Arseneau, KMA; Driscoll, CT; Cummings, CM; Pope, G; Cumming, BF
Researchers are increasingly tasked with identifying
biological recovery targets as ecosystems recover from anthropogenic stressors. Attempts to
define such recovery targets are often hampered by two problems: (1) a lack of long-term
monitoring data; and (2) the confounding influence of multiple stressors, especially regional
stressors like climate warming. Paleolimnological studies of minimally disturbed reference sites
can help address both these issues. Using paleoecological techniques, researchers can isolate the
long-term impact of regional stressors like climate change on species assemblages largely
independent of other confounding stressors such as acidification, eutrophication, and land-use
change, thereby providing a framework to assess biological recovery in lakes that are recovering
from acid deposition or other stressors. This manuscript provides a theoretical paleolimnological
framework for the use of reference lakes in studying biological recovery from acidification, and
provides an example of how assemblages of scaled-chrysophytes have changed in Adirondack-region
reference lakes (NY, USA) from pre-ca. 1900 to present. The thirty-one reference lakes were
selected from a database of over 1400 lakes, using criteria to minimize the influence of
acidification, eutrophication, road-salt seepage, and piscivore introductions. As such, these
lakes provide a unique opportunity to examine the effects of regional stressors in the Adirondack
ecological region, which can inform biological recovery in lakes that have acidified
historically. The modern chrysophyte assemblages from the reference lakes were significantly
related to modern limnological variables including pH, dissolved organic carbon and ionic
concentration as well as important physical variables including lake depth, which were used to
help understand changes in the chrysophyte assemblages over the last century. Changes in
chrysophyte assemblages from pre-1900 to present were determined by comparing the modern surface
assemblages to a sediment interval representing pre-1900 conditions, revealing significant
increases in the abundance of colonial chrysophyte taxa, especially S. petersenii, S.
sphagnicola, and S. echinulata, and corresponding decreases in the relative abundance of many
Mallomonas taxa. These changes suggest that regional warming and/or oligotrophication have
influenced the species assemblages of minimally disturbed reference lakes, suggesting that lakes
currently recovering from acidification are unlikely to return to their pre-disturbance
assemblages.