No description available.

This thesis investigates stable isotope signals (i.e. δ18O and δ2H) in various information carriers such as lake water and lacustrine sediments, aiming to develop and refine the use of isotope tracers in hydrology and paleohydrology studies. Located at the confluence of the Peace and Athabasca Rivers at the western end of Lake Athabasca, the PAD is a key node in the Mackenzie River Drainage system, the single large freshwater source discharging into the Arctic Ocean from continental Northern America. The delta is one of the world’s largest freshwater deltas, has hundreds of shallow lakes and wetlands, and has been regularly monitored for isotopic composition in surface water bodies over a 7-year period. Because of the hydrological significance of the delta, as well as the availability of a wealth of ancillary information collected by previous studies, the PAD serves as a natural laboratory to develop and refine the application of stable isotopes in understanding landscape hydrological conditions in present and past. The outcomes also provide critical information for the development of scientifically informed management strategies for water resources in the delta. In the study of modern processes, a novel coupled isotope tracer method was developed to characterize the isotopic composition of input water to lakes. The method is based on coupling the well-known Craig-Gordon model, which describes the evaporative enrichment process for both isotopes, with the Local Meteoric Water Line to constrain the isotopic composition of input water to lakes. The application of this method in two sampling campaigns (2000 and 2005) demonstrated significant temporal changes in source water to PAD lakes at landscape scale. The results also revealed the previously underestimated role of snowmelt to the northern part of the delta. In a laboratory culture experiment, effort was undertaken to understand the constant fractionation between aquatic cellulose and environmental water, which is routinely observed in field studies. This led to the development of a new conceptual characterization of the apparent cellulose-water relation that reconciles discrepancies among previous observations. This new interpretation supports the notion that oxygen in cellulose is fully inherited from CO₂during photosynthesis, but that aquarium studies may incorporate an unintended artefact from CO₂that has not undergone complete biochemically mediated exchange with water. The variable slope of the cellulose-water δ18O relation observed in culture experiments is attributed to varying degree of exchange, related to the residence time of CO₂in the water. This is in contrast to natural systems where long residence time of CO₂is likely to ensure full exchange, thus supporting the application of a constant apparent cellulose-water oxygen isotope fractionation in paleoenvironmental studies. Insights gained from these studies were applied in a multiproxy paleolimnological investigation of a shallow lake in the central part of the delta near the shoreline of Lake Athabasca. The Craig-Gordon modelling approach was applied to quantitative interpretation of a cellulose d18O record from lake sediments. Constraints provided by interpretation of other proxies allowed the development of a semi-quantitative assessment of changes in lake water balance over the past one thousand years. The inferred hydrological history indicated significant shifts in the source of water to the lake, including persistent influence from Lake Athabasca during the Little Ice Age (~ AD 1540-1880), as well as rapid change during the last century that is unprecedented in the last millennium. Overall, the thesis demonstrates our improved understanding of hydrological conditions based on various isotopic archives such as lake water and aquatic cellulose. New information acquired from these studies concerning the range and rate of hydrological variability in the present and past provides a fundamental baseline for evaluating the potential impacts of future climate change and human disturbance in the Peace-Athabasca Delta.

This thesis investigates stable isotope signals (i.e. δ18O and δ2H) in various information carriers such as lake water and lacustrine sediments, aiming to develop and refine the use of isotope tracers in hydrology and paleohydrology studies. Located at the confluence of the Peace and Athabasca Rivers at the western end of Lake Athabasca, the PAD is a key node in the Mackenzie River Drainage system, the single large freshwater source discharging into the Arctic Ocean from continental Northern America. The delta is one of the world’s largest freshwater deltas, has hundreds of shallow lakes and wetlands, and has been regularly monitored for isotopic composition in surface water bodies over a 7-year period. Because of the hydrological significance of the delta, as well as the availability of a wealth of ancillary information collected by previous studies, the PAD serves as a natural laboratory to develop and refine the application of stable isotopes in understanding landscape hydrological conditions in present and past. The outcomes also provide critical information for the development of scientifically informed management strategies for water resources in the delta. In the study of modern processes, a novel coupled isotope tracer method was developed to characterize the isotopic composition of input water to lakes. The method is based on coupling the well-known Craig-Gordon model, which describes the evaporative enrichment process for both isotopes, with the Local Meteoric Water Line to constrain the isotopic composition of input water to lakes. The application of this method in two sampling campaigns (2000 and 2005) demonstrated significant temporal changes in source water to PAD lakes at landscape scale. The results also revealed the previously underestimated role of snowmelt to the northern part of the delta. In a laboratory culture experiment, effort was undertaken to understand the constant fractionation between aquatic cellulose and environmental water, which is routinely observed in field studies. This led to the development of a new conceptual characterization of the apparent cellulose-water relation that reconciles discrepancies among previous observations. This new interpretation supports the notion that oxygen in cellulose is fully inherited from CO₂during photosynthesis, but that aquarium studies may incorporate an unintended artefact from CO₂that has not undergone complete biochemically mediated exchange with water. The variable slope of the cellulose-water δ18O relation observed in culture experiments is attributed to varying degree of exchange, related to the residence time of CO₂in the water. This is in contrast to natural systems where long residence time of CO₂is likely to ensure full exchange, thus supporting the application of a constant apparent cellulose-water oxygen isotope fractionation in paleoenvironmental studies. Insights gained from these studies were applied in a multiproxy paleolimnological investigation of a shallow lake in the central part of the delta near the shoreline of Lake Athabasca. The Craig-Gordon modelling approach was applied to quantitative interpretation of a cellulose d18O record from lake sediments. Constraints provided by interpretation of other proxies allowed the development of a semi-quantitative assessment of changes in lake water balance over the past one thousand years. The inferred hydrological history indicated significant shifts in the source of water to the lake, including persistent influence from Lake Athabasca during the Little Ice Age (~ AD 1540-1880), as well as rapid change during the last century that is unprecedented in the last millennium. Overall, the thesis demonstrates our improved understanding of hydrological conditions based on various isotopic archives such as lake water and aquatic cellulose. New information acquired from these studies concerning the range and rate of hydrological variability in the present and past provides a fundamental baseline for evaluating the potential impacts of future climate change and human disturbance in the Peace-Athabasca Delta.

