Sonja Jaari
Project Manager
John Nurminen Foundation
Finland
sonja.jaari@jnfoundation.fi
Reed beds have expanded significantly along the Baltic Sea’s coastline due to changes in land use, such as the decline of traditional grazing, and excess nutrients runoff from agriculture and forestry. While reeds play an essential role in stabilizing sediments and preventing erosion, their unchecked growth has contributed to reduced water flow and lower biodiversity. However, these dense reed beds also function as natural nutrient sinks, containing substantial amounts of nitrogen and phosphorus.
Nutrient removal through reed harvesting
Harvesting reeds provides an effective way to remove excess nutrients from coastal ecosystems. Research shows that one hectare of summer reed can absorb 5–10 kg of phosphorus and 50–100 kg of nitrogen, while winter harvest removes approximately one-tenth of the amount of nutrients. If properly harvested and utilized, these nutrients can be repurposed instead of entering the water system, where they would contribute to eutrophication and algal blooms.
To maximize nutrient removal, harvesting should be completed by mid-August before nutrients start accumulating in the rhizomes for the next growing season. Late-summer mowing removes more biomass and associated nutrients, while early-summer cutting significantly suppresses regrowth. Each reed harvest must be carefully planned, ensuring that rare species habitats, bird-nesting periods and fish spawning seasons are considered to minimize ecological disruption.
Large-scale impact on nutrient recirculation
Projects such as BalticReed, led by the John Nurminen Foundation, demonstrate the potential for large-scale reed harvesting to improve water quality while creating valuable biomass resources. Research has indicated that if reeds were systematically harvested from 10,000 hectares 50 –100 tons of phosphorus and 500–1000 tons of nitrogen could be removed, significantly reducing nutrient pollution in the Baltic Sea.
Beyond water purification, sustainable reed harvesting has broader ecological and economic benefits. Removal of reed may improve water flow in shallow coastal bays, and may prevent excessive organic matter accumulation, which accelerates habitat overgrowth. In addition, the harvested biomass provides opportunities for industries seeking alternative raw materials, reducing reliance on traditional agricultural or forest-based biomass.
Sustainable utilization of harvested reed
The biomass from harvested reeds has a wide range of sustainable applications that contribute to nutrient recycling. One important use is as green manure and for soil enrichment, where reeds can be composted or processed into organic soil amendments, thereby returning valuable nutrients to agricultural land. Reed also may play a role in mulching and erosion control. When used as a protective mulch layer, it can enhance soil structure and reduce water loss.
Reed biomass can also be converted into biogas, offering a renewable energy source while repurposing nutrients. Early summer reed, when still soft, can be used as a supplementary feed for cattle.
Challenges and best practices
For effective nutrient recirculation, it is crucial to collect harvested reed from the water and shoreline promptly. If left to decompose, the reeds would release nutrients back into the ecosystem, negating the benefits of harvesting. Additionally, improper cutting techniques—such as mowing too early or disturbing sediments—can lead to nutrient resuspension, undermining the positive environmental impact.
When reeds are cut in early summer, the nutrients stored in the root system may be released back into the water through stems that are cut below the waterline. To prevent this, it is advisable to schedule the cutting for late summer or ensure that cuts are made above the water surface. In shallow waters, using heavy mowing machinery can disturb the bottom sediments, which may cause turbidity and release nutrients from the sediment into the water.
To maximize the benefits of reed harvesting, several best practices should be followed. First, cutting should be timed for late summer to optimize nutrient removal. Additionally, careful planning of the harvesting location and machinery is essential to avoid disturbing sediments and causing nutrient resuspension. All harvested material should be collected to prevent emissions resulting from decomposition. Finally, exploring diverse applications for the harvested biomass is key to promoting a circular economy.
Conclusion
Reed harvesting presents an opportunity to recirculate nutrients, reduce eutrophication, and promote sustainable biomass use. With careful planning, reeds can be transformed from an ecological challenge into a valuable resource, helping to restore the Baltic Sea while supporting a circular bioeconomy. Sustainable reed management is essential to balance environmental conservation with economic benefits, making it a key component of future nutrient recycling efforts. By implementing well-managed harvesting strategies and supporting innovative uses of reed biomass, we can turn an environmental issue into a solution for healthier coastal ecosystems and sustainable industries.