Upwelling, atmospheric nitrogen (N2) fixation by cyanobacteria, and freshwater inputs from the Mississippi River system have been shown to stimulate new production by alleviating nitrogen (N) limitation in the northern Gulf of Mexico (GoM). Stable carbon (delta13C) and nitrogen (delta15N) isotopes were used to investigate whether these sources are utilized differentially by coastal and marine pelagic food webs. Particulate organic matter (POM), Trichodesmium, and zooplankton were collected from the Mississippi River plume and Loop Current (LC) which were detected using remote sensing data. Stable isotope values were used to separate coastal and marine water masses and environmental data (salinity, nutrient and pigment concentrations) allowed me to relate variability to the degree of freshwater influence. Published food web data from these two environments were then assessed to establish whether isotopic baseline shifts observed in our data occur at an ecosystem level. Isotope values of the POM and zooplankton were found to be significantly different between coastal and marine water masses. This was not the case for Trichodesmium whose isotope values were not significantly different between the two water masses. We found that marine water masses (sal > 35) exhibited silicate concentrations, cyanobacterial pigments and DIN: P that suggest an increased abundance of diazotrophs. In contrast, coastal water masses (sal < 35) exhibited increased diatom pigments and molar C:N indicating terrestrial sources fuel phytoplankton production. When published food web data were compared, we found producer and consumer delta15N values were enriched in the coastal compared to the marine environments. This work suggests that differences in delta15N values within my data set and published data reflect a shift in the use of biologically available N where higher trophic levels are sustained by diazotrophic activity in marine environments versus those supported by terrestrial sources in coastal ones. Food webs that have been constructed without considering Trichodesmium as a significant source of organic matter in the GoM should be reconsidered. By re-evaluating published data, this research gives insight into the early life ecology of larval fishes and works to help answer questions about the structure and function of pelagic food webs.

The blue crab, Callinectes sapidus, supports a successful fishery in the Atlantic Ocean and throughout the Gulf of Mexico, with a total landing of 8,158,788 lb. and a total value of $10,562,128 for the state of Florida during 2012 (FWC 2012 Annual Landings Summary). An accurate and comprehensive understanding of the blue crab's life history and seasonal migration behavior is essential in defining effective management strategies for the fishery. Tag recapture studies and ultrasonic tracking methods for studying blue crab migrations are costly in terms of time and resources. In this study an alternative approach, microchemical natural tagging, was successfully used to determine a female's mating habitat. This approach assumes that the exoskeleton of the post-terminal molt female blue crab reflects the mating habitat's chemical signature and that the chemical signals are stable over time. To test these hypotheses, mature female blue crabs were collected from two Tampa Bay locations. Collected crabs were placed in tanks for 29 days, a subset was sacrificed at T = 0 and then twice per week, and the exoskeletons were analyzed via Inductively Coupled Plasma Mass Spectrometry (ICP-MS) and Elemental Analyzer Infrared Mass Spectrometry (EA-IRMS) to observe the stability of the exoskseletal chemical signature over time. Over the 29 day time series, no significant change in the concentrations of Li, Ca, and Ba, or the isotopic ratios of 13C/12C (δ13C) and 15N/14N (δ15N) were observed (ANOVA p-value > 0.05). A Canonical Analysis of Principal Coordinates (CAP)-based discriminate analysis with leave-one-out cross-validation collectively compared Li concentrations, δ13C, and δ15N among five Tampa Bay locations, producing a confusion matrix successfully classifying field collected crabs into: Alafia River 33%#37;, Little Manatee River 71%#37;, Palm River 67%#37;, Safety Harbor 30%#37;, and Skyway Fishing Pier 83%#37;, with an overall classification success of 66%#37;. These results suggest that the largest biomass component of the migratory pulse collected near the mouth of Tampa Bay was dominated by crabs originating from an area not widely harvested by commercial fishermen, as relatively few of the migrating females were matched to riverine locations that were intensively fished. Instead, most appeared to originate from open waters of Tampa Bay. It is possible that low densities of blue crab inhabiting a large area that is not commercially fished, effectively shields a proportion of the individuals in the Tampa Bay estuary from economic exploitation, creating a density-dependent natural harvest refugium.

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.

