The Baltic Sea is highly affected by eutrophication as a result of excessive nitrogen and phosphorus runoff. The main cause of nutrient transport to the Baltic Sea from Sweden is agriculture. Many wetlands have been constructed in Sweden in order to intercept these transports, especially in the southern parts of Sweden. However, the efficiency of these wetlands, i.e. how much nutrients they remove, is only studied in certain Swedish regions and understudied in otherregions of Sweden.
In this study, we have studied nutrient removal over the course of three years in five wetlands and one drainage ditch (henceforth are all six referred to as wetlands) in Kalmar county on the south-eastern coast of Sweden. The aim of this study was to evaluate the function of these wetlands as nutrient sinks. This is the most comprehensive study with continuous automatic sampling of nitrogen and phosphorus removal ever made in Swedish wetlands, and the first study of its type in Kalmar county.
Our results show that wetlands in Kalmar county can achieve high nutrient removal, and that nutrient removal can vary greatly between wetlands in the same region (see figure below). In this study, even wetlands with relatively low percentage of agricultural land within their catchment could achieve high nitrogen and phosphorus removal, and small wetlands without an initial deep area for phosphorus sedimentation could achieve very high phosphorus removal. In the report we also present new calculation methods that have been developed to handle the uncertainties that follow with this type of in situ study.
Nitrogen and phosphorus removal per water surface area and year in six wetlands in Kalmar county. Each bar represents average removal for one year. Asterisks (*) indicate that outliers are excluded, and ones (1) indicate that inlet concentrations are corrected.
The results from this project can, together with previous studies, improve the accuracy of model calculations and contribute to improved measurement methods and analyses in future wetland studies.
This study was conducted in collaboration with the County Administrative Board of Kalmar County, and it was financed by the Swedish Agency for Marine and Water Management, the Swedish Board of Agriculture via the Rural Development Programme and the Rydberg Laboratory for Applied Sciences at Halmstad University.
The report is published and available in Swedish full text here.
Participants
Josefin Nilsson, PhD student
Antonia Liess, Senior Lecturer
Stefan Weisner, Senior Professor