123 research outputs found
RATES, IMPORTANCE, AND CONTROLS OF NITROGEN FIXATION IN OLIGOTROPHIC ARCTIC LAKES, TOOLIK, ALASKA
No full textBiological nitrogen (N) fixation of atmospheric N2 by free-living cyanobacteria in aquatic environments is common, and in many ecosystems, it can account for a significant portion of the biologically available N inputs. Although N fixation can compensate for N limitation, N limitation is maintained over relatively long time scales in many oligotrophic lake ecosystems. This dissertation examines the importance of benthic and pelagic N fixation in the N economies of oligotrophic lakes in arctic Alaska (Chapter 1) and examines nutrient, light, and grazer controls on benthic N fixation (Chapters 2 and 3). Both benthic and pelagic N fixation are prevalent in many lakes across the Alaskan arctic landscape, ranging from 0.12 ? 1.5 mg N m-2 day-1 and 0 ? 2.56 mg N m-2 day-1 respectively. Pelagic N fixation is much higher than has been reported elsewhere for oligotrophic lakes, and is more important than previously thought, comprising ~ 75% of N inputs to one lake. Benthic N fixation is lower than has been reported for other oligotrophic systems, and is roughly equivalent to N inputs from atmospheric deposition on an areal basis (~25 mg N m-2 year-1). On the landscape scale, N fixation in lakes roughly equal that in terrestrial ecosystems in this Arctic region. Benthic N fixation generally appears to have a saturating response to light availability within individual lakes, but light does not explain variation in benthic N fixation across lakes or years. Whole-lake fertilization and laboratory experiments indicate that P input stimulates benthic N fixation while N input suppresses N fixation when N is added either alone or in conjunction with P in Redfield proportion. Snails at ambient density cause a small decline in benthic N fixation (0.85 ? 1.8% reduction over the summer). These patterns are corroborated in the landscape: lakes on younger surfaces have higher P, more snails, and higher rates of N-fixation than lakes on older surfaces
Personality (11th Edition)
No full textIn Personality, the historical underpinnings of core theories and research come alive through biographical and contextual illustrations. Author Jerry M. Burger, and new co-author Gretchen M. Reevy, use vivid stories and discussions to challenge learners to critically consider the discipline’s approach to diversity, research science, and its future as a holistic field of study. With a balance of both theory and research, along with application sections and personality tests, you will gain hands-on experience and a comprehensive understanding of the subject matter. Every chapter in this Eleventh Edition has been thoroughly updated, such as sections on Extraversion-Introversion, Dream Interpretation, and Gender Roles, to reflect the most recent research. It also features 400 new references, a new research topic on Narcissism, and two new personality scales.https://scholarcommons.scu.edu/faculty_books/1551/thumbnail.jp
Controls of Benthic Nitrogen Fixation and Primary Production from Nutrient Enrichment of Oligotrophic, Arctic Lakes
No full text© The Author(s), 2013. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Ecosystems 16 (2013): 1550-1564, doi:10.1007/s10021-013-9701-0.We examined controls of benthic dinitrogen (N2) fixation and primary production in oligotrophic lakes in Arctic Alaska, Toolik Field Station (Arctic Long-Term Ecological Research Site). Primary production in many oligotrophic lakes is limited by nitrogen (N), and benthic processes are important for whole-lake function. Oligotrophic lakes are increasingly susceptible to low-level, non-point source nutrient inputs, yet the effects on benthic processes are not well understood. This study examines the results from a whole-lake fertilization experiment in which N and P were added at a relatively low level (4 times natural loading) in Redfield ratio to a shallow (3 m) and a deep (20 m) oligotrophic lake. The two lakes showed similar responses to fertilization: benthic primary production and respiration (each 50–150 mg C m−2 day−1) remained the same, and benthic N2 fixation declined by a factor of three- to fourfold by the second year of treatment (from ~0.35 to 0.1 mg N m−2 day−1). This showed that the response of benthic N2 fixation was de-coupled from the nutrient limitation status of benthic primary producers and raised questions about the mechanisms, which were examined in separate laboratory experiments. Bioassay experiments in intact cores also showed no response of benthic primary production to added N and P, but contrasted with the whole-lake experiment in that N2 fixation did not respond to added N, either alone or in conjunction with P. This inconsistency was likely a result of nitrogenase activity of existing N2 fixers during the relative short duration (9 days) of the bioassay experiment. N2 fixation showed a positive saturating response when light