Nutrient run-off from agricultural activities is a major contributor to freshwater and coastal eutrophication. Eutrophication and the resultant degradation of aquatic ecosystems has a major negative effect on biodiversity and ecosystem functioning. In order to achieve sustainable agricultural practices and a reduction in eutrophication, it is crucial to retain nutrients in agricultural landscapes.
A constructed floating wetland consists of a floating structure planted with emergent macrophytes that develop extensive root systems in the water column. These root systems can provide a vast surface area for denitrifying bacteria and hence enhance the nitrogen removal capacity of the wetland. Constructed floating wetlands can, for instance, be anchored either in the deeper part of the wetland where submerged macrophyte growth is limited due light limitation, or they can be directly placed in newly constructed wetlands to enhance macrophyte community development.
Constructed floating wetlands are typically made of plastic, but in this study, we wanted to use an eco-friendly and biodegradable material instead. We constructed our “eco floating wetlands” out of jute bags and wood chip and planted them with locally grown macrophytes. This had not been tested before, so this was a pilot study where we aimed to test if eco floating wetlands are feasible in situ and if they can enhance wetland nitrogen removal.
We have conducted the experiment in our experimental wetland facility. The wetlands were divided into two treatment groups and two control groups, as visualized in the figure below. Prior to experimental start-up, vegetation in the experimental wetlands was removed from treatments and control 1. Control 2 was left untouched to represent a mature wetland. In treatment 1, 20 % of the water surface area was covered by eco floating wetlands, and in treatment 2, 5 % was covered.
For four months, we measured flow rate and collected water samples once per week. After the experiment, we measured accumulated biomass in each eco floating wetland and measured the root lengths of the planted macrophytes
Pictures from the eco floating wetlands experiment. 1) Close-up of one of the eco wetlands. 2) Two eco wetlands in the water. Our eco wetlands did not actually float, so we let them rest on wood beams just below the water surface. 3) One of the experimental wetlands where 20 % of the surface was covered by eco wetlands. 4) Root growth after four months.
So far in this study, we have finished the experiment, the laboratory analyses and most of the data analyses. Results regarding nitrogen removal in the different treatments and controls are not finalized yet.
The experiment worked as intended: The jute bags did not break, and a majority of the plants survived and grew during the experiment. We can therefore conclude that this type of eco floating wetland is feasible, at least short-term.
This study was conducted in collaboration with Linnaeus University.
Participants
Maidul Choudhury, postdoc at Linnaeus University
Josefin Nilsson, PhD student
Stefan Weisner, Senior Professor
Samuel Hylander, Senior Lecturer at Linnaeus University
Per Magnus Ehde, Research Engineer
Antonia Liess, Senior Lecturer