, warming water and encouraging bacteria. The second picture illustrates the recovery after switching to spring-only use
Mid- to late-season rest on the plant community led to riparian vegetation returning and the stream banks were able to heal. Periods of non-use also prevent resuspension of stream sediments which may harbor fecal bacteria.
Forested riparian buffer – Riparian forest buffers are frequently part of conservation cost-share programs. This is because the deeper, larger roots systems of woody vegetation are important for holding together the soil of streambanks, much like rebar is important to the stability of concrete.
Shallower grass roots are like a skin or sealer to protect the concrete’s surface. Some have questioned the usefulness of riparian forests for improving water quality. Reviewing the principles for eliminating sediment and bacteria, we need stem density to filter sediment and soil penetration (infiltration) and water-holding capacity to keep bacteria onsite. A closed canopy riparian forest that has little herbaceous vegetation on the forest floor may do little to filter sediment from sheet flow, but water-holding capacity and infiltration tend to be high in soils occupied by riparian forest vegetation. This type of vegetation is also important for nutrient uptake and subsequent storage of carbon and nitrogen by the woody stems (Lowrance 1981). Forested riparian buffers must be managed for optimum efficacy.
Other practice considerations – Water quality is tied to ecosystem health. Ages-old methods for distributing livestock were developed to maintain the long-term health of
the plant community. If ecosystem health is poor, no amount of band-aid fixes will ultimately suffice to improve water quality. Focus on measures that improve the health of the land.
Fencing is an invaluable aid to better livestock distribution. Use fences to fence like areas or to break these larger paddocks into smaller ones if greater concentration or improved control of stock is needed. Provide offstream water when possible – this is good for animals, good for upland distribution, and good for avoiding overuse on riparian vegetation. In the winter, change feeding locations so that manure is distributed evenly across the landscape. Damage to pasture grass is minimal after the first killing frost or two as long as the sod is not broken. During the growing season, don’t allow livestock to graze any plants lower than 3-4”, taller if the dominant forage species are large bunchgrasses. Remember that not all plants are preferred equally. Where this is the case and livestock are at low enough densities that they are highly selective, time de-stocking based on the most palatable grass or the best plants will gradually decline. Facilitate the recovery of damaged riparian areas through changing timing or duration of use, and install hardened crossings and water gaps where appropriate. When confinement is necessary, berms and settling ponds can be strategically constructed to accept runoff water and prevent large quantities of concentrated manure from reaching surface water bodies. Create vegetative filter strips between confinement lots and surface water, managed either with controlled grazing or mowing to maximize stand density and prevent weed invasion.
The most important characteristic of a successful manager is a commitment to adaptive management. Be observant of the land under your control – when things don’t look right, change the plan. Common sense will go a long way. Extension offices and Conservation Districts are prepared to help you with answers as well.
Water quality is a product of the health of the watershed. Grazing management that maintains or improves rangeland, pasture, riparian, and forest health will protect water quality.
WSU Extension Central WA Animal Ag Team: http://animalag.wsu.edu
WSU publications: http://pubs.wsu.edu/cgi-bin/pubs/index.html
WSU Small Farms Team: http://smallfarms.wsu.edu
National Sustainable Agriculture Information Service: http://www.attra.org/
Grass Growth & Regrowth for Improved Management (Oregon State Univ.): http://forages.oregonstate.edu/projects/regrowth/default.cfm
EPA Compliance Center: http://cfpub.epa.gov/npdes/afo/compliance.cfm