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Schirmer, Mario

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Schirmer, Mario
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https://libra.unine.ch/handle/123456789/163

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  • Publication
    Accès libre
    Quasi-Online Groundwater Model Optimization Under Constraints of Geological Consistency Based on Iterative Importance Sampling
    (2020-4)
    Ramgraber, Maximilian 
    ;
    Camporese, Matteo
    ;
    Renard, Philippe 
    ;
    Salandin, Paolo
    ;
    Schirmer, Mario 
    The increasing use of wireless sensor networks and remote sensing permits real‐time access to environmental observations. Data assimilation frameworks tap into such data streams to autonomously update and gradually improve numerical models. In hydrogeology, such methods are relevant in areas of long‐term interest in water quality and quantity, for example, in drinking water production. Unfortunately, accurate hydrogeological predictions often demand a degree of geological realism, which is difficult to reconcile with the operational limitations of many data assimilation frameworks. Alluvial aquifers, for example, are sometimes characterized by paleo‐channels of unknown extent and properties, which may act as preferential flow paths. Gradually optimizing such fields in real‐time or quasi‐real‐time settings is a formidable task. Besides subsurface properties, ill‐specified model forcings are a further source of predictive bias, which an optimizer could learn to compensate. In this study, we explore the use of a quasi‐online optimizer based on the iterative batch importance sampling framework for a groundwater model of a field site near Valdobbiadene, Italy. This site is characterized by the presence of paleo‐channels and heavily exploited for drinking water production and irrigation. We use Markov chain Monte Carlo steps to explore new parameterizations while maintaining consistency between states and parameters as well as conformance to a multipoint statistics training image. We also optimize a preprocessor designed to compensate for potential bias in the model forcing. We achieve promising and geologically consistent quasi‐real‐time optimization, albeit at the loss of parameter uncertainty.
  • Publication
    Accès libre
    Topsoil structure stability in a restored floodplain: Impacts of fluctuatingwater levels, soil parameters and ecosystem engineers
    (2017-6)
    Schomburg, Andreas Cédric 
    ;
    Schilling, Oliver 
    ;
    Guenat, C.
    ;
    Schirmer, Mario 
    ;
    Le Bayon, Renée-Claire 
    ;
    Brunner, Philip 
    Ecosystem services provided byfloodplains are strongly controlled by the structural stability of soils. The developmentof a stable structure infloodplain soils is affected by a complex and poorly understood interplay of hydrological,physico-chemical and biological processes. This paper aims at analysing relations betweenfluctuating groundwaterlevels, soil physico-chemical and biological parameters on soil structure stability in a restoredfloodplain. Water levelfluctuations in the soil are modelled using a numerical surface-water–groundwaterflow model and correlated tosoil physico-chemical parameters and abundances of plants and earthworms. Causal relations and multiple interactionsbetween the investigated parameters are tested through structural equation modelling (SEM). Fluctuating water levelsin the soil did not directly affect the topsoil structure stability, but indirectly through affecting plant roots and soil pa-rameters that in turn determine topsoil structure stability. These relations remain significant for mean annual days ofcomplete and partial (N25%) water saturation. Ecosystem functioning of a restoredfloodplain might already be affectedby thefluctuation of groundwater levels alone, and not only through completeflooding by surface water during afloodperiod. Surprisingly, abundances of earthworms did notshow any relation to other variables in the SEM. Thesefindingsemphasise that earthworms have efficiently adapted to periodic stress and harsh environmental conditions. Variabilityof the topsoil structure stability is thus stronger driven by the influence offluctuating water levels on plants than by theabundance of earthworms. This knowledge about the functional network of soil engineering organisms, soil parametersandfluctuating water levels and how they affect soil structural stability is of fundamental importance to define man-agement strategies of near-natural or restoredfloodplains in the future.
