Modeling the impact of Trichodesmium and nitrogen fixation in the Atlantic Ocean

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95044/1/jgrc9275.pd

Regulation of nitrogen metabolism in the marine diazotroph Trichodesmium IMS101 under varying temperatures and atmospheric CO2 concentrations

We examined the influence of forecasted changes in global temperatures and pCO2 on N2 fixation and assimilation in the ecologically important cyanobacterium Trichodesmium spp. Changes of mRNA transcripts (nifH, glnA, hetR, psbA, psaB), protein (nitrogenase, glutamine synthetase) pools and enzymatic activity (nitrogenase) were measured under varying pCO2 and temperatures. High pCO2 shifted transcript patterns of all genes, resulting in a more synchronized diel expression. Under the same conditions, we did not observe any significant changes in the protein pools or in total cellular allocations of carbon and nitrogen (i.e. C : N ratio remained stable). Independently of temperature, high pCO2 (900 µatm) elevated N2 fixation rates. Levels of the key enzymes, nitrogenase and glutamine synthetase that mediate nitrogen assimilation did not increase, implying that the high pCO2 allowed higher reaction turnover rates through these key enzymes. Moreover, increased temperatures and high pCO2 resulted in higher C : P ratios. The plasticity in phosphorous stoichiometry combined with higher enzymatic efficiencies lead to higher growth rates. In cyanobacteria photosynthesis, carbon uptake, respiration, N2 fixation and nitrogen assimilation share cellular components. We propose that shifted cellular resource and energy allocation among those components will enable Trichodesmium grown at elevated temperatures and pCO2 to extend its niche in the future ocean, through both tolerance of a broader temperature range and higher P plasticity

Global patterns of phytoplankton nutrient and light colimitation inferred from an optimality-based model

The widely used concept of constant ”Redfield” phytoplankton stoichiometry is often applied for estimating which nutrient limits phytoplankton growth in the surface ocean. Culture experiments, in contrast, show strong relations between growth conditions and cellular stoichiometry with often substantial deviations from Redfield stoichiometry. Here we investigate to what extent both views agree by analyzing remote sensing and in situ data with an optimality-based model of nondiazotrophic phytoplankton growth in order to infer seasonally varying patterns of colimitation by light, nitrogen (N), and phosphorus (P) in the global ocean. Our combined model-data analysis suggests strong N and N-P colimitation in the tropical ocean, seasonal light, and N-P colimitation in the Northern Hemisphere, and strong light limitation only during winter in the Southern Ocean. The eastern equatorial Pacific appears as the only ocean area that is essentially not limited by N, P, or light. Even though our optimality-based approach specifically accounts for flexible stoichiometry, inferred patterns of N and P limitation are to some extent consistent with those obtained from an analysis of surface inorganic nutrients with respect to the Redfield N:P ratio. Iron is not part of our analysis, implying that we cannot accurately predict N cell quotas in high-nutrient, low-chlorophyll regions. Elsewhere, we do not expect a major effect of iron on the relative distribution of N, P, and light colimitation areas. The relative importance of N, P, and light in limiting phytoplankton growth diagnosed here by combining observations and an optimal growth model provides a useful constraint for models used to predict future marine biological production under changing environmental conditions

Incorporating a prognostic representation of marine nitrogen fixers into the global ocean biogeochemical model HAMOCC

Nitrogen (N2) fixation is a major source of bioavailable nitrogen to the euphotic zone, thereby exerting an important control on ocean biogeochemical cycling. This paper presents the incorporation of prognostic N2 fixers into the HAMburg Ocean Carbon Cycle model (HAMOCC), a component of the Max Planck Institute Earth System Model (MPI‐ESM). Growth dynamics of N2 fixers in the model are based on physiological characteristics of the cyanobacterium Trichodesmium. The applied temperature dependency confines diazotrophic growth and N2 fixation to the tropical and subtropical ocean roughly between 40°S and 40°N. Simulated large‐scale spatial patterns compare well with observations, and the global N2 fixation rate of 135.6 Tg N yr−1 is within the range of current estimates. The vertical distribution of N2 fixation also matches well the observations, with a major fraction of about 85% occurring in the upper 20 m. The observed seasonal variability at the stations BATS and ALOHA is reasonably reproduced, with highest fixation rates in northern summer/fall. Iron limitation was found to be an important factor in controlling the simulated distribution of N2 fixation, especially in the Pacific Ocean. The new model component considerably improves the representation of present‐day N2 fixation in HAMOCC. It provides the basis for further studies on the role of diazotrophs in global biogeochemical cycles, as well as on the response of N2 fixation to changing environmental conditions

