Growing pressures from climate change are leading to increased nutrient and pesticide concentrations entering our natural water networks as the farming industry battles to meet demand and balance its books. Where will the contamination alert hotspots be 20 years from now if we do nothing? And what measures are most effective to combat the situation?
In Drenthe, Netherlands, water authorities and the regional council have joined forces with Acacia Water BV and RPS to create an ingenious computer model to answer these questions, funded in part by the European Union.
Desperate times and desperate measures: how can we meet demand and deal with impacts?
Today’s farmers face numerous challenges from economic pressures, production demand, and increasing natural impacts related to climate change. Good crop yield relies on effective arable nutrition and pest and disease management: most easily achieved on a large-scale with chemical agents. A changing climate does not bode well for this – with more periods of heavy rainfall and drought increasing reliance on chemical fertilisers and pesticides, and thus concentrations of chemicals entering the water network.
How do we ensure ecological quality in this environment?
The European Water Framework Directive is setting new standards for maximum permissible levels of introduced chemicals in surface water in 2021 to ensure that chemical concentrations entering the network must be reduced to improve our natural water quality.
In anticipation of these standards, and in response to climate change, the Hunze en Aa’s water board is monitoring the situation in their region closely: specifically focusing on the Drentsche Aa catchment area – where the water is processed for potable water – and the Hunze catchment area, where the ecological water quality is especially critical for aquatic life.
Given the long-term matter of climate change, the water board must consider what the situation will realistically look like in 2040 to plan its actions effectively. To begin, it was essential to specify the starting point conditions:
So many sample points, so little time
Opting for a precise program of sampling and continuous monitoring of numerous entry and downstream points would far exceed time and cost constraints so was not a viable option for gathering accurate data.
The solution: starting with a computer model and input from all
With help from EU-inputted international subsidy project Topsoil , RPS is working with Acacia Water to deliver an ingenious computer model to identify current and future hotspots for leaching and run-off from nitrogen, phosphor and pesticides. Topsoil is a unique multi-stakeholder venture between governments, water boards and academics examining solutions for climate change impacts on the environment and environmental practices to eventually create climate-resistant areas that can survive extreme weather swings.
RPS is managing data coordination for the project, and Acacia is customising and implementing the model. The model is being produced for the Hunze en Aa’s water board, Groningen water company and Province of Drenthe who are providing data for the calculations. This is further supplemented with data from the Royal Netherlands Meteorological Institute (KNMI) to simulate weather predictions, and from the Wageningen Environmental Research and metrology specialist Nederlands Meetinstituut on soil and nutrients. Arable landowners and farmers are also involved, ensuring that all the necessary information informs the computer model.
We are using an open-source universal computer model available from the US, which is primarily used to improve agricultural area management practices. The model allows for a large number of variables in the model that Acacia has fine-tuned and adapted specifically to suit our project.
Firstly, the average standard values prescribed by the model were added to a topographical image of the study area to get a rough baseline. This was then enhanced with specific data for Drenthe including:
The model is then calibrated to the outputs, nutrients and pesticide concentrations measured in the area.
The end product is a number of maps of the catchment area for the Huze and Drentse Aa, defining the areas with the highest risk of leaching and run-offfor the agricultural parcels. Not surprisingly, this is usually along the stream, but the model also revealed other unexpected locations, including points where impermeable boulder clay  lies just below surface level.
The model also reveals the effects of drainage pipes on leaching and run-off: many such pipes are used on agricultural land to drain excess surface water. The model provides output for 2007-2016, using colours to indicate leaching and run-off on the parcels:
The colours also indicate nutrient and pesticide levels in drainage towards ditches. Area consultation sessions have been held to discuss the maps with local farmers.
Soil improvement measures
The Freshwater Delta Program  prescribes the creation of a climate-resilient system that also offers the right farming conditions in the future. The hypothesis is that soil improvement measures lead to less leaching and run-off. This in turn contributes positively to water quality and achieving European Water Framework Directive goals, while improving farming conditions and reducing reliance on nutrient and pesticide use.
The maps of the Hunze and Drentsche Aa show the water authorities exactly where efforts must be directed, enabling them to work with farmers and determine the most effective measures to take, such as building field margins that act as a filter for run-off.
The second step is to calculate the scenarios, and see how the chosen measure will affect the situation in 2040, through simulating the weather forecasts from the KNMI. This prevents costly investments that impact business practices or may prove ineffective. If no action is taken, the model shows clear transitions: orange areas become redder and yellow areas more orange. It is up to the water authorities to implement measures as effectively as possible, so that the water quality remains climate-proof – both today and in the future.
Author: Jeroen Wolbers
Further information and notes:
Travel time study
In spring 2018, the RPS - Acacia Water consortium conducted a travel time study in the Drentsche Aa (as a separate Topsoil project) to gather data on time taken for water, and any contamination dissolved in it, to travel from the catchment area to the Groningen water company’s collection point for drinking water. Such data is essential to guide response plans for contamination disaster events.
 About Topsoil
The goal of Topsoil is to share knowledge, experience and possible solutions pertaining to water management and the effects of climate change in which soil plays a key role. Together with Denmark, Germany, Great Britain and Belgium, we are learning from each other on an international level. Topsoil was established in 2015 and will run until 2020 with a total budget of around €7.3 million, including European subsidies. The participating water authorities in the Netherlands are the Noorderzijlvest water company, Province of Drenthe and Hunze en Aa’s water board.
 Boulder clay (till)
A solid and compact mixture of sand and clay with gravel and pebbles, formed under a glacier during the Ice Age. It is impermeable to water, so that the sandy soil on top of it saturates quickly, leading to faster run-off.
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