Using algae to recycle farm runoff into fertilizer

Agricultural runoff, rich in nutrients, can harm marine ecosystems. This is a reader's digest of a scientific book chapter with the same title, which explores a biomimicry approach that utilises algae to capture these nutrients before they reach marine waters. Harvested algae are then processed into soil amendments for urban and peri-urban olive tree agroforestry systems, promoting a circular economy and enhancing environmental sustainability. The chapter identifies three potential pilot locations and highlights the need for further research on algae and aquatic plants for large-scale bioremediation applications.

Introduction

The bountiful yields of the Mediterranean basin are intricately linked to the health of its ecosystems. Olive trees, a cornerstone of Greek and Mediterranean agriculture and culture in general for well over millennia, thrive in this region. However, intensive agricultural practices can lead to environmental challenges, including nutrient runoff from fertilisers. This excess of nutrients harms marine ecosystems when it reaches waterways, triggering algal blooms and disrupting delicate ecological balances within our marine ecosystems.

This article proposes a novel approach to address this challenge, drawing inspiration from nature's inherent wisdom – biomimicry. By mimicking natural processes, we can create innovative solutions that are not only effective but also sustainable. Here, we explore the potential of using algae to capture excess nutrients from agricultural runoff before it reaches marine waterways, and subsequently transforming the harvested algae into valuable soil amendments for olive tree agroforestry systems in urban and peri-urban areas. While this research focuses on olive trees as their importance across the mediterranean basin is predominant, it does not exclude the same algae soil amendment application to any other tree species. 

The challenge: Nutrient runoff and its impact

Modern agricultural practices rely heavily on fertilisers to maintain soil fertility and crop yields. While this approach ensures food security in a short run, unintended consequences arise when excess nutrients, particularly nitrogen and phosphorus, are not fully absorbed by crops. These nutrients are then carried away by rain or irrigation water, eventually reaching rivers, streams, and coastal ecosystems.

In aquatic environments, these excess nutrients act as a fertiliser, triggering the rapid growth of algae. This phenomenon, known as algal blooms, can have devastating consequences. As algae grow and decompose, they deplete oxygen levels in the water, creating hypoxic zones where marine life struggles to survive. This disrupts the entire food chain, impacting biodiversity, marine ecosystems and fisheries.

The biomimicry solution: Algae as nutrient capture champions

Nature offers a solution to this predicament. Aquatic plants and algae have a remarkable capacity to absorb nutrients from water. Inspired by this natural process, we can leverage algae as a bioremediation tool to capture excess nutrients from agricultural runoff before it reaches marine waterways.

Several microalgae species, such as Desmodesmus, Scenedesmus, and Cosmarium, are particularly adept at nutrient uptake due to their fast growth rates and tolerance to high nutrient concentrations. Additionally, duckweed (Lemna) is another promising candidate for its rapid growth and effectiveness in removing excess nitrogen and phosphorus. All these are native to the Mediterranean basin, and there are many more freshwater aquatic plants to explore globally. 

A circular economy approach: from agricultural runoff via freshwater algae to soil amendments

Eutrophic streams and rivers, overloaded with nutrients from fertiliser runoff, provide the perfect environment for some aquatic plants to thrive. These fast-growing plants, like duckweed and certain algae species, act as natural bioremediators. Their rapid growth allows them to absorb excess nutrients, particularly nitrogen and phosphorus, at high rates.  This helps to purify the water by preventing algal blooms and the associated oxygen depletion that can devastate aquatic ecosystems.  By utilising these plants strategically, we can harness their natural capacity for nutrient uptake to improve water quality and create a more balanced aquatic environment. 

Once harvested, the captured nutrients within the algae biomass can be transformed into valuable soil amendments. Through various processing techniques, such as blending, mixing fresh with soil/sane, drying, composting, or anaerobic digestion, algae can be converted into nutrient-rich organic fertilisers or biostimulants. These amendments can then be used to nourish olive trees or any other tree in an agroforestry system for example, promoting a circular economy within the agricultural landscape.

The role of olive trees in agroforestry

Olive trees are not only a symbol of Greek heritage but also hold immense potential for sustainable agriculture. Their deep root systems help prevent soil erosion and improve water infiltration. Additionally, the foliage provides shade for other crops growing beneath, creating a microclimate that reduces water evaporation and heat stress. This synergy between olive trees and companion crops defines the concept of agroforestry.

