• We investigate the dynamics of pollutants and nutrients in the environment.

  • We elucidate processes and mechanisms in the field and laboratory.

  • Nanogeosciences: exploring the nanoscale to understand processes of global relevance.

  • We use models to quantify processes and mechanisms.


Latest publications

Chemosymbiotic bivalves contribute to the nitrogen budget of seagrass ecosystems

In many seagrass sediments, lucinid bivalves and their sulfur-oxidizing symbionts are thought to underpin key ecosystem functions, but little is known about their role in nutrient cycles, particularly nitrogen. We used natural stable isotopes, elemental analyses, and stable isotope probing to study the ecological stoichiometry of a lucinid symbiosis in spring and fall. Chemoautotrophy appeared to dominate in fall, when chemoautotrophic carbon fixation rates were up to one order of magnitude higher as compared with the spring, suggesting a flexible nutritional mutualism. In fall, an isotope pool dilution experiment revealed carbon limitation of the symbiosis and ammonium excretion rates up to tenfold higher compared with fluxes reported for nonsymbiotic marine bivalves. These results provide evidence that lucinid bivalves can contribute substantial amounts of ammonium to the ecosystem. Given the preference of seagrasses for this nitrogen source, lucinid bivalves’ contribution may boost productivity of these important blue carbon ecosystems.
Ulisse Cardini, Marco Bartoli, Sebastian Lücker, Maria Mooshammer, Julia Polzin, Raymond W. Lee, Vesna Micić, Thilo Hofmann, Miriam Weber, Jillian M. Petersen
2019 - The ISME journal, in press

Mercury Isotope Fractionation in the Subsurface of a Hg(II) Chloride-Contaminated Industrial Legacy Site

To understand the transformations of mercury (Hg) species in the subsurface of a HgCl2-contaminated former industrial site in southwest Germany, Hg isotope analysis was combined with an investigation of Hg forms by a four-step sequential extraction protocol (SEP) and pyrolytic thermodesorption. Data from two soil cores revealed that the initial HgCl2was partly reduced to metallic Hg(0) and that Hg forms of different mobility and oxidation state coexist in the subsurface. The most contaminated sample (K2-8, 802 mg kg–1 Hg) had a bulk δ202Hg value of around −0.43 ± 0.06‰ (2SD), similar to published average values for industrial Hg sources. Other sample signatures varied significantly with depth and between SEP pools. The most Hg-rich samples contained mixtures of Hg(0) and Hg(II) phases, and the water-extractable, mobile Hg pool exhibited heavy δ202Hg values of up to +0.18‰. Sequential water extracts revealed slow dissolution kinetics of mobile Hg pools, continuously releasing isotopically heavy Hg into solution. This was further corroborated by heavy δ202Hg values of groundwater samples. Our results demonstrate that the Hg isotope signature of an industrial contamination source can be significantly altered during the transformations of Hg species in the subsurface, which complicates source tracing applications but offers the possibility of using Hg isotopes as process tracers in contaminated subsurface systems.

Flora M. Brocza, Harald Biester, Jan-Helge Richard, Stephan M. Kraemer, Jan G. Wiederhold
2019 - Environmental Science & Technology, 13: 7296-7305

In situ remediation of subsurface contamination: opportunities and challenges for nanotechnology and advanced materials

Complex subsurface contamination domains and limited efficacy of existing treatment approaches pose significant challenges to site remediation and underscore the need for technological innovation to develop cost-effective remedies. Here, we discuss opportunities for nanotechnology-enabled in situ remediation technologies to address soil and groundwater contamination. The discussion covers candidate nanomaterials, applications of nanomaterials to complement existing remediation approaches and address emerging contaminants, as well as the potential barriers for implementation and strategies and research needs to overcome these barriers. Promising nanomaterials in subsurface remediation include multi-functional nanocomposites for synergistic contaminant sequestration and degradation, selective adsorbents and catalysts, nano-tracers for subsurface contaminant delineation, and slow-release reagents enabled by stimuli-responsive nanomaterials. Limitations on mixing and transport of nanomaterials in the subsurface are severe constraints for in situ applications of these materials. Mixing enhancements are needed to overcome transport limitations in laminar flow environments. Reactive nanomaterials may be generated in situ to remediate contamination in low hydraulic conductivity zones. Overall, nano-enabled remediation technologies may improve remediation performance for a broad range of legacy and emerging contaminants. These technologies should continue to be developed and tested to discern theoretical hypotheses from feasible opportunities, and to establish realistic performance expectations for in situ remediation techniques using engineered nanomaterials alone or in combination with other technologies.

Tong Zhang, Gregory V. Lowry, Natalie L. Capiro, Jianmin Chen, Wei Chen, Yongsheng Chen, Dionysios D. Dionysiou, Daniel W. Elliott, Subhasis Ghoshal, Thilo Hofmann, Heileen Hsu-Kim, Joseph Hughes, Chuanjia Jiang, Guibin Jiang, Chuanyong Jing, Michael Kavanaugh, Qilin Li, Sijin Liu, Jie Ma, Bingcai Pan, Tanapon Phenrat, Xiaolei Qu, Xie Quan, Navid Saleh, Peter J. Vikesland, Qiuquan Wang, Paul Westerhoff, Michael S. Wong, Tian Xia, Baoshan Xing, Bing Yan, Lunliang Zhang, Dongmei Zhouaa, Pedro J. J. Alvarez
2019 - Environmental Science: Nano, 5: 1283-1302