The bioaccumulation of organic contaminants in aquatic ecosystems has been a key focus in environmental toxicology over the last decades. Bioaccumulation is a key concept in ecological risk assessments since it controls the internal dose of potential environmental contaminants. Information on the bioaccumulation of contaminants is used by regulatory authorities in the development of water quality standards, categorizing substances that are potential hazards and quantifying the risk of chemicals to human health. A basis for identifying priority chemicals has been the use of the octanol-water partition coefficient (KOW) as a criterion to estimate bioaccumulation potential. However, recognizing that the bioaccumulation process is not controlled by the hydrophobicity of a chemical alone, this thesis proposes a set of tools, incorporating chemical properties, environmental characteristics and physiological properties of organisms, to study the bioaccumulation of contaminants in aquatic ecosystems.  In striving to achieve this objective, a tool based on an equilibrium lipid partitioning approach was used in Paper I to evaluate monitoring data for bioaccumulation of organic contaminants. In Papers II and III, mechanistic based modelling tools were developed to describe bioaccumulation of hydrophobic compounds in aquatic food webs. In Paper IV, the bioaccumulation of organic compounds in aquatic food chains was studied using stable isotopes of nitrogen. The mechanistic fate and food web models developed in this thesis provide regulators and chemical manufacturers with a means of communicating scientific information to the general public and readily applicable mechanistic fate and food web models that are easily modified for evaluative assessments purposes.

This thesis describes the development and the use of quantitative deuterium Nuclear Magnetic Resonance spectroscopy (NMR) as a tool in two areas of environmental research: the study of long term climate-plant interactions and the source tracking of persistent organic pollutant. Long-term interactions between plants and climate will influence climate change during this century and beyond, but cannot be studied in manipulative experiments. We propose that long tree rings series can serve as records for tracking such interactions during past centuries. The abundance of the stable hydrogen isotope deuterium (D) is influenced by physical and biochemical isotope fractionations. Because the overlapping effects of these fractionations are not understood, studies of the D abundance of tree rings led to conflicting results. We hypothesized that both types of fractionations can be separated if the D abundance of individual C-H groups of metabolites can be measured, that is if individual D isotopomers are quantified. The first paper describes a technique for quantification of D isotopomers in tree-ring cellulose by NMR. The technique showed that the D isotopomers distribution (DID) was non-random. Therefore, the abundance of each isotopomer potentially contains individual information which suggests an explanation for the conflicting results obtained by measuring the overall D abundance (dD). In the second paper, this technique was used to study hydrogen isotope exchange during cellulose synthesis in tree rings. This revealed that some C-H positions exchange strongly with xylem water, while others do not. This means that the exchanging C-H positions should acquire the D abundance of source water, which is determined by physical fractionations, while non-exchanging C-H positions of tree-ring cellulose should retain biochemical fractionations from the leaf level. Therefore, the abundance of the corresponding D isotopomers should contain information about climate and physiology. When analysing tree-ring series, the DIDs should reflect information about temperature, transpiration and regulation of photosynthesis. In the third paper, we showed that CO2 concentration during photosynthesis determines a specific abundance ratio of D isotopomers. This dependence was found in metabolites of annual plants, and in tree-ring cellulose. This result shows that D isotopomers of tree-ring series may be used to detect long-term CO2 fertilisation effects. This information is essential to forecast adaptations of plants to increasing CO2 concentrations on time scales of centuries. In the fourth paper, the source of persistent organic pollutants in the environment was tracked using DID measurements. The dD values of two compounds of related structures were not enough to show indisputably that they did not originate from the same source. However, the DIDs of the common part between the two compounds proved that they did not originate from the same source. These results underline the superior discriminatory power of DIDs, compared to dD measurements. The versatility of DID measurements makes them a precious tool in addressing questions that can not be answered by dD measurements. / Betson, Tatiana R

