Thesis (Ph. D.)--University of Florida, 1983. / Description based on print version record. Typescript. Vita. REPL* Includes bibliographical references (leaves 237-248).

Food web biomanipulations provide the means to partly control water quality problems (i.e. algal blooms) in lakes by altering internal ecological mechanisms. However biomanipulation mechanisms are complex and the results are often confounded through the interactions of various stressors. This study used paleolimnological approaches using the fossil remains of diatoms, Cladocera and Chaoborus indicators to explore the effects of past fish manipulations of two oligotrophic lakes (Mouse and Ranger lakes) located in south-central Ontario. A major focus was the temporal period associated with the most recent Dorset Food Web Piscivore Manipulation Project (1991-1997). The diatom assemblages recorded only subtle changes over time, with the most pronounced variation in the past decade, likely responding to recent warming and bottom-up processes. Following the smallmouth (Micropterus dolomieu) and largemouth (Micropterus salmoides) bass addition to Mouse Lake, the zooplankton and Chaoborus fossil record revealed that a reduction in planktivorous fish led to expected shifts in community size structure, but with changes apparently delayed by ~5-10 years. Primary production, as inferred from VRS chlorophyll-a concentrations, had been relatively stable for over ~200 years but increased significantly following the piscivore addition. A shift to larger, more efficient herbivorous zooplankton (i.e. Daphnia) may have been expected to suppress phytoplankton as they are able to filter food particles at a much faster rate and graze a wider size-range of algae compared to the less effective grazer, Bosmina. Additionally, changes to the lake system from climate warming may have uncoupled the trophic interactions, producing a mismatch in the timing of favourable environmental conditions in an algal-herbivore interaction. In addition, these oligotrophic lakes support algal communities often classed as being ungrazable, which would also substantially reduce grazer-mediated responses in the phytoplankton. Ranger Lake did not respond to reductions to piscivores as expected in terms of zooplankton and Chaoborus size structure. Larger-bodied Cladocera (i.e. Daphnia, Holopedium gibberum and Polyphemus pediculus) increased in abundance while small Bosmina species decreased markedly in the uppermost sediments. While some results of this study corroborated the expected effects of biomanipulation theory (i.e. species-specific shifts in size), the inconsistencies encountered highlight that other drivers (i.e. climate) are likely to mediate the effects of biomanipulations, particularly in temperate lake systems experiencing multiple stressors. / Thesis (Master, Biology) -- Queen's University, 2012-10-17 19:22:40.972

Thesis (M.S.) in Ecology and Environmental Science--University of Maine, 2007. / Includes vita. Includes bibliographical references (leaves 78-89).

The stratigraphy of the Middle Devonian Orcadian Basin is summarized and a regional review of all related structural and sedimentological data suggests that the basin area formed by the reactivation of old Caledonian thrusts as normal faults bounding extensional basin areas, within an overall regional sinistral strike slip tectonic regime. The depositional environment of Orcadian Basin fish beds is reassessed on the basis of preservational predictions for fish and the delicate sedimentary hicrolamination with the result that the deep stratified lake origin is upheld. The major Achanarras lacustrine transgression event is investigated and the sedimentary and palaeontological data collected allow the development of palaeogeographic and palaeoecologic schemes for this spectacular phase of lake extension. Two fish bed horizons from the Upper Caithness Flagstone Group are described and relationships between high salinity levels and mass fish mortalities are shown by fish distribution, carbonate isotope geochemistry and penecontemporaneous chert development. Patterns of fish preservation are related to taphonomic variables in turn reflecting changing levels of hydrodynamic energy during fish bed formation. Using a variety of bulk and molecular organic goechemical analyses, the primary organic production is shown to have comprised predominantly algae, cyanobacteria and a varied microbial assemblage including a halophilic component. The principal organic carbon cycles are suggested and the critical lack of lake sediment bioturbators within such schemes is notable. Aspects of carbonate chemistry, C/S ratios, and sedimentary features are used to suggest palaeosalinity levels consistent with a brackish-saline lake system. A model of brine evolution via a zonal precipitation sequence of insoluble carbonates is used to postulate the presence of evaporites in the Orcadian Basin centre during low lake stands. The oxygen and carbon isotape compositions of coexisting calcite and dolomite are used to suggest that dolomite formed principally as a primary or early diagenetic mineral within Orcadian lakes. Lake depth/time curves are generated from facies associations and inferred sedimentation rates from average varve thicknesses, within Upper Flagstone Group cyclic lacustrine sequences. Frequency analyses of these time curves demonstrates the importance of 20 Kyr and 90 Kyr periodicities in cycle development, in turn related to long term Milankovitch climatic control. A synthesis of the various aspects of the Orcadian Basin discussed is presented, and comprises a summary description of the physical environment and of the biota together with a discussion of community palaeoecology and probable functional adaptations within early gnathostome lineages. Three examples, of progressively younger lacustrine systems, the Upper Devonian Escuminac Formation, the Early Mesozoic Newark Supergroup and the Eocene Green River Formation are investigated as comparative examples with emphasis on the content and structure of biotic communities represented and the ontogeny of lake environments. A final synthesis is presented which attempts to identify the aspects most important in the evolution of lacustrine ecosystems through the Phanerozoic; lacustrine cycling, related to the Milankovitch theory of extrinsic climatic forcing by orbital parameters, is considered to have been the single most important physical influence, after the formation of a continental area fit to drain water into, in driving the evolutionary patterns seen in lacustrine biotic communities.

