Oxygen isotopes and major and trace element geochemistry have been used to evaluate the geochemical and tectonic history of a Franciscan hornblende-amphibolite and a eclogite block from Ring Mountain, Tiburon and three eclogite/blueschist blocks from Jenner Beach, California, all blocks have experienced varying amounts of retrogression. Relative to the presumed basaltic protolith, enrichments in large ion lithophile elements (LILEs) indicate interaction with sediment derived fluids in the retrograde eclogite and retrograde blueschist samples and high Mg, Cr, and Ni in actinolite rind indicate interaction with ultramafic rock. The [delta]¹⁸O values of chlorite from the Ring Mountain hornblende-amphibolite and the eclogite block have a narrow range of [delta]¹⁸O values (+7.7-8.2%₀, n=8) and actinolite from actinolite rind on the eclogite block from Ring Mountain and the blueschist/eclogite blocks from Jenner Beach are (+7.8-8.5%₀, n=5). Chlorite-actinolite geothermometry yields temperatures of 200-280°C for actinolite rind formation. Additionally, the [delta]¹⁸O values of both chlorite and actinolite at these temperatures indicates equilibrium with the measured value of Tiburon serpentinites, (7.6 to 8.1%₀, n = 3 Wenner and Taylor, 1974). Oxygen isotope analyses of garnet mineral separates from the eclogite and hornblende-amphibolite from Ring Mountain have [delta]¹⁸O values of +6.8±0.3%₀ (n=7), and +8.2±0.2%₀ (n=7), respectively. Garnets from the three eclogite/blueschist blocks at Jenner Beach have a [delta]¹⁸O value of +9.8±0.7%₀, (n=23). The difference in [delta]¹⁸O values of garnets between the high-grade blocks is likely due to in situ hydrothermal alteration of the seafloor basalt prior to subduction. The geochemical trends can be explained by a model in which during the early stages of subduction pieces of altered oceanic crust are detached from the downgoing slab and incorporated into the mantle wedge soon after reaching peak eclogite or amphibolite facies conditions. As subduction continues, the hanging wall cools and fluids released from subducted sediments infiltrate the overlying mantle wedge. As the blocks cool they develop a retrograde blueschist facies overprint under relatively static conditions. With cooling of the hanging wall and infiltration of sedimentary fluids, serpentinization induces reaction between the blocks and surrounding mantle wedge and Mg-rich actinolite rind is formed. The blocks are then plucked from the mantle wedge and incorporated into the subduction channel where they flow back to the surface via corner flow. / text

The rate of carbon turnover in soil is a balance between the input of carbon by plants through their roots and associated fungi and the loss of carbon due to plant and microbial respiration, oxidation and leaching. Soil carbon dynamics are notoriously difficult to measure, and being able to separate total soil respiration into its autotrophic and heterotrophic components would help understanding of carbon cycling processes. Where autotrophic respiration originates from roots and their associated mycorrhizal fungi, using newly fixed carbon, and heterotrophic respiration originates from the breakdown of older soil organic matter. By calculating the δ¹³C signature of respired CO₂ (the ratio of the abundances of C isotopes ¹²C and ¹³C) it is possible to determine whether it is of heterotrophic or autotrophic origin. In this study a 6 chamber, constant CO₂ concentration measuring apparatus was developed to determine both the rate of CO₂ efflux and to collect undisturbed CO₂ samples for isotope analysis. This apparatus was tested using live soil samples with different δ¹³C values (-22 ‰ to -27 ‰) and respiration rates (2 – 8 µmol m⁻² s⁻¹) obtained from various locations in New Zealand. Testing involved taking samples using the respiration apparatus, then incubating the same samples in a bag, and then comparing the two. There was no difference between the results from the soil respiration apparatus and the bags (R²=0.96, p=0.0002). Twelve microcosms including soil and grass were extracted from a newly converted dairy farm and placed into in growth cabinets. Diurnal courses of partitioned soil respiration were made over 24 hours with constant soil temperature to eliminate temperatures effect on soil respiration. Half were then covered with 90% shade cloth for 12 days to test if a reduction in light (and therefore newly fixed carbon) would have any effect on soil respiration. There was a significant reduction in soil respiration, yet no detectable change in the δ¹³C of soil respired CO₂ under heavily shaded treatment. There was however there was a shift towards heterotrophic dominated respiration. This shows that while L. perenne is resilient to surrounding conditions it is susceptible to change if exposed to different conditions for prolonged periods of time. The use of this new technique in the field will allow improved understanding of factors effecting soil C efflux.

