ARCTIC CHAR OTOLITH RECORDS OF RECENT LIMNOLOGICAL CHANGE IN HIGH ARCTIC LAKES
Arctic lakes have been undergoing significant physical and chemical changes in recent years due to climate warming and permafrost thaw. These changes have the potential to impact organisms residing in these environments such as Arctic Char (Salvelinus alpinus) which represent the top predatory fish in Arctic lakes. Otoliths, the inner ear bones of fish, offer a method to monitor these impacts through chemical analysis of their annual rings. However, not only are long-term limnological records in the Arctic limited, but the impacts of climate-driven change on Arctic aquatic ecosystems are not well known. This research investigates a long-term record (2003-16) of the physiochemical properties of two High Arctic lakes at the Cape Bounty Arctic Watershed Observatory on Melville Island, Nunavut. Additionally, 2013 and 2015 otoliths were analyzed to investigate elemental changes associated with limnological and catchment change. Results indicate that both lakes underwent significant chemical change following a catchment permafrost disturbance episode in 2007 that caused widespread slope disturbances and a deep seasonal active layer thaw. Both lakes have seen increased solute loads, most notably a 500% and 300% increase in water column SO42- in the West and East Lakes, respectively. Ionic ratios indicate that the source for the SO42- is compositionally similar to disturbed catchment streams. In addition, the West Lake has seen substantial and sustained increases in turbidity associated with internal subaqueous slumps and similar effects are absent from the East Lake. Hence, the synchronous change in solute loading to the lakes reflects increased contributions from the catchment due to deep active layer development. Otolith analysis reveals an abrupt increase in Mg and a decrease in Ba in fish from both lakes. Results further show that not only is the otolith chemistry statistically different within each individual fish from beginning to end of life, but also between the two lakes. These chemical changes are thought to reflect differential responses to multiple environmental stressors including the chemical and physical changes in the lakes. Collectively, these studies demonstrate the rapid threshold responses of Arctic lakes and highlights the fact that these physiochemical changes have implications for the whole aquatic ecosystem.
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