Chemical Self-Enrichment of HII Regions by the Wolf-Rayet Phase of an 85 Msun star

It is clear from stellar evolution and from observations of WR stars that massive stars are releasing metal-enriched gas through their stellar winds in the Wolf-Rayet phase. Although HII region spectra serve as diagnostics to determine the present-day chemical composition of the interstellar medium, it is far from being understood to what extent the HII gas is already contaminated by chemically processed stellar wind. Therefore, we analyzed our models of radiative and wind bubbles of an isolated 85 Msun star with solar metallicity (Kr\"oger et al. 2006) with respect to the chemical enrichment of the circumstellar HII region. Plausibly, the hot stellar wind bubble (SWB) is enriched with 14N during the WN phase and even much higher with 12C and 16O during the WC phase of the star. During the short period that the 85 Msun star spends in the WC stage enriched SWB material mixes with warm HII gas of solar abundances and thus enhances the metallicity in the HII region. However, at the end of the stellar lifetime the mass ratios of the traced elements N and O in the warm ionized gas are insignificantly higher than solar, whereas an enrichment of 22 % above solar is found for C. Important issues from the presented study comprise a steeper radial gradient of C than O and a decreasing effect of self-enrichment for metal-poor galaxies.Comment: 5 pages, 3 figures, accepted for publication in A&A Letter

Plant biomass nitrogen and effects on the risk of nitrate leaching of intercrops under organic farming in Eastern Austria

Data on the potential of intercrops to reduce soil nitrate contents, on their N accumulation and biological nitrogen fixation (BNF) are lacking for organic farming in the dry, pannonic region of Eastern Austria. The effect of legumes, non-legumes, and legumes + non-legumes used as intercrops on inorganic soil nitrogen, crop yield and biomass N, and BNF were tested in comparison to bare fallow. Non-legumes and legumes + non-legumes were more efficient than legumes in reducing inorganic soil N contents in autumn and nitrate contents in soil solution from the subsoil in winter. This reduction in inorganic soil N did not last until March of the following year due to an N mineralisation from the mulch. The legume + non-legume mixture contained a larger amount of crop N than both legumes and non-legumes. This was due to the combined effect of soil-N uptake by the non-legumes and BNF by the legumes in the mixture

Konsequenzen einer großflächigen Umstellung auf ökologischen Landbau

Die aktuellen Schwierigkeiten im Agrarsektor haben ein bisher nicht dagewesenes Interesse an einer verstärkten Förderung des ökologischen Landbaus durch gezielte agrarpolitische Maßnahmen geweckt. Es werden Zielvorstellungen von bis zu 20% biologisch wirtschaftender Betriebe geäußert. Eine deutliche Zunahme dieser Betriebe ist aufgrund der weitgehend anerkannten und vielfach nachgewiesenen ökologischen Vorzüglichkeit der biologischen Landwirtschaft wünschenswert. Gleichzeitig stellt sich aber auch die Frage nach den ökonomischen und sozialen Konsequenzen einer weitgehenden Umstellung auf ökologischen Landbau. In einer Reihe von Studien wurde versucht, die Wirkungen einer flächendeckenden Umstellung ganzer Länder (Olson et al., 19821), Langley et al., 1983, für die USA; Bechmann et al., 1992, Zerger & Bossel, 1994, Seemüller, 2000, für Deutschland; Lampkin, 1994, für Großbritannien; Alroe & Kristensen, 2001, für Dänemark) oder Regionen (Rist et al., 1989, für den Kanton Zug; Braun, 1995, für Baden-Württemberg; Pommer & Rintelen, 1997, für Bayern) bzw. einer teilweisen Umstellung (Lampkin, 1994: 10 % ökologischer Landbau in Großbritannien; Wynen, 1998: 10 bis 80 %in Dänemark; Zander et al., 1999: in Brandenburg) abzuschätzen. Die Ergebnisse der zitierten Untersuchungen sollen hier vergleichend dargestellt und daraus Handlungsbedarf hinsichtlich einer großflächigen Umstellung abgeleitet werden

Mediating Incentive Use: A Time-Series Assessment of Economic Development Deals in North Carolina

State incentive granting for the purpose of firm retention or recruitment remains highly controversial and is often portrayed as antithetical to long-range economic development planning. This paper uses quasi-experimental methods to measure the impact of state-level economic development incentives on employment growth at the establishment level in North Carolina. Using North Carolina’s rich history of strategic planning and sector-based economic development as a backdrop, we develop a theory of sectoral “mediation.” This enables us to compare the effectiveness of incentives offered in mediated and nonmediated industries and show that when incentives are coupled with sectoral economic development efforts they generate substantially stronger employment effects than at establishments with limited sector-based institutional support

Versuch der monetären Bewertung ökologischer Leistungen des Biologischen Landbaus im Bereich Grund- und Trinkwasser am Beispiel des Einzugsgebietes der Fernwasserversorgung Mühlviertel/OÖ

Die tatsächlichen oder potentiellen volkswirtschaftlichen (externen) Kosten durch Umweltbelastung der intensiven Landbewirtschaftung werden der Allgemeinheit aufgebürdet, anstatt als Preis- bzw. Kostenfaktor in das betriebliche Rechnungswesen einzugehen. U.a. in Hinblick auf eine Verringerung externer Kosten der Landwirtschaft infolge Grund- und Trinkwasserbelastung wird der Ökologische Landbau als wirksame Alternative diskutiert. Eine Vielzahl wissenschaftlicher Untersuchungen belegt denn auch das hohe Maß an Grundwasserverträglichkeit des Biologischen Landbaus: So wiesen u. a. VEREIJKEN und WIJNANDS (1990),BRANDHUBER und HEGE (1992), MATTHEY (1992), SCHULTE (1996), BERG et al. (1997) sowie SCHLÜTER et al. (1997) deutlich niedrigere Nitratgehalte des Sickerwassers unter biologisch bewirtschafteten Flächen als unter konventionell oder integriert bewirtschafteten Vergleichsflächen nach. Aufgrund der Verringerung der Nitrat- und Vermeidung der Pestizidbelastung von Grund- und Trinkwasser durch Biologischen Landbau ist daher zu prüfen, in welchem Ausmaß durch diese Bewirtschaftungsform externe Kosten eingespart werden können

Breeding Lesser Black-backed Gulls Larus graellsii and Herring Gulls Larus argentatus: coexistence or competition?

