Does upward seepage of river water and storm water runoff determine water quality of urban drainage systems in lowland areas? A case study for the Rhine–Meuse delta

The water quality of urban drainage ditches in lowlands in the Rhine‐Meuse delta was analysed with principal component analysis (PCA) during a dry period and a rain storm, and related to the seepage of polluted river water and effective impervious area (EIA). This was done in order to test the hypothesis that seepage of river water and storm water runoff from impervious areas strongly determine the water quality of urban drainage systems along large lowland rivers. Our analysis revealed that upward seepage of groundwater originating from rivers Rhine and Meuse was positively correlated with nitrate, potassium, sodium and chloride and negatively correlated with alkalinity, calcium, magnesium and iron. EIA was correlated with very few environmental variables (i.e. phosphate, pH and iron in the dry period and iron during the rain storm). Nickel and zinc concentrations generally exceeded the maximum allowable concentrations (MAC), while lead and phosphorus concentrations were just above the nutrient standards and MAC in a few locations during the rain storm. To optimize water quality in urban water systems, attention should be paid to all sources of pollution and not only to EIA. The impact of local groundwater seepage originating from large rivers in lowlands on the chemistry of urban water systems is often underestimated and should be taken into account when assessing water quality and improving water quality status. Copyright © 2009 John Wiley & Sons, Ltd.     

Mass fluxes of xenobiotics below cities: challenges in urban hydrogeology

Urban areas are the focus of major ecological, social and economical activity. They are thus also prime locations of increasing conflict with regard to water use and water protection. As a direct and/or indirect consequence of urban land use and human activity, urban water systems are frequently polluted with organic contaminants including waste water-born xenobiotics such as pharmaceuticals, personal care products (collectively known as PPCPs) and endocrine-active substances. This study reviews new integrated methodologies including flux calculations as well as chemical investigations for determining the impact of human activities on urban water systems and on processes within the urban watershed. The use of indicator substances, representing different contaminant sources and pathways, integral pumping tests and mass balance approaches are suitable alternatives within these environments. The issues are explored using contaminant mass balance examples from Halle/Saale and Leipzig, Germany.     

Carbon Sequestration and Release from Antarctic Lakes: Lake Vida and West Lake Bonney (McMurdo Dry Valleys)

Perennial ice covers on many Antarctic lakes have resulted in high lake inorganic carbon contents. The objective of this paper was to evaluate and compare the brine and CO₂ chemistries of Lake Vida (Victoria Valley) and West Lake Bonney (Taylor Valley), two lakes of the McMurdo Dry Valleys (East Antarctica), and their potential consequences during global warming. An existing geochemical model (FREZCHEM-15) was used to convert measured molarity into molality needed for the FREZCHEM model, and this model added a new algorithm that converts measured DIC into carbonate alkalinity needed for the FREZCHEM model. While quite extensive geochemical information exists for ice-covered Taylor Valley lakes, such as West Lake Bonney, only limited information exists for the recently sampled brine of >25 m ice-thick Lake Vida. Lake Vida brine had a model-calculated pCO₂ = 0.60 bars at the field pH (6.20); West Lake Bonney had a model-calculated pCO₂ = 5.23 bars at the field pH (5.46). Despite the high degree of atmospheric CO₂ supersaturation in West Lake Bonney, it remains significantly undersaturated with the gas hydrate, CO₂·6H₂O, unless these gas hydrates are deep in the sediment layer or are metastable having formed under colder temperatures or greater pressures. Because of lower temperatures, Lake Vida could start forming CO₂·6H₂O at lower pCO₂ values than West Lake Bonney; but both lakes are significantly undersaturated with the gas hydrate, CO₂·6H₂O. For both lakes, simulation of global warming from current subzero temperatures (?13.4 °C in Lake Vida and ?4.7 °C in West Lake Bonney) to 10 °C has shown that a major loss of solution-phase carbon as CO₂ gases and carbonate minerals occurred when the temperatures rose above 0 °C and perennial ice covers would disappear. How important these Antarctic CO₂ sources will be for future global warming remains to be seen. But a recent paper has shown that methane increased in atmospheric concentration due to deglaciation about 10,000 years ago. So, CO₂ release from ice lakes might contribute to atmospheric gases in the future.     

Runout analysis of a large rockfall in the Dolomites/Italian Alps using LIDAR derived particle sizes and shapes

LiDAR data were used to quantify and analyse a rockfall event which occurred in 2003 in the Western Dolomites (Italian Alps). In addition to previously existing airborne laserscanning (ALS) data, high resolution terrestrial laserscanning (TLS) data were collected. By using the original point clouds, the volume, axial ratio and runout length of single boulders as well as the surface roughness in the runout zone of the rockfall were derived. The total volume of the rockfall event of approximately 10 000 m³ was estimated by a reconstruction of the pre‐event surface at the detachment zone. The analysis of the laser scanning data of the accumulation zone revealed a power law scaling for boulder volumes larger than 8 m³. The dependence of runout length on boulder volume is complex; it is moderated by particle sphericity. In addition, we used ALS and TLS data to derive the spatial distribution of surface roughness on the talus cone. TLS allow for more accurate roughness mapping than ALS data, but for most applications the point density of ALS data seems to be sufficiently high to derive measures of roughness. Different sampling approaches for plane fitting on the scale of 5 m did not show significant effects besides the computational time. The results of our analyses provide important perspectives for rockfall modelling and process understanding with potential applications in both ‘applied’ (natural hazards) and ‘pure’ geomorphological research. Copyright © 2012 John Wiley & Sons, Ltd.     

