Life history, habitat utilisation, and biomass of introduced Mysis relicta     

T.F. Nsje  R. Saksga rd  A.J. Jensen  O.T. Sandlund 《Limnologica》2003,33(4):244-257

Life history, habitat utilisation, and biomass of benthic and pelagic opossum shrimp (Mysis relicta) were studied in the oligotrophic Lake Jonsvatn, central Norway. Sampling in the pelagic zone was done by means of a closing zooplankton net; in the benthic zone by means of a benthic beam trawl.

M. relicta had a mixed one or two year life cycle. In the autumn, the proportion of mature females and males were larger in the pelagic than in the benthic habitat. Copulation took place in late autumn, and the first females with eggs occurred in November. In February, the first juvenile M. relicta were released in the benthic habitat. In May and July, however, juveniles were found in large numbers in all parts of the lake. The length distribution of M. relicta indicates that juveniles partly segregate between benthic and pelagic habitats.

Both juvenile and adult M. relicta performed vertical diel migrations in the pelagic habitat. In the benthic habitat, diel vertical migrations along the bottom were not as pronounced as vertical migrations in the pelagic habitat. In the benthic habitat, major migrations were performed only by adults in the autumn. Our results indicate that the light intensity in the green part of the spectrum gives the proximate cue for regulation of vertical distribution of M. relicta.

The mean total biomass varied between 288 and 1576 kg dry weight, corresponding to 23.2–127.1 mg dry weight m⁻² surface area. M. relicta had smallest biomass during late spring/early summer and largest biomass during autumn and early winter. Estimated pelagic biomasses were largest in February, August, October and November, while benthic biomasses were largest in May and July. Estimated biomass of pelagic M. relicta during autumn was approximately 1/10 of the estimated biomass of zooplankton in this lake.  相似文献   

Holocene sedimentary and environmental development of Aarhus Bay,Denmark – a multi-proxy study     

Peter Rasmussen  George Pantopoulos  Jørn B. Jensen  Jesper Olsen  Hans Røy  Ole Bennike 《Boreas: An International Journal of Quaternary Research》2020,49(1):108-128

Holocene sedimentation patterns and environmental development in Aarhus Bay, Denmark, were reconstructed based on proxy analyses of two sediment cores (M1 and M5). Together, the two cores offer an opportunity to examine the history of the area during the past c. 10 000 years. The investigation consisted of acoustic mapping and multi-proxy analyses of the sediment cores including macrofossils, sediment physical properties, sediment accumulation rates, grain size, and X-ray fluorescence elemental counts. Radiocarbon dating of the two sediment successions revealed that they cover the periods c. 10 000–3700 cal. a BP (M1) and c. 4400 cal. a BP to the present (M5). The data from the M1 site indicate the presence of a near-shore lake environment between c. 10 000 and 9000 cal. a BP. The first intrusion of marine water into the area is dated to c. 9000 cal. a BP. In the following c. 1300 years, brackish-water conditions prevailed in the area characterized by a mixture of taxa from marine, limnic and terrestrial habitats, reflecting a shallow estuarine environment. Around 7700 cal. a BP full marine conditions were established, accompanied by a marked increase in sedimentation rates. The changes to full marine conditions and higher sedimentation rates are probably due to a significant sea-level rise leading to flooding of former land areas and intensified erosion. A subsequent distinct decrease in sedimentation rates around 6350 cal. a BP is presumably linked to a previously documented sea-level drop about this time. Continuous sedimentation ceased around 3700 cal. a BP in the central part of the bay, most probably due to a major sea-level lowering involving widespread erosion. In the eastern and deeper part of the bay, sedimentation continued until today. Fully marine conditions prevailed there for at least the last 4400 years.  相似文献   

Spatially resolved fish population analysis for designing MPAs: influence on inside and neighbouring habitats     

Christensen  Asbjorn; Mosegaard  Henrik; Jensen  Henrik 《ICES Journal of Marine Science》2009,66(1):56-63

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Natural background and anthropogenic inputs of polycyclic aromatic hydrocarbons (PAH) in sediments of South-Western Barents Sea     

Stepan Boitsov  H.K.B. Jensen  Jarle Klungsyr 《Marine environmental research》2009,68(5):236-245