Incorporating olive trees into urban and peri-urban agroforestry systems offers numerous environmental and social benefits. These systems can:

• Reduce reliance on chemical fertilisers: By utilising algae-derived soil amendments, agroforestry systems can eliminate the need for synthetic fertilisers, decreasing environmental pollution and promoting a more sustainable approach to agriculture.

• Enhance urban green spaces: Agroforestry systems create pockets of green infrastructure in urban and peri-urban areas, improving air quality, reducing the urban heat island effect, and promoting biodiversity. 

• Support local communities: Urban and peri-urban agroforestry systems can provide income opportunities for local communities through olive oil production and the cultivation of other crops within the system. And with their fruits they inspire care and nurture early childhood connection with nature. 

Identifying pilot locations for biomimicry implementation

To assess the feasibility and effectiveness of this biomimicry approach, the book chapter identifies three potential pilot locations in Greece:

1. Kozani-Florina: This region is characterised by intensive agriculture and experiences challenges with nutrient runoff. The presence of established olive groves and a willingness to collaborate with researchers make it a suitable candidate.

2. Pieria-Thessaloniki: This area boasts a thriving olive oil industry and faces similar concerns regarding nutrient runoff. Its proximity to urban areas and existing research infrastructure adds to its potential for a pilot project.

3. Volos: This region combines agricultural activity with a bustling port city, offering a unique opportunity to test the integration of algae cultivation systems with existing infrastructure for nutrient capture and utilisation in nearby olive groves.

Conclusion

The proposed biomimicry approach, uses freshwater aquatic plants to capture excess nutrients from agricultural runoff and transform them into soil amendments for olive tree agroforestry systems, offers a promising strategy for promoting a circular economy and enhancing environmental sustainability in Greece. By mimicking natural processes, this approach has the potential to address the challenges of nutrient runoff while simultaneously promoting the growth of vibrant urban and peri-urban agroforestry systems.

The identification of three pilot locations (Kozani-Florina, Pieria-Thessaloniki, and Volos) paves the way for further research and implementation. Implementing pilot projects will allow researchers to assess the effectiveness of algae-based nutrient capture at a practical scale. Additionally, it will provide valuable insights into the processing and application of algae-derived soil amendments within olive tree agroforestry systems.

Further research recommendations

To fully realise the potential of this biomimicry approach, further research is recommended in several key areas:

• Optimization of algae cultivation: Research is needed to identify the most efficient and cost-effective methods for cultivating algae species best suited for nutrient capture from agricultural runoff. This might involve optimising growth conditions, such as pools, or mechanical obstacles or a whole new river canals, to maximise algae productivity and nutrient uptake as much as water purification.

• Large-scale bioremediation applications: Studies are needed to evaluate the feasibility and scalability of using algae for large-scale bioremediation of agricultural runoff. This could involve designing and testing integrated systems that combine efficient methods for harvesting algae with effective processing techniques to convert them into usable soil amendments focusing to preserve the most of the bioavailable nutrients.

• Integration with existing infrastructure: Research should explore ways to integrate algae cultivation systems with existing agricultural infrastructure, such as irrigation canals and drainage channels. This would minimise the need for additional land and resources, promoting cost-effectiveness and seamless integration with current agricultural practices.

• Economic viability analysis: A thorough economic analysis is crucial to assess the long-term viability of this approach. This analysis should consider the cost of establishing and operating algae cultivation systems, processing techniques, and the potential economic benefits for farmers participating in urban and peri-urban agroforestry.

• Social and policy considerations: The success of this approach will hinge on social acceptance and supportive policies. Research is needed to understand the needs and concerns of stakeholders, including farmers, local communities, and policymakers. Additionally, policy frameworks could be developed to incentivize the adoption of biomimicry approaches for nutrient management and the development of urban and peri-urban agroforestry systems.

By addressing these research areas and fostering collaboration between scientists, farmers, and policymakers, we can harness the power of biomimicry to create a more sustainable future for agriculture in Greece and far beyond.

References 

Gassner, V.T., Symeonidis, D., Koukaras, K. (2024). Harvesting of Agricultural Nutrient Runoff with Algae, to Produce New Soil Amendments for Urban and Peri-urban Olive Tree Agroforestry Systems in Southern Europe. In: Stefanakis, A., Oral, H.V., Calheiros, C., Carvalho, P. (eds) Nature-based Solutions for Circular Management of Urban Water. Circular Economy and Sustainability. Springer, Cham. https://doi.org/10.1007/978-3-031-50725-0_23