The Intergovernmental Panel on Climate Change (IPCC) Technical Paper Climate Change and Water draws together and evaluates the information in IPCC Assessment and Special Reports concerning the impacts of climate change on hydrological processes and regimes, and on freshwater resources – their availability, quality, use and management. It takes into account current and projected regional key vulnerabilities, prospects for adaptation, and the relationships between climate change mitigation and water. Its objectives are:

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Climate change and water.

Mercury is one of the most hazardous contaminants that may be present in the aquatic environment, but its ecological and toxicological effects are strongly dependent on the chemical species present. Species distribution and transformation processes in natural aquatic systems are controlled by various physical, chemical, and biological factors. Depending on the prevailing environmental conditions, inorganic mercury species may be converted to many times more toxic methylated forms such as methylmercury, a potent neurotoxin that is readily accumulated by aquatic biota. Despite a considerable amount of literature on the subject, the behavior of mercury and many of the transformation and distribution mechanisms operating in the natural aquatic environment are still poorly understood. This review examines the current state of knowledge on the physicochemical behavior of mercury in the aquatic environment, and in particular the environmental factors influencing its transformation into highly toxic methylated forms.

Mercury in the Aquatic Environment: A Review of Factors Affecting Methylation

Despite uncertainty in all levels of analysis, recent and long-term changes in our climate point to the distinct possibility that greenhouse gas emissions have altered mean annual temperatures, precipitation and weather patterns. Modeling efforts that use doubled atmospheric CO2 scenarios predict a 1–7°C mean global temperature increase, regional changes in precipitation patterns and storm tracks, and the possibility of “surprises” or sudden irreversible regime shifts. The general effects of climate change on freshwater systems will likely be increased water temperatures, decreased dissolved oxygen levels, and the increased toxicity of pollutants. In lotic systems, altered hydrologic regimes and increased groundwater temperatures could affect the quality of fish habitat. In lentic systems, eutrophication may be exacerbated or offset, and stratification will likely become more pronounced and stronger. This could alter food webs and change habitat availability and quality. Fish physiology is inextricably linked to temperature, and fish have evolved to cope with specific hydrologic regimes and habitat niches. Therefore, their physiology and life histories will be affected by alterations induced by climate change. Fish communities may change as range shifts will likely occur on a species level, not a community level; this will add novel biotic pressures to aquatic communities. Genetic change is also possible and is the only biological option for fish that are unable to migrate or acclimate. Endemic species, species in fragmented habitats, or those in east–west oriented systems will be less able to follow changing thermal isolines over time. Artisanal, commercial, and recreational fisheries worldwide depend upon freshwater fishes. Impacted fisheries may make it difficult for developing countries to meet their food demand, and developed countries may experience economic losses. As it strengthens over time, global climate change will become a more powerful stressor for fish living in natural or artificial systems. Furthermore, human response to climate change (e.g., increased water diversion) will exacerbate its already-detrimental effects. Model predictions indicate that global climate change will continue even if greenhouse gas emissions decrease or cease. Therefore, proactive management strategies such as removing other stressors from natural systems will be necessary to sustain our freshwater fisheries.

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Potential impacts of global climate change on freshwater fisheries

Marine biogeochemical cycling of mercury.

Wild piscivorous fish, mammals, and birds may be at risk for elevated dietary methylmercury intake and toxicity. In controlled feeding studies, the consumption of diets that contained Hg (as methylmercury) at environmentally realistic concentrations resulted in a range of toxic effects in fish, birds, and mammals, including behavioral, neurochemical, hormonal, and reproductive changes. Limited field-based studies, especially with certain wild piscivorous bird species, e.g., the common loon, corroborated laboratory-based results, demonstrating significant relations between methylmercury exposure and various indicators of methylmercury toxicity, including reproductive impairment. Potential population effects in fish and wildlife resulting from dietary methylmercury exposure are expected to vary as a function of species life history, as well as regional differences in fish-Hg concentrations, which, in turn, are influenced by differences in Hg deposition and environmental methylation rates. However, population modeling suggests that reductions in Hg emissions could have substantial benefits for some common loon populations that are currently experiencing elevated methylmercury exposure. Predicted benefits would be mediated primarily through improved hatching success and development of hatchlings to maturity as Hg concentrations in prey fish decline. Other piscivorous species may also benefit from decreased Hg exposure but have not been as extensively studied as the common loon.

https://bioone.org/journals/AMBIO-A-Journal-of-the-Human-Environment/volume-36/issue-1/0044-7447(2007)36[12:EOEMOT]2.0.CO;2/Effects-of-Environmental-Methylmercury-on-the-Health-of-Wild-Birds/10.1579/0044-7447(2007)36[12:EOEMOT]2.0.CO;2.pdf

Effects of Environmental Methylmercury on the Health of Wild Birds, Mammals, and Fish

A field experiment was conducted to determine the degree to which fish accumulated methylmercury (MeHg) via their food or via passive uptake from water through the gills. Finescale dace (Phoxinus neogaeus) were held in 2000 L enclosed pens floating in an undisturbed, oligotrophic lake in northwestern Ontario. Fish were exposed to water containing either low (0.10–0.40 ng L-1), intermediate (0.45–1.30 ng L-1), or high (0.80–2.1 ng L-1) concentrations of MeHg. Zooplankton with either low (0.16–0.18 µg g-1 d.w.) or high (0.28–0.76 µg g-1 d.w.) concentrations of MeHg were added daily to each pen. Fish fed zooplankton with high concentrations of MeHg had significantly higher concentrations of mercury in muscle after 32 days than fish fed zooplankton with low concentrations of MeHg (ANCOVA, P<0.0001). Fish feeding on zooplankton with low concentrations of MeHg had the same amount of Hg in their tissues as fish at the start of the experiment. Uptake from water was at most 15%. This is the first experiment to confirm that food is the dominant pathway of MeHg bioaccumulation in fish at natural levels of MeHg.

Food as the Dominant Pathway of Methylmercury Uptake by Fish

Mercury concentrations in planktivorous, omnivorous, and piscivorous fishes were inversely related to lake size in six lakes in northwestern Ontario. The lakes were remote from direct anthropogenic...

R. J. P. Fudge

Papers

Food as the Dominant Pathway of Methylmercury Uptake by Fish

Mercury Concentrations in Fish Related to Size of Remote Canadian Shield Lakes

Bioaccumulation of mercury in the aquatic food chain in newly flooded areas