Mercury Threat to Oceans Escalating due to Climate Change
Posted by feww on January 29, 2017
More mercury than ever before threaten aquatic ecosystems –Study
Mercury levels in fish could increase by up to seven times the current levels as temperatures continue rising, say researchers.
Marine ecosystems, and mainly their coastal zones, have been estimated to contribute more than 60% of the total economic value of the biosphere . These ecosystem services are currently threatened by anthropogenic pollution and a changing climate. Increased terrestrial water runoff and accompanied input of terrestrial NOM and nutrients to lakes and coastal sea areas have been observed in several regions during the late 20th century. These increases are predicted to escalate for large regions worldwide following increased air temperatures and precipitation events.
The study Terrestrial discharges mediate trophic shifts and enhance methylmercury accumulation in estuarine biota has been published in Science Advances.
The input of mercury (Hg) to ecosystems is estimated to have increased two- to fivefold during the industrial era, and Hg accumulates in aquatic biota as neurotoxic methylmercury (MeHg). Escalating anthropogenic land use and climate change are expected to alter the input rates of terrestrial natural organic matter (NOM) and nutrients to aquatic ecosystems. For example, climate change has been projected to induce 10 to 50% runoff increases for large coastal regions globally. A major knowledge gap is the potential effects on MeHg exposure to biota following these ecosystem changes. We monitored the fate of five enriched Hg isotope tracers added to mesocosm scale estuarine model ecosystems subjected to varying loading rates of nutrients and terrestrial NOM. We demonstrate that increased terrestrial NOM input to the pelagic zone can enhance the MeHg bioaccumulation factor in zooplankton by a factor of 2 to 7 by inducing a shift in the pelagic food web from autotrophic to heterotrophic. The terrestrial NOM input also enhanced the retention of MeHg in the water column by up to a factor of 2, resulting in further increased MeHg exposure to pelagic biota. Using mercury mass balance calculations, we predict that MeHg concentration in zooplankton can increase by a factor of 3 to 6 in coastal areas following scenarios with 15 to 30% increased terrestrial runoff. The results demonstrate the importance of incorporating the impact of climate-induced changes in food web structure on MeHg bioaccumulation in future biogeochemical cycling models and risk assessments of Hg.
Terrestrial discharges mediate trophic shifts and enhance methylmercury accumulation in estuarine biota
Sofi Jonsson et al. http://advances.sciencemag.org/content/3/1/e1601239.full