PROBE 3: an innovative model for vegetation development, groundwater recharge and nitrate leaching in a changing climate

Climate change can be expected to have big consequences for groundwater-independent vegetations, precisely because they rely entirely on the atmosphere for their water. Over the past few years, KWR, often at the request of the water sector, has conducted extensive research into the soil, water and vegetation system, and how it reacts to changes in climate. Two themes stand out in this research: (1) the impact of water management on vegetation, and (2) the impact of the vegetation on evapotranspiration and groundwater recharge. This work has produced a number of building blocks which can, as it were, be picked up and put together to build a dynamic model, with which to calculate how the amount of organic matter changes over time as a result of natural succession and of climate change.

The objective of the project is to develop a succession model for the simulation of vegetation development, and of the amount of, and nitrate-concentration in, the groundwater recharge in groundwater-independent soils.

There are several reasons for the water sector’s interest in a model of the dynamic development of the soil-water-vegetation system, under the impact of nitrogen input and the climate. Such a model would, for different scenarios, make the following possible:

Testing the feasibility of nature objectives on higher sandy grounds and dunes.
Understanding and predicting groundwater recharge (relevant in discussions about background groundwater level decline).

Understanding and predicting nitrate concentration in the upper groundwater layer.

Watch the video (in Dutch, translation soon available):

PROBE as the basis

In this project we develop a version of the PROBE ecohydrological model for groundwater-independent systems, which permits the dynamic calculation of the composition and decomposition of organic matter, the vegetation development and the availability of water and nutrients in the soil. Because the development of such a dynamic model is far from easy, we develop it only for groundwater-independent profiles, where most of the groundwater abstraction areas are located.

Since water companies have a big interest in the management of large strategic supplies of fresh groundwater, we apply the model to the abstraction areas of their groundwater wells (push moraines, dunes, South-Limburg). We will feed the model with historical data on atmospheric nitrogen deposition and, for South-Limburg, fertilisers. Testing will be based on nitrate concentrations in the upper groundwater layer and, if available, the soil moisture below the root zone. In natural ecosystems, we also test the model on known vegetation succession and accumulation of organic matter.

The PROBE-simulated development in the amount of biomass and nitrate leaching over a 30-year ecosystem succession. The succession begins with bare dune sand; a distinction is made between high and low atmospheric nitrogen deposition.

Dynamic succession model

The project has the following outcomes:

A dynamic succession model for vegetation development and groundwater recharge in groundwater-independent soils.
An analysis of historical series for a number of locations and a validation of simulation results (nitrate concentration, vegetation).
Model results of two scenarios with different climates and atmospheric nitrogen depositions.
Report and publication in a trade journal.

For budgetary reasons, we limit ourselves to the development of a single one-dimensional process model that is applicable at the level of individual plots with short vegetation. Reprofunctions for PROBE 3 to make comprehensive calculations, and a module for woods and thickets, are expressly not part of the assignment.