Kooperativer Bibliotheksverbund

Berlin Brandenburg

and
and

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
Filter
  • Elsevier (CrossRef)  (36)
Type of Medium
Language
Year
  • 1
    Language: English
    In: Journal of Hydrology, 2005, Vol.310(1), pp.294-315
    Description: Simulating infiltration in soils containing macropores still provides unsatisfactory results, as existing models seem not to capture all relevant processes. Recent studies of macropore flow initiation in natural soils containing earthworm channels revealed a distinct flow rate variability in the macropores depending on the initiation process. When macropore flow was initiated at the soil surface, most of the macropores received very little water while a few macropores received a large proportion of the total inflow. In contrast, when macropore flow was initiated from a saturated or nearly saturated soil layer, macropore flow rate variation was much lower. The objective of this study was to develop, evaluate, and test a model, which combines macropore flow variability with several established approaches to model dual permeability soils. We then evaluate the INfiltration–INitiation–INteraction Model (IN M) to explore the influence of macropore flow variability on infiltration behavior by performing a sensitivity analysis and applying IN M to sprinkling and dye tracer experiments at three field sites with different macropore and soil matrix properties. The sensitivity analysis showed that the flow variability in macropores reduces interaction between the macropores and the surrounding soil matrix and thus increases bypass flow, especially for surface initiation of macropore flow and at higher rainfall intensities. The model application shows reasonable agreement between IN M simulations and field data in terms of water balance, water content change, and dye patterns. The influence of macropore flow variability on the hydrological response of the soil was considerable and especially pronounced for soils where initiation occurs at the soil surface. In future, the model could be applied to explore other types of preferential flow and hence to get a generally better understanding of macropore flow.
    Keywords: Macropore Flow ; Infiltration ; Soil Moisture ; Unsaturated Zone ; Dual-Permeability Model ; Earthworm Burrow ; Geography
    ISSN: 0022-1694
    E-ISSN: 1879-2707
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 2
    Language: English
    In: Journal of Hydrology, 2011, Vol.396(3), pp.277-291
    Description: ► Specification of spatially distributed lateral fluxes affects solute transport parameter estimates. ► Information contained on the breakthrough curve alone is insufficient to select the appropriate model structure. ► Implementation of , the lateral ouflow, in OTIS leads to solute mass to groundwater. ► The absence of implementation of in OTIS promotes the storage of solute mass in the transient storage zone. Interactions between mobile stream water and transient storage zones have been the subject of careful attention for decades. However, few studies have considered explicitly the influence of water exchange between the channel and neighbouring hydrological units when modelling transient storage processes, especially the lateral inflow coming from hillslope contributions and outflow to a deep aquifer or to hyporheic flow paths extending beyond the study reach. The objective of this study was to explore the influence of different conceptualizations of these hydrologic exchanges on the estimation of transient storage parameters. Slug injections of sodium chloride (NaCl) were carried out in eight contiguous reaches in the Cotton Creek Experimental Watershed (CCEW), located in south-east British Columbia. Resulting breakthrough curves were subsequently analysed using a Transient Storage Model (TSM) in an inverse modelling framework. We estimated solute transport parameters using three distinct, hypothetical spatial patterns of lateral inflow and outflow, all based on variations of the same five-parameter model structure. We compared optimized parameter values to those resulting from a distinct four-parameter model structure meant to represent the standard application of the TSM, in which only lateral inflow was implemented for net gaining reaches or only lateral outflow for net losing reaches. In the five-parameter model, solute mass was stored predominantly in the transient storage zone and slowly released back to the stream. Conversely, solute mass was predominantly removed from the stream via flow losses in the four-parameter model structure. This led to contrasting estimates of solute transport parameters and subsequent interpretation of solute transport dynamics. Differences in parameter estimates across variations of the five-parameter model structure were small yet statistically significant, except for the transient storage exchange rate coefficient , for which unique determination was problematic. We also based our analysis on , the fraction of median transport time due to transient storage. Differences across configurations in estimates were consistent but small when compared to the variability of among reaches. Optimized parameter values were influenced dominantly by the model structure (four versus five parameters) and then by the conceptualization of spatial arrangement of lateral fluxes along the reach for a set model structure. When boundary conditions are poorly defined, the information contained in the stream tracer breakthrough curve is insufficient to identify a single, unambiguous model structure representing solute transport simulations. Investigating lateral fluxes prior to conducting a study on transient storage processes is necessary, as assuming a certain spatial organization of these fluxes might set ill-defined bases for inter-reach comparisons. Given the difficulty in quantifying the spatial patterns and magnitudes of lateral inputs and outputs, we recommend small-scale laboratory tracer experiments with well-defined and variable boundary conditions as a complement to field studies to provide new insights into stream solute dynamics.
