Abstract: Acidification was categorized as the main environmental problem in Scandinavia during the 1960’s. Fortunately for Sweden, as with other countries in Scandinavia, has shown a process of recovery from acidification, by emission control. Further Sweden has had an extended liming program to mitigate the effects from acidification. Regarding the acidification assessment of the EU Water Framework Directive, it requires that EU members attain a ‘good ecological status’ in their surface waters. The status is defined as a deviation from a reference value and this is achieved using a reference reflecting a preindustrial state. As the waters are recovering from acidification the liming program can be reduced. Hence, there is a need to develop tools that can be used for decisions to stop liming in single waters. This study states three approaches: the well known hydrochemical model MAGIC, a meta-MAGIC model which calibrates the reference value computed by MAGIC model and paleolimnology studies. The latter is the key because it is the one that measures the reference value by immediate samples insitu. However, all methods have advantages and disadvantages, which allowed the development of an additional tool called meta-paleo for the same purpose. This meta-paleo model is designed based on an 11 years mean of contemporary water chemistry and paleolimnology data of 71 lakes. This tool for acidification assessment enables to work with few parameters of water chemistry. However it is concluded that the model has uncertainties, which should be evaluated so it can be used as a tool for decision making.

Diatom analyses were carried out on sediment cores collected from two low-lying, closed-drainage basins (PAD 9 - 58º46. 46?N, 111º19. 48?W; PAD 12 - 58º57. 29?, 111º19. 74?) in the Peace sector of the Peace-Athabasca Delta (PAD), Alberta, Canada, to provide >1000 year long records of hydro-ecological change. Results from diatom analyses were compared with macrofossil and stable isotope records from the same cores and assessed within the framework of an Athabasca River headwater climate record inferred from isotope dendroclimate data. Results from PAD 9 and PAD 12 sediment cores indicated closed-drainage conditions during the Medieval Warm Period (MWP) and the post-Little Ice Age and high water conditions during the Little Ice Age (LIA). High water levels at PAD 9 and PAD 12 reflected high water conditions on Lake Athabasca and the Rivière des Rochers or possibly the Peace River during the LIA (~AD 1600-1900). High water conditions were also observed at low-lying sites in the central and southern regions of the PAD (PAD 31 and PAD 37), and corresponded with evidence of high streamflows on the North Saskatchewan River. In contrast, desiccation evident at PAD 5, a site largely isolated from river influence, reflected atmospherically dry conditions during the LIA. Consistent with changes observed at PAD 5, sediment records at PAD 15, an oxbow lake off the Revillion Coupé, demonstrated low flood frequency during the early to mid-1700s. Increased water levels evident at low-lying sites located in proximity to the central open-drainage network of lakes and rivers were likely due to higher flows on the Athabasca River and potentially on the Peace River. High flows on rivers of the PAD may be attributed to snowmelt-dominated runoff during the LIA relative to the rainfall-dominated runoff during MWP (prior to ~AD 1600) and the post-LIA period (~AD 1900 to present).