How much groundwater flows to boreal streams depends on the relative contributions from each landscape unit (forested uplands, lakes, and peatlands) within a catchment along with its hydrogeologic setting. Although there is an understanding of the hydrologic processes that regulate groundwater outputs from individual landscape units to their underlying aquifers (both coarse- and fine-textured) in the boreal forest, less understood is how the topography, typology, and topology (i.e. hydrologic connectivity) of the landscape units regulates groundwater flow to streams. Improved understanding of groundwater-stream interactions in the Boreal Plain of Alberta and Saskatchewan is critical as this region is undergoing substantial environmental change from land cover disturbances for energy and forestry industries and climate change. This thesis determines groundwater-stream interactions during the autumn low-flow period in a 97 km2 glacial outwash sub-catchment of White Gull Creek Research Basin, Boreal Ecosystem Research and Modelling Site, Saskatchewan. The catchment (Pine Fen Creek) is comprised of a large (30 km2) valley-bottom peatland, two lakes, and jack pine (Pinus banksiana) uplands. The pine uplands are important areas of annual groundwater recharge for the catchment. Vertical hydraulic gradients (VHGs) show frequent flow reversals between the lakes and sand aquifer, and spatially diverse VHGs between the peatland and sand aquifer. Groundwater flow nets and lateral hydraulic gradients indicate the stream receives groundwater along its length. Isotopic samples of end members corroborate the hydrometric data. Catchment streamflow response during the 2011 low flow period was not simply the addition of net groundwater inputs from each landscape unit. Instead, the large size, valley-bottom position, and short water ‘memory’ of the peatland were the critical factors in regulation of catchment streamflow during low flow periods. Peatland hydrologic function alternated between a source and sink of runoff (surface and subsurface) to the stream, dependent on the position of the water table; a value of 0.15 m below peat surface was the critical functional tipping point. Given the high percentage of peatlands (21%) within the Boreal Plain, incorporating their runoff threshold is required in parameterizing runoff generation in hydrological models, and thus predicting impacts of peatland degradation and forest clearing on streamflow.

I studied carotenoids in the eggs of American coots (<i>Fulica americana</i>) from 3 study sites in Saskatchewan, Canada. I supplemented two diet types designed to reduce carotenoids in the diet of laying coots to investigate the relationship of carotenoids and the size of eggs and to examine the allocation of carotenoids into eggs.</p><p>In chapter 2, I examined influences of local environment, food quantity and food quality on egg size. Carotenoid content and stable nitrogen and carbon isotopes in yolk were measured and used to elucidate whether variation in type of food eaten contributes to egg size. By analyzing isotopes in coot tissues, I confirmed that coots use endogenous lipid reserves for egg formation but not endogenous protein reserves, and the size of eggs is more dependent on exogenous sources of nutrients. My data demonstrate that carotenoids are not causal in egg size, but are components of natural, high quality diets.</p> <p>Carotenoids are obtained through the diet and deposited into egg yolk. It has been hypothesized that concentrations and percentages of individual carotenoids can be labile and dependent on diets or maintained in an optimal balance to meet requirements of embryos. In chapter 3, I investigate deposition of carotenoids in egg yolk among nesting locales, among hens within a site and among treatments in a diet manipulation experiment. My data show maintenance in the percent composition of a suite of 3 important carotenoids, lutein, zeaxanthin and âcarotene, independent of scale of investigation and in contrast to other individual carotenoids that appear to vary in proportions based on diet. These results suggest that birds can maintain nutritional balances in their eggs despite variation in diets.</p><p>In chapter 4, I tested 3 hypotheses regarding the apportionment of carotenoids into egg yolk over the laying sequence. Without exception, concentrations of these nutrients have previously been shown to decline with egg sequence. In contrast to these findings, coots actually increased the carotenoid concentration in yolks over the laying sequence. My experimental evidence supports the explanation that this pattern of deposition depends on carotenoid availability to the laying female.

