Thesis (Ph. D.)--Duke University, 1970. / eContent provider-neutral record in process. Description based on print version record.

Thesis (M.S.) in Ecology and Environmental Science--University of Maine, 2008. / Includes vita. Includes bibliographical references (leaves 95-101).

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Cyanobacterial and algal blooms can negatively affect water quality particularly when producing toxins that affect human health and wildlife. While reports of blooms are on the rise globally, their underlying causes remain unclear. The goal of this thesis was to determine temporal changes in cyanobacterial abundance and composition through sediment cores in relation to (1) altered land-use leading to cultural eutrophication and (2) warmer air temperatures that have been recorded in the past few decades. This involved evaluating the use of DNA extracted from lake sediments to quantify cyanobacterial abundance and composition. Lake sediments preserved under appropriate storage conditions showed the potential to yield high quality DNA for downstream molecular applications. Cyanobacteria, quantified using the 16S rRNA gene, were found to have increased over the last three decades in comparison to historical averages (since the 1850s) both inside and outside a protected area in western Quebec, Canada, in concert with recent regional warming. Copy numbers of 16S rRNA genes specific to cyanobacteria largely correlated to temporal trends in cyanobacterial pigments. Larger percent increases were seen in cyanobacterial genes in recent times compared to changes in the eubacterial glutamine synthetase (glnA) gene. The mcyD gene was quantified as a proxy for microcystin production through sediment cores from two lakes of western Canada. Copy numbers of both mcyD and Microcystis 16S rRNA correlated with chemical analyses of microcystin through time in cores. Cyanobacteria in the more eutrophic of these lakes shifted toward less diverse assemblages and more toxigenic taxa in recent years. Lastly, temporal and spatial changes in cyanobacterial diversity were analyzed through pyrosequencing of cyanobacterial 16S rRNA along a latitudinal transect representative of northern Canada. Significant shifts towards less diverse assemblages were found, composed of potentially toxigenic strains, suggestive of climate warming in northern latitudes. These results support recent reports of increased abundance and geographic expansion of cyanobacteria and point to increases in cyanotoxins in some cases. Using DNA archived in sediments to determine the historical state of cyanobacterial abundance and diversity could help inform lake management policies.

Environmental conditions can lead to mercury accumulations in fish that are highly variability among spatially close lakes in Ontario, Canada. Mercury methylation caused by sulfate reduction can influence total mercury concentrations in fish (THgfish). Kahshe and Mountain lakes were chosen to assess temporal trends of THgfish and using paleolimnological tools described the lake environment in terms of total mercury (THgsed), total sulfur (TSsed), chromium-reducible sulfur (CRSsed), and chrysophyte-inferred lake-water pH (CI-pH). THgfish were standardized by length (LS-THgfish) to identify trends and make comparisons with archived fish from the Royal Ontario Museum. In Kahshe Lake, LS-THgfish for 30-cm smallmouth bass and 40-cm walleye displayed peak concentrations in the early 1980s (0.74 +/- 0.17 µg/g d.w; n=41 and 1.40 +/- 0.42 µg/g d.w; n=16, respectively) with clear declines starting in 1999 (0.33 µg/g d.w +/- 0.13, n=12). At Mountain Lake, LS-THgfish in smallmouth bass (0.31 – 0.45 µg/g) and walleye (0.30 – 0.49 µg/g) were low and stable through the period of observation. Peak concentrations at Kahshe Lake were over 300% higher than the 1926 archival sample (0.22 µg/g d.w, 22.1 cm total length), while the 1948 Mountain Lake sample (0.28 µg/g, 24.4 cm total length) is consistent with modern concentrations. As expected from LS-THgfish , THgsed was higher in Kahshe Lake, although enrichment was seen at both sites. Temporal trends for TSsed and CRSsed diverged with enrichment in Kahshe Lake and depletion in Mountain Lake. CI-pH showed minimal temporal changes. Although trends of CRSsed indicate sulfate is processed differently among the lakes, geochronology highlighted a consistent spatio-temporal relationship between THgfish and CRSsed. This strongly supports a relationship between sulfate reduction rates and Hg methylation, independent of THgsed and pH. Therefore, if THgfish is used as an indicator of aquatic health CRSsed may be a useful tool for rapid assessment. / Thesis (Master, Biology) -- Queen's University, 2013-01-11 15:48:02.718