    Keywords: Transient Storage ; Flow Loss ; Flow Gain ; Otis ; Uncertainty ; Model Structure ; Geography
    ISSN: 0022-1694
    E-ISSN: 1879-2707
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 3
    Language: English
    In: Journal of Hydrology, 2006, Vol.319(1), pp.339-356
    Description: The delivery mechanisms of labile nutrients (e.g. NO , DON and DOC) to streams are poorly understood. Recent work has quantified the relationship between storm DOC dynamics and the connectedness of catchment units and between pre-storm wetness and transient groundwater NO flushing potential. While several studies have shown N and C flushing during storm events as the important mechanism in the export of DOC and DON in small catchments, the actual mechanisms at the hillslope scale have remained equivocal. The difficulty in isolating cause and effect in field studies is made difficult due to the spatial variability of soil properties, the limited ability to detect flow pathways within the soil, and other unknowns. Some hillslopes show preferential flow behavior that may allow transmission of hillslope runoff and labile nutrients with little matrix interaction; others do not. Thus, field studies are only partially useful in equating C and N sources with water flow and transport. This paper presents a new approach to the study of hydrological controls on labile nutrient flushing at the hillslope scale. We present virtual experiments that focus on quantifying the first-order controls on flow pathways and nutrient transport in hillslopes. We define virtual experiments as numerical experiments with a model driven by collective field intelligence. We present a new distributed model that describes the lateral saturated and vertical unsaturated water flow from hypothetical finite nutrient sources in the upper soil horizons. We describe how depth distributions of transmissivity and drainable porosity, soil depth variability, as well as mass exchange between the saturated and unsaturated zone influence the mobilization, flushing and release of labile nutrients at the hillslope scale. We argue that this virtual experiment approach may provide a well-founded basis for defining the first-order controls and linkages between hydrology and biogeochemistry at the hillslope scale and perhaps form a basis for predicting flushing and transport of labile nutrients from upland to riparian zones.
    Keywords: Virtual Experiments ; Hillslope Hydrology ; Nutrients ; Mobilization ; Flushing ; Runoff Generation ; Geography
    ISSN: 0022-1694
    E-ISSN: 1879-2707
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 4
    Language: English
    In: Agriculture, Ecosystems and Environment, 15 April 2016, Vol.222, pp.185-192
    Description: The European Water Framework Directive (EWFD) aims to achieve a good chemical status for the groundwater bodies in Europe by the year 2015. Despite the effort to reduce the nitrate pollution from agriculture within the last two decades, there are still many groundwater aquifers that exceed nitrate concentrations above the EWFD threshold of 50 mg L . Viticulture is seen as a major contributor of nitrate leaching and sowing of a green cover was shown to have a positive effect on lowering the nitrate loads in the upper 90 cm of the soil. However, the consequences for nitrate leaching into the subsoil were not yet tested. We analyzed the nitrate concentrations and pore water stable isotope composition ( H) to a depth of 380 cm in soil profiles under an old vineyard and a young vineyard with either soil tillage or permanent green cover in between the grapevines. The pore water H data was used to calibrate a soil physical model, which was then used to infer the age of the soil water at different depths. This way, we could relate elevated nitrate concentrations below an old vineyard to tillage processes that took place during the winter two years before the sampling. We further showed that the elevated nitrate concentration in the subsoil of a young vineyard can be related to the soil tillage prior to the planting of the new vineyard. If the soil was kept bare due to tillage, a nitrate concentration of 200 kg NO -N ha was found in 290⿿380 cm depth 2.5 years after the set-up of the vineyard. The amount of nitrate leaching was considerably reduced due to a seeded green cover between the grapevines that took up a high share of the mineralized nitrate reducing a potential contamination of the groundwater.
