Gregory T. Carling

Dust-mediated loading of trace and major elements to Wasatch Mountain snowpack

Depth-integrated snow columns were collected at 12 sites across the central Wasatch Mountains, Utah, during March and April 2010 to determine concentrations of trace elements, major anions and cations, and pH. Sample collection was conducted at or near maximum snow accumulation prior to the onset of melt, and included spring dust events driven by southerly pre-frontal winds. Snow samples were melted in the laboratory and subsampled for analyses on filtered (0.45 μm) and unfiltered fractions. All measured elements (Al, As, Ba, Ca, Co, Cr, Cu, Fe, Hg, K, Li, Mg, Mn, Na, Ni, Pb, Sb, Sr, Ti, Tl, U, V, and Zn) and major anions (Cl, NO(3), and SO(4)) displayed significant increases in concentration (for example, factor of 2 to 5 increases for As, Cr, Hg, and Pb) between the six sites sampled in March (prior to dust events) and the six sites sampled in April (after dust events). Acid neutralizing capacity and pH were also elevated in April relative to March snowpack. Comparison of elemental concentration in the particulate (>0.45 μm; difference between unfiltered and filtered concentration) and soluble (<0.45 μm; filtered concentration) fractions shows that the concentration increase between March and April snowpack for the trace elements is primarily a result of association with dust particles >0.45 μm. The results suggest that the majority of trace element loading to the Wasatch snowpack occurs via dust deposition. The major elements were primarily loaded in the <0.45 μm fraction, suggesting deposition of soluble dust particles. The overall findings of this paper are similar to other studies regarding the role of dust on nutrient and trace element accumulation in soils and lake sediments, but to our knowledge this is the first study that compares trace element chemistry of seasonal snowpack before and after dust deposition events.

Relationships of surface water, pore water, and sediment chemistry in wetlands adjacent to Great Salt Lake, Utah, and potential impacts on plant community health.

We collected surface water, pore water, and sediment samples at five impounded wetlands adjacent to Great Salt Lake, Utah, during 2010 and 2011 in order to characterize pond chemistry and to compare chemistry with plant community health metrics. We also collected pore water and sediment samples along multiple transects at two sheet flow wetlands during 2011 to investigate a potential link between wetland chemistry and encroachment of invasive emergent plant species. Samples were analyzed for a suite of trace and major elements, nutrients, and relevant field parameters. The extensive sampling campaign provides a broad assessment of Great Salt Lake wetlands, including a range of conditions from reference to highly degraded. We used nonmetric multidimensional scaling (NMS) to characterize the wetland sites based on the multiple parameters measured in surface water, pore water, and sediment. NMS results showed that the impounded wetlands fall along a gradient of high salinity/low trace element concentrations to low salinity/high trace element concentrations, whereas the sheet flow wetlands have both elevated salinity and high trace element concentrations, reflecting either different sources of element loading or different biogeochemical/hydrological processes operating within the wetlands. Other geochemical distinctions were found among the wetlands, including Fe-reducing conditions at two sites and sulfate-reducing conditions at the remaining sites. Plant community health metrics in the impounded wetlands showed negative correlations with specific metal concentrations in sediment (THg, Cu, Zn, Cd, Sb, Pb, Ag, Tl), and negative correlations with nutrient concentrations in surface water (nitrite, phosphate, nitrate). In the sheet flow wetlands, invasive plant species were inversely correlated with pore water salinity. These results indicate that sediment and pore water chemistry play an important role in wetland plant community health, and that monitoring and remediation efforts should consider pore water and sediment chemistry in addition to surface water chemistry.

