Current knowledge of past vegetation and faunal diversity has been based on pollen and macrofossil analysis from lake sediments. The innovative method of sedimentary ancient DNA (sedaDNA) is a promising, complementary proxy to reconstruct information about past environments. However, to what extent animal DNA can be extracted from old sediments and soils has not been frequently studied. This study explored if ancient DNA of moose (Alces alces), reindeer (Rangifer tarangus), goat (Capra aegagrus) and plants could be extracted from millennia old lake sediments of Lake Krigstjärn and archaeological soil samples in northern Sweden. SedaDNA was successfully extracted and detected from both reindeer and plants DNA, while goats sedaDNA was absent in all sediments. Moose ancient DNA (aDNA) was only detected in the archaeological soils. Yet, there were signs that the applied moose primer set was not optimal for heavily degraded DNA and the validity of this primer needs further research. Earliest detections of reindeer DNA can be dated to ~6500 c. years ago. Oldest sediments contained DNA, indicating sufficient DNA preservation conditions in the sediments of Lake Krigstjärn. Finds of plants DNA in pre-deglaciational sediments may indicate the existence of >9500 year old glacial vegetation. Altogether is sedaDNA a highly promising tool to reconstruct diversity, origin and immigration routes of mammals, but technical issues such as primer set specificity and its purpose should be considered and tested carefully in advance.

A pollen profile from varved lake sediments sampled at 10-year intervals and spanning the past 1000 years is analyzed to understand the effects of climate change and anthropogenic activity on forests in southwestern Quebec. The forests responded rapidly to changes in temperature and precipitation during the Medieval Warm Period and Little Ice Age as well as to land-use changes associated with the European Settlement of the area. The transition into the Little Ice Age was abrupt and had significant impact on the pollen production within a couple of decades. A synthesis of this record with other high-resolution and well-dated pollen data from the conifer-hardwood forest of eastern North America shows consistent results across the whole area, indicating that very-high resolution pollen data can provide insight into multi-decadal climate variability and its impact on forest vegetation. Tree-ring records from the region show inter-annual fluctuations not always consistent between sites, while high-resolution pollen data record multi-decadal to century changes which enable us to interpret climatic effects on plant communities.

A high-resolution pollen record from Path Lake (43°87’00”N, 64°92’42”W, 10m asl) in Port Joli Harbour, Nova Scotia, Canada, was used to provide a paleo-ecological perspective on Holocene climate and vegetation variability within the context of local archaeological research. Pollen assemblages in the early Holocene reflect a post-glacial forest dominated by Pinus, Tsuga, Betula and Quercus. Shallow water aquatic and wetland taxa increased after 3400 cal. yr. BP in response to wetter climatic conditions. Increased settlement intensity of native inhabitants coincides with late-Holocene climate change at a regional scale, suggesting that environmental conditions may have influenced prehistoric human activities. European settlement, after 350 cal. yr. BP, was marked by a rise in Ambrosia, and peak charcoal accumulation rates after this time showed evidence of human disturbance on the landscape. This study suggests that environmental changes affected human exploitation of the landscape, and human activity altered forest composition in the late Holocene.

Lake Pa Kho is a fresh water lake in Northeastern Thailand, where the East Asian summer monsoon prevails. The monsoon climate and associated variability has tremendous impacts on the life and environmental aspects of the region. In this study, climate and palaeo-environmental history of Lake Pa Kho has been extracted from geochemical proxy indices during the Holocene time. Geochemical variables like total organic carbon (TOC), total nitrogen (TN), atomic Carbon-Nitrogen ratio (C/N) of organic matter, stable isotope fractionations (δ13C, δ15N, δ34S) and radiocarbon 14C dating of the lake sedimentary core samples were analyzed during the past >7000 cal yr BP in terms of palaeo-climate interpretation. The Loss-on-ignition (LOI%) curve, TOC% value, higher C/N ratio indicate that organic materials in lake sediments has been mostly derived from terrestrial sources. δ13C value supports the terrestrial source of organic matter. TN% and δ15N value indicate low organic productivity in the lake. δ34S value indicate possible anoxic condition in the bottom of the lake due to lowering water level. Lower Aquatic productivity and deposition of organic material from terrestrial sources show that the lake was shallow and dry climate condition prevailed at ~7000 to 2000 cal yr BP due to weak monsoon precipitation. Moreover, monsoon played a significant role in controlling the lake level and overall Aquatic productivity. Progressive lowering of water level due to a lack in precipitation might have transformed the lake into a wetland and subsequently into a peatland at around 1500 cal yr BP. A possible explanation for the gradual shift up to 200 cal yr BP might be invasion of terrestrial vegetation from the surrounding catchment sources due to weak monsoon intensity.

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During the latter half of the 20th century until present day there has been an unprecedented rise in global annual mean temperatures accompanied by rising sea levels and a decrease in Northern Hemisphere snow cover, which if it continues will lead to widespread disruption of climate patterns, ecosystems, and present-day landscapes. It is therefore of critical importance to establish an expanded network of paleoclimate records across the globe in order to better assesses how the global climate system has changed in the past, that we may create a metric by which to address modern change. Herein is presented a7,700 years record of Holocene climatic and environmental variability in Sermilik Valley, located on Ammassalik Island, SE Greenland. This objective of this study is to determine the timing of major Holocene climate transitions as expressed in the physical, elemental, and geochemical parameters preserved in the 484 cm sediment record of Lower Sermilik Lake. Major transitions observed in this study include the deglaciation of Sermilik Valley, the onset and termination of the Holocene Climatic Optimum, the transition into neoglacial conditions, and the Little Ice Age.