No description available.

Thesis (Ph.D.)--University of Nebraska-Lincoln, 2006. / Title from title screen (site viewed on September 12, 2006). PDF text of dissertation: viii, 148, [323] p. : ill. ; 21.65Mb. UMI publication number: AAT 3208120. Includes bibliographical references. Also available in microfilm and microfiche format.

Relationships between hydrology, limnology and ecology are analyzed in a comprehensive study of water bodies in the Slave River Delta, Northwest Territories, Canada, at a variety of temporal and spatial scales, including seasonal, inter-annual and multi-decadal timescales at individual sites to delta-wide perspectives. Water chemistry and surface sediments were analyzed from 41 shallow lakes representing three previously-defined hydrological categories in the Slave River Delta, in order to identify relationships between hydrological and limnological conditions and their associations with recently deposited diatom assemblages. Evaporation-dominated lakes are physically removed from the influence of the Slave River, and are characterized by high alkalinity and high concentrations of nutrients and ions. In contrast, flood-dominated lakes tend to receive a pulse of floodwater from the Slave River during the spring thaw and have low alkalinity and low concentrations of most nutrients and ions. Exchange-dominated lakes are variably influenced by floodwaters from the Slave River and seiche events from Great Slave Lake throughout the spring thaw and open-water season, and are characterized by a broad array of limnological conditions that are largely dependent on the strength of the connection to these sources of floodwater. Specific diatom ‘indicator’ taxa have been identified that can discriminate these three hydrological lake categories. Evaporation-dominated lakes are associated with high relative abundance of common epiphytic diatom taxa, while diatoms indicative of flood- and exchange-dominated lakes span a wide range of habitat types (epiphytic, benthic) but also include unique planktonic diatoms (Stephanodiscus and Cyclostephanos taxa) that were not found in surface sediments of evaporation-dominated lakes. Water chemistry, diatom phytoplankton communities and macrophyte biomass were monitored seasonally over three years (2003-05) from six hydrologically-diverse lakes of varying flood susceptibility to determine the effects of river flooding on the seasonal and inter-annual hydroecological conditions of lakes in the Slave River Delta. Results indicate that river flooding is the dominant hydrological process controlling the temporal dynamics of limnological and ecological conditions in lakes of the Slave River Delta. In the absence of river flooding, lakes have relatively high concentrations of nutrients and low concentrations of most ions, but when flooded, concentrations of nutrients decrease and ions increase. The limnological and ecological conditions in frequently-flooded and non-flooded lakes are relatively stable from year to year, whereas lakes that are intermittently flooded fluctuate widely and are subject to variable conditions depending on whether or not they flood. Lakes that do not flood lack planktonic diatom communities, while spring flooding from the Slave River introduces an abundance of planktonic, centric diatoms that persist only for a few weeks in the water column before settling out. Flooding reduces lake water transparency, which decreases macrophyte biomass, while non-flooded lakes exhibit higher macrophyte biomass. To improve understanding of the role of river flooding and other hydrological factors on epiphytic diatom communities, a natural experiment was conducted to compare diatom communities in two hydrologically distinct lakes in the Slave River Delta (Northwest Territories, Canada) over two years (2004 and 2005) of varying spring flood magnitude of the Slave River. Magnitude and spatial extent of flooding was low in 2004 and high in 2005. Replicate samples were collected from three dominant macrophyte species (Lake SD28: Potamogeton friesii, Myriophyllum exalbescens and a species of Equisetum; and, Lake SD29: Potamogeton friesii, Ceratophyllum demersum, and a species of floating filamentous green algae) in three separate basins from each lake. Multivariate analyses (PCA, analysis of similarities) of the common macrophyte in both lakes (Potamogeton friesii) revealed that yearly differences due to frequency and intensity of flooding account for the greatest differences in epiphytic diatom community composition (PCA axis 1 = 0.302 and ANOSIM SD29 – 2004 versus 2005 Global R value = 0.982, p < 0.001 and d.f. = 23), followed by hydrolimnological differences between the two study lakes (PCA axis 2 = 0.262 and ANOSIM SD28 versus SD29 – 2004 and 2005 Global R value = 0.814, p < 0.001 and d.f. = 47), and by spatial variability within lakes (variation along both PCA axes and ANOSIM from both lakes in both years Global R value = 0.940-1.000, p < 0.001 and d.f. = 47). Epiphytic diatom community composition differed significantly (p < 0.001) at all levels of comparison. Observed patterns of epiphytic diatom composition between years and lakes indicated that hydrological effects on the limnological conditions, coupled with changes in the light environment, exert the strongest control on epiphytic diatom community composition, whereas spatial variability of limnological conditions within lakes and host-macrophyte specificity appear to play statistically significant but less important roles. Epiphytic diatom community composition is a sensitive indicator of hydrological change and knowledge gained concerning the roles of hydrological factors, limnological conditions and macrophyte host species on epiphytic diatom communities is important to inform interpretations of hydroecological changes from analyses of sedimentary diatom assemblages, which are often dominated by epiphytic taxa, in ongoing monitoring and paleolimnological studies in the Slave River Delta and other floodplain environments. Sediment cores were collected from a lake in each of the three hydrological lake categories in the Slave River Delta, to evaluate the ability of diatom assemblages to detect differences in the hydrological state and temporal variability of hydroecological conditions within individual lakes of this complex deltaic environment. Results indicate that diatoms provide sensitive records of environmental change and important information on past changes in hydrological conditions such as river flooding. The composition and temporal patterns of variation in diatom assemblages differ among lakes from different hydrological categories in consistent and predictable ways. The flood-dominated lake (SD2) provides a high resolution record of hydroecological variability and changes in flood-frequency over time. Sedimentary diatom assemblages repeatedly shift in dominance from taxa indicative of low river influence to taxa indicative of high river influence. Sedimentary diatom assemblages from the exchange-dominated lake (SD28) are dominated by taxa indicative of high river influence and were relatively static during the past ~100 years, but the total sum of planktonic diatoms (% abundance) can provide robust records of large, spatially extensive flood events in the Slave River Delta. Both flood- and exchange-dominated lakes show marked correspondence with gauged Slave River discharge levels over the past 46 years indicating an ability of diatoms to track periods of higher and lower flood frequency and high- magnitude flood events. Sedimentary diatom assemblages from the evaporation-dominated lake (SD20) in this study were poorly preserved below 6 cm depth, but assemblages from above 6 cm had distinct community composition similar to assemblages in surface sediments of evaporation-dominated lakes of the Slave River Delta. These diatoms correctly identify this lake as having evaporation-dominated hydrology. Overall, the sediment records provide no evidence for reduced flood frequency or a decrease in high magnitude flood events to indicate that upstream river regulation or another driver of change may be causing perceived changes of lower flood frequency and low water levels throughout the delta.