The carbonate storm-dominated sedimentary succession superbly exposed on Anticosti Island in Eastern Canada represents one of the most complete and well-preserved paleotropical stratigraphic records spanning the Ordovician-Silurian (O-S) boundary. We sampled the nearly continuous coastal outcrop exposed at low tide along the west coast of Anticosti Island for high-resolution δ13C and δ18O chemostratigraphy. These new isotopic curves comprise more than 500 data points spaced at ~0.6 m intervals; for a total of 320 m of strata across the O-S boundary. The δ13C curve displays two distinctive positive excursions in the Hirnantian Ellis Bay Formation; a small lower excursion (+2.5‰) and an upper larger excursion (+4.5‰). These two positive isotopic carbon excursions provide a distinctive chemostratigraphic signature for regional and global correlations with other Hirnantian sections. The continuing descending δ13C trend, at least 30 m above the currently interpreted O-S boundary, suggests a readjustment of that boundary on the Anticosti succession. The δ18O curve, similarly to the Quaternary δ18O marine curve, is tightly coupled with multi-order cyclic facies changes. Our tightly coupled lithological and oxygen isotopic data suggest that the Anticosti succession was influenced by glacio-eustatic fluctuations during the end-Ordovician. Furthermore, the estimated duration of these multi-order cycles supports an astronomical forcing. A primary isotopic signal record is also supported by the lack of significant covariance between δ13C and δ18O, by the excellent microfabric preservation of both macro and microfossils in petrographic, cathodoluminescence, and SEM microscopy, and by little or no diagenetic resetting as suggested by the trace element geochemistry, which is unusual in the deep geological time.

Feeding ecology and trophic interactions of six species of wading birds were explored through a combined analysis of stable isotope profiles and endoparasite communities. Stable isotopes broadly characterize the feeding preferences and geographic information, while parasite communities reflect long-term trends in feeding ecology. Deceased birds were obtained from four South Florida wildlife rehabilitation organizations. Of the 81 birds dissected, 73 contained parasites. Parasites were predominately found within the gastrointestinal tract. Host and range extensions were noted for several parasite taxa. Bird host species had a significant effect on the parasite community (P=0.001) while wildlife center location and maturity status did not. Stable nitrogen (δ15N) values for pectoral muscle tissues, representing approximately 24 days, ranged from 6.44 to 13.48‰ while stable carbon (δ13C) values ranged from -33.39 to -11.66‰. δ13C varied significantly among location (P=0.0002) and δ15N varied significantly among species (P15N and δ13C was analyzed in combination; bird species (P=0.001) and location (P=0.001) were significantly different. By using this combined approach of stable isotope analysis and parasite identification, it was possible to elucidate more components of bird feeding ecology. Stable isotope analysis provided knowledge on trophic interactions based on δ15N values, while δ13C was used to determine the differences in geographic foraging location. As endoparasites are acquired trophically via food-web interactions, identifying the parasite community allowed for trophic links to be drawn between organisms present within the same environment. Combining these two techniques allows for an abundance of information on feeding ecology and trophic interactions to be obtained.

Plant carbon isotopes were used to track assimilation of riparian resources by small mammals. Voles and shrews derived significant portions of their carbon from riparian vegetation. Deer and harvest mice were abundant in riparian habitat but assimilated little riparian vegetation indicating that the riparian corridor provided resources other than food. This is first use of stable carbon isotopes to trace riparian resources into a vertebrate community. Conifer encroachment in sagebrush ecosystems negatively affects many wildlife populations. Conifer removal is recommended across millions of hectares in the Great Basin. However the effects of conifer encroachment and conifer removal are unknown for most wildlife species. We show that the consequences of conifer encroachment, a press impact, far outweigh the pulse impact of sagebrush restoration, on small mammal diversity. Lack of demographic data limit the development of effective management, conservation and recovery goals for rattlesnakes. We used a long-term dataset and capture mark recapture models to quantify demography of four rattlesnake populations. Mean population growth indicated an overall stable population across the study, with two of the four sites declining. Survival overwhelmingly contributed to population growth relative to recruitment. No small mammals drank stream water even during periods of environmentally high water stress and high aridity, extension of the linear regression equation for small mammal body water towards the meteoric waterline, captures stream water, the weighted mean average for regional meteoric waters. Similar regression of fossilized small mammal tissues would also capture local meteoric waters. Even in arid regions, small mammal fossils are a suitable proxy for climate reconstructions. In the Great Basin, snowmelt overwhelmingly contributes to local precipitation, plant production, and stream flows. Snowmelt supports riparian and upland plants, and small mammals. Rattlesnakes prey primarily on small mammals, indirectly depending on snow melt for survival and reproduction. Climate models and rattlesnake emergence strongly indicate an earlier onset of spring and reduced ratio of snow to rain. Declining snowpack will have major impacts on biodiversity and management such as riparian vegetation, native plant restoration, trophic interactions, and ecological goods and services.

