Are Livestock Grazing and Healthy Streams Compatible? Livestock Grazing Systems that Reduce Erosion and Improve Stream Bank Stability

Final Report for GNC03-022

Project Type: Graduate Student
Funds awarded in 2003: $10,000.00
Projected End Date: 12/31/2005
Grant Recipient: Iowa State University
Region: North Central
State: Iowa
Graduate Student:
Faculty Advisor:
Richard Schultz
Iowa State University
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Project Information

Summary:

Soil and phosphorus losses from stream bank erosion among different land-use practices were compared in three Iowa regions. Stream bank erosion was measured with erosion pins (estimate erosion rate), and by surveying the severe and very severe eroding banks of all treatments. Soil samples from the stream bank face were collected to estimate bulk density and soil total phosphorus. Row-cropped fields and continuous pastures had the highest soil and phosphorus losses, while riparian forest buffers, grass filters and pastures with cattle completely excluded from the stream the lowest. Erosion rates of individual banks did not differ between grazing practices or between buffers and pastures with cattle excluded from the channel. The differences in soil and phosphorus losses between practices were the result of percentages of the total bank lengths that were eroding within each practice. Intensive rotational pastures showed some indications of reducing soil and phosphorus losses from bank erosion compared to continuous pastures. Total eroding lengths varied from about 11% for the buffered and cattle excluded streams to 27% for the intensive rotational and 38% for the continuously grazed pastures. These losses translate to 4 to 7 tons km-1 yr-1 to 155 to 235 tons km-1 yr-1 for the two sets of practices.

Introduction:

Rotational and intensive rotational grazing are slowly replacing traditional continuous grazing in Iowa because these new practices better utilize pasture forages, and increase profitability (USDA-NRCS, 1997a; Undersander et al., 1993). Although many studies have been conducted in the Western United States on the influence of intensive rotational and rotational grazing on stream ecosystems, very few studies have been conducted in the Midwest (Lyons et al., 2000). Belsky et al. (1999) reported that many studies have shown that livestock grazing reduces stream bank stability in the Western United States. In most cases, decreased stream bank stability is the result of decreased vegetation cover that decreases the root length and mass in the soil (Kleinfelder et al., 1992; Dunaway et al., 1994). In rotational and intensive rotational grazing, in contrast to continuous grazing, the pasture is divided into smaller sections (paddocks) providing rest periods for the paddocks that allow above- and below-ground portions of the forage to recover thus increasing stream bank stability.

Stream bank erosion is a natural process and Simonson et al. (1994) suggest that high quality natural streams should have less than 20% of the total length of stream banks eroding. Major removal of the natural prairie, forest, and wetland vegetation in Iowa to promote agricultural practices has altered the hydrologic cycle causing larger and higher discharge events through streams. As a result most Iowa stream are incised with stream bank erosion contributing significant amounts of sediment and phosphorus to the stream. Stream bank erosion has been shown to contribute 30-45% of the sediment load in streams in Minnesota (Sekely et al., 2002), 45-50% in Iowa (Odggard, 1984; Schilling and Wolter, 2000), and up to 80-90% in other regions of the United States (Simon et al., 1996) and other countries (Krovang et al., 1997). Very few studies have quantified stream bank contribution to the total phosphorus load (Sekely et al., 2002). A study in Minnesota reported that only 7-10% of the total phosphorus in the stream was from stream bank erosion (Sekely et al., 2002) in contrast to a study in Illinois that found 56% (Roseboom, 1987). A study in Denmark found that stream bank erosion contributed more than 90% of the total phosphorus load to a stream (Krovang et al., 1997).

Phosphorus has been identified as the primary nutrient limiting eutrophication of many surface waters (Daniel et al., 1998) while sediment is the number one water quality problem in the United States (Simon and Darby, 1999).
Phosphorus, in most cases, is attached to sediment when transported (David and Gentry, 2000; Sharpley and Smith 1990) and therefore, should be studied together with sediment.

LITERATURE CITED

Belsky, A.J., A. Matzke and S. Uselman. 1999. Survey of livestock influences on stream and riparian ecosystems in the western United States. J. Soil Water Conserv. 54:419-431.

Blake, G.R. and K.H. Hate. 1986. Bulk Density. In: Clute A. Ed. Methods of soil
analysis: Part 1. Physical and mineralogical methods. 2nd ed. Madison, WI: ASA and SSSA. pp. 363-375.

Clary, W.P. and J.W. Kinney. 2002. Streambank and vegetation response to simulated
cattle grazing. Wetlands 22:139-148.

Daniel, T.C., A.N. Sharpley, D.R. Edwards, R. Wedepohl, and J.L. Lemunyon. 1994. Minimizing surface water eutrophication from agriculture by phosphorus management. J. Soil Water Conser. 49(2, supplement):30-38.

Daniel, T.C., A.N. Sharpley, and J.L. Lemunyon. 1998. Agricultural phosphorus and eutrophication: A review. J. Environ. Qual. 27:251-257.

David, M.B. and L.E. Gentry. 2000. Anthropogenic inputs of nitrogen and phosphorus and riverine export for Illinois, USA. J. Environ. Qual. 29:494-508.

