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TECHNICAL REPORTS

Wetlands and Aquatic Processes

A Methodology to Estimate the Denitrifying Capacity of a Riparian Wetland

^a Ecole Polytechnique Fédérale de Lausanne (EPFL), GEOLEP, GR B 1 383 (Bâtiment GC), Station no. 18, CH-1015 Lausanne, Switzerland
^b Ecole Polytechnique Fédérale de Lausanne (EPFL), LPE, GR B 1 423 (Bâtiment GR), Station no. 2, CH-1015 Lausanne, Switzerland

^* Corresponding author (claire.guenat{at}epfl.ch)

Received for publication May 10, 2004. Numerous studies have shown that riparian wetlands can play an important role in reducing nitrate concentrations before the ground water discharges into streams. Denitrification has been identified as an important process for this removal. Several approaches have been proposed to predict the denitrifying removal capacity of a riparian wetland, but no widely used tool exists to precisely quantify this capacity at the landscape scale. We propose such a methodology based on modeling the spatial variation of soil–water interactions in the entire riparian wetland. Mean values of denitrification enzyme activity (DEA) within three soil-denitrifying classes were 604, 212, and 24 ng N g^–1 h^–1 for Classes 3, 2, and 1, respectively. The study area, having a ground surface of about 15000 m², was underlain by an aquifer with a calculated volume of 60000 m³, less than 10000 m³ of which corresponded to active denitrifying horizons (Classes 2 and 3). By volume, approximately 30% of Class 3 and 70% of Class 2 were interacting with ground water. The denitrifying removal capacity of our wetland was calculated to be about 1.8 kg N m^–2 yr^–1. The calculated denitrifying capacity of our site was less than expected. This is due to the fact that not all ground water interacts with the horizons having the highest denitrifying capacity. Thus, we show that whatever the system is, specific local pedological and hydrogeological conditions and their interactions are paramount in controlling the denitrification process.

Abbreviations: DEA, denitrification enzyme activity • DNT, in situ denitrification • OC, organic carbon • TDBN, total dissolved bacterial nitrogen

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This Issue in Journal of Environmental Quality

JEQ 2005 34: 403-407. [Full Text]