Seasonal variations of natural ventilation and radon-222 exhalation in a slightly rising dead-end tunnel

The concentration activity of radon-222 has been monitored, with some interruptions, from 1997 to 2005 in the end section of a slightly rising, dead-end, 38-m long tunnel located in the Phulchoki hill, near Kathmandu, Nepal. While a high concentration varying from 6 x 10(3) Bq m(-3) to 10 x 10(3) Bq m(-3) is observed from May to September (rainy summer season), the concentration remains at a low level of about 200 Bq m(-3) from October to March (dry winter season). This reduction of radon concentration is associated with natural ventilation of the tunnel, which, contrary to expectations for a rising tunnel, takes place mainly from October to March when the outside air temperature drops below the average tunnel temperature. This interpretation is supported by temperature measurements in the atmosphere of the tunnel, a few meters away from the entrance. The temporal variations of the diurnal amplitude of this temperature indeed follow the ventilation rate deduced from the radon measurements. In the absence of significant ventilation (summer season), the radon exhalation flux at the rock surface into the tunnel atmosphere can be inferred; it exhibits a yearly variation with additional transient reductions associated with heavy rainfall, likely to be due to water infiltration. No effect of atmospheric pressure variations on the radon concentration is observed in this tunnel. This experiment illustrates how small differences in the location and geometry of a tunnel can lead to vastly different behaviours of the radon concentration versus time. This observation has consequences for the estimation of the dose rate and the practicability of radon monitoring for tectonic purposes in underground environments.     

When attempts at robbing prey turn fatal

Because group-hunting arboreal ants spread-eagle insect prey for a long time before retrieving them, these prey can be coveted by predatory flying insects. Yet, attempting to rob these prey is risky if the ant species is also an effective predator. Here, we show that trying to rob prey from Azteca andreae workers is a fatal error as 268 out of 276 potential cleptobionts (97.1?%) were captured in turn. The ant workers hunt in a group and use the “Velcro?” principle to cling firmly to the leaves of their host tree, permitting them to capture very large prey. Exceptions were one social wasp, plus some Trigona spp. workers and flies that landed directly on the prey and were able to take off immediately when attacked. We conclude that in this situation, previously captured prey attract potential cleptobionts that are captured in turn in most of the cases.     

Anaerobic digestion and recycling of kitchen waste: a review

About 1.6 billion tons of food are wasted worldwide annually, calling for advanced methods to recycle food waste into energy and materials. Anaerobic digestion of kitchen waste allows the efficient recovery of energy, and induces low-carbon emissions. Nonetheless, digestion stability and biogas production are variables, due to dietary habits and seasonal diet variations that modify the components of kitchen waste. Another challenge is the recycling of the digestate, which could be partly solved by more efficient reactors of anaerobic digestion. Here, we review the bottlenecks of anaerobic digestion treatment of kitchen waste, with focus on components inhibition, and energy recovery from biogas slurry and residue. We provide rules for the optimal treatment of the organic fraction of kitchen waste, and guidelines to upgrade the anaerobic digestion processes. We propose a strategy using an anaerobic dynamic membrane bioreactor to improve anaerobic digestion of kitchen waste, and a model for the complete transformation and recycling of kitchen waste, based on component properties.

     

The underground industry of wastewater adulteration: how to trick legal testing with COD removers

Environmental Chemistry Letters - Adulteration is an illegal practice often committed in food and cosmetic industries, yet rarely in environmental regulation compliance. The Chinese Ministry of...     

Improved electricity production and nitrogen enrichment during the treatment of black water using manganese ore-modified anodes

Environmental Chemistry Letters - The decline of fossil fuel availability is calling for alternative energy such as electricity produced by degradation of waste in microbial fuel cells. The...     

Meta-ecosystem engineering: nutrient fluxes reveal intraspecific and interspecific feedbacks in fragmented mussel beds

Ecologists still have to elucidate the complex feedback interactions operating among biodiversity and ecosystem processes in engineered systems. To address this, a field experiment was conducted to mimic natural mussel bed meta-ecosystems (Mytilus spp.) of the lower St. Lawrence Estuary (Quebec, Canada) and partition the effects of their biotic and abiotic properties and spatial structure on ecosystem processes and community dynamics of associated macro-invertebrates. We found positive intraspecific feedbacks between mussels and their recruits, and negative interspecific feedbacks between mussels and their associated ecosystem. These feedbacks were associated with mussel bed ecosystem processes (fluxes of ammonium and oxygen). In addition, we showed that proximity between mussel patches increased within-patch nutrient fluxes. Our study revealed the potential for meta-ecosystem engineering to drive feedback interactions between community and ecosystem functioning in marine fragmented systems. It also shows the relevance of meta-ecosystem theories as a conceptual framework to elucidate biotic and abiotic processes controlling ecosystem and community structure. Such framework could contribute to ecosystem-based management of spatially structured systems such as reserve networks and fragmented ecosystems.     

13C-dating, the first method to calculate the relative age of molecular substance homologues in soil

This article reports the design of ¹³C-dating, the first method to calculate the relative age of molecular substance homologues occurring in fractions from the same soil sample. Soil is a major carbon pool impacting modern climate by CO₂ release and uptake. Molecular substances that sequester carbon in soils are poorly known due to the absence of methods to study molecular-level C dynamics over agricultural time scales, e.g., 0–200 years. Here, I design a method to calculate the relative age of the plant-derived C₃₁ n-alkane occurring in 6 fractions from a soil sample naturally ¹³C-labelled by maize cropping during 23 years. Soil fractions are the bulk soil extract, two humin-encapsulated fractions and three particle-size fractions. Results show that C₃₁ n-alkane homologues have relative ages ranging from −6.7 years for the humin-encapsulated homologue to +25.1 years for the 200–2,000-μm fraction homologue. Such a wide variation of 31.8 years evidences temporal pools of molecular substances in soil. This finding also reveals that physical encapsulation can strikingly change the dynamics of a single molecular substance. ¹³C-dating thus allows to assess the carbon storage potential of molecular substances from crop soils. Such knowledge will help to identify molecular compounds, associated soil pools and agricultural practices that favour carbon sequestration. ¹³C-dating is further applicable to any environmental sample containing organic matter subjected to a ¹³C isotope shift with time. ¹³C-dating will also help to study the sequestration and delayed release of chemicals in various disciplines, such as pollutants in environmental sciences, pharmaceuticals in medicine, and nutrients in food science.