Recent drought over West Africa (1970s-present) has been a global concern, and the ability to predict the frequency and severity of future droughts is important to mitigate the devastating socio-economic effects of drought. The Sahel region, situated at 10-20°N just south of the arid Sahara Desert and north of the forested Guinea Coast, is particularly vulnerable to drought periodicity because rainfall is already low at 400 mm yr-1. The ability to predict future climate variability depends on adequate knowledge of fluctuations in the past. In West Africa, meteorological records are too sparse and too short in duration to characterize the drought frequency. Consequently, climate reconstructions from lacustrine sediment records are increasingly recognized as an important source of information on past climate variability. Lake Bosomtwe, Ghana (6o30N and 1o25W) was formed over one million years ago by a meteorite impact crater in the Guinea Coast region, just south of the Sahel region. Lake Bosomtwe has a closed-drainage hydrology and lake levels are known to fluctuate with the net flux in rainfall inputs relative to evaporative outputs. In 2004, the International Continental Scientific Drilling Program recovered the complete sediment record for paleoclimatic reconstructions. However, very little has been studied of the limnological conditions that lead to the formation of laminated sediments in Lake Bosomtwe. This thesis has set out to understand the influence climate has on the physical, chemical and biological in-lake processes that generate sedimenting materials, which are preserved as laminated sediment layers. Two years of water column sampling of temperature, oxygen and nutrients at a central deep-water site (78 m water depth maximum) found that this quiescent crater lake is thermally stratified during much of the year, with anoxia persisting below 35 m water depth. During the short dry season of July and August, the monsoon rains that are associated with the intertropical convergence zone (ITCZ) are displaced northwards over the Sahel region (and away from lake Bosomtwe), and cool air temperatures and clear night skies lead to the disruption of the thermocline and circulation of dissolved nutrients nitrogen (N) and phosphorus (P) in Lake Bosomtwe. Phytoplankton primary productivity, as measured by particulate carbon and chlorophyll a concentrations, was found to increase markedly following the nutrient upwelling event in August. Sediment trap samplers deployed at 20 and 30 m water depth captured the pattern of organic matter deposition and a high flux of organic sediment was deposited shortly after the nutrient upwelling episode in August. The composition of these organic-rich sediments was distinguished by a marked depletion in δ13C and enrichment of δ15N, as compared to sediments deposited before and after this event. Spatial assessment of sediment cores identified that presently, visible laminations were preserved at and below 35 m water depth, but, not at shallower depths. Water depth was also positively correlated with the organic matter content in sediment records and could be used to reconstruct pre-historic lake levels down core. The relationship between lake level and organic content in sediments predicted that water levels were likely 22 m lower than present levels during the period ~1425-1610 CE, which corresponds with a climatic periods known as the Little Ice Age (LIA). The spatial sediment trends also revealed that inorganic sedimentation rates had increased since the onset of recent land clearance and road construction in the catchment, particularly to the north, near the town of Abono. For this reason, two cores from the central deep-water region of Lake Bosomtwe were analysed for organic and carbonate content, δ13C and δ15N, nutrients (C, N, P), magnetic susceptibility, greyscale imagery of the x-radiograph and micro-X-ray analysis of elemental constituents. Paleoenvironmental reconstructions during the past 550 years found that climate-driven lake level change was a prominent factor contributing to the organic content of sediments. High inorganic content, iron concentrations and depleted δ13C distinguished a low stand during the LIA (~1425-1610) when pelagic sediments were likely exposed to periodic oxygenation. High concentrations of organic matter, calcium (Ca) and strontium (Sr), enrichment of δ13C and low C:N ratios were indicative of wet years that likely increased lake levels and the depth of water column mixing. However, sediments with high organic content, depleted δ13C signatures and reduced Ca and Sr concentrations were suggestive of drought years that restricted the depth of seasonal water column mixing and nutrient circulation and did not necessarily result in pronounced lake-level change. During the past century, δ13C of bulk matter was positively correlated with the rainfall anomalies (r2 = 0.45, P < 0.002), indicating that droughts can result in reduced primary productivity, which may ultimately lower fishery yields. The communities living within the crater are dependent on subsistence fishing and farming, and predicting the drought frequency and magnitude in this region is essential to protecting both the ecosystem and the human population. Long-range climate forecasts for West Africa predict greater drought and increasing air temperature. However, with a detailed long-term paleoclimatic reconstruction from Lake Bosomtwe sediment records, potentially the accuracy of these predictions can be improved and better equip policy makers to enact a viable action plan in the best interests of the people.