was increased in the laboratory, but was not statistically related to ambient light level in the field, leading us to conclude that light limitation of the benthos from increasing water-column production was not important. Thus, increased N availability in the sediments through direct uptake likely caused a reduction in N2 fixation. These results show the capacity of the benthos in oligotrophic systems to buffer the whole-system response to nutrient addition by the apparent ability for significant nutrient uptake and the rapid decline in N2 fixation in response to added nutrients. Reduced benthic N2 fixation may be an early indicator of a eutrophication response of lakes which precedes the transition from benthic to water-column-dominated systems.This project was supported by
NSF-OPP 9732281, NSF-DEB 9810222, NSF-DEB
0423385, and by a Doctoral Dissertation Improvement
Grant NSF-DEB 0206173. Additional funding
was provided by the Small Grants Program through
the NSF-IGERT Program in Biogeochemistry and
Environmental Change at Cornell University
A comparison of whole and thin-sectioned otolith aging techniques and validation of annuli for Arctic grayling
No full textInformation on age and growth is essential for the conservation and management of fish species. Age is often estimated using the banding structure in otoliths, but the technique used can influence the estimate, especially in slow-growing, long-lived species. Counts of translucent bands from both whole and thin-sectioned Arctic grayling (Thymallus arcticus) otoliths from the Kuparuk River, Alaska, gave similar age estimates. Age estimates from whole otoliths were less variable, particularly for older age groups, and were much easier to prepare and read than thin-sections. Comparison of growth of individual tagged fish to a von Bertalanffy growth model revealed that the translucent rings are true annuli. This approach to validation may be most useful in northern latitudes where other techniques are impractical. Our study shows that whole otoliths provide a fast, reliable, cost-effective technique for age estimation of this long-lived, slow-growing fish species common to the North American ArcticGettel et al "A comparison of whole and thin-sectioned otolith aging techniques and validation of annuli for Arctic grayling." Northwest Science. 1997; 71(3): 224-23
The effects of grazing by the snail, Lymnaea elodes, on benthic N2 fixation and primary production in oligotrophic, arctic lakes
No full textPFI-ZEKE SPECTROSCOPY OF , (M=Sc, Y, La)
No full textAuthor Institution: Department of Chemistry, University of KentuckyPulsed field ionization-zero electron kinetic energy (PFI-ZEKE) photoelectron spectroscopy was used to study Group III-trimethylamine association complexes. The complexes (M=Sc, Y, La) were produced in a pulsed molecular jet by laser ablation of the metal rod in the presence of a trimethylamine/helium mixture. Photoelecton spectra of the complexes were measured, allowing for the determination of the adiabatic ionization potential of the neutral radicals and the intermolecular vibrational frequencies for the neutrals and their ions. Spectral assignments were aided by ab initio and Franck-Condon factor calculations
Developments in water quality monitoring and management in large river catchments using the Danube River as an example
No full textEffective management of water quality in large rivers requires information on the influence of activities within the catchment (urban and rural) throughout the whole river basin. However, traditional water quality monitoring programmes undertaken by individual agencies normally relate to specific objectives, such as meeting quality criteria for wastewater discharges, and fail to provide information on basin-scale impacts, especially in transboundary river basins. Ideally, monitoring in large international river basins should be harmonised to provide a basin-scale assessment of sources and impacts of human activities, and the effectiveness of management actions. This paper examines current water quality issues in the Danube River basin and evaluates the approach to water quality monitoring in the context of providing information for a basin-wide management plan. Lessons learned from the monitoring programme in the Danube are used to suggest alternative approaches that could result in more efficient generation of water quality data and provide new insights into causes and impacts of variations in water quality in other large international river basins
Unaccounted CO<sub>2</sub> leaks downstream of a large tropical hydroelectric reservoir
