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Assessing the effectiveness of riparian vegetation in a flat sandy soiled system

O'Toole, P., Chambers, J., Robson, B. and Bell, R.W. (2012) Assessing the effectiveness of riparian vegetation in a flat sandy soiled system. In: Australian Society for Limnology Congress 2012, 26 - 29 November, Armidale, NSW, Australia.

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Ellen Brook contributes only ~7% of flow, but 39% and 28% of the total phosphorus and nitrogen load into the Swan River, Perth, Western Australia (Swan River Trust 2009). To reduce this nutrient export, riparian vegetation is promoted as a best management practice. International literature has shown significant benefits of riparian vegetation to reduce incoming nutrients and improve water quality. The riparian paradigm relies on there being sufficient slope to generate flow through the riparian vegetation to allow plant/sediment and water interaction. However, in Ellen Brook the majority of the catchment is flat and dominated by sandy soils, resulting in little subsurface flow but rather vertical rise and fall of shallow groundwater. To assess whether riparian vegetation is functioning to reduce nutrient input into streams under these conditions, three rows of nested piezometers (1.5m and 2.5m) were installed in a transect across the riparian zone and into the paddock. Nutrient concentrations were significantly (p=>0.05) higher and more variable in shallower groundwater. From the first flush of winter rains to the dry early summer period, redox potentials declined in shallow groundwater to highly reducing values (-33.71mv to -121.55mv). Nitrate decreased exponentially from the paddock (x= 733µg.N/L) to the stream (x=42 µg.N/L). Ammonium concentrations remained relatively stable over time and space. This indicates the potential for nitrogen removal in the riparian zones of Ellen Brook through denitrification. Organic carbon and soluble reactive phosphorus concentrations peaked in the middle of the riparian zone (TOC: x=113 µg.C/L, SRP: x= 691 µg.P/L) and decreased closer to the stream (TOC: x= 77 µg.C/L, SRP: x=341 µg.P/L). Understanding the mechanisms behind phosphorus distribution throughout the riparian zone is being investigated through groundwater hydrological testing, and is pivotal for assessing the effectiveness of riparian vegetation as a best management practice.

Publication Type: Conference Item
Murdoch Affiliation: School of Environmental Science
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