DeWolfe, M.N., W.C. Hession, and M.C. Watzin. 2004. Sediment and phosphorus loads from streambank erosion in Vermont, USA. In: G. Sehlke, D.F. Hayes, and D.K. Stevens (eds.), Critical transitions in water and environmental resources management, Reston, VA: Amer. Soc. of Civil Eng. pp. 1-10.

Dick, W.A. and M.A. Tabatabai. 1977. An alkaline oxidation method for determination of total phosphorus in soils. Soil Sci. Soc. Amer. J. 41:511-514.

Dunaway, D., S.R. Swanson, J. Wendel, and W. Clary. 1994. The effect of herbaceous
plant communities and soil textures on particle erosion of alluvial streambanks.
Geomor. 9:47-56.

Johnson, C and B. Frazee. 2003. 5 low-cost methods for slowing streambank erosion. J.
Soil Water Conserv. 58:13-17.

Hagerty, D.J., M.F. Spoor, and C.R. Ullrich. 1981. Bank failure and erosion on the Ohio
River. Eng. Geol. 17:141-158.

Hooke, J.M. 1980. Magnitude and Distribution of Rates of River Bank Erosion. Earth Surf. Process. Landforms 5:143-157.

Kleinfender, D., S. Swanson, G. Norris, and W. Clary. 1992. Unconfined compressive
strength of some streambank soils with herbeceaous roots. Soil Sci. Soc. Amer. J. 56:1920-1925.

Krovang, B., R. Grant, and A.L. Laubel. 1997. Sediment and phosphorus export from a lowland catchment: Quantification of sources. Water Air Soil Pol. 99:465-476.

Laubel, A., B. Krovang, A.B. Hald, and C. Jensen. 2003. Hydromorphological and biological factors influencing sediment and phosphorus loss via bank erosion in small lowland rural streams in Denmark. Hydrological Processes 17:3443-3463.

Lawler, D.M. 1993. The Measurement of River Bank Erosion and Lateral Channel Change: A Review. Earth Surf. Process. Landforms 18:777-821.

Lyons, J., B.M. Weasel, L.K. Paine, and D.J. Undersander. 2000. Influence of intensive rotational grazing on bank erosion, fish habitat quality, and fish communities in southwestern Wisconsin trout streams. J. Soil Water Conserv. 55: 271-276.

McInnis, M.L. and J. McIver. 2001. Influence of off-stream supplements on streambanks of riparian pastures. J. Range Manage. 54:648-652.

Murphy J. and J.P. Riley. 1962. A modified single solution method for the determination of phosphate in natural waters. Anal. Chim. Acta 27:31-36.

National Oceanic and Atmospheric Administration (NOAA). 2002-4a. Hourly Precipitation Data Iowa. Volumes:51(8)-54(8)
Available at: http://www.ncdc.noaa.gov/oa/climate/stationlocator.html (retrieved 11-20-04)

National Oceanic and Atmospheric Administration (NOAA). 2002-4b. Climatological Data Iowa. Volumes:112(8)-115(8)
Available at: http://www.ncdc.noaa.gov/oa/climate/stationlocator.html (retrieved 11-20-04)

Odgaard, A.J. 1987. Streambank Erosion Along Two Rivers in Iowa. Water Resource Research 23:1225-1236.

Pearson, R.W., R. Spry, and W.H. Pierre. 1940. The vertical distribution of total and dilute acid-soluble phosphorus in twelve Iowa soil profiles. Journal of American Society of Agronomy 32:683-696.

Platts, W.S. and F.J. Wagstaff. 1984. Fencing to control livestock grazing on riparian habitat along streams: is it a viable alternative? N. Amer. J. Fish Manage. 4:266-272.

Porath, M.L., P.A. Momont, T. DelCurto, N.R. Rimbey, J.A. Tanaka, and M. McInnis. 2002. Offstream water and trace mineral salt as management strategies for improved cattle distribution. J. Anim. Sci. 80:346-356.

Riecken, F.F. and E. Poetsch, 1956. Genesis and classification considerations of some prairie-form soil profiles from local alluvium in Adair county, Iowa. Proc, Iowa Acad. of Sci. 67:277-289.

Roseboom, D.P. 1987. Case studies of stream and river restoration. Management of the Illinois River system: The 1990’s and beyond. Illinois River Resource Management. A Governor’s Conference held April 1-3. Peoria, IL.

SAS Institute. 1999. SAS Release 8.1 ed. SAS Inst., Cary, NC.

Schilling K.E. and C.F. Wolter. 2000. Applications of GPS and GIS to map channel
features in Walnut Creek, Iowa. J. Amer. Water Resour. Assoc. 36:1423-1434

Schumm, S.A., M.D. Harvey, and C.C. Watson. 1984. Incised channels. Morphology, dynamics and control. Water Resource Publication, Littleton, CO.

Sekely, A.C., D.J. Mulla, and D.W. Bauer. 2002. Streambank slumping and its contribution to the phosphorus and suspended sediment loads of the Blue Earth River, Minnesota. J. Soil Water Conserv. 57:243-250.

