Department Water Resources and Drinking Water

Master thesis topics 2018

Coupling between surface- and ground-carbon cycling delineated by millifluidics: Implications for soil respiration in a changing environment

The respiratory release of carbon dioxide (CO2) from the Earth’s soil into the atmosphere is a major, yet poorly understood, flux in the global carbon cycle. Understanding soil respiration sensitivity to elevated atmospheric CO2 (eCO2) and/or climatic warming remains one of the key sources of uncertainty in projecting terrestrial carbon balance and likely future shifts in the global climate. This study aims to deepen our mechanistic understanding of hidden mechanisms neither accounted for by large-scale Earth system models nor readily quantified by field experiments. We specifically explore the role of leaf-level response to eCO2 and/or temperature in regulating soil moisture (water saving effects) and the resulting impacts on CO2 release from soil due to root and rhizomicrobial respiration.

Over the course of this project, students have the opportunity to carry out some of the following tasks as part of their Master thesis:

  1. (1)  Design and fabrication of millifluidic setups resembling natural soil with microbial habitat subject to various water saturation conditions

  2. (2)  Perform experiments to visualize spatio-temporal distribution of soil water and subsurface O2 and/or CO2 gas concentrations (i.e., soil respiration hot spots) in response to changes in environmental conditions

  3. (3)  Develop a numerical model and perform simulations to study the flow field and transport through the micromodel

  4. (4)  Develop an analytical model to parametrize carbon balance dynamics under prescribed environmental conditions and determine whether (and how) the whole system could be maintained as a carbon sink

For more information, contact Dr. Erfan Haghighi (erfan.haghighi@eawag.ch) or Dr. Joaquin Jimenez-Martinez (jjimenez@ethz.ch).

Characterization of long-lived photooxidants in aquatic photochemistry

Direct and indirect phototransformations are important processes for the abatement of organic contaminants in the aquatic environment. Dissolved organic matter (DOM) is the main absorber of sunlight in most surface waters and can induce the indirect phototransformation of a variety of organic contaminants, thus enhancing their transformation in the aquatic environment. The dominant reactive intermediates in these indirect phototransformations are currently assumed to be excited triplet states of the DOM. However, there is evidence that other photooxidants, formed upon absorption of sunlight by DOM and termed as long-lived photooxidants (LLPOs), are particularly effective in the phototransformation of electron-rich contaminants. These still largely undefined photooxidants might drastically enhance the abatement of such contaminants with respect to current estimates. The main goals of the overarching project (funded by the Swiss National Science Foundation) consist in identifying the classes and types of contaminants prone to transformation induced by LLPOs and in characterizing the chemical nature of LLPOs.

Within the master thesis project, diagnostic kinetic tests are planned to elucidate the chemical nature of long-lived photooxidants (LLPOs). These kinetic tests will consist in investigating the effect of oxygen concentration, pH and addition of scavengers of LLPOs on the rate constants for the indirect phototransformation of selected organic contaminants. The evaluation of the transformation induced by LLPOs will be done by quantifying the difference in pseudo-first-order transformation rate constants measured for two initial concentration values of the selected contaminants (1.0 × 10˗7 M and 5.0 × 10˗6M, respectively).

Further experimental methods will include steady-state irradiations using photoreactors and HPLC analyses to quantify the residual concentration of the studied contaminants.

For further information, contact Dr. Silvio Canonica or Stephanie Remke.