Model evaluation of simultaneous injection of inert and reactive tracers in treatment wetlands
Abstract
Treatment wetlands have shown to play an important role in reducing the nutrient content of recipient waters. The overall objective of this study is to evaluate simultaneous tracer experiment in Ekeby treatment wetland in Eskilstuna, Sweden, with tritiated water, nitrogen (N15) and phosphorus (P32). Particular modelling tools are essential to be able to understand the complexity of the wetland processes and to reveal the role underlying mechanisms. The model evaluation is based on a 2D physical description of stationary water flow and an uncoupled 1D formulation of the transport and transformation of nitrogen (N) and phosphorus (P). The overall N and P response of the wetland is obtained from averaging responses over the distribution of flow pathways. The flow modelling, described in a companion presentation, is thus a prerequisite for the interpretation of the P and Nprocesses. Both P and N are affected by retention in the wetland, which is clear from comparing the slope of the tails of the breakthrough of P32 and N15 with tritium. The lower slopes of the reactive tracers compared to tritium indicate a slow washout for N and P. Nitrogen was also partly removed due to denitrification, which is evident from a larger degree of removal than phosphorus. A firstorder loss rate coefficient, k, for N averaged for the entire wetland is about k = 0.12 1/days. The rate coefficient was defined from the expression Meff/Min=Exp(k <T>), where <T> is the mean residence time, the effluent Nmass is Meff and the influent Nmass is Min. However, laboratory experiments indicate that the microbiological activity in the bed sediment is generally much higher than the average for the wetland. Therefore, a consistent model interpretation of the denitrification process required that we accounted for both a ratelimited exchange with the hyporheic zone (sediments) and the firstorder loss of N2 from the hyporheic zone to the atmosphere.
 Publication:

AGU Spring Meeting Abstracts
 Pub Date:
 May 2005
 Bibcode:
 2005AGUSMNB43D..04W
 Keywords:

 1719 Hydrology;
 1890 Wetlands;
 4842 Modeling