Oct 26, 2012 - We thank Dirk Erler, Damien Maher, Maria Matthes and local residents ..... Johnston, S., P. Hirst, P. Slavich, R.T. Bush, and T. Aaso. 2009.
Estuaries and Coasts (2013) 36:56–73 DOI 10.1007/s12237-012-9561-4
The Contribution of Groundwater Discharge to Nutrient Exports from a Coastal Catchment: Post-Flood Seepage Increases Estuarine N/P Ratios Isaac R. Santos & Jason de Weys & Douglas R. Tait & Bradley D. Eyre
Received: 24 April 2012 / Revised: 9 September 2012 / Accepted: 28 September 2012 / Published online: 26 October 2012 # Coastal and Estuarine Research Federation 2012
Abstract Four months of daily nutrient and radon (a natural groundwater tracer) observations at the outlet of a heavily drained coastal wetland illustrated how episodic floods and diffuse groundwater seepage influence the biogeochemistry of a sub-tropical estuary (Richmond River, New South Wales, Australia). Our observations downstream of the Tuckean Swamp (an acid sulphate soil floodplain) covered a dry stage, a flood triggered by a 213-mm rain event and a post-flood stage when surface water chemistry was dominated by groundwater discharge. Significant correlations were found between radon and ammonium and N/P ratios and between radon and dissolved organic nitrogen (DON) during the post-flood stage. While the flood lasted for 14 % of the time of the surface water time series, it accounted for 18 % of NH4, 32 % of NOx, 66 % of DON, 58 % of PO4 and 55 % of dissolved organic phosphorus (DOP) catchment exports. Over the 4-month study period, groundwater fluxes of 35.0, 3.6, 36.3, 0.5 and 0.7 mmolm−2 day−1 for NH4, NOx, DON, PO4 and DOP, respectively, were estimated. The groundwater contribution to the total surface water catchment exports was nearly 100 % for ammonium, and
