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ARS Home » Midwest Area » Ames, Iowa » National Laboratory for Agriculture and The Environment » Agroecosystems Management Research » Research » Publications at this Location » Publication #242099
Title: Sediment and Phosphorus Losses from Stream Banks in Grazed Riparian Pastures

Author
item Kovar, John
item RUSSELL, JAMES - Iowa State University
item NELLESEN, SHELLY - Iowa State University
item HAAN, MATHEW - Iowa State University

Submitted to: Symposium Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 7/28/2009
Publication Date: 7/28/2009
Citation: Kovar, J.L., Russell, J.R., Nellesen, S.L., Haan, M.M. 2009. Sediment and Phosphorus Losses from Stream Banks in Grazed Riparian Pastures. 2009 SERA-17 Annual Meeting, July 28-31, 2009, Windsor, Ontario, Canada. In: Great Lakes Phosphorus Forum Proceedings. Available: http://www.sera17.ext.vt.edu/Meetings/greatlakespforum/poster.shtml

Interpretive Summary:

Technical Abstract: Managed grazing can reduce the amounts of sediment and nutrients transported in surface runoff from upland areas of pastures. However, sediment and phosphorus (P) in surface waters also originate from stream banks and riparian areas, suggesting that improved grazing management practices can reduce losses from these areas. In this three-year study (2005-2007), we utilized six 12-ha cool-season grass pastures, each bisected by a 196-m stream segment. Two replications of three management treatments [continuous stocking with unrestricted stream access (CSU), continuous stocking with restricted stream access (CSR), and rotational stocking (RS)] were assigned to the six pastures. Pastures were stocked with 15 fall-calving Angus cows from May to October of each year. To estimate stream bank erosion within each of the grazing treatments, erosion pins were driven into the ground at 1-m intervals from the stream’s edge to the top of the bank on both sides of the stream along 10 equidistant transects in each pasture. Pin length was measured before grazing, monthly during the grazing season, and after grazing ceased to determine sediment erosion and deposition. To determine P content of the stream bank soils, samples were collected less than one meter from the stream channel in each of the pastures. Total soil P values, in conjunction with soil bulk density and erosion pin measurements, were used to estimate how much P is being lost through erosion of the stream banks. During the period from May 2005 to December 2007, the rate of net soil erosion from stream banks averaged 0.0016 cm of soil per day for the entire stream reach. No differences in net bank erosion were observed among grazing management practices in any year. Estimated total P losses from stream banks during three years of erosion/deposition measurements were 35 kg for the CSU treatment, 29.5 kg for the CSR treatment, and 9.5 kg for the RS treatment. Although no differences were observed in the amount of stream bank erosion during the study period, differences in forage characteristics within the riparian area and cattle distribution patterns were observed, suggesting that alternative grazing management practices, such as rotational stocking and the use of reinforced stream access points, may positively impact riparian conditions and surface water quality over time.