Thesis (M.Sc.)--College of William and Mary. / Vita. Includes bibliographical references.

No description available.

Determining sustainable water resource utilization rates is an important problem faced by regulatory agencies all around the world. One of the key parameters in determining accurate water budgeting schemes is the rate of water resource replenishment, or ‘recharge’ in groundwater systems. Fundamental questions regarding groundwater recharge include: What is the source of recharge? What is the spatial distribution of recharge? What is the annual average recharge rate, from potentially disparate sources in disparate areas? Answers to these questions can be gained through combining physical and chemical hydrogeological research tools, including stable isotopic compositions. Land-use intensification, including significant increases in dairying, has placed a priority on developing water resource management practices throughout New Zealand. Here we present the first compilation of delta oxygen-18 and delta hydrogen-2 values from individual precipitation events, local surface waters, depression springs, and groundwaters from the greater-Christchurch area. A variety of analytical methods were used in an effort to evaluate the potential use of stable isotopic compositions as tracers of surface-groundwater interaction in the local hydrologic cycle. The results of this thesis found the isotopic variability of Christchurch precipitation to be highly varied. Back-trajectory analysis of single precipitation events exhibit pathways arriving from three principal sources: the Southern Pacific Ocean, the Tasman Sea, and the Tropical Pacific Ocean. Separately, delta oxygen-18 and delta hydrogen-2 values values from these sources show three distinct local meteoric water lines, which are determined to be largely affected by the environmental conditions present in these areas at the time water vapour formation. Intra-storm variation of extra-tropical cyclones support these findings as significant changes in deuterium excess as moisture sources change with southward movement of the low pressure system. Three line-conditioned tests were subsequently developed to compare the relationship between monthly surface rainfall, surface water, and groundwater samples to the respective moisture origins. Surface rainfall, rainfall infiltration, surface waters, and groundwaters all exhibit the least amount of deviation from the Southern Pacific Ocean local meteoric water line. These observations suggest the principle moisture source to Christchurch to be from west-south westerly flow from the mid-latitudes. However, these similarities do not make partitioning their relative contributions to the groundwater system easy. Previous physical and isotopic investigations have shown the dominant sources of recharge to the Christchurch Groundwater System (CGS) are alpine rivers and local precipitation of which there is statistically significant difference with respect to delta oxygen-18 values. A binary single-isotope mixing model allows for quantification of the relative contributions of alpine river and precipitation derived inputs to local depression springs. The isotopic model indicates that approximately 80% of spring discharge was derived from alpine rivers, in good agreement with recently published physical mass balance model results. Deep groundwater flow paths however show groundwater to flow from the Central Canterbury Plains to the CGS. Potentially including losses from the upper Waimakariri River reaches. If included, this places a net recharge amount to the CGS water budget, which if using losses from only the lower Waimakariri River, there is a net loss. Losses from the upper reaches and subsequent groundwater flow into the CGS are likely as there have been no observed declines in groundwater levels even though there is currently a net loss by only using recharge components within the CGS. Ultimately, recharge from groundwater movement from the Central Canterbury Plains may play significant role; however, a much more sophisticated geochemical model is needed to test these theories and determine contributions. This research demonstrates the utility of stable isotopes as tracers of hydrogeological processes, particularly in shallow groundwater, and their potential contributions to the water resource allocation decision making process.