Sharpley, A.R. and S.J. Smith. 1990. Phosphorus transport in agricultural runoff: the role of soil erosion. In: J. Boardman, I.D.I. Foster, and J.A. Dearing, Soil erosion on agricultural land: Chichester, England. John Wiley and Sons Press. pp. 349-366.

Simon, A. and S. Darby. 1999. The Nature and Significance of Incised River Channels. In: Darby S.E. and A. Simon (ed.), Incised River Channels: Processes, forms, engineering and management: Chichester, England. John Wiley and Sons Press. pp. 1-18.

Simonson, T.D., J. Lyons, and P.D. Kanehl. 1994. Guidelines for evaluating fish habitat in Wisconsin streams. U.S.D.A Forest Service, North Central Forest. Experiment Station, St. Paul, MN. General Technical Report NC-164.

Strahler, A.N. 1957. Quantitative analysis of watershed geomorphology. Trans. Am. Geophys. Union 38:913-920.

Trimble, S.W. and A.C. Mendel. 1995. The cow as a geomorphic agent – A critical review. Geomor. 13:133-153.

Undersander, D.J., B. Albert, P. Porter, and A. Croslley. 1993. Pastures for profit: a hands-on guide to rotational grazing. University of Wisconsin Extension Service Pub. No. A3529. Madison, WI.

United States Department of Agriculture-Natural Resource Conservation Service (USDA-NRCS). 1997a. Profitable pastures. A guide to grass, grazing and good management. USDA-NRCS. Des Moines, IA.

United States Department of Agriculture-Natural Resource Conservation Service (USDA-NRCS). 1998. Erosion and Sediment Delivery. Field Office Technical Guide Notice no. IA-198. USDA-NRCS, Des Moines, IA.

Wolman, M.G. 1959. Factors Influencing Erosion of a Cohesive River Bank. Amer. J. Sci. 257:204-216.

Zaimes, G.N., R.C. Schultz, and T.M. Isenhart. 2004. Stream Bank Erosion Adjacent to Riparian Forest Buffers, Row-crop Fields, and continuously-grazed Pastures along Bear Creek in Central Iowa. J. Soil Water Conserv. 59:19-27.

Project Objectives:

The overall goal of this project was to collect and present data to convince farmers who continuously graze livestock in riparian corridors to adopt rotational and intensive rotational grazing practices because of environmental and monetary benefits. The goal would be accomplished by conducting research on the environmental benefits of rotational and intensive rotational grazing and by education/training. The specific research objective of this project was to compare the impact of different grazing practices and other agricultural practices on stream bank erosion and phosphorus movement. Bank erosion rates along continuous, rotational, and intensive rotational pastures were compared to bank erosion rates along riparian forest buffers and grass filters, pastures with cattle fenced out of the stream, and row-cropping adjacent to the streams. The hypothesized order from highest to lowest stream bank erosion was: row-cropped fields adjacent to streams, continuous pastures, rotational pastures, intensive rotational pastures, pastures with the stream excluded to cattle, grass filters, and riparian forest buffers.

Cooperators

Click linked name(s) to expand
  • Richard Schultz

Research

Materials and methods:

The research for this project was conducted in northeast, central, and southeastern Iowa. Northeast and southeast Iowa were chosen because these are the two major livestock grazing regions in Iowa. In central Iowa, we wanted to compare sites that had already been established for another study to the sites in the other two region. One of our sites in the central region is in the Bear Creek National Restoration Demonstration Watershed where extensive riparian buffer research has been conducted (Clean Water Action Plan, 1999). The land-use practices used for the study were riparian forest buffers, grass filters, pastures with the cattle excluded from the stream, intensive rotational grazing, rotational grazing, continuous grazing, and annual row-cropping. The major constraint was to find these land-use practices on 1 to 3 order (Strahler, 1957), deeply incised streams owned by private farmers. We focused on small order streams because they can contribute a significant portion of the sediment in streams. An Illinois State Water survey found that small order streams contribute 30-50% of sediment in the Illinois River (Johnson and Frazee, 2003). It was also important to work on farms owned by private farmers to evaluate the management of rotational and intensive rotational grazing. We also believed it would probably be easier to convince local farmers to change their management practices by demonstrating the results from land-use practices on their own or their neighbor’s farms. Unfortunately, due to the lack of certain land-use practices in some regions and time constraints, it was not possible to find all the practices in every region. In the central region, we found riparian forest buffers, grass filters, rotational pastures, continuous pastures, and annual row-cropped fields. In the northeast region, we only had riparian forest buffers, pastures with the cattle excluded from the stream, intensive rotational pastures, and continuous pastures. In the southeast region, we had grass filters, pasture with the cattle excluded from the stream, intensive rotational pastures, rotational pastures, and continuous pastures.

