Variability in inorganic and organic nitrogen uptake associated with riverine nutrient input in the Gulf of Riga, Baltic Sea     

Gry Mine Berg  Patricia M. Glibert  Niels O. G. Jørgensen  Maija Balode  Ingrida Purina 《Estuaries and Coasts》2001,24(2):204-214

Concentrations and rates of uptake of dissolved organic nitrogen (DON, free amino acids, and urea) and inorganic nitrogen (DIN, nitrate, and ammonium) were measured along two transects in the Gulf of Riga, a sub-basin of the Baltic Sea, during May and July 1996. Concentrations of total dissolved nitrogen (TDN) were 23±3 μg-at N 1⁻¹ in the northern region (mouth) and 41±5 μg-at N 1⁻¹ in the southern region (head) of the Gulf. Rates of nitrogen uptake, determined with¹⁵N-labeled substrates, reflected differences in TDN concentration between the regions. In May, uptake of DIN+DON measured 0.17 and 0.43 μg-at N 1⁻¹ h⁻¹ in the northern and southern parts of the Gulf, respectively. In July, DIN+DON uptake measured 0.38 and 0.68 μg-at N 1⁻¹ h⁻¹ in the north and south, respectively. Most of the variability in total nitrogen flux between the northern and southern regions was due to heterogeneity of DON utilization. Uptake of urea and dissolved free amino acid were up to 6 and 3 times greater in the south compared to the north. As evidenced by size-fractionation, plankton size structure appeared to play a role in the uptake of DON. The community in the southern part was largely composed of cells <5 μm, while up to 67% of the community in the northern part was composed of cells >5 μm. Our results indicate that DON was a major source of nitrogen to phytoplankton, particularly in the southern part of the Gulf.  相似文献   

Similarity Scaling Of Surface-Released Smoke Plumes     

Torben Mikkelsen  Hans E. Jørgensen  Morten Nielsen  Søren Ott 《Boundary-Layer Meteorology》2002,105(3):483-505

Concentration fluctuation data from surface-layer released smokeplumes have been investigated with the purpose of finding suitable scaling parametersfor the corresponding two-particle, relative diffusion process.Dispersion properties have been measured at downwind ranges between 0.1 and 1 km from a continuous, neutrally buoyant ground level source. A combinationof SF₆ and chemical smoke (aerosols) was used as tracer. Instantaneous crosswind concentration profiles of high temporal (up to 55 Hz) and spatialresolution (down to 0.375 m) were obtained from aerosol-backscatter Lidar detectionin combination with simultaneous gas chromatograph (SF₆) reference measurements. The database includes detailed crosswind concentration fluctuation measurements. Each experiment, typically of 1/2-hour duration, containsplume mean and variance concentration profiles, intermittency profiles andexceedence and duration statistics. The diffusion experiments were accompanied by detailed in-situ micrometeorological mean and turbulence measurements. In this paper, a new distance-neighbour function for surface-released smoke plumes is proposed, accompanied by experimental evidence in its support. The new distance-neighbour function is found to scale with the surface-layer friction velocity,and not with the inertial subrange dissipation rate, over the range of distance-neighbour separations considered.  相似文献   

Aquifer vulnerability to pesticide migration through till aquitards   总被引：1，自引：0，他引：1  

Jørgensen PR  McKay LD  Kistrup JP 《Ground water》2004,42(6-7):841-855

This study investigates the influence of key factors-mainly recharge rate and degradation half-life--on downward migration of the widely used pesticide mecoprop (MCPP) through a typical clayey till aquitard. The study uses the numerical model FRAC3Dvs, which is a three-dimensional discrete fracture/matrix diffusion (DFMD) numerical transport model. The model was calibrated with laboratory and field data from a site near Havdrup, Denmark, but the overall findings are expected to be relevant to many other sites in similar settings. Fracture flow and MCPP transport parameters for the model were obtained through calibration using well-characterized laboratory experiments with large (0.5 m diameter by 0.5 m high) undisturbed columns of the fractured till and a field experiment. A second level of upscaling and sensitivity analysis was then carried out using data on hydraulic head, fracture spacing, and water budget from the field site. The simulations of downward migration of MCPP show that MCPP concentration and mass flux into the underlying aquifer, and hence the aquifer vulnerability to this pesticide compound, is mainly dependent on the degradation rate of the pesticide, the overall aquitard water budget, and the ground water recharge rate into the aquifer. The influence of flow rate, matrix diffusion, and degradation rate are intertwined. This results in one to four orders of magnitude higher MCPP flux into the aquifer from aquifer recharge rates of 20 and 120 mm/yr, respectively, for no degradation and MCPP half-life of 0.5 yr. From a sensitivity analysis it was found that the range of MCPP flux into the aquifer varied less than one order of magnitude due to (1) changing fracture spacing from 1 to 10 m, or (2) preferential flow along inclined thin sand layers, which represent common conditions for the current and other settings of clayey till in Denmark and other glaciated areas in Europe and North America. The results indicate that for aquifers overlain by fractured clayey tills, the vulnerability to contamination with pesticides (pesticide flux into the aquifer) and other widespread agricultural contaminants is going to vary strongly in the watershed as a function of the distribution of aquitard water budget (flow rate) and aquitard redox environment (controlling contaminant degradation rates), even if the thickness of the till is relatively constant. DFMD modeling of cause-effect relationships within such systems has great potential to support decisions in planning, regulation, and contaminant remediation.  相似文献   