Recently, the growth and condition of Lake Whitefish (Coregonus clupeaformis), an important commercial fishery commodity, has declined in some areas of the Great Lakes. As Lake Whitefish are benthic feeders, historically the bulk of their diet was made up of the energy rich Diporeia hoyi, an amphipod whose abundances declined concurrently with reductions in Lake Whitefish growth and condition. Lake Whitefish populations from lakes Michigan, Erie and Superior have been used to determine whether there is a plausible link between the declines in Lake Whitefish condition and Diporeia abundance as indicated by stable isotope analysis, dietary and condition indices for Lake Whitefish. The first study was Lake Michigan specific and tested the hypothesis that condition, in terms of relative weight, percent lipid and docosahexaenoic acid (DHA), improved as the proportion of high quality prey (e.g., Diporeia) in the diet increased. Samples of spawning whitefish from four regions (northwest, Naubinway, Elk Rapids and southeast) around Lake Michigan had distinct mean carbon and nitrogen isotope signatures. The signatures indicated Lake Whitefish may be using a variety of prey items, especially the Naubinway population where fish occupy the largest isotopic niche space. Relative weight was significantly higher in the southeast and lower for all northern regions. The mean measured lipid from Lake Whitefish dorsal skinless muscle biopsies was highest for northwest region fish. DHA was significantly different among studied regions, with higher mean values in Elk Rapids and the northwest. No linear relationships between stable isotope measures and condition metrics were found. These results suggest that Lake Whitefish are coping with declining Diporeia abundances by feeding on alternate prey. Results do not substantiate the hypothesis of a relationship between condition and prey use, although Lake Whitefish from Elk Rapids and the northwest had high quality prey and good condition. The second study incorporated eight spawning populations around lakes Michigan, Erie and Superior to determine if there were differences in energy available to female Lake Whitefish. The hypotheses tested were three fold: (1) observed differences in growth and reproduction among populations were driven by energy availability, (2) populations with low energy reserves exhibit reproductive trade-offs and (3) high energy reserves are related to Diporeia consumption. Lake Whitefish from lakes Erie and Superior both displayed high growth and no trade-offs between egg size and number. Populations from Lake Michigan all had low investment in growth, significantly lower gonadosomatic index (GSI) and four of these populations displayed significant trade-offs between egg size and number. Growth and GSI tended to increase with mean total lipid stored in muscle and populations displaying reproductive trade-offs had significantly lower muscle lipid, however, these trends were not evident when using DHA as a measure of good nutrition. No relationship was evident between Diporeia consumption and populations with high muscle lipid stores. Overall, my results suggest that while changes in the availability of prey resources has had an effect on Lake Whitefish populations, the impact of declining abundances of Diporeia alone cannot explain the systemic changes in Lake Whitefish condition across the Great Lakes basin.

Thesis (Ph. D.)--Drexel University, 2005. / Includes abstract and vita. Includes bibliographical references (leaves 191-199).

Thesis advisor: Amy E. Frappier / A ~7,000 year stable isotope record from a Central American stalagmite is presented as a record of rainfall and consequently Intertropical Convergence Zone (ITCZ) tropical rain belt strength over the late Pleistocene to mid-Holocene. The "amount effect" explains the well-documented inverse relationship between rainfall amount and stable oxygen isotope values observed in tropical monsoon regions and consequently in stalagmite calcite from those regions. ITCZ rainfall influences much of the Central American tropical region and here a ~7,000 year stable isotope record from stalagmite ATM1 harvested from Actún Tunichil Muknal Cave in Belize is presented as a record of ITCZ influenced rainfall during the late Pleistocene to mid-Holocene (5,561 ± 2,488 BP - 12,605 ± 284 BP). Three major oxygen isotope excursions occur within the record. These excursions correspond to the global cold Younger Dryas and 8.2 ka events and a relatively undocumented wet period around 6,300 bp. The Younger Dryas manifests as a relatively moist period in central Belize while the 8.2 ka event manifests as a relatively dry period. The reason for the opposite responses to cooling elsewhere in the globe is posited to be due to orbital forcings. The 6,300 bp relatively wet period appears to be synoptic in scale and two possible triggers for the isotope excursion are presented: eustatic sea level rise causing lagoonal constriction, warming of water off the coast of Belize, and thus increased evaporation and precipitation over the study region; and hurricane clusters, evidenced in the region in the succeeding 1,000 years, in which the location of the Azores High funnels hurricanes to make landfall near the central Belize region. ATM1 provides evidence for tropical leads and/or lags to global climate events and bolsters the idea that high and low latitude climate relationships are complexly interlinked. / Thesis (MS) — Boston College, 2010. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Geology and Geophysics.

No description available.