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Numerous anthropogenic disturbances have occurred in large lakes over recent decades. These may alter concentrations of the biomagnifying contaminant mercury (Hg) in fish, but long-term impacts of disturbances on Hg trophodynamics are poorly understood. Elemental analyses of archived museum ichthyology specimens could be used to study historical, pre-disturbance fish food webs, but there is uncertainty about effects of chemical preservatives on the results of such analyses. In this thesis, long-term preservation effects were studied, and archived fish were used to reconstruct historical food webs and Hg trophodynamic patterns in three large North American lakes, Nipigon, Simcoe and Champlain. After 24 months of formalin/ethanol preservation, fish muscle delta-15N and delta-13C had average changes of +0.4 ‰ and -0.9 ‰, respectively. Shifts in mean Hg concentration was +5 % after 12 months. A suite of 26 other elements analyzed over 24 months showed consistent responses to preservation, usually involving an increase in concentration immediately following preservation. In the second phase of the thesis, stable isotope and Hg analyses were performed on archived and modern fish from the study lakes, dating to the 1920s-60s and 2006-7, respectively. Trophic relationships were often relatively stable over time, but stable isotope metrics revealed a decrease in Lake Nipigon delta-15N range and less pelagic feeding among Lake Simcoe pumpkinseed and yellow perch. In Lake Champlain, the re-introduction of lake trout in recent decades did not have a major effect on overall food web dimensions. Significant Hg biomagnification factors were found in 1920s and 2006-7 Lake Nipigon (which were not statistically distinguishable from each other) and 2006 Lake Champlain. These biomagnification factors ranged from 0.09 to 0.17, which is within the range found in other studies globally. Archived fish and government monitoring records indicated that fish Hg concentrations decreased in Lakes Simcoe and Champlain since historical periods, but remained similar or increased in Lake Nipigon. This thesis confirms the utility of archived fish for elemental analyses. It highlights the risks of Hg contamination and food web change that may be faced by remote lakes, and it provides evidence for relatively stable Hg biomagnification rates in large lakes. / Thesis (Ph.D, Biology) -- Queen's University, 2013-01-30 15:43:33.438

Recent advances in the analysis of intrinsic markers, particularly stable isotopes, have allowed great insight into interactions between different stages of the annual cycle of migratory birds. Hydrogen isotope ratios, because of strong latitudinal trends in their distribution, have been widely used to address long-distance movements of migratory birds. Likewise, carbon isotope ratios have been useful in examinations of habitat quality because of their responsiveness to changes in plant community composition. However, basic assumptions underlying the use of certain isotopes have yet to be adequately examined. Additionally, much of the research regarding seasonal interactions in migratory songbirds comes from study of a single species, and it is unclear whether these findings are applicable to a wider range of migrant songbirds. In this study, I collected tissue samples from black-throated blue warblers (Dendroica caerulescens) at a breeding site in New Hampshire to address two important questions regarding stable isotopes and the investigation of seasonal interactions. First, using feather samples from both adult and juvenile birds, I investigated the influence of age, molt timing, and reproductive effort in determining the stable hydrogen isotope ratios that are incorporated into tissue samples. Secondly, I took claw samples from adult birds to examine the importance of winter habitat quality, as inferred through carbon isotope ratios, in determining subsequent reproductive success. I found that hydrogen isotope ratios in feather samples were significantly influenced by both age and molt timing, though not by reproductive effort. The mechanism underlying age-related isotopic variation is unclear, but may be widespread among passerines. In addition, this study is the first to note a significant seasonal trend in feathers grown throughout a breeding season, although the mechanism for this pattern is also unclear. Taken together, these findings have important implications for the use of hydrogen isotope ratios for purposes of geographic assignment. Further research is needed to determine the prevalence and magnitude of age-related and seasonal trends in hydrogen isotope ratios. I recommend that future studies note the age class of birds when sampling for hydrogen isotopes, and researchers should attempt to collect feathers grown early in the molt cycle. Analysis of carbon isotope ratios from claw samples indicated that winter habitat quality did not directly influence subsequent reproductive success. However, winter habitat quality may have an indirect influence on reproductive output. Females from higher quality wintering sites were in significantly better body condition on the breeding grounds, and settled on more insect-rich breeding territories. Both body condition on the breeding grounds and breeding territory quality have previously been shown to influence subsequent reproductive success, in this and other songbird species. These results indicate that winter habitat quality may be important in determining future reproductive success for black-throated blue warblers, and interactions between events during the wintering and breeding periods may need to be incorporated into future population models for this species.

