University of Rostock models phosphorus removal in Belgian Kemmelbeek watershed

11 December 2020 - Published by Charlotte Boeckaert
After assessing the nutrient reduction potential of nutrient filtration systems in the German Warnow basement, University of Rostock (UROS) estimated the effect of nutrient mitigation strategies on phosphorus (P) export rates in the Belgian Kemmelbeek watershed, using its coupled eco-hydrological Soil and Water Assessment Tool (SWAT-Model).

UROS successfully calibrated the monthly discharge and acquired a satisfactory Nash-Sutcliffe-Efficiency coefficient (used to assess the predictive skill of hydrological models) of 0.58 (Figure 1). The loads of dissolved reactive phosphorus (DRP) in the stream achieved a Nash-Sutcliffe-Efficiency of 0.66.


Figure 1: Calibration time curve of discharge (left panel) and DRP loads (right panel). The blue lines represent the observed values; the red lines represent the modeled values.

The Nash-Sutcliffe-Efficiency alone is not sufficient to evaluate the quality of a hydrological model. The distribution of flow constituents should likewise be considered in the evaluation process. During the discharge season, 40% of the water is transported to adjacent surface waters via tile drains, typical for intensively drained lowland catchments. Only 5% of the total flow originates from surface runoff.
Filter boxes with iron-coated sand
Field data for the P reduction scenarios were obtained from the NuReDrain project partners at Ghent University. They tested in-situ filter boxes at drainage outlets to reduce P loads in surface waters using iron-coated sand (ICS), a reused waste product from drinking water production. The reported filter efficiencies were implemented into the model. The filter boxes were applied to 5, 10, 15, 25, 50, 75, and 100% of tile drainage outlets of the drained agricultural areas within the watershed.


Figure 2: Base model (P) and P reduction potential of each reduction scenario (R5 to R100).

The filter installation's P reduction potential at outlets of drainage plots ranged from 254 kg to 6592 kg P for the 5% and the 100% reduction scenario, respectively (Figure 2). However, it should be emphasized that the modeling results are only a rough estimation of the P filter installation's possible effects.
Further work will include the calibration of nitrate loads and the implementation of N reduction scenarios.