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111.
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
112.
Nils Lenhardt Harald Böhnel Klaus Wemmer Ignacio S. Torres-Alvarado Jens Hornung Matthias Hinderer 《Bulletin of Volcanology》2010,72(7):817-832
The volcaniclastic Tepoztlán Formation (TF) represents an important rock record to unravel the early evolution of the Transmexican
Volcanic Belt (TMVB). Here, a depositional model together with a chronostratigraphy of this Formation is presented, based
on detailed field observations together with new geochronological, paleomagnetic, and petrological data. The TF consists predominantly
of deposits from pyroclastic density currents and extensive epiclastic products such as tuffaceous sandstones, conglomerates
and breccias, originating from fluvial and mass flow processes, respectively. Within these sediments fall deposits and lavas
are sparsely intercalated. The clastic material is almost exclusively of volcanic origin, ranging in composition from andesite
to rhyolite. Thick gravity-driven deposits and large-scale alluvial fan environments document the buildup of steep volcanic
edifices. K-Ar and Ar-Ar dates, in addition to eight magnetostratigraphic sections and lithological correlations served to
construct a chronostratigraphy for the entire Tepoztlán Formation. Correlation of the 577 m composite magnetostratigraphic
section with the Cande and Kent (1995) Geomagnetic Polarity Time Scale (GPTS) suggests that this section represents the time
intervall 22.8–18.8 Ma (6Bn.1n-5Er; Aquitanian-Burdigalian, Lower Miocene). This correlation implies a deposition of the TF
predating the extensive effusive activity in the TMVB at 12 Ma and is therefore interpreted to represent its initial phase
with predominantly explosive activity. Additionally, three subdivisions of the TF were established, according to the dominant
mode of deposition: (1) the fluvial dominated Malinalco Member (22.8–22.2 Ma), (2) the volcanic dominated San Andrés Member
(22.2–21.3 Ma) and (3) the mass flow dominated Tepozteco Member (21.3–18.8 Ma). 相似文献
113.
Jens Bange Peter Zittel Thomas Spieß Jörg Uhlenbrock Frank Beyrich 《Boundary-Layer Meteorology》2006,119(3):527-561
The low-level flight method (LLF) has been combined with linear inverse models (IM) resulting in an LLF+IM method for the determination of area-averaged turbulent surface fluxes. With this combination, the vertical divergences of the turbulent latent and sensible heat fluxes were calculated from horizontal flights. The statistical errors of the derived turbulent surface fluxes were significantly reduced. The LLF+IM method was tested both in numerical and field experiments. Large-eddy simulations (LES) were performed to compare ‘true’ flux profiles with ‘measurements’ of simulated flights in an idealised convective boundary layer. Small differences between the ‘true’ and the ‘measured’ fluxes were found, but the vertical flux divergences were correctly calculated by the LLF+IM method. The LLF+IM method was then applied to data collected during two flights with the Helipod, a turbulence probe carried by a helicopter, and with the research aircraft Do 128 in the LITFASS-98 field campaign. The derived surface fluxes were compared with results from eddy-covariance surface stations and with large-aperture scintillometer data. The comparison showed that the LLF+IM method worked well for the sensible heat flux at 77 and 200 m flight levels, and also for the latent heat flux at the lowest level. The model quality control indicated failures for the latent heat flux at the 200 m level (and higher), which were probably due to large moisture fluctuations that could not be modelled using linear assumptions. Finally the LLF+IM method was applied to more than twenty low-level flights from the LITFASS-2003 experiment. Comparison with aggregated surface flux data revealed good agreement for the sensible heat flux but larger discrepancies and a higher statistical uncertainty for the latent heat flux 相似文献
114.