Hydroelectric reservoirs account for 59% of the installed electricity generating capacity in Canada and 26% in Ontario. Reservoirs also provide irrigation capacity, drinking water, and recreational opportunities. Further, they continue to be built in northern Canada, neighbouring boreal countries, and around the world. Yet given their socio-economic importance, they are understudied with respect to greenhouse gas emissions, nutrient and mercury cycling, and aquatic metabolism. As one of many electricity generating options, hydroelectricity is viewed as well-tested because of its long history and diverse applications in mega-projects, run-of-the-river dams, and small, local applications. It is also considered renewable from a fuel stand-point because an adequate long-term supply of water is assumed. One of several significant criticisms of hydroelectric development is that reservoirs may be a significant source of greenhouse gases to the atmosphere relative to the amount of electricity produced due to flooding the landscape. As a result of the dearth of information on reservoir development and both greenhouse gases and aquatic metabolism, a pair of whole-ecosystem reservoir experiments were conducted staring in 1991. Three upland boreal forest reservoirs with differing amounts of pre-flood stored organic carbon were built in northwestern Ontario and flooded for five years. The rates of net greenhouse gas production in these reservoirs were determined by calculating mass budgets for carbon dioxide and methane. Additionally, rates of biological processes were determined by combining the mass budgets with measurements of the stable isotopes of carbon and oxygen. Assembling mass and isotope-mass budgets required three related projects on gas exchange, methane oxidation, and oxygen isotopes. To estimate the gas exchange coefficient for each of the upland reservoirs, a comparative-methods study was undertaken. Methane oxidation enrichment factors were determined in upland and wetland boreal reservoirs so that the importance of methane oxidation in these ecosystems could be assessed. In order to interpret the diel changes in both oxygen concentrations and their isotopic ratios, a dynamic model was developed. This model, PoRGy, was successfully applied to the upland boreal reservoirs as well as prairie rivers and ponds. Further, PoRGy was used to understand the interplay between the key parameters that control oxygen concentrations, to compare aquatic ecosystems, to make quantitative estimates of ecosystem metabolism, and to assess the vulnerability of aquatic ecosystems under various environmental stressors. Carbon isotope-mass budgets were used to conclude that community respiration rates declined quickly in the upland reservoirs and had declined by half over five years. This suggested that the most labile organic carbon is quickly consumed but decomposition continued for the five-year life of the project. Net primary production rates were similar for three years, with a small peak in the second or third year, before declining by half by the fifth year. Together, these results indicated that aquatic metabolism slowed over five years while the reservoirs remained a source of greenhouse gases to the atmosphere each year. Net methane production was greatest in the third year of flooding then decreasing by about half by the fifth year. Methane ebullition also peaked in the third year and declined by two-thirds by the fifth year. Together, these results indicated that methanogenesis was greatest in the third year of flooding. The flux of methane to the atmosphere grew in importance relative to that of carbon dioxide over the five years of the experiment. Community respiration and primary production could not be estimated directly from the oxygen isotope-mass budgets since the oxygen respiration enrichment factor remains poorly constrained. Instead, three estimates were made, each based on a different assumption. In general, these estimates suggested that rates of community respiration and primary production decreased slightly for three years and most rapidly in the final two years. The oxygen isotope-mass budgets provided a new method for assessing and constraining community metabolism and greenhouse gas fluxes to the atmosphere. One of the major hypotheses of the whole-ecosystem reservoir experiments was that pre-flood organic carbon stores less tree boles were positively related to greenhouse gas fluxes. Within the three upland boreal forest reservoirs, this hypothesis did not hold true. Over five years, community respiration in the three reservoirs was within 5% of each other. When methane is included, to assess total greenhouse gas fluxes to the atmosphere, the reservoirs were within 1% of each other. Organic carbon stores were therefore poor short-term predictors of carbon lability and greenhouse gas fluxes. This research presented two methods for determining biological rates at the whole-ecosystem scale: one using carbon isotopes and one using oxygen isotopes. Temporal evolution of greenhouse gas cycling within the upland reservoirs was different than in the wetland reservoir and should inform how reservoir development is done vis-à-vis the amount of flooded land of each type versus electricity production. Medium-term estimates of greenhouse gas fluxes suggest that upland reservoirs do not have adequate pre-flood organic carbon stores to sustain elevated levels of decomposition the way wetlands do. The strong evidence of continued production of dissolved organic carbon in the upland reservoirs should concern operators of municipal drinking water reservoirs since elevated dissolved organic carbon can make disinfection difficult.

