06 Jun 2023
 | 06 Jun 2023

Does stream remediation reduce phosphorus and sediment exports from agricultural catchments?

Lukas Hallberg, Faruk Djodjic, and Magdalena Bieroza

Abstract. Agricultural headwater streams are important pathways for diffuse sediment and nutrient losses, requiring mitigation strategies beyond in-field measures to intercept the transport of pollutants to downstream freshwater resources. As such, floodplains can be constructed along existing agricultural streams and ditches to improve fluvial stability and promote deposition of sediments and particulate phosphorus. In this study, we evaluated 10 remediated agricultural streams in Sweden for their capacity to reduce sediment and particulate phosphorus export and investigated the interplay between fluvial processes and phosphorus dynamics. Remediated streams with different floodplain designs (either on one side or both sides of channel, with different width and elevation) were paired with upstream trapezoidal channels as controls. We used sedimentation plates to determine seasonal patterns in sediment deposition on channel beds and floodplains and monthly water quality monitoring. This was combined with continuous flow discharge measurements to examine suspended sediment and particulate phosphorus dynamics and reduction along reaches. Remediated streams with floodplains on both sides of the channel reduced particulate phosphorus concentrations and loads (-54 μg L-1, -0.21 kg ha-1 yr-1) along reaches, whereas increases occurred along streams with one-sided floodplains (27 μg L-1, 0.09 kg ha-1 yr-1) and control streams (46.6 μg L-1). Sediment deposition in remediated streams was five times higher on channel beds compared to floodplains and there was no evident lateral distribution of sediments from channel to floodplains. There was no effect from sediment deposition on particulate phosphorus reduction, suggesting that bank stabilization was the key determinant for phosphorus mitigation in remediated streams, which can be realized with two-sided but not one-sided floodplains. Further, the overall narrow floodplain widths likely restricted reach-scale sediment deposition and its impact on P reductions. To fully understand remediated streams’ potential for reductions in both nitrogen and different phosphorus species and avoid pollution swapping effects, there is a need to further investigate how floodplain design can be optimized to achieve a holistic solution towards improved stream water quality.

Lukas Hallberg et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2023-585', Anonymous Referee #1, 25 Jul 2023
    • AC1: 'Reply on RC1', Lukas Hallberg, 24 Aug 2023
  • RC2: 'Comment on egusphere-2023-585', Anonymous Referee #2, 27 Jul 2023
    • AC2: 'Reply on RC2', Lukas Hallberg, 24 Aug 2023

Lukas Hallberg et al.


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Short summary
Floodplains can be constructed along agricultural streams with the purpose to increase water residence time and thereby reduce instream erosion and intercept nutrient export. In this paper we show how this remediation measure can reduce phosphorus concentrations with up to 30 % through optimized floodplain designs and placement. These reductions were primarily facilitated by protection against erosion rather than promotion of deposition on floodplains.