Morten A. D. Larsen Peter Thejll Jens H. Christensen Jens C. Refsgaard Karsten H. Jensen 《Climate Dynamics》2013,40(11-12):2903-2918
We investigate the simulated temperature and precipitation of the HIRHAM regional climate model using systematic variations in domain size, resolution and detailed location in a total of eight simulations. HIRHAM was forced by ERA-Interim boundary data and the simulations focused on higher resolutions in the range of 5.5–12 km. HIRHAM outputs of seasonal precipitation and temperature were assessed by calculating distributed model errors against a higher resolution data set covering Denmark and a 0.25° resolution data set covering Europe. Furthermore the simulations were statistically tested against the Danish data set using bootstrap statistics. The results from the distributed validation of precipitation showed lower errors for the winter (DJF) season compared to the spring (MAM), fall (SON) and, in particular, summer (JJA) seasons for both validation data sets. For temperature, the pattern was in the opposite direction, with the lowest errors occurring for the JJA season. These seasonal patterns between precipitation and temperature are seen in the bootstrap analysis. It also showed that using a 4,000 × 2,800 km simulation with an 11 km resolution produced the highest significance levels. Also, the temperature errors were more highly significant than precipitation. In similarly sized domains, 12 of 16 combinations of variables, observation validation data and seasons showed better results for the highest resolution domain, but generally the most significant improvements were seen when varying the domain size. 相似文献
115.
Antonio Segalini Jens H. M. Fransson P. Henrik Alfredsson 《Boundary-Layer Meteorology》2013,148(2):269-283
An analysis of velocity statistics and spectra measured above a wind-tunnel forest model is reported. Several measurement stations downstream of the forest edge have been investigated and it is observed that, while the mean velocity profile adjusts quickly to the new canopy boundary condition, the turbulence lags behind and shows a continuous penetration towards the free stream along the canopy model. The statistical profiles illustrate this growth and do not collapse when plotted as a function of the vertical coordinate. However, when the statistics are plotted as function of the local mean velocity (normalized with a characteristic velocity scale), they do collapse, independently of the streamwise position and freestream velocity. A new scaling for the spectra of all three velocity components is proposed based on the velocity variance and integral time scale. This normalization improves the collapse of the spectra compared to existing scalings adopted in atmospheric measurements, and allows the determination of a universal function that provides the velocity spectrum. Furthermore, a comparison of the proposed scaling laws for two different canopy densities is shown, demonstrating that the vertical velocity variance is the most sensible statistical quantity to the characteristics of the canopy roughness. 相似文献
116.
The oil content in the sediment and the marine life along the arctic shores of Van Mijenfjord, Spitzbergen, were investigated about two years after a spill from diesel storage tanks. High values of oil were recorded in the sediment along the shore near the tanks. The shore fauna is generally poor in these areas and the only biological effect detected was the disappearance of the amphipod Gammarus setosus from the surface layers. 相似文献
117.
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
118.
Predicting riverine dissolved silica fluxes to coastal zones from a hyperactive region and analysis of their first-order controls 总被引:1,自引:1,他引:1
Jens Hartmann Nils Jansen Hans H. Dürr Akira Harashima Kenji Okubo Stephan Kempe 《International Journal of Earth Sciences》2010,99(1):207-230
Silicate weathering and resulting transport of dissolved matter influence the global carbon cycle in two ways. First by the
uptake of atmospheric/soil CO2 and second by providing the oceanic ecosystems via the fluvial systems with the nutrient dissolved silica (DSi). Previous
work suggests that regions dominated by volcanics are hyperactive or even “hot spots” concerning DSi-mobilization. Here, we
present a new approach for predicting DSi-fluxes to coastal zones, emphasizing “first-order” controlling factors (lithology,
runoff, relief, land cover and temperature). This approach is applied to the Japanese Archipelago, a region characterized
by a high percentage of volcanics (29.1% of surface area). The presented DSi-flux model is based on data of 516 catchments,
covering approximately 56.7% of the area of the Japanese Archipelago. The spatial distribution of lithology—one of the most
important first order controls—is taken from a new high resolution map of Japan. Results show that the Japanese Archipelago
is a hyperactive region with a DSi-yield 6.6 times higher than the world average of 3.3 t SiO2 km−2 a−1, but with large regional variations. Approximately 10% of its area exceeds 10 times the world average DSi-yield. Slope constitutes
another important controlling factor on DSi-fluxes besides lithology and runoff, and can exceed the influence of runoff on
DSi-yields. Even though the monitored area on the Japanese Archipelago stretches from about 31° to 46°N, temperature is not
identified as a significant first-order model variable. This may be due to the fact that slope, runoff and lithology are correlated
with temperature due to regional settings of the Archipelago, and temperature information is substituted to a certain extent
by these factors. Land cover data also do not improve the prediction model. This may partly be attributed to misinterpreted
land cover information from satellite images. Implications of results for Earth System and global carbon cycle modeling are
discussed. 相似文献
119.
