Andreas Krein - Academia.edu (original) (raw)

Papers by Andreas Krein

Research paper thumbnail of Spatio-temporal variability of behavioral patterns in hydrology in meso-scale basins of the Rhineland Palatinate (1972–2002)

Changes in spatio-temporal rainfall patterns have an effect on the hydrological behavior of river... more Changes in spatio-temporal rainfall patterns have an effect on the hydrological behavior of river basins, the magnitude of the effects depending among others on the physiographic basin characteristics. To assess climate and discharge fluctuations, a visualization tool was developed as a contribution to exploratory data analysis. The tool combined statistical tests of hydro-climatological variables with physiographic basin characteristics. Test results

Research paper thumbnail of Air pollution characteristics associated with mesoscale atmospheric patterns in northwest continental Europe

An impact related daily air quality index (DAQx), calculated for 15 air quality monitoring statio... more An impact related daily air quality index (DAQx), calculated for 15 air quality monitoring stations (traffic, background, and industry) in Belgium, France, Germany and Luxembourg, was compared to mesoscale atmospheric patterns between 2001 and 2007. Meteorological conditions were described by the Hess and Brezowsky synoptic weather classification system and gridded data of the EU FP6 ENSEMBLES project of total precipitation and mean surface temperature. DAQx values indicate sufficient to poor air quality in the urban area of Brussels and at urban traffic stations, as well as satisfactory air quality at the background stations. The air quality index refers to more than 90% to the presence of high PM 10 , O 3 and NO 2 concentrations. SO 2 and CO play only a minor role. The investigation of weather regimes indicates that zonal and mixed cyclonic circulation regimes are associated with better air quality than meridional and anticyclonic weather regimes. In general, weather regimes with high daily precipitation lead to better air quality than dryer air masses because of lower contribution of PM 10 to the air quality index. A trend analysis of weather regimes from 1978 to 2007 shows significant (a ¼ 0.05) positive trends for weather classes associated with lower PM 10 concentrations. The results of a case study at a German station examining the relationship between PM 10 concentrations and local meteorological quantities (wind speed and precipitation) confirm the results of the regional analysis.

Research paper thumbnail of Dynamics of storm-driven suspended sediments in a headwater catchment described by multivariable modeling

Purpose Previous research has shown that the rate at which suspended sediment is transported in w... more Purpose Previous research has shown that the rate at which suspended sediment is transported in watercourses depends primarily on discharge (Q) as the first-order control, but additional factors are thought to affect suspended sediment concentrations (SSC) as well. Among these, antecedent hydrological and meteorological conditions (e.g., rainfall depth and intensity, discharge prior to a runoff event and the duration of runoff events) may represent significant transport controlling mechanisms. Univariate models using Q-SSC rating curves often produce large scatter and nonlinearity, because many of the hydrological and biotic processes affecting the dynamics of sediment are non-linear and exhibit threshold behavior. The simulation of such highly non-linear processes is therefore an elusive task requiring consideration of several interrelated controlling variables. The aim of this study was to identify the major hydrological and meteorological controls determining the dynamics of

Research paper thumbnail of Towards more systematic perceptual model development: a case study using 3 Luxembourgish catchments

Hydrological Processes, 2014

The synthesis of experimental understanding of catchment behaviour and its translation into quali... more The synthesis of experimental understanding of catchment behaviour and its translation into qualitative perceptual models is an important objective of hydrological sciences. We explore this challenge by examining the cumulative understanding of the hydrology of three experimental catchments and how it evolves through the application of different investigation techniques. The case study considers the Huewelerbach, Weierbach and Wollefsbach headwater catchments of the Attert basin in Luxembourg. Subsurface investigations including bore holes and pits, analysis of soil samples and Electrical Resistivity Tomography measurements are presented and discussed. Streamflow and tracer data are used to gain further insights into the streamflow dynamics of the catchments, using end-member mixing analysis and hydrograph separation based on dissolved silica and electrical conductivity. We show that the streamflow generating processes in all three catchments are controlled primarily by the subsolum and underlying bedrock. In the Huewelerbach, the permeable sandstone formation supports a stable groundwater component with little seasonality, which reaches the stream through a series of sources at the contact zone with the impermeable marls formation. In the Weierbach, the schist formation is relatively impermeable and supports a 'fill and spill'-type of flow mechanism; during wet conditions, it produces a delayed response dominated by pre-event water. In the Wollefsbach, the impermeable marls formation is responsible for a saturation-excess runoff generating process, producing a fast and highly seasonal response dominated by event water. The distinct streamflow generating processes of the three catchments are represented qualitatively using perceptual models. The perceptual models are in turn translated into quantitative conceptual models, which simulate the hydrological processes using networks of connected reservoirs and transfer functions. More generally, the paper illustrates the evolution of perceptual models based on experimental fieldwork data, the translation of perceptual models into conceptual models and the value of different types of data for processes understanding and model representation.

Research paper thumbnail of Redox-sensitivity and mobility of selected pharmaceutical compounds in a low flow column experiment

Science of The Total Environment, 2012

Laboratory column experiments are suitable to investigate the sediment water interaction and to s... more Laboratory column experiments are suitable to investigate the sediment water interaction and to study the transport behaviour of solutes. Processes like retardation and degradation can be identified and quantified. The conducted experiment, which is closely connected to a field study in Luxembourg, investigated the transport behaviour of selected pharmaceutical compounds and their redox-dependent metabolism under water saturated conditions. Fine-grained natural sediment with a low hydraulic conductivity from a study site in Luxembourg was filled into the column. The water for the experiment was taken from a small stream at the same fieldsite. It was spiked with four pharmaceutical compounds (carbamazepine, diclofenac, ibuprofen, sulfamethoxazole) with concentrations between 170 and 300 ng/L for the different substances. The chosen pharmaceuticals were also detected in groundwater and surface water samples at the study site and used to qualify exchange/mixing of surface water and groundwater (BANZHAF et al., 2011). As some of the substances are known to exhibit redox-sensitive degradation, the redox-conditions were systematically varied throughout the experiment. This was realised by adding nitrate at the inflow of the column. During the experiment, which lasted for 2.5 months, four different nitrate concentrations (20-130 mg/L) were applied, beginning with the highest concentration. During the experiment water from the reservoir tank was sampled daily in order to detect a potential degradation of the pharmaceutical compounds before they enter the column. The effluent water was sampled every three hours to guarantee a maximum resolution for the analysis of the pharmaceuticals where necessary. In addition, major ions were analysed in the influent and effluent samples. Throughout the experiment physicochemical parameters (oxidation reduction potential (ORP), dissolved oxygen, electrical conductivity, and pH-value) were measured and logged at the outflow of the column. At the beginning, the ORP was positive (200 mV) and then dropped continuously. Negative values were reached after 1 month and at the end of the experiment -300 mV were measured. Apart from nitrate and nitrite no significant changes in ion concentrations were detected in the effluent. However, the added pharmaceuticals showed very different behaviour in the column. Diclofenac and especially carbamazepine were highly absorbed by the sediment. They were detected significantly later at the outflow of the column than sulfamethoxazole and ibuprofen. Sulfamethoxazole was heavily influenced by the redox-conditions. Its time variation curve in the effluent is negatively correlated with nitrite and nitrate: during nitrite formation the concentrations of sulfamethoxazole dropped considerably. The presented experiment yields a better understanding of the processes influencing the occurrence and transport behaviour of the studied compounds. In addition, some general findings on redox-dependent transport behaviour and metabolism of the antibiotic sulfamethoxazole are gained. This emphasizes the role of the ORP as a key parameter for the behaviour of this compound, which has to be considered.