Relationships between hydrology, limnology and ecology are analyzed in a comprehensive study of water bodies in the Slave River Delta, Northwest Territories, Canada, at a variety of temporal and spatial scales, including seasonal, inter-annual and multi-decadal timescales at individual sites to delta-wide perspectives. Water chemistry and surface sediments were analyzed from 41 shallow lakes representing three previously-defined hydrological categories in the Slave River Delta, in order to identify relationships between hydrological and limnological conditions and their associations with recently deposited diatom assemblages. Evaporation-dominated lakes are physically removed from the influence of the Slave River, and are characterized by high alkalinity and high concentrations of nutrients and ions. In contrast, flood-dominated lakes tend to receive a pulse of floodwater from the Slave River during the spring thaw and have low alkalinity and low concentrations of most nutrients and ions. Exchange-dominated lakes are variably influenced by floodwaters from the Slave River and seiche events from Great Slave Lake throughout the spring thaw and open-water season, and are characterized by a broad array of limnological conditions that are largely dependent on the strength of the connection to these sources of floodwater. Specific diatom ‘indicator’ taxa have been identified that can discriminate these three hydrological lake categories. Evaporation-dominated lakes are associated with high relative abundance of common epiphytic diatom taxa, while diatoms indicative of flood- and exchange-dominated lakes span a wide range of habitat types (epiphytic, benthic) but also include unique planktonic diatoms (Stephanodiscus and Cyclostephanos taxa) that were not found in surface sediments of evaporation-dominated lakes. Water chemistry, diatom phytoplankton communities and macrophyte biomass were monitored seasonally over three years (2003-05) from six hydrologically-diverse lakes of varying flood susceptibility to determine the effects of river flooding on the seasonal and inter-annual hydroecological conditions of lakes in the Slave River Delta. Results indicate that river flooding is the dominant hydrological process controlling the temporal dynamics of limnological and ecological conditions in lakes of the Slave River Delta. In the absence of river flooding, lakes have relatively high concentrations of nutrients and low concentrations of most ions, but when flooded, concentrations of nutrients decrease and ions increase. The limnological and ecological conditions in frequently-flooded and non-flooded lakes are relatively stable from year to year, whereas lakes that are intermittently flooded fluctuate widely and are subject to variable conditions depending on whether or not they flood. Lakes that do not flood lack planktonic diatom communities, while spring flooding from the Slave River introduces an abundance of planktonic, centric diatoms that persist only for a few weeks in the water column before settling out. Flooding reduces lake water transparency, which decreases macrophyte biomass, while non-flooded lakes exhibit higher macrophyte biomass. To improve understanding of the role of river flooding and other hydrological factors on epiphytic diatom communities, a natural experiment was conducted to compare diatom communities in two hydrologically distinct lakes in the Slave River Delta (Northwest Territories, Canada) over two years (2004 and 2005) of varying spring flood magnitude of the Slave River. Magnitude and spatial extent of flooding was low in 2004 and high in 2005. Replicate samples were collected from three dominant macrophyte species (Lake SD28: Potamogeton friesii, Myriophyllum exalbescens and a species of Equisetum; and, Lake SD29: Potamogeton friesii, Ceratophyllum demersum, and a species of floating filamentous green algae) in three separate basins from each lake. Multivariate analyses (PCA, analysis of similarities) of the common macrophyte in both lakes (Potamogeton friesii) revealed that yearly differences due to frequency and intensity of flooding account for the greatest differences in epiphytic diatom community composition (PCA axis 1 = 0.302 and ANOSIM SD29 – 2004 versus 2005 Global R value = 0.982, p < 0.001 and d.f. = 23), followed by hydrolimnological differences between the two study lakes (PCA axis 2 = 0.262 and ANOSIM SD28 versus SD29 – 2004 and 2005 Global R value = 0.814, p < 0.001 and d.f. = 47), and by spatial variability within lakes (variation along both PCA axes and ANOSIM from both lakes in both years Global R value = 0.940-1.000, p < 0.001 and d.f. = 47). Epiphytic diatom community composition differed significantly (p < 0.001) at all levels of comparison. Observed patterns of epiphytic diatom composition between years and lakes indicated that hydrological effects on the limnological conditions, coupled with changes in the light environment, exert the strongest control on epiphytic diatom community composition, whereas spatial variability of limnological conditions within lakes and host-macrophyte specificity appear to play statistically significant but less important roles. Epiphytic diatom community composition is a sensitive indicator of hydrological change and knowledge gained concerning the roles of hydrological factors, limnological conditions and macrophyte host species on epiphytic diatom communities is important to inform interpretations of hydroecological changes from analyses of sedimentary diatom assemblages, which are often dominated by epiphytic taxa, in ongoing monitoring and paleolimnological studies in the Slave River Delta and other floodplain environments. Sediment cores were collected from a lake in each of the three hydrological lake categories in the Slave River Delta, to evaluate the ability of diatom assemblages to detect differences in the hydrological state and temporal variability of hydroecological conditions within individual lakes of this complex deltaic environment. Results indicate that diatoms provide sensitive records of environmental change and important information on past changes in hydrological conditions such as river flooding. The composition and temporal patterns of variation in diatom assemblages differ among lakes from different hydrological categories in consistent and predictable ways. The flood-dominated lake (SD2) provides a high resolution record of hydroecological variability and changes in flood-frequency over time. Sedimentary diatom assemblages repeatedly shift in dominance from taxa indicative of low river influence to taxa indicative of high river influence. Sedimentary diatom assemblages from the exchange-dominated lake (SD28) are dominated by taxa indicative of high river influence and were relatively static during the past ~100 years, but the total sum of planktonic diatoms (% abundance) can provide robust records of large, spatially extensive flood events in the Slave River Delta. Both flood- and exchange-dominated lakes show marked correspondence with gauged Slave River discharge levels over the past 46 years indicating an ability of diatoms to track periods of higher and lower flood frequency and high- magnitude flood events. Sedimentary diatom assemblages from the evaporation-dominated lake (SD20) in this study were poorly preserved below 6 cm depth, but assemblages from above 6 cm had distinct community composition similar to assemblages in surface sediments of evaporation-dominated lakes of the Slave River Delta. These diatoms correctly identify this lake as having evaporation-dominated hydrology. Overall, the sediment records provide no evidence for reduced flood frequency or a decrease in high magnitude flood events to indicate that upstream river regulation or another driver of change may be causing perceived changes of lower flood frequency and low water levels throughout the delta.