Allochthonous carbon can be a large proportion of the carbon budget in northern temperate and boreal lakes. This thesis uses stable carbon and oxygen isotopes to examine the fate of allochthonous dissolved organic matter (DOM) in northern temperate lakes, and to determine the importance of dissolved organic carbon (DOC) in lake carbon mass balances and in the δ¹³C of lake sediments. To use stable isotopes as a tool for studying DOC loss and sedimentation within lakes requires an understanding of processes that affect the δ¹³C and δ¹⁸O in aquatic systems. Photolysis is one mechanism that can account for the large allochthonous DOC loss within northern temperate lakes. There is, however, little research examining the effects of photolysis on stable isotopes (e.g. δ¹³C and δ¹⁸O) in aquatic systems, or how photodegradation of DOM affects the δ¹³C of lake sediments. To study the effects of DOM photodegradation on carbon and oxygen isotopes, stream waters from catchments with varying peatland coverage were incubated in Tedlar bags placed in water baths under natural sunlight. Results from three streams flowing into two oligotrophic headwater lakes (Harp and Dickie Lakes) indicate that O₂ consumption rates and dissolved inorganic carbon (DIC) production rates were an order of magnitude greater in light exposed treatments than in dark treatments, suggesting that light mediated processes control O₂ consumption and DIC production in incubations. The similarity between filtered, inoculated, and sterile treatments, indicate that photolysis was the dominant O₂ consuming and DIC producing process in the incubations, while the contribution of respiration to these processes was not detectable. Differences in both O₂ consumption rates and DIC production rates (normalized to DOC loss) among streams suggest that DOM photolability was an important factor in both O₂ loss and DIC production on a volumetric basis. A concomitant increase in δ¹⁸O-O₂ was observed with O₂ loss indicating that during the photo-oxidation of DOM, the lighter ¹⁶O isotopomer was preferentially consumed in the oxidation of DOC to CO₂. Fractionation factors for respiration, photolysis and other abiotic reactions were not a function of O₂ consumption rates and ranged between 0.988 and 0.995, which lies outside the range published for respiration (0.975-0.982). These are the first published photolytic fractionation factors. The δ¹³C-DIC produced collectively by photolysis, respiration, and other abiotic reactions in incubations exposed to natural sunlight ranged between –23‰ and –31‰, and were similar in the light incubations for each treatment, but different among streams. Together, the light and dark incubation data suggest that photolysis and other abiotic reactions were largely responsible for the DIC concentration and δ¹³C-DIC changes observed, while respiration is a relatively minor contributor. During the incubations, as DOC photodegraded to CO₂, the lighter ¹²C isotope was preferentially mineralized (or the moieties cleaved were depleted in ¹³C) leaving the residual δ¹³C-DOC 1‰ to 4‰ enriched, creating enrichment (ε) values up to ~–3‰. The change in final δ¹³C-DOC after DOM photodegradation was different for each inflow, ranging from ~1 ‰ to 8.0 ‰, and provides an average enrichment of –2.1‰ (Harp Inflows ε: –1.2‰; Dickie Inflows ε: –3.4‰). These ε values are in agreement with the average ε from previous incubations on 3 of the inflows and 3 published studies based on UV exposed bog water (Osburn et al., 2001), riverine waters (Opsahl and Zepp, 2001), and lyophilized Juncus leachate dissolved in lake water (Vähätalo and Wetzel, 2008) (average ε = –2.9‰). The structure of DOM changed during photolysis. Absorbance data indicated that the aromaticity, colour, UV absorption and the average molecular size of the DOC decreased. Additionally, after exposure to sunlight, C/N ratios of the DOC changed from high values (24-55), indicative of terrestrial inputs, to lower values (4-13) traditionally thought to be representative of algal or microbial inputs. This contradicts the conventional