Research paper thumbnail of The Importance of Precedent Hydro-climatological Conditions for the Mass Transfer of Pollutants in Separated Sewer Systems and Corresponding Tributaries During Storm Events

Water, Air, and Soil Pollution, 2007

Runoff events were analysed in separated sewer systems in the town of Luxembourg. The relationshi... more Runoff events were analysed in separated sewer systems in the town of Luxembourg. The relationships between Event Mean Concentrations of different pollutants and runoff patterns were evaluated. In addition, the inter-storm and intra-storm variability of the material transport were determined. Primarily, the variations in pollutant concentrations and loads are determined by the antecedent weather conditions. The presence of illicit sanitary inputs in one of the sewers produced a significant first flush effect as well as higher Event Mean Concentrations for pollutants. Furthermore, near the town of Trier 40 storms were analyzed in a small natural basin mainly influenced by runoff from a separated sewer system. Natural and artificial storm events were investigated in order to estimate the relationship between the pollutant sources in the channel and from the separated sewer system. Just like in the canalization of Luxembourg City the pollutant dynamics during natural storms are strongly influenced by pre-event hydrological conditions. The artificial storms behave differently. Despite little prerain, the maximum concentrations of toxic substances are comparatively low. A resuspension of sediment only occurs in the natural channel system, without the introduction of fines from the sewer system.

Research paper thumbnail of Imaging Chemical Patches on Near-surface Atmospheric Dust Particles with NanoSIMS 50 to Identify Material Sources

Water, Air, & Soil Pollution: Focus, 2008

The increase of traffic and the rising energy consumption mean a challenge to the air pollution c... more The increase of traffic and the rising energy consumption mean a challenge to the air pollution control and to environmental protection. Measures of air pollution control concentrated primarily on the reduction of gaseous pollutants. However, in the field of air hygiene in Central Europe, especially the load of near-surface atmospheric dust becomes threatening to human health. A SIMS microprobe for ultra fine feature analysis is used to image the elemental composition at the surface of submicrometer urban dust particles collected at two measurement stations in the Grand Duchy of Luxembourg. The NanoSIMS 50 has been chosen because it creates one intensity image for each selected element in a high spatial resolution down to 50 nm. The atmospheric fine dust consists of a mixture of organic and inorganic compounds. The elemental composition at the surface of particles was studied using a global image segmentation technique to separate the signal from the background of the particles. The analysis of the binary intensity images was carried out using several shape and proximity measures. The patch shape complexity and distribution for industrial/urban particles were found to differ significantly from the solids collected from a forest site. We conclude that the methodology developed in the study is a reliable tool to differentiate between potential sources of airborne particulate matter.

Research paper thumbnail of Behaviour and Fluxes of Dissolved Antibiotics, Analgesics and Hormones During Flood Events in a Small Heterogeneous Catchment in the Grand Duchy of Luxembourg

Water, Air, and Soil Pollution, 2009

The objective of this investigation is to analyse the variations of xenobiotic concentrations and... more The objective of this investigation is to analyse the variations of xenobiotic concentrations and the fluxes of dissolved xenobiotics during runoff events in the small rural Mess catchment (35 km 2 ) in the Southwestern part of Luxembourg. Sulfonamides, tetracyclines, analgesics and hormones, dissolved nutrients, sulphate and chloride were measured to gather information about runoff generation. Typically, the highest values can be found during the first flush mainly in the rising limb of the flood hydrographs. The highest concentrations in eleven flood events are measured for ibuprofen (2,383 ng l -1 ), estrone (27 ng l -1 ) and diclofenac (20 ng l -1 ). From the tetracycline group tetracycline (9 ng l -1 ) itself is of relevance, while the sulfonamides are mainly represented by sulfamethoxazole (5 ng l -1 ). The variable patterns of chemographs are attributed to the hetero-geneous runoff generation characterised by different reactions of storm overflows from the combined sewer systems. During single flood events, the fluxes of ibuprofen (maximum 24,000 mg), 17α-ethinylestradiol (122 mg), 17β-estradiol (32 mg) or estrone (274 mg) are rather low.

Research paper thumbnail of Long-term Persistence of Stream Nitrate Concentrations (Memory Effect) Inferred from Spectral Analysis and Detrended Fluctuation Analysis

Water, Air, & Soil Pollution, 2012

Previous research in agricultural catchments showed that past inputs of nitrate continue to influ... more Previous research in agricultural catchments showed that past inputs of nitrate continue to influence present observations and future characteristics of nitrate concentrations in stream water for a long period of time. This persistence manifests itself as a "memory effect" with a prolonged response of stream water nitrate levels to reductions of nitrate inputs on the catchment scale. The question we attempt to resolve is whether such a memory effect also exists in mountainous catchments with a snowmelt-dominated runoff regime. We analyzed long-term records (∼20 years) of nitrate-nitrogen concentrations measured in stream at three stations on the upper Váh River (Slovakia). Applying spectral analysis and detrended fluctuation analysis, we found a varying degree of persistence between the three analyzed sites. With increasing catchment area, the fluctuation scaling exponents generally increased from 0.77 to 0.93 (fluctuation exponents above 0.5 are usually considered as a proof of persistence while values close to 0.5 indicate "white" uncorrelated noise). The nitrate-nitrogen signals temporally scaled as a power-low function of frequency (1/f noise) with a strong annual seasonality. This increase in persistence might be attributable to the catchment areas upstream the sampling sites. These results have important implications for water quality management. In areas where reduction of nitrate in surface waters is imposed by legislation and regulatory measures, two catchments with different persistence properties may not respond to the same reduction of sources of nitrogen at the same rate.

Research paper thumbnail of Identifying the origins of local atmospheric deposition in the steel industry basin of Luxembourg using the chemical and isotopic composition of the lichen Xanthoria parietina

Science of The Total Environment, 2008

Trace metal atmospheric contamination was assessed in one of the oldest European industrial sites... more Trace metal atmospheric contamination was assessed in one of the oldest European industrial sites of steel production situated in the southern part of the Grand-Duchy of Luxembourg. Using elemental ratios as well as Pb, Sr, and Nd isotopic compositions as tracers, we found preliminary results concerning the trace metal enrichment and the chemical/isotopic signatures of the most important emission sources using the lichen Xanthoria parietina sampled at 15 sites along a SW-NE transect. The concentrations of these elements decreased with increasing distance from the historical and actual steel-work areas. The combination of the different tracers (major elements, Rare Earth Element ratios, Pb, Sr and Nd isotopes) enabled us to distinguish between three principal sources: the historical steel production (old tailings corresponding to blast-furnace residues), the present steel production (industrial sites with arc electric furnace units) and the regional background (baseline) components. Other anthropogenic sources including a waste incinerator and major roads had only weak impacts on lichen chemistry and isotopic ratios. The correlation between the Sr and Nd isotope ratios indicated that the Sr-Nd isotope systems represented useful tools to trace atmospheric emissions of factories using scrap metal for steel production.

