Thesis (doctoral)--Universität Potsdam, 2002. / "April 2003"--P. [2] of cover. Lebenslauf. Includes bibliographical references (p. 118-133). Also available via the World Wide Web.

Recent anecdotal evidence has suggested that Lake Diefenbaker, a large reservoir in southern Saskatchewan, Canada, has been experiencing an increased frequency and severity of algal blooms, suggesting significant alterations in water quality. Due to limited historical water quality monitoring, a paleolimnological investigation of Lake Diefenbaker sediments was conducted in order to interpret spatial and temporal trends in the physicochemistry of sediment cores collected from mid-channel locations along a spatial gradient. Total phosphorus and three sediment species of phosphorus (apatite inorganic phosphorus, non-apatite inorganic phosphorus (NAIP) and organic phosphorus (OP) were measured along the vertical profile of the cores to interpret nutrient loading trends. Trends in historical primary productivity were inferred based on total organic carbon, total nitrogen, δ15N values and the organic carbon to nitrogen (C:N) ratios. In addition, sub-fossil biological remains of diatoms and chironomid larvae were isolated from selected subsections of the sediment cores and identified to assess shifts in community compositions and to infer historical changes in reservoir water quality conditions. Up-reservoir sampling locations showed consistent concentrations of total phosphorus and the three species of phosphorus, organic carbon, nitrogen, δ15N values and C:N ratios in the vertical profile of collected sediment cores. This suggested relatively consistent nutrient loading and primary production in the up-reservoir regions for the period represented by the core profiles. Down-reservoir sediment cores showed an increasing trend in total phosphorus concentration, mainly in the more biologically available NAIP and OP fractions, and enrichment in organic carbon, nitrogen and 15N in more recently deposited sediments. This combined with a decreasing C:N ratio in more recent sediments suggests increased nutrient loading to the sediments and increasing primary productivity at down-reservoir sites. Strong correlations between sediment total organic carbon content and the more biologically available sediment phosphorus fractions (NAIP and OP) suggest that phosphorus deposition patterns are strongly influenced by primary productivity within the reservoir. The compositions of diatom and chironomid communities were consistent over time at up-reservoir locations, with Stephanodiscus parvus dominating the diatom communities and Procladius sp. dominating the chironomid communities. This suggests relatively stable and consistent trophic status and primary productivity in this region. Conversely, major shifts occurred in the diatom and benthic chironomid communities at down-reservoir locations. These shifts were consistent with typical reservoir ontogeny. A shift in dominance from Stephanodiscus parvus to Asterionella formosa, Tabellaria flocculosa and Stephanodiscus medius followed by a shift to Aulacosiera ambigua suggests an initial period of eutrophy, followed by a period of mesotrophy, and finally a transition into a more productive system in recent years. The increase in relative abundance of the chironomid tribe Tanytarsini suggests rising levels of organic matter sedimentation, likely due to increased autochthonous primary productivity. Low chironomid head capsule counts were observed at all locations within Lake Diefenbaker. Despite the low head capsule counts, a 10-day whole-sediment toxicity test using Chironomus dilutus, revealed that Lake Diefenbaker sediments, in proximity to two potential point sources of contamination (aquaculture and municipal discharge), as well as two reference locations, were not of toxicological concern. Despite the lack of toxicity associated with Lake Diefenbaker sediments, it was concluded that Lake Diefenbaker sediments are likely poor habitat for chironomids. This study suggests that primary productivity and nutrient status has remained relatively constant at up-reservoir locations for the period represented by the collected cores. This is likely due to up-reservoir locations being more riverine than down-reservoir regions, which results in increased turbidity causing phytoplankton populations to be light limited. Primary productivity appears to increase spatially with increased distance down reservoir, likely due to a gradual transition to more lacustrine environments, resulting in less turbidity and less light limitation. Temporally, down-reservoir locations appear to be showing increases in primary productivity and nutrient entrainment in sediments. This is likely a result of increased nutrient availability over time and entrainment of these nutrients in sediments at down-reservoir locations by primary producers.

