How Artificial Islands Restore Black-Odorous Waters Through Plant-Microbe Synergy
Explore the ScienceImagine a river so polluted that it turns dark, emitting foul odors that drive people away. These are black-odorous water bodies—aquatic environments where oxygen has been depleted, allowing harmful substances to thrive.
This alarming phenomenon is increasingly common in lakes and rivers worldwide, from China to the United States and Europe 1 .
Characterized by excessive nutrients, low dissolved oxygen, and production of toxic sulfur compounds 1 .
The search for solutions has led environmental scientists to an ingenious approach that harnesses nature's own purification powers: Combined Artificial Floating Islands (AFIs). These innovative structures are transforming polluted waterways through a elegant combination of plants, microbes, and simple engineering.
At first glance, an artificial floating island may appear to be simply plants growing on a raft. But beneath the surface lies a sophisticated water treatment system that mimics the functions of natural wetlands.
Plants directly absorb excess nutrients like nitrogen and phosphorus from the water 2 .
| Plant Species | Primary Functions | Root Structure | Climate Adaptation |
|---|---|---|---|
| Bulrush (Typha latifolia) | Nutrient absorption, habitat provision | Dense, fibrous roots | Temperate to tropical |
| Sweet Flag Grass (Acorus gramineus) | Dominant root system for microbial support | Well-established, extensive | Temperate regions |
| Baltic Rush (Juncus balticus) | Heavy metal absorption, wastewater treatment | Strong, penetrating roots | Cold-hardy, widespread |
| Bearded Iris (Iris germanica) | Aesthetic appeal, supplemental nutrient uptake | Rhizomatous system | Various climates |
| Water Sedge (Carex aquatilus) | Nutrient removal, bank stabilization | Deep, robust roots | Cold regions |
The remarkable purification ability of artificial floating islands stems from the synergistic relationship between plants and microorganisms—a natural partnership that scientists have learned to optimize.
The process begins with the root zone, which serves as a dynamic living filter. As water passes through the tangled root networks, suspended particles become trapped, effectively reducing turbidity.
A recent study in Portugal identified 30 different freshwater bacterial strains living among the roots of floating islands, including many capable of producing plant-growth-boosting molecules and breaking down pollutants 1 .
This sophisticated plant-microbe partnership creates a self-maintaining treatment system that naturally adapts to changing pollution levels and requires minimal human intervention—making it both effective and cost-efficient compared to conventional wastewater treatment technologies.
To understand how researchers test and validate the effectiveness of artificial floating islands, let's examine a compelling study conducted in Portugal and published in 2025.
Perimeter of installed floating islands
Depth of the artificial stormwater pond
Native plant species used in the study
Researchers established cork-based floating islands in an artificial stormwater pond to assess both water purification capabilities and ecological benefits 1 .
The team selected four locally available perennial plant species: bearded iris, marsh marigold, sweet flag grass, and bulrush 1 .
The islands were established in 2018 and carefully monitored over several years, with comprehensive data collected in 2022 1 .
The islands functioned as biodiversity hotspots, supporting the complete life cycle of at least 10 different species of dragonflies and damselflies 1 .
The research revealed that the islands provided shelter, food, and breeding sites for various insects, supporting the complete life cycle of at least 10 different species of dragonflies and damselflies 1 .
Bacteria capable of producing plant-growth-boosting molecules were thriving on the rafts, creating a self-reinforcing cycle of ecosystem health improvement 1 .
The true test of any pollution control technology lies in its measurable results. Across multiple studies, combined artificial floating islands have demonstrated impressive removal efficiencies for key pollutants.
| Pollutant Type | Removal Efficiency | Study Context |
|---|---|---|
| Ammonia | 69% more removal | Cattle feedlot ponds |
| Total Phosphorus | 55% more removal | Cattle feedlot ponds |
| Total Nitrogen | 27% more removal | Cattle feedlot ponds |
| Copper | 93% more removal | Cattle feedlot ponds |
| Zinc | 77% more removal | Cattle feedlot ponds |
| Phosphorus | 2.3 g/m²/year | Urban river (Charles River) |
| Characteristic | Single Plant System | Mixed Plant System |
|---|---|---|
| Root Structure | Uniform depth and density | Varied depths and densities |
| Nutrient Uptake | Specific to one plant's preferences | Broader spectrum of nutrient absorption |
| Ecosystem Resilience | Vulnerable to species-specific threats | Buffered against seasonal or disease impacts |
| Habitat Value | Limited to specific niches | Provides diverse microhabitats |
| Seasonal Performance | Peak performance in specific seasons | More consistent year-round performance |
At cattle feedlots in Alberta, Canada, floating islands equipped with Baltic rush demonstrated remarkable purification performance. Compared to a control pond without islands, the treated ponds showed dramatic reductions in multiple pollutant categories 3 .
The Charles River Floating Wetland project in Massachusetts demonstrated that floating treatment wetlands could achieve phosphorus removal rates of approximately 2.3 grams per square meter per year through plant uptake alone 4 .
The research team calculated that just one acre of floating wetlands could offset nutrient pollution from 7-15 acres of dense urban development—a level of effectiveness comparable to infiltration-based green infrastructure 4 .
Creating an effective artificial floating island requires careful selection of materials and components, each serving specific functions in the purification process.
As we face growing challenges of water pollution worldwide, combined artificial floating islands offer a promising nature-based solution that harnesses ecological processes to restore damaged waterways.
The European Commission has recognized the potential of such nature-based solutions, funding research and innovation through programs like Horizon Europe to help achieve Sustainable Development Goals 1 .
Projects like the Charles River Floating Wetland demonstrate how these technologies can be integrated into urban environments, combining scientific innovation with community engagement 4 .
What makes this solution particularly powerful is its accessibility and scalability. From small courtyard ponds to vast agricultural wastewater systems, the same fundamental principles can be applied to create effective, self-sustaining treatment systems.
As research continues and implementation expands, artificial floating islands may become standard features in our efforts to restore and maintain healthy aquatic ecosystems worldwide—creating floating oases of purification and life where once there was only polluted water.