Buoyancy - Design of a dynamic racing sports accommodation

Abweichender Titel laut Übersetzung der Verfasserin/des VerfassersZsfassung in engl. SpracheDie Masterarbeit Auftrieb befasst sich mit dem Entwurf einer Sportunterkunft für das Regattazentrum Oberösterreich in Ottensheim. Das Regattazentrum liegt an einem olympiatauglichen Altarm der Donau und war in den letzten Jahren mehrmals von Hochwasser betroffen. Viele Bewohner des Eferdinger Beckens haben in den Jahren 2002 und 2013 am eigenen Leib erfahren was es heißt Hab und Gut zu verlieren. Architektur könnte bei Hochwasser und die daraus resultierenden Überschwemmungen eine Schutzfunktion einnehmen. In der Arbeit wird die Frage gestellt, wie Architektur unter solch schwierigen Umständen funktionieren kann und wie sie die Energie eines solchen Ereignisses sogar noch ausnutzen kann. Zum einen nimmt sich die Architektur heraus genauso wie ein Ruderboot zu schwimmen und zum anderen reizt sie die neuen Möglichkeiten aus, die sich mit unterschiedlichen Wasserständen ergeben. Der Baukörper folgt in seiner Formgebung dem Konzept der Kokons der Köcherfliegenlarven und ist an einer horizontalen Achse fixiert. Bei Wasserstands-Änderungen rotiert der Baukörper um bis zu 40 Prozent bei 10 Meter Wasseranstieg an dieser. Dadurch ergeben sich ganz neue Möglichkeiten den Innenraum zu gestalten: Der Boden, der gleichzeitig Wand und Decke ist, Möbel, Belichtung, Stiegen und Öffnungen sind bei allen Wasserständen benutzbar und in ihrer Form an die Rotation des Baukörpers angepasst. Ein Benutzer legt sich abends schlafen und bemerkt die Änderung der Lage des Baukörpers am nächsten Morgen sofort im Inneren am Raum, an der Veränderung der Möbel und des Bodens. Diese Architektur ermöglicht das Erleben der unterschiedlichen Wasserstände der Donau in einer völlig neuen Art und Weise.The master thesis Auftrieb focuses on the design of a sports accommodation for a rowing centre in Ottensheim, Upper Austria. The rowing centre lies at a backwater of the river Danube with conditions suitable for Olympic Games. In the last couple of years, two floods in this area severely affected people-s lives and the rowing facility. Many inhabitants of the surrounding villages had to experience how the protective function of the built environment disappears when confronted with a natural catastrophe like a flood. First the question is raised how architecture can still function under such conditions and how it can use the energy that is present. On the one hand, it can adopt the capabilities of a boat; on the other hand, it can make use of the new possibilities that are given by a change of the water level. The developed structure follows a concept adopted of the great variety of shapes of the cocoons of the caddisfly larvae. Fixed at a horizontal axis the structure owns the ability to rotate up to 40% if the water level rises 10m above normal levels. This opens up new ways of possibilities and frame conditions to design the interior: The floor represents wall and ceiling. Furniture, lighting, stairways and openings can used in all positions. A user would go to sleep in the evening and realize the change of position of the structure immediately with the change of the interior. This architecture enables to experience all possible water levels in a complete new fashion.10

Affektive Verstärkung beim kontrafaktischen Denken : Laientheorie der Verantwortung vs. Mutabilitätstheorie

eingereicht von Eva Krauk, B. Sc.Literaturverzeichnis: Blatt 27-28Zusammenfassung in Deutsch und EnglischParis-Lodron-Universität Salzburg, Masterarbeit, 2019(VLID)506713

Plasticity of N:P ratios in laboratory and field populations of Trichodesmium spp.

© 2006 Inter-Research.DOI:10.3354/ame042243We followed changes in N:P ratios in batch cultures of the planktonic marine cyanobacterium Trichodesmium (IMS 101) grown in 2 different media and in field populations from 4 different oceanic regions. Cultures grown on low P media showed a rapid rise in N:P ratio upon depletion of phosphate. Ratios exceeding 125 were reached in 1 experiment before attaining stationary phase. A transect across the North Atlantic Ocean along 32°N showed a monotonic decrease in the N:P ratio of field collected colonies, dropping from about 60:1 on the western side of the basin to about 30:1 on the eastern side. A second cruise sampled colonies and surface slicks in waters along the north coast of Australia, where ratios of N:P were generally lower than in the North Atlantic, ranging from 11:1 to 47:1 with an average of 22:1. A comparison of rising and sinking colonies collected at 8 stations in the Gulf of Mexico shows a higher mean N:P ratio among sinking colonies than floating colonies. Overall, the average N:P in the Gulf of Mexico was about 68:1. N:P ratios of Trichodesmium around the Hawaiian Islands were very consistent between 2 consecutive years of sampling, with an average colony N:P for both years of about 38:1. Our research demonstrates high variability in the cellular N:P in Trichodesmium both in the laboratory and in the field. Trichodesmium N:P ratio may provide an index to the relative severity of P limitation in these diazotrophs. Geochemical and ecological modeling efforts which rely on using the N:P ratio of diazotrophs in deriving nitrogen fixation rates should account for the variability of these ratios in situ

Inorganic nitrogen release from sediment slurry of riverine and estuarine ecosystems located at different river regimes

The purpose of the present study was to compare the nature of dissolved inorganic nitrogen (DIN = ammonium (NH4+) and nitrite + nitrate (NO2+3 = (NO2– + NO3–)) release from aerobic sediment slurry at two different hydrologic flow regimes. The watershed of the Guadalupe River–Estuary system receives more freshwater inflow than does the watershed of the Nueces River–Estuary system; thus, the Nueces Estuary is more saline than is the Guadalupe Estuary. Sediment samples were collected using cores, analysed for organic matter and grain size, and used to perform laboratory experiments to measure DIN release. During the experiments, DIN concentrations in overlying water were measured for 48 h in five different salinity treatments. Ammonium concentrations were higher in the Nueces River and Estuary treatments than in similarly treated samples from the Guadalupe River and Estuary. An increase in NO2+3 concentrations along salinity gradients of the Nueces Estuary treatments indicated favourable condition for nitrification. The Guadalupe River sediments that were not exposed to salinity had an increase in NH4+ concentration at 7.5 ppt. The different DIN release among salinity treatments indicated that hydrologic forcing on organic matter deposition and salinity have an important role on the retention and release of inorganic nitrogen at the sediment–water aerobic layers in rivers and estuaries