Close correlation between the nitrate elimination rate by denitrification and the organic matter content in hardwood forest soils of the Upper Rhine floodplain (France)

Abstract

Denitrification is a major process for reducing the nitrogen load in floodplains. Soil samples from depth profiles of a hardwood forest of the floodplain of the Upper Rhine were analyzed for their potential to denitrify under permanent nitrate supply. The soils were silty to silty-clayey in the surface layer and had increasing sand content with depth. The rate of denitrification was greatest in top soil and decreased with depth. Organic matter content along profiles decreased exponentially with depth. The denitrification rate showed a very close correlation with the organic matter content of the hardwood forest soil. A denitrification rate of 0.57 mg N day−1 g−1 organic matter present in the soil was calculated for all depths and sites and was constant for up to 23 days. This rather straightforward relationship may support predictions of the (maximum) potential denitrification rates in situ. Furthermore, this relationship may support modeling of the nitrogen balance and contribute to an efficient flood management strategy for the restored floodplains of the Upper Rhine in order to support nitrate removal by denitrification.