The study of long-term climatic change in the Arctic, a region both particularly sensitive to the effects of a warming climate and an important driver of global climate, is pertinent to understanding the rates and magnitude of current ecosystem changes. Analyses on geological time frames provide insight into the variability of Arctic climate, allowing a contextualized understanding of recent ecosystem changes that have been documented across the Arctic. Lake CF8, a mid-Arctic lake on Clyde Foreland, Baffin Island, contains a unique sedimentary archive of the present and last two interglacial periods, due to past non-erosive glaciation patterns, providing an opportunity to study interglacial climate trends. Diatom assemblages were analyzed through the organic sediment record of the past three interglacials. Trends in the ontogeny of this lake were revealed: the early, post-glacial environment was dominated by species of the colonial Fragilaria genera, which transitioned into high relative abundances of tychoplanktonic Aulacoseira species. Benthic/periphytic taxa, such as Psammothidium marginulatum, tended to increase in relative abundance in the mid- to late-interglacial periods. The ecological interpretation of this pattern is examined in this study, and suggests that climate drives the succession of the diatom community primarily through indirect effects on lake ice and pH. The extent of ice cover likely plays a large role in the biotic community of this lake; the diatom assemblages within the past ~ 50 years indicate increasing littoral habitat complexity with a peak in Eunotia species and a slightly acidic pH, which is discussed in relation to changing habitat availability associated with decreasing ice cover. In-lake production was examined through the use of spectrally-inferred chlorophyll a trends, which also indicate elevated production in the past ~ 50 years. As climate change becomes an increasingly significant threat to the stability of Arctic ecosystems, interest in paleoclimate records that extend into past, non-anthropogenically mediated warm periods, is increasing. This sediment record extends our understanding of past environmental trends beyond the longest records in this part of the Arctic, the Greenland ice core records, and enhances our understanding of the variability of Arctic climate. / Thesis (Master, Biology) -- Queen's University, 2009-05-06 17:04:38.302

