Impact of Nitrate Fluxes to Water from Seasonally Frozen Soils under Climate Warming

Present climate models predict an increase in the average air temperature of 1.5C and average soil temperature within 8m soil depth of 1.2-3.3C, by the end of this century. Increasing temperatures during winter can have a significant impact on soil biogeochemical cycles, increasing the production of nitrate in the soil. It is also likely to increase the number of snow-free days, reduce soil freezing depth and increase the frequency of freeze-thaw cycles in soil. Due to the lack of sufficient vegetation or biomass to utilize the excess soil nitrate during winter, nitrate may move in soil moisture towards the soil surface or migrate to groundwater, influenced by the ambient temperature gradient. The transport of excess nitrate in this way can lead to both surface water and groundwater contamination. This research will study the impacts of rising winter temperatures on the soil nitrogen cycle, the direction of movement of soil nitrate produced during winter, and quantify the amount of soil nitrate produced for a given temperature regime. The research will use soil column experiments to study the production of nitrate under different soil freezing depths and soil temperature variations. The experimental results will be interpreted using numerical models and machine learning algorithms to develop transfer functions that describe the production and release of nitrate from soil under various conditions. The outcomes of this study will help scientists understand the effects of climate warming on the release of nitrate from soil to water resources and develop best management practices to mitigate this impact.