The determination of maximum water discharges of floods and rain floods at small mountain streams is relevant for engineering and construction purposes. However, currently, the accounting of the surface runoff of small watercourses is often neglected when construction works are being carrying out. This fact leads to various problems with the exploitation of constructed objects. The purpose of this work is to assess the impact of the construction of the biathlon complex in the recreational area of Yuzhno-Sakhalinsk on the maximum surface runoff from the territory that it occupies. Maps of natural and anthropogenically transformed catchments of the territory were created with the usage of the data, collected during the field work in the summer of 2018. Hydrographical characteristics of both kinds of catchments were determined in accordance with generally accepted recommendations. On the basis of the obtained data, there was carried out the comparative analysis of the current state of the study area and its characteristics before the creation of sports facilities in years 2016–2017. The calculations of the maximum runoff in periods of flood and rain floods according to analytical formulas recommended in the literature were made. The results of the calculations clearly show that water discharges from this area during the period of flood and rain floods increased after the construction of the complex in comparison with discharges observed before construction. Studies have confirmed that the construction of biathlon tracks on the mountainside led to the increase in surface runoff from this area, which is the reason for the overflow of the urban storm sewer of Yuzhno-Sakhalinsk during the period of flood and rain floods, stormwater outlets on the day surface and the activation of erosion processes, suffusion on the considered territory.

In this study the laboratory analysis of water samples from three representative regions of the Arctic for content of coloured dissolved organic matter (CDOM) – the important component of natural waters, which has a direct impact on state of aquatic ecosystems, was made. Samples were collected from water objects from the Kola Peninsula, the Yamal Peninsula and the Lena River Delta. The results of the analysis made it possible to determine CDOM concentrations in water. According to the average values, the highest values were obtained for the Yamal Peninsula and lowest – for the Kola Peninsula. The predominance of allochthonous CDOM in the water objects from all three regions was revealed. Moreover, the complete absence of photodegradation processes was determined. For the lakes and rivers from the Kola Peninsula it was also possible to follow seasonal dynamic of CDOM concentration in water and to compare it with earlier obtained data concerning seasonal CDOM dynamic in the Lena River Delta. Results are actual due to the currently existing tendency of climate change which leads to intensification of thermal denudation and thermal erosion processes in the cryolithozone, which are consequently increasing income of allochthonous CDOM in water objects.