The Hirnantian mass extinction was the second largest of the Phanerozoic. A global sea level fall resulting from a glaciation on Gondwanaland caused significant changes in ocean circulation patterns and nutrient cycling that is recorded as a worldwide positive δ13C excursion.<p> In chapter 2, carbon and nitrogen isotope profiles were reconstructed from two North American carbonate platforms in Nevada and one in the Yukon with the purpose of gaining a better understanding of proximal to proximal gradients in δ13C values from Hirnantian epeiric seaway sediment. Positive δ13C excursions are recorded in bulk inorganic and organic carbon fractions from all three sections, and in graptolite periderms from one section. A larger positive excursion is recorded in the proximal sediment (7) compared to proximal sediment (3-4). This gradient appears to reflect differences in surface water dissolved inorganic carbon δ13C values across epeiric seas. These findings are consistent with the carbonate weathering hypothesis, that predicts larger positive δ13C shifts in proximal settings of tropical epeiric seas resulting from changes in the local carbon weathering flux caused by the exposure of vast areas of carbonate sediment during glacioeustatic sea level fall and restricted shelf circulation. A 2 positive excursion in δ15N is interpreted to result from increased ocean ventilation, greater partitioning of atmospheric oxygen into downwelling surface waters, oxygen minimum zone shrinkage, and declining denitrification rates. This allowed for upwelling of recycled nitrogen with high 15N values into the photic zone that forced exported organic matter from the photic zone to higher 15N values, consistent with the observed positive shift in 15N during the Hirnantian glaciation. This study presents a conceptual model to explain secular changes in δ13C and δ15N during the transition from a greenhouse to icehouse climate.<p> The second focus of this research, presented in chapter 3, was on improving the chemical and analytical methods for δ18O analysis of biogenic apatites. The technique applies cation exchange chromatography that allows for small sample sizes of apatite (200 µg) to be used for chemical conversion to Ag3PO4. The precision (0.15, 1) of δ18O analysis obtained using a Thermal Conversion Elemental Analyser Continuous Flow Isotope Ratio Mass Spectrometer (TC/EA CF-IRMS), and the ability to collect multipe isotopes (O, Ca, Sr, REE) using a cation exchange column, makes this technique valuable for high-resolution, multi-isotope studies of biogenic apatites.

The Hirnantian mass extinction was the second largest of the Phanerozoic. A global sea level fall resulting from a glaciation on Gondwanaland caused significant changes in ocean circulation patterns and nutrient cycling that is recorded as a worldwide positive δ13C excursion.<p> In chapter 2, carbon and nitrogen isotope profiles were reconstructed from two North American carbonate platforms in Nevada and one in the Yukon with the purpose of gaining a better understanding of proximal to proximal gradients in δ13C values from Hirnantian epeiric seaway sediment. Positive δ13C excursions are recorded in bulk inorganic and organic carbon fractions from all three sections, and in graptolite periderms from one section. A larger positive excursion is recorded in the proximal sediment (7) compared to proximal sediment (3-4). This gradient appears to reflect differences in surface water dissolved inorganic carbon δ13C values across epeiric seas. These findings are consistent with the carbonate weathering hypothesis, that predicts larger positive δ13C shifts in proximal settings of tropical epeiric seas resulting from changes in the local carbon weathering flux caused by the exposure of vast areas of carbonate sediment during glacioeustatic sea level fall and restricted shelf circulation. A 2 positive excursion in δ15N is interpreted to result from increased ocean ventilation, greater partitioning of atmospheric oxygen into downwelling surface waters, oxygen minimum zone shrinkage, and declining denitrification rates. This allowed for upwelling of recycled nitrogen with high 15N values into the photic zone that forced exported organic matter from the photic zone to higher 15N values, consistent with the observed positive shift in 15N during the Hirnantian glaciation. This study presents a conceptual model to explain secular changes in δ13C and δ15N during the transition from a greenhouse to icehouse climate.<p> The second focus of this research, presented in chapter 3, was on improving the chemical and analytical methods for δ18O analysis of biogenic apatites. The technique applies cation exchange chromatography that allows for small sample sizes of apatite (200 µg) to be used for chemical conversion to Ag3PO4. The precision (0.15, 1) of δ18O analysis obtained using a Thermal Conversion Elemental Analyser Continuous Flow Isotope Ratio Mass Spectrometer (TC/EA CF-IRMS), and the ability to collect multipe isotopes (O, Ca, Sr, REE) using a cation exchange column, makes this technique valuable for high-resolution, multi-isotope studies of biogenic apatites.