view that terrestrial DOC has C/N ratios >20, and shows that abiotic processes can alter allochthonous carbon structure and the residual allochthonous carbon can have C/N values similar to, or overlapping with, C/N ratios expected from algal or microbial carbon. With the loss of 61-90% of the DOC, the particulate organic carbon (POC) created accounted for 20-90% of the DOC lost. Values of δ¹³C-POC ranged from –25.7‰ to –27.7‰, with 80% of the samples within 1‰ of the initial δ¹³C-DOC indicating that the particulate carbon created from the photodegradation of DOM that settles to the lake sediments could be isotopically similar to the source DOC. Overall, these incubations indicate that the photodegradation of DOM can affect both concentrations and isotopes of O₂, DIC, DOC, and POC of the stream waters flowing into Harp and Dickie Lakes and are important to consider in lake dynamics of high DOC retention lakes. Two independent methods were used to examine the importance of allochthonous DOC to lake sediments. The first method used a two end-member mixing model to estimate the proportion of allochthonous and autochthonous carbon within the lake sediments. Inflow δ¹³C-POC data, δ¹³C-leaf litter measurements, and DOC photodegradation experiments were used to calculate average annual δ¹³C-POC values for the allochthonous end member. The average annual δ¹³C-POC values for the autochthonous end member were calculated using estimates of productivity, surface δ¹³C-CO₂ values and estimated average annual fractionation factors. Average annual δ¹³C-POC values from allochthonous and autochthonous sources for these lakes were distinct. Using the end members to calculate the relative contributions of allochthonous and autochthonous carbon to lake sediments revealed that the δ¹³C of the lake sediment can be significantly affected by the ratio of autochthonous and allochthonous contributions. Furthermore, peaks in the allochthonous contributions of carbon accompany the δ¹³C peaks in the sediment records to the lake sediments. This suggests that climate change and/or anthropogenic changes to the landscape, and the concomitant changes in DOC inputs to lakes, can be recorded in the sediment record indicating that sediment records are not just productivity signals, but also mass balance signals in high DOC retention lakes. In the second method carbon isotope budgets were completed to accompany the carbon mass budgets for Harp and Dickie Lakes. Mass-weighted average annual δ¹³C-DOC values from the inflows and outflows and δ¹³C-DIC values from the inflows varied by 0.2‰ to 1.3‰, suggesting the values are well constrained. Conversely, the range of weighted δ¹³C-DIC values from the outflows were larger (2.2‰) than those of the inflows. Calculated δ¹³C values of the lake sediment were not equal to the measured δ13C values of the lake sediments for either Harp or Dickie Lakes suggesting a problem lies within the mass balances, or the weighted average annual δ¹³C values used in the isotope budgets. To examine the sensitivity of the average annual weighted δ¹³C values for the carbon entering and exiting the lakes, and the mass of carbon entering the lakes δ¹³C of the lake sediments, a mass and isotope budget model was created. The model indicated that the δ¹³C of the lake sediments is sensitive to a number of parameters including the amount of DOC entering the lake, the δ13C-CO2 evaded from the lake, the areal water discharge rate (qs), the gas exchange coefficient (k), and pH. Many of these parameters required adjustments for the masses of carbon to match those presented in the mass balances suggesting that the mass balances averaged over 8 years have errors associated with them. However, changing the DOC load to the lakes in the model by the variability observed over all the years of the mass balances) indicates that the isotopic signature of the lake sediment could change by up to 2.5‰. This isotope change is large enough to account for the historical δ¹³C changes observed in the δ¹³C sediment record, suggesting that allochthonous DOC can drive the sediment record.

