No abstract

Stable isotopes provide a powerful means of elucidating the trophic ecology of organisms. Analyses of variation in the ratio of nitrogen isotopes (d 15 N) can provide insights into the trophic position of species with broad diets and the ability to occupy multiple positions in food webs, such as ants. The most powerful studies compare subjects across various spatial scales, but to do so, local variation in d 15 N baselines must be taken into account. To date, a wide variety of baseline calibration methods have been employed, leading some authors to suggest that a standard approach is needed, and that the reality of environmental variation necessitates that this should be at fine scales. In this study, we examine the fine-scale variation in d 15 N value of colonies of the ant Formica kozlovi Dlussky (Hymenoptera: Formicidae: Formicini) along a sloped transect in Mongolia, and compare these with values for associated soils in an effort to shed further light on this issue. We find variation in ant d 15 N to the order of one trophic level (ca. 3&), over a distance of only 1 km. Ant d 15 N was highly correlated with soil d 15 N, and variation in mineral soil d 15 N explained ca. 81% of the variation in ant d 15 N. This study underlines the importance of local-scale baseline corrections for isotopic studies, particularly in environments where baseline variation might be expected. It further suggests that d 15 N of mineral soils may provide a suitable baseline for ecological studies of terrestrial arthropods.

The soil organic matter (SOM) is searched for the biomarkers and specific features associated with the effect of wildfires by the case study of peat soil, Rheic Hemic Histosol (Lignic), in the south of the middle taiga of the Komi Republic. It is shown that fires considerably influence the peat organic matter. Pyrogenic activity is assessed according to the content of charcoal particles. SOM is examined using solid-state 13C-NMR spectroscopy to determine the concentrations of polycyclic aromatic hydrocarbons (PAHs) and benzene polycarboxylic acids (BPCAs). The used methods allow for diagnosing the effects of wildfires on the SOM composition. In the horizons with the signs of pyrogenesis, the share of carbon represented by aromatic fragments increases as well as the PAH concentration, mainly at the expense of naphthalene, phenanthrene, and chrysene. The carbon stock of pyrogenically modified compounds, amounting to 4.4 kg/m2, is for the first time assessed in the European north based on the BPCA content. The characteristics of pyrogenically changed organic compounds and their fragments obtained by different methods correlate well: the Pearson coefficient for the correlation of the carbon content in aromatic compounds (Caryl) with total BPCA content is R = 0.84 (p < 0.05) and with individual BPCAs, R = 0.81–0.90 (p < 0.05).

&lt;p&gt;With the Anthropocene, thermogenic organic carbon, also known as black carbon (BC) is increasingly introduced to ecosystems worldwide. BC is formed by incomplete combustion or pyrolysis of fossil fuels, at wildfires or by the intentional burning of biomass, emitted to the atmosphere and hydrosphere or remaining in the bio-/pedosphere. With its high molecular proportion of elemental carbon, BC is regraded to be protected from fast microbial degradation by its inherent molecular properties. In aquatic systems, BC is partly sedimented or buried when reaching endorheic lakes or the ocean, where it is withdrawn from the carbon cycle. The biogeochemical implications of BC or its degradation products in aquatic systems have therefore not received much attention. Especially in sensitive oligotrophic alpine systems, such as the treeless Tibetan Nam Co catchment, part of the biggest connected alpine pasture system in the world, which is exposed to increasing anthropogenic pressure, any nutrient and carbon surplus can threaten the ecological status.&lt;/p&gt;&lt;p&gt;This was studied by an ultra-high resolution mass spectrometry approach that identifies several thousands of molecular formulae in dissolved organic matter (DOM). Including polycondensed aromatics (pcAro) that are considered to include thermogenic DOM.&lt;/p&gt;&lt;p&gt;Incubation experiments of water samples indicated that pcAro DOM was transformed by microbes to a comparable degree such as other natural organic matter (NOM) in the samples, removing pcAro DOM by defunctionalization or metabolization. In the environmental samples we found that pcAro DOM discharged to the endorheic Nam Co Lake was transformed by photodegradation along with other aromatic compounds. For DOM of streams and the lake of the high-alpine Nam Co watershed, most pcAro is likely of local origin, i.e. derived from burning of yak faeces by pastoralist households. This pcAro formed from cellulose-rich and lignin-poor &lt;em&gt;Cyperaceae&lt;/em&gt; fodder is chemically distinct from low-land natural biomass, usually including the burning of wood.&lt;/p&gt;&lt;p&gt;Thus pcAro DOM appeared to be a more viable part of the carbon cycle than previously assumed. Our data support the hypothesis that the fate of polycondensed aromatic DOM depends on several environmental factors, such as catchment characteristics, water opacity, solar irradiation and actual light penetration into the water column, as well as on the carbon source, driving the molecular composition of thermogenic NOM.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;

&lt;p&gt;Fires belong to the most intensive disturbances in ecosystems, but do have different effects on the soil depending on their intensity and fuel materials. Taiga ecosystems contain significant reserves of potentially fire-prone materials, and as temperatures rise in the circumpolar region and precipitation patterns change, an increase in the frequency and intensity of fires is observed. In these fires, incomplete combustion processes result in the formation of black carbon (BC), which is known as a long-term carbon sink due to its chemical properties. As the majority of forest fires are ground fires burning at a rather low intensity in terms of duration and temperature, it is discussed that the BC species formed under these circumstances are chemically less stable than those formed at high temperatures and should therefore only be considered as temporary carbon sinks.&lt;/p&gt;&lt;p&gt;Here we studied the effects of low intensity ground fire shortly after the event and tracked changes in BC within the first four years after the fire event at the southern edge of the boreal forest. We analysed a fire transect running through the two main forest types of this region, focusing on the BC species that we could quantify using the BPCA method. Our results indicate a decline in BC after the fire within the four years of observations, which mainly mainly occurred for the low condensed BPCAs. This finding is independent of the forest typ. Since the precipitation within the experimental period was also negligible and only occurred in very small amounts, we exclude leaching as well as a possible significant aeolian losses, since the trees remained unaffected by the fire and covered the soil against strong wind. We therefore deduce that &lt;em&gt;in situ&lt;/em&gt; degradation of the BC must have occurred. &lt;br&gt;Concluding, the general assumption that BC is a stable, long-term carbon sink needs to be questioned more critically. Together with other studies, our results show a quite fast decrease in the concentration of low-condensed BC species in soil over time, indicating a potential for degradation.&lt;/p&gt;