2015 25.1 Water Quality Risk Assessment
Water Quality Risk Assessment for Grazing Areas
Positive management factors for reducing livestock pollution
Tipton Hudson, WSU
More than 15,000 households in Washington State have livestock. Many of those animals are occasionally in proximity to surface water. Proactive efforts to stop pollution before it happens and promote the drivers of water quality (healthy vegetation and soils) are critical. Prevention, not dilution, is the solution to pollution.
Pollutants from livestock
While any single contributor (landowner) of nonpoint source pollution may not be significant, the cumulative effects of multiple sources in a watershed can be a major problem. The contaminants of water typically associated with or influenced by livestock are bacteria, sediment, nutrients (especially nitrogen and phosphorus), and water temperature. It is important to note that these are pollutants by degree. These substances or conditions occur naturally in a healthy environment; they are only a problem when they are at unnatural levels for a given site, outside some natural range of variation. This stands in contrast to pollutants that are unnatural substances at any level, foreign to the environment: pharmaceuticals, pesticides, etc. When unnatural levels of sediment, fecal bacteria, nitrogen, phosphorus, or (high) temperature are present and persistent, they may be very ecologically destructive. Numerous studies have documented the adverse effects of improper grazing on riparian, aquatic, and upland ecosystems.
The effects of livestock grazing on streams are highly variable, depending on site factors such as stream type, substrate type, vegetation composition, hydrology, as well as on grazingrelated factors such as timing, duration, intensity, and frequency of grazing use. The dominant effect of livestock grazing on riparian zones is vegetation removal. This has a much greater potential influence on streams with sediment substrate (stabilized by vegetation) than on those with rock and cobble substrate (less susceptible to destabilization if vegetation is altered).
Livestock grazing is a water quality risk less for the immediate contribution of fecal bacteria or nutrients, although that can be significant, but for the long-term changes to the functioning of stream processes that are collectively responsible for filtering and assimilating external inputs of sediment, nutrients, and bacteria and creating conditions that moderate stream temperature.
Nonpoint source pollution is, by nature, difficult to track—any single contributor may not be significant. In addition, many other organisms in the environment have potential to contribute pollutants such as fecal bacteria, which are shed by all warmblooded animals. Single-pollutant thinking won’t solve the problem. We can’t say categorically that grazing is good or bad. We must say that all these factors influence interactions among pollutants, influence the environmental conditions which interact with pollutants, and that livestock grazing affects all of the pollutants and the factors that drive the pollutants. The indicators of biological function can be observed without expensive and laborious water testing procedures and equipment, but they are necessarily subjective, requiring thoughtful analysis and interpretation.
Improper livestock grazing can have serious and wide-ranging effects on riparian ecosystems and the streams they depend on. However, proper grazing can only be defined specific to a given site. This dilemma is not unique to riparian grazing; it applies to many natural resource management questions. The dilemma is addressed by what is called adaptive management: determine what the desired future condition is, devise a plan to move from the current condition to the defined future condition or at least in that direction, implement the plan, and evaluate the results to determine whether the resource conditions under new management are improving. But the next step is equally critical—if the conditions are not improving, you must adjust the plan and repeat the process! This is adaptive management.
The two keys for mitigating livestock-related water quality problems are manure management and maintaining riparian vegetation.
- Manure management encompasses what is sometimes called source control. This is the negative aspect of water quality protection. Preventing manure and associated pollutants from getting into surface water has two major components:
- Minimizing or preventing direct deposition of manure into surface water is important. Most bacterial input to a stream is the result of fecal deposition directly into the water, not overland movement of fecal material deposited on land adjacent to surface water.
- Preventing overland flow. Precipitation or irrigation runoff can be a significant source of pollutants when soils are saturated, manure is concentrated near a stream, streamsides lack sufficient vegetation, and/or soils are compacted from overgrazing. Besides avoiding concentrating manure, a key to minimizing overland flow is maintaining conditions at the plant-soil interface that maximize the soil’s ability to capture, store, and safely release water. We should think of a watershed as a water catchment instead.
- Maintaining riparian-type vegetation is the second key to protecting water quality. This is the positive side of water quality protection. Riparian-type plant species, like sedges, rushes, and riparian shrubs and trees, are uniquely adapted to withstanding the high energy of moving water at the transition zone between the aquatic and the upland environments. Vegetation is the ecological “driver” of water quality because it provides direct physical filtration of pollutants in the water column, it creates and maintains healthy soil in the riparian zone, and it anchors sediment and smaller rock which creates and maintains stream channel shape. Preventing excessive defoliation of this vegetation and the subsequent conversion of this vegetation to a less adapted plant community more tolerant of heavy grazing pressure is essential to protecting stream function and water quality.
Proper v. Improper Grazing
“A riparian-wetland area is considered to be in proper functioning condition when adequate vegetation, landform, or large woody debris is present to:
- dissipate stream energy associated with high water flow, thereby reducing erosion and improving water quality;
- filter sediment, capture bedload, and aid floodplain development;
- improve flood-water retention and ground-water recharge;
- develop root masses that stabilize streambanks against cutting action;
- develop diverse ponding and channel characteristics to provide the habitat and the water depth, duration, and temperature necessary for fish production, waterfowl breeding, and other uses;
- support greater biodiversity.”
