Effect of pasture buffer length and pasture type on runoff water quality following prescribed burning in the Wivenhoe Catchment H. Ghadiri A , J. Hussein A,B , and C. W. Rose A A Environmental Futures Centre, Griffith University, Nathan, Qld 4111, Australia. B Corresponding author. Email: janethussein@bigpond.com Abstract. Burning of pastures is a management practice adopted by graziers worldwide. When rain falls on burnt pastures, it can lead to increased pollutant transport in runoff. However, this transport can be modified by vegetative buffers which intercept the runoff downslope of burnt areas. This study examines the effects of different pasture buffer lengths (0, 2, and 5 m) on sediment and chemical transport from two pasture sites near Wivenhoe Dam, the main water reservoir for Brisbane City. Simulated rainfall (100 mm/h) was applied to 18 plots on pasture sites after they were burnt, and insoluble and soluble components were measured in the runoff. Most eroded sediment/organic debris accumulated against the first row of the grass buffer strips or was deposited in the upslope backwater region. Buffer length had little impact on the runoff concentrations of NO 3 – and NO 2 – (NO x ), total Kjeldahl nitrogen, and total nitrogen from the 5-m-length upslope plots but was significant for sediment loss rate, filterable reactive phosphate, ammonium, and total and dissolved organic carbon. Pasture type was significant for NO x , ammonium, sediment loss rate, and total organic carbon only. Burning increased enrichment ratios of nutrients and carbon in the runoff compared with unburnt plots, but a 2-m buffer strip subsequently reduced the enrichment ratio values by >30%. Buffers strips of unburnt pasture grass may provide an effective tool for post-fire erosion control following prescribed burning; however, further work including scaling to larger plot sizes and catchment level is required. Additional keywords: buffer strip, nutrient loss, pasture burning, post-fire erosion control, sediment loss. Introduction Burning of pasture is commonly practised in many parts of the world for its perceived ability to improve pasture quality and palatability, reduce woody shrubs, control weeds, and increase nutrient supply (see for example Svejcar 1989; Orr and Paton 1997) However, burning is known to affect soil erodibility and runoff quality (DeBano et al. 1998; Johansen et al. 2001; Burke et al. 2005; Llovet et al. 2008). Water reservoirs in many areas are surrounded by pastures, so when burning is followed by rainfall, this causes runoff pollutants such as sediment, nutrients, and carbon to enter the water and affect water quality. The intensity of the burning affects the type and amount of ash produced as well as the properties of the underlying soil (Dragovich and Morris 2002; Coelho et al. 2004; Llovet et al. 2008), both of which have implications for the amount of runoff and sediment loss (Robichaud and Waldrop 1994; Benavides-Solorio et al. 2004). Vegetative buffer strips have been widely employed in catchments of water-supply reservoirs to reduce fluxes of pollutants which may affect water quality. The effectiveness of vegetative buffer strips in mitigating pollutant transport in overland flow has been the subject of extensive research (e.g. Meyer et al. 1995; Ghadiri et al. 2001; Rose et al. 2003; Blanco-Canqui et al. 2004; Hussein et al. 2007, 2008). There are potentially several variables that can influence sediment-trapping efficiency of buffers, including the type of vegetation used, the length of the buffer, sediment type, hydraulic load, flow rate, and topography. Several studies have shown that stiff grass buffers (hedges) as narrow as 20 cm are very effective in trapping sediment (Dabney et al. 1995). Shorter, less rigid vegetation, such as pasture grasses, is less effective in trapping sediment (Meyer et al. 1995), and longer buffer widths may be required to reduce fluxes of pollutants (Gharabaghi et al. 2002). However, it has also been reported that large increases in the length of grass barriers do not always result in substantial increases in sediment-trapping efficiency of the barriers (Ghadiri et al. 2001; Blanco-Canqui et al. 2004). While there are some data on runoff from Australian landscapes following burning, most of these data relate to sediment loss from forested areas (e.g. Prosser and Williams 1998; Dragovich and Morris 2002; Lane et al. 2006). There is less information on losses of sediment, nutrients, and carbon from burned pastures or on the enrichment of sediment-sorbed contaminants in runoff following burning (Johansen et al. 2001). With the used of prescribed burning, there is opportunity for specific areas to be left unburnt downslope of the burnt areas, to reduce runoff and contaminant transfer. However, there is also limited information worldwide on the use of vegetative buffers as a post-fire erosion control measure. Some research has been done on post-fire application of mulches, biosolids, or logs (e.g. Wohlgemuth 2003) but little quantitative work on buffer Ó CSIRO 2011 10.1071/SR11122 1838-675X/11/060513 CSIRO PUBLISHING www.publish.csiro.au/journals/sr Soil Research, 2011, 49, 513–522