NEPC2011 Meeting Index

At 10:00 AM, the final presentation session, Session 5 - Pastures and Chesapeake Bay Water Quality began with Dr. Lloyd B. Owens, research soil scientist, USDA-ARS, North Appalachian Experimental Watershed, Coshocton, OH as moderator.

Dr. James Russell, professor of animal science, Iowa State University, Ames, IA was our quest and first speaker. His presentation was entitled: Management Strategies to Minimize the Impacts of Grazing on Non-point Source Pollution of Pasture Streams in the Midwest. He started out by saying that many of Iowa’s 357 streams and 77 lakes are water quality impaired (Iowa DNR, 2008). Of the phosphorus delivery to the Gulf of Mexico, 37% of it comes from pasture and rangeland (Alexander et al., 2008). Hypothetical routes of non-point source (NPS) pollution by grazing cattle are:

  • Direct deposition of animal waste into the stream or lake,

  • Streambank erosion, or is it cut bank erosion?

  • Surface runoff from adjacent areas to the stream or lake.

Factors controlling the effects of grazing on water quality:

  • Location of grazing

  • Timing of grazing

  • Intensity of grazing

  • Length of grazing (CAST, 2002)

Many things need to be considered when trying to determine what effects grazing management has on pastured streams’ NPS pollution loadings. For instance, cow density per length of stream was thought to be important but was not statistically significant. Off-stream waterers work in dry years to keep cattle away from streams, but do not work in wet years. Pasture configurations that force the cows to be in close proximity to the stream at all times makes stream disturbance and pollution much more likely than a pasture that has more upland areas in it that are remote to the stream. In the Midwest linear pastures often occur along streams since the upland areas are cropped unless extremely steep or broken up by ravines. Treatments to control NPS pollution of pasture streams seem likely to be most effective on small or narrow pastures. Shade distribution can be another factor. Pastures with shade scattered around and in upland areas draw cattle away, while shade that is along streams attracts cattle to stream areas when they want to escape the sun’s rays. Warmer air temperatures increase the percentage of time cattle are near or in streams, but this varies widely with little percentage increase to quite high depending on shade factors and pasture configuration.

Model for Quantifying the Effects of Grazing Management on Non-point Source Pollution of Pasture Streams

pasture size model

Effects of pasture size on the congregation of grazing cows in and within 100 feet of a pasture stream or pond on six pastures were studied over three years. Pastures less than 20 acres had more cows within a 100 feet of a pasture stream or pond, but pastures greater than 120 acres also had more cows within a 100 feet of a pasture stream or pond as well compared to pastures that ranged in size between 40 and 100 acres. In smaller pastures of under 20 acres they are forced to be close while in the 120 acre pastures, it is more of a creature comfort issue to be close to water especially in hot, humid weather and especially if on endophyte infected tall fescue pastures.

Off-stream water sources achieved mixed results in enticing cows away from streams and ponds. Of six studies reviewed, 3 studies said off-stream water seemed to reduce cattle congregation along pasture streams while the other 3 said there was no or minimal effect. One researcher had one of each, no effect on congregation and reduced congregation. Rather than air temperatures, a bigger factor is the temperature heat index (THI) previously mentioned by Dr. Larry Chase. When the THI is between 72 and 84, there is a dramatic increase in the amount of time cattle are in the riparian zone of a stream. The presence of off- stream water troughs had little effect in keeping cattle out of the riparian area.

Seeking shade, however, is driven by rising air temperatures alone, dramatically rising from 20C to 35C. It then makes a difference where the shade is, along the stream or away from it.

Cut bank erosion is by far the largest contributor to sediment pollution of pastured streams. Overland runoff sediment and direct deposition of manure is minuscule in comparison, except in pastures with streams with low streambanks or absence of oxbows. Grazing management does not play much of a role in cut bank erosion. Restricting access to the stream does and the main effect of rotational grazing is to reduce access to streams significantly. Cut bank erosion occurs along streams with or without cattle in or near them. It is more a function of sinuosity of the stream, the soil erodibility of the banks, and hydrology of the watershed. Ninety-nine percent of the in-stream sediment comes from cut bank erosion and 95% of the in-stream phosphorus also comes from cut bank erosion.

Pathogens, such as coliform bacteria and bovine enterovirus, coronavirus (BCV), and rotavirus (BRV), were studied. Coliform bacteria counts in streams showed there was no correlation with the presence or absence of cattle. The incidence of shedding coliform bacteria into the feces is very inconsistent. Bovine enterovirus, BCV, and BRV, may be better indicators of pathogen loading, but they are excreted by deer and geese too. However, Jim’s findings found there to be no correlation whatsoever between the presence of cattle and the numbers of these viruses in the water where these viruses were measured for 3 years in 13 different pastures. Yet, there were particular times when BEV did show up significantly, September and October.

Jim’s conclusions were:

  • Stream bank erosion is primarily related to hydrologic processes that supersede possible grazing effects.

  • Improper grazing management may increase:

    • Bare ground near pasture streams

    • Manure concentration near pasture streams

    • Sediment and nutrient loading of precipitation runoff.

  • Pathogen loading of pasture streams by grazing cattle is:

    • Poorly related to presence of total coliforms (Bovine enterovirus may be a better indicator.)

    • Confounded by upstream loading by domestic and wildlife species

    • Rare and controlled by:

Seasonal incidence of shedding of the pathogens

  • Manure distribution

  • Transport of the pathogens to the stream

  • Risks of grazing on non-point source pollution of pasture streams may be controlled by maintaining stream-side vegetation by use of:

    • Stabilized crossings with riparian buffers

    • Rotational grazing

    • Off-stream shade?

    • Off-stream water and/or nutrient supplementation (mineral & hay feeders & salt blocks) ???