Preliminary investigations of high-mountain soils from Bulgaria – Vitosha Mountain

1. Preliminary investigations of high-mountain soils from Bulgaria – Vitosha Mountain
1
*Zhivkova N., 2Mentler A. 3Markova K., 4Ottner F., 5Petrov P.P.
1
Department of Mineralogy, Petrology and Economic Geology – Sofia University (Bulgaria)
2
Department of Forest- and Soil Sciences - University of Natural Resources and Applied Life
Sciences (Austria)
3
Department of Geology and Paleontology – Sofia University (Bulgaria)
4
Department of Civil Engineering and Natural Hazards - University of Natural Resources and Applied
Life Sciences (Austria)
5
Department of Mineralogy, Petrology and Economic Geology – Sofia University (Bulgaria)
*Corresponding author (email: nzhivkova@gea.uni-sofia.bg; tel. +359 88 853 54 36; fax.
+35929445098)
Vitosha mountain is located in West Bulgaria and is the first (1934) National Park in the
country. Its territory comprises an exceptional biological and landscape diversity. Because of
the specific geological and geomorphologic evolution of this mountain, it is appropriate for
studying the initial interaction between parent material (basic and acid magmatic rocks) and
the high-mountain soils (Litosols and Rankers). The present study was undertaken as a
preliminary investigation of the mineralogical and geochemical features of rocks and soils on
high part (above 1800 m) of Vitosha. The aim is to add more data to the basic information
about the genesis and development of those soils and to determine the leading weathering and
soil-forming processes.
The mountain covers an area of about 310 km2 and it is located on 42° 32´ 39´´ N latitude
and 23° 15´ 43´´ E longitude. The highest peak is 2290 m (Cherni vruh). The climate is cool
continental-mountain. The parent materials are generally basalt, gabbro and monzonite with
the main minerals plagioclase, potassium feldspar, amphibole, biotite and rarely pyroxene.
The mountain consists of several concentric plain lands with different geological age. The
first and the oldest plain land is the slope surface above 2000 m; the second stands in the belt
with around 1800-2000 m; the third is developed at 1400-1600 m, and the fourth - at about
1200-1400 m.
The investigated soils (taken above 1800 m) are very shallow developed (average depth
20 cm), with low pH, wide range in CEC and high percentage of humus. Interesting result is
the very low content of exchangeable iron in comparison with the manganese. The value of
Ca corresponds to the characteristic results for Litosols and Rankers except of a few hot-
spots, which show a very high content of exchangeable Ca.
The XRD results show decrease of feldspars, mica and amphibole, enrichment of quartz
and the appearance of layer silicates, especially clay minerals with poor crystallinity. The
most interesting part of the clay mineral assemblage is a mixed layer mineral, containing
chlorite and illite. In all investigated clay fractions no sample contained smectites.
Those preliminary investigations lead to the conclusion, that high-mountain soils from
Vitosha have a quite complex genesis. Because of the low pH the chemical weathering is an
acid hydrolysis, which also affects the mobility of the chemical components and elements.
Based on the results from CEC the nutrient status has a wide variation. It would reflect on
biomass production. The analysis of pedogenic oxides will give more information on the low
content of exchangeable iron and on weathering processes. The XRD results could be
evidence, that not only local parent material influences the soil genesis, but also material,
which was reworked by solifluction processes and especially by glacial activity.
Key-words: mountain soils; clay minerals; weathering.
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