Watershed Science & Modelling Laboratory, Department of Earth and Atmospheric Sciences, Faculty of Science, University of Alberta, Edmonton, AB T6G 2R3, Canada.
Watershed Science & Modelling Laboratory, Department of Earth and Atmospheric Sciences, Faculty of Science, University of Alberta, Edmonton, AB T6G 2R3, Canada; Chinese Academy of Agricultural Sciences, Beijing 100193, China.
Sci Total Environ. 2022 Nov 20;848:157246. doi: 10.1016/j.scitotenv.2022.157246. Epub 2022 Jul 28.
Most previous water quality studies oversimplified in-stream processes for modeling the fate and transport of critical organic contaminants, such as Polycyclic Aromatic Hydrocarbons (PAHs). Taking four selected PAHs as representative organic contaminants, we developed a numerical modeling framework using a Water Quality Analysis Simulation Program 8 (WASP8) and a well-established watershed model, i.e., Soil and Water Assessment Tool (SWAT) to: (1) address the influence of in-stream processes, including direct photolysis, volatilization, partitioning of PAHs to suspended solids, and DOC complexation processes on PAH concentrations; and (2) establish relationships between spatiotemporal distribution of environmental factors (e.g., ice coverage, water temperature, wind, and light attenuation), in-stream processes, and PAH concentrations at a watershed scale. Using calibrated SWAT and WASP8 models, we evaluated the impacts of seasonal changes in environmental factors on in-stream processes in the Muskeg River watershed, which is part of the Athabasca Oil Sands Region (AOSR), the third-largest crude oil reserves of the world in western Canada. Among four selected PAHs, simulation results suggest that Naphthalene primarily decay in the water through volatilization or direct photolysis. For Phenanthrene, Pyrene, and Chrysene, DOC complexation, volatilization, and direct photolysis all contribute to their decay in the water, with a strong dependence on seasonality. Model simulations indicated that direct photolysis and volatilization rates are meager in cold seasons, mainly due to low river temperature and ice coverage. However, these processes gradually resume when entering the warm season. In summary, the model simulation results suggest that critical in-stream processes such as direct photolysis, volatilization, and partitioning and their relationship with environmental factors should be considered when simulating the fate and transport of organic contaminants in the river systems. Our results also reveal that the relationship between environmental factors and fate processes affecting PAH concentrations can vary across a watershed and in different seasons.
大多数先前的水质研究在模拟关键有机污染物（如多环芳烃（PAHs））的命运和迁移时过于简化了河流中的过程。本研究选取了四种代表性的有机污染物（PAHs），利用水质分析模拟程序 8（WASP8）和成熟的流域模型，即土壤和水评估工具（SWAT），开发了一个数值建模框架：（1）研究河流过程，包括直接光解、挥发、PAHs 分配到悬浮固体以及 DOC 络合过程对 PAH 浓度的影响；（2）在流域尺度上建立环境因子（如冰盖、水温、风和光衰减）、河流过程和 PAH 浓度的时空分布关系。使用校准的 SWAT 和 WASP8 模型，我们评估了季节性环境因子变化对 Muskeg 河流域河流过程的影响，该流域位于加拿大西部阿萨巴斯卡油砂区（AOSR），是世界第三大原油储量。在所选择的四种 PAHs 中，模拟结果表明萘主要通过挥发或直接光解在水中衰减。对于菲、芘和䓛，DOC 络合、挥发和直接光解都有助于它们在水中衰减，且强烈依赖于季节性。模型模拟表明，在寒冷季节直接光解和挥发速率很低，主要是由于河水温度低和冰盖。然而，随着进入温暖季节，这些过程逐渐恢复。总之，模型模拟结果表明，在模拟河流系统中有机污染物的命运和迁移时，应考虑直接光解、挥发、分配等关键河流过程及其与环境因子的关系。我们的结果还表明，影响 PAH 浓度的环境因子和命运过程之间的关系可能因流域而异，且在不同季节也有所不同。
