Abstract
Vegetated ditches and wetlands are important sites for nutrient removal in agricultural catchments. About half of the influx of inorganic nitrogen can be removed from these ecosystems by denitrification. Previous studies have shown that denitrification in aquatic ecosystems is strongly temperature dependent, resulting from temperature-dependent oxygen availability. Here, we study short-term temperature effects on sediment oxygen demand (SOD) and the maximum depth of oxygen penetration into the sediment (Z), in relation to overall denitrification rates. We set up sixteen wetland microcosms at four different temperatures (11–25 °C), in which we determined SOD and Z from sediment oxygen microprofiles. Denitrification rates were measured using 15N-labeling, analysed by membrane inlet mass spectrometry. Temperature strongly affected sediment oxygen dynamics. SOD exponentially rose with temperature, ranging from 0.37 to 1.53 g m−2 d−1 (Q10 = 2.4). Correspondingly, warming led to shallower oxygen penetration into the sediment, ranging from 4.12 to 2.08 mm. Denitrification rates increased with warming (Q10 = 2.6), ranging from 8.4 to 86 μmol N m−2 h−1. The results of this short-term experiment confirm the potential increase of denitrification with rising temperature, promoted by lower oxygen availability in the top layer of the sediment, which supports the understanding of denitrification variability in freshwaters.
Highlights
Vegetated ditches and wetlands are important sites for nutrient removal in agricultural catchments
Denitrification is a major sink for inorganic nitrogen in freshwater ecosystems, several studies in the past two decades have demonstrated that anaerobic ammonium oxidation can significantly contribute to N removal (Risgaard-Petersen et al 2003; Seitzinger et al 2006)
Oxygen concentrations remained more or less constant in the upper part of the profile, indicating a mixed water column. This was followed by a sharp decrease of oxygen across the diffusive boundary layer (DBL) and in the top layer of the sediment, until anoxic conditions were reached
Summary
Vegetated ditches and wetlands are important sites for nutrient removal in agricultural catchments. Denitrification rates increased with warming (Q10 = 2.6), ranging from 8.4 to 86 μmol N m−2 h−1 The results of this short-term experiment confirm the potential increase of denitrification with rising temperature, promoted by lower oxygen availability in the top layer of the sediment, which supports the understanding of denitrification variability in freshwaters. Wetlands (2017) 37:975–983 in wetland areas act as nitrogen filters in the agricultural landscape, removing a large proportion of nitrogen before they drain into connected rivers and lakes (de Klein 2008; Veraart et al 2016) These ditches are common freshwater ecosystems in low-lying agricultural areas and peatlands, constituting natural sediment and bank vegetation similar to wetlands (Herzon and Helenius 2008). Sediment oxygen concentrations, sediment oxygen demand and associated oxygen penetration depth will be important drivers of denitrification
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