    Keywords: Soil Hydrology ; Isotope Hydrology ; Nitrate Leaching ; Groundwater Protection ; Viniculture ; Agriculture ; Environmental Sciences
    ISSN: 0167-8809
    E-ISSN: 1873-2305
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 5
    Language: English
    In: Journal of Hydrology, 2010, Vol.392(3), pp.219-233
    Description: The past century has seen significant research comparing snow accumulation and ablation in forested and open sites. In this review we compile and standardize the results of previous empirical studies to generate statistical relations between changes in forest cover and the associated changes in snow accumulation and ablation rate. The analysis drew upon 33 articles documenting these relationships at 65 individual sites in North America and Europe from the 1930s to present. Changes in forest cover explained 57% and 72% of the variance of relative changes in snow accumulation and ablation, respectively. The incorporation of geographic and average historic climatic information did not significantly improve the ability to predict changes in snow processes, mainly because most of the studies did not provide enough information on site characteristics such as slope and aspect or meteorological conditions taking place during the experiments. Two simple linear models using forest cover as the sole predictor of changes in snow accumulation and ablation are provided, as well as a review of the main sources of variation that prevent the elaboration of more accurate multiple regression models. Further studies should provide detailed information regarding the main sources of variation influencing snow processes including the effect of year-to-year changes in weather variables during the monitoring period.
    Keywords: Snow Processes ; Forest Structure ; Forest Cover ; Snow Models ; Empirical Studies ; Snow Hydrology ; Geography
    ISSN: 0022-1694
    E-ISSN: 1879-2707
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 6
    Language: English
    In: Journal of Hydrology, 27 November 2014, Vol.519, pp.340-352
    Description: Assessing temporal variations in soil water flow is important, especially at the hillslope scale, to identify mechanisms of runoff and flood generation and pathways for nutrients and pollutants in soils. While surface processes are well considered and parameterized, the assessment of subsurface processes at the hillslope scale is still challenging since measurement of hydrological pathways is connected to high efforts in time, money and personnel work. The latter might not even be possible in alpine environments with harsh winter processes. Soil water stable isotope profiles may offer a time-integrating fingerprint of subsurface water pathways. In this study, we investigated the suitability of soil water stable isotope (δ O) depth profiles to identify water flow paths along two transects of steep subalpine hillslopes in the Swiss Alps. We applied a one-dimensional advection–dispersion model using δ O values of precipitation (ranging from −24.7 to −2.9‰) as input data to simulate the δ O profiles of soil water. The variability of δ O values with depth within each soil profile and a comparison of the simulated and measured δ O profiles were used to infer information about subsurface hydrological pathways. The temporal pattern of δ O in precipitation was found in several profiles, ranging from −14.5 to −4.0‰. This suggests that vertical percolation plays an important role even at slope angles of up to 46°. Lateral subsurface flow and/or mixing of soil water at lower slope angles might occur in deeper soil layers and at sites near a small stream. The difference between several observed and simulated δ O profiles revealed spatially highly variable infiltration patterns during the snowmelt periods: The δ O value of snow (−17.7 ± 1.9‰) was absent in several measured δ O profiles but present in the respective simulated δ O profiles. This indicated overland flow and/or preferential flow through the soil profile during the melt period. The applied methods proved to be a fast and promising tool to obtain time-integrated information on soil water flow paths at the hillslope scale in steep subalpine slopes.