Strontium-Isotope Studies Of Chloride-Contaminated Groundwater,Denmark     

N. O. Jørgensen  P. M. Holm 《Hydrogeology Journal》1995,3(2):52-57

Saline groundwater has three principal origins in Denmark: 1) Seawater infiltration into nearcoastal aquifers, 2) saline formation water in aquifers of marine sedimentary origin, and 3) intrusion of brines from deep saline formation waters and evaporitic deposits in the subsurface. Strontium-isotope studies of chloride-contaminated groundwater from a Quaternary sandy aquifer at Stautrup Waterworks, Denmark, indicate that the groundwater is heavily influenced by saline formation water from underlying Oligocene marine mica clay. Thus, strontium isotopic hydrochemical criteria were successfully used to identify the sources of saline groundwater.

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RESUMEN: La salinidad en las aguas subterráneas de Dinamarca tiene tres orígenes principales: 1) Infiltración de agua marina en acuíferos costeros, 2) agua de formación salina en acuíferos de origen sedimentario marino, y 3) intrusión de salmueras procedentes de aguas salinas de formaciones profundas y de depósitos evaporíticos subterráneos. Estudios isotópicos del estronico en las aguas subterráneas contaminadas or cloruros en un acuífero arenoso Cuaternario en Stautrup Waterworks, Dinamarca, indican que el agua está fuertement influenciada por el agua de formación salina correspondiente a una capa inferior de micas arcillosas oligocénicas. Por tanto, los criterios hidroquímicos isotópicos se pudieron utilizar satisfactoriamente para identificar las fuentes de salinidad de las aguas subterráneas.

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RéSUMé: La salinité des aux souterraines du Danemark possède trois origines principales: 1) l'intrusion d'eau de mer dans les aquifères littoraux, 2) les eaux connées des sédiments marins constituant l'aquifère, 3) la remontée dans les aquifères superficiels de saumures provenant d'eaux connées de sédiments et de formations évaporitiques profonds. L'étude des isotopes du strontium d'eaux souterraines chargées en chlorures d'un aquifère sableux du Quaternaire du champ captant de Stautrup (Danemark) montre que le chimisme des eaux souterraines est fortement marqué par les eaux connées des argiles micacées marines sous-jacentes de l'Oligocène. Des critères hydrochimiques des isotopes du strontium ont par conséquent permis d'identifier les sources de la salinité d'eaux souterraines.

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Formation of ³⁵S-labelled elemental sulfur and pyrite in coastal marine sediments (Limfjorden and Kysing Fjord,Denmark) during short-term ³⁵SO₄²⁻ reduction measurements     

Robert W. Howarth  Bo Barker Jørgensen 《Geochimica et cosmochimica acta》1984,48(9):1807-1818

