Spatial variability of nitrous oxide and methane emissions from an MBT landfill in operation: Strong N2O hotspots at the working face

Mechanical biological treatment (MBT) is an effective technique, which removes organic carbon from municipal solid waste (MSW) prior to deposition. Thereby, methane (CH₄) production in the landfill is strongly mitigated. However, direct measurements of greenhouse gas emissions from full-scale MBT landfills have not been conducted so far. Thus, CH₄ and nitrous oxide (N₂O) emissions from a German MBT landfill in operation as well as their concentrations in the landfill gas (LFG) were measured. High N₂O emissions of 20–200 g CO₂ eq. m^?2 h^?1 magnitude (up to 428 mg N m^?2 h^?1) were observed within 20 m of the working face. CH₄ emissions were highest at the landfill zone located at a distance of 30–40 m from the working face, where they reached about 10 g CO₂ eq. m^?2 h^?1. The MBT material in this area has been deposited several weeks earlier. Maximum LFG concentration for N₂O was 24.000 ppmv in material below the emission hotspot. At a depth of 50 cm from the landfill surface a strong negative correlation between N₂O and CH₄ concentrations was observed. From this and from the distribution pattern of extractable ammonium, nitrite, and nitrate it has been concluded that strong N₂O production is associated with nitrification activity and the occurrence of nitrite and nitrate, which is initiated by oxygen input during waste deposition. Therefore, CH₄ mitigation measures, which often employ aeration, could result in a net increase of GHG emissions due to increased N₂O emissions, especially at MBT landfills.     

Schadstoff-Ferntransport in die Arktis

The Arctic is still considered as one of the few unpolluted regions in the world. This is true if one compares the Arctic region with middle latitude regions which are influenced more by human activities. However, the Arctic region is not isolated from all human impacts. In recent years, high concentrations of persistent pollutants (organic chemicals, metals) were detected in top predators of the Arctic food chain and indigenous peoples from the Canadian and Greenland Arctic, although no local contamination sources are known. The comprehensive, scientific investigation of the past 20 years confirmed that the combination of atmospheric and waterborne long-range transport is the major source of the high concentrations of persistent organic pollutants (POPs) in the pristine Arctic environment. However, also pelagic marine organisms (e.g. Atlantic cod, marine mammals) can transport large amounts of persistent pollutants in their lipids and introduce contaminants into the Arctic food web. Thus, the pollutants are transported into the Arctic and subsequently accumulated through the short and unbranched Arctic food web of the top predators. The most accepted theory nowadays describes the long-range transport of persistent pollutants as a combination of atmospheric and sea current transport, or as a ‘global distillation’ process. Depending on such physical properties of the substances as vapour pressure and the ambient tempeature, persistent (semivolatile) contaminants are transported over different distances prior to deposition (sea surface, sediment, soil). After the deposition, however, and depending on the weather conditions and surrounding temperature, persistent pollutants will be re-evaporated into the atmosphere and undergo further atmospheric transport to the Arctic region. This process is also called the ‘grasshopper effect’. The global transport of persistent pollutants into Arctic regions can be described as a repeatedly occurring combination of atmospheric and waterborne transport in which the main transport vehicle depends on the physical properties of the transported compound. The role of characteristic meteorological conditions in the respective climate zones through which the contaminant is transported must not be underestimated. Strong seasonal differences in temperature and precipitation rule the global weather situation. Therefore, seasonal pattern differences occur for the distribution of some persistent pollutants in the Arctic environment depending on average temperature, main wind and sea current directions, humidity and day time light conditions (causing photochemical degradation). The consumption of traditionally hunted marine mammals (seals, whales) was identified as one of the main reasons for high contamination burdens in the Canadian and Greenland Inuit populations. Consequences and counter measures against high contamination loads in the Arctic human populations and ecosystems are currently under discussion. However, no comprehensive measures concerning restrictions of hunting traditions are taken by the respective governments to date due to the primary social consequences which are to be expected. The advising experts argue that such a restriction would destroy the original social structures of the Inuit populations. Therefore, the drawbacks of such a hunting restriction would weigh heavier than the expected positive effects of the reduction of contaminant burdens ‘Arctic dilemma’.     

