In the last 150 years, the City of Yellowknife has transitioned from an area of traditional subsistence living to the largest city in the Northwest Territories (Canada) due to the economic influence of resource extraction. As resource extraction in the area boomed, large quantities of pollutants from mine tailings and emissions from roaster stacks adjacent to gold mines were deposited on the landscape, leaving a known legacy of elevated surface water, sediment, and soil metal(loid) concentrations. Most of the research to date has focused on arsenic in the region, and my thesis expands the body of knowledge to include other metal(loids) of interest, including antimony, lead, and mercury. My thesis's main objective was to determine the spatial and temporal extent of legacy mining emissions near Yellowknife and assess the associated biological risk from these historic emissions. I analyzed select intervals from 20 lake sediment cores for time constrained metal(loid) contaminants of concern. I used a combination of paleotoxicity and paleoecotoxicology methods to establish a spatial and temporal footprint of biological risk associated with historic gold mining activities in the Yellowknife region. I determined that lakes close to the mine exhibited a low-level hazard to aquatic communities before mining, while the onset of mining increased the hazard posed by sediments deposited to acute levels. I also discovered that lakes within 5 km of Giant Mine exceeded guideline values for sedimentary mercury during active mining. Further, I developed methods in paleoecotoxicology that indicated a concordance between time deposited, estimated risk, and observed mortality of native Daphnia sp exposed to time-constrained sediment archives. My thesis demonstrates that paleotoxicity and paleoecotoxicology are effective methods to separate historic and modern influences of industrial development on aquatic biota. Additionally, my research has application extensions for policymakers, remediation scientists, Indigenous Peoples, and those proposing new industrial ventures.

It is well established that mining and metallurgy on a larger scale in Sweden originated in Bergslagen. The historical mining district Garpenberg in Bergslagen presently show the oldest signs of mining in Sweden (2300 BP) based on a study of a lake sediment profile from Gruvsjön. This report focuses on the mining history around Finnhytte-dammsjön (Garpenberg) to assess when the first signs of mining occur, what type of ore was being mined, when the first sign of modern mining was observed and when the lake development stabilized. A complete sediment profile was sampled from Finnhytte-dammsjön which was analyzed with X-Ray Fluorescence spectroscopy. An age-depth model was created for the sediment profile using the introduction of Norway Spruce (Picea Abies) pollen and by matching known peaks in historical atmospheric pollution of Pb as points of reference. Increased Fe concentrations (3.6 ± 0.4 %) compared to deeper sections (2.6 ± 0.2 %) was observed which were well correlated with Ca (R2: 0.73). Indications of increased Fe concentrations relative to Ca was found from 2000 BP. Stabilization of LOI550 and changes in sediment geochemistry indicates that a steady state in the lake development was reached around 4600 BP. Major increases in Zn and Cu that was presumed to be from modern mining was observed from 1800 CE. This report concludes that Fe-rich dolomite or skarn was mined from 500 CE with indications that mining started as early as 2000 BP.

A 147cm sediment core from Lake DV09, northern Devon Island, Nunavut, Canada (75° 34’34”N, 89° 18’55”W) contains annually-laminated (varved) sediments, providing a 1600-year record of climate variability. A minerogenic lamina deposited during the annual thaw period and a thin deposit of organic matter deposited during the summer and through the winter, together form a clastic-organic couplet each year. The thinnest varves occur from AD800-1050, and the thickest from AD1100-1300, during the Medieval Warm Period. The relative sediment density is also highest during this period suggesting increased sediment transport energy. The coldest period of the Little Ice Age appears to be during the AD1600s. Varve widths over the past century indicate climate warming in the region. / This research program was funded by the Natural Sciences and Engineering Research Council of Canada (NSERC), and the Canadian Foundation for Climate and Atmospheric Sciences (CFCAS). A tuition bursary from Ultramar Inc. also helped in making this research possible. Logistical support was provided by the Polar Continental Shelf Project (PCSP Contribution number 04508).

