The influence of calcium decline and climate change on the cladocerans within low calcium, circumneutral lakes of the Ex
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PRIMARY RESEARCH PAPER
The influence of calcium decline and climate change on the cladocerans within low calcium, circumneutral lakes of the Experimental Lakes Area Adam Jeziorski • Andrew M. Paterson • Ian Watson • Brian F. Cumming • John P. Smol
Received: 10 June 2013 / Revised: 3 September 2013 / Accepted: 14 September 2013 / Published online: 25 September 2013 Ó Springer Science+Business Media Dordrecht 2013
Abstract Calcium (Ca) concentrations of many softwater lakes on the Canadian Shield have been in decline for decades as a response primarily to regional acid deposition and repeated cycles of forest harvesting. These Ca declines are of ecological interest, as many lakes have fallen to Ca levels detrimental to the fitness of ecologically important Ca-rich cladoceran taxa such as Daphnia pulex. However, distinguishing the impacts of reduced Ca from acidification (i.e., decreasing pH) on Ca-demanding fauna has proven difficult due to strong correlations between pH and Ca in softwater lakes. Here, we examine cladoceran sedimentary assemblages from low Ca lakes (mean present-day Ca \ 2.0 mg l-1) in the Experimental Lakes Area (ELA) of Ontario, Canada, where Ca concentrations have declined since the 1980s, despite being closed to forestry and remote from (i.e., not downwind of) major sources of acid deposition.
Handling editor: Karl E. Havens A. Jeziorski (&) I. Watson B. F. Cumming J. P. Smol Paleoecological Environmental Assessment and Research Lab, Department of Biology, Queen’s University, Kingston, ON K7L 3N6, Canada e-mail: [email protected] A. M. Paterson Ontario Ministry of the Environment, Dorset Environmental Science Centre, 1026 Bellwood Acres Road, Post Office Box 39, Dorset, ON P0A 1E0, Canada
Differences between present-day and pre-industrial cladoceran assemblages were greatest among planktonic taxa, including Bosmina spp. and Holopedium glacialis. However, daphniid remains were present in only three of the ten study lakes with minimal directional trends. Overall, in these ELA lakes, daphniid abundance was low historically, and impacts possibly attributable to Ca declines have been obscured by the effects of regional climate warming. Keywords Lakes Calcium (Ca) pH Cladocera Zooplankton Experimental Lakes Area (ELA)
Introduction Declines in Ca concentration have been observed in large numbers of softwater lakes on the Canadian Shield (Stoddard et al., 1999; Jeziorski et al., 2008), and are generally attributed to depletion of the base cation reservoirs in watershed soils at rates faster than their replenishment via geochemical weathering of the underlying bedrock, as well as reduced leaching rates from these reservoirs (Kirchner & Lydersen, 1995; Houle et al., 2006). Two principal mechanisms are typically responsible for base cation depletion in the catchments of softwater boreal lakes: biomass removal via repeated timber harvesting cycles (Watmough & Dillon, 2003), and the mobilization of base cations by acid deposition (Likens et al., 1996). The impact of
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