Depth colonization of eelgrass (<Emphasis Type="Italic">Zostera marina</Emphasis>) and macroalgae as determined by water transparency in Danish coastal waters     

S?ren?Laurentius?NielsenEmail author  Kaj?Sand-Jensen  Jens?Borum  Ole?Geertz-Hansen 《Estuaries and Coasts》2002,25(5):1025-1032

We present a comparative analysis of lower depth limits for growth of eelgrass, large brown algae and other macroalgae measured by SCUBA-diving along 162 transects in 27 Danish fjords and coastal waters, coupled to 1,400 data series of water chemistry (especially nitrogen) and Secchi depth transparency collected between March and October. Danish coastal waters are heavily eutrophied and characterized by high particle concentrations, turbid water and lack of macrophyte growth in deep water. Median values are 3.6 m for Secchi depth and median lower-depth limits are 4.0 m for eelgrass, 5.3 m for brown algae and 5.0 m for other macroalgae. Depth limits for growth of eelgrass and macroalgae increase linearly with transparency in the coastal waters. The relationships are highly significant (p<10⁻⁶) and transparency accounts for about 60% of the variability of depth limits. Eelgrass extends approximately to half the maximum depth of macroalgae, presumably because of greater respiratory costs to maintain the below-ground rhizomes and roots of eelgrass, which often constitutes half the plant weight. As a reflection of the importance of total nitrogen (TN) in controlling phytoplankton biomass and thus Secchi depth in coastal marine waters, we found that TN could explain 48–73% of the variation in depth limits of eelgrass and macroalgae, according to a multiplicative model (Y=aX^b). As with Secchi depth, the relationship to eelgrass showed a lower slope, reflecting the higher respiratory costs of eelgrass. The models show great sensitivity and a profound quantitative response with proportional effects on Secchi depth and depth limits when total-N concentrations are reduced.  相似文献   

The dogma of matters neutrino-transparency     

Nils Aall Barricelli  Ole Martin Løvvik 《Astrophysics and Space Science》1991,180(2):321-323

In this paper the observed underrepresentation of solar neutrinos in the various detector experiments performed is tentatively interpreted as a result of a substantial and often variable obsorption of neutrinos by various layers of the Sun, contrary to the dogma of neutrino-transparency by matter.  相似文献   

The reactivity of iron oxides towards reductive dissolution with ascorbic acid in a shallow sandy aquifer (Rømø, Denmark)     

Ole Larsen  Dieke Postma  Rasmus Jakobsen 《Geochimica et cosmochimica acta》2006,70(19):4827-4835

The pool of iron oxides, available in sediments for reductive dissolution, is usually estimated by wet chemical extraction methods. Such methods are basically empirically defined and calibrated against various synthetic iron oxides. However, in natural sediments, iron oxides are present as part of a complex mixture of iron oxides with variable crystallinity, clays and organics etc. Such a mixture is more accurately described by a reactive continuum covering a range from highly reactive iron oxides to non-reactive iron oxide. The reactivity of the pool of iron oxides in sediment can be determined by reductive dissolution in 10 mM ascorbic acid at pH 3. Parallel dissolution experiments in HCl at pH 3 reveal the release of Fe(II) by proton assisted dissolution. The difference in Fe(II)-release between the two experiments is attributed to reductive dissolution of iron oxides and can be quantified using the rate equation J/m₀ = k′(m/m₀)^γ, where J is the overall rate of dissolution (mol s⁻¹), m₀ the initial amount of iron oxide, k′ a rate constant (s⁻¹), m/m₀ the proportion of undissolved mineral and γ a parameter describing the change in reaction rate over time. In the Rømø aquifer, Denmark, the reduction of iron oxides is an important electron accepting process for organic matter degradation and is reflected by the steep increase in aqueous Fe²⁺ over depth. Sediment from the Rømø aquifer was used for reductive dissolution experiments with ascorbic acid. The rate parameters describing the reactivity of iron oxides in the sediment are in the range k′ = 7·10⁻⁶ to 1·10⁻³ s⁻¹ and γ = 1 to 2.4. These values are intermediate between a synthetic 2-line ferrihydrite and a goethite. The rate constant increases by two orders of magnitude over depth suggesting an increase in iron oxide reactivity with depth. This increase was not captured by traditional oxalate and dithionite extractions.  相似文献   