Lake-rich thermokarst landscapes, such as Old Crow Flats (OCF) in northern Yukon, Canada have been identified as amongst the most vulnerable to climate change. This has raised concerns of the Vuntut Gwitchin First Nation (VGFN) and Parks Canada (Vuntut National Park) about the ecological integrity of this significant wetland. The influence of climate change on the hydroecological conditions of thermokarst lakes are complex and vary across the landscape, thus long-term hydroecological monitoring is essential to adequately assess the ecological integrity of the aquatic ecosystem and how it is changing over time. In a genuine interdisciplinary and collaborative approach, this thesis establishes an integrated approach using isotope hydrology, aquatic ecology, and paleolimnology to develop a robust long-term aquatic monitoring program that has already been adopted by Parks Canada. In collaboration with Parks Canada, 14 of 58 lakes that were previously studied during the International Polar Year from 2007-09 were selected to represent monitoring lakes. Lakes were sampled in early June and late August/early September 2010-11. Water samples for analysis of hydrogen and oxygen isotope composition and chemistry (i.e., ions and nutrients) were collected to track hydrological and limnological conditions. Artificial substrates were deployed in June and accrued algae were collected at the end of the ice-free season to assess community composition and abundance. Sediment coring was conducted in a culturally-significant lake (Zelma Lake – OCF06) to reconstruct long-term baseline hydroecological conditions over the past three centuries. Radiometric dating techniques (137Cs, 210Pb) were used to develop a sediment core chronology. Baseline hydroecological conditions were reconstructed through analyses of loss-on-ignition, bulk organic carbon and nitrogen elemental and isotope compositions, and pigments. Meteorological data and a multi-year evaporation pan experiment were used to develop a robust isotope framework, which provides the basis for interpreting five years (2007-11) of lake water isotope measurements and deriving knowledge of hydrological conditions for the monitoring lakes. Using this framework and the coupled-isotope tracer method, isotopic compositions of input water (δI) and evaporation-to-inflow (E/I) ratios were calculated and provide key hydrological information for each sampling interval. δ¬I values distinguish snowmelt- and rainfall-sourced lakes, with δP representing a threshold between the two isotopic-based hydrologic regimes. A Mann-Kendall test showed that three lakes (OCF11, 26, and 49) displayed significant increasing trends in δI values indicating a potential transition from snowmelt-sourced to rainfall-sourced isotope-based hydrologic-regimes. E/I ratios >0.5 signifies lakes that are evaporation-dominated with positive water balances and E/I ratios >1 indicates lakes that are evaporation-dominated with negative water balances. Six lakes in OCF (OCF06, 19, 37, 46, 49, and 58) surpass the 0.5 threshold and three of these lakes (OCF06, 19, and 46) crossed the significant evaporation threshold (E/I > 1) during dry climatic conditions. Multi-proxy paleolimnology analysis conducted on Zelma Lake reveals different hydroecological transitions during the past ~330 years that include: phase 1 (~1678-1900) characterized by stable hydroecological conditions; thermokarst expansion (~1900-1943) marked by decreases in productivity; phase 2 (~1943-2007) distinguished by increasing productivity; and a post drainage phase following rapid drainage in 2007 characterized by further increases in productivity. The stratigraphy of Zelma Lake shows that hydroecological conditions in dynamic landscapes such as OCF are complex and require multi-proxy paleolimnological analysis. In particular, organic matter, δ13Corg, and pigment concentrations are important parameters to consider when interpreting past hydroecological conditions, thermokarst expansion, and lake drainage events.