Due to accelerated climatic warming during the past fifty years, interest and concerns have been growing about changes in the ecological integrity of shallow freshwater ponds that dominate the landscape of the Hudson Bay Lowlands (HBL). Climatic warming is altering the hydrological processes that influence the water balances in these ponds, but knowledge remains insufficient to determine the effects these changes have on ecological conditions in the ponds. To address this knowledge gap, this study examines the relations between current hydrological and limnological conditions and recently deposited sedimentary assemblages of diatoms and photosynthetic pigments in 23 shallow ponds in the HBL. The knowledge from the contemporary studies will be used to inform paleolimnological reconstructions using multiple proxies at two ponds to assess how hydroecological conditions have changed during the past several centuries in response to climatic variations. Water samples were collected three times in 2010 to explore the relations between current hydrological and limnological conditions. The climatic conditions in 2010 provided an excellent opportunity to assess the effects that continued climate warming may exert on hydrolimnological conditions in the study ponds as the warm, dry conditions during the early thaw-season (May- mid-July) followed by extremely wet conditions for the remainder of the thaw-season are likely representative of future climate scenarios. The analysis revealed that the water chemistry in the ponds evolved along one of four different ‘trajectories’ throughout the thaw-season in 2010. These seasonal patterns of limnological conditions closely aligned with similar patterns identified in a study of contemporary hydrological conditions (Light, 2011; Wolfe et al., 2011). The patterns identified in both the hydrological and limnological studies were attributed to differences among ponds in catchment characteristics and hydrological connectivity with adjacent basins. Surface sediment samples were collected in 2010 to determine if hydrolimnological conditions are reflected in the distribution of recently deposited diatom and pigment communities. It was determined that diatom community composition was most highly influenced by the availability of microhabitat in the ponds which did not appear to be controlled by hydrological conditions. Nitrogen availability was determined to be indirectly influencing diatom community composition as the nitrogen-limited conditions in the ponds favoured the proliferation of N2-fixing cyanobacterial mats that provided a large amount of epiphytic habitat in the majority of the study ponds. This resulted in the complete domination of diatom assemblages by one diatom specie that was closely associated with these algal mats in the surface sediments of most ponds. Aphanizophyll, a photosynthetic pigment representative of nitrogen-fixing cyanobacteria, was also in the highest concentration in most of the study ponds as a result of the nitrogen-limiting conditions that allowed these organisms to dominate. Ponds located in the tundra ecozone were also found to have the highest overall pigment concentration which was related to a longer growing season due to the small size of these ponds that resulted in earlier ice-off conditions. The longer growing season of ponds in the tundra ecozone may also be due to high winds that cause a decrease in snow cover, lower surface albedos and an earlier onset of the spring thaw. The paleolimnological reconstruction of two of the ponds revealed similar shifts in diatom community composition in the stratigraphic record even though patterns of past change in their basin hydrology, as explored though the analysis of the δ18OPW record archived in the aquatic cellulose contained in the pond sediments, was very different. The water balance of “Left Lake” was found to be highly influenced by increased evaporation associated with recent warming trends as it is a relatively small basin that becomes hydrologically isolated after the melt period. However, “Erin Lake” was not as susceptible to evaporation during the recent warming trend due to its larger catchment and hydrological connections to other ponds. Both of these ponds experienced marked changes in the diatom assemblages. The changes were characterized by a shift from assemblages containing both small, adnate, benthic taxa that prefer mineral grain substrates and epiphytic taxa that are associated with the cyanobacterial mats covering the pond bottoms to assemblages entirely dominated by epiphytic taxa. The shift in diatom community composition occurred ~1820 in Left Lake, but the timing cannot be determined with any degree of confidence in Erin Lake as no diatoms are observed in the sediment record during the period when the change occurred (~1550 to 1850) due to preservation issues. Analysis of fossil pigments indicates that nitrogen-fixing cyanobacteria have been important to the ecology of the ponds over the entire sediment record. However, there is a trend towards lower concentrations of pigments representative of N2-fixing cyanobacteria in the most recent sediments. The trend in cyanobacterial pigment concentrations coincides with inferred changes in nitrogen availability from the geochemical analysis of the pond sediments by Light (2011). This recent shift in nutrient status may be the result of a number of factors including the increased atmospheric deposition of anthropogenically-derived nitrogen or changes in biogeochemical cycling in the ponds.