Research paper thumbnail of Solid phase extraction coupled to liquid chromatography-tandem mass spectrometry analysis of sulfonamides, tetracyclines, analgesics and hormones in surface water and wastewater in Luxembourg

Science of The Total Environment, 2009

In the early 1990s different studies highlighted the relationship between pharmaceuticals, human ... more In the early 1990s different studies highlighted the relationship between pharmaceuticals, human health and the environment. Among the emerging contaminants, antibiotics are obviously of high concern, because of their potential for inducing antibiotic resistance. In addition, natural and synthetic hormones are relevant because of their potential endocrine-disrupting effects on wildlife. This investigation focuses on the analysis of four classes of veterinary and human pharmaceuticals (sulfonamides, tetracyclines, analgesics and hormones) in surface water and wastewater in Luxembourg. The selected eleven pharmaceuticals include four sulfonamides (sulfathiazole, sulfamethoxazole, sulfadimethoxine and sulfamethazine), two tetracyclines (tetracycline and oxytetracycline), two analgesics (ibuprofen and diclofenac), and three hormones (2 naturals, estrone and β-estradiol, and a synthetic one, 17-α-ethinyl estradiol). The most innovative parts of this study are the simultaneous extraction of the above-mentioned pharmaceuticals as well as tracking their behaviour during flood events in a small river catchment. The method includes pre-concentration by solid phase extraction using Oasis® HLB (Hydrophilic Lipophilic Balance) which gave superior results compared to Chromabond® C-18EC, Chromabond® EASY and Bond Elut® PLEXA cartridges, also evaluated in this investigation. The analysis of the investigated pharmaceutical compounds is carried out by high performance liquid chromatography coupled to a triple quadrupole mass spectrometer. The limits of quantification were 1 ng L − 1 , except for β-estradiol (2 ng L − 1 ) and 17-α-ethinyl estradiol (6 ng L − 1 ). Recovery rates range from 70 to 94%, with relative standard deviations between 4 and 19%. Application of this method to river concentration and flood events revealed high concentrations of ibuprofen (10-4000 ng L − 1 ), with highest levels during flood events, while concentrations of estrogens (1-240 ng L − 1 ) and sulfonamides (1-20 ng L − 1 ) were comparatively low.

Research paper thumbnail of A rapid spectral-reflectance-based fingerprinting approach for documenting suspended sediment sources during storm runoff events

Journal of Soils and Sediments, 2010

Purpose This paper reports on the development of a rapid and simple spectra-reflectance-based fin... more Purpose This paper reports on the development of a rapid and simple spectra-reflectance-based fingerprinting approach for documenting suspended sediment sources during storm runoff events. The methodology was applied in the rural Wollefsbach catchment (4.4 km 2 , NW Luxembourg). Materials and methods Different chemical properties of the sediment retained on glass fibre filters after filtration were predicted from VIS/NIR spectra (ASD FieldSpec-II spectrometer, 0.4-2.5 µm) through partial least-square regression models (PLSR). Chemical property values measured on time-integrated suspended sediment, bed sediment and potential sediment sources samples (topsoil and channel banks) collected in the catchment were used to calibrate the PLSR models. Appropriate properties were selected and used to apply the 'spectral-reflectance-based fingerprinting approach', in order to estimate the sources of the suspended sediment retained on the filters. Uncertainty associated with model predictions was assessed using an inclusive approach to mixing models based on Bayesian error estimation, incorporating tracer property variability using a Monte Carlo simulation technique. Results and discussion The methodology proved to be a useful, fast and easy to apply approach not only for studying the variation of suspended sediment properties during storm runoff events from spectra, but also for documenting the variation of suspended sediment sources during individual storm events. Conclusions The spectral-reflectance-based fingerprinting approach possesses considerable potential, since it possesses a number of important advantages over conventional source fingerprinting techniques, in terms of cost and time and labour requirements.

Research paper thumbnail of The use of sediment colour measured by diffuse reflectance spectrometry to determine sediment sources: Application to the Attert River catchment (Luxembourg)

Journal of Hydrology, 2010

s u m m a r y Colour coefficients measured by diffuse reflectance spectrometry were used to quant... more s u m m a r y Colour coefficients measured by diffuse reflectance spectrometry were used to quantify suspended sediment sources using the fingerprinting approach. The investigations were undertaken in the Attert River catchment (NW Luxembourg), where time-integrated suspended sediment samples and samples of potential sediment sources (topsoil and channel bank samples) were collected, in order to test the ability of colour to provide a fingerprint property for sediment source tracing. Sediment colour coefficients were computed from diffuse reflectance spectrometry measurements (ASD FieldSpec-II spectrometer, 0.4-2.5 lm) taken over the visible wavelength range. The linearly additive behaviour of these colour coefficients, which is an important requirement for its use in the mixing models, was tested in the laboratory by means of artificial mixtures. Model prediction uncertainty associated with the spatial variability of source tracer properties was assessed using an inclusive approach to mixing models based on Bayesian error estimation and employing Monte-Carlo simulation. The results provided by the colour measurements were compared with those obtained using the classical fingerprinting approach in the same catchments (i.e. using geochemical, radionuclide and organic tracers). Even though neither of the two approaches is definitive, and the results involve considerable uncertainty, the consistency between the approaches encouraged the extension of the approach to include measurements on the particles retained on glass fibre filters. This permitted use of small samples collected by an automatic sampler to investigate source variability during a storm runoff event. Preliminary results obtained using this approach demonstrated that colour provides a useful property for use in sediment source fingerprinting investigations, which is both fast and easy to measure. It also provides a rapid and cheap means of investigating hillslope-to-channel coupling and the transfer of eroded material during storm runoff events, even at low concentrations. High spatial and temporal variability of the characteristics of suspended particles was observed. The use of sediment colour measured by diffuse reflectance spectrometry is seen to represent a useful development, in terms of reducing analytical costs associated with composite fingerprinting procedures.