    Keywords: Stable Isotopes ; Soil Water ; Steep Hillslopes ; Modeling ; Water Pathways ; Snowmelt ; Geography
    ISSN: 0022-1694
    E-ISSN: 1879-2707
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 7
    Language: English
    In: Forest Ecology and Management, 15 October 2014, Vol.330, pp.283-293
    Description: Future climate projections for Central Europe indicate a decrease in summer precipitation which might range between 15% and 50%, and equally important, changes in the climate variability, resulting in consecutive years with drought periods. With respect to Central European forests, we asked to which degree realistic drought conditions are tolerated by the recruits of the dominant tree species L , and how the effects depend on biotic interactions. To test the combined effects of drought, competition and provenance of recruits we set up a rain shelter experiment at three sites in different regions of Germany. Transposable roof panels allowed a flexible precipitation reduction between 10% and 70% corresponding with a return period of 40 years. We planted saplings of three provenances, exposed them to drought and competition. We tested if understorey herbaceous competitors have a negative impact on saplings, and thus, exacerbate drought effects and that provenances from drier regions are adapted to drought conditions and cope better with drought conditions. Six months after the drought treatment started, we encountered significant drought effects, seen in a reduced leaf stomatal conductance, although there was not yet a response in growth rates. Overall, the site had the greatest impact on phytometer performance, while we found no indication of adaptation to drought of the different provenances. Furthermore, drought effects increased in interaction with site effects, being highest at the driest site. At the driest site, leaf stomatal conductance decreased in the presence of competition but increased in the control subplots, while the site of intermediate moisture conditions showed the opposite pattern and the wettest site displayed no differences. Our results highlight the fact that biotic interactions can mitigate or exacerbate drought effects, depending on regional site conditions.
    Keywords: Global Change ; Fagus Sylvatica ; Drought ; Forest Understory ; Competition ; Provenances ; Forestry ; Biology
    ISSN: 0378-1127
    E-ISSN: 1872-7042
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 8
    Language: English
    In: Journal of Hydrology, 2009, Vol.369(3), pp.241-252
    Description: To address the effects of land use and land cover (LULC) on soil structure formation and the significance on preferential flow during infiltration, dye tracer experiments were conducted on five sites differing in LULC, yet displaying similar soil textural characteristics and parent material. Two grassland sites, two farmland sites (tilled and untilled) and one site located in a deciduous forest were investigated. At each site, the same sprinkling experiment was carried out with a Brilliant Blue FCF solution of 4 g L to visualize flow paths. To explore the effects of different rainfall amounts (20, 40 and 60 mm), each 1.2 × 1.5 m experimental plot was subdivided into three smaller subplots, which were irrigated with an intensity of 15 mm h for 80, 160 and 240 min, respectively. During the tracer application, water content changes were continuously measured with 16 time domain reflectometry probes horizontally installed into the profile at different depths. After the experiments vertical and horizontal soil sections were excavated and photographed. The pictures were processed using digital image analysis and the resulting dye patterns analyzed for volume and surface density, maximum infiltration depth and macropore structure. Additionally, flow processes were classified into distinct flow type categories. The tracer experiments revealed that preferential flow processes significantly differed among sites of differing LULC yet similar soil texture. As primary controlling factors soil structure, surface micro-topography, surface cover and topsoil matrix characteristics were identified. The effects of different rainfall application amounts were complex and strongly varied among sites, stressing the strong control LULC exerts on water flow in soils. Overall this suggests that land use effects on soil properties need to be considered in hydrological models to obtain realistic predictions concerning water quality and quantity.
