Denitrification rates measured in streams and inundated meadows

Denitrification rates measured in streams and inundated meadows

Anne Hasselholt*, Emil S. Henriksen*, Brian Kronvang, Hans Thodsen, Mette V. Carstensen, Joachim Audet

Department of Ecoscience, Aarhus University, Aarhus C, Denmark.

*Shared first authorship

 

Nitrogen (N) pollution in aquatic environments is a major concern worldwide due its negative effect on water quality and biodiversity. Part of the N applied as fertilizer and manure on agricultural fields is leached to streams and further exported to the sea. To mitigate N losses from agriculture, several mitigation strategies have been implemented in Denmark including field-level measures, constructed wetlands, and restoration of wetlands.

Most of the previous research have therefore focused on investigating the retention and turnover potential of these measures. However, streams and temporarily inundated riparian area also play an important role in retaining and removing N from surface waters but the overall effect at a larger scale such as Denmark (43,100 km²) is yet poorly investigated.

To estimate the significance of N turnover in streams and temporarily flooded riparian areas, we are conducting an in situ investigation of denitrification rates spanning four seasons during 2022-2023. The denitrification rates are measured using the N isotope pairing technique in six replicate measuring chambers in 15 streams and ditches. The study will also include in situ measurements of temporarily inundated riparian areas three times a year at three locations along typical Danish streams.

The results of the present study will contribute to a new update of an existing Danish N model consisting of three sub-models (leaching model, groundwater hydrological model and several surface water sub-models; Højbjerg et al., 2020). Each sub model deals with either calculation of N-leaching from arable fields, hydrological N-transport, and N-turnover in the groundwater zone and lastly N-turnover in surface waters such as streams and temporarily inundated meadows. The model complex has been used to develop national N-retention maps for groundwater and surface waters at a scale of app. 15 km². The new updated N-model is intended to deliver new N-retention maps on a finer scale.

 

References

Højberg, A.L., Thodsen, H., Børgesen, C.D., Tornbjerg, H., Nordstrøm, B.O., Troldborg, L., Hoffmann, C.C., Kjeldgaard, A., Holm, H., Audet, j., Ellermann, T., Christensen, J.H., Bach, E.O. & Pedersen, B.F. 2021. National kvælstofmodel – version 2020, Metode rapport. De Nationale Geologiske Undersøgelser for Danmark og Grønland. GEUS Specialrapport.