Arsenic-dissolved organic matter complexation in water soluble extracts from lignite.

Arsenic in groundwater is a global threat to public health. Recently, As mobility has been tied to the concentration and chemical characteristics of dissolved organic matter (DOM) through formation of As-DOM complexes. To date, there has been a wide range of DOM types studied to understand As-DOM interactions, but most of these have focused on surface water derived materials and not groundwater DOM. We address this gap in knowledge by simulating groundwater DOM using water extractable organic matter (WEOM) from two lignite deposits and treating the extracts with increasing concentrations of As. As-DOM complexes were measured using size-exclusion chromatography coupled to multiple detectors including an inductively coupled plasma mass spectrometer (ICPMS) for As detection as well as fluorescence and variable wave detectors for organic matter detection. First, we found two different size fractions of As-DOM, one of ∼1 kDa and another of ∼15 kDa, depending on the DOM types. The smaller As-DOM complex (∼1 kDa) was approximately 10 times more abundant than the larger complex (∼15 kDa). Second, we found that the lignite derived DOMs showed higher conditional distribution coefficients than did the surface water reference material (Suwanee River Natural Organic Matter, SRNOM). Finally, the data showed good fit (R2 > 0.92) to one-site ligand binding models, and the lignite derived DOMs showed higher maximum sorbate concentrations (Bmax) compared to SRNOM. Together, this study shows that As-DOM complexation is an important control on As speciation, even in groundwater systems.

Are bog plant/lichen tissue concentrations of Ca, Mg, K, and P affected by fugitive dust released from oil sands development in the Fort McMurray region of Alberta?

Bogs are ombrotrophic, relying solely on atmospheric deposition for new inputs of elements. Increased element deposition through anthropogenic activities has the potential to alter nutrient availability, and hence ecosystem function, in bogs. Further, because of efficient element retention, bogs may function as effective monitors of element deposition. To assess the potential effects of particulate fugitive dust from oil sands development in Alberta, Canada, we quantified plant/lichen tissue Ca, Mg, K, and P concentrations in 6 bogs ranging from 12 to 77 km from the oil sands industrial center. Deposition of Ca and Mg, but not K or P, quantified using ion exchange resin collectors, to bogs decreased with distance from the oil sands industrial center. Concentrations of Ca and Mg, but not K or P, in tissues of lichens (Cladonia mitis, Evernia mesomorpha) and Sphagnum (S. capillifolium, S. fuscum) decreased with distance from the oil sands industrial center. Tissue Ca concentrations were positively correlated with growing season Ca and Mg deposition in all species except Vaccinium oxycoccos, Rhododendron groenlandicum, and Picea mariana; leaf Mg concentrations were positively correlated with growing season Mg deposition for all species except P. mariana. Tissue concentrations of K and P were not correlated with growing season K and P deposition. For each species, receptor modeling identified two distinct sources, one dominated by Ca and Mg, presumed to represent particulate fugitive dust from oil sands activities, and a second dominated by K and P, which may reflect tight internal cycling and upward translocation of K and P in peat and/or K and P deposition as particulates generated in wildfires. Increasing Ca2+ and Mg2+ deposition may acidify bog porewaters through cation exchange in peat.

Is bog water chemistry affected by increasing N and S deposition from oil sands development in Northern Alberta, Canada?

Nitrogen and sulfur emissions from oil sands operations in northern Alberta, Canada have resulted in increasing deposition of N and S to the region's ecosystems. To assess whether a changing N and S deposition regime affects bog porewater chemistry, we sampled bog porewater at sites at different distances from the oil sands industrial center from 2009 to 2012 (10-cm intervals to a depth of 1 m) and from 2009 to 2019 (top of the bog water table only). We hypothesized that: (1) as atmospheric N and S deposition increases with increasing proximity to the oil sands industrial center, surface porewater concentrations of NH4+, NO3-, DON, and SO42- would increase and (2) with increasing N and S deposition, elevated porewater concentrations of NH4+, NO3-, DON, and SO42- would be manifested increasingly deeper into the peat profile. We found weak evidence that oil sands N and S emissions affect bog porewater NH4+-N, NO3--N, or DON concentrations. We found mixed evidence that increasing SO42- deposition results in increasing porewater SO42- concentrations. Current SO42- deposition, especially at bogs closest to the oil sands industrial center, likely exceeds the ability of the Sphagnum moss layer to retain S through net primary production, such that atmospherically deposited SO42- infiltrates downward into the peat column. Increasing porewater SO42- availability may stimulate dissimilatory sulfate reduction and/or inhibit CH4 production, potentially affecting carbon cycling and gaseous fluxes in these bogs.