The goal of this research fellowship was to determine the primary mechanisms of arsenic release or storage from streams impacted by acid rock drainage or historic mining activity. We also wanted to determine when and how microbial communities in the hyporheic zone, or the area around a stream where mixing of groundwater and surface water occurs, process arsenic. While our goal was to explore the behavior of arsenic in these systems, our work found that arsenic tended to sorb onto the surfaces of metal-oxides in hyporheic sediments and was not released into streams readily compared to other metals such as iron, aluminum, and manganese. Given this observation for arsenic, the focus of this fellowship (and associated project outcomes) shifted to exploring how the hyporheic zone functions as a whole in streams heavily impacted by abandoned mines and how the degree of connection between the stream and groundwater within the hyporheic zone influence the export of toxic metals such as copper, manganese, and aluminum, in addition to arsenic and iron.  

The primary finding of this work resulted in two conceptual models: one for systems characterized by a good connection between stream and groundwater within the hyporheic zone and one for systems characterized by a poor connection (summarized in Figure 1). Well-connected systems have a notable impact on the export of metals, particularly colloidal and particulate metals, from mine-impacted streams, whereas poorly connected systems do not have a notable impact on whole-stream metal export and concentrate metals in hyporheic sediments. The differences between these two systems also have an impact on microbial community composition, where well-connected systems have greater microbial biodiversity and these microbial communities may have an important influence on nutrient cycling and transformations. The findings associated with these studies also have broader impacts for remediation, where we suggest that the approach to remediation should be different for the well-connected stream-groundwater systems (i.e. water treatment) compared to poorly connected stream-groundwater systems (i.e. sediment treatment and removal in combination with the reduction of iron loads).

 The work associated with this fellowship resulted in three manuscripts: "Groundwater-stream connectivity mediates metal(loid) geochemistry in the hyporheic zone of streams impacted by historic mining and acid rock drainage" accepted by Frontiers in Water (in press), "Seasonal shifts in surface water-groundwater connections from electrical resistivity in a ferricrete-impacted stream" submitted to Geophysics (in review), and "Metal-oxide formation in well-connected hyporheic zones create diverse microbial communities that contribute to important nutrient transformations" for submission to Frontiers in Microbiology (in prep). Additionally, we submitted a streamflow dataset for this study site to Hydroshare (doi: 10.4211/hs.c9ef6ecde25640d4bd4c7a9c50575016) and plan to submit an additional dataset that includes diurnal geochemical data collected from the hyporheic zone of Cement Creek (an iron-rich stream at our study site) using a new auto-sampling method. In addition to these manuscripts and datsets, I also mentored two undergraduate students and one master's thesis student (graduated in August 2020), formed new collaborations with scientists from government agencies (USGS, Forest Service, BLM, EPA), a non-profit organization (Mountain Studies Institute), and continued work with collaborators at the NYU Global Justice Clinic. I also co-led a science club for middle school girls to expose them to various career paths and opportunities in STEM.

Last Modified: 12/21/2020
Modified by: Nell E Hoagland