报告人介绍：威廉.约翰逊（William Paul Johnson）为美国犹他大学地质和地理学系教授，矿业和地球科学院副院长，犹他大学学术理事会主席，环境领域权威期刊EST-L编委会成员。1993年获得科罗拉多大学博士学位，2000和2011分别获得犹他大学优秀教师科研奖。主持科研项目17项，项目经费达到245万美元。发表SCI论文101篇，总被引4216次，HI指数35。
Contaminant Removal andPrecious Metal Recovery
by Lateral Channel Filtration inMining-Impacted Rivers
William P Johnson, University of Utah
Artisanalor small-scale mining impacts on water quality occur globally, with greaterimpacts occurring in developing countries, often in remote and/orlesser-developed regions of South America, Africa, and Asia. Alluvialmining is a common practice downstream of mined areas to recover particle-boundprecious metals not recovered by upstream mining/processing activities.Alluvial mining involves excavation and processing of streambed alluvium,exacerbating turbidity and contaminant loads, and leaving behind a constructedchannel that is typically linear and not meandering, such that contaminants aredirectly transmitted to downstream water bodies without the beneficialcontaminant removal processes that are facilitated by hyporheic exchange inmeandering and braided channels. The strong economic incentives thatdrive alluvial mining requires development of solutions that minimizeenvironmental impacts while maximizing economic benefit from alluvial mining. Potential solutions must harness local materials in these typicallylesser-developed settings, and must work under dramatic seasonal shifts inflow, both of which limit options for remediation infrastructure.
Theutility of hyporheic transport to remove particle-bound contaminants has beenlong recognized. Following this idea, a case study in Southern Ecuador exploredwhether excavating channels lateral to the impacted stream in the alluvialfloodplain coaxes streamflow laterally through the alluvium and enhancesfiltration-driven deposition of particle-bound contaminants and precious metalsfor subsequent recovery. The advantage of lateral channel filtration isthat lateral flow is forced without built infrastructure, and withoutconstraining longitudinal flow, thereby minimizing damage in response toseasonal flooding. The case study explores whether alluvial mining bebetter managed to attenuate particle-bound contaminants and improve waterquality while increasing economic benefit.