Hydroelectric reservoirs account for 59% of the installed electricity generating capacity in Canada and 26% in Ontario. Reservoirs also provide irrigation capacity, drinking water, and recreational opportunities. Further, they continue to be built in northern Canada, neighbouring boreal countries, and around the world. Yet given their socio-economic importance, they are understudied with respect to greenhouse gas emissions, nutrient and mercury cycling, and aquatic metabolism. As one of many electricity generating options, hydroelectricity is viewed as well-tested because of its long history and diverse applications in mega-projects, run-of-the-river dams, and small, local applications. It is also considered renewable from a fuel stand-point because an adequate long-term supply of water is assumed. One of several significant criticisms of hydroelectric development is that reservoirs may be a significant source of greenhouse gases to the atmosphere relative to the amount of electricity produced due to flooding the landscape. As a result of the dearth of information on reservoir development and both greenhouse gases and aquatic metabolism, a pair of whole-ecosystem reservoir experiments were conducted staring in 1991. Three upland boreal forest reservoirs with differing amounts of pre-flood stored organic carbon were built in northwestern Ontario and flooded for five years. The rates of net greenhouse gas production in these reservoirs were determined by calculating mass budgets for carbon dioxide and methane. Additionally, rates of biological processes were determined by combining the mass budgets with measurements of the stable isotopes of carbon and oxygen. Assembling mass and isotope-mass budgets required three related projects on gas exchange, methane oxidation, and oxygen isotopes. To estimate the gas exchange coefficient for each of the upland reservoirs, a comparative-methods study was undertaken. Methane oxidation enrichment factors were determined in upland and wetland boreal reservoirs so that the importance of methane oxidation in these ecosystems could be assessed. In order to interpret the diel changes in both oxygen concentrations and their isotopic ratios, a dynamic model was developed. This model, PoRGy, was successfully applied to the upland boreal reservoirs as well as prairie rivers and ponds. Further, PoRGy was used to understand the interplay between the key parameters that control oxygen concentrations, to compare aquatic ecosystems, to make quantitative estimates of ecosystem metabolism, and to assess the vulnerability of aquatic ecosystems under various environmental stressors. Carbon isotope-mass budgets were used to conclude that community respiration rates declined quickly in the upland reservoirs and had declined by half over five years. This suggested that the most labile organic carbon is quickly consumed but decomposition continued for the five-year life of the project. Net primary production rates were similar for three years, with a small peak in the second or third year, before declining by half by the fifth year. Together, these results indicated that aquatic metabolism slowed over five years while the reservoirs remained a source of greenhouse gases to the atmosphere each year. Net methane production was greatest in the third year of flooding then decreasing by about half by the fifth year. Methane ebullition also peaked in the third year and declined by two-thirds by the fifth year. Together, these results indicated that methanogenesis was greatest in the third year of flooding. The flux of methane to the atmosphere grew in importance relative to that of carbon dioxide over the five years of the experiment. Community respiration and primary production could not be estimated directly from the oxygen isotope-mass budgets since the oxygen respiration enrichment factor remains poorly constrained. Instead, three estimates were made, each based on a different assumption. In general, these estimates suggested that rates of community respiration and primary production decreased slightly for three years and most rapidly in the final two years. The oxygen isotope-mass budgets provided a new method for assessing and constraining community metabolism and greenhouse gas fluxes to the atmosphere. One of the major hypotheses of the whole-ecosystem reservoir experiments was that pre-flood organic carbon stores less tree boles were positively related to greenhouse gas fluxes. Within the three upland boreal forest reservoirs, this hypothesis did not hold true. Over five years, community respiration in the three reservoirs was within 5% of each other. When methane is included, to assess total greenhouse gas fluxes to the atmosphere, the reservoirs were within 1% of each other. Organic carbon stores were therefore poor short-term predictors of carbon lability and greenhouse gas fluxes. This research presented two methods for determining biological rates at the whole-ecosystem scale: one using carbon isotopes and one using oxygen isotopes. Temporal evolution of greenhouse gas cycling within the upland reservoirs was different than in the wetland reservoir and should inform how reservoir development is done vis-à-vis the amount of flooded land of each type versus electricity production. Medium-term estimates of greenhouse gas fluxes suggest that upland reservoirs do not have adequate pre-flood organic carbon stores to sustain elevated levels of decomposition the way wetlands do. The strong evidence of continued production of dissolved organic carbon in the upland reservoirs should concern operators of municipal drinking water reservoirs since elevated dissolved organic carbon can make disinfection difficult.

