Buell, Mary-Claire

A significant portion (15-20%) of mercury (Hg) in the Arctic Ocean is believed to originate from Arctic rivers, such as the Mackenzie River watershed in the NWT. Recent (2005- 2020) Hg monitoring data of freshwater and fish tissue and environmental model outputs were compiled and used to develop a Bayesian Network Relative Risk model (BN-RRM), a probabilistic model capable of analyzing causal relationships. The objectives of the model were to estimate the risk posed to fish health and the subsequent dietary Hg-exposure to humans; to compare the relative risks between regions of the watershed; and to identify the influential Hg sources. The output of the BN-RRMs differed significantly throughout the watershed, with atmospheric Hg deposition and soil erosion Hg release consistently flagged as important explanatory variables. Analysis of the endpoint uncertainties revealed gaps in knowledge and in Hg datasets, which should be the focus of study for future monitoring programs.

Author Keywords: Aquatic Ecosystems, Arctic, Bayesian Network, Mercury, Risk Assessment, Toxicology

Extensive research has gone into measuring changes to the carbon storage capacity of Arctic terrestrial environments as well as large water bodies in order to determine a carbon budget for many regions across the Arctic. Inland Arctic waters such as small lakes and ponds are often excluded from these carbon budgets, however a handful of studies have demonstrated that they can often be significant sources of carbon to the atmosphere. This study investigated the CO2 cycling of tundra ponds in the Daring Lake area, Northwest Territories, Canada (64°52'N, 111°35'W), to determine the role ponds have in the local carbon cycle.

Floating chambers, nondispersive infrared (NDIR) sensors and headspace samples were used to estimate carbon fluxes from four selected local ponds. Multiple environmental, chemical and meteorological parameters were also monitored for the duration of the study, which took place during the snow free season of 2013.

Average CO2 emissions for the two-month growing season ranged from approximately -0.0035 g CO2-C m-2 d-1 to 0.12 g CO2-C m-2 d-1. The losses of CO2 from the water bodies in the Daring Lake area were approximately 2-7% of the CO2 uptake over vegetated terrestrial tundra during the same two-month period.

Results from this study indicated that the production of CO2 in tundra ponds was positively influenced by both increases in air temperature, and the delivery of carbon from their catchments. The relationship found between temperature and carbon emissions suggests that warming Arctic temperatures have the potential to increase carbon emissions from ponds in the future.

The findings in this study did not include ebullition gas emissions nor plant mediated transport, therefore these findings are likely underestimates of the total carbon emissions from water bodies in the Daring Lake area. This study emphasizes the need for more research on inland waters in order to improve our understanding of the total impact these waters may have on the Arctic's atmospheric CO2 concentrations now and in the future.

Author Keywords: Arctic, Arctic Ponds, Carbon dioxide, Carbon Fluxes, Climate Change, NDIR sensor