The role of freshwaterhoarses in the conclusion and transformation of nitrogen in estuary: a ecosystem N labelings study.

Project Details


We quantified the fate and transport of watershed-derived ammonium in a tidal freshwater marsh fringing the nutrient rich Scheldt River in a whole ecosystem 15N labeling experiment. 15N-NH4+ was added to the flood water entering a 3477 m2 tidal marsh area, and marsh ammonium processing and retention were traced in 6 subsequent tide cycles. We present data for the water phase components of the marsh system, where 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 Br- 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 4-9 times higher than those in the water column alone, implying a crucial role of 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
Effective start/end date1/01/0231/12/04


  • waters

Flemish discipline codes

  • Chemical sciences