Allochthonous carbon can be a large proportion of the carbon budget in northern temperate and boreal lakes. This thesis uses stable carbon and oxygen isotopes to examine the fate of allochthonous dissolved organic matter (DOM) in northern temperate lakes, and to determine the importance of dissolved organic carbon (DOC) in lake carbon mass balances and in the δ¹³C of lake sediments. To use stable isotopes as a tool for studying DOC loss and sedimentation within lakes requires an understanding of processes that affect the δ¹³C and δ¹⁸O in aquatic systems. Photolysis is one mechanism that can account for the large allochthonous DOC loss within northern temperate lakes. There is, however, little research examining the effects of photolysis on stable isotopes (e.g. δ¹³C and δ¹⁸O) in aquatic systems, or how photodegradation of DOM affects the δ¹³C of lake sediments. To study the effects of DOM photodegradation on carbon and oxygen isotopes, stream waters from catchments with varying peatland coverage were incubated in Tedlar bags placed in water baths under natural sunlight. Results from three streams flowing into two oligotrophic headwater lakes (Harp and Dickie Lakes) indicate that O₂ consumption rates and dissolved inorganic carbon (DIC) production rates were an order of magnitude greater in light exposed treatments than in dark treatments, suggesting that light mediated processes control O₂ consumption and DIC production in incubations. The similarity between filtered, inoculated, and sterile treatments, indicate that photolysis was the dominant O₂ consuming and DIC producing process in the incubations, while the contribution of respiration to these processes was not detectable. Differences in both O₂ consumption rates and DIC production rates (normalized to DOC loss) among streams suggest that DOM photolability was an important factor in both O₂ loss and DIC production on a volumetric basis. A concomitant increase in δ¹⁸O-O₂ was observed with O₂ loss indicating that during the photo-oxidation of DOM, the lighter ¹⁶O isotopomer was preferentially consumed in the oxidation of DOC to CO₂. Fractionation factors for respiration, photolysis and other abiotic reactions were not a function of O₂ consumption rates and ranged between 0.988 and 0.995, which lies outside the range published for respiration (0.975-0.982). These are the first published photolytic fractionation factors. The δ¹³C-DIC produced collectively by photolysis, respiration, and other abiotic reactions in incubations exposed to natural sunlight ranged between –23‰ and –31‰, and were similar in the light incubations for each treatment, but different among streams. Together, the light and dark incubation data suggest that photolysis and other abiotic reactions were largely responsible for the DIC concentration and δ¹³C-DIC changes observed, while respiration is a relatively minor contributor. During the incubations, as DOC photodegraded to CO₂, the lighter ¹²C isotope was preferentially mineralized (or the moieties cleaved were depleted in ¹³C) leaving the residual δ¹³C-DOC 1‰ to 4‰ enriched, creating enrichment (ε) values up to ~–3‰. The change in final δ¹³C-DOC after DOM photodegradation was different for each inflow, ranging from ~1 ‰ to 8.0 ‰, and provides an average enrichment of –2.1‰ (Harp Inflows ε: –1.2‰; Dickie Inflows ε: –3.4‰). These ε values are in agreement with the average ε from previous incubations on 3 of the inflows and 3 published studies based on UV exposed bog water (Osburn et al., 2001), riverine waters (Opsahl and Zepp, 2001), and lyophilized Juncus leachate dissolved in lake water (Vähätalo and Wetzel, 2008) (average ε = –2.9‰). The structure of DOM changed during photolysis. Absorbance data indicated that the aromaticity, colour, UV absorption and the average molecular size of the DOC decreased. Additionally, after exposure to sunlight, C/N ratios of the DOC changed from high values (24-55), indicative of terrestrial inputs, to lower values (4-13) traditionally thought to be representative of algal or microbial inputs. This contradicts the conventional view that terrestrial DOC has C/N ratios >20, and shows that abiotic processes can alter allochthonous carbon structure and the residual allochthonous carbon can have C/N values similar to, or overlapping with, C/N ratios expected from algal or microbial carbon. With the loss of 61-90% of the DOC, the particulate organic carbon (POC) created accounted for 20-90% of the DOC lost. Values of δ¹³C-POC ranged from –25.7‰ to –27.7‰, with 80% of the samples within 1‰ of the initial δ¹³C-DOC indicating that the particulate carbon created from the photodegradation of DOM that settles to the lake sediments could be isotopically similar to the source DOC. Overall, these incubations indicate that the photodegradation of DOM can affect both concentrations and isotopes of O₂, DIC, DOC, and POC of the stream waters flowing into Harp and Dickie Lakes and are important to consider in lake dynamics of high DOC retention lakes. Two independent methods were used to examine the importance of allochthonous DOC to lake sediments. The first method used a two end-member mixing model to estimate the proportion of allochthonous and autochthonous carbon within the