Particulate and Dissolved Trace Element Concentrations in Three Southern Ecuador Rivers Impacted by Artisanal Gold Mining

Water and sediment samples were collected along river transects at three artisanal gold mining areas in southern Ecuador: Nambija, Portovelo-Zaruma, and Ponce Enriquez. Samples were analyzed for a suite of major and trace elements, including filtered/unfiltered water samples and stream flow measurements to determine dissolved/particulate loads. Results show that the Q. Calixto, Calera, and Siete rivers (corresponding to Nambija, Portovelo-Zaruma, and Ponce Enriquez mining areas, respectively) have substantial trace element contamination due to mining inputs. Dissolved concentrations were elevated at Calera and Siete relative to Q. Calixto, possibly reflecting the input of soluble cyano-metal complexes in mining zones where cyanidation is used in ore processing. A negative correlation was found between MeHg:THg ratios and pH, indicating an inverse relationship of mercury methylation with cyanidation (since cyanidation increases water pH). This was the first comprehensive study to examine an extensive suite of trace elements in both water and sediment at the three main gold mining areas of southern Ecuador, including dissolved and particulate loads, and the first study to report MeHg concentrations in the mercury-contaminated rivers.

Thermal groundwater contributions of arsenic and other trace elements to the middle Provo River, Utah, USA

Groundwater inputs can impact river water quality but are difficult to disentangle from agricultural, urban, and storm runoff. To better understand the multiple processes affecting water quality, we used major solute and trace element concentrations with continuous measurements of flow rates and specific conductance to track temporal and spatial changes in surface water and groundwater solute inputs into the middle Provo River, located in northern Utah, USA. Thermal groundwater was the most important source of major solutes and trace elements to the middle Provo River, with concentrations of As, B, Cs, Li, Sr, and Rb increasing dramatically (twofold to tenfold) downstream of thermal water inputs in the Snake Creek tributary. Snake Creek accounted for only 20% of the flow to the Provo River but increased the As concentrations ~four-fold. Diffuse groundwater inputs, including thermal water, along the Provo River also contributed a measureable increase in solute concentrations. Mixing calculations indicate that groundwater contributed up to 10% of the total streamflow to the middle Provo River, causing an increase in thermal groundwater-derived trace element concentrations. In addition to natural groundwater inputs, water quality was impacted by anthropogenic trace and major element inputs from surface water tributaries. Nitrate, Ba, and V concentrations increased substantially downstream of agricultural/urban inputs. Specific conductance data showed that tributaries added solutes to the Provo River during runoff events, likely from the washoff of road salts. With evidence of both natural and anthropogenic inputs of trace and major elements to the middle Provo River, our study has implications for understanding water quality in complex coupled human–natural systems and demonstrates the influence of thermal groundwater inputs on water quality where such systems discharge.

Designing and Implementing a Network for Sensing Water Quality and Hydrology across Mountain to Urban Transitions

Water resources are increasingly impacted by growing human populations, land use, and climate changes, and complex interactions among biophysical processes. In an effort to better understand these factors in semiarid northern Utah, United States, we created a real-time observatory consisting of sensors deployed at aquatic and terrestrial stations to monitor water quality, water inputs, and outputs along mountain to urban gradients. The Gradients Along Mountain to Urban Transitions (GAMUT) monitoring network spans three watersheds with similar climates and streams fed by mountain winter-derived precipitation, but that differ in urbanization level, land use, and biophysical characteristics. The aquatic monitoring stations in the GAMUT network include sensors to measure chemical (dissolved oxygen, specific conductance, pH, nitrate, and dissolved organic matter), physical (stage, temperature, and turbidity), and biological components (chlorophyll-a and phycocyanin). We present the logistics of designing, implementing, and maintaining the network; quality assurance and control of numerous, large datasets; and data acquisition, dissemination, and visualization. Data from GAMUT reveal spatial differences in water quality due to urbanization and built infrastructure; capture rapid temporal changes in water quality due to anthropogenic activity; and identify changes in biological structure, each of which are demonstrated via case study datasets.

Effect of Atmospheric Deposition and Weathering on Trace Element Concentrations in Glacial Meltwater at Grand Teton National Park, Wyoming, U.S.A.