While Lesser Black-backed Gull Larus graellsii numbers increase substantially at the German North Sea coast since the late 1980s, Herring Gull Larus argentatus numbers have been roughly stable since the mid-1980s. In order to investigate whether a different ecology might explain the current trends, we studied diet, colony attendance, reproductive output and aggressive behaviour in a mixed-colony on Amrum, southeastern North Sea, in 1994 and 1995. During incubation Lesser Black-backed Gulls fed mainly upon crustaceans and molluscs which were taken from the intertidal zone. During chick-rearing, they took mainly crustaceans and fish which were gathered mostly as trawler discards. The main food of Herring Gulls throughout the reproductive season were molluscs and crustaceans which were obtained from the intertidal zone. Numbers of Lesser Black-backed Gulls in the colony mainly varied with season and time of day, those of Herring Gulls with tide and season. Numbers of Herring Gulls commuting to the open sea roughly equalled those commuting to the Wadden Sea. Lesser Black-backed Gulls generally flew to the open sea but hardly towards the Wadden Sea. Nest attendance was significantly higher in Lesser Black-backed Gulls than in Herring Gulls during the chick-rearing period. Hatching success and fledging success tended to be higher in Lesser Black-backed Gulls. Lesser Black-backed Gulls won interspecific aggressive interactions significantly more often than Herring Gulls in the chick-rearing period. Our study indicates that Lesser Black-backed Gulls currently enjoy a few ecological advantages compared with Herring Gulls, particularly because they feed on food of apparently higher quality. We conclude that Lesser Black-backed Gulls have filled an empty niche rather than have out-competed Herring Gulls during the past decade

Effizienz verschiedener Zwischenfruchtvarianten unterschiedlich hohen Leguminosenanteils in der Reduktion der Mineralstickstoffgehalte im Boden unter pannonischen Standortbedingungen

Der Zwischenfruchtanbau ist einerseits wichtig für die Speicherung von Stickstoff, der Vermeidung von Bodenerosion, der Bodenbelebung u.a.m. Andererseits muss gerade im pannonischen Klimagebiet mit einem Wasserverbrauch gerechnet werden, der zu Ertragseinbussen in den Folgekulturen führen kann. Ziel ist daher die Prüfung der Auswirkungen unterschiedlicher Zwischenfrüchte auf den Wasserhaushalt, den Stickstoffhaushalt und den Ertrag der Folgekulturen. Der Versuch wird in einer fünffeldrigen Fruchtfolge mit den ökonomisch wichtigsten Kulturarten des biologischen Landbaus (ausgenommen Feldgemüseanbau) unter Berücksichtigung von Fruchtfolgepaaren mit unterschiedlichen Zeitspannen für den Zwischenfruchtanbau angeleg

Stickstoffaufnahme und Biomasseertrag von Zwischenfrüchten und deren Auswirkungen auf Bodennitratgehalte und die Folgekultur unter den Bedingungen des Ökologischen Landbaus im pannonischen Klimagebiet

Data on the potential of catch crops to reduce soil nitrate contents, on their N accumulation and biological nitrogen fixation (BNF) are lacking for organic farming in the dry, pannonic region of Eastern Austria. The effect of legume, non-legume, and legume + non-legume crops used as catch crops on inorganic soil nitrogen, crop biomass and crop N, and BNF were tested in comparison to bare fallow. Non-legumes and legumes + non-legumes were more efficient than legumes in reducing inorganic soil N contents in autumn and nitrate contents in soil solution from the subsoil in winter. This reduction in inorganic soil N did not last until March of the following year due to N mineralisation from the mulch. The legume + non-legume mixture contained a larger amount of crop N than both legumes and non-legumes. This was due to the combined effect of soil-N uptake by the non-legumes and BNF by the legumes in the mixture

An HST Search for Lyman Continuum Emission From Galaxies at z=1.1--1.4

If enough of their Lyman limit continuum escapes, star-forming galaxies could be significant contributors to the cosmic background of ionizing photons. To investigate this possibility, we obtained the first deep imaging in the far ultraviolet of eleven bright blue galaxies at intermediate redshift (z=1.1--1.4). NO Lyman continuum emission was detected. Sensitive, model-independent, upper limits of typically 2 x 10**-19 erg/sec/cm2/Ang were obtained for the ionizing flux escaping from these normal galaxies. This corresponds to lower limits on the observed ratio of 1500 to 700Ang flux of 150 up to 1000. Based on a wide range of stellar synthesis models, this suggests that less than 6%, down to less than 1%, of the available ionizing flux emitted by hot stars is escaping these galaxies. The magnitude of this spectral break at the Lyman l imit confirms that the basic premise of `Lyman break' searches for galaxies at high redshift can also be applied at intermediate redshifts. This implies that the integrated contribution of galaxies to the UV cosmic background at z around 1.2 is less than 15%, and may be less than 2%.Comment: 20 manuscript pages, which includes two tables and two figures. To be published in 1 December 2003 issue of The Astrophysical Journa