Analyses of the specific products of ³⁵SO₄^2? reduction measurements were made in marine sediments in Denmark. We injected tracer quantities of ³⁵SO₄^2? into cores, incubated the cores, and assayed for ³⁵S-labelled acid volatile sulfides. Additionally, we assayed for ³⁵S-labelled elemental sulfur by extraction with CS₂, and for ³⁵S-labelled pyrite by reduction with chromium (II). We separately determined that elemental sulfur which formed in situ and that which formed by oxidation during the acid distillation of acid volatile sulfides.In subtidal sediments in Limfjorden, ³⁵S-labelled elemental sulfur and pyrite make up 14–32% of the reduced sulfur formed in short-term (0–48 hours) ³⁵SO₄^2? reduction experiments, at all depths studied (0–15 cm). Labelled elemental sulfur which formed in situ during the incubations at depths below 1 cm made up a fairly constant 5–11% of the total labelled reduced sulfur, from 0–1 cm, it made up 27%. An additional small amount (1–2% from 1–15 cm and 5% from 0–1 cm) of labelled elemental sulfur was formed during the acid-distillation step in our assay for labelled acid-volatile sulndes. Pyrite contained 4–13% of the total labelled reduced sulfur at all depths. Rates of sulfate reduction in Limfjorden were linear over the period 0–48 hours, and ³⁵S-pyrite made up a nearly constant percentage of the ³⁵S-labelled reduced sulfur formed over this time period.Estimates of sulfate reduction rates for Limfjorden which do not include elemental sulfur and pyrite as products are 19% too low. At Kysing Fjord, estimates of sulfate reduction which do not include elemental sulfur and pyrite are 24% to 32% too low. Thus, while previously published data on sulfate reduction in similar environments are probably low, they are not greatly in error.  相似文献   

E and S0 galaxies in the central part of the Coma cluster: ages, metal abundances and dark matter     

Inger Jørgensen † 《Monthly notices of the Royal Astronomical Society》1999,306(3):607-636

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DNAPL Transport Through Macroporous, Clayey Till Columns     

Peter R. Jørgensen  Kim Broholm  Torben O. Sonnenborg  Erik Arvin 《Ground water》1998,36(4):651-660

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The Importance of Microbial Iron Sulfide Oxidation for Nitrate Depletion in Anoxic Danish Sediments     

Sarka Vaclavkova  Christian Juncher Jørgensen  Ole Stig Jacobsen  Jens Aamand  Bo Elberling 《Aquatic Geochemistry》2014,20(4):419-435

Nitrate (NO₃ ^?) reduction processes are important for depleting the NO₃ ^? load from agricultural source areas before the discharge water reaches surface waters or groundwater aquifers. In this study, we experimentally demonstrate the co-occurrence of microbial iron sulfide oxidation by NO₃ ^? (MISON) and other NO₃ ^?-depleting processes in a range of contrasting sediment types: sandy groundwater aquifer, non-managed minerotrophic freshwater peat and two brackish muddy sediments. Approximately 1/3 of the net NO₃ ^? reduction was caused by MISON in three of the four environments despite the presence of organic carbon in the sediment. An apparent salinity limitation to MISON was observed in the most brackish environment. Addition of high surface area synthetically precipitated iron sulfide (FeS _x ) to the aquifer sediment with the lowest natural FeS _x reactivity increased both the relative fraction of NO₃ ^? reduction linked to MISON from approximately 30–100 % and the absolute rates by a factor of 17, showing that the potential for MISON-related NO₃ ^? reduction is environmentally significant and rate limited by the availability of reactive FeS _x .  相似文献   

Fishing‐induced evolution of growth: concepts,mechanisms and the empirical evidence     

Katja Enberg  Christian Jørgensen  Erin S. Dunlop  Øystein Varpe  David S. Boukal  Loïc Baulier  Sigrunn Eliassen  Mikko Heino 《Marine Ecology》2012,33(1):1-25

The interest in fishing‐induced life‐history evolution has been growing in the last decade, in part because of the increasing number of studies suggesting evolutionary changes in life‐history traits, and the potential ecological and economic consequences these changes may have. Among the traits that could evolve in response to fishing, growth has lately received attention. However, critical reading of the literature on growth evolution in fish reveals conceptual confusion about the nature of ‘growth’ itself as an evolving trait, and about the different ways fishing can affect growth and size‐at‐age of fish, both on ecological and on evolutionary time‐scales. It is important to separate the advantages of being big and the costs of growing to a large size, particularly when studying life‐history evolution. In this review, we explore the selection pressures on growth and the resultant evolution of growth from a mechanistic viewpoint. We define important concepts and outline the processes that must be accounted for before observed phenotypic changes can be ascribed to growth evolution. When listing traits that could be traded‐off with growth rate, we group the mechanisms into those affecting resource acquisition and those governing resource allocation. We summarize potential effects of fishing on traits related to growth and discuss methods for detecting evolution of growth. We also challenge the prevailing expectation that fishing‐induced evolution should always lead to slower growth.  相似文献   

Comparing Discrete Fracture and Continuum Models to Predict Contaminant Transport in Fractured Porous Media   总被引：1，自引：0，他引：1  

Peter R. Jørgensen  René Therrien 《Ground water》2014,52(1):84-95

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