A comparison of mercury fluxes across a range of Canadian subarctic streams: Implications for climate and land-use change
Abstract
It is well established that peatlands are important modifiers of downstream water quality in any catchment where they are found. Although small headwater peatlands are very important in controlling downstream water quality, there have been no attempts to scale up the process-based knowledge that we have about mercury cycling in small peatlands to the larger extensive peatland systems of the world. The Hudson Bay Lowlands (HBL) is the second largest peatland complex in the world with a total area of approximately 320000 sq km. In light the importance of the carbon stock and predictions of significant climate change impacts, research effort has gone into studying the carbon dynamics of the HBL peatlands however there has been no research on the role of the HBL peatlands in governing the water quality or quantity of the important tributaries of Hudson Bay. The published importance of mercury loading to the Hudson Bay/James Bay in terms of ecosystem and human impact stands in stark contrast with the limited data available for major tributaries. Perhaps of greatest importance are emerging concerns over land-use and/or climate changes in the HBL that affect peat hydrology and mercury dynamics; these concerns are based solely on conjecture because of the absence of empirical data. As part of a study of a broader study of the hydrology and biogeochemistry of the region, we have been investigating mercury and methylmercury fluxes across a wide range of catchments. Regular budget sampling (weekly to biweekly) for total mercury, methylmercury, and other solutes was undertaken over four years (2008-2011) in subcatchments of the Attiwapiskat River, spanning a wide range of catchment areas (~100, ~1000 sq. km) as well as the main stem of the Attiwapiskat, with an upstream catchment area of ~50 000 sq. km. Stream flows were measured nearly continuously (some interruptions due to ice impacts) using a combination of methods, depending on stream size. Our results over nearly four years of study indicate that there is dramatic between-year variation in surface water total mercury and methylmercury concentrations (sometimes >2x) for a given stream. Among streams of similar size, as well as across stream orders, there is a similar wide range of variability in concentrations, driven largely by differing natural hydrological processes, with higher stream concentrations occurring during wetter, higher flow years. Total and methylmercury concentrations are very low relative to more southerly peatland-dominated watersheds (e.g. 2008 mean THg and MeHg ~1 ng/L and ~ 50 pg/L respectively), and do not vary significantly with stream order. Annual solute fluxes tend to be controlled water flux and not variation in concentrations, however this depends somewhat on the solute of interest. Projected climate change conditions for this region (wetter, warmer) suggest that enhanced mercury methylation and landscape coupling to surface waters could increase the loading of both total and methylmercury in the future.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFM.B21L..03B
- Keywords:
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- 0414 BIOGEOSCIENCES / Biogeochemical cycles;
- processes;
- and modeling;
- 0432 BIOGEOSCIENCES / Contaminant and organic biogeochemistry;
- 1806 HYDROLOGY / Chemistry of fresh water;
- 1890 HYDROLOGY / Wetlands