lake sediments. Inflow δ¹³C-POC data, δ¹³C-leaf litter measurements, and DOC photodegradation experiments were used to calculate average annual δ¹³C-POC values for the allochthonous end member. The average annual δ¹³C-POC values for the autochthonous end member were calculated using estimates of productivity, surface δ¹³C-CO₂ values and estimated average annual fractionation factors. Average annual δ¹³C-POC values from allochthonous and autochthonous sources for these lakes were distinct. Using the end members to calculate the relative contributions of allochthonous and autochthonous carbon to lake sediments revealed that the δ¹³C of the lake sediment can be significantly affected by the ratio of autochthonous and allochthonous contributions. Furthermore, peaks in the allochthonous contributions of carbon accompany the δ¹³C peaks in the sediment records to the lake sediments. This suggests that climate change and/or anthropogenic changes to the landscape, and the concomitant changes in DOC inputs to lakes, can be recorded in the sediment record indicating that sediment records are not just productivity signals, but also mass balance signals in high DOC retention lakes. In the second method carbon isotope budgets were completed to accompany the carbon mass budgets for Harp and Dickie Lakes. Mass-weighted average annual δ¹³C-DOC values from the inflows and outflows and δ¹³C-DIC values from the inflows varied by 0.2‰ to 1.3‰, suggesting the values are well constrained. Conversely, the range of weighted δ¹³C-DIC values from the outflows were larger (2.2‰) than those of the inflows. Calculated δ¹³C values of the lake sediment were not equal to the measured δ13C values of the lake sediments for either Harp or Dickie Lakes suggesting a problem lies within the mass balances, or the weighted average annual δ¹³C values used in the isotope budgets. To examine the sensitivity of the average annual weighted δ¹³C values for the carbon entering and exiting the lakes, and the mass of carbon entering the lakes δ¹³C of the lake sediments, a mass and isotope budget model was created. The model indicated that the δ¹³C of the lake sediments is sensitive to a number of parameters including the amount of DOC entering the lake, the δ13C-CO2 evaded from the lake, the areal water discharge rate (qs), the gas exchange coefficient (k), and pH. Many of these parameters required adjustments for the masses of carbon to match those presented in the mass balances suggesting that the mass balances averaged over 8 years have errors associated with them. However, changing the DOC load to the lakes in the model by the variability observed over all the years of the mass balances) indicates that the isotopic signature of the lake sediment could change by up to 2.5‰. This isotope change is large enough to account for the historical δ¹³C changes observed in the δ¹³C sediment record, suggesting that allochthonous DOC can drive the sediment record.

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.

I studied carotenoids in the eggs of American coots (<i>Fulica americana</i>) from 3 study sites in Saskatchewan, Canada. I supplemented two diet types designed to reduce carotenoids in the diet of laying coots to investigate the relationship of carotenoids and the size of eggs and to examine the allocation of carotenoids into eggs.</p><p>In chapter 2, I examined influences of local environment, food quantity and food quality on egg size. Carotenoid content and stable nitrogen and carbon isotopes in yolk were measured and used to elucidate whether variation in type of food eaten contributes to egg size. By analyzing isotopes in coot tissues, I confirmed that coots use endogenous lipid reserves for egg formation but not endogenous protein reserves, and the size of eggs is more dependent on exogenous sources of nutrients. My data demonstrate that carotenoids are not causal in egg size, but are components of natural, high quality diets.</p> <p>Carotenoids are obtained through the diet and deposited into egg yolk. It has been hypothesized that concentrations and percentages of individual carotenoids can be labile and dependent on diets or maintained in an optimal balance to meet requirements of embryos. In chapter 3, I investigate deposition of carotenoids in egg yolk among nesting locales, among hens within a site and among treatments in a diet manipulation experiment. My data show maintenance in the percent composition of a suite of 3 important carotenoids, lutein, zeaxanthin and âcarotene, independent of scale of investigation and in contrast to other individual carotenoids that appear to vary in proportions based on diet. These results suggest that birds can maintain nutritional balances in their eggs despite variation in diets.</p><p>In chapter 4, I tested 3 hypotheses regarding the apportionment of carotenoids into egg yolk over the laying sequence. Without exception, concentrations of these nutrients have previously been shown to decline with egg sequence. In contrast to these findings, coots actually increased the carotenoid concentration in yolks over the laying sequence. My experimental evidence supports the explanation that this pattern of deposition depends on carotenoid availability to the laying female.