ABSTRACT Glaciers are reservoirs of atmospherically deposited trace elements that are released during melt. Weathering in glacial environments also contributes solutes to proglacial streams. To investigate the relative importance of atmospheric deposition and weathering on trace element chemistry of glacial streams, we sampled supraglacial and proglacial meltwater at two glacierized catchments in Grand Teton National Park, Wyoming, which is located downwind of agricultural/industrial emissions and dust sources. Concentrations of major ions (Mg2+, K+, Na+, Ca2+, SO42-), alkalinity, conductivity, and a subset of trace elements (U, Mo, Sr, Rb, Li, Ba) were low in supraglacial meltwater but increased in proglacial streams because of water-rock interactions. In contrast, concentrations of the trace metals Mn, Co, Zn, Pb, Cd, and Hg had relatively high concentrations in supraglacial meltwater and decreased downstream. These metals are not abundant in the local bedrock and thus are likely sourced from atmospheric deposition. Stable isotopes indicated different water sources in July (snowmelt-dominated) and August (ice melt-dominated), but water chemistry was similar during both months, indicating similar composition of recent snowfall and older ice. These findings have implications for evaluating the relative impacts of atmospheric deposition and weathering in glacier- and snow-dominated catchments.

Imaging the Margins of Pleistocene Lake Deposits with High-Resolution Seismic Reflection in the Eastern Basin and Range: Pilot Valley, Utah (USA)

Abstract A vast area of the northeastern Great Basin of the western USA was inundated by a succession of Pleistocene lakes, including Lake Bonneville. Playa-sediment deposition from these lakes onlapped onto alluvial fans that blanketed the slopes of adjacent mountain ranges to create prominent angular unconformities. Understanding these unconformities is useful for constraining the interpretation of the geologically recent tectonic evolution of the Basin and Range Province, as well as the interaction of lake sedimentation and alluvial fan development. The Pilot Valley playa, located just east of the Utah–Nevada border near Wendover, Utah, represents a remnant of these lakes. High-resolution seismic profiles have been acquired near the base of the bounding mountain ranges. The profiles reveal the stratigraphic relationships between Quaternary pluvial sediments as a shoreline depositional facies and the adjacent bounding fan deposits. On the western side of the basin, these profiles image subhorizontal playa sediments prograding over inclined alluvial fans. The boundary between the playa and fan sediments is marked by a prominent angular unconformity. Seismic images from the opposite side of the basin reveal a more heterogeneous structural and stratigraphic style, including down-to-the-basin normal faulting of shallow Paleozoic bedrock overlain by alluvial fan deposits, which are in turn onlapped by a thin veneer of playa sediments. The new geophysical images, when integrated with available geologic mapping, also aid in constraining how deep aquifers are locally recharged from an adjacent range. The results demonstrate the structural asymmetry of the range and playa system, consistent with a classic half-graben structure. Lastly, this study demonstrates the utility of the method of shallow seismic reflection to provide high-resolution subsurface images in the challenging environment of alluvial fan–playa geology.

Investigating Anthropogenic and Geogenic Sources of Groundwater Contamination in a Semi-Arid Alluvial Basin, Goshen Valley, UT, USA

Groundwater resources can be impacted by contamination from geogenic and anthropogenic inputs but it can be difficult to disentangle contaminant sources. In this study, we investigated the sources and distribution of NO3 and As in Goshen Valley, UT, a semi-arid alluvial basin in the western USA that contains geothermal waters, playa soils, agriculture, and legacy mining. Surface water, springs, and wells were analyzed for As and NO3 concentrations in relation to major ions, trace elements, and stable isotopes in water (δ18O and δD), and other isotopic tracers. Major ion concentrations showed high spatial variability ranging from freshwater to brackish water, with the highest salinity found in geothermal springs and springs discharging from playa sediments (Playa Springs). Radiogenic 87Sr/86Sr ratios in the Playa Springs suggest that Sr is sourced from crystalline basement rocks. The highest NO3 concentrations were found in groundwater beneath agricultural areas, particularly dairy farms, with isotopic values indicating manure, not fertilizers, as the major source. Many of the NO3-contaminated wells contained old groundwater (based on 14C and 3H), suggesting that reinfiltration of pumped groundwater may be a source of NO3 pollution. The Playa Springs also had the highest As concentrations, with moderate As concentrations found in other geothermal springs. Wells containing moderate As concentrations were found in areas where the groundwater interacts with alluvial sediments or carbonate rocks. Surprisingly, nearby mining and mineral processing seems to have minimal effect on As contamination in the alluvial aquifer. This study has implications for understanding water quality in regions that are impacted by multiple potential contaminant sources.