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Nitrogen processing in a tidal freshwater marsh: a whole ecosystem 15N labeling study

Gribsholt, B. and Boschker, H.T.S. and Struyf, E. and Andersson, M.G.I. and Tramper, A. and Brabandere de, L. and Damme van, S. and Brion, N. and Meire, P. and Dehairs, F. and Middelburg, J.J. and Heip, C.H.R. (2005) Nitrogen processing in a tidal freshwater marsh: a whole ecosystem 15N labeling study. Limnology and Oceanography, 50, 1945-1959. ISSN 0024-3590.

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We quantified the fate and transport of watershed-derived ammonium in a tidal freshwater marsh fringing the nutrientrich Scheldt River in a whole-ecosystem 15N labeling experiment. 15N-NH4+ was added to the floodwater entering a 3,477 14 m2 tidal marsh area, and marsh ammonium processing and retention were traced in six subsequent tide cycles. We present data for the water phase components of the marsh system, in which changes in concentration and isotopic enrichment of NO3-, NO2-, N2O, N2, NH4+, and suspended particulate nitrogen (SPN) were measured in concert with a mass balance study. Simultaneous addition of a conservative tracer (NaBr) confirmed that tracer was evenly distributed, and the Br2 budget was almost closed (115% recovery). All analyzed dissolved and suspended N pools were labeled, and 31% of added 15N-NH4+ was retained or transformed. Nitrate was the most important pool for 15N, with nitrification accounting for 30% of 15N-transformation. In situ whole-ecosystem nitrification rates were four to nine times higher than those in the water column alone, implying a crucial role for the large reactive marsh surface area in N-transformation. Under conditions of low oxygen concentrations and high ammonium availability, nitrifiers produced N2O. Our results show that tidal freshwater marshes function not only as nutrient sinks but also as nutrient transformers.

Item Type:Article
Institutes:Nederlands Instituut voor Ecologie (NIOO)
ID Code:11715
Deposited On:23 Nov 2011 01:00
Last Modified:15 Jan 2014 09:23

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