    Keywords: Dye Tracer Experiments ; Preferential Flow ; Soil Structure Formation ; Land Use and Land Cover (Lulc) ; Time Domain Reflectometry ; Geography
    ISSN: 0022-1694
    E-ISSN: 1879-2707
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 9
    Language: English
    In: International Journal of Radiation Oncology, Biology, Physics, 01 July 2010, Vol.77(3), pp.670-676
    Description: To evaluate the toxicity and efficacy of chemoradiotherapy with temozolomide (TMZ) administered in an intensified 1-week on/1-week off schedule plus indomethacin in patients with newly diagnosed glioblastoma. A total of 41 adult patients (median Karnofsky performance status, 90%; median age, 56 years) were treated with preirradiation TMZ at 150 mg/m (1 week on/1 week off), involved-field radiotherapy combined with concomitant low-dose TMZ (50 mg/m ), maintenance TMZ starting at 150 mg/m using a 1-week on/1-week off schedule, plus maintenance indomethacin (25 mg twice daily). The median follow-up interval was 21.7 months. Grade 4 hematologic toxicity was observed in 15 patients (36.6%). Treatment-related nonhematologic Grade 4-5 toxicity was reported for 2 patients (4.9%). The median progression-free survival was 7.6 months (95% confidence interval, 6.2–10.4). The 1-year survival rate was 73.2% (95% confidence interval, 56.8–84.2%). The presence of gene promoter methylation in the tumor tissue was associated with significantly superior progression-free survival. The dose-dense regimen of TMZ administered in a 1-week on/1-week off schedule resulted in acceptable nonhematologic toxicity. Compared with data from the European Organization for Research and Treatment of Cancer/National Cancer Institute of Canada trial 26981-22981/CE.3, patients with an unmethylated gene promoter appeared not to benefit from intensifying the TMZ schedule regarding the median progression-free survival and overall survival. In contrast, data are promising for patients with a methylated promoter.
    Keywords: Glioblastoma ; Indomethacin ; O6-Methylguanine-DNA Methyltransferase ; Mgmt ; Radiotherapy ; Temozolomide ; Medicine
    ISSN: 0360-3016
    E-ISSN: 1879-355X
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 10
    Language: English
    In: Computers and Geosciences, December 2013, Vol.61, pp.116-125
    Description: An analytical Excel-based toolkit called Gas-Tracer-Interpretation (GTI) was developed for determining mean residence time (MRT) of groundwater samples and for validating conceptual model assumptions. This novel data interpretation toolkit improves data handling during analysis and resolves some problems in the interpretation of data from environmental tracers. The toolkit can assist error detection, uncertainty and ambiguity during data analysis, particularly ambiguity due to the decline in atmospheric data of CFC input functions (air-mixing ratios of tracers). The innovative interpretation methodologies are: (1) corrections of environmental tracer data are conducted in concentrations in water instead of air (atmosphere), allowing comparison of different tracer input functions under similar conditions and thereby replacing the use of unique global atmospheric data; (2) a multi-model, multi-tracer approach is adopted to improve the number of different combinations of environmental tracers and lumped-parameter models (piston flow (PM), exponential (EM), exponential-piston flow (EPM), advection-dispersion (DM) and gamma (GM)); and (3) generation of sufficient information for determination of erroneous, unclear and ambiguous outcomes. Results are linked to graphical analysis to improve data view. GTI supports the environmental tracers CFC-11, CFC-12, CFC-113, SF , H, and also SF CF , which is included as it represents a promising environmental tracer in hydrological research. The toolkit compares modeled input functions of tracers and data from samples. The apparent recharge age and MRT are estimated by combining explicit graphical and numerical data presentation. Due to the multi-model approach, it is possible to contrast selected models and estimate the best fit for a given sample, which is particularly useful for validating conceptual model assumptions. The toolkit has been developed in Microsoft ®Excel, and hence is user-friendly such that advanced programming skills or detailed understanding of the calculations and mathematical procedures are unnecessary.
    Keywords: Lumped-Parameter Modeling ; Environmental Tracer ; Groundwater Dating ; Water Age ; Environmental Tracers Concentrations in Water ; Geology
    ISSN: 0098-3004
    E-ISSN: 1873-7803
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. Further information can be found on the KOBV privacy pages