Zooplankton community responses during recovery from acidification in Little Rock Lake, Wisconsin

Follow-up studies after whole-ecosystem-stress experiments can provide impo rtant insights into the recovery process itself and into basic ecosystem pr operties. We report here on zooplankton community recovery during the first 5 years following the experimental acidification of Little Rock Lake, Wisc onsin, U.S.A. Acidity in the lake's treatment basin returned quickly to nea r pre-manipulation levels. Zooplankton population shifts, however, did not support our hypothesis that species that had increased in abundance with ac idification would persist and resist the return of the pre-manipulation com munity. The three species that had proliferated most dramatically under low pH conditions-Daphnia catawba, Tropocyclops extensus, and Keratella tauroc ephala, returned close to their originally low, pre-acidification populatio n levels during the early stages of acid recovery. Some species that had be en reduced during low pH conditions, such as Diaptomus minutus and Daphnia dubia, did not recover to pre-manipulation levels. Overall, the zooplankton community in the treatment basin exhibits little similarity to that in the reference basin, a condition quite different from that which had occurred prier to the imposition of acid stress.