The uncertainty surrounding the impact of future changes in climate and water resources has created renewed interest on how lakes have responded to drought in the past. There is a need to determine potential future available water by understanding past changes in water levels; the underlying ecological characteristics of using diatoms as a proxy for lake-level reconstructions is the basis of this thesis. By integrating knowledge from past water-level fluctuation studies and theories, along with developing a better understanding of diatom ecology in lake systems, more effective techniques are being developed to improve water-depth reconstructions. Diatom assemblages were examined from eight lakes in northwestern Ontario collected in surface sediments along a depth gradient at ~1-m water-depth intervals. Three major zones, based on the composition of diatom assemblages in each lake were consistently identified in all lakes: i) a near-shore assemblage of Achnanthes (sensu lato) species and other benthic taxa (Nitzschia, Cymbella); ii) a mid-depth small Fragilaria (sensu lato)/ small Aulacoseira zone with various Navicula taxa, and iii) a deep-water planktonic zone. The depths at which transitions between these zones are located varied among lakes, and the depth of the transition between the planktonic and benthic zones was consistent with water chemistry variables (e.g. DOC, TP) that are related to light attenuation. Deeper pelagic to benthic transitions occurred in lakes with the lowest DOC and TP (i.e. generally more light attenuation in lakes with higher concentrations of TP or DOC). Other findings included a decrease in species evenness and numbers with depth, along with an increase in scaled chrysophyte relative to diatoms. / Thesis (Master, Biology) -- Queen's University, 2010-07-23 12:36:01.347

The Winnipeg River Drainage Basin (WRDB), located in the boreal forest region of Canada, is a pivotal region of focus for the assessment of water availability to determine susceptibility to drought in the past. To date, there have been relatively few paleolimnological studies focusing on how lake levels have changed in the past and whether these changes have been synchronous in the WRDB. This study investigates temporal patterns in effective moisture from Little Raleigh Lake over the last two millennia. Analyses are based on diatoms from two near-shore sediment cores from different locations and water depth in Little Raleigh Lake. Changes in diatom assemblages are used to reconstruct quantitative estimates of effective moisture in the past through the calibration of a diatom-inferred depth model developed from diatom assemblages in surficial sediments along a depth transect in Little Raleigh Lake. Declines of ~1-3m occurred during the late Holocene, with prolonged periods of aridity consistent with the timing of the Medieval Climate Anamoly (~950-1250AD) and the Little Ice Age (~1650-1750AD). The nearshore core retrieved closer to the present-day ecotone between the benthic and planktonic diatom assemblages was more sensitive to tracking water level changes in the lake than the deeper core. Conditions during the last two millennia can be used for the assessment of water availability in the past, and may offer insight on future conditions under increasing temperatures. / Thesis (Master, Biology) -- Queen's University, 2011-07-29 17:09:49.155

The Canadian province of Nova Scotia has an abundance of lakes impacted by multiple stressors, including acidification, lakewater calcium (Ca) decline, climate change, and fish introductions. In spite of this, little is known about long-term trends in aquatic biota, especially microfaunal communities that are useful indicators of lake trophy. This thesis helps address this knowledge gap by providing information on the ecological distribution and long-term dynamics of Cladocera in softwater lakes in Nova Scotia using their subfossil remains preserved in lake sediments. Based on a surface sediment survey of 49 lakes, Cladocera in Nova Scotia are mainly structured along gradients of maximum lake depth and dissolved organic carbon (DOC). Daphnia (generally considered sensitive to low pH and [Ca]) were common in the Cape Breton Highlands National Park, but were rare in southwestern Nova Scotia in both modern and pre-industrial sediments, although some lakes exhibited declines in Daphnia since pre-industrial times. The most notable example of this is Lake George (Kings County), where a striking decline in Daphnia, likely a result of declining [Ca], resulted in a marked increase in estimates of past algal production. In Kejimkujik National Park, which has experienced declines in pH and [Ca] since pre-industrial times, significant reductions in chydorid relative abundances were observed, as well as significant increases in the jelly-clad planktonic cladoceran species Holopedium. Cladoceran assemblages in lakes near Yarmouth have also changed significantly since pre-industrial times, but showed no consistent regional trends in the direction of cladoceran species shifts, reflecting the influence of local anthropogenic stressors. An extreme example of this is Trefry Lake, which was treated with copper sulphate in 1938 to remove the native fish community and provide better stocking conditions for brook trout. Copper sulphate treatment resulted in significant and permanent changes to the aquatic food web inferred from a strong decline in the body size of Bosmina. Collectively, these results suggest that many aquatic ecosystems in Nova Scotia are in a state of flux as a result of multiple anthropogenic stressors, and Cladocera subfossils can be effective for inferring the food web implications of these stressors. / Thesis (Ph.D, Biology) -- Queen's University, 2012-08-14 09:39:27.617

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