河流温度对潜流带氮素迁移的影响研究

The coupling mechanism of flow, solute and heat transport processes is the key issue to fully understand nitrogen dynamics in the hyporheic zone (HZ), and is also the most active frontier of many disciplines including hydrology, geochemistry, and environmental engineering, etc. This proposal plans to use high-fidelity flume experiments to measure the spatial distributions of temperature, dissolved oxygen, nitrate, and ammonia with a high temporal frequency. The experimental results will be further used to validate and calibrate the physical and chemical processes-based numerical simulations. Based on the calibrated simulations, the proposal aims to simulate nitrogen dynamics with varying temperature conditions. A sensitivity analysis will be conducted afterwards. Our proposal is to understand the fluid and nitrogen dynamics in the HZ and to reveal the effects of temperature on nitrification and denitrification occurring in the HZ. Our goal of this proposal is to establish an empirical model to relate river temperature to nitrogen removal efficiency. The proposal should shed light on understanding the effects of river temperature on nitrogen dynamics in the HZ, and thus provides the theoretical basis for assessing the dynamic nature of nitrogen-related contaminants in many aquatic environments.

潜流带渗流场-温度场-氮素浓度场等多场耦合机制是研究潜流带氮循环过程的重要科学问题，也是近些年水文学、地球化学、环境工程等学科非常活跃的研究领域。本项目将通过研发高仿真潜流带水槽实验，在时间上高频测量潜流带温度、以及溶解氧、硝酸根和铵根离子浓度的空间分布。通过室内水槽实验结果来分析、验证和校正多物理-化学过程耦合数值模型。然后利用校正后的数值模型模拟多场景（河流温度改变等）方案，对海量的数值模拟结果进行敏感性分析。基于实验和数值模拟结果，从机理上分析水和氮素在潜流带的运移规律，揭示河流温度对潜流带硝化作用-反硝化作用的控制机理，建立温度与潜流带氮去除率的数学模型，为预测水体中硝酸盐污染物浓度变化特征提供理论依据和科学支撑。

岩溶潜流带广泛分布在岩溶裂隙发育区，岩溶地下水与地表水混合交互，承担着重要的生态环境保护作用。我国岩溶潜流带分布广泛，但基础理论研究不足，保护措施不到位，岩溶潜流带的污染日益加重，究其原因是缺乏对裂隙中溶质运移的深入研究。为此，我们通过研究平行板（简化的裂隙模型）模型，从理论上和数值模拟两方面证明滑脱效应对弥散系数的影响微乎其微。另一方面，由于裂隙非均质性引起的流场变化对胶体运移的影响认识还比较欠缺，我们通过模拟6200种不同裂隙形貌情况下的胶体运移过程，发现胶体的吸附数量与裂隙粗糙度成正比，而与裂隙形貌的相关长度无关。为此建立了宏观模型参数与裂隙形貌间的数学模型，能更有效和快速模拟胶体在裂隙中的运移特征。以上研究针对裂隙中的溶质运移过程及相关影响因素开展了系统研究，为解决和治理岩溶潜流带的污染提供了新的科研视角和防控理论。