Whole-ecosystem study shows rapid fish-mercury response to changes in mercury deposition

Abstract

Methylmercury contamination of fisheries from centuries of industrial atmospheric emissions negatively impacts humans and wildlife worldwide. The response of fish methylmercury concentrations to changes in mercury deposition has been difficult to establish because sediments/soils contain large pools of historical contamination, and many factors in addition to deposition affect fish mercury. To test directly the response of fish contamination to changing mercury deposition, we conducted a whole-ecosystem experiment, increasing the mercury load to a lake and its watershed by the addition of enriched stable mercury isotopes. The isotopes allowed us to distinguish between experimentally applied mercury and mercury already present in the ecosystem and to examine bioaccumulation of mercury deposited to different parts of the watershed. Fish methylmercury concentrations responded rapidly to changes in mercury deposition over the first 3 years of study. Essentially all of the increase in fish methylmercury concentrations came from mercury deposited directly to the lake surface. In contrast, <1% of the mercury isotope deposited to the watershed was exported to the lake. Steady state was not reached within 3 years. Lake mercury isotope concentrations were still rising in lake biota, and watershed mercury isotope exports to the lake were increasing slowly. Therefore, we predict that mercury emissions reductions will yield rapid (years) reductions in fish methylmercury concentrations and will yield concomitant reductions in risk. However, a full response will be delayed by the gradual export of mercury stored in watersheds. The rate of response will vary among lakes depending on the relative surface areas of water and watershed.bioaccumulation ͉ mercury methylation ͉ stable isotopes ͉ whole-ecosystem experimentation ͉ methylmercury

Over three millennia of mercury pollution in the Peruvian Andes

“…3). The apparent discordance between the Hg profiles appears to support the suggestion that the watershed of LY2 continued to export legacy Hg to the lake during periods of declining atmospheric deposition, a mechanism that has also been observed in modern lake systems (23). The mine was permanently closed in 1975 AD, and currently the only mining of Hg at Huancavelica is artisanal.…”

The fate of mercury in Arctic terrestrial and aquatic ecosystems, a review

“…[203] In a temperate whole-ecosystem experiment that used additions of stable Hg isotopes to trace the movement of Hg, fish MeHg concentrations responded rapidly to inorganic Hg deposited directly onto the lake surface. [204] On a broad geographic scale, a study of wild fish populations in the United States found that approximately twothirds of the geographic variation in Hg levels of largemouth bass (Micropterus salmoides) was related to the rate of wet atmospheric Hg deposition. [51] Similarly, MeHg bioaccumulation in a fresh water aquatic invertebrate (mosquitoes) was positively correlated with wet atmospheric Hg deposition across a latitudinal gradient in North America that included Alaska.…”

“…does AMDE Hg take a 'fast track' to biota?). [4,204] In considering the MeHg burden in high trophic level species, it is difficult to estimate which component derives from AMDEs and which derives from the now globally contaminated pool of Hg II cycling in the atmosphere-ocean system. It seems clear that ecosystems in the Arctic Ocean are contaminated with industrial Hg, [255] but it is unclear whether AMDEs contribute significantly to making Arctic ecosystems especially vulnerable to the global Hg cycle.…”

Polar firn air reveals large-scale impact of anthropogenic mercury emissions during the 1970s

“…The connection between deposition of inorganic mercury, enhanced during the 1970s, and contamination of ecosystems, due to methylation processes is more complex. Mercury levels in lakes respond rapidly (within years) to changes in mercury deposition directly to their surfaces, but much more slowly (in decades) to changing inputs to their watersheds (6). Although decreases in fish mercury have been reported recently for lakes exposed to reduced mercury deposition (53), other aquatic ecosystems may continue to bio-accumulate Hg due to higher anthropogenic emissions in the 1970s.…”

“…Harris et al (6) recently reported, however, a whole ecosystem study demonstrating a rapid and direct change in mercury levels in fish resulting from a change in atmospheric mercury. Thus, recent evolution of the atmospheric mercury burden, strongly influenced by anthropogenic emissions, could have played a key role in contamination of many ecosystems.…”