Contrasts between dystrophic and clearwater lakes in the long‐term effects of acidification on cladoceran assemblages

Abstract

Summary 1. Most studies on zooplankton responses to acidification have focused on clearwater lakes with a dramatic acidification history. The role of dissolved organic carbon (DOC) in moderating zooplankton responses to acidification in naturally acidic, dystrophic lakes is less well understood and is partially impeded by a lack of baseline data. 2. Cladocera leave identifiable remains preserved in lake sediments that can be used to provide information on pre‐industrial species assemblages and their responses to environmental stressors such as acidification. Therefore, we used palaeolimnological approaches to track cladoceran assemblage responses to acidification since c.1850 (inferred from sedimentary diatom assemblages) in three acidified lakes in Kejimkujik National Park (Nova Scotia, Canada) that differ markedly in DOC content. These include two highly dystrophic lakes (Kejimkujik and Pebbleogittch lakes), and one clearwater lake (Beaverskin Lake). 3. In dystrophic Pebbleogittch Lake, an increase in the acid‐tolerant, jelly‐clad, pelagic taxon Holopedium glacialis occurred coincident with diatom‐inferred pH (DI‐pH) declines, but no other notable cladoceran assemblage shifts occurred. Similarly, Cladocera assemblages did not appear to respond to lakewater acidification in dystrophic Kejimkujik Lake. 4. In contrast, in the clearwater Beaverskin Lake, several observed shifts in cladoceran assemblage corresponded to DI‐pH declines, including an increase in the proportion of littoral taxa and an increase in Hill’s N2 species diversity. This may indicate increased water clarity as a result of acidification‐related decreases in DOC, which may have enhanced growth of emergent aquatic macrophytes and improved visibility for planktivorous fish, leading to increased predation on pelagic taxa. Species shifts within the littoral assemblage of Beaverskin Lake may reflect the differing tolerances of littoral taxa to low pH and aluminium toxicity. 5. Overall, our results suggest that cladoceran assemblages in naturally acidic, dystrophic lakes may be resilient against additional pH declines related to industrial emissions of acidifying agents, as dystrophic lakes are less vulnerable to increased aluminium toxicity and acidification‐induced increases in water clarity and often have a pre‐industrial cladoceran assemblage already adapted to acidic conditions.

Establishing past environmental conditions and tracking long-term environmental change in the Canadian Maritime provinces using lake sediments

“…Although the regional "top-bottom" analysis of cladoceran subfossils suggested a decrease in the relative abundance of littoral cladocerans in KNP (Korosi and Smol 2012a), analysis of detailed sediment cores from three KNP lakes, including two humic (Pebbleogittch and Kejimkujik lakes) and one clearwater (Beaverskin Lake) lake, did not show significant declines in littoral cladocerans (Korosi and Smol 2012b). In fact, the relative abundance of littoral species actually increased in Beaverskin Lake, suggesting a potential acidification-mediated increase in water clarity (Korosi and Smol 2012b). This suggests that, while acidification may have negatively affected the littoral cladocerans in some KNP lakes, the Environ.…”

“…Downloaded from www.nrcresearchpress.com by UNIVERSITY OF PITTSBURGH on 12/01/14 response of littoral cladocerans to acidification may vary between lakes. Interestingly, while a decrease in Hill's N2 diversity (Hill 1973) of the diatom sedimentary assemblage was observed for Kejimkujik Lake with acidification (Ginn et al 2007d), no decrease in Hill's N2 diversity for cladoceran sedimentary assemblage was observed with acidification, and Hill's N2 diversity actually increased in Pebbleogittch and Beaverskin lakes (Korosi and Smol 2012b). In these lakes, there appeared to be no negative impact of pH declines on cladoceran species diversity.…”

“…Holopedium shows a clear preference for low-pH lakes (Hessen et al 1995;Korosi and Smol 2011), and this taxon's increase in KNP could be related to surface-water acidification. To assess the timing of the appearance of Holopedium and relate it to acidification, cladoceran subfossils were later analyzed in detailed sediment cores from three lakes in KNP (Korosi and Smol 2012b) and one lake in nearby Bridgewater (Korosi and Smol 2012c). In Pebbleogittch Lake (KNP), the appearance and increase in Holopedium corresponded to DI pH declines; but in Kejimkujik Lake (KNP), the increase in Holopedium occurred much later, postacidification (Korosi and Smol 2012b).…”

“…To assess the timing of the appearance of Holopedium and relate it to acidification, cladoceran subfossils were later analyzed in detailed sediment cores from three lakes in KNP (Korosi and Smol 2012b) and one lake in nearby Bridgewater (Korosi and Smol 2012c). In Pebbleogittch Lake (KNP), the appearance and increase in Holopedium corresponded to DI pH declines; but in Kejimkujik Lake (KNP), the increase in Holopedium occurred much later, postacidification (Korosi and Smol 2012b). Similarly, Holopedium appeared in Hirtle Lake (Bridgewater), a lake that never acidified, in the 1990s (Korosi and Smol 2012c).…”

“…Similar increases in Holopedium have been observed in acid-sensitive lakes in southcentral Ontario, a region that is subjected to similar anthropogenic stressors as KNP, including acidification, calcium decline, and climate change (Jeziorski et al 2012). Although the regional "top-bottom" analysis of cladoceran subfossils suggested a decrease in the relative abundance of littoral cladocerans in KNP (Korosi and Smol 2012a), analysis of detailed sediment cores from three KNP lakes, including two humic (Pebbleogittch and Kejimkujik lakes) and one clearwater (Beaverskin Lake) lake, did not show significant declines in littoral cladocerans (Korosi and Smol 2012b). In fact, the relative abundance of littoral species actually increased in Beaverskin Lake, suggesting a potential acidification-mediated increase in water clarity (Korosi and Smol 2012b).…”