Rapid tropical glacier retreat over the last 50 years has been well documented, and has received significant media attention. Many studies suggest these changes are due to rising global surface air temperatures, however disentangling the effects of temperature and precipitation has hampered scientific consensus. Furthermore, because of the shortness of the instrumental record, it is difficult to assess the larger significance of the climate changes associated with the decline of tropical glaciers. Here, we present a locally calibrated, independent temperature reconstruction for the past 1,500 years from Laguna Chingaza, Colombia based on distributions of branched Glycerol Dialkyl Glycerol Tetraethers (brGDGTs) in order to assess the controls on long term temperature variability in the tropical Andes, and their relationship with growth and demise of Andean glaciers. Comparison of reconstructed temperatures with the instrumental record suggests that our proxy record faithfully records decadal to century scale trends in temperature. The largest temperature decline over the last 1,500 years was a decrease of 2.5 ± 0.3 °C during the Little Ice Age (LIA), reaching lowest temperatures during the mid-17th century, and is broadly consistent with terrestrial temperature reconstructions throughout the tropics and the higher latitudes. The structure and timing of temperature changes at Laguna Chingaza are remarkably similar to recent terrestrial temperature reconstructions from elsewhere in the tropics, including sites in the tropical Pacific and equatorial Africa, suggesting that these changes are widespread in the tropics. Together, these records suggest that warming over the last few decades is unprecedented over the last 1,500 years, including the Medieval Climate Anomaly (800-1150 AD). Comparison of these temperature changes with records of Andean glacier limits suggests that temperature is the dominant driver of glacial retreat, particularly over the past few decades. Additionally, paleotemperatures inferred from LIA and recent glacial equilibrium line altitudes (ELAs) underestimate past changes in temperature when compared with brGDGTs reconstructions, suggesting that changes in precipitation complicate the use of glacier ELAs to reconstruct past temperatures. The coupling of temperature and ice extent in South America suggests that with projected future warming, the health of tropical glaciers could be in jeopardy, significantly impacting the communities and ecosystems that depend on them. / text

No description available.

Recent drought over West Africa (1970s-present) has been a global concern, and the ability to predict the frequency and severity of future droughts is important to mitigate the devastating socio-economic effects of drought. The Sahel region, situated at 10-20°N just south of the arid Sahara Desert and north of the forested Guinea Coast, is particularly vulnerable to drought periodicity because rainfall is already low at 400 mm yr-1. The ability to predict future climate variability depends on adequate knowledge of fluctuations in the past. In West Africa, meteorological records are too sparse and too short in duration to characterize the drought frequency. Consequently, climate reconstructions from lacustrine sediment records are increasingly recognized as an important source of information on past climate variability. Lake Bosomtwe, Ghana (6o30N and 1o25W) was formed over one million years ago by a meteorite impact crater in the Guinea Coast region, just south of the Sahel region. Lake Bosomtwe has a closed-drainage hydrology and lake levels are known to fluctuate with the net flux in rainfall inputs relative to evaporative outputs. In 2004, the International Continental Scientific Drilling Program recovered the complete sediment record for paleoclimatic reconstructions. However, very little has been studied of the limnological conditions that lead to the formation of laminated sediments in Lake Bosomtwe. This thesis has set out to understand the influence climate has on the physical, chemical and biological in-lake processes that generate sedimenting materials, which are preserved as laminated sediment layers. Two years of water column sampling of temperature, oxygen and nutrients at a central deep-water site (78 m water depth maximum) found that this quiescent crater lake is thermally stratified during much of the year, with anoxia persisting below 35 m water depth. During the short dry season of July and August, the monsoon rains that are associated with the intertropical convergence zone (ITCZ) are displaced northwards over the Sahel region (and away from lake Bosomtwe), and cool air temperatures and clear night skies lead to the disruption of the thermocline and circulation of dissolved nutrients nitrogen (N) and phosphorus (P) in Lake Bosomtwe. Phytoplankton primary productivity, as measured by particulate carbon and chlorophyll a concentrations, was found to increase markedly following the nutrient upwelling event in August. Sediment trap samplers deployed at 20 and 30 m water depth captured the pattern of organic matter deposition and a high flux of organic sediment was deposited shortly after the nutrient upwelling episode in