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Agriculture must use help from Mother Nature

Nature can give a helping hand to avoid nitrogen loss from agriculture to the aquatic environment. This was one of several important points at an international workshop regarding landscape filters organized by Aarhus University. 

2017.06.02 | Janne Hansen

Nature is good at filtering nutrients from the soil before they proceed further into the aquatic environment. Photo: Janne Hansen

We need to avoid leaching of nitrogen from agricultural fields into the aquatic environment. This is a huge challenge but does not need to be a problem. On the contrary, it can be turned around to a win-win situation for agriculture and the environment if nature is taken on board as an active team player. This was one of the messages at an international workshop, that was organised by DCA – Danish Centre for Food and Agriculture in collaboration with the Department of Agroecology at Aarhus University and held on April 20, 2017.

The workshop comprised presentations and discussions regarding knowledge and experience of various landscape filter solutions with the aim of reducing nutrient losses to the aquatic environment. Constructed ”natural” wetlands, subsurface flow wetlands, intelligent buffer zones and controlled drainage were some of the measures that were presented to the approximately 55 participants from authorities, universities, advisory services and commercial companies in the USA, Netherlands, Sweden, Czech Republic and Denmark.

Senior researcher Finn Plauborg from the Department of Agroecology at Aarhus University is the leader of a new and extremely timely four-year project funded by the Ministry of Environment and Food of Denmark. The aim of the project is to strengthen the knowledge base for assessment of cost efficiency and effect on nitrogen removal of subsurface flow wetlands with biofilters. 

Read Biofilters and mini-wetlands can reduce nitrogen leaching.

Finn Plauborg initiated the meeting by stating that Denmark must gradually reduce its leaching of nitrogen to coastal areas by 7,000 tons of nitrogen per year before the end of 2021, but that political circles are discussing a need for an additional reduction of 6,000 tons per year before the end of 2027. 

- Denmark uses a relatively large proportion of its area for producing food but there are large variations with regard to where in the country reduction requirements are most necessary. Catch crops have a good effect but they are not sufficient. We must therefore find a range of efficient off-field measures, such as natural wetlands, forests, controlled drainage and constructed mini-wetlands with or without subsurface flow, he said.

Denmark does not stand alone with the challenge of ensuring that unwanted nutrients, pesticides and similar substances do not end up in the aquatic environment. We can turn this around to an advantage because it means that there are many experts with whom we can exchange knowledge and experience. The international workshop was clear proof of this. 

Let Mother Nature do the work

Over and above the wealth of data, knowledge and experience that the workshop offered, it also had many important messages. One of these was that we should let nature do some of the work. 

Years ago, a patchwork of natural wetlands spread across the Danish landscape. Plants, microorganisms, soil, water and the sun each contributed to making wetlands act as the landscape’s kidneys. Re-creating this type of nature can be a good solution in many cases. In other cases, we must strive to copy or borrow elements of nature’s processes in constructed systems that do not take up as much agricultural land and enable the farmer to continue cultivating most of his land.    

The road to constructing a wetland will be shorter and more successful if certain guidelines are followed:

  • Keep the design simple.
  • Design for minimal maintenance.
  • Design for the extremes of weather and climate, not the average.
  • Design the system to use natural energies, such as gravity flow.
  • Design the wetland with the landscape, not against it. Integrate the design with the natural topography of the site.
  • Avoid over-engineering the design with rectangular basins, rigid structures and channels, and regular morphology. Mimic natural systems.
  • The system should as far as possible have several functions (e.g. nutrient removal, recreation, biodiversity, recirculation of retained phosphorous).
  • Give the system time. Wetlands do not necessarily become functional overnight and several years may elapse before performance reaches optimal levels.

One size does not fit all – and we need more knowledge

Another important take-home message from the workshop was that one size does not fit all. There is no single solution that is best in all cases or localities, and the efficiency of a certain solution will differ from place to place and from year to year.   

This makes it difficult to provide standard figures for the efficiencies of individual solutions and for what it costs to remove one kg of nitrogen. This brings us to the next important point, namely that there is insufficient knowledge about costs, efficiency, unintentional and unwanted effects, and short- and long-term maintenance of the various solutions. This is one of the reasons that the Ministry of Food and Environment of Denmark has initiated the new four-year project. 

Local roots, motivation and easy routines

In order for a filter project to be successful, it is important that farmers and other local stakeholders hop on the bandwagon. It is usually more fun to be involved in an idea if you feel co-ownership of it and do not feel that it has been forced on you. It also helps if you can see that it benefits you in some way.  

There are several carrots to choose between. A financial benefit is almost always a hit. This could, for example, be some kind of partial cost sharing scheme. Another benefit could be in the form of less bother; Americans have experience with giving environmentally accredited farmers freedom from following new environmental legislation the following 10 years. Another important driver is if red tape and bureaucracy are kept to an absolute minimum when implementing new schemes.  

It is also easier to convince farmers and other locals about the benefits of wetlands and filter projects if they can see that there is something in it for them. This is where multi-functionalism enters the scene. It might be that the best sales pitch to some stakeholders for establishing a wetland is that it can attract birds, while other stakeholders could be open to improved hunting conditions, and yet others would be pleased by the knowledge that the wetland removes nitrogen. 

Important to choose the right direction

Landscape filters will become an integral part of the Danish landscape and are a measure that all Denmark’s citizens will be paying for. It is therefore crucial to generate more knowledge and experience before the various types of solutions are spread across the country. It is also important to share knowledge and experience with each other in Denmark and abroad, and to test results from pilot systems and models that calculate results on a large scale and over longer periods so that they imitate real life conditions.  

- It will be a big investment for Danish society so even though there are many stakeholders that are eager to get started as quickly as possible in order to avoid nitrogen loss to the aquatic environment, it is important that we do not do anything rash, says Finn Plauborg. 

For more information

You can view selected presentations from the workshop here:


Senior researcher Finn Plauborg, Department of Agroecology, email: finn.plauborg@agro.au.dk, telephone: +45 8715 7714, mobile: +45 2218 1809

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