Department of Civil and Environmental Engineering, Colorado State University, 1372 Campus Delivery, Fort Collins, CO 80523-1372, United States.
Sci Total Environ. 2020 Oct 10;738:140318. doi: 10.1016/j.scitotenv.2020.140318. Epub 2020 Jun 18.
Selenium toxicity in groundwater and surface water in many regions globally has resulted in toxicity in the food chain thus harming terrestrial and aquatic animals. Here we assess the environmental controls on selenium fate and transport in soils, groundwater, and rivers at the watershed scale using the SWAT watershed simulation model. We modify the SWAT modeling code to simulate selenium fate and transport in surface runoff, lateral flow, soil percolation, groundwater flow, streamflow, and irrigation water within a watershed subject to oxidation-reduction reactions. This modified SWAT model is applied to an irrigated watershed with selenium problems in the Arkansas River Valley, Colorado. The model is calibrated and tested using observed groundwater and surface water selenium data in different locations of the study area, whereupon global sensitivity analysis is performed to assess controls on selenium fate and transport in soil water, groundwater and streams. The impacts of reaction rates of selenate, selenite, oxygen and nitrate along with 14 hydrologic parameters are assessed. For the baseline model, selenium loading to streams during growing season is mostly via groundwater discharge (365 kg/ha; 85% of total), followed by surface runoff (14%), and soil lateral flow (1%), which are about 4-fold the loading that occurs during non-growing season. Results from the sensitivity analysis indicate that hydrologic factors (timing of recharge, soil hydraulic conductivity, and groundwater storage thresholds) are the principal controls on selenium content in soils, groundwater, and stream water, followed by the first-order reaction rates of selenate and selenite, amount of selenium-bearing shale in the aquifer, and sulfur to selenium ratio in the shale material. These results suggest that selenium mitigation procedures should focus on water management practices rather than influencing microbial redox reactions. Overall, the SWAT-Se model introduced here can be used to assess Se contamination and mitigation practices in watersheds worldwide.
在全球许多地区，地下水和地表水的硒毒性已经导致食物链中的毒性，从而危害陆地和水生动物。在这里，我们使用 SWAT 流域模拟模型评估了在流域尺度上土壤、地下水和河流中硒的命运和传输的环境控制因素。我们修改了 SWAT 建模代码，以模拟受氧化还原反应影响的流域中地表水、侧向流、土壤渗流、地下水流动、水流和灌溉水中硒的命运和传输。该修改后的 SWAT 模型应用于科罗拉多州阿肯色河谷有硒问题的灌溉流域。该模型使用研究区域不同位置的地下水和地表水硒观测数据进行校准和测试，随后进行全局敏感性分析，以评估土壤水、地下水和溪流中硒命运和传输的控制因素。评估了硒酸盐、亚硒酸盐、氧气和硝酸盐的反应速率以及 14 个水文参数的影响。对于基线模型，生长季期间向溪流输送的硒主要通过地下水排泄（365kg/ha；占总排放量的 85%），其次是地表径流（14%）和土壤侧向流（1%），这是非生长季期间排放量的 4 倍左右。敏感性分析结果表明，水文因素（补给时间、土壤水力传导率和地下水储存阈值）是控制土壤、地下水和溪流水中硒含量的主要因素，其次是硒酸盐和亚硒酸盐的一级反应速率、含水层中含硒页岩的数量以及页岩材料中的硫硒比。这些结果表明，硒缓解措施应侧重于水管理实践，而不是影响微生物氧化还原反应。总的来说，这里引入的 SWAT-Se 模型可用于评估全球流域中的硒污染和缓解措施。
