The response of soils, streambanks and instream coliform bacteria levels to grazing management in a riparian area Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/g158bm25g

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  • This thesis describes a case study of the effects of five systems of grazing on watershed values in a deteriorated riparian area. Soil infiltration, bulk density and penetrability, streambank edge movement and coliform bacteria were monitored for seven years along a stream in the Blue Mountains of northeastern Oregon. For five consecutive years, no grazing, four pasture rest rotation, deferred rotation, season-long and late season systems of grazing were applied to small streamside pastures stocked with yearling heifers from June-October at the moderate rate of 3.2 ha/AUM. Infiltration and sediment production were monitored with Rocky Mountain and ring infiltrometers. Measurements with a proving ring penetrometer and bulk density cores indexed compaction. Soil and hydrologic data from ungrazed areas suggested that a process of recovery from the historical heavy use period was occurring. Although season-long grazing for five years did not promote the recovery of soil infiltration, sediment production and soil density and penetrability, the soil response to rest rotation and season-long grazing for one or two years (with four or three years of prior rest) usually corresponded to the ungrazed areas. Generally, soil properties appeared to fluctuate seasonally, showing greater soil infiltration and penetrability and lower bulk density when measured at the end of winter and the opposite conditions after the grazing season. Ungrazed areas fluctuated less than did grazed areas. Streambank movement was monitored by change in distance from the bank edges to permanent reference stakes. Bank movement tended to increase with amount of use---use in terms of number of animals and number of years. No grazing and occasional season-long use appeared to be associated with the least bank loss, while season-long grazing for four or five years and deferred rotation grazing were associated with the most bank loss. Rest rotation results were intermediate and variable, but generally low. Late season grazing treatments did not differ between September and October grazing and were not compared to the other systems due to differences in grazing pressure. Although winter processes and livestock grazing exerted a similar amount of pressure per week on streambanks, livestock were present for a relatively short period. Consequently, there was greater total bank loss in the winter on four of the sixteen treatments. These four treatments were season-long grazing for three, four or five years with big game access. The other twelve treatments did not demonstrate significant seasonal differences. Escherichia colt were monitored by the membrane filter technique to indicate the level of fecal contamination in the stream. Although large numerical differences were sometimes seen, coliform concentrations seldom changed significantly across the 400 meter long pastures. Large numerical reductions in coliform counts were also seen in the first year after livestock removal, but the changes were not statistically significant at the .05 level, either. The bacteria concentrations typically responded to changes in stream discharge due to storms by peaking with the hydrograph and again on the recession limb.
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