The stable isotopic composition of groundwater within a watershed in eastern Iowa was studied in order to understand how water moves through the system. Samples were gathered using multiple observation wells and pore water samplers and then analyzed to determine the δ18O and δ2H of each sample. Shallow pore water is much more variable in its isotopic composition than deeper water and seems to be more greatly affected by evapotranspiration, whereas groundwater below the water table appears to show a stable isotopic signature suggesting the integration of multiple rain events. Other samples of similar depths across the slope of a hill were also used to observe differences across the area. By observing changes over time in the signatures of these samples, it can be seen that the crest of the hill is most greatly influenced by infiltration from precipitation while the side of the hill is influenced more by throughflow. By combining stable isotope analyses, knowledge of the medium through which the water is moving and the general mechanics of a watershed, a more advanced understanding of how water interacts with and moves through the ground can be gained.

The reliability of foraminifera as stratigraphic index fossils, and as isotopic proxies of marine environments, is based on the assumption that the fossil concepts represent uniform species, responding consistently to their ambient environments. Understanding sources of uncertainty is, therefore, critical. In this dissertation, I explore a potential bias in the application of planktonic foraminifera utilized extensively for Cenozoic paleo-reconstruction and, to a lesser extent, biostratigraphy: the Globigerinoides ruber-elongatus plexus (‘plexus’ meaning a complex network of interconnected members). Taxonomic revisions since 1826 have resulted in the merging of multiple Globigerinoides species names under one general designation (“Globigerinoides ruber”), the implications of which are now under scrutiny. These “morphotypes” of G. ruber have been shown to incorporate stable isotopes and trace elements in seawater dissimilarly, and correspond to multiple genetic species, some of which occupy different environments. Various criteria exist to sub-divide, group, or distinguish members of the Globigerinoides plexus, most notably the recurring use of Globigerinoides elongatus as a less spherical, less symmetrical counterpart to G. ruber. But the efficacy of these various taxonomic criteria has not been tested quantitatively. Most rely on the traits of visually distinctive “end-members,” while specimens in the morphological “transitional zone” are left to an observer’s subjective interpretation. This prevents quantification in census counts, and may lead to erroneous geochemical analyses. Furthermore, molecular clock estimates suggest that the G. elongatus species evolved significantly later than G. ruber, affecting its potential as a biomarker. In this dissertation, I examine the potential of a minimal-criteria system for classifying Globigerinoides-type morphologies using only three conditions: final chamber compression, final chamber asymmetry, and aperture compression. Morphometric analyses on specimens grouped according to this new system allow us to assess to what degree visual classification reflects morphospace discontinuity. Armed with this information, I then explore potential isotopic offsets between members of the Globigerinoides plexus, and its use in reconstructing regional differences in climate or habitat influences in the Gulf of Mexico and Caribbean basins. Finally, having shown that G. ruber and G. elongatus can be reliably visually distinguished, I tracked the species’ fossil presence individually in a deep core from the South China Sea, and confirmed the presence of G. ruber in the South China Sea through the late Miocene, and G. elongatus through the Pleistocene. While it is believed that neither species was traced to its true first occurrence (FO), the relative FO of G. ruber was shown to be 4–5 Ma before G. elongatus

Surface mining of oil sands in northern Alberta requires stripping of saline-sodic shale overburden, which is typically placed in large upland overburden dumps. Due to the chemical nature of this shale, engineered soil covers must be constructed over the shale to support the growth of forest vegetation. A research site on South Bison Hill (SBH), a shale overburden dump at the Syncrude Canada Ltd. Mildred Lake Mine, has been used by researchers over the past decade to study the performance of a reclamation cover. This study was undertaken to improve the understanding of salt and moisture dynamics in the cover-shale system. In particular, the objective of this study was to develop an estimate of the net percolation rate through the cover soil and into the shale overburden. Stable isotope (ä2H and ä18O) measurements obtained from the pore water of soil samples were used to develop stable isotope profiles at various sampling locations along the slope and plateau of the SBH. Simulated profiles were then generated using 2D, finite element numerical modelling software and compared to the measured profiles. Model parameters were obtained from testing and the work of previous researchers. The model results revealed that the net percolation is greatest (32-50 mm/yr) for the plateau and mid-slope bench sample locations. Net percolation rates for sample locations on the slope were lower at 0-12 mm/yr. The results from the stable isotope modelling were utilized in a SO42- transport model to ascertain if calculated net percolation rates could explain measured salinity profiles. This modelling exercise revealed that calculated SO42- profiles are highly dependent on the assumed SO42- production rates in the shale, which is primarily attributed to pyrite oxidation. The model results showed the isotope-based net percolation rates could explain the measured SO42-profiles for a reasonable range SO42- production rates. The SO42- production rates calculated in the model were greatest for the plateau and mid-slope bench locations and lesser for the sloped locations. The model also showed that the mass of SO42- removed by interflow was minimal compared to the mass generated by pyrite oxidation and that net percolation is the dominant flushing mechanism at net percolation rates of 8 mm/yr or more.

