Spatial distribution of the relationship between nitrate residues in soil and surface water quality revealed through attenuation factors

Thanks to the intense efforts over the past decades to reduce nutrient losses, the annual average nitrate (NO3-) concentrations in the European surface waters have decreased between 1990 and 2010, but the reduction has levelled off since then. Nitrogen (N) mitigation measures adapted to the local conditions are needed to further reduce the N pressure from agriculture on surface water quality. The NO3--N residue measured before the onset of winter has been used as a simple indicator of the N pressure from agriculture. However, the vulnerability of a stream to NO3- inputs depends on dilution and reduction of NO3- during its transport towards the surface water, which can be expressed by the attenuation factor for surface water (AFsw), i.e. the ratio of the average NO3- concentration at the bottom of the rooting zone and the average NO3- concentration in the surface water. In this study, we combined NO3--N measurements in the soil in autumn, NO3- concentrations measured in the surface water during the winter period and a relatively simple soil-crop model to calculate AFsw at subcatchment level, in order to estimate the effect of mitigation measures without collecting detailed information on the subsoil and groundwater processes. Simulations demonstrated that in Flanders (the northern part of Belgium) the further optimisation of the N fertilisation rate is the most effective measure to reduce surface water NO3- concentrations. Maximising the acreage of catch crops had a limited additional effect on the NO3- concentrations in surface water given that this is already widely practiced at present. Although the removal of N rich crop residues is highly effective at field level, it contributed little to the reduction of NO3- concentrations in the surface water because of the small acreage of these crops. The implemented scenarios show that in subcatchments with low AFSw, targeted and subcatchment-specific combinations of measures, but including the trade-off with the potential economic and other negative effects, may not be sufficient to obtain acceptable NO3- concentrations in the surface water at subcatchment level. In regions with low AFsw, end–of-pipe technologies might be more cost-effective and even imperative to avoid the risk of eutrophication and a low surface water quality.

Jaar van publicatie:2022

Trefwoorden:Attenuation processes, Mitigation measures, Modelling, Nitrogen reduction, Spatially targeted measures

Toegankelijkheid:Closed