Mercury contamination in aquatic ecosystems under a changing environment: Implications for the Three Gorges Reservoir

Abstract

Mercury is one of the primary contaminants of global concern. As anthropogenic emissions of mercury are gradually placed under control, evidence is emerging that biotic mercury levels in many aquatic ecosystems are increasingly driven by internal biogeochemical processes, especially in ecosystems that have been undergoing dramatic environmental changes. Here we review the unique properties of mercury that are responsible for the exceptional sensitivity of its biogeochemical cycles to changes in climatic, geochemical, biological and ecological processes. We show that, due to rapid climate warming, a shift from sources-driven to processes-driven mercury bioaccumulation is already happening in the Arctic marine ecosystem. We further suggest that such a shift might also be operating in the Three Gorges Reservoir due to changes in these biogeochemical processes induced by the damming. As a result, the effectiveness of mercury emission control is expected to be followed by long delays before ensuing reduction is seen in food-web levels, making it all the more pressing to control and reduce mercury emissions to the reservoir. Long-term monitoring and targeted studies are urgently needed to understand how biotic mercury levels in the reservoir are responding to changes in mercury emissions and in biogeochemical processes.

How closely do mercury trends in fish and other aquatic wildlife track those in the atmosphere? – Implications for evaluating the effectiveness of the Minamata Convention

“…However, major changes in landscape and Table 1 Properties of mercury (Hg) and their implications for its biogeochemistry. (Modified from Wang and Zhang, 2013).…”

“…The impact of climate change on biotic Hg has also been observed in lower latitude regions (e.g., Pinkney et al, 2014). Wang et al (2010) and Wang and Zhang (2013) proposed that the divergence between biotic and environmental Hg trends is an indication that an aquatic ecosystem has entered a new 'paradigm' in which the key controls on Hg bioaccumulation have switched from being 'emissions-driven' to 'processes-driven'. This switch occurs because the biotic Hg concentrations in an aquatic ecosystem are influenced not only by Hg influx (natural or anthropogenic) to the system, but also by the internal processes in the ecosystem that control the recycling, speciation, bioavailability, methylation and biological uptake of Hg.…”

Spatial and temporal patterns of mercury concentrations in freshwater fish across the Western United States and Canada

“…These modifications have had profound impacts on ecological dynamics of the region (Herbert and Gelwick, 2003;Ligon et al, 1995;Martinez et al, 1994;Richter et al, 1997). Moreover, through their influence on the biogeochemistry of aquatic ecosystems, they could also influence Hg cycling (Kasper et al, 2012;Wang and Zhang, 2013). A unique aspect of western North America with respect to Hg dynamics is that compared to the central and eastern regions, the West is disproportionally impacted by the extensive legacy of gold, silver, and Hg mining activities (Davis et al, 2008;Domagalski, 2001;Hornberger et al, 1999;Rytuba, 2000;Singer et al, 2013).…”

Remote Sensing Monitoring of the Bottom Topography in a Shallow Reservoir and the Spatiotemporal Changes of Submerged Aquatic Vegetation Under Water Depth Fluctuations

“…It is a special seasonal wetland ecosystem [1]. Fluctuating redox conditions, dynamic exchanges across the water-soil interface, and vegetation decomposition and revegetation in the WLFZ make it a sensitive area for the biogeochemical cycling of redox-sensitive elements, nutrients and chemical contaminants [2][3][4]. As a part of the WLFZ, submerged aquatic vegetation (SAV) is important for environmental protection in shallow lakes, such as purifying water and maintaining fishery production [5].…”