PARENT SESSION
Oral Session # 51: Limnology II: Plankton; Carbon.
Presiding: K Forshay
Wednesday, August 6. 1:30 PM to 5:00 PM, SITCC Meeting Room 101.
The effects of intra-annual pH fluctuations on recovering zooplankton communities in Swan Lake, Sudbury, Ontario.
Dawson, Amy1, Arnott, Shelley1, 1 Queen's University, Kingston, Ontario
ABSTRACT- Very little is known about the role that environmental variability plays in the recovery of damaged ecosystems. The environmental variability characterized by pH variability within one year can be very high in lakes recovering from historical acid deposition. Swan Lake, a small lake that was historically acidified by mining-related sulphur dioxide emissions, is beginning to show chemical recovery (i.e. increased mean annual pH) in response to reduced emissions. Despite improvements in water quality, there has been little recovery of the biota. One explanation is that pH fluctuations prevent re-colonization of sensitive species. These environmental fluctuations may play a significant role in the recovery of species that have been extirpated by historic stresses. To test whether or not short term pH fluctuations influence the ability of a zooplankton community to recover from acidification, pH levels were experimentally manipulated within large epilimnetic enclosures (2800L). A two-factor experimental design was established to test the effects of small magnitude (pH fluctuation from 6.5 to 5.8) versus large magnitude (pH fluctuation from 6.5 to 5.0) pulses and short frequency (3-day) versus long frequency (9-day) pH pulses. Several species showed decreased abundance for the large magnitude pulse (lowered to 5.0), when compared to the small pulse (lowered to 5.8), but the frequency of the fluctuation had no effect. Other species showed a similar response to magnitude, but also responded positively to the frequency of the pulse (i.e. higher abundance in 9-day treatments). Finally, pulse magnitude and frequency had an interactive effect on some species. These different species responses to short term pH fluctuations suggest that, in lakes recovering from acidification, this variability may influence the recovery trajectory of individual species, shaping zooplankton community dynamics and ultimately recovery.
Key words: biological recovery, intra-annual variability, zooplankton, acidification