August. The composition of these organic-rich sediments was distinguished by a marked depletion in δ13C and enrichment of δ15N, as compared to sediments deposited before and after this event. Spatial assessment of sediment cores identified that presently, visible laminations were preserved at and below 35 m water depth, but, not at shallower depths. Water depth was also positively correlated with the organic matter content in sediment records and could be used to reconstruct pre-historic lake levels down core. The relationship between lake level and organic content in sediments predicted that water levels were likely 22 m lower than present levels during the period ~1425-1610 CE, which corresponds with a climatic periods known as the Little Ice Age (LIA). The spatial sediment trends also revealed that inorganic sedimentation rates had increased since the onset of recent land clearance and road construction in the catchment, particularly to the north, near the town of Abono. For this reason, two cores from the central deep-water region of Lake Bosomtwe were analysed for organic and carbonate content, δ13C and δ15N, nutrients (C, N, P), magnetic susceptibility, greyscale imagery of the x-radiograph and micro-X-ray analysis of elemental constituents. Paleoenvironmental reconstructions during the past 550 years found that climate-driven lake level change was a prominent factor contributing to the organic content of sediments. High inorganic content, iron concentrations and depleted δ13C distinguished a low stand during the LIA (~1425-1610) when pelagic sediments were likely exposed to periodic oxygenation. High concentrations of organic matter, calcium (Ca) and strontium (Sr), enrichment of δ13C and low C:N ratios were indicative of wet years that likely increased lake levels and the depth of water column mixing. However, sediments with high organic content, depleted δ13C signatures and reduced Ca and Sr concentrations were suggestive of drought years that restricted the depth of seasonal water column mixing and nutrient circulation and did not necessarily result in pronounced lake-level change. During the past century, δ13C of bulk matter was positively correlated with the rainfall anomalies (r2 = 0.45, P < 0.002), indicating that droughts can result in reduced primary productivity, which may ultimately lower fishery yields. The communities living within the crater are dependent on subsistence fishing and farming, and predicting the drought frequency and magnitude in this region is essential to protecting both the ecosystem and the human population. Long-range climate forecasts for West Africa predict greater drought and increasing air temperature. However, with a detailed long-term paleoclimatic reconstruction from Lake Bosomtwe sediment records, potentially the accuracy of these predictions can be improved and better equip policy makers to enact a viable action plan in the best interests of the people.

The current study developed a paleolimnological approach to assess changes in diatom assemblages (class Bacillariophyceae) from present-day lake sediments in comparison to those deposited before significant human impact (ca. pre-1850) from 51 Halifax (Nova Scotia, Canada) region lakes in conjunction with a regional diatom-based transfer functions for pH and total phosphorus. All 51 lakes showed changes in diatom assemblages between the present-day and pre-industrial assemblages that was greater than would be expected (i.e. similarity between ‘top’ and ‘bottom’ samples was much less than the similarities within triplicate ‘top’ and ‘bottom’ samples). To help identify the most important environmental stressors impacting diatom assemblages in these lakes, diatom-based reconstructions of inferred changes in pH (DI-pH) and total phosphorus (DI-TP) that were greater than the Root Mean Squared Error (RMSE) of the respective inference models were reconstructed for each of the 51 lakes. For example, a decrease in DI-pH greater than the RMSE of the pH model would be a strong indication of recent acidification, whereas an increase in DI-TP greater than the RMSE of the model indicates nutrient enrichment. Based on this approach, 4% of the lakes are showing acidification-related trends occurring in lakes with low pre-industrial pH values and relatively undisturbed watersheds. Almost 14% of the study lakes have been impacted by nutrients and characterized by watershed development and high concentrations of TP. Approximately 4% of lakes showed oligotrophication and acidification. Diatom assemblages from almost 20% of the study lakes that were relatively unimpacted by the afore-listed environmental stressors show trends consistent with climate warming. These lakes show an increase in DI-pH greater than the RMSE of the inference model, and floristic changes typically showed a decrease in the relative abundance of Aulacoseira distans paralleled with increase in Cyclotella stelligera and other planktonic diatoms in the modern sediments. In addition, Diatoma tenue and Diploneis parma, diatoms tolerant of high conductivity, increased in 45% of the study lakes suggesting road salt as an additional stressor. This thesis provides a rapid paleolimnological-based technique to assess regional water-quality changes, and further demonstrates the complexity of ecological changes within freshwater resources. / Thesis (Master, Biology) -- Queen's University, 2009-09-10 15:18:07.01

