An overview of nutrient transport mitigation measures for improvement of water quality in Denmark

Nutrient losses from agricultural areas constitute a major cause for the degradation of aquatic ecosystems worldwide. In this paper, we use the intensively cultivated country of Denmark as an example to synthesise and discuss results, experiences and challenges for an optimised implementation of nutrient transport mitigation measures targeting agricultural nutrient losses to fresh and marine water. A new era in the regulation of agricultural nutrient losses to aquatic ecosystems in Denmark was initiated when the Agricultural Package was adopted in 2016 by the Danish Parliament. Danish farmers were again allowed to fertilise their crops to economic optimum and to compensate for the consequent increase in fertilisation rates and the potential negative consequences on water quality, a new nitrogen (N) and phosphorus (P) management plan was introduced. The new plan consists of measures to mitigate N losses in smaller catchments (< 15 km(2)) and knowledge of the N attenuation capacity of the individual catchments is used for optimisation of the implementation of mitigation measures. A suite of nutrient transport mitigation measures has been scientifically approved for use in this new regulation, and more measures are currently undergoing scientific testing. This study focuses on already approved nutrient transport mitigation measures, such as restoration of riparian wetlands, fens and swamps, re-establishment of shallow lakes, constructed wetlands (surface flow and subsurface flow), as well as measures not yet approved and still under development such as integrated buffer zones, saturated buffer zones and controlled drainage.