Surface Elevation Change and High Resolution Surface Velocities for Advancing Outlets of Jostedalsbreen   总被引：1，自引：0，他引：1  

Bjørn Wangensteen  Ole Magnus Tønsberg  reas Kääb  Trond Eiken  Jon Ove Hagen 《Geografiska Annaler: Series A, Physical Geography》2006,88(1):55-74

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A summary of the PRUDENCE model projections of changes in European climate by the end of this century   总被引：3，自引：0，他引：3  

Jens Hesselbjerg Christensen  Ole Bøssing Christensen 《Climatic change》2007,81(1):7-30

An overview of the PRUDENCE fine resolution climate model experiments for Europe is presented in terms of their climate change signals, in particular 2-meter temperature and precipitation. A comparison is made with regard to the seasonal variation in climate change response of the different models participating in the project. In particular, it will be possible to check how representative a particular PRUDENCE regional experiment is of the overall set in terms of seasonal values of temperature and precipitation. This is of relevance for such further studies and impact models that for practical reasons cannot use all the PRUDENCE regional experiments. This paper also provides some guidelines for how to select subsets of the PRUDENCE regional experiments according to such main sources of uncertainty in regional climate simulations as the choice of the emission scenario and of the driving global climate model.  相似文献   

Development of python-FALL3D: a modified procedure for modelling volcanic ash dispersal in the Asia-Pacific region     

A. N. Bear-Crozier  Nugraha Kartadinata  Anjar Heriwaseso  Ole Nielsen 《Natural Hazards》2012,64(1):821-838

Volcanic ash is the most widespread of all volcanic hazards and has the potential to affect hundreds of thousands, or even millions, of people in the densely populated islands of Indonesia. There is limited information available for this region on the hazard posed by volcanic ash, particularly from volcanoes that have not erupted in recent times. There is a need for computational models capable of accurately predicting volcanic ash dispersal at ground level when coupled with field observations of historical or ongoing eruptive activity. To maximise the effectiveness of such models, they should be readily accessible, easy to use and well tested. Geoscience Australia in collaboration with the Australia-Indonesia Facility for Disaster Reduction and the Indonesian Centre for Volcanology and Geohazard Mitigation has collaboratively adapted an existing open-source volcanic ash dispersion model for use in Indonesia. The core model is the widely used, open-source volcanic ash dispersion model FALL3D. A Python wrapper (name here python-FALL3D) has been developed, which modifies the modelling procedure of FALL3D in order to simplify its use for those with little or no background in computational modelling. The modified procedure does not alter the core functionality of FALL3D, but simplifies the modelling procedure by streamlining the installation process, automating both the pre-processing of input meteorological datasets and configuring and executing each utility program in a single-step process. An application example was presented using python-FALL3D for an active volcano in West Java, Indonesia. The example showed that communities located on the western side of Gunung Gede are always susceptible to volcanic ash ground loading regardless of the seasonal variations in wind conditions, whereas communities on the eastern side of Gunung Gede have a marked increase in susceptibility to ground loading during rainy season conditions when prevailing winds include a strong easterly component.  相似文献   

Deglaciation chronology,sea-level changes and environmental changes from Holocene lake sediments of Germania Havn Sø, Sabine Ø, northeast Greenland     

Ole Bennike  Bernd Wagner 《Quaternary Research》2012,78(1):103-109

Germania Havn Sø is located at the outermost coast of northeastern Greenland. According to radiocarbon dating, the lake basin was deglaciated in the early Holocene, around 11,000 cal yr BP. At that time the lake was a marine bay, but the lake was isolated soon after deglaciation at ~ 10,600 cal yr BP. The marine fauna was species-poor, indicating harsh conditions with a high sedimentation rate and lowered salinity due to glacial meltwater supply. The pioneer vegetation around the lake was dominated by mosses and herbs. Deposition of relatively coarse sediments during the early Holocene indicates erosion of the newly deglaciated terrain. Remains of the first woody plant (Salix herbacea) appear at 7600 cal yr BP and remains of other woody plants (Salix arctica, Dryas octopetala, Cassiope tetragona and Empetrum nigrum) appear around one millennium later. Declining concentrations of D. octopetala and the caddis fly Apatania zonella in the late Holocene probably imply falling summer temperatures. Only moderate changes in the granulometric and geochemical record during the Holocene indicate relatively stable environmental settings in the lake, which can probably be explained by its location at the outer coast and the buffering effect of the neighboring ocean.  相似文献