The acidification and metal contamination of freshwater resources are major environmental concerns in many areas, with Sudbury (Ontario, Canada) having been amongst the most severely impacted. Many scientific investigations have examined the effects of these environmental stressors on aquatic systems, but relatively little is known about the biological recovery process following smelter emission reductions. Therefore, paleolimnological techniques were utilized to determine if diatom and scaled chrysophyte assemblages have recovered toward their pre-disturbance conditions as a result of reduced anthropogenic inputs. Pre-industrial algal assemblages were primarily dominated by circumneutral to alkaline and pH-indifferent taxa. However, there was a shift toward acid-tolerant species in all study lakes with the onset of open pit roasting and smelting operations. Coinciding with emission reductions, scaled chrysophyte assemblages in two of the three study sites have shown evidence of biological recovery. Given the population growth of the city of Sudbury over the last century, and the lack of scientific information regarding cultural eutrophication trends in the region, paleolimnological techniques were also used to track long-term biological changes within diatom assemblages related to cultural disturbances. Historically, oligotrophic diatom taxa primarily dominated the algal assemblages in each of the four study lakes. With the onset of urban environmental stressors there was a shift toward taxa which thrive in more productive systems. In addition, diatom assemblages appear to track increased lakewater pH through time. Finally, geochemical analysis tracked the increase in copper and nickel concentrations in lake sediment with the onset of open pit roasting and smelting activities and the subsequent decline in concentration with emission controls. Metal concentrations in recently deposited lake sediments remain elevated compared to pre-industrial concentrations. Paleolimnological studies comparing pre- and post-disturbance algal assemblages are of interest to lake managers as these data will aid in setting realistic mitigation targets for freshwater systems impacted by acidification, cultural eutrophication, and metal contamination, and will help gauge biological recovery mechanisms. Furthermore, this study provides insight in to the role other environmental stressors (e.g., climate change) may play in the biological recovery process. / Thesis (Master, Biology) -- Queen's University, 2008-07-10 12:04:59.828

In response to sulphur dioxide emission reductions in North America and Europe, there has been a recent shift in research focus towards understanding ecosystem recovery. Evidence for reversibility in the effects of acidification on lake ecosystems within North America has been, for the most part, constrained to a single locality (Sudbury, Ontario). Lakes in a fume-kill area near Wawa, Ontario, present a new and rare opportunity for studying potentially rapid chemical and biological recovery patterns from extreme acidification. Several lakes acidified (pH ~3) during a period of local iron sintering from 1939 to 1998, and although minimal historical data are available, striking biological recovery has recently been observed. This study used paleolimnological techniques to track diatom (class Bacillariophyceae) responses to historical water quality changes in five fume-kill lakes near Wawa. Prior to the onset of iron sintering, the sediment-recorded diatom assemblages were dominated by species that are typically found in circumneutral or slightly alkaline lakes. Following the known occurrence of lake acidification, there was a striking shift in the sediment record towards dominance by acid- and metal-tolerant species. Water quality of the fume-kill lakes has since improved (i.e. pH has increased from ~3 to ~7 and metal concentrations have decreased). In four of the five lake cores, this was reflected by a decrease in the relative abundance of acid-tolerant species. Surprisingly, diatom communities were not progressing towards pre-disturbance species assemblages. Factors impeding the return of native species might include metal enrichment in surface sediment and potentially altered lake thermal regimes. Documenting and understanding recovery trajectories is necessary to help lake managers evaluate policy decisions regarding the efficacy of emission reduction programs and mitigation measures. This thesis provides evidence from one location in addition to Sudbury that the ecological effects of severe lake acidification can be reversed if SO2 emissions are sufficiently reduced. It also further demonstrates the complexity of recovery patterns in acidified and metal-contaminated lakes. / Thesis (Master, Biology) -- Queen's University, 2009-04-26 18:38:20.58

Freshwater ecological issues are increasingly being recognized within the context of multiple stressors, even though relatively little is known about the limnological and biological consequences of the interactions between various environmental impacts. Moreover, long-term monitoring data are often lacking. To help address these issues, the overall goal of this thesis was to use paleolimnological approaches to document how multiple environmental stressors have altered limnological communities in south-central Ontario lakes. During the last two centuries, Ontario lakes have been subjected to varying intensities of different environmental impacts, including increases in shoreline residential development, forest clearance and regrowth, the deposition of strong acids via the atmosphere, invasion by non-indigenous species, and climate change. I used multiple paleolimnological approaches to: 1) demonstrate how multiple natural and anthropogenic stressors have affected biological assemblages across lakes in the Muskoka-Haliburton region of south-central Ontario, and 2) reconstruct the limnological histories of four lakes from Algonquin Park that have recorded the near complete extirpation of native crayfish species. In the Muskoka-Haliburton lakes, I assessed the extent of limnological changes that have occurred during the past ~15 years by resampling lakes from an earlier survey, using identical paleolimnological methods. Limnological monitoring data document that, since 1992, the lakes have experienced declines in lakewater calcium and SO4 concentrations, while pH declined marginally; in contrast dissolved organic carbon, silica and Total Kjeldahl Nitrogen increased. Marked regional increases in planktonic diatom taxa, including Cyclotella stelligera, Asterionella formosa and Fragilaria crotonensis, occurred in many lake systems, while colonial scaled chrysophyte algae have undergone a widespread decline in favour of unicellular forms (i.e., Mallomonas spp.), driven by interactions between resource limitation and climate change. In the Algonquin Park study lakes, crustacean zooplankton remains revealed a marked decline in daphniid species with high Ca requirements, in favour of smaller Bosmina spp., while diatom and chrysophyte analysis suggest varying degrees of industrial acidification in the four study lakes. The paleolimnological data suggest that the crayfish decline may have began prior to the long-term monitoring record, likely as a result of declines in pH and lakewater Ca related to atmospheric acid deposition. / Thesis (Ph.D, Biology) -- Queen's University, 2012-09-27 12:53:20.518

In protists a biodiversity hotspot could be defined as region with exceptionally high ratio of local to global species diversity. In 2012 Aquitaine (France) was revealed to represent a hotspot of Synurales (lineage within silica-scaled chrysophytes). To investigate how the diversity is distributed and where the species are hidden, samples from 42 lakes were collected during spring peak of Chrysophyte occurrence (from March 27th to March 31st ). Samples were taken in two microbiotopes - phytoplankton and metaphyton. Metaphyton was represented by different substrates (aquatic plants). I identified seventy-six species from genera Mallomonas and Synura, which confirmed Aquitaine to be a hotspot. In this thesis, I investigated ecological drivers of chrysophytes diversity and community structure. The chrysophyte diversity was driven mostly by mutual impact of pH and conductivity, north-south gradient of lakes location and sampled microbiotopes. Number of identified species increased with increasing pH and conductivity, with increasing size of waterbody and with location of the lake more towards the South. More taxa were revealed from metaphyton (77) than from plankton (61), substrates played an important role. Lakes in Aquitaine are rich in different species of aquatic plant, which immersed create...