Steel rods 762 mm long and 6.4 mm in diameter were inserted perpendicularly into the bank face to measure stream bank erosion rates (Wolman, 1959). These erosion pins are used to measure stream bank erosion rates especially when measuring over short-time-scales and when high resolution is wanted (Lawler, 1993). Five erosion pin network plots were randomly selected in each land-use practice site. Each erosion pin network plot had 5 columns, 1 m apart, and 2 rows at 1/3 and 2/3 the stream bank height, apart. Only severe and very severe eroding stream banks were selected for erosion pin network plots because they are the major source of sediment in channels compared to moderate and slightly eroding banks that are more vegetated. Severe eroding banks were defined as bare with slumps, vegetative overhang and/or exposed tree roots (USDA-NRCS, 1998). Very severe eroding banks were defined as bare with massive slumps or washouts, severe vegetative overhang and many exposed tree roots (USDA-NRCS, 1998). Approximately 50 mm of the erosion pins were initially exposed. Exposed pin lengths were measured three times a year, spring, summer, and fall from August 2001 to August 2004.

In August 2002, the total length and height was measured for all the severe and very severe stream banks along each land-use practice site. These measurements enabled us to estimate the severe and very severe eroding stream bank length percentages and the severe and very severe eroding bank areas for each land-use practice. These values were used to calculate the total contribution of different land-use practices to stream bank sediment and phosphorous loads.

Along the stream bank face adjacent to three out of the five erosion pin network plots soil samples were collected to estimate bulk density and total phosphorus. Starting at the top of the stream bank (0.0 m), two 7.5 x 3 cm soil cores for bulk density and two 5 x 3 cm soil cores for soil total phosphorus were extracted every 0.5 m from the top to the bottom of the bank and consolidated into one sample for each depth. The bulk density soil samples were weighed after drying for 1 d at 105C (221F) (Blake and Hartge, 1986). For total phosphorus determinations, the soil samples were air dried for 48 hr, sieved through a 2-mm screen, and then digested with a sodium hypobromide solution (Dick and Tabatabai, 1977) and the extracted phosphorus identified colorimetrically by a modified molybdenum blue reaction (Murphy and Riley, 1962).

The product of the mean stream bank erosion rate, the mean bulk density and the total eroding area of the severe and very severe eroding banks for each land-use practice reach was used to estimate the total stream bank soil loss for the practice. Then, by multiplying the total soil loss by the mean phosphorus stream bank concentrations of each land-use practice, the total phosphorus loss from stream banks was estimated. The stream bank soil and phosphorus loss per unit length of stream bank was estimated by dividing the total stream bank soil loss for each land-use practice by its total stream bank length (none, slight, severe, and very severe eroding banks). This was necessary because each land-use practice did not have the same total stream length.

The rainfall data from the closest National Oceanic and Atmospheric Administration weather station to each land-use practice site was used to correlate yearly rainfall data with yearly stream bank erosion (NOAA, 2002-4a and b).

The analysis of covariance in SAS was used to examine the impact of treatments on stream bank erosion rate for each year and for the sum of all three years (SAS Institute, 1999). The covariant for the model was precipitation. The analysis of variance in SAS was used to compare the severe and very severe eroding lengths (%) and the model included regions and land-use practices.

Research results and discussion:

In the central region in year one, erosion rate differences among treatments were not significant. For year two, the riparian forest buffer stream banks had significantly lower erosion rates than those in the row-cropped fields (p=0.0179). The row-cropped field banks had the highest erosion rate during this year and were significantly greater than the rates of the grass filters (p=0.0767) and the rotational grazing banks (p=0.0893). In year three, which was the wettest, the continuous pasture banks had significantly higher erosion rates than the riparian forest buffer banks (p=0.0009), the grass filter banks (p=0.0247), and the rotational pasture banks (p=0.0746). The erosion rates for the row-cropped field banks were significantly higher than those of the riparian forest buffer banks (p=0.0022) and grass filter banks (p=0.0634). The three year cumulative erosion rates of the row-cropped field banks were significantly higher than those of the riparian forest buffers (p=0.0072), grass filters (p=0.0501), and rotational grazing banks (p=0.0561). The three-year cumulative erosion rates of the continuous pasture banks were only significantly higher than those of the riparian forest buffer banks (p=0.0776).

In year one, in the northeast region, the riparian forest banks and the banks of the pastures with cattle excluded from the stream had net deposition rates instead of erosion rates while the two grazing system banks had low erosion rates. Because the pastures with cattle excluded from the stream had net deposition, differences were significant compared to the continuous pasture banks that had erosion (p=0.0997). In year two, the erosion rates of the continuous pasture banks were significantly higher than the riparian forest buffer banks (p=0.0815). Year three had higher precipitation amounts than the other two years, which led to higher erosion rates. The intensive rotational grazing pasture banks had significantly higher erosion rates than the riparian forest buffer banks (p=0.0006), banks of pastures with cattle excluded from the stream (p=0.0010), and the continuous pasture banks (p=0.0321). The erosion rates on continuous pasture banks were significantly higher than the riparian forest banks (p=0.0317), and the banks of pastures with cattle excluded from the stream (p=0.0444). The continuous pasture banks had a higher cumulative erosion rate over the three years of the study than the riparian forest banks (p=0.0317) and the banks of pastures with the stream excluded from the cattle (p=0.0444). The three year cumulative erosion rates of the intensive rotational pasture banks were also higher than those of the riparian forest banks (p=0.0255) and the banks of pastures with the stream excluded from cattle (p=0.0357).

