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Glacial meltwater contributions to streams depend on watershed characteristics that impact water quantity and quality, with potential changes as glaciers continue to recede. The purpose of our study was to investigate the influence of glacier and bedrock controls on water chemistry in glacial streams, focusing on a range of small to large watersheds in Alaska. Southcentral Alaska provides an ideal study area due to diverse geologic characteristics and varying amounts of glacial coverage across watersheds. To investigate spatial and temporal variability due to glacial coverage and bedrock type, we analyzed water samples (n= 343) from seven watersheds over 2 years for major and trace element concentrations and water stable isotopes. We found variable water chemistry across the glacial rivers related to glacial coverage and the relative amount of metamorphic, sedimentary, and igneous bedrock. Some sites had elevated concentrations of harmful trace elements like As and U from glacier melt or groundwater. Longitudinal (upstream to downstream) variability was apparent within each river, with increasing inputs from tributaries, and groundwater altering the water chemistry relative to glacier meltwater contributions. The water chemistry and isotopic composition of river samples compared with endmember sources suggested a range from glacier-dominated to groundwater-dominated sites along stream transects. For example, water chemistry in the Knik and Matanuska rivers (with large contributing glaciers) was more influenced by glacier meltwater, while water chemistry in the Little Susitna River (with small glaciers) was more influenced by groundwater. Across all rivers, stream chemistry was controlled by glacier inputs near the headwaters and groundwater inputs downstream, with the water chemistry reflecting bedrock type. Our study provides a greater understanding of geochemical and hydrological processes controlling water resources in rapidly changing glacial watersheds. 

Dust events originate from multiple sources in arid and semi-arid regions, making it difficult to quantify source contributions. Dust geochemical/mineralogical composition, if the sources are sufficiently distinct, can be used to quantify the contributions from different sources. To test the viability of using geochemical and mineralogical measurements to separate dust-emitting sites, we used dust samples collected between 2018 and 2020 from ten National Wind Erosion Research Network (NWERN) sites that are representative of western United States (US) dust sources. Dust composition varied seasonally at many of the sites, but within-site variability was smaller than across-site variability, indicating that the geochemical signatures are robust over time. It was not possible to separate all the sites using commonly applied principal component analysis (PCA) and cluster analysis because of overlap in dust geochemistry. However, a linear discriminant analysis (LDA) successfully separated all sites based on their geochemistry, suggesting that LDA may prove useful for separating dust sources that cannot be separated using PCA or other methods. Further, an LDA based on mineralogical data separated most sites using only a limited number of mineral phases that were readily explained by the local geologic setting. Taken together, the geochemical and mineralogical measurements generated distinct signatures of dust emissions across NWERN sites. If expanded to include a broader range of sites across the western US, a library of geochemical and mineralogical data may serve as a basis to track and quantify dust contributions from these sources. 

Atmospheric particulate matter (PM) in urban areas is derived from natural and anthropogenic sources, but it is difficult to identify how these various sources contribute to air quality. To characterize PM sources in an urban setting, we collected PM in three size fractions (PM2.5, PM10, and total suspended particulates, TSP) for two-week intervals from 2019 through 2021 in the Wasatch Front of northern Utah. The PM samples were analyzed for major and trace element concentrations and 87Sr/86Sr ratios. Using principal components analysis, we identified mineral dust, urban pollution, and fireworks as the primary PM sources affecting Wasatch Front air quality. Dust contributed Al, Be, Ca, Fe, Mg, Rb, Y, and REEs, which are typical components of carbonate and silicate minerals, with highest concentrations in the TSP fraction. Urban sources produced PM that was enriched in As, Cd, Mo, Pb, Sb, Se, and Tl, and fireworks smoke had high concentrations of Ba, Cr, Cu, K, Sr, and V. Dust events dominated PM chemistry during spring through fall, punctuated by fireworks smoke over the Independence Day holiday, while urban pollution dominated PM chemistry from November through February during winter inversions. 87Sr/86Sr ratios revealed that Sr was sourced from regional playas, local sediment, and fireworks. Strontium released from fireworks had relatively low 87Sr/86Sr ratios that dominated the PM isotopic composition during holidays. Sequential leaching showed that potentially harmful elements such as Se, Cd, and Cu were readily removed by weak acids, suggesting that they are readily available in the environment or through human inhalation. This is the first study to describe seasonal variations in PM chemistry in the Wasatch Front and serves as an example of investigating air quality in complex urban areas impacted by desert dust.