Ozone Production Efficiency in Savanna and Forested Areas during the EXPRESSO Experiment

NO, NO_x, NO_y and O₃ have been measuredduring the airborne EXPRESSO experiment, November 96,which took place near Bangui (Central Africa) at thebeginning of the dry season. This period correspondsto an intense burning activity. Chemical andphotochemical characteristics of the planetaryboundary layer, which corresponds most of the time tothe monsoon layer, and the Harmattan layer, which issituated above the latter, have been studied forsavanna as well as rain forest areas. These two layersare very different when considering the chemicalcomposition (especially for ozone and NO_z) andthe photochemical age.The relationship of photochemical ozone productionversus photochemical NO_x oxidation products hasbeen investigated. Results indicate an ozoneproduction efficiency (OPE) ranging from 6.3 to 14.8in the planetary boundary layer. Thus, this layer ischaracteristic of a photochemically young and activeair mass. In this layer, the ozone potentialproduction increases with the air mass photochemicalage. On the other hand, the Harmattan layer shows anOPE ranging from 4.6 to 7.4. These values arecharacteristic of photochemically well-aged airmasses. In this layer, the ozone potential productionseems to be exhausted with values around 4.0 (i.e., 4ozone molecules produced for each NO_x moleculeemitted).     

Identification of Atlantic water inflow on the north Svalbard shelf during the Holocene

Nordaustlandet is located in the northeastern part of the Svalbard archipelago, within the northernmost reach of the West Spitsbergen Current. This current transports Atlantic water to the Arctic Ocean along the western and northern Svalbard margins. This region is well-suited for reconstructing the history of changing Atlantic water inflow to the Arctic Ocean. We studied the marine sediment core HH12-04-GC from Rijpfjorden. Benthic foraminiferal assemblages and sedimentological data are combined to reconstruct the palaeoenvironment of the fjord from the end of the last local deglaciation to the late Holocene. The local deglaciation, between 11.3 and 10.6 cal ka bp , was dominated by active glacier calving processes, associated with a strong inflow of Atlantic water. This led to the establishment of glaciomarine conditions. The Holocene was initially characterised by a relatively stable and warm environment associated with a strong contribution of Atlantic water. Glaciomarine influence progressively decreases after 9.7 cal ka bp and the Atlantic water contribution increases. The late Holocene displayed a similar environment to today, with the influence of glaciomarine conditions and limited Atlantic water inflow. These results confirm that Atlantic water inflows made a continuous contribution to northern Nordaustlandet throughout the postglacial period.     

The BEAM-project: prediction and assessment of mixture toxicities in the aquatic environment

Freshwater and marine ecosystems are exposed to various multi-component mixtures of pollutants. Nevertheless, most ecotoxicological research and chemicals regulation focus on hazard and exposure assessment of individual substances only, the problem of chemical mixtures in the environment is ignored to a large extent. In contrast, the assessment of combination effects has a long tradition in pharmacology, where mixtures of chemicals are specifically designed to develop new products, e.g. human and veterinary drugs or agricultural and non-agricultural pesticides. In this area, two concepts are frequently used and are thought to describe fundamental relationships between single substance and mixture effects: Independent Action (Response Addition) and Concentration Addition. The question, to what extent these concepts may also be applied in an ecotoxicological and regulatory context may be considered a research topic of major importance, as the concepts would allow to make use of already existing single substance toxicity data for the predictive assessment of mixture toxicities. Two critical knowledge gaps are identified: (a) There is a lack of environmental realism, as a huge part of our current knowledge about the applicability of the concepts is restricted to artificial situations with respect to mixture composition or biological effect assessment. (b) The knowledge on what exactly is needed for using the concepts as tools for the predictive mixture toxicity assessment is insufficient. Both gaps seriously hamper the necessary, scientifically sound consideration of mixture toxicities in a regulatory context.In this paper, the two concepts will be briefly introduced, the necessity of considering the toxicities of chemical mixtures in the environment will be demonstrated and the applicability of Independent Action and Concentration Addition as tools for the prediction and assessment of mixture toxicities will be discussed. An overview of the specific aims and approaches of the BEAM project to fill in the identified knowledge gaps is given and first results are outlined.     

On the determination of the closure parameters in higher-order closure models

In higher-order closure models at least the pressure redistribution and the dissipation of the turbulent kinetic energy and the temperature variance have to be parameterized. Due to this, the introduction of proportionality coefficients — the so-called closure parameters — is forced, which have to be determined before the model is used. We compare a group of models which use the return-to-isotropy hypothesis (Rotta, 1951) to describe the pressure redistribution and assume local isotropy for the smallest eddies in order to parameterize the dissipation. Special concern is given to the method of Mellor and Yamada (1982). Some of the closure parameters are re-derived on the basis of sensitivity studies requiring that both shear production and buoyancy behave in a realistic way if pressure redistribution or dissipation is changed by varying the closure parameters. This set of parameters is compared with those obtained by fitting to experimental data, by use of the Monin-Obukhov similarity theory and by considering ratios of variances, covariances and mean flow gradients, respectively. It is shown that the various sets of closure parameters are at least of the same order. The differences give some insight into the advantages and disadvantages of the various determination procedures. However, the general accordance of the different parameter sets supports the assumption of universal constants.