Polycyclic aromatic hydrocarbons (PAH) were measured in sediment cores from 13 locations in South-Western Barents Sea as part of a detailed study of the Norwegian seabed under the MAREANO program. The generally low PAH levels found, an average around 200 ng g⁻¹ dry weight for sum PAH, indicate low inputs of petroleum hydrocarbons to the marine environment in the area. Differences in PAH composition and various PAH ratios indicate a natural, mostly petrogenic origin of PAH in sediments from the open sea locations, while the fjord locations show higher pyrogenic PAH contents with an increase towards upper sediment layers, indicating low inputs from human activities. Petrogenic PAH levels increase in deeper sediments at open sea locations, also when normalised to total organic carbon (TOC) contents, suggesting natural leakages of oil-related hydrocarbons in the area.  相似文献   

Multisite campaign on the open cluster M67 – III. δ Scuti pulsations in the blue stragglers     

H. Bruntt  D. Stello  J. C. Suárez  T. Arentoft  T. R. Bedding  M. Y. Bouzid  Z. Csubry  T. H. Dall  Z. E. Dind  S. Frandsen  R. L. Gilliland  A. P. Jacob  H. R. Jensen  Y. B. Kang  S.-L. Kim  L. L. Kiss  H. Kjeldsen  J.-R. Koo  J.-A. Lee  C.-U. Lee  J. Nuspl  C. Sterken  R. Szabó 《Monthly notices of the Royal Astronomical Society》2007,378(4):1371-1384

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Distinguishing Carbonate Reservoir Pore Facies with Nuclear Magnetic Resonance Measurements   总被引：1，自引：0，他引：1  

Coralie Genty  Jerry L. Jensen  Wayne M. Ahr 《Natural Resources Research》2007,16(1):45-54

  Characterization of carbonate rocks may involve identifying the important pore types which are present. In the past, this task has required detailed petrographic analysis of many core samples. Here, we describe a method which uses nuclear magnetic resonance (NMR) measurements to reduce the amount of petrographic analysis needed for porosity typing of carbonate reservoir rocks. For a rock sample which has been measured with NMR, our method decomposes the log(T₂) spectrum into at most three Gaussian-shaped components and gives a set of nine parameters. Two characteristic quantities having geological significance are extracted from the nine parameters. Values of the two quantities are compared with a reference set, established from samples having both NMR and petrographic evaluations of porosity types. We use a Bayesian approach to the classification of the dominant porosity type. Tests of our method on 103 samples show a correct prediction in 60 to 90 percent of the samples. The lower success rate was obtained for samples with five porosity types from three fields; the higher success rate obtained with samples with three porosity types from one well. The use of geologically significant quantities extracted from the decomposition gives comparable success rate to those obtained using a standard, non-geological approach such as canonical variates.  相似文献   

Perspectives in using a remotely sensed dryness index in distributed hydrological models at the river‐basin scale     

J. Andersen  I. Sandholt  K. H. Jensen  J. C. Refsgaard  H. Gupta 《水文研究》2002,16(15):2973-2987

In a previous study a spatially distributed hydrological model, based on the MIKE SHE code, was constructed and validated for the 375 000 km² Senegal River basin in West Africa. The model was constructed using spatial data on topography, soil types and vegetation characteristics together with time‐series of precipitation from 112 stations in the basin. The model was calibrated and validated based on river discharge data from nine stations in the basin for 11 years. Calibration and validation results suggested that the spatial resolution of the input data in parts of the area was not sufficient for a satisfactory evaluation of the modelling performance. The study further examined the spatial patterns in the model input and output, and it was found that particularly the spatial resolution of the precipitation input had a major impact on the model response. In an attempt to improve the model performance, this study examines a remotely sensed dryness index for its relationship to simulated soil moisture and evaporation for six days in the wet season 1990. The index is derived from observations of surface temperature and vegetation index as measured by the NOAA Advanced Very High Resolution Radiometer (AVHRR) sensor. The correlation results between the index and the simulation results are of mixed quality. A sensitivity analysis, conducted on both estimates, reveals significant uncertainties in both. The study suggests that the remotely sensed dryness index with its current use of NOAA AVHRR data does not offer information that leads to a better calibration or validation of the simulation model in a spatial sense. The method potentially may become more suitable with the use of the upcoming high‐resolution temporal Meteosat Second Generation data. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

Effects of suspended sediment on development and hatching of herring (Clupea harengus) eggs     

Thomas Kiørboe  Erik Frantsen  Carsten Jensen  Gorm Sørensen 《Estuarine, Coastal and Shelf Science》1981,13(1):107-111

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Oslo Solar Observatory     

Eberhart Jensen 《Solar physics》1968,4(1):114-117

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Is trophic state or regional location the strongest determinant for Chl-a/TP relationships in lakes?     

Knut L. Seip  Erik Jeppesen  Jens Petter Jensen  Bj?rn Faafeng 《Aquatic Sciences - Research Across Boundaries》2000,62(3):195-204

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