Research paper thumbnail of Hydrogeologic and landscape controls of dissolved inorganic nitrogen (DIN) and dissolved silica (DSi) fluxes in heterogeneous catchments

Journal of Hydrology, 2012

Nutrient fluxes Hydrology Physiography Land cover Dissolved silica Dissolved inorganic nitrogen s... more Nutrient fluxes Hydrology Physiography Land cover Dissolved silica Dissolved inorganic nitrogen s u m m a r y This paper examines the combined effects of catchment complexity in terms of physiography, land use patterns, and lithology on the export of dissolved inorganic nitrogen and dissolved silica from heterogeneous nested catchments in the Grand-Duchy of Luxembourg. Using results from water quality monitoring at 24 sampling sites, we determined the first-order controls on these fluxes. Land cover with four classes (forest, agriculture, grassland and urban), dominant lithology (schist, marls, sandstone, limestone, alluvial sediments), physiographic indices (elevation, flow path length, ratio of flow path length to flow path gradient, topographic wetness index, and other), and a suite of hydrological indices (baseflow, flashiness index and runoff coefficient), were calculated and used as potential controls. Given the high codependence of the predictors, Partial Least Square Regression was used to shed light on the linkages between export fluxes and the metrics composed of the 19 selected catchment characteristics. The first-order controls were determined by calculating the Variable Influence on Projection (VIP). These values revealed that the overall dissolved inorganic nitrogen fluxes are controlled primarily by lithology, land cover, topographic wetness index and flow path length. The first-order controls of dissolved silica fluxes are runoff coefficient, average topographic slope and land cover. Fluxes of dissolved inorganic nitrogen and dissolved silica did not show any strong relation to catchment scale. Apart from the widely accepted effect of land cover, our results indicate that catchment topography has an essential impact on the fluxes of dissolved inorganic nitrogen. The ratio of flow path length and flow path gradient, previously suggested as a proxy of mean water transit time, exerted a relatively strong control on dissolved inorganic nitrogen fluxes (VIP > 1) with a negative relation to dissolved inorganic nitrogen fluxes, suggesting that dissolved inorganic nitrogen fluxes decrease with an increasing flow path gradient.

Research paper thumbnail of Simulation of sediment transport during flood events: laboratory work and field experiments

Hydrological Sciences Journal, 2001

This paper aims at initiating a fundamental understanding of the suspended load transport of rive... more This paper aims at initiating a fundamental understanding of the suspended load transport of river sediment in unsteady flow. Laboratory erosion tests as well as artificial flood experiments are used to evaluate the influence of the transient regime on the transport efficiency of the flow. The erosion experiments reveal that the transport capacity is augmented when the unsteadiness of the flow increases. However, the influence of the transient regime is counteracted by the cohesive properties of the river bed. Field experiments with artificial floods released from a reservoir into a small canal confirm these findings and show a relationship between the friction velocity and the suspended load transport. An appropriate parameter [3 is proposed to evaluate the impact of the transient regime on the transport of suspended sediment.

Research paper thumbnail of Use of artificial flood events to demonstrate the invalidity of simple mixing models

Hydrological Sciences Journal, 2002

Page 1. Hydrofogical Sciences-J ournal-des Sciences Hydrologiques. 47(5) October 2002 §33 DISCUSS... more Page 1. Hydrofogical Sciences-J ournal-des Sciences Hydrologiques. 47(5) October 2002 §33 DISCUSSION Use of artificial flood events to demonstrate the invalidity of simple mixing models* TOMMY SW WONG School of Civil ...

Research paper thumbnail of Concentrations and loads of dissolved xenobiotics and hormones in two small river catchments of different land use in Luxembourg

Hydrological Processes, 2013

Research paper thumbnail of Assessment of different colour parameters for discriminating potential suspended sediment sources and provenance: A multi-scale study in Luxembourg

Geomorphology, 2010

Sediment colour has recently been used successfully to estimate suspended sediment sources in sma... more Sediment colour has recently been used successfully to estimate suspended sediment sources in small catchments using the fingerprinting approach. The methodology offers opportunity for further research since it provides a rapid and cheap means for investigating sediment sources. However, the colour-based fingerprinting approach has not yet been tested in medium and large catchments. This paper aims to test whether colour parameters are capable of discriminating sediment sources in a nested system of seven subcatchments ranging from 0.7 to 247 km 2 of the Attert River catchment, NW Luxembourg. Time-integrated suspended sediment samples and samples of potential sediment sources (land-use types and channel banks) were collected in all catchments. Sediment colour was then computed from diffuse reflectance spectrometry measurements (ASD FieldSpec-II spectrometer, 0.4-2.5 µm) taken over the visible wavelength range. Twenty-four colour parameters were derived from several colour space models (CIE xyY, CIE XYZ, RGB, Munsell HVC, Helmholtz chromaticity, CIELUV and CIELAB) and their ability to discriminate potential suspended sediment sources and provenance was evaluated and compared. Results demonstrated that timeintegrated suspended sediment samples collected in the study catchments had statistically different colour values. Moreover, these values always represented a mixture of the colour values measured on potential suspended sediment sources in the catchment. Inter-source colour contrasts (land-use types and channel banks) were observed in all catchments (Kruskal-Wallis H-test). However, although colour is able to distinguish potential sediment sources in small catchments, the level of source discrimination decreases as the catchment size increases, probably due to heterogeneous geology and pedology, intra-source variability and to source overlap. Nevertheless, in the studied medium-sized catchments (ranging from 19.4 to 247 km 2 ), colour could differentiate between topsoil and sub-surface (i.e. channel bank) material and/or up to three sources types. No single colour model had discrimination power across catchments, instead in each catchment a different combination of colour parameters gathered from different colour space models produced optimal discrimination of potential sediment sources. Furthermore, a colour-based fingerprinting approach did not possess potential for integrating spatial provenance and source type information because colour parameters could not discriminate between contrasting geological sub-areas. In summary, although colour parameters were not capable of discriminating the range of land-use type and channel banks as potential suspended sediment sources in medium-sized catchments, they afford substantial information and could be integrated into the classical fingerprinting approach together with other constituents (e.g. geochemistry, radionuclides and/or organic compounds).

Research paper thumbnail of Facing Hazardous Matter in Atmospheric Particles with NanoSIMS (2 pp)

Environmental Science and Pollution Research - International, 2007

Corresponding author (krein@lippmann.lu) hot spots in a nanometer scale. In regard to the health ... more Corresponding author (krein@lippmann.lu) hot spots in a nanometer scale. In regard to the health aspect, the hot spots consisting of toxic elements are particularly relevant as they react directly with the lung tissues.

Research paper thumbnail of Concentrations of dissolved herbicides and pharmaceuticals in a small river in Luxembourg

Environmental Monitoring and Assessment, 2011

Urban and agricultural areas affect the hydraulic patterns as well as the water quality of receiv... more Urban and agricultural areas affect the hydraulic patterns as well as the water quality of receiving drainage systems, especially of catchments smaller than 50 km 2 . Urban runoff is prone to contamination due to pollutants like pesticides or pharmaceuticals. Agricultural areas are possible sources of nutrient and herbicide contamination for receiving water bodies. The pollution is derived from leaching by subsurface flow, as well as wash-off and erosion caused by surface runoff. In the Luxembourgish Mess River catchment, the pharmaceutical and pesticide concentrations are comparable with those detected by other authors in different river systems worldwide. Some investigated pesticide concentrations infringe current regulations. The maximum allowable concentration for diuron of 1.8 μg l −1 is exceeded fourfold by measured 7.41 μg l −1 in a flood event. The load of dissolved pesticides reaching the stream gauge is primarily determined by the amount applied to the surfaces within the catchment area. Storm water runoff from urban areas causes short-lived but high-pollutant concentrations and moderate loads, whereas moderate concentrations and high loads are representative for agricultural inputs to the drainage system. Dissolved herbicides, sulfonamides, tetracyclines, analgesics and hormones can be used as indicators to investigate runoff generation processes, including inputs from anthropogenic sources. The measurements prove that the influence of kinematic wave effects on the relationship between hydrograph and chemographs should not be neglected in smaller basins. The time lag shows that it is not possible to connect analysed substances of defined samples to the corresponding section of the hydrograph.

