LeeAnn Munk

Sorption of trace metals to an aluminum precipitate in a stream receiving acid rock-drainage; Snake River, Summit County, Colorado

The quality of water in streams that are contaminated by acid drainage from mines and from the weathering of mineralized rocks improves as the water flows downstream. The purpose of this study was to investigate the geochemical processes that occur in one such stream and to determine the fate of the trace metals that are removed from the water. The stream chosen for this purpose was the Snake River, Summit County, Colorado, which is affected by natural acid rock-drainage (ARD) containing SO4, Al, Fe, and various trace elements such as Zn, Cu, Pb, Ni, and others. Most of the Fe in the Snake River is removed from solution by the oxidation of Fe2+ to Fe3+ and the subsequent precipitation of Fe-oxyhydroxides that form a massive ferricrete deposit near the springs that feed the river. Further downstream, the Snake River (pH=3.0) mixes with water from Deer Creek (pH= 7.0) thereby increasing its pH to 6.3 and causing SO4-rich precipitates of Al-oxyhydroxide to form. The precipitates and associated organic C complexes sorb trace metals from the water and thus have high concentrations of certain elements, including Zn (540–11,400 ppm), Cu (34–221 ppm), Pb (90–340 ppm), and Ni (11–197 ppm). The concentrations of these elements in the precipitates that coat the streambed rise steeply in the zone of mixing and then decline downstream. The trace element concentrations of the water in the mixing zone at the confluence with Deer Creek decrease by 75% or more and are up to 3 orders of magnitude lower than those of the precipitates. Sorption curves for Zn, Cu, Pb, Ni, and SO4 were derived by stepwise neutralization of a sample of Snake River water (collected above the confluence with Deer Creek) and indicate that the trace metals are sorbed preferentially with increasing pH in the general order Pb, Cu, Zn, and Ni. Sulfate is removed between pH 4 and 5 to form an Al-hydroxysulfate and/or by sorption to microcrystalline gibbsite. The sorption data determined from the neutralization experiment were used to account for the downstream decrease of trace-metal concentrations in the precipitates. The results of this study demonstrate that the partitioning of trace metals in the Snake River is not only a function of pH, but also depends on the progressive removal of trace metals as the water of the Snake River flows through its confluence with Deer Creek. The chemical composition of the water also determines what compounds precipitate with increasing pH.

Regional groundwater flow and accumulation of a massive evaporite deposit at the margin of the Chilean Altiplano

Focused groundwater discharge in closed basins provides opportunities to investigate mechanisms for closing hydrologic and solute budgets in arid regions. The Salar de Atacama (SdA), adjacent to the Central Andean Plateau in the hyperarid Atacama Desert, provides an extreme example of halite (>1800 km3) and lithium brine (~5,000 ppm) accumulation spanning late Miocene to present. Minimum long-term water discharge needed to sustain halite accumulation over this timescale at SdA is 9–20 times greater than modern recharge (and double wet-climate paleo recharge) within the topographic watershed. Closing this imbalance requires sourcing water from recharge on the orogenic plateau in an area over 4 times larger than the topographic watershed. Prolonged water discharge at SdA requires long residence times, deep water tables in recharge zones coupled with persistent near surface water tables in discharge areas, and large contributing areas characterized by strong gradients in landscape and climate resulting from plateau uplift.

Predicting risk of trace element pollution from municipal roads using site-specific soil samples and remotely sensed data

Studies of environmental processes exhibit spatial variation within data sets. The ability to derive predictions of risk from field data is a critical path forward in understanding the data and applying the information to land and resource management. Thanks to recent advances in predictive modeling, open source software, and computing, the power to do this is within grasp. This article provides an example of how we predicted relative trace element pollution risk from roads across a region by combining site specific trace element data in soils with regional land cover and planning information in a predictive model framework. In the Kenai Peninsula of Alaska, we sampled 36 sites (191 soil samples) adjacent to roads for trace elements. We then combined this site specific data with freely-available land cover and urban planning data to derive a predictive model of landscape scale environmental risk. We used six different model algorithms to analyze the dataset, comparing these in terms of their predictive abilities and the variables identified as important. Based on comparable predictive abilities (mean R2 from 30 to 35% and mean root mean square error from 65 to 68%), we averaged all six model outputs to predict relative levels of trace element deposition in soils-given the road surface, traffic volume, sample distance from the road, land cover category, and impervious surface percentage. Mapped predictions of environmental risk from toxic trace element pollution can show land managers and transportation planners where to prioritize road renewal or maintenance by each road segments relative environmental and human health risk.

Bucking the Trend: Three New Geoscience Programs

At a time when geoscience departments are being eliminated or dispersed, three new undergraduate geoscience degree-granting programs were approved during the past decade. These programs have grown into sustainable academic entities that maintain solid enrollments and place students into high quality graduate programs and geoscience careers. The curricula at all three institutions focus on graduate school preparation and/or career placement, and include a strong commitment to fieldwork and undergraduate research. Each program has faculty members who have made program development their primary professional goal. The faculty also faced similar challenges in the early stages of program development, such as having to teach a wide variety of upper division courses, needing to establish program credibility, finding the time and funding necessary for faculty and undergraduate research, obtaining materials for laboratory courses, and recruiting majors. The experience and knowledge gained through the development of these new programs should be valuable for others working to establish new programs and maintain existing programs.