Understanding the paleoclimate of a region is important, especially when trying to determine the extent of natural climate variability within the context of anthropogenic impacts. Recent anomalous periods of climate change in the Late Holocene, including the Little Ice Age and Medieval Warm Period, could possibly repeat in the future, having significant worldwide consequences. This holds especially true for tropical and subtropical karst environments, where limited paleoclimate proxies provide minimal data regarding past climate change. An investigation into past climate change in Belize using fulvic acids from cave sediments shows periods of drought during the collapse of the Maya society around 1400 years ago. Comparison of changes in the carbon isotope data from the fulvic acids agree with speleothem records, but more closely reflect changes in the vegetation above the cave, showing Maya population decline through waning agriculture. Further investigation of using fulvic and other organics acids are examined from cave sediments in Florida. The data show fulvic acid carbon isotopes are the most robust recorders of climate change, agreeing with several nearby speleothem d¹8O and d¹³C records from west-central Florida. A more detailed record of climate change in Florida through a calibration study of precipitation and cave dripwater oxygen and hydrogen isotopes revealed that the amount effect dominates rainfall in west-central Florida. Homogenization of epikarst dripwater gives average d¹8O values representative of the annual amount-weighted average of precipitation d¹8O for the area, suggesting speleothem isotope records reflect changes in rainfall amount. Examination of two speleothems from west-central Florida show complex teleconnection and solar forcing mechanisms responsible for past climate changes. A high-resolution stable isotope, trace element, and time series analysis study for the last 1500 years shows variability during the LIA and MWP, pointing to a combined influence of Pacific and Atlantic teleconnection mechanisms, especially the ITCZ, NAO and PDO, being responsible for precipitation variability. Long-term reconstruction of the mid-Holocene and Late Pleistocene from another speleothem reveals differences in temperature and precipitation between glacial and interglacial conditions in Florida. Climate proxies from the tropics and subtropics provide additional clues to global climate change crucial to understanding future water availability.

Sulfate, nitrate, and certain trace elements are common groundwater contaminants observed at mining sites. Their source, fate, and remediation were investigated at a former uranium mining site. First, groundwater samples collected across the site were analyzed for geochemistry, stable isotopes, and trace elements. Then, two pilot-scale ethanol injection tests were conducted for biostimulation of nitrate and sulfate reduction. Groundwater was monitored in the test area before and after the tests. The results showed a mixing of two discrete sources of sulfate. Quantification of these two sources using two methods showed that sulfide-mineral oxidation of the mine tailings served as a steady but low-discharge source while sulfuric acid (applied during ore processing in the 1960s) served as a variable, strong source. It appears that sulfuric acid served as a sustained source of sulfate for approximately 40 years. This source may be from accumulation of sulfate salts (formed from sulfuric acid) in the source zone due to the arid climate of the site. Results showing correspondence of isotopic compositions of ammonium and nitrate confirmed the generation of nitrate via nitrification. Moreover, it was observed that ammonium concentration is closely related to concentrations of uranium and a series of other trace elements including chromium, selenium, vanadium, iron, and manganese. It is hypothesized that ammonium-nitrate transformation processes influence the disposition of the trace elements through mediation of redox potential, pH, and possibly aqueous complexation and solid-phase sorption. As for the biostimulation, sulfate reduction condition has been maintained for a period of approximately 3 years after a single input. Atypical fractionation behavior of the delta34S in sulfate was hypothesized to be caused by release of sulfate from sulfate minerals associated with the sediments. Elevated hydrogen sulfide concentrations were not observed until approximately four months after the start of the test. This behavior, in concert with the observed changes in aqueous iron and manganese species, suggests that hydrogen sulfide produced from sulfate reduction was precipitated, presumably in the form of iron sulfides, until the exhaustion of readily reducible iron oxides. Hydrogen sulfide produced thereafter appears to have been in part re-oxidized.

