Daily denitrification rates in floodplains under contrasting pedo-climatic and anthropogenic contexts: modelling at the watershed scale

Abstract

Floodplains play a crucial role in water quality regulation via denitrification. This biogeochemical process reduces nitrate (NO3 -), with aquifer saturation, organic carbon (OC) and N availability as the main drivers. To accurately describe the denitrification in the floodplain, it is necessary to better understand nitrate fluxes that reach these natural bioreactors and the transformation that occurs in these surface areas at the watershed scale.At this scale, several approaches tried to simulate denitrification contribution to nitrogen dynamics in study sites. However, these studies did not consider OC fluxes influences, hydrological dynamics and temperature variations at a daily time step. This paper focuses on a new model that allows insights on nitrate, OC, discharge and temperature influences on daily denitrification for each water body. We used a process-based deterministic model to estimate daily alluvial denitrification in different watersheds showing various pedo-climatic conditions.To better understand global alluvial denitrification variability, we applied the method to three contrasting catchments: The Amazon for tropical zones, the Garonne as representative of the temperate climate and the Yenisei for cold rivers. The Amazon with a high discharge, frequent 2 flooding and warm temperature, leads to aquifers saturation, and stable OC concentrations.Those conditions favour a significant loss of N by denitrification. In the Garonne River, the low OC delivery limits the denitrification process. While Arctic rivers have high OC exports, the low nitrate concentrations and cold temperature in the Yenisei River hinder denitrification. We found daily alluvial denitrification rates of 119.4 ± 47.5, 7.6 ± 5.4 and 0.1 ± 0.5 kgN.ha -1 .yr -1 during the 2000-2010 period for the Amazon, the Garonne and the Yenisei respectively. This study quantifies the floodplains influence in the water quality regulation service, their contribution to rivers geochemical processes facing global changes and their role on nitrate and OC fluxes to the oceans.

Denitrification in wetlands: A review towards a quantification at global scale

“…The largest dimension for the study of denitrification is at Earth scale (10 7 m). Modelling and compilation of data of many ecosystem and landscape level studies can give more information about denitrification and its role to the regulated fluxes into the oceans in a more integrative context and with a long term dynamic vision (Fabre et al, 2020;Trepel and Palmeri, 2002). Hence, integration of information and multidisciplinary research, at different spatial-temporal scale need to be promoted.…”

Soil Characteristics and Hydromorphological Patterns Control Denitrification at the Floodplain Scale

“…There are numerous studies that address the factors influencing denitrification (Pinay et al, 2007;Saggar et al, 2013) and also several larger-scale modelling approaches (e.g., Nielsen et al, 2001;Natho et al, 2013;Fabre et al, 2020). However, the lack of integrated regional soil DP measurements and flood duration assessments may limit a precise assessment of environmental factors controlling DP at the landscape level.…”

“…There are diverse approaches for measuring denitrification (Groffman et al, 2006) but it has remained a difficulty to date. Along with temporal and spatial variability, this leads to highly varying estimations of the nitrate retention capacity of floodplains, ranging from less than 1 kg N ha −1 a −1 to more than 600 kg N ha −1 a −1 (Arheimer and Wittgren, 2002;Forshay and Stanley, 2005;Gergel et al, 2005;Fabre et al, 2020;Walton et al, 2020). In Germany, knowledge about the spatial distribution of the denitrification potential in floodplains on the landscape scale is rather limited.…”

Dissolved organic carbon fluxes to oceans under climate change

“…Organic carbon (OC) exported by rivers to the oceans is essential for many biological processes (Cole et al, 2007;Drake et al, 2017). For example, riverine OC in uences denitri cation in the river, the coastal areas (Taylor and Townsend, 2010), and the oodplains (Fabre et al, 2020a). Riverine OC exports are also directly used by the oceanic food web (Follett et al, 2014;Steinberg and Landry, 2017;Ward et al, 2017).…”