Zooplankton Community Responses during Recovery from Acidification in Little Rock Lake, Wisconsin

Abstract

Follow-up studies after whole-ecosystem-stress experiments can provide important insights into the recovery process itself and into basic ecosystem properties. We report here on zooplankton community recovery during the first 5 years following the experimental acidification of Little Rock Lake, Wisconsin, U.S.A. Acidity in the lake's treatment basin returned quickly to near pre-manipulation levels. Zooplankton population shifts, however, did not support our hypothesis that species that had increased in abundance with acidification would persist and resist the return of the pre-manipulation community. The three species that had proliferated most dramatically under low pH conditions-Daphnia catawba, Tropocyclops extensus, and Keratella taurocephala , returned close to their originally low, pre-acidification population levels during the early stages of acid recovery. Some species that had been 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 differ-ent from that which had occurred prior to the imposition of acid stress.

Multiple stresses from a single agent: Diverse responses to the experimental acidification of Little Rock Lake, Wisconsin

“…Responses during acidification largely paralleled patterns observed in several other acidification experiments and in lakes that were acidified by atmospheric deposition (Schindler et al 1991). Recovery patterns exhibited less in common with other acidified systems particularly in that the rate of return to preacidified chemical conditions in LRL seemed particularly rapid (Frost et al 1998). Delayed biological recovery in LRL, however, suggests that such recovery may be slow in most stressed systems.…”

“…Acidified lakes may be particularly sensitive to further environmental stresses because ecosystems that have been subjected to one stress may be more sensitive, in general, to additional stresses that follow the first. Although general ecosystem function appears to have been relatively insensitive to a stress in several different situations (e.g., Schindler 1987;Howarth 1991;Lawton and Brown 1993;Frost et al 1995), this might not indicate that system processes are resistant to a sequence of different stresses or even to repeated impacts of the same stress. In LRL, ecosystem processes were unaffected by acidification despite the loss of several species because of complementary responses by remaining species .…”

“…For zooplankton, we assessed the abundance and biomass of crustacean and rotifer species (Frost and Montz 1988). Animals reported here were sampled at 0, 4, and 8 m in the treatment basin and 0, 4, and 6 m in the reference basin with a Schindler-Patalas trap with a 53-m mesh bucket, and estimates were made of the average population throughout the entire lake basin.…”

Geographic and Environmental Sources of Variation in Lake Bacterial Community Composition

“…Another important source of variation in this study was pH, which has been implicated by other workers in studies of aquatic bacterial communities (44,47,53) and communities of organisms likely to influence BCC (21,24,25,38). pH may reflect the influence of geology on water chemistry and is itself an important control of the biogeochemical transformations which can take place in a given environment.…”

Mechanisms underlying recovery of zooplankton in Lake Orta after liming

“…Persistence was also low after liming intervention, until the end of 1990s when pH was neutral and concentration of metals abated; therefore, during this period chemical conditions cannot explain our results. Certainly biological recovery occurs gradually and typically lags behind chemical recovery (Keller et al, 2002;Frost et al, 1998;Keller and Yan, 1991;Locke et al, 1994).…”