Earth's climate is prone to natural and episodic cycles. The most recent period of climate change, the only one to be caused by humans, is significantly affecting species composition and landscapes. Northern expansion of the Boreal Forest in Canada is one of the expected outcomes, and tree line migration northward is one of the anticipated changes. Previous studies have found that many human activities like agriculture, grazing, and pastoralism can significantly affect tree line movement. Improving our ability to examine past tree line dynamics can be achieved using archival records in lake sediments. In this study, we focused on three sediment biomarkers that may be related to the presence of trees in a lake's catchment: n-alkanes, lignin-derived phenols, and stable isotopes of carbon. We examined the composition of these markers in sediment from 19 lakes in Saskatchewan spanning 4 ecoregions, from Prairie Grassland to Boreal Plain, to determine the biomarker signature for lakes in each ecoregion and relating them to land cover (trees vs herbaceous plants) in the catchments of each lake. The results showed that n-alkane composition was significantly correlated to the proportion of trees to herbaceous plants in a lake's catchment, raising the possibility that these can be used to infer the presence of trees in sediment records. The C/N ratio and δ¹³C were not effective in distinguishing ecoregions or land cover composition, likely due to algal production in the lake and agricultural activities in the surrounding farmland, while lignin-derived phenols appeared to be affected by unknown factors.

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Eastern North America experiences large intracratonic earthquakes that are not well understood but pose a risk to urban centers and other infrastructure. Compilation of regional earthquake epicentres for south-central Ontario and western Quebec demonstrate a close association with sutures and failed rifts (the St. Lawrence Rift) recording the formation and breakup respectively of successive supercontinents Rodinia and Pangea. Where seismic potential could be underestimated through lack of historical seismicity or where little is known about active faults, lake deposits can provide a valuable record of past seismic shaking events in the form of sediment deformation structures (i.e. ‘seismites’). In central Canada, the lacustrine seismographic record began approximately 10,000 years before present with the retreat of the Laurentide Ice Sheet, older records having been removed by glacial erosion. Most bedrock lake basins are structurally-controlled and underlain by the same Precambrian basement structures (shear zones, terrane boundaries and other lineaments) implicated as the source of ongoing mid-plate earthquake activity. High resolution seismo-stratigraphic data presented here supports the model that ongoing mid-plate earthquake activity is a consequence of brittle deformation of the upper crust of the North American plate. Such activity appears to have been greatest during deglaciation but continues today. The detailed geophysical and sedimentary studies, as shown here, have major societal relevance in areas of eastern North America affected by intraplate earthquakes. The recognition and mapping of earthquake related features in lakes for seismic risk analysis is a means of constraining seismic recurrence intervals and more realistically assess seismic risk across the populated area of Ontario and Quebec where events occur on time scales much longer than recorded history. / Dissertation / Doctor of Philosophy (PhD)

Much of the current research into the processing and storage of carbon (C) in small lakes has focused on arctic and boreal lake systems, due to their global abundance. However this has led to an imbalance in the interpretation of lake functioning. Oligotrophic lakes are prevalent in the arctic and boreal zone, but are typically net heterotrophic due to loading of catchment-derived dissolved organic carbon (DOC) which alters their metabolic balance. In comparison, temperate lake systems tend to be more nutrient rich, typically due to anthropogenic activity, and would therefore be expected to exhibit the signs of net autotrophy, as a result of higher rates of gross primary production (GPP) and lower rates of catchment-derived DOC potentially subsidising respiration (R). In order to test the hypothesis that temperate, eutrophic lakes are net autotrophic (GPP > R) on an annual basis the C-dynamics of Rostherne Mere (maximum depth, zm, 31 m) and Tatton Mere (zm = 11 m), two monomictic Cheshire-Shropshire meres, were quantified over an 18 months period from 2010 2012. This monitoring study used high-resolution (hourly) oxygen (O2) sonde measurements, combined with high-resolution data from an automated on-lake monitoring buoy at Rostherne Mere (as part of the national UKLEON lake network) to calculate rates of epilimnion C-fixation. For both lakes, sediment traps were also used to determine water column C-flux and sediment core data to establish C-burial efficiency of these strongly stratifying lakes. Water column profiles of dissolved O2 and CO2 was also measured at 2 4 weekly intervals across both lakes. Particular attention was focused on: i) the long term C-storage of eutrophic, monomictic lakes; ii) up-scaling C-accumulation estimates from these two meres to the Cheshire-Shropshire meres region and all UK eutrophic waters; and iii) methodological sensitivity for estimating C-fixation, flux and burial efficiency and upscaling C-accumulation estimates. The results show that both lakes are net autotrophic on an annual basis, on average fixing 121 ± 2 g C m-2 yr-1 and sequestering 68 ± 4 g C m-2 yr-1, a C-burial efficiency of ~60%. If up-scaled to the Cheshire-Shropshire meres region, annual C-accumulation was estimated to be 506 ± 32 t C yr-1 or 0.05 ± 0.001 Mt C since 1900. From this, it was estimated that UK eutrophic waters could be sequestering 0.12 ± 0.01 Mt C yr-1 or 13.3 ± 0.2 Mt C since 1900. Annual UK CO2 emissions are ~128.85 Mt C yr-1, therefore UK eutrophic waters currently offset 0.09% of yearly UK CO2 emissions. Despite the finding that eutrophic, stratifying lakes have high C-fixation and sequestration values, lakes in other areas of the globe such as the arctic and boreal zones are typically a more important long term C-sink as they are far more abundant within the landscape and local soils are typically very poor within low C retention rates. Further investigation is needed into how lakes function on a regional and national scale, the importance of lake type and number when up-scaling C accumulation estimates and the potential impact on future C accumulation as a result of a changing environment and supra-regional policies in areas such as Europe.