Phosphorus loss from agricultural land to the aquatic environment in Denmark must be reduced to achieve the quality goals for surface waters. Researchers are in the process of mapping high-risk areas and finding effective mitigation options.

The impact of agricultural phosphorus loss on the aquatic environment is a current problem with roots in the past. Due to intensive agriculture and fertilisation in Denmark, phosphorus has accumulated in soils over the past 100 years and especially since the 1950s.

The consequences are felt now. Phosphorus losses have a negative effect on surface water quality and decrease the biological diversity in the aquatic environment.

Climate change exacerbates the problem. The transfer of phosphorus to the aquatic environment may rise, partly in response to changing rainfall patterns. Also, the turnover and release of phosphorus from lake sediments is likely to increase due to higher temperatures.

Researchers from the Faculty of Agricultural Sciences (DJF) and the National Environmental Research Institute (NERI), both at University of Aarhus, therefore, are actively investigating options that can minimise phosphorus losses to the aquatic environment. They have recently hosted a large, international, phosphorus workshop with participation of some of the world’s leading experts in the area. The workshop shed light on the various aspects of phosphorus loss and how to abate it.

No black sheep

- Twenty years ago nobody knew better. It was presumed that phosphorus applied to fields would remain in soils until taken up by crops. Nobody expected significant phosphorus losses from agricultural land to the aquatic environment. Now we know better and it is important to focus on strategies that minimize phosphorus losses. We must improve our understanding of risk assessment, mitigation planning and not least of the ecological impacts on the aquatic environment, says senior scientist Goswin Heckrath from the Department of Agroecology and Environment at DJF, who currently is working with the mapping of high-risk areas.

To reduce phosphorus loss from agricultural land effectively, it is necessary to know where the high-risk areas lie.

- In Denmark we have plenty of data on phosphorus loads in waters. However, we do not know which fields contribute most to this load. The main reason is that we are still unable to predict how much phosphorus is transported along different pathways such as surface runoff or land drainage. This is crucial information that we need to be able to work our way back to the high-risk areas in landscapes, points out Goswin Heckrath.

The research groups are also evaluating mitigation options for reducing phosphorus losses. Examples include alternative cultivation practices, such as reduced tillage, or different methods or timing for animal manure application.

- At the International Phosphorus Workshop we saw a new consensus among many experts on the need for effective regulation in order to reduce agricultural phosphorus losses. This could, for example, include new requirements for the handling of animal manure, controlled drainage, or the establishment of buffer zones, says Goswin Heckrath.

The current research efforts are closely linked to Denmark’s obligations in the EU’s Water Framework Directive and the national Action Plan for the Aquatic Environment. Their successful implementation essentially depends on a constructive dialogue between researchers, agricultural advisors and environmental planners.

- If you want to implement effective mitigation, then good communication between the parties involved is a key issue. The feedback from land-users and environmental planners is essential, says senior scientist Gitte Holton Rubæk, Department of Agroecology and Environment.

The proceedings of the ‘ The 5th International Phosphorus Workshop (IPW5), Diffuse Phosphorus Loss – Risk Assessment, Mitigation Options and Ecological Effects in River Basins ’ can be downloaded.

For further information please contact:

Senior scientist Gitte Holton Rubæk, Department of Agroecology and Environment, Faculty of Agricultural Sciences, University of Aarhus, telephone: (+45) 8999 1859, e-mail: Gitte.Rubaek@agrsci.dk

Senior scientist Goswin Heckrath, Department of Agroecology and Environment, Faculty of Agricultural Sciences, University of Aarhus, telephone: (+45) 8999 1715, e-mail: Goswin.Heckrath@agrsci.dk

Text: Janne Hansen

Photo: Bob Foy, Agri-Food and Biosciences Institute, United Kingdom