Comparing the yearly erosion rates in the southeast region, there were no significant differences in stream bank erosion between land-use practices. Even for the three year cumulative erosion rate, there were no significant differences between land-use practices.

Overall, there were some significant differences in stream bank erosion rates between land-use practices in the central and the northeast regions, but differences were not significant in the southeast region. Riparian forest buffers and grass filters had the lowest erosion rates (differences were not significant in the southeast region). The pastures with the cattle excluded from the streams had much lower erosion rates than the other three pasture systems (differences were not significant in the southeast region). The three pasture systems with full access to the stream did not always follow the expected trends. Differences were typically not significant and in many cases the erosion rates were comparable to the row-cropped fields. We did expect to see more clear-cut trends in the differences between land-use practices since other studies have shown the impact of different adjacent land-use practices on stream bank erosion (Hagerty et al., 1981; Hooke, 1980, Lyons et al., 2000; Zaimes et al., 2004). One of the major reasons for not seeing these trends was that we conducted this observational study on private farms. In many cases, farmers used their own definitions of the grazing practices that in many cases, did not fit the textbook definitions. In addition, upstream land-use practices in this project were not considered, but they may be equally as important as land-use adjacent to the bank and channel (Lyons et al., 2000; Zaimes et al., 2004). The high variability of stream bank erosion rates even within a plot has been found to confound the results of similar studies (Lawler, 1993). Finally, all erosion pin network plots were established on severe and very severe eroding sites that, by definition, should have high erosion rates. The fact that erosion rates for banks along land-use practices that had no livestock access to the stream were generally lowest suggests that those severely eroding banks had lower rates because of the effect of more extensive plant above- and below-ground cover.

The lengths of severe and very severe eroding stream banks followed our initial hypothesis in most cases. In the central region, the row-crop field reaches had significantly higher percentages of severe and very severe eroding bank lengths than the rotational pasture (p=0.0326), grass filter (p=0.0035), and riparian forest buffer reaches (p=0.0024). The percentages of severe and very severe eroding bank length for the continuous pasture reaches were significantly higher than those for the grass filter (p=0.0124) and the riparian forest buffer reaches (p=0.0085). In the northeast region, the continuous pasture reaches had significantly higher percentages of severe and very severe eroding bank lengths than the riparian forest buffer reaches (p=0.0019) and the pastures with the stream excluded to the cattle reaches (p=0.0021). The continuous pastures also had higher percentages of severe and very severe eroding bank lengths but were only slightly different than the intensive rotational pastures (p=0.1048). The intensive rotational pasture reaches had significantly higher percentages of eroding lengths than the riparian forest buffers (p=0.0437) and the pastures with the stream excluded to cattle (p=0.0496). In the southeast region the continuous pasture reaches had significantly higher percentages of severe and very severe eroding bank lengths than those of the intensive rotational pasture (p=0.0117), the pastures with the stream excluded to cattle (p=0.0012), and the grass filter reaches (p=0.0001). Similarly, the rotational pasture reaches had significantly higher percentages of severe and very severe eroding bank lengths than the intensive rotational pastures (p=0.0202), the pastures with cattle excluded from the stream (p=0.0021), and the grass filter reaches (p=0.0004). Finally, the grass filter reaches had significantly lower percentages of severe and very severe eroding bank lengths than the intensive rotational pasture reaches (p=0.0730).

