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

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).
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