Temporal trends and factors influencing Hg levels in upper catchment boreal lakes
Abstract
In boreal lakes, mercury (Hg) origins from both natural and anthropogenic sources. It may vary in space and time as a function of lake and watershed characteristics, and atmospheric deposition trends. The aim of this study was to quantify Hg and MeHg in 37 unperturbed upper catchment boreal lakes in the Eastern Canadian Shield (Québec, Canada) and to identify the factors that influence their spatial and temporal variations. Previous measurements (mid 90s) in 10 lakes of this network would provide a snapshot of long-term surface water Hg temporal trends as function of atmospheric Hg transport and the influence of deposition. We tested the hypothesis that (1) lake Hg concentration would decrease between the two sampling periods and (2) that variations in dissolved organic carbon (DOC) concentration, catchment characteristics and atmospheric Hg deposition would explained the spatial variations in lake Hg and MeHg concentration. Our data shows that total gaseous mercury (TGM) and Hg deposition in this region decreased significantly, between the 1990s to the 2010s, due to the significant control and reduction of anthropogenic emission in Eastern Canada and in the Northeastern USA. Mercury model deposition data across the boreal lake network shows a significant decrease of wet and dry deposition between the two sampling dates, 10 % and 19 % respectively. However, preliminary results show that surface Hg concentration in 30 % of headwater lakes does not follow the atmospheric trends, and show an increase of surface water Hg concentration between the two sampling dates, suggesting a strong influence of processes taking place in catchments or lakes. Preliminary results also show strong relationship of lake Hg concentration with DOC, as well as with iron (Fe) and aluminum (Al), highlighting a strong link with the surrounding catchment. However, the control of catchment and lake characteristics such as lake depth, drainage ratio (watershed area / lake area) as well as water residence time is limited. A deeper investigation is needed in order to better understand the geochemical processes involved. Higher concentrations of Hg and MeHg in boreal lakes may potentially increase transfer to biota, and cause a potential risk to native communities, and human health.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.B51I2351P
- Keywords:
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- 3339 Ocean/atmosphere interactions;
- ATMOSPHERIC PROCESSES;
- 0409 Bioavailability: chemical speciation and complexation;
- BIOGEOSCIENCES;
- 0414 Biogeochemical cycles;
- processes;
- and modeling;
- BIOGEOSCIENCES;
- 0461 Metals;
- BIOGEOSCIENCES