Research paper thumbnail of Spatio-temporal variability of behavioral patterns in hydrology in meso-scale basins of the Rhineland Palatinate (1972–2002)

Changes in spatio-temporal rainfall patterns have an effect on the hydrological behavior of river... more Changes in spatio-temporal rainfall patterns have an effect on the hydrological behavior of river basins, the magnitude of the effects depending among others on the physiographic basin characteristics. To assess climate and discharge fluctuations, a visualization tool was developed as a contribution to exploratory data analysis. The tool combined statistical tests of hydro-climatological variables with physiographic basin characteristics. Test results

Research paper thumbnail of Air pollution characteristics associated with mesoscale atmospheric patterns in northwest continental Europe

An impact related daily air quality index (DAQx), calculated for 15 air quality monitoring statio... more An impact related daily air quality index (DAQx), calculated for 15 air quality monitoring stations (traffic, background, and industry) in Belgium, France, Germany and Luxembourg, was compared to mesoscale atmospheric patterns between 2001 and 2007. Meteorological conditions were described by the Hess and Brezowsky synoptic weather classification system and gridded data of the EU FP6 ENSEMBLES project of total precipitation and mean surface temperature. DAQx values indicate sufficient to poor air quality in the urban area of Brussels and at urban traffic stations, as well as satisfactory air quality at the background stations. The air quality index refers to more than 90% to the presence of high PM 10 , O 3 and NO 2 concentrations. SO 2 and CO play only a minor role. The investigation of weather regimes indicates that zonal and mixed cyclonic circulation regimes are associated with better air quality than meridional and anticyclonic weather regimes. In general, weather regimes with high daily precipitation lead to better air quality than dryer air masses because of lower contribution of PM 10 to the air quality index. A trend analysis of weather regimes from 1978 to 2007 shows significant (a ¼ 0.05) positive trends for weather classes associated with lower PM 10 concentrations. The results of a case study at a German station examining the relationship between PM 10 concentrations and local meteorological quantities (wind speed and precipitation) confirm the results of the regional analysis.

Research paper thumbnail of Dynamics of storm-driven suspended sediments in a headwater catchment described by multivariable modeling

Purpose Previous research has shown that the rate at which suspended sediment is transported in w... more Purpose Previous research has shown that the rate at which suspended sediment is transported in watercourses depends primarily on discharge (Q) as the first-order control, but additional factors are thought to affect suspended sediment concentrations (SSC) as well. Among these, antecedent hydrological and meteorological conditions (e.g., rainfall depth and intensity, discharge prior to a runoff event and the duration of runoff events) may represent significant transport controlling mechanisms. Univariate models using Q-SSC rating curves often produce large scatter and nonlinearity, because many of the hydrological and biotic processes affecting the dynamics of sediment are non-linear and exhibit threshold behavior. The simulation of such highly non-linear processes is therefore an elusive task requiring consideration of several interrelated controlling variables. The aim of this study was to identify the major hydrological and meteorological controls determining the dynamics of

Research paper thumbnail of Towards more systematic perceptual model development: a case study using 3 Luxembourgish catchments

Hydrological Processes, 2014

The synthesis of experimental understanding of catchment behaviour and its translation into quali... more The synthesis of experimental understanding of catchment behaviour and its translation into qualitative perceptual models is an important objective of hydrological sciences. We explore this challenge by examining the cumulative understanding of the hydrology of three experimental catchments and how it evolves through the application of different investigation techniques. The case study considers the Huewelerbach, Weierbach and Wollefsbach headwater catchments of the Attert basin in Luxembourg. Subsurface investigations including bore holes and pits, analysis of soil samples and Electrical Resistivity Tomography measurements are presented and discussed. Streamflow and tracer data are used to gain further insights into the streamflow dynamics of the catchments, using end-member mixing analysis and hydrograph separation based on dissolved silica and electrical conductivity. We show that the streamflow generating processes in all three catchments are controlled primarily by the subsolum and underlying bedrock. In the Huewelerbach, the permeable sandstone formation supports a stable groundwater component with little seasonality, which reaches the stream through a series of sources at the contact zone with the impermeable marls formation. In the Weierbach, the schist formation is relatively impermeable and supports a 'fill and spill'-type of flow mechanism; during wet conditions, it produces a delayed response dominated by pre-event water. In the Wollefsbach, the impermeable marls formation is responsible for a saturation-excess runoff generating process, producing a fast and highly seasonal response dominated by event water. The distinct streamflow generating processes of the three catchments are represented qualitatively using perceptual models. The perceptual models are in turn translated into quantitative conceptual models, which simulate the hydrological processes using networks of connected reservoirs and transfer functions. More generally, the paper illustrates the evolution of perceptual models based on experimental fieldwork data, the translation of perceptual models into conceptual models and the value of different types of data for processes understanding and model representation.

Research paper thumbnail of Redox-sensitivity and mobility of selected pharmaceutical compounds in a low flow column experiment

Science of The Total Environment, 2012

Laboratory column experiments are suitable to investigate the sediment water interaction and to s... more Laboratory column experiments are suitable to investigate the sediment water interaction and to study the transport behaviour of solutes. Processes like retardation and degradation can be identified and quantified. The conducted experiment, which is closely connected to a field study in Luxembourg, investigated the transport behaviour of selected pharmaceutical compounds and their redox-dependent metabolism under water saturated conditions. Fine-grained natural sediment with a low hydraulic conductivity from a study site in Luxembourg was filled into the column. The water for the experiment was taken from a small stream at the same fieldsite. It was spiked with four pharmaceutical compounds (carbamazepine, diclofenac, ibuprofen, sulfamethoxazole) with concentrations between 170 and 300 ng/L for the different substances. The chosen pharmaceuticals were also detected in groundwater and surface water samples at the study site and used to qualify exchange/mixing of surface water and groundwater (BANZHAF et al., 2011). As some of the substances are known to exhibit redox-sensitive degradation, the redox-conditions were systematically varied throughout the experiment. This was realised by adding nitrate at the inflow of the column. During the experiment, which lasted for 2.5 months, four different nitrate concentrations (20-130 mg/L) were applied, beginning with the highest concentration. During the experiment water from the reservoir tank was sampled daily in order to detect a potential degradation of the pharmaceutical compounds before they enter the column. The effluent water was sampled every three hours to guarantee a maximum resolution for the analysis of the pharmaceuticals where necessary. In addition, major ions were analysed in the influent and effluent samples. Throughout the experiment physicochemical parameters (oxidation reduction potential (ORP), dissolved oxygen, electrical conductivity, and pH-value) were measured and logged at the outflow of the column. At the beginning, the ORP was positive (200 mV) and then dropped continuously. Negative values were reached after 1 month and at the end of the experiment -300 mV were measured. Apart from nitrate and nitrite no significant changes in ion concentrations were detected in the effluent. However, the added pharmaceuticals showed very different behaviour in the column. Diclofenac and especially carbamazepine were highly absorbed by the sediment. They were detected significantly later at the outflow of the column than sulfamethoxazole and ibuprofen. Sulfamethoxazole was heavily influenced by the redox-conditions. Its time variation curve in the effluent is negatively correlated with nitrite and nitrate: during nitrite formation the concentrations of sulfamethoxazole dropped considerably. The presented experiment yields a better understanding of the processes influencing the occurrence and transport behaviour of the studied compounds. In addition, some general findings on redox-dependent transport behaviour and metabolism of the antibiotic sulfamethoxazole are gained. This emphasizes the role of the ORP as a key parameter for the behaviour of this compound, which has to be considered.

