Floating wetlands: A sustainable solution for addressing nutrient pollution
School of Earth Sciences graduate student Zhaozhe Chen is running an experiment on the OSU Mansfield Milliron Research Wetlands to assess the nutrient removal efficiency of floating artificial wetlands (AFIs). Results from this research have been published at the journal Sustainability (https://doi.org/10.3390/su15086553). The goal is to eventually upscale these floating wetlands as a low-cost, environmentally-friendly, and effective remediation/prevention treatment for nutrient pollution in lakes/wetlands/streams in Ohio (and beyond). Nutrient pollution in streams/lakes/wetlands is one of the most widespread and costly environmental problem in the United States (and around the world) – see more at https://www.epa.gov/nutrientpollution.
We are focusing on two species of native aquatic plants very common in Ohio’s wetlands: Carex comosa (the bristly sedge) and Eleocharis palustris (the common spike-rush). The setup for the experiment is shown in the images below. There are three larger “cells”, each containing SIX AFIs: two have plugs of Carex comosa, two have plugs of Eleocharis palustris, and two AFIs have no plants (used as experimental controls). Plant shoots are above water and plant roots are under water.
The deployment of the floating wetlands was finalized in June 2020 and, within a few weeks, a bacterial film developed on the roots and on the AFI floating structure (photo below). This bacterial film is essential for the removal of nutrients from the water. The better developed the bacterial film, the higher the nutrient-removal efficiency of the floating wetland, with the aquatic plant and the bacteria working together in a mutually beneficial relationship. The main biological processes driving nutrient removal in wetlands are uptake (or assimilation) by plants, algae, and bacteria, as well as chemical transformation processes conducted by these microbes.
Both plant species are doing well in the wetland, growing at a fast pace (both shoots and roots). Below is a photo of the experiment about 5 weeks after deployment. Below that is a time-series image showing 1-month growth of the roots from Carex comosa.
In addition to this natural field experiment, we are also running a mesocosm experiment at the wetland, containing small versions of the AFIs in controlled conditions (figures below). The justification for this controlled experiment is the fact that many other natural processes may be acting to remove nutrients from the water (in addition to the floating wetlands) which makes it difficult to isolate the specific contribution of the AFIs. These controlled experiments will allow him to isolate and measure how much of the nutrient-removal work done by the wetland is due specifically to the presence of the AFIs.
Like the natural-setting experiment on the wetland, the mesocosm experiment has three replicates (or three groups of 4 tanks). In each group there is one tank containing an AFI with Carex comosa, one tank with Eleocharis palustris, one tank with just the AFI and no plants, and one tank with only water from the wetland.
We are performing weekly sampling of plant biomass as well as water in the tanks and in the wetland for chemical/nutrient analysis. The plan is to run the experiments through the summer and fall to account for changing environmental conditions.
You can read the full article at: https://doi.org/10.3390/su15086553
This work has the generous support of grants provided by the Friends of Orton Hall Student Research Fund and the OSU Sustainability Institute.