The boreal forest of Canada extends across 58% of Canada’s land area providing a large range of ecosystem services including flood control, water filtration, and carbon storage. Despite conservation efforts to protect this ecosystem, the boreal region is still under stress from global stressors including climate change. Anthropogenic climate-change is expected to raise temperatures and decrease precipitation over much of the boreal region increasing the duration and magnitude of droughts. This potential change to a more arid climate could have drastic affects on water levels and stream flows across much of the boreal region. Changes in hydrology, as a consequence of anthropogenic climate change, may result in large changes to aquatic ecosystems. To assess the susceptibility of lakes to climate in northwestern Ontario over the past two millennia, sediment cores from a headwater lake were obtained from near-shore cores to reconstruct changes in drought. The cores were located at a depth where changes in pelagic and benthic diatom assemblages (P: B boundary) were apparent in modern-day sediments because the location has been shown to be susceptible to change. The lake chosen for reconstruction was Gall Lake, a small (surface area = 19 ha, max depth = 18 m, mean depth = 8.5 m), mesotrophic lake (total phosphorus (TP) level of 12.3 μg/L, July 2008), with a gentlysloping eastern basin. This headwater lake in the Winnipeg River Drainage Basin (WRDB) is part of a hydrologically-rich region that is expected to experience increased aridity. Multivariate analysis of diatom assemblages over the past two millennia suggested that the instrumental record does not encompassed the natural variability of this system. The largest decreases in diatom-inferred (DI) depth were synonymous with iii the Medieval Climate Anomaly (MCA), a phenomenon not yet observed this far northeast in North America. The MCA has been proposed as a surrogate for climate change over the next century, therefore the prolonged aridity observed in Gall Lake could aid in the calibration of general circulation models currently used to forecast changes in climate, as well as a scenario that can be used to develop adaptation strategies to future environmental change. / Thesis (Master, Biology) -- Queen's University, 2011-05-27 17:41:02.022