title: Beaver ponds increase methylmercury concentrations in Canadian shield streams along vegetation and pond-age gradients.
abstract: Beaver impoundments flood forested areas and may be important production sites for methylmercury (MeHg) because of the resulting enhanced microbial activity and oxygen depletion. The influence of 17 beaver impoundments on streamwater chemistry (total mercury (THg), MeHg, nutrients, cations, and anions)] was investigated by sampling sites located along vegetation and pond-age gradients in southwestern Quebec (Canada). Recently inundated beaver ponds (< 10 years old) and those located in coniferous watersheds had the highest MeHg concentrations (range, 0.10-4.53 ng L(-1)) and greatest methylation efficiencies (% THg as MeHg; range, 10-74%). High heterotrophic activity likely occurred in the beaver ponds as suggested by depletions of dissolved oxygen, sulfate and nitrite-nitrate concentrations, and increases in nutrients (e.g., dissolved organic carbon, total phosphorus, and total nitrogen) in outlets compared to inlets. Acidic waters at coniferous sites may have stimulated more MeHg production than in mixed woodland regions. Lower methylation efficiencies in older ponds (> 20 years old) may be due to the degradation of less labile organic matter as ponds age. Beavers actively alter watersheds by building impoundments, and our findings indicate that this landscape disturbance may be a significant source of MeHg to downstream water bodies.
authors.affiliation: Université de Montréal, Groupe de Recherche Interuniversitaire en Limnologie (GRIL), Département des sciences biologiques, C.P. 6128, Succursale Centre-Ville, Pavilion Marie-Victorin, Montréal, Quebec, Canada H3C 3J7.
authors.forename: Virginie
authors.initials: V
authors.lastname: Roy
authors.forename: Marc
authors.initials: M
authors.lastname: Amyot
authors.forename: Richard
authors.initials: R
authors.lastname: Carignan
mesh_terms: D000818:Animals; D002170:Canada; D004784:Environmental Monitoring / Q000379:methods; D006863:Hydrogen-Ion Concentration; D008628:Mercury / Q000032:analysis*; D008767:Methylmercury Compounds / Q000032:analysis*; D009566:Nitrates / Q000032:analysis; D009573:Nitrites / Q000032:analysis; D009930:Organic Chemicals / Q000032:analysis; D010100:Oxygen / Q000032:analysis / Q000737:chemistry; D025341:Principal Component Analysis; D012044:Regression Analysis; D012377:Rodentia; D014867:Water; D014874:Water Pollutants, Chemical
chemical_list: D008767:Methylmercury Compounds; D009566:Nitrates; D009573:Nitrites; D009930:Organic Chemicals; D014874:Water Pollutants, Chemical; D014867:Water; D008628:Mercury; D010100:Oxygen