  • Publication
    Accès libre
    An integrated spatial snap-shot monitoring method for identifying seasonal changes and spatial changes in surface water quality
    (2016-8)
    Viswanathan, Vidhya Chittoor
    ;
    Jiang, Yongjun
    ;
    Berg, Michael
    ;
    Hunkeler, Daniel 
    ;
    Schirmer, Mario 
    Integrated catchment-scale management approaches in large catchments are often hindered due to the poor understanding of the spatially and seasonally variable pathways of pollutants. High-frequency monitoring of water quality at random locations in a catchment is resource intensive and challenging. A simplified catchment-scale monitoring approach is developed in this study, for the preliminary identification of water quality changes – Integrated spatial snap-shot monitoring (ISSM). This multi-parameter monitoring approach is applied using the isotopes of water (δ18O-H2O and δD) and nitrate (δ15N-NO3− and δ18O-NO3−) together with the fluxes of nitrate and other solutes, which are used as chemical markers. This method involves selection of few sampling stations, which are identified as the hotspots of water quality changes within the catchment. The study was conducted in the peri-alpine Thur catchment in Switzerland, with two snap-shot campaigns (representative of two widely varying hydrological conditions), in summer 2012 (low flow) and spring 2013 (high flow). Significant spatial (varying with elevation) and seasonal changes in the sources of water were observed between the two seasons. A spatial variation of the sources of nitrate and the solute loads was observed, in tandem with the land use changes in the Thur catchment. There is a seasonal shift in the sources of nitrate, it varies from a strong treated waste water signature during the low flow season to a mixture of other sources (like soil nitrogen derived from agriculture), in the high flow season. This demonstrates the influence of other sources that override the influence of waste water treatment plants (WWTPs) during high flow in the Thur River and its tributaries. This method is expected to be a cost-effective alternative, providing snap-shots, that can help in the preliminary identification of the pathways of solutes and their seasonal/spatial changes in catchments.
  • Publication
    Accès libre
    Perchloroethene source delineation using carbon-chlorine isotopic analysis: field investigations of isotopic signature variability / Perchlorethen-Quellendifferenzierung mittels Kohlenstoff-Chlor-
    (2015-12)
    Badin, Alice 
    ;
    Schirmer, Mario 
    ;
    Wermeille, Christiane
    ;
    Hunkeler, Daniel 
    When dealing with contaminated sites, identifying the source of contamination is critical for regulatory purposes. For chlorinated ethenes, previous studies have shown that dual carbon-chlorine (C-Cl) stable isotope analysis could be a key to address this issue as isotopic signatures vary between manufacturers and therefore, supposedly between sources. A successful application of this method relies on the assumption that different sources in the field will also show different signatures. Since the solvents used in the past are no longer available, this study aimed at investigating the extent of applicability of C-Cl stable isotope measurements for source identification based on field investigations. Ten sites which covered all of Switzerland and various sectors employing perchloroethene (PCE) were chosen. Differences were observed between some sites, suggesting that this method could be successfully applied. Other sites showed very similar isotopic signatures, indicating that this method applicability is site-specific. Additionally, the isotopic signature variability between sites was less significant than between the values previously reported for solvents from various manufacturers from North America. It was also confirmed that PCE reductive dechlorination should be considered when applying C-Cl isotope analysis for source identification. © 2015, Springer-Verlag Berlin Heidelberg.
  • Publication
    Métadonnées seulement
    Pulsed gas injection: A minimum effort approach for enhanced natural attenuation of chlorobenzene in contaminated groundwater
    (2009)
    Balcke, Gerd Ulrich
    ;
    Paschke, Heidrun
    ;
    Vogt, Carsten
    ;
    Schirmer, Mario 
    Chlorobenzene-contaminated groundwater was used to assess pulsed gas sparging as a minimum effort aeration strategy to enhance intrinsic natural attenuation. In contrast to existing biosparging operations, oxygen was supplied at minimum rate by reducing the gas injection frequency to 0.33 day(-1). Field tests in a model aquifer were conducted in a 12 m long reactor, filled with indigenous aquifer material and continuously recharged with polluted groundwater over 3 years. The closed arrangement allowed yield balances, cost accounting as well as the investigation of spatial distributions of parameters which are sensitive to the biodegradation process. Depending on the injection frequency and on the gas chosen for injection (pure oxygen or air) oxygen-deficient conditions prevailed in the aquifer. Despite the limiting availability of dissolved oxygen in the groundwater, chlorobenzene degradation under oxygen-deficient conditions proved to be more effective than under conditions with dissolved oxygen being available in high concentrations. (C) 2009 Elsevier Ltd. All rights reserved.
