The following paper represents results from a research focused on the soil associations and their corresponding vegetation communities (soil-plant catenas), located on the northern slopes (N, NW, NE) of the Rila Mountains. Data from eight key sites located between 815 and 2041 m above sea level is discussed. The slope in each site varies from 2° to 25°, and most often the tests and descriptions were carried out on sites with a slope of 10-15°. Vegetation cover is analyzed with plant community plots which provides data on species composition, abundance and coverage. The size of each plot varies from 16 up to 225 m2 depending on the vegetation type. Topsoil horizons were tested in each site in order to diagnose the subspecies diversity of brown forest soils (Cambisols) using ratio of humic acids to fulvic acids. That ratio varies from 0,69 up to 1,61 in all studied sites. Both acids are associated with the dominance of different vegetation types – deciduous, mixed or coniferous forest or herbaceous canopy. The results are interrupted in terms of the diagnosis and classification of Cambisols and Umbrosols in the area of interest. Differences in soil and vegetation cover of Northwest and Eastern Rila Mountain are highlighted and analyzed.

The current study focuses on the investigation of soil organic carbon in Technosols in Kula Municipality. It has several aims. There is a need of a provision of more data, regarding carbon sequestration rates in topsoils in plains that are formed in subhumid climatic conditions. Another aim is to check the comparability of the in-profile cultural layer with other ones that are built in different climatic conditions. Objects of the research are contemporary since buried soil horizons play a major part on the provision of essential ecosystem services. The characteristics of soil organic matter are determined by a chemical analysis of six soil samples in the laboratories of the Institute of Soil Science, Agrotechnologies and Plant Protection (ISSAPP) "N. Pushkarov". The total carbon content is determined by the test of Turin and soil color is determined by Munsell Soil Color Charts (1975). Soil organic carbon values in topsoil vary from 670,000 tons/ha to 1,240,000 tons/ha. Organic carbon in the studied sites represents less than 1% of the soil sample. The study may be regarded as the first step in the assessment of Bulgarian Technosols and their role in the global carbon cycle.

The following case study aims to analyze morphometric properties of the drainage network in selected river basins, covering the northeastern parts of the Sashtinska Sredna Gora Mountain. Drainage network is extracted from а digital elevation model (DEM). Several morphometric linear and areal parameters are calculated and interpreted – number of streams, total stream length, bifurcation ratio, circularity ratio drainage density, stream frequency, Melton ratio, hypsometric integral, etc. The hierarchy of tributaries and main rivers is also discussed.

The aim of the following case study is to analyze quantitatively the drainage network in the Vitosha Mountain, SW Bulgaria. Drainage network is outlined from topographic maps and extracted from digital elevation model (DEM). Several morphometric parameters are calculated – drainage density, channel-segment frequency, total stream length, etc. Hierarchy of tributaries and main rivers is also discussed.

The aim of the present study is to evaluate soil organic carbon in Gulyantsi Municipality, Pleven District. The case study area of “Ulpia Eskus” Reserve was chosen for the research. The composition of soil organic substance of Arenosols + Fluvisols is distinguished by the use of a chemical analysis and the application of the Turin method. The results show a prevalence of humic acids over fulvic acids in the sampled soil profile. Keywords: soil organic carbon, soil horizons, excavations.