As expected, the percentage of eroding stream bank length had more significant differences between land-use practices in all regions than the erosion rates. It was expected that with more direct access to stream channels greater lengths of channel reaches would be eroding. In southwestern Wisconsin, Simonson et al., (1994) suggest that the highest quality streams should have less than 20% of the total lengths of stream banks eroding. The riparian forest buffers, grass filters and the pastures with cattle excluded from the stream were always below this percentage in all regions. In contrast, the pasture systems with full access to the stream and the row-cropped fields had 30% or more of the stream banks eroding. In another study in Wisconsin, stream bank erosion under different land-use practices ranged from <1 to 66% (Lyons et al., 2000), which is similar to the ranges found in our study (10-54%). Lyons et al., (2000) also found that continuous grazing had significantly higher severe and very severe eroding bank length percentages than intensive rotational grazing, grass filters and riparian forest buffers. We also found that riparian forest buffers and grass filters and intensive rotational pastures had significantly lower percentages than the continuous pastures. However, lengths of severe and very severe eroding banks between continuous and rotational pastures were not statistically significant. When comparing stream bank total phosphorus concentrations among land-uses within a region, there were not many differences. In addition we did not see any real trends from the top to the bottom of the stream bank profile. In soil profiles, total phosphorus concentrations are typically high at the top and the bottom and decrease in the densest rooting zone (Pearson et al., 1940). We did not see differences between treatments and in the stream bank profile because riparian soils are developing in recent alluvial deposits that are much more irregular and less cohesive than non alluvial soils (Riecken and Poetsch, 1956; Schumm et al., 1984). The total phosphorus concentrations of the stream bank soils were within the range of 300 to 1,200 mg kg-1 of phosphorus that occurs naturally in soil, although phosphorus concentration can vary from 100 to 2,500 mg kg-1 (Daniel et al., 1994). Stream bank erosion soil and phosphorus losses per unit length followed our initial hypothesis. In the central region, the row-cropped fields had the highest losses while both conservation practices had lower losses with the riparian forest buffers having the lowest. In the grazing practices the continuous pastures had more than double the losses of the rotational pastures. In the northeast region, the pastures with cattle excluded from the stream and the riparian forest buffers had minimal losses (lower than any other region) that were much lower than the continuous and intensive rotational pastures of this region. The continuous pastures had approximately 33% higher soil and phosphorus losses than the intensive rotational pastures. Finally, in the southeast region the grass filters had the lowest soil and phosphorus losses while the pastures with the stream excluded to cattle followed and were more than 50% lower than the intensive rotational pastures. Interestingly, the rotational pastures had much higher losses than the continuous pastures. The hypothesized trends of soil erosion become even clearer when comparing soil losses per unit length of stream bank. The land-use practices in the central and northeast regions followed the exact hypothesized trends from highest soil losses to lowest: row-cropped fields adjacent to streams, continuous pastures, rotational pastures, intensive rotational pastures, pastures with cattle excluded from the stream, grass filters, and riparian forest buffers. In the southeast region, soil losses for the rotational pastures were higher than those for the continuous pastures. As expected, the row-crop fields had the highest losses, with 311 tons km-1 yr-1, followed by the continuous pastures that ranged from 193 to 258 tons km-1 yr-1. Losses for the rotational pastures and intensive rotational pastures ranged from 92 to 263 tons km-1 yr-1 and 63 to 157 tons km-1 yr-1, respectively. The pastures with cattle excluded from the stream and the grass filters had lower soil loses that ranged from 7 to 55 tons km-1 yr-1 and 21 to 57 tons km-1 yr-1, respectively. The riparian forests had the least soil losses ranging from 5 to 16 tons km-1 yr-1. De Wolfe et al. (2004) found similar soil losses (10 to 663 tons km-1 yr-1) from different watersheds in Vermont that had similar drainage areas to streams in this study. The phosphorus losses from stream banks followed a similar trend to the soil losses. Total phosphorus concentration differences in the stream bank soils between land-use practices were not significant because of their high variability (Zaimes, 2004). In the row-cropped fields total phosphorus losses were high with 110 kg km-1 yr-1, while the continuous pastures lost 70 to 122 kg km-1 yr-1. The rotational pastures and intensive rotational pastures ranged from 37 to 120 kg km-1 yr-1 and 38 to 68 kg km-1 yr-1, respectively. The pastures with cattle excluded from the stream, grass filters and riparian forest buffers had the smallest phosphorus losses ranging from 3 to 30 kg km-1 yr-1, 9 -17 kg km-1 yr-1, and 2 to 6 kg km-1 yr-1, respectively. In 10 Vermont watersheds phosphorus losses ranged 10 to 840 kg km-1 yr-1, similar to the losses in this study (DeWolfe et al., 2004). The phosphorus losses per unit length from the pastures with full access to the stream and the row-cropped fields indicate that stream bank erosion can be a significant contributor to the stream phosphorus load with these land-use practices. Based on all the variables discussed above, the riparian forest buffers were the land-use practice with the most stable stream banks and minimum soil and phosphorus loss. Grass filters followed riparian forest buffers. This could have been because the grass filters were more recently established in some cases. In addition, we believe that the tree root systems provide more protection to stream banks than the introduced cool-season grass roots on deeply incised, nearly vertical stream banks. Stream bank stability was greater where the cattle were excluded from the stream than in those practices that allowed cattle full access to the stream. Cattle are attracted to riparian areas and spend time in and around the stream (Trimble and Mendel, 1995). Improvements in stream bank stability when cattle are excluded from streams have also been found in other studies (Laubel et al., 2003) but this practice is not socially and economically acceptable to many farmers (Platts and Wagstaff, 1984). In cases where off-stream water is provided as an alternative to fencing, stream bank erosion has been dramatically reduced (McInnis and McIver, 2001; Sheffield et al., 1997) and Porath et al. (2002), even saw an increase in cattle weight. We are not sure how effective off-stream water would be without fencing where pastures are confined to narrow riparian areas along low order streams. There were mixed results when comparing rotational and intensive rotational pastures to continuous pastures. In some cases we saw significant decreases in erosion rates and soil and phosphorus losses while in others we saw increases. These differences are most likely due to the fact that many landowners do not follow the textbook definition of rotational and intensive rotational grazing and because many of the systems have only recently been converted from continuously grazing to rotational or intensively rotational systems. In general, intensive rotational pastures should improve the stream bank stability (Lyons et al., 2000) and decrease soil and phosphorus losses. Bank stabilization would probably increase more when the number of paddocks along streams are decreased. Fewer stream paddocks would mean more rest time for the stream reach and less impact of up-stream paddocks on down-stream paddocks. Finally, other studies have shown that stocking rates and the season and number of days the pastures are grazed, are as important, if not more important, than manipulating the grazing system (Clary and Kinney, 2002).
LITERATURE CITED

Belsky, A.J., A. Matzke and S. Uselman. 1999. Survey of livestock influences on stream and riparian ecosystems in the western United States. J. Soil Water Conserv. 54:419-431.

