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Presented at the NABS Annual meeting, Vancouver, British Columbia, 2004
in Biogeochemistry 1
Nitrate removal in the riparian zone of an ephemeral agricultural stream, southeast Queensland, Australia
C.S. Fellows1,2,3, D Rassam2,3,4, N.J. Beard1,2, R. DeHayr2,3,4, H.M. Hunter2,3,4, and P. Bloesch3,4. 1Centre for Riverine Landscapes, Griffith University, Nathan, Queensland, 4111, Australia, 2Cooperative Research Centre for Catchment Hydrology , 3Cooperative Research Centre for Coastal Zone, Estuary and Waterway Management, 4Natural Resources and Mines, Resources Sciences Centre, 80 Meiers Road, Indooroopilly, Queensland, 4068, Australia
The effectiveness of riparian zones in removing nutrients, especially nitrate, from shallow groundwater inflows is strongly influenced by site hydrology, but data on riparian zone functioning in non-perennial streams are sparse. We investigated nitrate removal in the well-vegetated riparian zone of an ephemeral stream in an agricultural catchment in southeast Queensland, Australia. When the stream flows, a shallow perched aquifer develops via lateral subsurface flow from the stream. This groundwater typically has a residence time of days to weeks before discharging back to the stream. Nitrate removal in the perched aquifer was estimated to be 16% over 5 days using a subsurface addition of nitrate and a conservative tracer (chloride). Laboratory incubations of aquifer soil were used to assess rates of denitrification (acetylene block technique) and total nitrate removal. Rates of denitrification were relatively high and were greater for shallow soil (0-30 cm; 5.6 mg nitrate-N/kg dry soil/day) than deeper soil (30-100 cm; 2.1 mg nitrate-N/kg dry soil/day). For both depths, more than 85% of nitrate removal was attributed to denitrification. In this ephemeral system, riparian zones could make a significant contribution to nitrate removal, especially in situations where surface water enters subsurface environments multiple times as it flows downstream.
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