Low-permeability Ordovician shale and limestone formations of the Michigan Basin are a target of interest for a deep geological repository for the long-term isolation of low and intermediate-level radioactive waste. Porewater studies contribute to an understanding of the age and evolution of paleofluids as part of ongoing research. Sulfur and oxygen isotope data presented here add to the characterization of these formations. For this work, a method was developed and used to extract porewater sulfate from low permeability rocks for the analysis of sulfate concentration and its δ34S and δ18O values, using an elemental analyzer interfaced with an isotope ratio mass spectrometer (EA-IRMS). Porewater sulfate concentrations were very low, varying from 0.02 to 228.88 mmol/ kgw. Values for δ34S were all near or below those for Ordovician seawater. The earlier work examined the δ34S and the morphology of framboidal pyrite in the Ordovician formations provides strong evidence for diagenetic sulfate reduction (Jautzy et al. in prep.). The lack of enrichment for δ34S and δ18O in porewater sulfate suggests that diagenetic sulfate reduction was quantitative and that the porewater sulfate measured in these samples is not residual sulfate remaining from that time. The distribution of sulfur isotope values between that of Silurian seawater and those of the framboidal pyrite suggests an origin from the infiltration of Silurian brines with contributions from pyrite oxidation. The δ18O values are consistent with this, showing mixtures between Silurian seawater sulfate and sulfide oxidation without the involvement of atmospheric oxygen. This evidence for anoxic sulfide oxidation indicates that inadvertent exposure to atmospheric O2 during porewater leaching in the laboratory is unlikely and that in-situ oxidation involving electron acceptors with lower electromotive potential took place, possibly over geological time. The combination of sulfate mass and the stable isotopes of porewater sulfate, along with the presence of Fe (III) and Mn (IV) bearing minerals indicate potential evidence of in-situ sulfide oxidation in one third of twenty-six core samples. The relative timing of events is not clear as to whether sulfide oxidation could have occurred during the Ordovician and/or after the infiltration of evaporated Silurian seawater into the Ordovician strata. This study adds a new understanding of the redox evolution within this sedimentary system with implications for contaminant transport.

Sediment Oxygen Demand (SOD) is the fluctuation of dissolved oxygen between the sediment from the overlying water. The method to acquire SOD values is inefficient and troubled by unreliable equipment. Diffusion gradients in thin film (DGT) are proposed as a potential method to collect geochemical proxy measures that can be used as SOD predictors. Field deployment of the DGTs was conducted at two locations to compare recovery and accuracy against ex-situ centrifuge methods. The results indicated DGT can be used as a statistically significant geochemical method. A principle component analysis was used to determine if reduced iron and manganese collected using DGTs clustered with SOD. Results indicated reduced iron and manganese cannot be used to predict SOD. Sulfide measurement by microelectrode from the same matrix of geochemical methods however did cluster with SOD. A stepwise multiple linear regression concluded sulfide measurement by microelectrode is a statistically significant predictor of SOD.

Radioactive decay of U, Th and K contributes to noble gas radiogenic ingrowth in different geological reservoirs, which distinguish mass origin and reveal its transport pathway. Compared with minerals and fluid inclusions, porewater is more relevant in revealing the mobile mass origin and transport in the porous, deep subsurface environment. Hence, the approaches for porewater noble gas extraction and analysis are of great meaning to geochemistry and hydrogeology. However, all five stable noble gases in rock porewater are difficult to acquire because of possible air contamination during storage and difficulty of noble gas separation. This dissertation is dedicated to exploring novel noble gas extraction and analysis methods from rock porewater. Two porewater gas extraction methods were developed for crystalline and sedimentary rocks, respectively. Temperature-controlled heating was applied to crystalline rocks. Out-diffusion in Al-foil bags was used for Ordovician sedimentary rocks. Regarding noble gas methodology, a newly designed pneumatic processing line was built to explore an iterative polished stainless steel wool trapping method to separate Kr from Ar. The iterative trapping method yields > 95% trapping efficiency for Kr and > 99% trapping efficiency for Xe. Simultaneously, comparable and steady noble gas sensitivities and noble gas isotope ratios were attained from air standard aliquots. From heating experiments on crystalline rock porewater, the consistency of noble gas ratios between headspace gas and rock porewater illustrates that this extraction method is valid for crystalline rock. This work provides a benchmark for noble gas extraction from crystalline rock porewater. With room-temperature out-diffusion method in Al-bag, noble gas ratios and concentrations of Ordovician sedimentary rocks reveal crustal features. The measured noble gas ratios in Ordovician sedimentary cores agree with measurements previously made in the Ordovician brine samples from the western flank of the Michigan Basin. The Ordovician porewater residence time is quantitatively estimated with both He and Xe radiogenic ingrowth, yielding an average of 251 million years (m.y.), which is comparable with the previous He accumulation time estimate at the same study site that yielded 260 m.y.. The remarkable preservation of gases in Al-foil bags provides an economic and efficient possibility for noble gas out-diffusion sampling. In summary, the exploration of porewater noble gas extraction and all five noble gas analysis methodology gives satisfying noble gas results and geological information. These original developments are of great meaning to the future work of the noble gas laboratory at the University of Ottawa.

