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Abundance and structure of the communities of neutrophilic lithotrophic iron oxidizing bacteria (FeOB) inhabiting four low mineralized ferruginous springs of the Marcial Waters Resort (South Karelia, Russia) and the brackish chalybeate spring of the Staraya Russa Resort (Novgorod region, Russia), were investigated, as well as the physicochemical conditions of these environments. In fresh iron containing pre cipitates collected near the spring outlets and within the spring discharge areas, as well as along the spring watercourses, the numbers of unicellular FeOB enumerated on nutrient media ranged from 10 5 to 10 7 cells per 1 mL of sediments irrespective of the initial Fe(II) concentration (11-126 mg L -1 ). In the spring waters and along the spring watercourses inhabited by iron oxidizing bacteria, the concentration of dissolved oxygen did not exceed 0.05-0.1 mg L -1 . Unicellular FeOB were predominant in three springs, while in the springs with relatively low Fe(II) concentrations (11-22 mg L -1 ), various morphological forms of Gallionella and uncultured forms of the iron oxidizing bacterium Toxothrix trichogenes prevailed. In the model experiments with the water samples collected in the ferruginous springs and bogs under controlled conditions, the frac tionation of stable iron isotopes and the rate of iron oxidation were found to depend on the oxygen regime and, to a lesser extent, on the initial Fe(II) concentration. The maximum enrichment of the iron oxides formed during the simulation experiments with the light 54 Fe isotope was observed during bacterial oxidation under microaerobic conditions at O 2 concentrations of 0.1-0.3 mg L -1 and in the cultures of iron oxidizing bacteria. During the abiogenic oxidation of Fe(II), the extent of stable isotope fractionation was 1.5-2 times lower. Enrichment of Fe(III) oxides with the light 54 Fe isotope (3 to 5 fold) was considerably lower at high rates of both the biogenic and abiogenic processes of iron oxidation under aerobic conditions; however, it was more intense during the bacterial processes. Comparison of the rates of enrichment of Fe(III) oxides with the light isotope during the model experiments with pure and enrichment cultures of iron oxidizing bacteria from the sediments of ferruginous springs and bogs revealed that the biogenic factor plays a key role in the oxidation processes of the iron cycle, as well as in the differentiation of the composition of stable iron isotopes in the studied ecosystems.

The paper gives results of the digitization of the status and spatial position of a cliff in the Western Crimea coastal zone. The modern equipment and methods accelerate the survey from the time perspective and improve the quality of the outcomes; namely a high precision GNSS receiver in RTK mode and PHANTOM-3 PRO copter. The digital terrain model was generated with used the Agisoft Photoscan software. The paper shows that the precision of the mathematical model of the relief constructed by aerial photographs provides more detailed data in comparison to those obtained in the field observations. Furthermore, aerial photography makes it possible to calculate the number of spatial characteristics of hazardous for surveying and latent natural objects out of reach for an on-location investigation. As a result, the very detailed data about current condition of dangerous cliff were obtained. The paper also evaluates the linear and volumetric characteristics of cleavages that are prone to collapse.