Coal beds are one of the most promising reservoirs for geologic carbon dioxide (CO₂) sequestration, as CO₂ can strongly adsorb onto organic matter and displace methane; however, little is known about the long-term fate of CO₂ sequestered in coal beds. The "2800' sand" of the Olla oil field is a coal-bearing, oil and gas-producing reservoir of the Paleocene–Eocene Wilcox Group in north-central Louisiana. In the 1980s, this field, specifically the 2800' sand, was flooded with CO₂ in an enhanced oil recovery (EOR) project, with 9.0×10⁷m³ of CO₂ remaining in the 2800' sand after injection ceased. This study utilized isotopic and geochemical tracers from co-produced natural gas, oil and brine from reservoirs located stratigraphically above, below and within the 2800' sand to determine the fate of the remaining EOR-CO₂, examining the possibilities of CO₂ migration, dissolution, mineral trapping, gas-phase trapping, and sorption to coal beds, while also testing a previous hypothesis that EOR-CO₂ may have been converted by microbes (CO₂-reducing methanogens) into methane, creating a microbial "hotspot". Reservoirs stratigraphically-comparable to the 2800' sand, but located in adjacent oil fields across a 90-km transect were sampled to investigate regional trends in gas composition, brine chemistry and microbial activity. The source field for the EOR-CO₂, the Black Lake Field, was also sampled to establish the δ¹³C-CO₂ value of the injected gas (0.9‰ +/- 0.9‰). Four samples collected from the Olla 2800' sand produced CO₂-rich gas with δ¹³C-CO₂ values (average 9.9‰) much lower than average (pre-injection) conditions (+15.9‰, average of sands located stratigraphically below the 2800' sand in the Olla Field) and at much higher CO₂ concentrations (24.9 mole %) than average (7.6 mole %, average of sands located stratigraphically below the 2800' sand in the Olla Field), suggesting the presence of EOR-CO₂ and gas-phase trapping as a major storage mechanism. Using δ¹³C values of CO₂ and dissolved organic carbon (DIC), CO₂ dissolution was also shown to be a major storage mechanism for 3 of the 4 samples from the Olla 2800' sand. Minor storage mechanisms were shown to be migration, which only affected 2 samples (from 1 well), and some EOR-CO₂ conversion to microbial methane for 3 of the 4 Olla 2800' sand samples. Since methanogenesis was not shown to be a major storage mechanism for the EOR-CO₂ in the Olla Field (CO₂ injection did not stimulate methanogenesis), samples were examined from adjacent oil fields to determine the cause of the Olla microbial "hot-spot". Microbial methane was found in all oil fields sampled, but indicators of methanogenesis (e.g. alkalinity, high δ¹³C-DIC values) were the greatest in the Olla Field, and the environmental conditions (salinity, pH, temperature) were most ideal for microbial CO₂ reduction in the Olla field, compared to adjacent fields.