Lakes sediments from the Lofoten Islands, Norway, can be used to generate well resolved records of past climate and environmental change. This dissertation presents three lacustrine paleoenvironmental reconstructions that show evidence for Holocene climate changes associated with North Atlantic climate dynamics and relative sea-level variations driven by glacio-isostatic adjustment. This study also uses distal tephra deposits (cryptotephra) from Icelandic volcanic eruptions to improve the chronologies of these reconstructions and explores new approaches to crypto-tephrochronology. Past and present conditions at Vikjordvatnet, Fiskebølvatnet, and Heimerdalsvatnet were studied during four field seasons conducted from 2007-2010. Initially, each lake was characterized by measuring water column chemistry, logging annual temperature fluctuations, and conducting bathymetric and seismic surveys. Sediment cores were then collected and analyzed using multiple techniques, including: sediment density, magnetic susceptibility, loss-on-ignition, total carbon and nitrogen, δ13C and δ15N of organic matter, and elemental compositions acquired by scanning X-ray fluorescence. Chronologies were established using radiocarbon dating and tephrochronology. A 13.8 cal ka BP record from Vikjordvatnet provides evidence for glacial activity during the Younger Dryas cold interval and exhibits trends in Ti, Fe, and organic content during the Holocene that correlate with regional millennial-scale climate trends and provide evidence for more rapid events. A 9.7 cal ka BP record from Fiskebølvatnet shows a strong signal of sediment inwashing likely driven by local geomorphic conditions, although there is evidence that increased inwashing at the onset of the Neoglacial could have been associated with increased precipitation. Heimerdalsvatnet provides a record of relative sea-level change. A 7.8 cal ka BP sedimentary record reflects changes in salinity and water column conditions as the lake was isolated and defines sea-level regression following the Tapes transgression. Cryptotephra horizons were identified in sediments of Heimerdalsvatnet, Vikjordvatnet, and Sverigedalsvatn. They were also found in a Viking-age boathouse excavated along the shore of Inner Borgpollen. These include the GA4-85, BIP-24a, SILK-N2, Askja, 860 Layer B, Hekla 1158, Hekla 1104, Vedde Ash, and Saksunarvatn tephra. This research project also explored the use of scanning XRF to locate cryptotephra in lacustrine sediments and presents experimental results of XRF scans of tephra-spiked synthetic sediment cores.

Historically, peat mining has involved drainage processes that alter water chemistry, increase rates of organic matter, release nutrients and therefore impacting downstream recipients. In the catchment of Håtjärnen, Håsjön and Yttersjön, three peat mining sites have been draining into the lakes since the 1980s. This study aimed to investigate the potential impact of these peat mining sites on the lake sediment geochemistry as a complement to a previous study in the area. Four sediment profiles were sampled using an HTH-corer and the sediment geochemistry was analyzed using X-ray fluorescence, Loss on Ignition, Near Infrared spectroscopy, C/N-ratio and Si/Al-ratio. The results from these analyses show that the contribution of peat mining to variations in sediment quality in Håtjärnen, Håsjön and Yttersjön is minimal and that other logical explanations can explain the small variability of the data. In comparison with ratios from other studies, the C/N ratio did not indicate a significant input of organic matter derived from peat. The findings of this study contradict the conclusions from the previous study in the area which highlights the importance of analyzing all the major components of sediment to achive a comprehensive insight of the variations in chemical composition of sediments.

This study aimed to investigate the influence of historical peat mining on current sedimentation and sediment quality in Håtjärnen, Håsjön and primarily Yttersjön. One sediment sample were collected from Håtjärnen and from Håsjön, along with 23 additional samples from Yttersjön. Sampling sites in Yttersjön were strategically located from upstream to downstream, near an inlet draining the nearest peat mining site, to assess its impact on sediment composition. This study analyzed subaqueous sediments, which consists of three constituents: minerogenic material, organic material (OM), and biogenic silica (Si). The sediment geochemistry was analyzed through loss on ignition, X-ray fluorescence, Near Infrared spectroscopy, Si/Al-ratio and lastly C/N ratio serving as a proxy for the origin of OM. No patterns in variation were observed in OM, Si/Al ratio, chlorophyll content, or C/N ratios between the upstream and downstream samples in Yttersjön, suggesting that the peat drainage inlet has a negligible impact on the sediment composition. In comparison, Håtjärnen and Håsjön displayed similar compositions of the sediment. An earlier study conducted in this area reported high sediment accumulation rates for the lakes investigated, as well as a substantial organic composition that included peat residues. These new findings, which contradict the earlier study, highlights the importance of analyzing all constituents of sediment to obtain a comprehensive understanding of the sediment composition.

This study investigates environmental signals of early mining activities in Garpenberg by analysing sediment core samples from three lakes: Gruvsjön, Stora Jälken, and Trehörningen. In addition, a comparison between two methods for analysing the geochemical composition of lake sediment, energy dispersive X-ray fluorescence (ED-XRF) and wavelength dispersive X-ray fluorescence (WD-XRF) was conducted for Gruvsjön. Age-depth models for the sediment profiles was conducted by matching known peaks in historical atmospheric Pb-pollution as points of reference together with the introduction of Norway spruce (Picea abies) pollen in Gruvsjön, and lake formation in Stora Jälken and Trehörningen. The earliest signs of mining activity in Gruvsjön date back to approximately 300-500 CE, as evidenced by the gradual increase in Zn levels. Similarly, the earliest signs of anthropogenic influence in Stora Jälken are around 500 CE, likely related to Zn extraction. However, the absence of changes in other mining-related elements suggests that the observed geochemical shifts in Pb, Cu, Fe, Br and Ti must be explained by other factors. Furthermore, no clear evidence of local mining was identified around Trehörningen. Hence, the observed geochemical changes in this lakes sediment record were attributed to other anthropogenic influences such as damming and agriculture. Lastly, the method comparison between ED-XRF and WD-XRF demonstrates a high degree of coherence for most of the tested elements from the sedimentprofile from Gruvsjön.