No full textRecent studies show that tropical hydroelectric reservoirs may be responsible for substantial greenhouse gas emissions to the atmosphere, yet emissions from the surface of released water downstream of the dam are poorly characterized if not neglected entirely from most assessments. We found that carbon dioxide (CO2) emission downstream of Kariba Dam (southern Africa) varied widely over different timescales and that accounting for downstream emissions and their fluctuations is critically important to the reservoir carbon budget. Seasonal variation was driven by reservoir stratification and the accumulation of CO2 in hypolimnetic waters, while subdaily variation was driven by hydropeaking events caused by dam operation in response to daily electricity demand. This “carbopeaking” resulted in hourly variations of CO2 emission up to 200% during stratification. Failing to account for seasonal or subdaily variations in downstream carbon emissions could lead to errors of up to 90% when estimating the reservoir’s annual emissions. These results demonstrate the critical need to include both limnological seasonality and dam operation at subdaily time steps in the assessment of carbon budgeting of reservoirs and carbon cycling along the aquatic continuum.</p
Discerning our standpoint: African American women as 'subject' Ida B. Wells-Barnett & Mary E. Church Terrell women of fortitude and resolution, 2000
No full textThis thesis examines the contributions of early twentieth-century activists Ida B. Wells-Barnett and Mary Church Terrell to the social and political advancements of the African-American race. In an effort to rectify the study of African-American women as the other, the research sets as its goal to make African-American womens experiences subject and central to analysis. The tools employed are taken from three disciplines: African-American Studies, Women Studies and Political Science. The writer has also employed Black feminist thought as a research tool for examining the history and ideological concepts of African-American women. Key primary sources are utilized in constructing the foundation of the research. The writer relied on The Memphis Diary of Ida B. Wells, by editor Miriam DeCosta-Willis; Crusade for Justice an Autobiography of Ida B. Wells-Barnett, edited by Alfreda M. Duster; A Colored Woman in a White World, by Mary Church Terrell and A Voice from the South, by Anna Julia Cooper. Essential to the theorectical framework are tenets found in Black Feminist Thought: Knowledge, Consciousness, and the Politics of Empowerment, by Patricia Hill Collins, which offers a paradigm through which the experiences of African-American women can best be interpreted. By selecting this research tool, the efforts of Wells-Barnett and Terrell as activists, educators, crusaders and clubwomen become crucial in understanding the significance of African-American womens contributions to racial uplift and social and political tolerance
Are large herbivores vectors of terrestrial subsidies for riverine food webs?
No full textThe tropical savannas of Africa have witnessed a dramatic reduction in native large mammalian herbivore populations. The consequences of these changes for terrestrial-aquatic food-web linkages are poorly documented. We used natural abundances of stable carbon and nitrogen isotopes (δ13C, δ15N) to determine spatial and temporal patterns in the importance of herbivore-mediated subsidies for consumers in the Mara River, Kenya. Potential primary producers (terrestrial C3 and C4 producers and periphyton) and consumers (invertebrates and fish) were collected during dry and wet seasons from different sites along the river, representing a gradient from forested highlands to natural savanna grasslands with high herbivore densities across mixed agricultural and livestock-dominated zones. Bayesian mixing models were used to estimate the relative contributions of terrestrial and algal sources of organic carbon supporting consumer trophic groups. Organic carbon sources differed for consumer groups and sites and with season. Overall, periphyton was the major energy source for most consumer groups during the dry season, but with wide 95% confidence intervals. During the wet season, the importance of terrestrial-derived carbon for consumers increased. The importance of C3 producers declined from 40 and 41% at the forested upper reaches to 20 and 8% at river reaches receiving hippo inputs during the dry and wet seasons, respectively. The reciprocal increase in the importance of C4 producers was higher than expected based on areal cover of riparian vegetation that was mainly C3. The importance of C4 producers notably increased from 18 and 10% at the forested upper reaches to 33 and 58% at river reaches receiving hippo inputs during the dry and wet seasons, respectively. This study highlights the importance of large herbivores to the functioning of riverine ecosystems and the potential implications of their loss from savanna landscapes that currently harbor remnant populations. Although the importance of C4 terrestrial carbon in most river systems has been reported to be negligible, this study shows that its importance can be mediated by large herbivores as vectors, which enhance energetic terrestrial-aquatic linkages in rivers in savanna landscapes
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