Significant nitrate attenuation in a mangrove-fringed estuary during a flood-chase experiment

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Wadnerkar, PD, Santos, IR, Looman, A, Sanders, CJ, White, S, Tucker, JP & Holloway, C 2019, 'Significant nitrate attenuation in a mangrove-fringed estuary during a flood-chase experiment', Environmental Pollution, vol. 253, pp. 1000-1008.

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Intertidal wetlands can sequester pollutants along estuarine conduits. Here we test the effectiveness of a mangrove-dominated estuary in removing dissolved nitrogen during a rain event. We intensively and simultaneously sampled surface water nutrients upstream and downstream of an estuary before, during and after a 63 mm rain event in Coffs Creek (Australia). NOx was the main form of dissolved nitrogen upstream of the estuary (∼60%), while dissolved organic nitrogen (DON) was an important form at the downstream station (∼46%) during observations. High NOx attenuation (71%) occurred during the rain event when the loads reached 31 μmol m−2 catchment area day−1. In contrast, the estuary was found to be a source of NH4+ (∼5 μmol m−2 catchment area day−1). This implies a moderate conversion of upstream NOx into NH4+ and DON along the transport pathway, likely due to tidally-driven pore water exchange within the anoxic estuarine mangrove sediments. Overall, the mangrove-lined estuary attenuated upstream total dissolved nitrogen loads, maintaining water quality and minimizing exports to the coastal ocean even during high flow conditions.

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