Terrestrial inputs of organic matter contribute greatly to the functioning of aquatic ecosystems, subsidizing between 30-70% of secondary production. This contribution of terrestrial resources is especially important in boreal lakes that are largely nutrient-poor and thus more responsive to these additions. Yet the mechanisms underlying initial processing of terrestrial resources by microbial communities at the base of lake food webs remain poorly understood. With this in mind, this thesis aims to advance our understanding of lake sediment microbial community assembly and functioning along abiotic gradients, primarily reflecting variation in terrestrial organic matter inputs that are predicted to increase with future environmental change. Chapter 1 reviews current knowledge on the terrestrial support of lake food webs and highlights gaps in understanding the factors influencing the microbial processing of terrestrial resources. It also provides an overview of metagenomics methods for microbial community analysis and their development over the course of the thesis. Chapter 2 tests how much of ecosystem functioning is explained by microbial community structure relative to other ecosystem properties such as the present-day and past environment. Theory predicts that ecosystem functioning, here measured as CO2 production, should increase with diversity, but the individual and interactive effects of other ecosystem properties on ecosystem functioning remain unresolved. Chapter 3 further questions the importance of microbial diversity for ecosystem functioning by asking whether more diverse microbial communities stabilize ubiquitous functions like CO2 production and microbial abundances through time. It also aims to identify the biotic and abiotic mechanisms underlying positive diversity-stability relationships. Chapter 4 then explores how microbial communities assemble and colonize sediments with varying types and amounts of terrestrial organic matter in three different lakes over a two-month period. Understanding how microbial communities change in relation to sediment and lake conditions can help predict downstream ecosystem functions. Finally, Chapter 5 discusses the main findings of the thesis and ends with proposed avenues for future research.

This thesis investigates how variations in the oxygen isotopic composition of lake waters in northern Fennoscandia are recorded in lake sediment archives, especially diatoms, and how these variations can be used to infer past changes in climate and atmospheric circulation. Results from analyses of the oxygen isotopic composition of lake water samples (δ18Olakew) collected between 2001 and 2006 show that δ18O of northern Fennoscandian lakes is mainly controlled by the isotopic composition of the precipitation (δ18Op). Changes in local δ18Op depend on variations in ambient air temperature and changes in atmospheric circulation that lead to changes in moisture source, vapour transport efficiency, or winter to summer precipitation distribution. This study demonstrates that the amount of isotopic variation in lake water δ18O is determined by a combination of the original δ18Olakew, the amount and timing of the snowmelt, the amount of seasonally specific precipitation and groundwater, any evaporation effects, and lake water residence time. The fact that the same isotope shifts have been detected in various δ18Olakew proxies, derived from hydrologically different lakes, suggests that these records reflect regional atmospheric circulation changes. The results indicate that diatom biogenic silica isotope (δ18Odiatom) records can provide important information about changes in atmospheric circulation that can help explain temperature and precipitation changes during the Holocene. The reconstructed long-term Holocene decreasing δ18Op trend was likely forced by a shift from strong zonal westerly airflow (relatively high δ18Op) in the early Holocene to a more meridional flow pattern (relatively low δ18Op). The large δ18Olakew depletion recorded in the δ18O records around ca. 500 cal yr BP (AD 1450) may be due to a shift to more intense meridional airflow over northern Fennoscandia resulting in an increasing proportion of winter precipitation from the north or southeast. This climate shift probably marks the onset of the so-called Little Ice Age in this region. / At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 1: In press. Paper 2: Submitted. Paper 5: In progress.

Increasing concerns over future anthropogenic effects on climate change as a result of increasing greenhouse gases generate concomitant efforts to better characterize recent climate in order to more accurately predict climate in the future. To this end, a multiproxy study of climate variability in western Ireland from lacustrine sediment was undertaken. The interpretation of paleoclimate records derived from lacustrine carbonate minerals is difficult without a good understanding of the mechanisms that generate variation in isotope values of modern surface waters. Variation in surface waters are ultimately incorporated into lacustrine sediment records conflated by temperature. Therefore, a study of the spatial distribution of ä¹⁸O and äD values of lake and river waters from 144 locations in Ireland has been conducted to provide insight into the behavior of lakes and rivers in Ireland, including source, recycling and loss through evapotranspiration. A 7.6 m sediment core was recovered from Lough Inchiquin that provides evidence for rapid and long-term climate change from the Late Glacial to the Holocene. This was determined using carbon and oxygen isotope analyses of lacustrine calcite as well as carbon from bulk organic sediment fractions. Several significant climate perturbations were identified in the ä¹⁸O_calcite record such as the Oldest Dryas, Younger Dryas, and the 8.2 ka cold event. A previously undescribed climate anomaly between 7,300 to 6,700 cal. yr B.P. characterized by low ä¹⁸O</span>_calcite values with high frequency variability. Variations in carbon isotopes of calcite and bulk organics from the Late Glacial to the Holocene are significant in magnitude (~12) and have similar trends that record temporal shifts in the relative contributions of carbon from the weathering of limestone versus the weathering of terrestrial organic matter. ä¹³C_calcite and ä¹³C_org suggest a rapid recovery of terrestrial vegetation following the Younger Dryas. Change in Ää¹³C_{calcite - org} documents a rapid increase in exogenous fluxes of carbon into the lake at ~9 ka.