Biowater’s PhD student Mette Vodder Carstensen (University of Aarhus) and co-authors asked themselves: How efficient are mitigation measures targeting nutrient losses from drainage system in the Nordic region?
Main author Mette V. Carstensen writes: “This was our first question setting the stage for this study, as despite many initiatives and efforts, the losses of nutrients to our rivers, lakes and marine waters are still too high, and with climate change and the green shift, it is possible that it will remain a threat to our ecosystems in the coming decades.
In many Nordic countries, soils have been tile drained to enable food production. In Denmark, around 40-60 % of the agricultural land is tile drained. However, such drainage systems are fast tracks for nutrients being leached from the soil though matrix or macropore flow, leading them directly from the root zone to surface waters. Therefore, we wanted to compile the information from studies on mitigation measures that treat and reduce the losses of nutrients from drainage systems.
The drainage mitigation measures we collected information on, was commonly applied measures (free water surface constructed wetlands, denitrifying bioreactors, controlled drainage) and novel techniques (saturated buffer zones and integrated buffer zones).
We used Web Of Science to search for peer-reviewed studies using multiple search strings and obtained in total 8126 studies. However, only 42 studies containing 84 sites passed our four selection criteria. To aggregate and analyse the nutrient removal efficiencies, we used meta-analysis, where the removal efficiency from each study was weighted according to study precision and size, and then aggregated into a weighted mean across studies.
Our data analysis showed that the load of nitrate was substantially reduced by all five types of drainage mitigation measures, while they mainly acted as sinks of total phosphorus, but occasionally, also as sources. The reported removal efficiencies varied considerable between studies, which was not surprising given that the factors influencing performance, such as design, runoff characteristics and hydrology, differed in the studies.”
The paper is one of the Biowater papers in our special issue in AMBIO:
Carstensen, M.V., Hashemi, F., Hoffmann, C.C. et al. Efficiency of mitigation measures targeting nutrient losses from agricultural drainage systems: A review. Ambio (2020). https://doi.org/10.1007/s13280-020-01345-5
We congratulate Mette and her colleagues and co-authors on an interesting paper that should find interest both amongst scientists, advisors and managers!
Feature photo: Eva Skarbøvik.