Decoupling of chemical and biological recovery from acidification in a montane lake, Vermont, USA

Lakes in the northeast United States are recovering from acidification, but it is unclear if species assemblages will return to pre-acidification conditions, in light of new, interacting climate change pressure. This study explored the impact of past acidification on Beaver Pond, an acid-impaired lake in Vermont, USA. We analyzed long-term seasonal trends in water chemistry data collected by the Vermont Department of Environmental Conservation to assess the extent of acidification and subsequent chemical recovery since the beginning of the monitoring period (1985-present). Biological recovery in acidified waterbodies often lags chemical recovery, as changes in community composition occur at a slower rate. To assess both, we integrated analysis of long-term changes in lake physical and chemical characteristics (pH, dissolved organic carbon, Secchi depth, surface water temperature) with a paleolimnological analysis to analyze shifts in sediment diatom community composition and changes in sediment geochemistry in the past similar to 180 years. Long-term water chemistry analysis indicates that both pH and DOC concentration in Beaver Pond increased over the monitoring period, and that the greatest rate of increase for both variables occurred between 2001 and present. We identified shifts in sediment diatom assemblages from acid-sensitive taxa (D. stelligera, L. affinis) pre-acidification, to acid-tolerant taxa (Eunotia spp.) during acid deposition, and different acid-sensitive taxa (F. rhomboides, B. brebissonii) in the post-acidification recovery period. Together, paleolimnological and modern data in our study indicate that Beaver Pond is experiencing chemical and biological recovery from acid deposition, though diatom communities in the recovery period differ in composition from those in the lake prior to acidification.

Automated summary

Lakes in the northeast United States are recovering from acidification, but the effects of climate change on species assemblages are uncertain. This study examined the impact of past acidification on Beaver Pond in Vermont, USA, using long-term water chemistry analysis and paleolimnological analysis. The results suggest that Beaver Pond is experiencing chemical and biological recovery from acid deposition, although the diatom communities in the recovery period differ from those before acidification.