Proper grazing promotes these riparian attributes and processes; improper grazing impairs them. Consider the photograph on the cover, of a typical sagebrush-steppe stream. Both sides of the fence are grazed. They could even be grazed at a sustainable stocking rate. The problem is not whether the site is grazed or even by how many animals it is grazed; rather, the problem is the timing, duration, and frequency of grazing.
Plants are overgrazed when the recovery period following a grazing event is not long enough for the primary forage species to fully recover. In the overgrazed pasture, the riparian grasses and grass-like plants are grazed severely for an extended period of time, causing multiple defoliations of the same plants. Late summer use has also led to the near elimination of any woody species on this overgrazed segment of the stream. In the properly grazed pasture, the riparian plants are grazed for a short period of time and allowed to grow unimpeded for the remainder of the growing season. The total pounds of forage removed per acre may be the same in both cases, but the combined effects of differing timing, duration, and frequency of grazing is dramatic. The landowner or livestock owner/manager should develop a landscape goal, or desired future condition, which incorporates riparian function and develop an informed grazing plan to get from current conditions to the desired conditions.
If animals have extended access to a stream and riparian vegetation, there is likely a water quality problem. This persistent use will cause vegetation to shift away from the types of plants that are effective at maintaining streambank stability and toward plants that will tolerate more frequent defoliation, usually non-riparian species that have lower root strength. In addition, loss of riparian vegetation can lead to downcutting events during peak flows which effectively lower the water table and lead to long-term reductions in the riparian area’s production capacity. The combination of a long grazing period with animals near the stream and the loss of vegetation results in significantly larger amounts of manure entering the stream, through both direct deposition and overland movement of the manure during rainfall events or irrigation events. This multi-season grazing, because of the heavy defoliation, lack of regrowth opportunity, and more frequent hoof activity, also tends to cause soil compaction, exacerbating the problem of overland flow and decreasing root development. A conscientious livestock owner must manage to prevent or reduce direct deposition and prevent or reduce the likelihood and severity of overland flow that could carry nutrients and bacteria into the water.
Conditions within the stream zone which increase risk of a water quality problem include: bare soil, visibly eroding streambanks, erosional features similar to miniature gullies following livestock trails, and replacement of riparian-type vegetation with uplandtype vegetation and/or invasive plants. Any one of these factors is not necessarily evidence of substantial pollution but represents increased potential to pollute and increased risk; multiple risk factors increase the likelihood of a water quality violation.
Conditions which are indicative of a healthy plant community which maintains water quality and riparian function include:
- Diversity and vigor of riparian vegetation, including woody species where such are an expected and important component of a specific riparian system
- Majority of the “greenline” (soil at the water’s edge) is occupied by desirable riparian-wetland plants
- Livestock have offsite water or hardened access point such that animal time in the water is prevented or minimized
- Healthy upland vegetation Remember that uplands are tied to their drainages, and what happens in the uplands doesn’t stay in the uplands. In grazing areas, there must be sufficient residual at the end of the grazing and growing season to facilitate plant regrowth in spring and to provide for soil stability.
The following practices and principles tend to maintain riparian health and decrease risk of pollution:
- Off-stream water, which dramatically reduces animal time in the riparian zone
- Short grazing periods, which reduce the risk of severe defoliation
- Long recovery periods (time between grazing events)
- Change season of grazing use on range and forest each year
- Moderate defoliation of primary forage species
- Riparian fencing, temporary or permanent, which controls livestock impacts to the stream. Permanent exclusion fence prevents any livestock impacts; establishing a riparian pasture allows the manager complete control over timing, duration, and intensity of riparian grazing.
- Using utilization of preferred forage species and/or woody species as a “trigger” for moving animals out of a grazing unit with a riparian system
- Grazing during late spring/early summer only every other year
- Early spring grazing: In early spring animals spend less time in the riparian zone because it’s colder, upland forage has higher water content and is abundant; this practice provides a long recovery period and plenty of standing biomass going into winter. Exceptions to this include regions with heavy spring rainfall and saturated soils where intensively grazed pastures are likely to discharge manure into their adjacent drainages/ streams
- Herding animals: done properly, herding places rather than chases animals out of the riparian zone until avoidance becomes their idea
- Hardened access points or crossing points on streams
- Annual grazing use monitoring and trend monitoring as part of an adaptive management strategy
There are multiple cost-sharing programs that pay for exclusion fencing, off-stream livestock water, and stream crossings so that landowners do not bear the entire cost. Many livestock owners in Washington have used available funding to protect riparian areas with fence. In combination with upland grazing management these practices have been shown to be effective at preventing pollution and can also benefit an operation through better livestock distribution and pasture utilization.
Tags: Grazing, Livestock, Management, Manure, overgrazed, pollution, stream zone, water quality