BackgroundBeavers in the Taiga PlainsSince near extirpation of beaver (Castor canadensis) in the 1800s, Canadian beaver populations have increased and expanded their range distribution (Hood & Larson, 2015). Since their return, beaver dam construction is becoming more common at key hydrological areas in northern peatlands which leads to the creation of new ponds and highly saturated soils. Changes to water flow directly resulting from beaver-created ponds will lead to secondary changes to the water chemistry. Oxygen levels are known to be one of the many water chemistry parameters that are changed by beaver pond creation (Hood & Larson, 2015) which means these ponds may be important areas of toxic methylmercury production in the Taiga Plains. Elevated methylmercury levels resulting from beaver pond development has been documented in other boreal regions globally (Levanoni et al. 2015; Roy et al. 2009), however, climate and landscape conditions vary regionally, and are likely to influence methylmercury levels in beaver ponds.
MethylmercuryDuring anaerobic decomposition of organic material, inorganic mercury (Hg)can be transformed to toxic methylmercury (MeHg) through a process called methylation (Lehnherr, 2014) (Figure 2). Factors known to influence methylation include oxygen and nutrient availability which are properties altered by beaver ponds, and the amount of available mercury on the landscape. The Taiga Plains peatlands have large stores of atmospherically deposited mercury originating both from natural and anthropogenic sources (Lehnherr, 2014; Gordon et al., 2016). Any methylmercury exported from wetlands through direct transportation in the water column can biomagnify and accumulate in the fatty tissue of fish (Lehnherr, 2014). This threatens both fish population health, as well as the health of consumers. Recently, fish consumption advisories have been issued in Northern Canada in regions where fishing is culturally and nutritionally significant for Indigenous communities (Gordon et al., 2016). Thus far, these increases have been linked to rapidly occurring ecosystem changes in the Taiga Plains resulting from global climate change and related significant alterations to the water cycle, permafrost stability, and forest composition (Gordon et al., 2016).
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Research Objectives
The broad objective of this study is to evaluate methylmercury production caused by beaver ponds in the Taiga Plains. The objective is broken down into two main components;
1: Determine whether beaver ponds in the Taiga Plains are sites of methylmercury production hotspots.
2: Identify water chemistry conditions that correlate with methylmercury concentration changes in beaver ponds.
While beaver dam-related water chemistry changes are natural, it is critical to understand the sources of toxic methylmercury on the landscape. The results of this study will provide important insight into water chemistry changes resulting from beaver ponds in the context of the many intersecting disturbances to the Taiga Plains peatlands.
1: Determine whether beaver ponds in the Taiga Plains are sites of methylmercury production hotspots.
2: Identify water chemistry conditions that correlate with methylmercury concentration changes in beaver ponds.
While beaver dam-related water chemistry changes are natural, it is critical to understand the sources of toxic methylmercury on the landscape. The results of this study will provide important insight into water chemistry changes resulting from beaver ponds in the context of the many intersecting disturbances to the Taiga Plains peatlands.
Citations
Gordon, J., Quinton, W., Branfireun, B. A., and Olefeldt, D. (2016) Mercury and methylmercury biogeochemistry in a thawing permafrost wetland complex, Northwest Territories, Canada. Hydrol. Process., 30: 3627– 3638. doi: 10.1002/hyp.10911.
Hood, G. A., & Larson, D. G.. (2015). Ecological engineering and aquatic connectivity: a new perspective from beaver-modified wetlands. Freshwater Biology, 60(1), 198–208. https://doi.org/10.1111/fwb.12487
Lehnherr, I.. (2014) Methylmercury biogeochemistry: a review with special reference to Arctic aquatic ecosystems. Environmental Reviews. 22(3): 229-243. https://doi.org/10.1139/er-2013-0059
Levanoni, O., Bishop, K., Mckie, B. G., Hartman, G., Eklöf, K., & Ecke, F.. (2015). Impact of Beaver Pond Colonization History on Methylmercury Concentrations in Surface Water. Environmental Science & Technology, 49(21), 12679–12687. https://doi.org/10.1021/acs.est.5b03146
Roy, V., Amyot, M., & Carignan, R.. (2009). Beaver Ponds Increase Methylmercury Concentrations in Canadian Shield Streams along Vegetation and Pond-Age Gradients. Environmental Science & Technology, 43(15), 5605–5611. https://doi.org/10.1021/es901193x
St. Louis, V. L., Rudd, J. W., Kelly, C. A., Beaty, K. G., Flett, R. J., Roulet, N. T. Production and Loss of Methylmercury and Loss of Total Mercury from Boreal Forest Catchments Containing Different Types of Wetlands. Environ. Sci. Technol. 1996, 30 (9), 2719–2729.
Pugh, E. A. (2021). From Drought to Deluge: Implications of variable hydrologic connectivity on lake ecosystem functions in the Boreal Plains of Western Canada [Doctoral Thesis, University of Alberta]. Doi: https://doi.org/10.7939/r3-mz5w-wq09
Hood, G. A., & Larson, D. G.. (2015). Ecological engineering and aquatic connectivity: a new perspective from beaver-modified wetlands. Freshwater Biology, 60(1), 198–208. https://doi.org/10.1111/fwb.12487
Lehnherr, I.. (2014) Methylmercury biogeochemistry: a review with special reference to Arctic aquatic ecosystems. Environmental Reviews. 22(3): 229-243. https://doi.org/10.1139/er-2013-0059
Levanoni, O., Bishop, K., Mckie, B. G., Hartman, G., Eklöf, K., & Ecke, F.. (2015). Impact of Beaver Pond Colonization History on Methylmercury Concentrations in Surface Water. Environmental Science & Technology, 49(21), 12679–12687. https://doi.org/10.1021/acs.est.5b03146
Roy, V., Amyot, M., & Carignan, R.. (2009). Beaver Ponds Increase Methylmercury Concentrations in Canadian Shield Streams along Vegetation and Pond-Age Gradients. Environmental Science & Technology, 43(15), 5605–5611. https://doi.org/10.1021/es901193x
St. Louis, V. L., Rudd, J. W., Kelly, C. A., Beaty, K. G., Flett, R. J., Roulet, N. T. Production and Loss of Methylmercury and Loss of Total Mercury from Boreal Forest Catchments Containing Different Types of Wetlands. Environ. Sci. Technol. 1996, 30 (9), 2719–2729.
Pugh, E. A. (2021). From Drought to Deluge: Implications of variable hydrologic connectivity on lake ecosystem functions in the Boreal Plains of Western Canada [Doctoral Thesis, University of Alberta]. Doi: https://doi.org/10.7939/r3-mz5w-wq09