Assessment of soil development during rapid urbanization using the carbon and nitrogen stable isotope composition.

The proposed paper is devoted to the analysis of the urbanization effects on soil cover using physico-chemical parameters and stable isotopic signatures on the example of Tyumen. The study methods included analysis of C and N elemental and isotope (δ13C and δ15N) composition, analysis of soil physico-chemical properties and major oxides content. The results of the survey have shown that soil properties within the city limits vary significantly depending on both anthropogenic activities and geomorphological context. The urban soils of Tyumen differ from very strongly acidic with pH values down to 4.8 to strongly alkaline with pH values reaching 8.9, and from sandy loams to silty loams by texture. The study results have shown that δ13C values varied from - 33.86 to - 25.14‰ and δ15N values varied in range, especially, from - 1.66 to 13.38‰. The range of these signatures was smaller than those reported for urbanized areas in Europe and USA. The δ13C values in our case were more related to the geological and landscape parameters of the study area, rather than with urban disturbances and development of urban ecosystems. At the same time, the δ15N values probably indicate zones with increased atmospheric N deposition in the case of Tyumen. The application δ13C and δ15N is a promising tool for analysis of urban soil disturbances and functions, though the regional context should be taken into account.

Diet and life history reduce interspecific and intraspecific competition among three sympatric Arctic cephalopods.

Trophic niche and diet comparisons among closely sympatric marine species are important to understand complex food webs, particularly in regions most affected by climate change. Using stable isotope analyses, all ontogenetic stages of three sympatric species of Arctic cephalopods (genus Rossia) were studied to assess inter- and intraspecific competition with niche and diet overlap and partitioning in West Greenland and the Barents Sea. Seven traits related to resource and habitat utilization were identified in Rossia: no trait was shared by all three species. High boreal R. megaptera and Arctic endemic R. moelleri shared three traits with each other, while both R. megaptera and R. moelleri shared only two unique traits each with widespread boreal-Arctic R. palpebrosa. Thus all traits formed fully uncrossing pattern with each species having unique strategy of resource and habitat utilization. Predicted climate changes in the Arctic would have an impact on competition among Rossia with one potential 'winner' (R. megaptera in the Barents Sea) but no potential 'losers'.

Counterion Concentration Profiles at the Graphene Oxide/Water Interface.

Despite enormous interest toward graphene oxide (GO) from the research community, surprisingly, little is known about its solutions. In particular, the questions related to the structure of the GO/liquid interface have not been yet properly addressed. In this report, we use a simple but efficient experimental approach to investigate the distribution of the four metal cations Na+, Cs+, Ni2+, and Gd3+ at the GO/water interface. We demonstrate that the concentration of the cations decreases exponentially with the distance from the GO surface. Such distribution for colloid systems was theoretically predicted and commonly accepted for a century but, to the best of our knowledge, has been never proved experimentally. We further demonstrate that the shape of the counterion distribution profiles depends on the pH of solution and on the fine chemical structure of GO. In particular, organic sulfates and vinylogous acids that are ionizable at different pH levels are responsible for the difference in the shapes of the concentration profiles. Unlike classical colloid systems, the diffuse layer in the GO solutions is rather broad (30-55 nm), and the concentration gradient is registered even at distances of >55 nm from the GO surface, which is typically considered as the bulk solution. The latter observation is explained by the immobilized character of the GO flakes in the nematic phase, impeding the flow of liquid and the migration of hydrated metal cations. This helps to establish and maintain the long-range concentration gradient in the space between the two parallel neighboring GO flakes. Based on the new findings and on the previously reported data, we formulate some basic principles of GO solutions.