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

目前的气候模式预测，到本世纪末，平均气温将上升1.5 ℃，8米土壤深度内的平均土壤温度将上升1.2- 3.3 ℃。冬季气温升高会对土壤生物地球化学循环产生重大影响，增加土壤中硝酸盐的产生。它还可能增加无雪天数，减少土壤冻结深度，增加土壤冻融循环的频率。由于冬季缺乏足够的植被或生物量来利用过量的土壤硝酸盐，受环境温度梯度的影响，硝酸盐可能会在土壤水分中向土壤表面移动或迁移到地下水中。以这种方式运输过量的硝酸盐会导致地表水和地下水污染。这项研究将研究冬季气温上升对土壤氮循环的影响，冬季土壤硝酸盐的运动方向，并量化给定温度条件下土壤硝酸盐的含量。本研究将利用土柱实验，研究不同土壤冻结深度和土壤温度变化下硝酸盐的产生。实验结果将使用数值模型和机器学习算法进行解释，以开发描述各种条件下土壤中硝酸盐的产生和释放的传递函数。这项研究的结果将有助于科学家了解气候变暖对土壤中硝酸盐释放到水资源的影响，并制定最佳管理措施来减轻这种影响。

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.