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

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.

Individual specialization occurs when individuals selectively consume a subset of their population's diet. Intraspecific diet variation can stabilize population and community dynamics, promote species coexistence, and increase ecosystem productivity. Ecological variation also provides the variability necessary for natural or sexual selection to act. Individual threespine stickleback select different prey from a shared environment, and this variation is not simply a result of sex, size, or spatial heterogeneity. I use longitudinal observation of stickleback foraging microhabitat to support more commonly used cross-sectional metrics. Among recaptured individuals there were correlations between microhabitat use and functional morphology, and microhabitat use and long term dietary differences between individuals. I quantify individual specialization across populations using cross-sectional sampling to understand how and why ecological variation may itself be variable. All populations showed significant individual specialization. Specialization varied between populations and this variation seems to be a long-term property of populations. Overall morphological variance was positively correlated with ecological variation. Ecological variation, like all types of heritable variation, provides raw material for evolutionary change. For example, lacustrine populations of stickleback are commonly under disruptive selection due to intraspecific competition for prey resources. Speciation with gene flow may be driven by a combination of positive assortative mating and disruptive selection, particularly if selection and assortative mating act on the same trait. We present evidence that stickleback exhibit assortative mating by diet, using the isotopes of males and eggs within their nests. In concert with disruptive selection, this assortative mating should facilitate divergence. However, the population remains phenotypically unimodal, highlighting the fact that assortative mating and disruptive selection do not guarantee evolutionary divergence and speciation. There are several not-mutually-exclusive mechanisms by which assortative mating by diet may occur in these populations, such as shared microhabitat preference among individuals of similar diet. Stable isotopes reveal diet differences between different nesting areas and among individuals using different nest habitat within a nesting area. Spatial segregation of diet types may generate some assortative mating, but is insufficient to explain the observed assortment strength. We therefore conclude that sticklebacks' diet-assortative mating arises primarily from behavioral preference rather than from spatial isolation. / text

The stable isotope compositions (chlorine, oxygen, and hydrogen), major anion concentrations, and major/minor cation concentrations of 37 thermal (any spring water with temperature at least 6.5° C above mean ambient air temperature) and mineral springs from the Cascade volcanic arc system were measured in order to better determine chlorine sources within the Cascades hydrothermal systems, and thus place better constraints on halogen flux through the subduction zone. Typically, most subduction zone flux calculations have been limited to the study of the erupted magmas and gases from fumarole vents, yet magmatic discharge through thermal springs may be considerable, particularly those in the often ignored forearc. Additionally, 9 geochemically well characterized lavas from across the Mt. St. Helens/Mt. Adams region of the Cascade arc (Leeman et al. 2001, 2005) were analyzed for their halogen concentrations, as well as their Cl stable isotope composition. Cl concentrations in the thermal springs range from 6 to 13,850 ppm and have δ37Cl values that range from -0.1‰ to + 1.9‰ (average = +0.8 ± 0.4‰; error = ± 0.2‰), with no systematic variation along or across the arc. The slightly positive values (~0.0 to +0.9‰) may be explained by fluid-rock interaction with underlying lithologic units, such as 37Cl-enriched volcanic sequences, and/or serpentinites or oceanic crust of accreted oceanic terranes. Another process possibly contributing to these positive δ37Cl values, particularly those with δ37Cl > 1‰, is magmatic HCl fractionation during degassing generating an enriched 37Cl vapor which mixes with thermal waters. We cannot completely rule out slab-derived altered oceanic crustal chlorine that has degassed into the springs, although most slab Cl is believed to have already been devolatilized from the slab before reaching sub-arc depths corresponding to longitudes where these springs are located at the surface. Lavas from the Columbia transect across the arc exhibit highest Cl concentrations at the volcanic front compared to the forearc and backarc. Br, like Cl, exhibits highest concentrations along the volcanic front. F and I show a progressive decrease in concentration from forearc to backarc which may demonstrate the putative early surge of fluids/fluid mobile element loss early in subduction at relatively shallow depth. δ37Cl values range from -0.1 to +0.8‰ (error = ± 0.2‰) and may reflect a component of assimilation of crustal material, or is derived from an enriched mantle, although we cannot completely rule out some isotopic fractionation and/or slab-derived chlorine. / text

Seagrasses are extremely productive coastal plant communities that serve as habitat for various types of marine and estuarine fauna and provide numerous ecosystem services. Seagrass meadows around the world have become threatened by environmental and anthropogenic pressures such as altered hydrologic regimes, physical disturbances, and eutrophication. Monitoring programs that provide high-resolution information and document changes in cover, morphometric characteristics, species composition, and tissue nutrient content across large spatial scales are critical in global conservation and management efforts. In an attempt to address the uncertainties regarding the current distribution and condition of seagrasses in the southwest Gulf of Mexico, I conducted annual sampling from 2011-2013 to examine seagrass cover and condition at 558 permanent stations. Sampling occurred in three regions of the Texas coast: the Coastal Bend (CB), Upper Laguna Madre (ULM), and Lower Laguna Madre (LLM), which together comprise over 94% of the seagrasses in Texas. Significant trends in seagrass coverage and tissue elemental composition were highly location- and species-specific. In the CB, I did not observe significant changes in seagrass cover and no spatial patterns in tissue nitrogen (N) or phosphorus (P) were apparent. However, I observed a species shift in the northern ULM, where significant decreases in Syringodium filiforme cover were coupled with significant increases in Halodule wrightii cover. Long-term salinity records at four stations throughout the study area suggest that S. filiforme mortality in the ULM in 2013 was a product of an extended period of high salinity (> 55) that began in late 2012. In LLM, there were significant increases in H. wrightii cover in the north and significant decreases in T. testudinum cover in the south, which cannot be explained based on underwater light levels, salinity, or nutrient availability. Both H. wrightii and T. testudinum displayed lower C:N, C:P, and N:P ratios, along with enriched δ¹⁵N signatures nearest urban areas, particularly in the LLM. This study illustrates the value of integrating rapid-assessment field sampling and rigorous statistical and spatial analysis into a large-scale seagrass monitoring program to uncover patterns in seagrass community structure. I detected significant trends in seagrass coverage and condition across multiple spatial and temporal scales, including a massive species replacement that coincided with a prolonged period of hypersaline conditions.