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Research article - Peer-reviewed, 2022

Catchment controls of denitrification and nitrous oxide production rates in headwater remediated agricultural streams

Hallberg, Lukas; Hallin, Sara; Bieroza, Magdalena

Abstract

Heavily modified headwater streams and open ditches carry high nitrogen loads from agricultural soils that sustain eutrophication and poor water quality in downstream aquatic ecosystems. To remediate agricultural streams and reduce the export of nitrate (NO3-), phosphorus and suspended sediments, two-stage ditches with constructed floodplains can be implemented as countermeasures. By extending hydrological connectivity between the stream channel and riparian corridor within constructed floodplains, these remediated ditches enhance the removal of NO3- via the microbial denitrification process. Ten remediated ditches were paired with upstream trapezoidal ditches in Sweden across different soils and land uses to measure the capacity for denitrification and nitrous oxide (N2O) production and yields under denitrifying conditions in stream and floodplain sediments. To examine the controls for denitrification, water quality was monitored monthly and flow discharge continuously along reaches. Floodplain sediments accounted for 33% of total denitrification capacity of remediated ditches, primarily controlled by inundation and stream NO3- concentrations. Despite reductions in flow-weighted NO3- concentrations along reaches, NW removal in remediated ditches via denitrification can be masked by inputs of NW-rich groundwaters, typical of intensively managed agricultural landscapes. Although N2O production rates were 50 % lower in floodplains compared to the stream, remediated ditches emitted more N2O than conventional trapezoidal ditches. Higher denitrification rates and reductions of N2O proportions were predicted by catchments with loamy soils, higher proportions of agricultural land use and lower floodplain elevations. For realizing enhanced NO3- removal from floodplains and avoiding increased N2O emissions, soil type, land use and the design of floodplains need to be considered when implementing remediated streams. Further, we stress the need for assessing the impact of stream remediation in the context of broader catchment processes, to determine the overall potential for improving water quality.

Keywords

Mitigation measures; Two-stage ditches; Constructed floodplains; Denitrification; Nitrous oxide; Eutrophication

Published in

Science of the Total Environment
2022, volume: 838, number: Part 3, article number: 156513

Authors' information

Swedish University of Agricultural Sciences, Department of Soil and Environment
Swedish University of Agricultural Sciences, Department of Forest Mycology and Plant Pathology
Swedish University of Agricultural Sciences, Department of Soil and Environment

Sustainable Development Goals

SDG6 Clean water

UKÄ Subject classification

Water Engineering
Soil Science
Oceanography, Hydrology, Water Resources

Publication Identifiers

DOI: https://doi.org/10.1016/j.scitotenv.2022.156513

URI (permanent link to this page)

https://res.slu.se/id/publ/118308