  • Publication
    Métadonnées seulement
    Mass fluxes and spatial trends of xenobiotics in the waters of the city of Halle, Germany
    (2008)
    Reinstorf, Frido
    ;
    Strauch, Gerhard
    ;
    Schirmer, Kristin
    ;
    Gläser, Hans-Reinhard
    ;
    Möder, Monika
    ;
    Wennrich, Rainer
    ;
    Osenbrück, Karsten
    ;
    Schirmer, Mario 
  • Publication
    Métadonnées seulement
    Evaluation and field-scale application of an analytical method to quantify groundwater discharge using mapped streambed temperatures
    (2007)
    Schmidt, Christian
    ;
    Conant, Brewster
    ;
    Bayer-Raich, Marti
    ;
    Schirmer, Mario 
    A method for calculating groundwater discharge through a streambed on a sub-reach to a reach scale has been developed using data from plan-view mapping of streambed temperatures at a uniform depth along a reach of a river or stream. An analytical solution of the one-dimensional steady-state heat-diffusion-advection equation was used to determine fluxes from observed temperature data. The method was applied to point measurements of streambed temperatures used to map a 60 m tong reach of a river by Conant Jr. [Conant Jr. B., 2004. Delineating and quantifying ground water discharge zones using streambed temperatures. Ground Water 42(2), 243-257] and relies on the underlying assumption that streambed temperatures are in a quasi-steady-state during the period of mapping. The analytical method was able to match the values and pattern of flux previously obtained using an empirical, relationship that related streambed temperatures to fluxes obtained from piezometers and using Darcy's taw. A second independent test of the analytical method using temperature mapping and seepage meter fluxes along a first-order stream confirmed the validity of the approach. The USGS numerical. heat transport model VS2DH was also used to evaluate the thermal. response of the streambed sediments to transient variations in surface water temperatures and showed that quasi-steady-state conditions occurred for most, but not all, conditions. During mapping events in the winter, quasi-steady-state conditions were typically observed for both high and tow groundwater discharge conditions, but during summer mapping events quasi-steady-state conditions were typically not achieved at low flux areas or where measurements were made at shallow depths. Major advantages of using this analytical method include: it can be implemented using a spreadsheet; it does not require the installation or testing of piezometers or seepage meters (although they would help to confirm the results); and it needs only a minimal amount of input data related to water temperatures and the thermal properties of water and the sediments. The field results showed the analytical solution tends to underestimate high fluxes. However, a sensitivity analysis of possible model inputs shows the solution is relatively robust and not particularly sensitive to small uncertainties in input data and can produce reasonable flux estimates without the need for calibration. (c) 2007 Elsevier B.V. All rights reserved.
  • Publication
    Métadonnées seulement
    Comparative assessment of regionalisation methods of monitored atmospheric deposition loads
    (2005)
    Reinstorf, Frido
    ;
    Binder, Maja
    ;
    Schirmer, Mario 
    ;
    Grimm-Strele, Jost
    ;
    Walther, Wolfgang
    The objective of this investigation is to assess the suitability of well-known regionalisation methods of data from existing deposition monitoring networks for use in water resources management. For this purpose a comparison of the applicability and accuracy of various regionalisation. methods was made. A crucial point is the data demand of the various methods. In,this investigation the deterministic and geostatistical methods inverse distance weighting (113W), ordinary kriging (OK) and external drift kriging (EDK) as well as the chemical transport models METRAS-MUSCAT, EMEP, EDACS add EUTREND have been characterised and evaluated. The methods IDW and OK have been applied to the investigation areas-the German Federal States of Lower Saxony and Saxony. An evaluation of these methods was carried out with a cross-validation procedure. The result was in most cases a higher accuracy for the OK method. The EDK method has been investigated in order to find suitable drift variables from the parameters precipitation amount, altitude and wind direction. With help of a correlation analysis a suitable drift variable could not be found. After the application of OK, verification was. carried out by a comparison of the estimated data set with an independently determined data set. The result was a relatively smaller deviation of the estimated data set. The investigation considers data from routine monitoring networks as well as networks for special applications and has been carried out on the basis of monitoring networks of the two. states. The investigated database was wet and bulk deposition of the substances NH4+, SO42-, NO3-, Na+, Pb2+, and Cd2+, in Lower Saxony SO42- in Saxony. From this, a consistent database of bulk deposition data was built. From all applied methods OK proved to cope best with the data deficiencies that were found. (c) 2005 Elsevier Ltd. All rights reserved.