Blake, G.R. and K.H. Hate. 1986. Bulk Density. In: Clute A. Ed. Methods of soil analysis: Part 1. Physical and mineralogical methods. 2nd ed. Madison, WI: ASA and SSSA. pp. 363-375.

Clary, W.P. and J.W. Kinney. 2002. Streambank and vegetation response to simulated cattle grazing. Wetlands 22:139-148.

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Participation Summary

Educational & Outreach Activities

Participation Summary:

Education/outreach description:

Poster presentations

American Society of Agronomy-Crop Science Society of America-Soil Science Society
of America annual meeting. November 5-9, 2000. Minneapolis, MN. Title: Streambank Erosion Adjacent to Differing Land-Use Practices in Central Iowa. Authors: G. N. Zaimes, R. C. Schultz, and T. M. Isenhart.

Agriculture and the Environment: State and Federal Water Initiatives. March 5-7 2001. Ames, IA. Title: Streambank Erosion Adjacent to Differing Land-Use Practices in Central Iowa. Authors: G. N. Zaimes, R. C. Schultz, and T. M. Isenhart.

American Society of Agronomy-Crop Science Society of America-Soil Science Society of America annual meeting. November 10-14, 2002. Indianapolis, IN. Title: Stream bank erosion along different types of land-use practices with an emphasis on different grazing practices. Authors: G. N. Zaimes, E. E. Stauffer, R. C. Schultz, T. M. Isenhart, J. R. Russell, W. J. Powers, S. K. Mickelson, J. L. Kovar.

Agriculture and the Environment: Research and Technology Update for Water Quality and Air. March 7, 2003. Ames, IA. Title: Stream bank erosion along different types of land-use practices with an emphasis on different grazing practices. Authors: G. N. Zaimes, E. E. Stauffer, R. C. Schultz, T. M. Isenhart, J. R. Russell, W. J. Powers, S. K. Mickelson, J. L. Kovar.

American Society of Agronomy-Crop Science Society of America-Soil Science Society
of America annual meeting. November 2-6, 2003. Denver, CO. Title: Land-use practice impacts on stream bank erosion with an emphasis on grazing practices. Authors: G. N. Zaimes, R. C. Schultz, T. M. Isenhart, J. R. Russell, W. J. Powers, S. K. Mickelson, J. L. Kovar.

Society for Range Management annual meeting. January 25-30, 2004, Salt Lake, UT. Title: Grazing practice impacts on stream bank erosion. Authors: G. N. Zaimes, R. C. Schultz, T. M. Isenhart, J. R. Russell, W. J. Powers, S. K. Mickelson, J. L. Kovar.

Fourth Annual Water Monitoring Conference. February 18-19, 2004, Ames, IA. Title:
Grazing practice impacts on stream bank erosion. Authors: G. N. Zaimes, R. C.
Schultz, T. M. Isenhart, J. R. Russell, W. J. Powers, S. K. Mickelson, J. L. Kovar.

American Water Resources Association Summer Specialty Conference, Riparian Ecosystems and Buffers: Multi-scale Structure, Function, and Management. June 28-30, Olympic Valley, CA. Title: Impacts of different land-use practices on stream bank erosion. Authors: G. N. Zaimes, R. C. Schultz, T. M. Isenhart, S. K. Mickelson, J. L. Kovar, J. R. Russell, W. J. Powers.

American Society of Agronomy-Crop Science Society of America-Soil Science Society
of America with the Canadian Society of Soil Science, international annual meeting. October 31 - November 4, 2004, Seattle, WA. Title: Influence of Land-use Practices on Stream Bank Erosion in Iowa. Authors: G. N. Zaimes, R. C.
Schultz, T. M. Isenhart, S. K. Mickelson, J. L. Kovar, J. R. Russell, W. J. Powers.

Fifth Annual Water Monitoring Conference. January 13-14, 2005, Ames, IA. Title: Influence of Land-use Practices on Stream Bank Erosion in Iowa. Authors: G. N. Zaimes, R. C. Schultz, T. M. Isenhart, S. K. Mickelson, J. L. Kovar, J. R. Russell, W. J. Powers.

Society for Range Management annual meeting. February 5-11, 2005, Ft. Worth, TX.
Title: Grazing practice Impacts on Phosphorus and Soil Losses from Stream Bank Erosion in Iowa. Authors: G. N. Zaimes, R. C. Schultz, T. M. Isenhart, S. K. Mickelson, J. L. Kovar, J. R. Russell, W. J. Powers.

Oral Presentations

Agriculture and Environment Conference. March 8-9, 2005, Ames, Iowa. Title: Land-use impacts on stream bank erosion. Authors: R.C. Schultz, G.N. Zaimes.