Despite the documented sensitivity of polar environments, long-term monitoring data are especially sparse in these regions. Diatom-based paleolimnology has contributed significantly to understanding the response of Arctic lakes to climate change, but most studies have been conducted in regions with relatively high lakewater buffering capacity. As such, Pim Island (Nunavut, Canada) is a region of limnological interest because, due to the local geology, its surface waters are of relatively lower pH and previous research suggests that such softwater lakes may be especially responsive to climate fluctuations and therefore provide the best paleoclimate records. This thesis has two separate but related chapters, as well as an exploratory study included in appendix. First, a novel approach using visible-near-infrared spectroscopy (VNIRS) was used to infer lakewater dissolved organic carbon (DOC), from a 160-lake calibration set from the Canadian Arctic. Historically sound and similar trends were reconstructed when compared against a Canadian diatom-based DOC and Swedish VNIRS-based total organic carbon (TOC) model on Arctic Holocene sediment records. Second, a diatom and spectroscopically-based multi-proxy approach was utilized on Holocene sedimentary records from two lakes on Pim Island to assess long-term environmental change from this region. Benthic and epiphytic diatom taxa dominated the pre-19th century assemblages, although marked shifts in dominant species were recorded during the mid-Holocene. The mid-Holocene diatom assemblages underwent an abrupt ecological shift from alkaliphilous Fragilaria sensu lato to slightly acidophilous Achnanthes and Navicula. The post-19th century was characterized by an increase in the planktonic species (Cyclotella radiosa), indicating marked lakeice reductions. Third, the limnological properties and modern diatom assemblages of ponds and lakes surveyed from 1979 to 2009 on Pim Island were examined as part of an exploratory study. The ponds and lakes displayed typical characteristics observed in high Arctic lacustrine environments (i.e. oligotrophic, very dilute) but with overall relatively low alkalinity. Poorly-buffered sites had diatom assemblages that were distinct from well-buffered lakes elsewhere in the High Arctic. Our findings contribute to an improved understanding of the interactions between local environments and limnological changes, and also provide insight on the biological responses of lakes to Holocene environmental change and allow us to compare responses to those in more alkaline sites. / Thesis (Master, Biology) -- Queen's University, 2010-12-22 19:53:45.03

A two-part paleolimnological study was conducted to: i) understand the important factors that are related to the present-day distribution of scaled-chrysophytes; ii) investigate changes in the scaled-chrysophyte assemblages in the Experimental Lakes Area northwestern Ontario, in response to recent climate warming. Scaled-chrysophyte assemblages were analyzed in the modern sediments of 40 ELA lakes to determine their relationship to measured environmental variables. The sediment record from 210Pb dated cores from six ELA lakes were analyzed at a sub-decadal resolution to evaluate if chrysophytes were changing in a consistent fashion and if these changes could be accounted for by measured climatic factors. Ordination analysis of the modern chrysophyte flora was significantly related to pH, lake depth, and the degree of thermal stratification, as well as water temperature. Mallomonas punctifera ‘small’ and Mallomonas acaroides were indicators of warm surface-waters. High-resolution analysis of six ELA lakes revealed pronounced shifts in the chrysophyte assemblages over the last ca. 150 years. The most notable shift in the chrysophyte assemblage was characterized by an overall shift towards higher relative abundances of colonial taxa. In several lakes increases in unicellular warm-water taxa were also observed. Breakpoint Analysis identified significant changes in the chrysophyte assemblages beginning in the late-1800s to mid-1900s in most lakes. An interclass correlation coefficient (ri) was used to assess the temporal coherency of the chrysophyte assemblages over the past ca. 100 years. All lakes displayed a similar directional change which was significantly coherent (p<0.05). A Brien’s Test identified sub-sets of lakes that were temporally coherent and homogenous. The high coherency of two groups, (Group A, grand mean=0.89, p-value=5.3x10-15; Group B, grand mean=0.38, p-value=0.038), suggests the dominance in extrinsic factors in governing the lake responses. The average PCA axis-1 scores of Group A (r-value=0.62, p=0.03) and Group B (r-value=0.60, p=0.038) were significantly correlated to regional mean annual temperature. Collectively, the results of this study suggest that changes observed in the scaled-chrysophyte assemblages in the ELA region are consistent with recent climate warming. / Thesis (Master, Biology) -- Queen's University, 2011-09-29 16:42:06.753