How warmer winters are changing the biogeochemistry of soils
Background
We don’t often think about what is beneath our feet, but soil is key to our survival. We depend on it to grow food, protect us from drought and floods, and to maintain the global carbon and nutrient cycle. Researchers have long known that soil is susceptible to changes in the climate, especially in high latitude cold regions such as Canada. However, there is much to learn about how warmer winters will impact carbon cycling, microbial processes, and biogeochemical transformations of nutrients and contaminants. Such insights can be used to assess the vulnerability of northern cold region ecosystems to winter warming, and to ultimately inform Greenhouse Gas (GHG) emissions estimates, predict the fate of vulnerable carbon and nutrient stocks, and develop effective climate adaptation and mitigation strategies.
In the Winter Soil Processes project, researchers are focusing on soil processes in cold region ecosystems during the non-growing season (NGS), when plants stop growing between fall and spring. They found that warmer winters are leading to a greater frequency of freeze-thaw events and colder soils due to the loss of the insulating snowpack. This is influencing the soil biogeochemical processes that govern water, carbon, and nutrient transformations in soils during the winter.
Through laboratory-based experiments, the team determined that more frequent freeze-thaw events disrupt oxygen levels in the soil’s vadose zone. This alters microbial activity and the processes that control the decomposition of organic matter, nutrient cycling and GHG emissions. As a result, we see pulses of carbon dioxide (CO2) and nitrous oxide (N2O) being released into the atmosphere. This indicates that the enhanced access to relatively organic matter during freezing may additionally contribute to the observed post-thaw CO2 and N2O pulses, reflecting the cumulative effects of winter soil microbial and geochemical processing on belowground pools of nutrients during the NGS.
The team also used machine-learning model and synthesis data-driven approaches to demonstrate that changes in soil moisture, temperature, and photosynthesis are the primary drivers of changes in the net release of carbon during the NGS. The model is based on 13 years of measurements from the Mer Bleue Bog (located in Ottawa, Canada) and regional climate projections. Results predict a 103 per cent increase in peatland carbon loss by 2100 under an extreme scenario, highlighting that peatland carbon loss is expected to contribute to a strong positive climate feedback loop in the future. Corresponding laboratory studies and data analyses suggest that temperature is a key factor in determining how much carbon loss to expect from peatlands during the NGS in cold regions.
Principal Investigator:
Fereidoun Reznezahad, Research Associate Professor & Faculty Lead, Earth and Environmental Sciences
Co-investigators from UW:
Laura Hug, Philippe Van Cappellen, David Rudolph
Project duration:
2017-2020
GWF funding support:
$300,000
Key messages for Environment and Climate Change Canada
- This work has global and international implications for climate policy. With a better understanding of the factors that affect soil temperature variability, Canada could improve the accuracy of itsGHG estimatesin the annual GHG National Inventory Report required by the United Nations Framework Convention on Climate Change.
- Understanding winter soil processes can enable more robust future projections of soil carbon stability.
- GHG emissions from boreal peatlands are more sensitive to temperature than peatlands from more temperate regions. The CO2 production rates in boreal peatlands increase more sharply with temperature than in temperate peatlands. This indicates that in the future, we may see more CO2 losses in boreal peatlands during the NGS than in temperate peatlands.
- Improved understanding of biogeochemical soil processes and modeling capabilities will significantly enhance the interpretation of field-based data on greenhouse gas emissions from middle and high latitude soils and form the basis for predicting the response of cold region soil biogeochemistry to future climate scenarios.
Key publications and research outputs
Krogstad, K., Gharasoo, M., Jensen,G.,Hug, L.A., Rudolph, D., Van Cappellen, P., Rezanezhad, F. (2022).Nitrogen leaching from agricultural soils under imposed freeze-thaw cycles: a column study with and without fertilizer amendment. Frontiers in Environmental Science, 10:915329.
Jensen, G., Krogstad, K., Rezanezhad, F., Hug, L.A. (2022).Microbial community compositional stability in agricultural soils during freeze-thaw and fertilizer stress. Frontiers in Environmental Science, 10:908568.
Rafat, A., Byun, E., Rezanezhad, F., Quinton, W.L., Humphreys, E.R., Webster, K., Van Cappellen, P. (2022). The definition of the non-growing season matters: a case study of net ecosystem carbon exchange from a Canadian peatland. Environmental Research Communications, 4, 021003.
Byun, E., Rezanezhad, F., Fairbairn, L.,Slowinski, S., Basiliko, N., Price, J.S., Quinton, W.L., Roy-Léveillée, P., Webster, K., Van Cappellen, P. (2021). Temperature, moisture and freeze–thaw controls on CO2 production in soil incubations from northern peatlands. Scientific Reports, 11:23219.
Rafat, A., Rezanezhad, F., Quinton, W. L., Humphreys, E. R., Webster, K., VanCappellen, P. (2021). Non-growing season carbon emissions in a northern peatland are projected to increase under global warming. Communications Earth & Environment, 2:111.
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