Riparian pasture retirement effects on sediment, phosphorus, and nitrogen in channellised surface run‐off from pastures

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Abstract
Riparian pasture retirement effects on the chemistry of channellised surface run‐off from 2 moderately steep hillslopes was examined in a 22‐month study. Seventy‐one surface run‐off events occurred. They varied in size by about 2 orders of magnitude. Sediment, phosphorus, particulate‐ and nitrate‐nitrogen concentrations in the run‐off (in each event) at retired riparian pasture sites were significantly (P < 0.001) and substantially lower than concentrations in run‐off at grazed riparian pasture sites. Concentrations also varied less extensively at retired sites (P < 0.001). Riparian pasture retirement impacts on total loads were examined by comparing the average concentrations in run‐off in 22 months at retired and grazed sites. These event‐flow‐weighted total and volatile suspended solids, particulate P and N, dissolved P, and nitrate‐nitrogen means were <87%, <84%, < 80%, < 85%, < 55%, and < 67%, respectively, lower at the retired sites. It was concluded that riparian pasture retirement is an effective means of reducing surface run‐off pollutant loads to waterways in the short term, but long‐term impacts need to be examined.