What are the agronomic and environmental impacts of recycling lake sediments to crop production? Our 4-y field study published, Mina's PhD defense soon!

 We are trying to find a sustainable solution for closing the leaking agricultural #phosphorus (P) cycle by #recycling P-rich lake #sediments back to the agriculture. It is globally the first study that covers environmental aspects of recycling lake sediments to agriculture over several years:

 

Excavating all the 7500 m³ of sediment from a 1-ha shallow eutrophic Lake Mustijärv (Viljandi, Estonia) was the starting point of this work. During the lake restoration, 6.4 Mg of P was removed, including at least 2.4 Mg of P that was potentially bioavailable.

During a four-year field experiment on the shore of the restored lake, various application methods were examined to use large quantities of lake sediments for grass production with the following treatments: the agricultural control soil (Soil) surrounding the lake, pure sediment (Sed), #biochar treated sediment (SB), and biochar and soil mixed with sediment (SSB). In addition to the plant growth investigation, we estimated the environmental impacts of different sediment application methods by analyzing greenhouse gas emissions, N and P leaching, aggregate stability, and soil biota.

From this study we learned that the sediment-based growing media sustained grass biomass yield in the field condition, even though yield enhancement was less obvious compared with our previous lysimeter experiment. Sediment from Lake Mustijärv was rich in organic matter and was a good source of several essential nutrients, including P, in plant-available form. In addition to P, the sediment had high solubility of essential plant nutrients including sulfur (S), calcium (Ca), magnesium (Mg), boron (B), zinc (Zn), and a fair supply of copper (Cu). Also, the sediment continuously provided a moderate supply of N to the plants over the four-year field experiment, which was likely due to mineralization of the organic reserves of the sediment.

Considering the environmental impacts, the sediment-based growing media had higher carbon dioxide (CO2) emissions yet broadly similar nitrous oxide (N2O) emissions compared with the soil surrounding the lake. Also, applying a thick layer of excavated sediment (~2000 t ha⁻¹) increased the risk of P and mineral N leaching. The application of biochar increased the amount of N taken up by the plants but did not significantly reduce emissions or leaching.

In addition, sediment-based growing media had different bacterial and fungal community compositions compared with soil. This could result in different mineralization pathways in soil and sediment-based treatments. The bacterial phyla associated with solubilizing P, including Proteobacteria and Chloroflexi, were more abundant in the sediment material than in Soil. This is while the relative abundances of Actinobacteria and Planctomycetes, with the potential to accumulate bioavailable P fractions, were higher in Soil.

Further study is required to determine if the GHG emissions and nutrient leaching from recycled lake sediment can be reduced by using it in lower quantities, similar to organic fertilizers and soil amendment materials. Also, the life-cycle assessment of environmental impacts of sediment recycling of eutrophic lakes for agricultural purposes is suggested for the future research.

This novel study was third chapter of the doctoral thesis of Mina Kiani. Her thesis “Closing the Phosphorus Cycle by Recycling Lake Sediments in Agriculture” is currently being prepared for printing. 

 Those interested on latest research and developments in the field of recycling phosphorus from lake sediments are most welcome to join the public defense of her doctoral thesis this spring. The details are published soon in the website of AgriChar research group (http://biochar-hy.blogspot.com/) but tentatively, the public examination is planned for 21 April 2023. Save the date!

Please check the following recently published articles for more:

 Kiani, M., Zrim, J., Simojoki, A., Tammeorg, O., Penttinen, P., Markkanen, T., & Tammeorg, P. (2023). Recycling eutrophic lake sediments into grass production: A four-year field experiment on agronomical and environmental implications. Science of The Total Environment, 161881.

Kiani, M., Tammeorg, P., Niemistö, J., Simojoki, A. and Tammeorg, O., 2020. Internal phosphorus loading in a small shallow Lake: Response after sediment removal. Science of The Total Environment, p.138279.

Kiani, M., Raave, H., Simojoki, A., Tammeorg, O. and Tammeorg, P., 2021. Recycling lake sediment to agriculture: Effects on plant growth, nutrient availability, and leaching. Science of The Total Environment, p.141984.

This project was supported by AGROREE doctoral school, Maa- ja vesitekniikan tuki ry, Suomen luonnonsuojelunsäätiö Itämerirahasto, Ella ja Georg Ehrnrooth Foundation, Finnish Cultural Foundation, Niemi Foundation, Tiina and Antti Herlin Foundation& great help of colleagues & friends including Martin Voll, Kalle Köömnemägi, Heli Ahola, Merve Kujala,Helena Soinne, Ave Truhanov, Miia Collander, Markku Tykkyläinen, Marjo Kilpinen, Kaj-Roger Hurme, Sanna Peltola, and Subin Kalu.