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During the Fall of 2009, a pilot study was conducted at the McCormick and Baxter (M&B) Superfund Site to evaluate polydimethylsiloxane (PDMS) profilers as a method for sediment cap performance monitoring. The profilers are shielded solid phase microextraction fibers, silica rods coated with polydimethylsiloxane (PDMS) as the sorbent. The deployment explored whether profiling PDMS could be used as a low impact, highly sensitive, long term monitoring strategy at M&B since the sediment operable unit will be transitioning to the “Operable & Maintenance” phase of Superfund cleanup. To evaluate sediment cap performance, a good understanding of the flux of contaminants from the sediment is required. While surface waters can illustrate this flux, they can also contain contaminants originating from upstream sources. The existing sampling plan at M&B uses a conventional porewater pumping sampling technique that measures both dissolved and particulate fractions. PDMS profilers measure only the freely dissolved fraction which has been shown to be a good indicator of bioavailability. These profilers also have lower detection limits (ng/L) and the ability to measure vertical concentration gradients which can help identify sources and mechanisms of the contamination. Each sampler was analyzed at three depths for the USEPA Priority Pollutant List of 16 polycyclic aromatic hydrocarbons (PAHs). PDMS measurements showed clear vertical profiling with large reductions in PAH concentrations through the sediment cap offshore. Nearshore, uniform concentration profiles were observed indicating increased vertical mixing as a result of tidal smearing. Further, ANOVA and Tukey-Kramer HSD analysis of sample variability revealed PAH concentrations were statistically different at two locations compared to the remainder of the sampling locations- indicating areas requiring closer attention. PDMS profilers were co-located at 13 of the 22 conventional porewater extraction sampling locations. The correlation of PDMS and conventional porewater extraction techniques was limited due to the low detection frequency by conventional porewater extraction methods as a result of the higher detection limits by that method. The correlation was good for light molecular weight PAHs with most measurements of the same order of magnitude and improved with increasing depth (due to the greater number of detections). 72% of the direct comparisons between PDMS-derived and conventionally-derived porewater concentrations were of the same order of magnitude. Any comparison between the two datasets is necessarily limited especially for the higher molecular weight PAHs, however, due to the large number of non-detects in the conventionally collected data. / text

This study is part of a project aiming for the long-term burying of nuclear wastes in Kincardine, Ontario. Bedrock formations as well as their associated waters were analyzed in drill cores from the Michigan sedimentary basin, southwest Ontario. This research utilizes geochemistry combined to strontium and rubidium isotope ratios in order to determine the origin of porewaters from Ordovician shales and limestones. It is demonstrated that these waters are the result of a mixing line between the Silurian (Guelph) and Cambrian groundwaters. This last end-member was also mixed with Precambrian brines to some extent. Strontium and rubidium isotopes also demonstrated rubidium in clays were leached by porewaters over time. Once in solution, radioactive rubidium decayed into strontium over time. This process explains the accumulation of radiogenic strontium observed in porewaters. An age estimate for the deposition of carbonates and other evaporates was calculated with the Rb-Sr isotope system. The calculated age is 453.7 million years before present for dolomites, which is consistent with the history of the site. It was possible to gen an approximate age of 339.7 million years for the formation of illites. This corresponds to the illitization process that occurred after the deposition of rocks, when the Silurian brines infiltrated the deeper Ordovician shale. It was also possible to estimate of porewaters ages.

Global sea levels are expected to rise as a result of climate change, which will lead to the inundation and erosion of low lying coastal areas and accelerate the intrusion of seawater into sub-surface sediments. Many of the UK’s legacy nuclear facilities are located in close proximity to the shore, raising questions regarding the potential mobilisation of radionuclides during sea level rise. Here batch and column experiments were used to simulate and investigate the effect of these processes on the mobilisation of key radionuclides Tc, 90Sr and U from oxic and reduced sediments under sea level rise scenarios. Strontium-90 was rapidly mobilised from exchangeable surface sites from oxic sediments during inundation and erosion scenarios with seawater (≈ 60%). Strontium release was driven by ion exchange between Sr90 and Mg2+ cations present in high concentrations in seawater. Uranium release from oxic and reduced sediments was kinetically controlled, characterised by slow release from a range of binding sites, promoted by the formation of U-carbonate complexes. Uranium mobilisation was slower from reduced sediments compared with oxic sediments under seawater flow conditions; therefore reduced sediments would act as a longer term source of U to marine environments. Release was more extensive from initially nitrate reducing sediments (53%) compared with extensively iron reducing sediments (38%), with the difference in release explained by the longer contact period of U(VI) with the iron reducing sediment relative to the nitrate reducing sediment which would lead to slower desorption. Additionally, U(IV) species would be released more slowly than U(VI) species sorbed to the sediments. The release of Tc was dependent on sediment re-oxidation coupled with the oxidation of Tc(IV) to Tc(VII). Batch experiments showed that only a small proportion of Tc was rapidly (within 5 days) released from the sediments into seawater and groundwater which suggests that the majority of any Tc(IV) contamination will be released slowly as the seawater plume migrates through the sediments. Technetium release was slowest, and ultimately limited to the greatest extent (17%), in initially Fe-reducing sediments, when they were re-oxidised in seawater. Thus the cycling of iron and the impact of the water chemistry on iron mineralogy were important for hindering Tc release. Column experiments showed that iron minerals were less effective at retarding Tc release under flow-through conditions. Kinetically controlled and solubility limited Fe dissolution led to on-going Tc release from the sediments, i.e. the retarding effect of iron phases was temporary and significantly more Tc was mobilised (79-93%) compared with the batch experiments (17-45%). This study has shown for the first time that radionuclides will be released from reduced and oxic sediments as a result of future sea level rise. Contaminated sediments have the potential to act as a secondary source of radionuclide contamination entering the marine environment from coastal nuclear sites. This information is essential when siting new nuclear facilities and when developing effective remediation, decommissioning and management strategies for legacy coastal sites.

