Permafrost, geomorphic, and hydroclimatic controls on mercury, methylmercury, and lead concentrations and exports in Old Crow River, arctic western Canada

Concentrations and Yields of Mercury, Methylmercury, and Dissolved Organic Carbon From Contrasting Catchments in the Discontinuous Permafrost Region, Western Canada

“…The yields and yield ratios (MeHg:THg, THg:DOC, and MeHg:DOC) of the peatland catchment were most similar to the Churchill River (Kirk & St. Louis, 2009), a large wetland‐influenced river system. The mixed catchment had analyte yields and yield ratios falling in between the wetland‐influenced Churchill and the more sediment‐laden Old Crow and Mackenzie rivers (Emmerton et al., 2013; Kirk & St. Louis, 2009; Staniszewska et al., 2022), which aligns with mixed‐landscape contributions from peatlands, mountains, and uplands. Both the peatland and mixed catchments had lower analyte yields than the Eastern James Bay rivers of variable size (Chinusaw and Nottaway rivers), likely explained by a much wetter regional climate than the dry Interior Plains (de Melo et al., 2022; Fink‐Mercier, Lapierre, et al., 2022).…”

“…The proportion of particulate MeHg increased with discharge; while THg did not linearly increase with discharge, the catchment had a consistently high particulate fraction of THg relative to the peatland catchment. In catchments with readily erodible sediments, sediment supply has been identified as an important control on concentrations and fluxes of THg and MeHg (e.g., Staniszewska et al., 2022; St. Pierre et al., 2018). The mountainous regions of the mixed catchment could thus deliver sediments, and associated metals, to the catchment outlet.…”

“…The species (i.e., THg or MeHg), fraction (i.e., dissolved or particulate), and concentration of Hg drive biotic uptake, where elevated concentrations of dissolved MeHg maximize uptake (Blanchfield et al., 2022; Gagnon & Fisher, 1997). Peatland‐dominated catchments predominantly deliver dissolved Hg species bound with DOC (Emmerton et al., 2022; Kirk & St. Louis, 2009), with a higher proportion of MeHg to THg (%MeHg) than sediment‐laden rivers carrying particulate‐bound Hg species (St. Pierre et al., 2018; Staniszewska et al., 2022). Discharge and changing water sources can drive variability in water chemistry concentrations, where concentration‐discharge metrics identify chemodynamic (i.e., high variability in response to discharge) or chemostatic (i.e., low variability or non‐systematic in response to discharge) behavior and thus the hydrological or biogeochemical controls on an analyte (N. B. Basu et al., 2010; Pohle et al., 2021).…”

Glacial Erosion Drives High Summer Mercury Exports from the Yukon River, Canada

“…56 Additionally, mercury concentrations are very low�despite the presence of pervasive thermokarst�in the Old Crow River basin, which is underlain by continuous permafrost and drains into the Porcupine and Yukon rivers (Figure 1C). 57 Understanding the present drivers of mercury export in the Yukon River is crucial to modeling the Yukon River basin's response to climate change. Decreasing contributions from glacierized tributaries may be balanced in the future by increasing contributions from thermokarst.…”

“…However, organic-rich streams and rivers in permafrost regions of the Yukon River basin have modern 14 C-DOC values; this suggests that present-day permafrost thaw is mobilizing little old carbon (and mercury) . Additionally, mercury concentrations are very lowdespite the presence of pervasive thermokarstin the Old Crow River basin, which is underlain by continuous permafrost and drains into the Porcupine and Yukon rivers (Figure C) …”