| Summary: | Mercury, Hg, is found in Arctic biota in alarming quantity, posing a potential health risk for the local population. It is believed that the large Arctic rivers contribute to this. The Mackenzie River annually transports approximately 325 km3 water to the Arctic Ocean, which is ca 10% of the freshwater received. The annual water flow also transports ca 2 ton of Hg. In order to investigate the source of Hg within the Mackenzie River Basin and the path of transport, a hydro-chemical river mixing model is constructed using field data gathered in summer 2018 and publicly available data. However, since the Hg concentration is very low in the river water and it is known that Hg binds very strongly to dissolved organic carbon (DOC) and particulate organic carbon (POC), both DOC and POC are utilized instead as proxies for Hg. The purpose of the model is to allow for estimations to be made of the relative contributions of different sub-basins and effluents to the total outflow of (e.g.) DOC at the mouth of the Mackenzie River, based on limited hydrographic and riverine water quality data. The model was used to estimate the mixing of DOC and POC sources for summer 2018 as an initial test of its performance. It performs adequately as it can estimate the amount of water discharge and DOC/TOC (total organic carbon) load that each node contributes to the Mackenzie River. The results from the model suggest that the contribution of organic carbon from each sub-watershed is not solely dependent on either drainage area size or water discharge; additionally, it appears to be determined by the local environment and geology. Water from catchment areas containing peatlands have high DOC content, and water passing through regions with coal layers have high POC content. The loss of POC towards the end of the model coincides well with the expected deceleration of the water discharge entering the Mackenzie River delta. It is concluded that the model should be useful for the study of Hg origin and transport in the Mackenzie River. Also, ...
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