Until recently it has been widely believed that significant anthropogenic influences on the environment began in Canada following the onset of European colonization. However, our paleolimnological data indicate that centuries prior to European settlement, ponds on Ellesmere and Bathurst Island were impacted by Thule Inuit whalers, whose activities altered nutrient levels in nearby ponds. Two Thule Inuit whaling sites were selected based on input from several archaeologists, to ensure good coverage of the Thule geographic range and proximity to freshwater ponds. Multiple independent paleolimnological proxies have been used to analyze a pond from Ellesmere Island, showing taxonomic shifts in diatoms assemblages coinciding with 1.5 - 2‰ shifts in d15N, during the period of Thule occupation (ca. 1000 – 1670 AD). Increases in the relative abundance of Amphora ovalis, indicate nutrient concentrations above average for the High Arctic. Elevated levels of nitrogen and phosphorus were observed in the pond indicating the continuing influence of nutrient inputs centuries after the abandonment of the camp. Meanwhile, on Bathurst Island, the orientation of the Deblicquy site, such that the large majority of the Thule nutrient inputs are focused towards one of our two study ponds, provided us with the opportunity to compare two ponds that are essentially identical with the exception of the degree of Thule influence. In our “impacted” site, a marked increase in Stephanodiscus minutulus, coincides with a 2‰ shift in d15N. While our a priori determined control site shows no major changes in geochemistry or algal composition. Previous research on Bathurst Island used water chemistry and surface sediment diatoms to construct a diatom-inferred total nitrogen model for Bathurst Island. However, this study was limited by excluding unbuffered, low pH sites which characterize the western half of Bathurst Island. By expanding the previous Bathurst Island dataset to include western sites, we have been able to construct a diatom-inferred pH model which will prove invaluable in future climate research in this region. Together, these three studies serve to highlight the sensitivity of freshwater ecosystems to relatively minor anthropogenic disturbances and represent some of the earliest known anthropogenic impacts on North American aquatic ecosystems. / Thesis (Master, Biology) -- Queen's University, 2007-12-20 15:20:46.342

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

Paleoclimatic research in the Canadian Arctic has increased in recent decades; however, there is still much to learn about the nature and extent of past climate change in this vast, environmentally sensitive region. This thesis uses diatom assemblages in dated lake sediment cores as proxy indicators to infer how climate has changed over the Holocene in two very different lakes in the central Canadian Arctic: one located in a poorly-studied geographical region, and another possessing limnological characteristics that are unusual in an Arctic context. Lake TK-2 is located in the low Arctic tundra. Paleolimnological studies from this region are lacking, as most have centered on sites in the High Arctic Archipelago or around Subarctic treeline. Marked changes in the diatom assemblages in TK-2 throughout the Holocene included potential evidence for the 8.2k cooling event, which has not been previously reported from other Canadian Arctic paleolimnological studies. In addition, diatom shifts occurring ~7000 and ~3500 cal yr BP are indicative of mid-Holocene warming and subsequent Neoglacial cooling, respectively, the timings of which agree with those from other studies farther south. Finally, shifts in the diatom assemblages in the upper sediment layers, beginning in the early-to-mid 19th century, are consistent with reduced ice cover, related to recent warming. Stygge Nunatak Pond, a small, closed-basin pond located on a nunatak in the High Arctic on Ellesmere Island, is characterized by unusually high ionic concentrations for an inland Arctic pond. As in TK-2, Stygge’s diatom assemblages changed substantially throughout the Holocene, but especially in the most recent sediments. Diatom shifts near ~10,500 cal yr BP suggest an early onset for the Holocene Thermal Maximum (and for the successive Neoglacial cooling trend) in this region, consistent with previous studies from the High Arctic. Marked diatom assemblage changes occurred in the most recent sediments, and are indicative of climate warming and reduced ice cover, as well as increased ionic concentration due to enhanced evaporative concentration. The dynamic nature of the diatom assemblage changes at the Stygge site suggests that sediments from these rare athalassic ponds represent an especially sensitive archive of Arctic climatic and environmental change. / Thesis (Master, Biology) -- Queen's University, 2008-11-12 16:46:47.174

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

A two-part paleolimnological study was conducted to examine changes in historical and modern water-quality in Lake of the Woods (LoW) in response to multiple stressors, such as climate change and shoreline residential development. Changes in diatom assemblages were analyzed in the modern and pre-industrial sediment intervals of 17 study sites, and in high-resolution 210Pb-dated sedimentary records from three northwestern bays (Clearwater, Poplar, and White Partridge bays). Patterns in diatom assemblage changes revealed pronounced and synchronous shifts over the last ca. 150 years. The most notable shift in the diatom community structure (~1970 AD) was characterized by an overall shift towards a higher relative abundance of small, centric Cyclotella taxa and planktonic, pennate diatoms (e.g., Asterionella formosa, Fragilaria crotonensis), and a corresponding lower relative abundance of heavily silicified Aulacoseira taxa and small benthic Fragilaria taxa and Achnanthes taxa. Lakewater total phosphorus (TP) concentrations were inferred from sedimentary diatom assemblages. DI-TP reconstructions revealed either no change or a decline in DI-TP since pre-industrial (pre-1850) times at majority (88%) of the top-bottom study sites, and no distinct directional change over the past ca. 150 years at the northwestern bays. Therefore, we concluded that TP was not an important driver of the floristic changes we observed. Chl-a trends indicate that primary production increased during the last ca. 100 years, likely tracking increases in microbial blooms. Changes in diatom assemblage composition and primary productivity have occurred during a period of substantial warming for this region of northwestern Ontario. Strong correlations (r >0.50, p<0.005) between diatom compositional changes, chl-a trends, and local air temperature records and lake-ice phenology suggest that climate-induced changes in lakewater properties may have been key factors driving the observed changes. From these data, we conclude that climate warming, rather than changing shoreline development and TP changes, has had the most pronounced effect on algal communities in the LoW. Estimates of pre-impact lake trophic status can aid in setting realistic mitigation targets for lakes impacted by multiple stressors. Therefore, paleolimnological studies comparing pre- and post-disturbance algal assemblages, such as the investigations we have conducted, are of interest from a lake management perspective. / Thesis (Master, Biology) -- Queen's University, 2010-05-28 13:38:59.472

