Sustainable land use in Tikopia: Food production and consumption in an isolated agricultural system   总被引：3，自引：3，他引：0  

Ole Mertz  Thilde Bech Bruun  Bjarne Fog  Kjeld Rasmussen  Jytte Agergaard 《Singapore journal of tropical geography》2010,31(1):10-26

The land use system on Tikopia – a Polynesian outlier in Solomon Islands – is analyzed to determine how it has developed since it was first described in the 1930s and again in the 1970s. Fieldwork included a household questionnaire survey, in-depth interviews on farming practices and decision making, and the collection of soil samples from the major soil and garden types. The Tikopian land use system has not undergone significant changes since the 1970s; indeed the focus on self-sufficiency in food crops may have been strengthened over the past 30 years as ship arrivals have become increasingly unreliable. Local agricultural production and exploitation of marine resources are essential to sustain the population, and with few exceptions farming and fishing techniques remain unchanged. Most of the island is still farmed permanently and the intensive agricultural system has not suffered long-term setbacks, not even from extreme events such as Cyclone Zoe in 2002. The high fertility of Tikopian soils reported in the 1960s was found to be unchanged. It is concluded that the land use system is highly resilient to shocks and that there are no indications that Tikopian villagers would not be able to support their subsistence in the future, provided there is no substantial increase in the resident ( de facto ) population.  相似文献   

IAG Newsletter     

Ole Baltazar?AndersenEmail author 《Journal of Geodesy》2003,77(9):554-557

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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   

Statistical lensing by galactic discs     

A. W. Blain  Ole Möller  Ariyeh H. Maller 《Monthly notices of the Royal Astronomical Society》1999,303(2):423-432

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The importance of wind forcing in fjord wave modelling     

Christakos  Konstantinos  Furevik  Birgitte R.  Aarnes  Ole Johan  Breivik  Øyvind  Tuomi  Laura  Byrkjedal  Øyvind 《Ocean Dynamics》2020,70(1):57-75

Ocean Dynamics - Accurate predictions of surface ocean waves in coastal areas are important for a number of marine activities. In complex coastlines with islands and fjords, the quality of wind...  相似文献   

Seismic on floating ice: data acquisition versus flexural wave noise     

Tor Arne Johansen  Bent Ole Ruud  Ronny Tømmerbakke  Kristian Jensen 《Geophysical Prospecting》2019,67(3):532-549

Geophysical surveying of the Arctic will become increasingly important in future prospecting and monitoring of the terrestrial and adjacent areas in this hemisphere. Seismic data acquired on floating ice are hampered with extensive noise due to ice vibrations related to highly dispersive ice flexural waves generated by the seismic source. Several experiments have been conducted on floating ice in van Mijenfjorden in Svalbard in the Norwegian Arctic to specifically analyse the extent of flexural waves recorded with various seismic receivers and sources deployed both on top of ice and in the water below. The data show that flexural waves are severely damped at 5 m or deeper below the ice and hydrophone data suffer less from these vibrations compared with data recorded on the ice. Aliasing of single receiver hydrophone data can to some extent be suppressed using an in-line line source of detonating cord. Experiments on ice on shallow water show prominent guided wave modes often referred to as Scholte waves propagating along the seabed. In this case, both flexural and Scholte waves interfere and make a complicated pattern of coherent noise. On shallow water, the positioning and type of the seismic source must be evaluated with respect to the coherent noise generated by these waves. Geophone strings of 25 m effectively suppress both flexural and Scholte waves due to their relative short wavelengths. An airgun generates relative more low-frequency energy than a surface source of detonating cord. Accordingly, seismic mapping of deep seismic horizons seem to be best achieved using geophone strings of such length and an airgun source. For shallow targets, the use of hydrophones in combination with detonating cord is an appropriate solution. Seismic surveying in the Arctic always have to follow environmental restrictions of not disturbing or harming wildlife and not causing permanent footprints into the vulnerable tundra, which implies that the choice of seismic acquisition strategy might occur as a trade-off between optimum data quality and environmental constraints.  相似文献