Search

Throughout much of the 20th century, unprecedented industrial emissions have led to widespread acidification of regions in North America and Europe and, as lake water pH dropped, aquatic ecosystems have experienced dramatic declines in biodiversity. International emission‐control agreements have led to sweeping increases in lake pH, however acid‐structured zooplankton communities still persist in many lakes. Concomitantly, calcium concentrations have been declining as a legacy of acidification and are approaching or have reached concentrations that could represent a barrier to the re‐establishment of zooplankton communities similar to those in non‐acidified or circumneutral reference lakes. To understand how declining calcium may influence the re‐establishment of zooplankton in acid‐damaged lakes we manipulated calcium and pH using a factorial in‐lake mesocosm experiment and assessed their individual and combined effects on a regionally diverse zooplankton assemblage. We found that the impacts of low calcium on zooplankton species were similar to those of acidification and, consequently, may prevent the recovery of acid‐structured communities. Abundance of the larger bodied and acid‐sensitive Daphnia pulex/pulicaria increased in high pH treatments, albeit nonsignificantly yet, by the end of our experiment, only two individuals were sampled among our 10 low calcium enclosures. In contrast, small acid‐tolerant cladocerans, such as Daphnia catawba, Daphnia ambigua, and eubosminids maintained significantly higher abundances in low calcium treatments relative to all other treatment combinations. Although we did not detect an effect of calcium on mean body size, the disproportionately high abundance of small cladocerans in low calcium treatments resulted in low calcium communities with higher overall abundance and lower cladoceran evenness. Our results, along with a landscape comparison demonstrating parallel changes in zooplankton relative abundance from 34 historically acidified lakes, suggests that declining calcium will be an important, on‐going factor that may limit the recovery of zooplankton, despite regional improvements in lake pH. [ABSTRACT FROM AUTHOR]

Assessing biological recovery in damaged aquatic environments requires the consideration of multiple spatial and temporal scales. Past research has focused on assessing lake recovery from atmospheric or catchment disturbance at regional or catchment levels. Studies have also rarely considered the influences of adjacent terrestrial characteristics on within-lake habitats, such as subcatchment delta confluences. We used Hyalella azteca, a ubiquitous freshwater amphipod, as a sensitive indicator to assess the importance of local subcatchment scale factors in the context of multiscale lake recovery within the metal mining region of Sudbury, Canada following a period of major reductions in atmospheric pollution. At the regional scale, data from repeated surveys of 40 lakes showed higher probabilities of H. azteca occurrence with higher lake water conductivity, alkalinity, and pH and lower metal concentrations. The importance of metals decreased through time and the importance of higher conductivity, alkalinity, and pH increased. At the subcatchment scale, a subset of six lakes sampled across a colonization gradient revealed higher H. azteca abundances at subcatchment delta sites than non-delta sites in early colonization stages, and that abundance at delta sites was correlated with both within-lake habitat and terrestrial subcatchment characteristics. For example, wetland cover reduced the strength of positive associations between H. azteca abundance and macrophyte density. A single lake from this subset also revealed higher abundances at delta sites associated with higher concentrations of terrestrial organic matter and larger subcatchments. Our results demonstrate that factors affecting recovery can change with the scale of study, and that managing terrestrial-aquatic linkages is important for facilitating recovery processes within damaged lake ecosystems. [ABSTRACT FROM AUTHOR]

Anthropogenic acidification has affected biota in thousands of lakes in eastern North America and Europe. To measure the degree and extent of biological recovery following pH recovery in acidified lakes, many studies have assessed changes occurring in acid-damaged zooplankton communities. In this review we synthesize studies of zooplankton recovery from regions severely affected by acidification. In doing so, we provide a critical overview of: (1) the design of studies used to detect recovery; (2) the status of communities in acidified regions; and (3) our current understanding of the factors that limit recovery. The design of most studies assessing zooplankton recovery fall into three categories based on their selection of data to be used for recovery benchmarks: (1) historical; (2) reference-lakes; and (3) temporal. Within these study designs, the most commonly used metrics include species richness, indicator species, and relative species abundances. Many studies have used species richness as the sole indicator of recovery; however, we argue that additional metrics should be considered in analyses to make conclusions more robust. Studies conducted in eastern North America and Northern Europe have demonstrated significant, though often incomplete, recovery of zooplankton communities in lakes that reach a pH > 6.0. Data collected in central Europe indicate little recovery in the heavily affected Bohemian Forest lakes, but complete recovery of species richness in the moderately acidified Tatra Mountain lakes. Factors limiting biological recovery, including slow chemical recovery, dispersal limitation, and community resistance, vary in importance among and within regions, suggesting that region- and lake-specific management approaches may be required. [ABSTRACT FROM AUTHOR]

Community responses to acidification and recovery of boreal lakes are poorly understood, particularly after several years of recovered lake-water pH (pH ≥ 6.0). We tested if zooplankton communities in two circumneutral lakes with different acidification histories were adapted to historical lake-water pH with a reciprocal transplant field enclosure experiment. A second objective was to assess the influence of local environments on zooplankton survival and abundance. Differences in acid tolerance could be detected in some zooplankton among the two lakes with different acidification histories — zooplankton from acid-recovering Carlyle Lake, recovered to pH ≥ 6.0 for 6 years were more speciose and maintained higher total abundance at pH 4.8 than the community from a buffered lake. The zooplankton community in this historically acidified lake was comprised of two dominant species with acid-adaptable tolerances, Holopedium gibberum and Leptodiaptomus minutus. High establishment of transplanted zooplankton in our experiment has important implications for the recovery of zooplankton communities because it suggests that local conditions are suitable for most species in acid-recovering lakes with pH ≥ 6.0 and that other factors such as dispersal limitation and biotic interactions may be impeding recovery. [ABSTRACT FROM AUTHOR]

The article investigates the roles of local environmental conditions and dispersal limitation in crustacean zooplankton recovery from acidification in Swan Lake, Ontario, a historically acidified, metal-contaminated lake. Mesocosm and emergence trap experiments were conducted. The preindustrial pH of the lake was estimated to be between 5.6 and 6.1 but sulphur dioxide emissions from nearby smelters caused a reduction in pH to 4.0 in 1977. Three colonist species-C. b. thomasi and S. ore-gonensis and, to a lesser extent,. M. edax-were not affected by the pH treatment in the enclosure experiment but were reduced in abundance by the resident zooplankton community indicating an effect of local biotic conditions. The results suggests that local and regional processes are instrumental in zooplankton community assembly. This indicates that a multifaceted management solution will be required for complete restoration of acidified ecosystems. Recovery of some - taxa, such as Ceriodaphnia and Daphnia, will be affected without further reductions in acid deposition and subsequent increases in take pH.