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

Global climate change is threatening both our water quality and quantity. Specifically, the influence of climate change on freshwater lakes includes decreased water availability, increased evapotranspiration, changes in nutrient availability, and shifts in species composition. Understanding the changes that are occurring to our freshwater ecosystems is imperative to understanding the full impact of climate change on both the environment and society. This thesis examines a shift in sedimentary diatom assemblages towards increased relative abundances of Discostella species, a phenomenon that has been documented across the Northern Hemisphere. One of the central tenants of this work is that it has been done at the Experimental Lakes Area (ELA) in the boreal region of Canada, a study site that is uniquely devoid of large-scale anthropogenic disturbances. An analysis of the long-term monitoring records at the ELA show that Discostella species are primarily spring bloomers, and recent increases in their abundance is linked to changes in spring thermal conditions. To link the changes recorded in the sedimentary records of eight lakes to climate change, and assess whether Discostella species are in fact showing a response to climate change, a novel approach utilizing the theory of temporal synchrony was applied to eight paleo records. Discostella stelligera was found to be synchronous in all eight lakes studied, suggesting that a broad-scale forcing factor is influencing its abundance. Further, it was significantly correlated with annual and winter temperatures, supporting a link to changes in spring thermal conditions as a possible explanation. To assess the relative sensitivity of the study lakes, particularly in comparison to other boreal and temperate region lakes, an analysis was conducted of the timing of the first change in Discostella species. Several statistical techniques were employed and all approaches showed that the study lakes from ELA responded earlier in comparison to other lakes studied from other boreal and temperate regions (ca. 1900 vs ca. 1970), but later than Arctic and Sub-Arctic lakes. We suggest that this may be due to the lack of local disturbances at the ELA and/or the comparably small size of our study lakes. / Thesis (Ph.D, Biology) -- Queen's University, 2014-06-30 15:03:04.447

Lakes in the Adirondack Park (NY, USA) are undergoing chemical recovery from acidification. There is now a pressing research need to define recovery targets for acid-impacted sites. Researchers attempting to designate such targets are hampered by two issues: 1) a lack of long-term monitoring data, and 2) the influence of multiple stressors on recovering lakes. This thesis addresses both difficulties by applying paleolimnological techniques within a regional reference lake framework. Using a set of stringent selection criteria, 31 lakes protected from acidification, eutrophication, road salt seepage, and piscivore introductions were identified from 1,469 Adirondack lakes. Ordination techniques showed that the lakes are representative of 24-36% of the chemical/morphological variation of Adirondack lakes. Qualitative and quantitative historic analyses found that many of the lakes experienced early watershed and/or fisheries disturbance, highlighting the danger of assuming that a lake’s condition remains static over time. A top-bottom paleolimnological study revealed that the reference lakes have undergone a ‘shifting baseline’ in species assemblages, with increases in colonial and/or warm-water chrysophyte taxa from pre-1900 to present, changes most likely due to regional warming and/or oligotrophication. A subset of three reference lakes were then paired with two Adirondack lakes that acidified and are undergoing chemical recovery from acidification. The acidified lakes underwent a significant shift in species composition since the 1995 implementation of the US Acid Rain Program, indicating biological recovery from acidification. However, both reference and acidified lakes showed increases in colonial chrysophytes since ca. 1970-1980, a trend correlated with mean annual air temperature and ice-cover measures in the two reference lakes. Long-term species changes in acidified/reference lakes suggest that the recovering lakes will not return to their pre-disturbance state but will instead move to a state characterized by an increased abundance of colonial taxa/warm-water species. Overall, this thesis demonstrates the utility of pairing paleolimnological techniques with a regional reference site dataset for tracking shifting baselines and defining recovery targets, a method that could be applied to examine other stressors in other regions, thereby addressing a critical management need. / Thesis (Ph.D, Biology) -- Queen's University, 2014-05-03 13:17:09.613