Surface mining of oil sands in northern Alberta requires stripping of saline-sodic shale overburden, which is typically placed in large upland overburden dumps. Due to the chemical nature of this shale, engineered soil covers must be constructed over the shale to support the growth of forest vegetation. A research site on South Bison Hill (SBH), a shale overburden dump at the Syncrude Canada Ltd. Mildred Lake Mine, has been used by researchers over the past decade to study the performance of a reclamation cover. This study was undertaken to improve the understanding of salt and moisture dynamics in the cover-shale system. In particular, the objective of this study was to develop an estimate of the net percolation rate through the cover soil and into the shale overburden. Stable isotope (ä2H and ä18O) measurements obtained from the pore water of soil samples were used to develop stable isotope profiles at various sampling locations along the slope and plateau of the SBH. Simulated profiles were then generated using 2D, finite element numerical modelling software and compared to the measured profiles. Model parameters were obtained from testing and the work of previous researchers. The model results revealed that the net percolation is greatest (32-50 mm/yr) for the plateau and mid-slope bench sample locations. Net percolation rates for sample locations on the slope were lower at 0-12 mm/yr. The results from the stable isotope modelling were utilized in a SO42- transport model to ascertain if calculated net percolation rates could explain measured salinity profiles. This modelling exercise revealed that calculated SO42- profiles are highly dependent on the assumed SO42- production rates in the shale, which is primarily attributed to pyrite oxidation. The model results showed the isotope-based net percolation rates could explain the measured SO42-profiles for a reasonable range SO42- production rates. The SO42- production rates calculated in the model were greatest for the plateau and mid-slope bench locations and lesser for the sloped locations. The model also showed that the mass of SO42- removed by interflow was minimal compared to the mass generated by pyrite oxidation and that net percolation is the dominant flushing mechanism at net percolation rates of 8 mm/yr or more.

Nitrogen (N) contained in roots and rhizodeposits represents a significant input of crop residue-N into soil that is often unaccounted, despite its contribution to the total N budget and its influence on soil nutrient cycling. Utilizing 15N-labeling methodologies under controlled conditions, the goal of this research was to quantify the input of belowground N (BGN), including rhizodeposits and roots, to soil and to investigate the influence of BGN on soil N cycling processes from the major pulse and oilseed crop grown across the Canadian prairies—namely, field pea and canola, respectively. Using continuous 15N2 labeling, the input of fixed-N to rhizosphere soil from pea plants amounted to less than 2% of the total plant N assimilated via fixation. Nodulation and root 15N enrichment were positively related to rhizosphere 15N enrichment, suggesting that the relatively low input of fixed-N to soil was due to low N fixation in this system. Shoot 15N-labeling techniques enabled a higher 15N enrichment in roots; as a result, rhizodeposition was detected in the rhizosphere as well as the surrounding bulk soil. Rhizodeposition accounted for 7.6 and 67% of plant N and BGN, respectively, in mature pea. Temporal changes in the pattern of rhizodeposition were detected as evidenced by differing 15N enrichment in rhizosphere versus bulk soils. In comparison to pea, a higher proportion of BGN contributed to the total residue-derived N from canola. The higher quantity of N rhizodeposition by canola was related to greater root biomass. However, pea rhizodeposition contributed more to soil inorganic N pools; this was sustained over time, as a higher proportion of pea BGN contributed to the growth of a subsequent wheat crop. In addition, wheat uptake of residue-derived N was twice as much from belowground compared to straw residues. Whereas the abundance of denitrifying bacterial communities in the rhizosphere was uncoupled from rhizodeposition and denitrification enzyme activity (DEA), root-derived 15N correlated with DEA in pea and canola. This research highlights the importance of belowground inputs from differing crop species on N budgets and soil N cycling.

Hypoxia, with dissolved oxygen levels < 1.4 ml L-1, is a recurring summer feature of Louisiana shelf bottom waters. Stable isotope characterization (delta^18O and delta D) of surface waters over the hypoxic zone shows a shift of dominant river influence from the Mississippi River during April to the Atchafalaya in July. Carbon isotopes of dissolved inorganic carbon (δ13CDIC) in bottom waters reveal the respiration of terrestrial organic carbon (OC) at inshore localities of 10 m depth and the respiration of marine OC at depths equal to and greater than 20 m. delat^18O and delta^13C profiles of Louisiana shelf Conus shells collected in 1972 show no evidence for summer hypoxia. Comparison with modern Conus records reveal a delta^13CDIC reduction during the last four decades associated with intrusion of ^13C-depleted fossil fuel CO2. Summer delta^13C reductions in Texas shelf Pteria shells may imply dissolved oxygen (DO) was reduced by ≈0.7 ml L-1, although this may be attributed to influence of Brazos River discharge on shell delta^18O and delta^13C. Foraminifera fauna measured in age-calibrated sediments from the Texas shelf reveal a low oxygen conditions on between 1960 and modern sediments. From 1950 to 1960, fauna indicate oxygenated bottom waters. Contemporaneous increases of foraminifera delta^13Cand delta^18O suggest this event is associated with severe drought (the Little Dust Bowl). The synchronicity of these data suggests a link between Brazos River discharge and shelf hypoxia.

Thesis (Ph. D.)--Open University. BLDSC no. DX225509.