Preprints
https://doi.org/10.5194/bg-2021-100
https://doi.org/10.5194/bg-2021-100

  20 Apr 2021

20 Apr 2021

Review status: a revised version of this preprint is currently under review for the journal BG.

Identification of the natural background of phosphorus in the Scheldt river using tidal marsh sediment cores

Florian Lauryssen1, Philippe Crombé2, Tom Maris3, Elliot Van Maldegem2, Marijn Van de Broek4, Stijn Temmerman3, and Erik Smolders1 Florian Lauryssen et al.
  • 1Division of Soil and Water Management, Department of Earth and Environmental Sciences, KU Leuven, Kasteelpark Arenberg 20 bus 2459, 3001 Leuven, Belgium
  • 2Department of Archaeology, Ghent University, Sint-Pietersnieuwstraat 35, 9000, Ghent, Belgium
  • 3University of Antwerp, Ecosystem Management Research Group, Campus Drie Eiken, D.C.120, Universiteitsplein 1, 2610 Wilrijk , Belgium
  • 4Sustainable Agroecosystems group, Department of Environmental Systems Science, Swiss Federal Institute of Technology, ETH Zürich, Zürich, Switzerland

Abstract. Elevated phosphate (PO4) concentrations can harm the ecological status in water by eutrophication. In the majority of surface waters in lowland regions such as Flanders (Belgium), the local PO4 levels exceed the limits defined by environmental policy and fail to decrease, despite decreasing total phosphorus (P) emissions. In order to underpin the definition of currents limits, this study was set up to identify the pre-industrial background PO4 concentration in surface water of the Scheldt river, a tidal river in Flanders. We used the sedimentary records preserved in tidal marsh sediment cores as an archive for reconstructing historical changes in surface water PO4. For sediment samples at different depths below the sediment surface, we dated the time of sediment deposition and analysed the extractable sediment-P. The resulting time series of sediment-P was linked to time series of measured surface water PO4 concentrations (data 1967–present). By combining the sediment-P and water-PO4 data, the sorption characteristics of the sediment could be described. Those sorption characteristics allowed us to estimate a pre-industrial background surface water PO4 levels, based on deeper sediment-P that stabilised at concentrations smaller than the modern. In three out of the four cores, the sediment-P peaked around 1980, coinciding with the peak in surface water PO4. The estimated pre-industrial (~1800) background PO4-concentration in the Scheldt river water was 62 [57; 66 (95 %CI)] µg PO4-P/L. That concentration exceeds the previously estimated natural background values for lakes in Flanders (15–35 µg TP/L) and is about half of the prevailing limit in the Scheldt river (120 µg PO4-P/L). In the 1930s, river water concentrations were estimated at 140 [128; 148] µg PO4-P/L, already exceeding the current limit. The method developed here proved useful for reconstructing historical, background PO4 concentrations of a lowland tidal river. A similar approach can apply to other lowland tidal rivers to provide a scientific basis for local, catchment specific PO4 backgrounds.

Florian Lauryssen 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 bg-2021-100', Anonymous Referee #1, 11 Jun 2021
    • AC1: 'Reply on RC1', Florian Lauryssen, 20 Sep 2021
  • RC2: 'Comment on bg-2021-100', Anonymous Referee #2, 30 Aug 2021
    • AC2: 'Reply on RC2', Florian Lauryssen, 20 Sep 2021

Florian Lauryssen et al.

Florian Lauryssen et al.

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Short summary
Surface waters in lowland regions, have a poor surface water quality, mainly due to excess nutrients like phosphate. Therefore, we wanted to know the phosphate levels without humans, also called the pre-industrial background. Phosphate binds strongly to sediment particles, suspended in the river water. In this research we used sediments deposited by a river as an archive for surface water phosphate back to 1800 CE. Pre-industrial phosphate levels were estimated at one third of the modern.
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