Peatlands are associated with a range of ecosystem services such as long-term carbon storage and sequestration, biodiversity, and potential water reservoirs, mitigating floods and droughts. However, in the 20th century, large peatland areas in the northern temperate and boreal regions were drained by ditching, primarily to enhance forest and agricultural production and peat harvesting. Drainage of peatland is associated with a reduction in wet tolerant peatland species, reduced long term carbon sequestration and increased carbon emissions, conflicting with the goals of the Convention on Biological Diversity (CBD) and the Paris Agreement. Today, there is a big ongoing effort from society to rewet and restore drained peatlands in Sweden, but post- restoration monitoring to evaluate success are often scarce. Here, I examine the recovery of a restored drained and afforested bog in Southern Sweden, using a pristine area of the bog as the reference target. The aim was to ascertain to what extend the restoration had succeed and its potential to fully recover. During one year pore water quality, water level and peat surface level were monitored. In the fall peat cores were collected to investigate differences in peat physical and elemental and the microbial biomass and composition. I found that there are still considerable differences between restored and reference area, most marked by the deeper water level in the restored area, but this was not due to a reduced capacity of peat oscillation (i.e. the peats ability to expand and shrink to follow the water table. However, the restoration had raised the water table closer to the surface when compared to other drained areas in Sweden. The study also found considerable higher quantities and higher aromaticity of dissolved organic matter (e.g. DOC) in the porewater of the restored area and an overall lower total amount of microbial biomass with altered community composition, with higher relative amounts’ of fungi and G- negative bacteria’s in the restored area. The nutrient profile in the porewater (inorganic N,P,K) were similar to what was found in the reference area. In conclusion, both the hydrological and porewater chemistry status are currently most likely sufficient for wet-dwelling peat mosses to establish. Here, I argue that the restoration effect is noticeable but complete recovery is yet far away and there is a risk of recession towards afforestation if peat mosses fails to re-establish.

Manual collection and processing of seawater samples for dissolved gas analyses are technically challenging, time consuming and costly. Accordingly, in situ analysis techniques present attractive alternatives to conventional gas measurement procedures. To meet the demands of sustained, high-resolution chemical observations of the oceans, the University of South Florida and SRI International developed underwater mass spectrometer systems for quantitative measurements of dissolved gases and volatile organic compounds. This work describes the influence of variable in situ conditions on the performance of a membrane introduction mass spectrometer used for measurements in both the water column and sediment porewater. Laboratory experiments to simulate the effects of field conditions on the membrane were performed by varying sample flow rate, salinity, hydrostatic pressure, and chemistry. Data indicate that membrane permeability has a strong dependence on hydrostatic pressure, and a weak dependence on salinity. Under slow flow conditions bicarbonates in solution contributed to carbon dioxide instrument response as a result of carbon system equilibration processes in the boundary layer at the membrane interface. In addition, method development was undertaken to enable underwater sediment porewater analyses and quantitative (calibrated) measurements of total dissolved inorganic carbon (DIC). This work establishes the capability of membrane introduction mass spectrometry to measure two compatible variables (DIC and dissolved CO2) for comprehensive CO2-system characterizations. In addition to laboratory studies three types of field observation were obtained in this work. High-resolution vertical profiles of dissolved gases in the Gulf of Mexico were obtained through system calibration and characterization of the influence of hydrostatic pressure on the behavior of polydimethylsiloxane membranes. In the South Atlantic Bight, sediment porewater profiles of dissolved gases were repeatedly obtained over a 54 hr period. Data trends were in agreement with high remineralization rates facilitated by porewater advection. Finally, time-series underwater DIC measurements that were undertaken proved to be in good accord with results obtained using conventional techniques. These measurements constitute the first quantitative observations of dissolved gas ocean profiles, sediment porewater profiles, and DIC measurements by underwater mass spectrometry.