Mapping carbon sequestration in forests at the regional scale - a climate biomonitoring approach by example of Germany

Background

The United Nations Framework Convention on Climate Change recognizes carbon (C) fixation in forests as an important contribution for the reduction of atmospheric pollution in terms of greenhouse gases. Spatial differentiation of C sequestration in forests either at the national or at the regional scale is therefore needed for forest planning purposes. Hence, within the framework of the Forest Focus regulation, the aim of this investigation was to statistically analyse factors influencing the C fixation and to use the corresponding associations in terms of a predictive mapping approach at the regional scale by example of the German federal state North Rhine-Westphalia. The results of the methodical scheme outlined in this article should be compared with an already-published approach applied to the same data which were used in the investigation at hand.

Methods

Site-specific data on C sequestration in humus, forest trees/dead wood and soil from two forest monitoring networks were intersected with available surface information on topography, soil, climate and forestal growing areas and districts. Next, the association between the C sequestration and the influence factors were examined and modelled by linear regression analyses. The resulting regression equations were applied on the surface data to predicatively map the C sequestration for the entire study area.

Results

The computations yielded an estimation of 146.7 mio t C sequestered in the forests of North Rhine-Westphalia corresponding to 168.6 t/ha. The calculated values correspond well to according specifications given by the literature. Furthermore, the results are almost identical to those of another pilot study where a different statistical methodology was applied on the same database. Nevertheless, the underlying regression models contribute only a low degree of explanation to the overall variance of the C fixation. This might mainly be due to data quality aspects and missing influence factors in the analyses.

Discussion

In another study, an alternative approach was introduced to map the spatial differentiation of C sequestration in North Rhine-Westphalia based on the combination of geostatistics, decision tree analyses and GIS techniques. As a result, the overall mean of C sequestration amounted for 177 t C/ha which is 8.4 t C/ha higher than what was calculated in the study at hand and 14 t C/ha below the roughly guessed German-wide mean of 191 t C/ha.

Conclusions

The surface estimations of C pools in living forest trees/dead wood, the humus layer and the mineral soil enable to map the fixation of the greenhouse gas CO₂ in forests at the regional scale. The estimations that were derived in this study are in good accordance with estimations based on techniques which, in contrast, did neither allow for spatial differentiation nor for mapping. The presented approach should be validated by application of other statistical techniques and by use of German wide inventory data. Furthermore, C sequestration should be modelled according to different climate change scenarios by combining statistical methods and dynamic modelling.     

Migratory orientation of red-eyed vireos,Vireo olivaceus,in relation to energetic condition and ecological context

How and when migrants integrate directional information from different sources may depend not only on the bird’s internal state, including fat stores, but also on the ecological context during passage. We designed experiments to (1) examine the influence of stored fat on the decision to migrate and on the choice of migratory direction and (2) investigate how the integration of orientation cue information is tied to energetic status in relation to migration across an ecological barrier. Migratory orientation of red-eyed vireos (Vireo olivaceus) at twilight was recorded using two different techniques, orientation cage experiments and free-flight release tests, during both fall and spring migration. During fall migration, the amount of stored fat proved decisive for directional selections of the vireos. Fat birds chose directions in accordance with migration across the Gulf of Mexico. Lean birds oriented either parallel to the coast line (cage tests) or moved inland (free-flight releases). Whereas only fat birds showed significant responses to experimental deflections of the geomagnetic field, lean birds displayed a tendency to shift their activity in the expected direction, making it difficult to evaluate the prediction that use of the magnetic compass is context dependent. Fat loads also had a significant effect on the decision to migrate, i.e., fat individuals were more likely to embark on migration than were lean birds (true for both cage and release experiments). During spring migration, a majority of experimental subjects were classified as lean, following their arrival after crossing the Gulf of Mexico, and oriented in seasonally appropriate directions. The vireos also showed significant responses to experimental deflections of the geomagnetic field regardless of their energetic status. Free-flight release experiments during spring migration revealed a significant difference in mean directions between clear sky and overcast tests. The difference may indicate a compensatory response to wind drift or possibly a need for celestial cues to calibrate the magnetic compass. Finally, this is the first demonstration of magnetic compass orientation in a North American vireo. Received: 15 December 1995/Accepted after revision: 24 March 1996