A dearth of reliably-dated paleolake records from the southern Basin and Range has limited knowledge of past water balance changes there, precluding a more complete understanding of late Pleistocene atmospheric circulation across western North America. Paleoshorelines in closed basins throughout the region can provide accurately dated records of local effective moisture variations, representing a largely untapped source of paleohydrologic information. This dissertation presents paleohydrologic reconstructions from depositional successions in two basins at 32°N, approximately 100 km apart: Willcox basin, in southeastern Arizona, and Playas Valley, in southwestern New Mexico. Also presented are the results of ¹⁴C dating of charcoal samples from the El Fin del Mundo Clovis archaeological site, in northwestern Sonora, Mexico. In depth analysis of these results allowed constraint of the "small sample effect" on the charcoal ages, found to be smaller than 1σ of analytical uncertainty. The magnitude of the problem in ages from miniscule shell samples in the Willcox and Playas chronologies was found to be similar. The successions record moist pluvial conditions from ~20-13 ka in Playas, and>37-11 ka in Willcox, with most dates younger than 19 ka--before which there is no solid evidence for lake transgressions. There is clear evidence for overlapping highstands between ~18.3 and 17.9 ka and a brief highstand of Cochise at ~12.9 ka, coinciding with Heinrich events H1b and H0, respectively. Temporal concordance between wet periods and perturbations in the North Atlantic ocean and/or southern Laurentide ice sheet supports the idea that abrupt paleoclimatic changes in the southwestern U.S. occurred in response to large-scale atmospheric linkages to the northern high latitudes. The H1b highstands fill a hiatus in ¹⁴C dates compiled from paleoshorelines throughout the western U.S., and correspond to the first part of a lowstand in paleo-Lake Estancia (35°N), in north-central New Mexico. Anti-phasing within New Mexico suggests that the newly documented highstands resulted from an increase in southerly-sourced precipitation. This is consistent with paleoenvironmental evidence from southern Arizona and New Mexico that points toward periodic intensification of the summer monsoon during the late Pleistocene.

Precipitation, more than any other environmental factor, controls patterns of ecosystem production and biogeochemical cycling in arid and semiarid environments. Growing-season rains in these regions are highly unpredictable as they come in intermittent pulses varying in size, frequency and spatial extent, thereby producing unique hydrological patterns that constrain the location and residence time of soil water available for biological activity. In order to understand how arid and semiarid ecosystems respond to inputs of precipitation within the context of ecosystem science and global change studies, knowledge is needed on how plants and other organisms respond as an integrated system to such environmental control. The focus of my research was to understand how the distribution of precipitation events influences the dynamics of carbon cycling in semiarid ecosystems. At a semiarid riparian woodland, measurements of CO2 exchange and evapotranspiration revealed that following precipitation events occurring soon after prolonged dry periods the efficiency of rain-use (amount of carbon gain per unit of precipitation over a specific period time) was low. Precipitation did not readily stimulate primary productivity, water was mainly lost as soil evaporation and large respiratory CO2 effluxes were observed. This commonly observed features in seasonally dry ecosystems might have profound consequences for the seasonal and annual carbon balance. In this woodland, 47% of the precipitation within a single growing season (May-October) was returned to atmosphere as soil evaporation and the CO2 efflux observed just during the first rainy month (July) was equivalent to almost 50% of the net carbon gain observed over the six-month growing season. Results from experimental irrigations in understory plots of riparian mesquite woodland revealed that the magnitude and duration of the large CO2 fluxes occurring soon after rainfall was higher in plots located under tree canopies where, relative to intercanopy plots, the amount of plant litter was higher, soil evaporation and plant photosynthetic rates were lower. Efficiency of rain-use in semiarid ecosystems during the growing season apparently was determined by the degree of coupling between gross photosynthesis and ecosystem respiration, by the fraction of precipitation lost as soil evaporation and by the water-use efficiency of the component vegetation.

Chlorine stable isotope analysis (?37Cl ) means of stream water (- 0.95 ‰, n = 22), rainwater (- 1.51 ‰, n = 12), fog water (- 1.08 ‰, n = 7) and silicate mineral bound chloride (+ 0.13 ‰, n = 3) are used in an isotope mass balance approach to estimate sources of stream chloride. During summer-baseflow conditions, the chloride budget of two catchments in southwestern Nova Scotia is approximately 39 % from rainfall, 37 % from fog water and 24 % from rock/water interactions. The results of a significant source of geological chloride suggest the use of chloride in stream water as a proxy for marine derived sulphate may not be valid. This conclusion implies that anthropogenic sources of sulphate to acid sensitive ecosystems of southwestern Nova Scotia have been underestimated when chloride is assumed to be a conservative ion in the hydrological cycle.

