PhD position: Groundwater dynamics in Flanders and impact on denitrification

Updated: over 1 year ago
Job Type: FullTime
Deadline: 12 Oct 2022

Flemish agriculture needs to rapidly evolve because of the nitrogen crisis and more frequent droughts. Flemish agriculture has to reduce its emissions of nitrogen into water and there is a need for more and more efficient irrigation. There are two interrelated bottlenecks for both challenges: (i) Flanders does not have a calibrated dynamic groundwater model and (ii) Flanders has no spatial model to estimate denitrification in soil and groundwater.

The surplus nitrogen in Flemish agriculture causes nitrate leaching from soil to groundwater. However, the conversion of nitrate to N2O or N2 in the soil and groundwater ensures that a large part of the residual nitrogen in the soil does not end up as nitrate in the surface water. This denitrification depends on the redox potential in the soil and the residence time of the water in the soil, both of which are related to the structure of the soil and the groundwater flow. Flanders has a very good digital soil map and map of the subsoil (DOV) and has an extensive phreatic monitoring network with digitally available data on the groundwater level and its chemical composition. That data is rarely statistically analyzed to know where and when denitrification takes place. Moreover, there is no link between existing models for nitrate leaching and groundwater models because the latter are not available as a dynamic (non-stationary) model. Jülich's research group developed a dynamic groundwater model for Germany with a resolution of 600x600 m and makes 10-day predictions. This spatial model also covers Flanders, but it has never been verified with the time series of groundwater levels in Flanders.

The aim of the research is to calculate denitrification in the Flemish subsoil so that area-specific N fertilization recommendations can be drawn up, namely the lowest recommendations where denitrification is low and vice versa. Roughly three steps are required for this. (1) the statistical analysis of data on nitrate concentrations in groundwater in relation to soil structure, land use and groundwater level; (2) calibrating the groundwater model with data from the phreatic groundwater and refine it to a resolution of 60x60 m (3) targeted periodic sampling of groundwater in 2-3 selected transects to estimate the dynamics of nitrate in the subsurface in relation to the redox zone. It is estimated that 2/3 of this research will consist of modelling and statistical analysis and 1/3 of fieldwork and associated analyses in the laboratory. The doctoral student will also be involved in educational activities and in dissemination of the results to the government.



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