Bottom sediment is an archive of the historical changes in a lake and its catchment. This thesis is apalaeoenvironmental reconstruction of catchment processes in Bolgoda Lake situated in western SriLanka. We studied a sediment core retrieved from this lake. In our study, we focus on multiplephysical and chemical proxies: grain-size, loss-on-ignition, total organic carbon content, C:N ratio,and δ13C stored in the organic matter. The aim of this study is to contribute to a better understandingof the palaeoenvironmental conditions in the region and allow a comparison between this site andothers.In the deepest part of the core, we see an overall high sand content, which indicates a period ofhigher discharge into the lake compared to what the other core parts indicate. This is probably aresult of higher precipitation. This is followed by a decline in C:N and a rise in TOC in the second partwhich indicates an increase of primary production in the lake. In the third part we again see a shift inthe C:N indicating a source change back to more terrestrial runoff. The increase in TOC and LOIvalues together with decrease in C:N ratio and a steady increase in δ13C indicate an increase inlacustrine productivity in the upper part of the core.By reconstructing the palaeoenvironmental history in Bolgoda Lake we can conclude that it isprobable that some other factor than diagenetic change affects the lake. Our results indicate thatthese changes most likely are due to more wet periods and anthropogenic activity, mainly throughland use changes.

Soil organic matter (SOM) is a dynamic soil property, sensitive and responsive to many factors. The possibility of increasing soil carbon (C) sequestration by changing land use and management practices has been of great interest recently due to concerns with global changes in the atmospheric carbon dioxide (CO2) balance. Nonetheless, as a result of the complex dynamics of SOM, there is still the need for SOM characterization procedures capable of monitoring SOM stabilization, taking into account all the factors involved. This study characterized SOM stabilization as affected by management practices in three long-term field experiments, considering physical, chemical and biological components. The field experiments are located near Lexington, Kentucky, on a Maury silt loam (fine, mixed, mesic Typic Paleudalfs). The first experiment evaluates tillage and nitrogen (N) rate effects. The second experiment studies manure and N rate effects. The third experiment evaluates the five corn components of three crop rotations [continuous (monoculture) corn, corn-wheat/double crop soybean, and hay-hay-corn-corn-corn]. Soil organic matter content, stability, and composition, for physically separated fractions, were assessed using δ13C natural abundance and diffuse reflectance Fourier transformed infrared (DRIFT) spectroscopy. In addition, management effects on microbial biomass and microbial function as indicated by phenol oxidase enzyme activity were evaluated. The results indicate that management practices affect SOM content, stability, and composition, and these effects differ by the soil aggregate fraction. No-tillage (NT), N fertilization, manure application and increased corn in crop rotations enhanced SOM levels. However, the effect of NT was observed mainly at the soil surface. Soil organic matter storage was determined by the aggregate size distribution. The proportion of recently deposited C was generally positively related to aggregate size, especially for the first and third experiments. Most of the recently deposited C was stabilized in microaggregates within macroaggregates, across the management treatments and field experiments. In addition, this fraction consistently exhibited low to medium SOM reactivity. These results suggest that SOM stabilization, as influenced by management practices, required achieving a specific composition and location within the soil matrix. This implies that soil C forms and aggregate size and stability are closely interrelated.