Research paper thumbnail of The Importance of Precedent Hydro-climatological Conditions for the Mass Transfer of Pollutants in Separated Sewer Systems and Corresponding Tributaries During Storm Events

Water, Air, and Soil Pollution, 2007

Runoff events were analysed in separated sewer systems in the town of Luxembourg. The relationshi... more Runoff events were analysed in separated sewer systems in the town of Luxembourg. The relationships between Event Mean Concentrations of different pollutants and runoff patterns were evaluated. In addition, the inter-storm and intra-storm variability of the material transport were determined. Primarily, the variations in pollutant concentrations and loads are determined by the antecedent weather conditions. The presence of illicit sanitary inputs in one of the sewers produced a significant first flush effect as well as higher Event Mean Concentrations for pollutants. Furthermore, near the town of Trier 40 storms were analyzed in a small natural basin mainly influenced by runoff from a separated sewer system. Natural and artificial storm events were investigated in order to estimate the relationship between the pollutant sources in the channel and from the separated sewer system. Just like in the canalization of Luxembourg City the pollutant dynamics during natural storms are strongly influenced by pre-event hydrological conditions. The artificial storms behave differently. Despite little prerain, the maximum concentrations of toxic substances are comparatively low. A resuspension of sediment only occurs in the natural channel system, without the introduction of fines from the sewer system.

Research paper thumbnail of Imaging Chemical Patches on Near-surface Atmospheric Dust Particles with NanoSIMS 50 to Identify Material Sources

Water, Air, & Soil Pollution: Focus, 2008

The increase of traffic and the rising energy consumption mean a challenge to the air pollution c... more The increase of traffic and the rising energy consumption mean a challenge to the air pollution control and to environmental protection. Measures of air pollution control concentrated primarily on the reduction of gaseous pollutants. However, in the field of air hygiene in Central Europe, especially the load of near-surface atmospheric dust becomes threatening to human health. A SIMS microprobe for ultra fine feature analysis is used to image the elemental composition at the surface of submicrometer urban dust particles collected at two measurement stations in the Grand Duchy of Luxembourg. The NanoSIMS 50 has been chosen because it creates one intensity image for each selected element in a high spatial resolution down to 50 nm. The atmospheric fine dust consists of a mixture of organic and inorganic compounds. The elemental composition at the surface of particles was studied using a global image segmentation technique to separate the signal from the background of the particles. The analysis of the binary intensity images was carried out using several shape and proximity measures. The patch shape complexity and distribution for industrial/urban particles were found to differ significantly from the solids collected from a forest site. We conclude that the methodology developed in the study is a reliable tool to differentiate between potential sources of airborne particulate matter.

Research paper thumbnail of Behaviour and Fluxes of Dissolved Antibiotics, Analgesics and Hormones During Flood Events in a Small Heterogeneous Catchment in the Grand Duchy of Luxembourg

Water, Air, and Soil Pollution, 2009

The objective of this investigation is to analyse the variations of xenobiotic concentrations and... more The objective of this investigation is to analyse the variations of xenobiotic concentrations and the fluxes of dissolved xenobiotics during runoff events in the small rural Mess catchment (35 km 2 ) in the Southwestern part of Luxembourg. Sulfonamides, tetracyclines, analgesics and hormones, dissolved nutrients, sulphate and chloride were measured to gather information about runoff generation. Typically, the highest values can be found during the first flush mainly in the rising limb of the flood hydrographs. The highest concentrations in eleven flood events are measured for ibuprofen (2,383 ng l -1 ), estrone (27 ng l -1 ) and diclofenac (20 ng l -1 ). From the tetracycline group tetracycline (9 ng l -1 ) itself is of relevance, while the sulfonamides are mainly represented by sulfamethoxazole (5 ng l -1 ). The variable patterns of chemographs are attributed to the hetero-geneous runoff generation characterised by different reactions of storm overflows from the combined sewer systems. During single flood events, the fluxes of ibuprofen (maximum 24,000 mg), 17α-ethinylestradiol (122 mg), 17β-estradiol (32 mg) or estrone (274 mg) are rather low.

Research paper thumbnail of Long-term Persistence of Stream Nitrate Concentrations (Memory Effect) Inferred from Spectral Analysis and Detrended Fluctuation Analysis

Water, Air, & Soil Pollution, 2012

Previous research in agricultural catchments showed that past inputs of nitrate continue to influ... more Previous research in agricultural catchments showed that past inputs of nitrate continue to influence present observations and future characteristics of nitrate concentrations in stream water for a long period of time. This persistence manifests itself as a "memory effect" with a prolonged response of stream water nitrate levels to reductions of nitrate inputs on the catchment scale. The question we attempt to resolve is whether such a memory effect also exists in mountainous catchments with a snowmelt-dominated runoff regime. We analyzed long-term records (∼20 years) of nitrate-nitrogen concentrations measured in stream at three stations on the upper Váh River (Slovakia). Applying spectral analysis and detrended fluctuation analysis, we found a varying degree of persistence between the three analyzed sites. With increasing catchment area, the fluctuation scaling exponents generally increased from 0.77 to 0.93 (fluctuation exponents above 0.5 are usually considered as a proof of persistence while values close to 0.5 indicate "white" uncorrelated noise). The nitrate-nitrogen signals temporally scaled as a power-low function of frequency (1/f noise) with a strong annual seasonality. This increase in persistence might be attributable to the catchment areas upstream the sampling sites. These results have important implications for water quality management. In areas where reduction of nitrate in surface waters is imposed by legislation and regulatory measures, two catchments with different persistence properties may not respond to the same reduction of sources of nitrogen at the same rate.

Research paper thumbnail of Identifying the origins of local atmospheric deposition in the steel industry basin of Luxembourg using the chemical and isotopic composition of the lichen Xanthoria parietina

Science of The Total Environment, 2008

Trace metal atmospheric contamination was assessed in one of the oldest European industrial sites... more Trace metal atmospheric contamination was assessed in one of the oldest European industrial sites of steel production situated in the southern part of the Grand-Duchy of Luxembourg. Using elemental ratios as well as Pb, Sr, and Nd isotopic compositions as tracers, we found preliminary results concerning the trace metal enrichment and the chemical/isotopic signatures of the most important emission sources using the lichen Xanthoria parietina sampled at 15 sites along a SW-NE transect. The concentrations of these elements decreased with increasing distance from the historical and actual steel-work areas. The combination of the different tracers (major elements, Rare Earth Element ratios, Pb, Sr and Nd isotopes) enabled us to distinguish between three principal sources: the historical steel production (old tailings corresponding to blast-furnace residues), the present steel production (industrial sites with arc electric furnace units) and the regional background (baseline) components. Other anthropogenic sources including a waste incinerator and major roads had only weak impacts on lichen chemistry and isotopic ratios. The correlation between the Sr and Nd isotope ratios indicated that the Sr-Nd isotope systems represented useful tools to trace atmospheric emissions of factories using scrap metal for steel production.