Maarten Haest Philippe Muchez Stijn Dewaele Adrian J. Boyce Albrecht von Quadt Jens Schneider 《Mineralium Deposita》2009,44(5):505-522
The Dikulushi Cu–Ag vein-type deposit is located on the Kundelungu Plateau, in the southeastern part of the Democratic Republic
of Congo (D.R.C.). The Kundelungu Plateau is situated to the north of the Lufilian Arc that hosts the world-class stratiform
Cu–Co deposits of the Central African Copperbelt. A combined petrographic, fluid inclusion and stable isotope study revealed
that the mineralisation at Dikulushi developed during two spatially and temporally distinct mineralising episodes. An early
Cu–Pb–Zn–Fe mineralisation took place during the Lufilian Orogeny in a zone of crosscutting EW- and NE-oriented faults and
consists of a sequence of sulphides that precipitated from moderate-temperature, saline H2O–NaCl–CaCl2-rich fluids. These fluids interacted extensively with the country rocks. Sulphur was probably derived from thermochemical
reduction of Neoproterozoic seawater sulphate. Undeformed, post-orogenic Cu–Ag mineralisation remobilised the upper part of
the Cu–Pb–Zn–Fe mineralisation in an oxidising environment along reactivated and newly formed NE-oriented faults in the eastern
part of the deposit. This mineralisation is dominated by massive Ag-rich chalcocite that precipitated from low-temperature
H2O–NaCl–KCl fluids, generated by mixing of moderate- and low-saline fluids. The same evolution in mineralisation assemblages
and types of mineralising fluids is observed in three other Cu deposits on the Kundelungu Plateau. Therefore, the recognition
of two distinct types of (vein-type) mineralisation in the study area has a profound impact on the exploration in the Kundelungu
Plateau region. The identification of a Cu–Ag type mineralisation at the surface could imply the presence of a Cu–Pb–Zn–Fe
mineralisation at depth. 相似文献
120.
Abstract This study quantifies global changes in irrigation requirements for areas presently equipped for irrigation of major crop types, using climate projections from 19 GCMs up to the 2080s. Analysis is based on results from the global eco-hydrological model LPJmL that simulates the complex and dynamic interplay of direct and indirect climate change effects upon irrigation requirements. We find a decrease in global irrigation demand by ~17% in the ensemble median, due to a combination of beneficial CO2 effects on plants, shorter growing periods and regional precipitation increases. In contrast, increases of >20% are projected with a high likelihood (i.e. in more than two thirds of the climate change scenarios) for some regions, including southern Europe, and, with a lower likelihood, for parts of Asia and North America as well. If CO2 effects were not accounted for, however, global irrigation demand would hardly change, and increases would prevail in most regions except for southern Asia (where higher precipitation is projected). We stress that the CO2 effects may not be realized everywhere, that irrigation requirements will probably increase further due to growing global food demand (not considered here), and that a significant amount of water to meet future irrigation requirements will have to be taken from fossil groundwater, environmental flow reserves or diverted rivers. Editor D. Koutsoyiannis; Associate editor A. Montanari Citation Konzmann, M., Gerten, D., and Heinke, J., 2013. Climate impacts on global irrigation requirements under 19 GCMs, simulated with a vegetation and hydrology model. Hydrological Sciences Journal, 58 (1), 1–18. 相似文献