Oral Presentation Australian Society for Limnology Congress 2013

Processes of nutrient removal in riparian zones in sandy soils. (#52)

Peter O'Toole 1
  1. Murdoch University, Murdoch, WA, Australia

Ellen Brook contributes only ~7% of the flow, but 39% and 28% of the total phosphorus and nitrogen load into the Swan River, Perth, Western Australia. To reduce nutrient export, riparian vegetation is promoted as a best management practice. International literature has shown the significant benefits of riparian vegetation to reduce incoming nutrients and improve water quality. The efficacy of riparian vegetation depends on the presence of slope and/or an impermeable subsurface layer (to generate flow through the riparian vegetation promoting plant/sediment and water interaction) and soil type (the capacity to take up and store nutrients). However, in Ellen Brook the majority of the catchment is flat and dominated by sandy soils. To assess whether riparian vegetation is effective at reducing nutrient concentrations, groundwater (three rows of nested piezometers; 0.5m,1.5m and 2.5m depth), stream, soil and vegetation parameters in the paddock and riparian zone were compared between a sloped and flat site. They indicated little subsurface flow but rather vertical rise and fall of shallow groundwater in the flat Ellen Brook catchment. Interestingly, this riparian zone also received inputs from the highly eutrophic stream during early winter flows. The capacity of the riparian zone to affect nutrient concentrations with primarily vertical flow was assessed using soil columns. At Ellen Brook, phosphorus removal was limited. However, it did facilitate nitrogen removal through denitrification. At the sloped site, riparian vegetation was found to have a higher capacity to remove nutrients, as flow passed through the active root zone.