Research paper thumbnail of Solid phase extraction coupled to liquid chromatography-tandem mass spectrometry analysis of sulfonamides, tetracyclines, analgesics and hormones in surface water and wastewater in Luxembourg

Science of The Total Environment, 2009

In the early 1990s different studies highlighted the relationship between pharmaceuticals, human ... more In the early 1990s different studies highlighted the relationship between pharmaceuticals, human health and the environment. Among the emerging contaminants, antibiotics are obviously of high concern, because of their potential for inducing antibiotic resistance. In addition, natural and synthetic hormones are relevant because of their potential endocrine-disrupting effects on wildlife. This investigation focuses on the analysis of four classes of veterinary and human pharmaceuticals (sulfonamides, tetracyclines, analgesics and hormones) in surface water and wastewater in Luxembourg. The selected eleven pharmaceuticals include four sulfonamides (sulfathiazole, sulfamethoxazole, sulfadimethoxine and sulfamethazine), two tetracyclines (tetracycline and oxytetracycline), two analgesics (ibuprofen and diclofenac), and three hormones (2 naturals, estrone and β-estradiol, and a synthetic one, 17-α-ethinyl estradiol). The most innovative parts of this study are the simultaneous extraction of the above-mentioned pharmaceuticals as well as tracking their behaviour during flood events in a small river catchment. The method includes pre-concentration by solid phase extraction using Oasis® HLB (Hydrophilic Lipophilic Balance) which gave superior results compared to Chromabond® C-18EC, Chromabond® EASY and Bond Elut® PLEXA cartridges, also evaluated in this investigation. The analysis of the investigated pharmaceutical compounds is carried out by high performance liquid chromatography coupled to a triple quadrupole mass spectrometer. The limits of quantification were 1 ng L − 1 , except for β-estradiol (2 ng L − 1 ) and 17-α-ethinyl estradiol (6 ng L − 1 ). Recovery rates range from 70 to 94%, with relative standard deviations between 4 and 19%. Application of this method to river concentration and flood events revealed high concentrations of ibuprofen (10-4000 ng L − 1 ), with highest levels during flood events, while concentrations of estrogens (1-240 ng L − 1 ) and sulfonamides (1-20 ng L − 1 ) were comparatively low.

Research paper thumbnail of A rapid spectral-reflectance-based fingerprinting approach for documenting suspended sediment sources during storm runoff events

Journal of Soils and Sediments, 2010

Purpose This paper reports on the development of a rapid and simple spectra-reflectance-based fin... more Purpose This paper reports on the development of a rapid and simple spectra-reflectance-based fingerprinting approach for documenting suspended sediment sources during storm runoff events. The methodology was applied in the rural Wollefsbach catchment (4.4 km 2 , NW Luxembourg). Materials and methods Different chemical properties of the sediment retained on glass fibre filters after filtration were predicted from VIS/NIR spectra (ASD FieldSpec-II spectrometer, 0.4-2.5 µm) through partial least-square regression models (PLSR). Chemical property values measured on time-integrated suspended sediment, bed sediment and potential sediment sources samples (topsoil and channel banks) collected in the catchment were used to calibrate the PLSR models. Appropriate properties were selected and used to apply the 'spectral-reflectance-based fingerprinting approach', in order to estimate the sources of the suspended sediment retained on the filters. Uncertainty associated with model predictions was assessed using an inclusive approach to mixing models based on Bayesian error estimation, incorporating tracer property variability using a Monte Carlo simulation technique. Results and discussion The methodology proved to be a useful, fast and easy to apply approach not only for studying the variation of suspended sediment properties during storm runoff events from spectra, but also for documenting the variation of suspended sediment sources during individual storm events. Conclusions The spectral-reflectance-based fingerprinting approach possesses considerable potential, since it possesses a number of important advantages over conventional source fingerprinting techniques, in terms of cost and time and labour requirements.

Research paper thumbnail of The use of sediment colour measured by diffuse reflectance spectrometry to determine sediment sources: Application to the Attert River catchment (Luxembourg)

Journal of Hydrology, 2010

s u m m a r y Colour coefficients measured by diffuse reflectance spectrometry were used to quant... more s u m m a r y Colour coefficients measured by diffuse reflectance spectrometry were used to quantify suspended sediment sources using the fingerprinting approach. The investigations were undertaken in the Attert River catchment (NW Luxembourg), where time-integrated suspended sediment samples and samples of potential sediment sources (topsoil and channel bank samples) were collected, in order to test the ability of colour to provide a fingerprint property for sediment source tracing. Sediment colour coefficients were computed from diffuse reflectance spectrometry measurements (ASD FieldSpec-II spectrometer, 0.4-2.5 lm) taken over the visible wavelength range. The linearly additive behaviour of these colour coefficients, which is an important requirement for its use in the mixing models, was tested in the laboratory by means of artificial mixtures. Model prediction uncertainty associated with the spatial variability of source tracer properties was assessed using an inclusive approach to mixing models based on Bayesian error estimation and employing Monte-Carlo simulation. The results provided by the colour measurements were compared with those obtained using the classical fingerprinting approach in the same catchments (i.e. using geochemical, radionuclide and organic tracers). Even though neither of the two approaches is definitive, and the results involve considerable uncertainty, the consistency between the approaches encouraged the extension of the approach to include measurements on the particles retained on glass fibre filters. This permitted use of small samples collected by an automatic sampler to investigate source variability during a storm runoff event. Preliminary results obtained using this approach demonstrated that colour provides a useful property for use in sediment source fingerprinting investigations, which is both fast and easy to measure. It also provides a rapid and cheap means of investigating hillslope-to-channel coupling and the transfer of eroded material during storm runoff events, even at low concentrations. High spatial and temporal variability of the characteristics of suspended particles was observed. The use of sediment colour measured by diffuse reflectance spectrometry is seen to represent a useful development, in terms of reducing analytical costs associated with composite fingerprinting procedures.

Research paper thumbnail of Hydrogeologic and landscape controls of dissolved inorganic nitrogen (DIN) and dissolved silica (DSi) fluxes in heterogeneous catchments

Journal of Hydrology, 2012

Nutrient fluxes Hydrology Physiography Land cover Dissolved silica Dissolved inorganic nitrogen s... more Nutrient fluxes Hydrology Physiography Land cover Dissolved silica Dissolved inorganic nitrogen s u m m a r y This paper examines the combined effects of catchment complexity in terms of physiography, land use patterns, and lithology on the export of dissolved inorganic nitrogen and dissolved silica from heterogeneous nested catchments in the Grand-Duchy of Luxembourg. Using results from water quality monitoring at 24 sampling sites, we determined the first-order controls on these fluxes. Land cover with four classes (forest, agriculture, grassland and urban), dominant lithology (schist, marls, sandstone, limestone, alluvial sediments), physiographic indices (elevation, flow path length, ratio of flow path length to flow path gradient, topographic wetness index, and other), and a suite of hydrological indices (baseflow, flashiness index and runoff coefficient), were calculated and used as potential controls. Given the high codependence of the predictors, Partial Least Square Regression was used to shed light on the linkages between export fluxes and the metrics composed of the 19 selected catchment characteristics. The first-order controls were determined by calculating the Variable Influence on Projection (VIP). These values revealed that the overall dissolved inorganic nitrogen fluxes are controlled primarily by lithology, land cover, topographic wetness index and flow path length. The first-order controls of dissolved silica fluxes are runoff coefficient, average topographic slope and land cover. Fluxes of dissolved inorganic nitrogen and dissolved silica did not show any strong relation to catchment scale. Apart from the widely accepted effect of land cover, our results indicate that catchment topography has an essential impact on the fluxes of dissolved inorganic nitrogen. The ratio of flow path length and flow path gradient, previously suggested as a proxy of mean water transit time, exerted a relatively strong control on dissolved inorganic nitrogen fluxes (VIP > 1) with a negative relation to dissolved inorganic nitrogen fluxes, suggesting that dissolved inorganic nitrogen fluxes decrease with an increasing flow path gradient.

