Effects of climate change on mercury concentrations in Arctic char (Salvelinus alpinus) in the high Arctic.

摘要

This thesis is an investigation of linkages of climate change and mercury concentrations in landlocked Arctic char and underlying food webs in Canadian Arctic lakes. Although the neurotoxin mercury is globally present in all environments, temporal and spatial trends in aquatic biota are often inconsistent, or do not exist for remote environments. Knowledge gaps include the influence of abiotic factors, possibly climate, and food web parameters on mercury accumulation in top predators. Furthermore, anthropogenic and natural mercury present in the environment are not well differentiated. To address these research needs, we collected landlocked Arctic char from 27 systems and food web organism from 18 lakes, and recorded abiotic lake characteristics expected to influence mercury cycling. Total mercury (THg) and monomethylmercury (MeHg) concentrations, and stable isotopes of carbon (delta13C), nitrogen (delta15N), and mercury (deltaxHg) were determined. Relationships among these measures and with environmental characteristics were investigated.;A temporal trend of mercury in Arctic char (muscle tissue) from the largest lake in the Canadian High Arctic from an existing dataset and newly collected char was investigated. Two abundant char morphotypes from Lake Hazen differed in mercury concentrations, and the resulting variability was accounted for using a statistical adjustment. Mercury concentrations did not change over the 16-year period (1990-2006), which is consistent with nearby measurements of gaseous elemental mercury at Alert (Nunavut, Canada).;Food chain lengths (FCL) of 18 lakes were characterized, biomagnification of mercury was investigated using delta15N, and results compared among regions. Food web biomagnification was confirmed using trophic magnification factors (TMFs) in 18 Arctic char bearing lakes (TMFs 3.5 -- 64.3). Benthic coupling was apparent from char delta13C signatures that resembled delta13C in chironomid midges. TMFs and FCL partly explained THg in adult char, but no latitudinal or other climatic trend was apparent. Mercury concentrations in adult Arctic char were positively related to catchment-to-lake area, and intra-regional, and regional differences in Hg in Arctic char were determined. No climatic factor we investigated was found to affect Hg in char directly; however, predicted climatic changes could affect THg in char indirectly through changes in the catchment (such as melting of permafrost).;Stable isotope ratios of mercury revealed region specific mass-independent fractionation (MIF) of up to ∼ 4.5 ‰ in Arctic char, which did reflect sediment ratios with a constant offset (MIF-factor). High MIF in zooplankton possibly reflected mercury assimilated from the water column. Char from Lake Pingualuk, known pelagic feeders, had high MIF, possibly reflecting an atmospheric Hg signal.