Numerous scientific, professional and farmer groups that visit my research sites and/or
Bear Creek in central Iowa, on my current research and on the research conducted
in USDA Bear Creek Riparian Buffer National Research and Demonstration Watershed.

Numerous pasture walks and farm field days throughout Iowa regarding the results of this research.

Newsletters

Riparian Buffer News 2002 (winter)

Riparian Buffer News 2004 (winter)

Publications

Zaimes, G.N. and R.C. Schultz. 2001. Phosphorus in Agricultural Watersheds: A Literature Review. Iowa State University, Ames, IA.
Available at:
http://www.buffer.forestry.iastate.edu/Assets/Phosphorus_review.pdf

Zaimes, G.N. 2004. Riparian land-use impacts on stream and gully bank soil and phosphorus losses with an emphasis on grazing practices. Iowa State University, Ph.D. Dissertation. 189 pp.

Zaimes, G.N., R.C. Schultz, and T.M. Isenhart. Submitted. Land-use practices and weather pattern influences on stream bank erosion in Iowa. J. Amer. Water Resour. Assoc. (submitted)

Project Outcomes

Project outcomes:

This project has provided a much-needed quantitative dataset on the impacts of different riparian grazing systems compared to other riparian agricultural and conservation practices in Iowa. Stream bank erosion can be a major source of sediment and phosphorus to streams and the land-use practice in the riparian area can strongly influence stream bank erosion. Excluding direct access of livestock to the stream channel and eliminating row-cropping near the stream bank dramatically improves stream bank stability. Excluding these agricultural activities can reduce soil loss from stream bank erosion by hundreds of metric tons and phosphorus by hundreds of kilograms. In general we did not find as many differences as we expected between the grazing systems although there are indications that moving to intensive rotational grazing could reduce stream bank erosion. We must also note that in many cases stocking rates, number of grazing days and/or time of year the pasture is grazed are more important than shifting to different grazing systems. Another reason for not detecting any significant differences between grazing treatments could be because rotational and intensive rotational pastures had been recently established, and these pastures were still impacted by past management practices. Also, on private farms, landowners often do not follow the textbook definitions of rotational and intensive rotational pastures so differences between the two practices were not consistent across the study. This shows the importance of proper education and training of the landowners by specialists (NRCS personnel, University extension etc.) when these systems are first implemented.

Our presentations at scientific meetings have increased the awareness of stream bank erosion contributions to stream sediment and phosphorus loads and will instigate further research in other regions of the United States. The importance of reducing stream bank erosion was also very evident to the landowners that we worked with because in many instances they checked on the own the erosion pins to see how much soil they were losing. Iowa farmers are becoming more interested in rotational and intensive rotational grazing and their impact on stream bank erosion. In many of the pastures walks in which we participated, farmers asked many questions on how they could implement these systems to increase their profitability as well as reduce stream bank erosion.

We have provided the cooperators and others a set of "Buffer Notes," which summarize the results of this study. We are preparing up to three publications for scientific journals that will move specific research data to a broad audience of scientists. We also plan to prepare one or two extension bulletins that will be used to transmit the results and implications of this study to NRCS and University extension personnel and to farmers.

Farmer Adoption

The awareness of rotational and intensive rotational grazing and interest in adopting these systems has significantly increased primarily in counties were we conducted the research and presented pasture walks and farm field days. Many professionals like NRCS and University extension personnel that have direct contact with farmers have also been exposed to this work and have shown interest in extending the information to farmers. Still, many farmers are reluctant to change and adopt rotational and intensive rotational grazing primarily due to increased initial costs because of fencing of the paddocks. When funding for fencing is provided from federal programs (EQIP), farmers are more open to adopt these grazing systems. From the farmers we are currently working with, one is moving from rotational grazing to intensive rotational grazing in central Iowa and one farmer is moving from continuous to intensive rotational grazing in northeast Iowa.

Recommendations:

Areas needing additional study

There are four main areas needing additional study. The first one is to conduct this research on rotational and intensive rotational pastures that have been established for longer periods of time (more than 10 years) – for example, redo this work in 5 to 7 years. In most cases, the rotational and intensive rotational pastures studied in this project had been established for only three years and we believe the stream banks were still demonstrating responses to past management practices that in all cases was continuous grazing. The second one is to implement rotational and intensive rotational pastures with various stocking rates to establish what the proper stocking rates should be to make the pastures economically profitable while also providing the maximum stream erosion reduction. More research should be conducted on complete fencing of cattle out of the streams. This project shows that when cattle are kept 3 to 5 m away from the banks, stream bank erosion is significantly reduced. This solution shows the greatest potential for stream bank erosion - especially if federal funding would be provided for alternate water sources (like cattle nose pumps) and for fencing along the stream. Finally, during this study we noticed many cow paths along the stream bank in all grazing systems with direct access to the channel. This suggests that if cattle have full access to a stream for even short periods of time (intensive rotational grazing), the construction of cattle crossings might be necessary to reduce the number of cow paths. Additional study is needed to determine the impact of these concentrated flow and high manure areas to stream sediment and phosphorus loads.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.