Thermal-elastic stresses and the criticality of the continental crust

Heating or cooling can lead to high stresses in rocks due to the different thermal-elastic properties of minerals. In the upper 4 km of the crust, such internal stresses might cause fracturing. Yet it is unclear if thermal elasticity contributes significantly to critical stresses and failure deeper in Earth's continental crust, where ductile creep causes stress relaxation. We combined a heating experiment conducted in a Synchrotron microtomograph (Advanced Photon Source, USA) with numerical simulations to calculate the grain-scale stress field in granite generated by slow burial. We find that deviatoric stresses >100 MPa can be stored during burial, with relaxation times from 100's to 1000's ka, even in the ductile crust. Hence, grain-scale thermal-elastic stresses may serve as nuclei for instabilities, thus rendering the continental crust close to criticality

Microeukaryotic gut parasites in wastewater treatment plants: diversity, activity, and removal

Background: During wastewater treatment, the wastewater microbiome facilitates the degradation of organic matter, reduction of nutrients, and removal of gut parasites. While the latter function is essential to minimize public health risks, the range of parasites involved and how they are removed is still poorly understood. Results: Using shotgun metagenomic (DNA) and metatranscriptomic (RNA) sequencing data from ten wastewater treatment plants in Switzerland, we were able to assess the entire wastewater microbiome, including the often neglected microeukaryotes (protists). In the latter group, we found a surprising richness and relative abundance of active parasites, particularly in the inflow. Using network analysis, we tracked these taxa across the various treatment compartments and linked their removal to trophic interactions. Conclusions: Our results indicate that the combination of DNA and RNA data is essential for assessing the full spectrum of taxa present in wastewater. In particular, we shed light on an important but poorly understood function of wastewater treatment - parasite removal

High diversity of diazotrophs in the forefield of a receding alpine glacier

ISSN:1432-184XISSN:0095-362

Large iron isotope fractionation at the oxic-anoxic boundary in Lake Nyos

The degassing of volcanic Lake Nyos (Cameroon) provides the opportunity to study the strong isotopic variation of dissolved Fe(II) in a well constrained redox cycle and to identify the governing processes by reaction-transport modeling. Two depth profiles sampled in the lake in March 2004 and 2005 reveal an increase in iron concentrations and δ57Fe from around 1 mg L- 1 and - 1.88‰ at 55 m depth up to 344 mg L- 1 and + 0.83‰ at the bottom of the lake, respectively. A steep increase in δ57Fe was observed across the oxic-anoxic boundary. As many biological and geochemical processes are known to fractionate Fe isotopes, we used a calibrated reaction-transport model to disentangle the processes governing the Fe cycle. The model combines the isotopic signatures of dissolved Fe(II) and settling Fe(III) particles with the concentration profiles and settling fluxes of the Fe particles in the lake. We show that the strong shift in δ57Fe is caused by isotopic fractionation via dissimilatory Fe reduction across the oxic-anoxic boundary of Lake Nyos. The shift towards more positive values below the oxic-anoxic interface could be attributed to vertical mixing of a heavier component from the bottom of the lake. © 2009 Elsevier B.V. All rights reserved

Nitrogen isotope effects can be used to diagnose N transformations in wastewater anammox systems

Anaerobic ammonium oxidation (anammox) plays an important role in aquatic systems as a sink of bioavailable nitrogen (N), and in engineered processes by removing ammonium from wastewater. The isotope effects anammox imparts in the N isotope signatures (N-15/N-14) of ammonium, nitrite, and nitrate can be used to estimate its role in environmental settings, to describe physiological and ecological variations in the anammox process, and possibly to optimize anammox-based wastewater treatment. We measured the stable N-isotope composition of ammonium, nitrite, and nitrate in wastewater cultivations of anammox bacteria. We find that the N isotope enrichment factor (15)epsilon for the reduction of nitrite to N-2 is consistent across all experimental conditions (13.5 parts per thousand +/- 3.7 parts per thousand), suggesting it reflects the composition of the anammox bacteria community. Values of (15)epsilon for the oxidation of nitrite to nitrate (inverse isotope effect, -16 to -43 parts per thousand) and for the reduction of ammonium to N-2 (normal isotope effect, 19-32 parts per thousand) are more variable, and likely controlled by experimental conditions. We argue that the variations in the isotope effects can be tied to the metabolism and physiology of anammox bacteria, and that the broad range of isotope effects observed for anammox introduces complications for analyzing N-isotope mass balances in natural systems