Research paper thumbnail of Simulation of sediment transport during flood events: laboratory work and field experiments

Hydrological Sciences Journal, 2001

This paper aims at initiating a fundamental understanding of the suspended load transport of rive... more This paper aims at initiating a fundamental understanding of the suspended load transport of river sediment in unsteady flow. Laboratory erosion tests as well as artificial flood experiments are used to evaluate the influence of the transient regime on the transport efficiency of the flow. The erosion experiments reveal that the transport capacity is augmented when the unsteadiness of the flow increases. However, the influence of the transient regime is counteracted by the cohesive properties of the river bed. Field experiments with artificial floods released from a reservoir into a small canal confirm these findings and show a relationship between the friction velocity and the suspended load transport. An appropriate parameter [3 is proposed to evaluate the impact of the transient regime on the transport of suspended sediment.

Research paper thumbnail of Use of artificial flood events to demonstrate the invalidity of simple mixing models

Hydrological Sciences Journal, 2002

Page 1. Hydrofogical Sciences-J ournal-des Sciences Hydrologiques. 47(5) October 2002 §33 DISCUSS... more Page 1. Hydrofogical Sciences-J ournal-des Sciences Hydrologiques. 47(5) October 2002 §33 DISCUSSION Use of artificial flood events to demonstrate the invalidity of simple mixing models* TOMMY SW WONG School of Civil ...

Research paper thumbnail of Concentrations and loads of dissolved xenobiotics and hormones in two small river catchments of different land use in Luxembourg

Hydrological Processes, 2013

Research paper thumbnail of Assessment of different colour parameters for discriminating potential suspended sediment sources and provenance: A multi-scale study in Luxembourg

Geomorphology, 2010

Sediment colour has recently been used successfully to estimate suspended sediment sources in sma... more Sediment colour has recently been used successfully to estimate suspended sediment sources in small catchments using the fingerprinting approach. The methodology offers opportunity for further research since it provides a rapid and cheap means for investigating sediment sources. However, the colour-based fingerprinting approach has not yet been tested in medium and large catchments. This paper aims to test whether colour parameters are capable of discriminating sediment sources in a nested system of seven subcatchments ranging from 0.7 to 247 km 2 of the Attert River catchment, NW Luxembourg. Time-integrated suspended sediment samples and samples of potential sediment sources (land-use types and channel banks) were collected in all catchments. Sediment colour was then computed from diffuse reflectance spectrometry measurements (ASD FieldSpec-II spectrometer, 0.4-2.5 µm) taken over the visible wavelength range. Twenty-four colour parameters were derived from several colour space models (CIE xyY, CIE XYZ, RGB, Munsell HVC, Helmholtz chromaticity, CIELUV and CIELAB) and their ability to discriminate potential suspended sediment sources and provenance was evaluated and compared. Results demonstrated that timeintegrated suspended sediment samples collected in the study catchments had statistically different colour values. Moreover, these values always represented a mixture of the colour values measured on potential suspended sediment sources in the catchment. Inter-source colour contrasts (land-use types and channel banks) were observed in all catchments (Kruskal-Wallis H-test). However, although colour is able to distinguish potential sediment sources in small catchments, the level of source discrimination decreases as the catchment size increases, probably due to heterogeneous geology and pedology, intra-source variability and to source overlap. Nevertheless, in the studied medium-sized catchments (ranging from 19.4 to 247 km 2 ), colour could differentiate between topsoil and sub-surface (i.e. channel bank) material and/or up to three sources types. No single colour model had discrimination power across catchments, instead in each catchment a different combination of colour parameters gathered from different colour space models produced optimal discrimination of potential sediment sources. Furthermore, a colour-based fingerprinting approach did not possess potential for integrating spatial provenance and source type information because colour parameters could not discriminate between contrasting geological sub-areas. In summary, although colour parameters were not capable of discriminating the range of land-use type and channel banks as potential suspended sediment sources in medium-sized catchments, they afford substantial information and could be integrated into the classical fingerprinting approach together with other constituents (e.g. geochemistry, radionuclides and/or organic compounds).

Research paper thumbnail of Facing Hazardous Matter in Atmospheric Particles with NanoSIMS (2 pp)

Environmental Science and Pollution Research - International, 2007

Corresponding author (krein@lippmann.lu) hot spots in a nanometer scale. In regard to the health ... more Corresponding author (krein@lippmann.lu) hot spots in a nanometer scale. In regard to the health aspect, the hot spots consisting of toxic elements are particularly relevant as they react directly with the lung tissues.

Research paper thumbnail of Concentrations of dissolved herbicides and pharmaceuticals in a small river in Luxembourg

Environmental Monitoring and Assessment, 2011

Urban and agricultural areas affect the hydraulic patterns as well as the water quality of receiv... more Urban and agricultural areas affect the hydraulic patterns as well as the water quality of receiving drainage systems, especially of catchments smaller than 50 km 2 . Urban runoff is prone to contamination due to pollutants like pesticides or pharmaceuticals. Agricultural areas are possible sources of nutrient and herbicide contamination for receiving water bodies. The pollution is derived from leaching by subsurface flow, as well as wash-off and erosion caused by surface runoff. In the Luxembourgish Mess River catchment, the pharmaceutical and pesticide concentrations are comparable with those detected by other authors in different river systems worldwide. Some investigated pesticide concentrations infringe current regulations. The maximum allowable concentration for diuron of 1.8 μg l −1 is exceeded fourfold by measured 7.41 μg l −1 in a flood event. The load of dissolved pesticides reaching the stream gauge is primarily determined by the amount applied to the surfaces within the catchment area. Storm water runoff from urban areas causes short-lived but high-pollutant concentrations and moderate loads, whereas moderate concentrations and high loads are representative for agricultural inputs to the drainage system. Dissolved herbicides, sulfonamides, tetracyclines, analgesics and hormones can be used as indicators to investigate runoff generation processes, including inputs from anthropogenic sources. The measurements prove that the influence of kinematic wave effects on the relationship between hydrograph and chemographs should not be neglected in smaller basins. The time lag shows that it is not possible to connect analysed substances of defined samples to the corresponding section of the hydrograph.