Global climate change threatens the survival of microtidal wetlands by altering fundamental hydrological aspects such as precipitation patterns and tidal exchange. The combination of these stressors results in increased flooding period and soil salinity in coastal wetlands. In this study, we combined the use of detailed hydrological measurements (wetland water level and salinity), LIDAR elevation models, and water stable isotopes tracers (δD, δ18O) to study the balance between freshwater and saltwater inputs on two microtidal wetlands: a saltmarsh in Matagorda, Texas and a freshwater-forested wetland in Humacao, Puerto Rico. In Matagorda, Texas, we described the process of connectivity between different hydrologic units (isolated and connected ponds) within the saltmarsh. Pond connectivity only occurred when water levels in major water bodies adjacent to our study site reached a threshold elevation of 0.39 m. Connections events were correlated to rainfall and— to a lesser extent— wind speed and direction. We conclude that connectivity within the saltmarsh is driven by the combined effect of tidal influence and rainfall inputs, factors that will be altered by sea level rise and climate change-related changes in long term weather patterns. In Humacao, Puerto Rico, we gathered a detailed dataset of changes in salinity and water level in a freshwater forested wetland dominated by the endangered salt intolerant species Pterocarpus officinalis. In addition, we studied tree water use and identified important water sources to the wetland using stable isotope tracers. Firstly, we provide evidence that recent hydrological alterations have effectively transformed the system from mostly freshwater, to a saltwater wedge estuary. Salinity inputs travel via a tidal creek channel that allows the progression of a saltwater wedge to the inland parts of the forest. Our results suggest that inland progression of the saltwater wedge is influenced by amplitude of tidal exchange in the middle portions of the tidal creek and by extended dry periods in the headmost part of the tidal creek. Isotope data showed that surface standing water was influenced by tidal water sources during the dry season, although the spatial extent of this influence was constrained to areas of the forest that had been previously deforested. The isotopic content of groundwater samples taken at increasing distances from the tidal creek revealed that— although surface waters are dominated by freshwater inputs (rainfall and runoff) during the wet season— the influence of tidal water sources at soil depths greater than 60 cm persists throughout the year. Nonetheless, isotopic content of Pterocapus officinalis stem water samples suggest that tree water uptake is constrained to very shallow, unsaturated parts of the soil. We conclude from both case studies that the long term vulnerability of microtidal wetlands to climate change is determined by the interaction of increased annual variability of freshwater inputs along with a steady increase in mean sea levels, and aggravated by extreme climatic events.

Species invasions are regarded as one of the most serious threats to biodiversity and native ecosystems and our ability to predict and quantify the impacts of invasive species has been an arduous task. Since the 1840s, the Laurentian Great Lakes have experienced an exponential increase in the number of identified invasive species. The most recent, Hemimysis anomala, is a littoral freshwater mysid native to the Ponto-Caspian region of Eastern Europe. They have been identified in all of the Great Lakes (except Lake Superior), the St. Lawrence River downstream to Québec City, and inland lakes in New York State and have the potential to destabilize energy flow in aquatic food webs. Using stable isotopes of carbon (13C) and nitrogen (15N), I evaluated nearshore food web structure at four sites along Lake Ontario’s north shore spanning a gradient of Hemimysis density to determine: 1) if dominant nearshore food web pathways change seasonally, and 2) whether fish exhibit a dietary shift towards consumption of Hemimysis. Also, the effects of Hemimysis consumption on the growth of yellow perch (Perca flavescens) were quantified using bioenergetics modeling and four predictive feeding scenarios simulating Hemimysis incorporation into yellow perch diets. My results suggest Hemimysis are being incorporated into diets of round gobies, alewife and small yellow perch, which has resulted in a trophic lengthening of the food web. As Hemimysis populations continue to establish and stabilize, fish may incorporate this species into their diets at a higher rate. Based on the bioenergetic modeling, the incorporation of Hemimysis into the diets of yellow perch will have a negative impact on their growth. These negative impacts on fish growth will likely be exacerbated when the limited seasonal availability of Hemimysis, patchy distribution and predator avoidance behaviours, are considered. These results have implications surrounding the sustainability of the Great Lakes fishery as Hemimysis will likely increase competition with young fish for food and fish consumption of this new invasive may lead to reduced fish growth. / Thesis (Master, Biology) -- Queen's University, 2012-04-03 23:04:18.612