The effect of parent material on physical and mineral soil properties on Medvednica nature park

Matični supstrat, uz klimu, reljef, organizme i vrijeme, predstavlja jedan od pet glavnih pedogenetskih čimbenika. S pedogeneskog stajališta najvažnija su svojstva matičnog supstrata: mineralni i kemijski sastav, način i intenzitet trošenja te sadržaj biogenih elemenata. Cilj ovog rada je utvrditi utjecaj različitih matičnih supstrata na fizičke i mineralne značajke tla. Na području PP Medvednice na šest različitih litoloških cjelina otvoreno je 80 pedoloških profila: metamorfne stijene – dominantno škriljevci, metamorfne stijene – dominantno filiti, magmatske stijene, pješčenjaci, lapori i lako trošivi vapnenci. Uzorci tla uzeti su po horizontima, a analizirani su oni iz humusnoakumulatinog (A-horizont) i B-horizonta. Određeni su sljedeći parametri: debljina horizonata, dubina profila, udjel skeleta, garnulometrijski sastav tla, postojanost strukturnih mikroagregata i mineralni sastav tla (XRD) metodom rendgenske difrakcije. Rezultati istraživanja pokazuju da postoje statistički značajne razlike između različitih litoloških cjelina za sve promatrane varijable osim debljine horizonata. Najveće dubine tla su povrh laporovitih stijena, a najmanje na dolomitiziranim vapnencima, što je ponajprije uvjetovano načinom trošenja matičnog supstrata. Na svim istraživanim litološkim cjelinama, tla na području PP Medvednice vrlo su postojanih mikroagregata. U odnosu na B-horizont u humusnoakumulativnom horizontu utvrđena je veća postojanost strukturnih mikroagregata. Tla povrh lakotrošivih vapnenaca imaju statistički veći udjel gline i manji udjel krupnog i sitnog pijeska od tla ostalih litoloških cjelina. Za sve litološke cjeline teksturna oznaka najčešće je u rasponu od praškaste do glinaste ilovače, dok je na litološkoj cjelini povrh vapnenaca udjel gline statistički značajno veći, pa je teksturna oznaka u rasponu od praškaste glinuše do glinuše. Litološke cjeline povrh magmatskih i metamorfnih stijena imaju statistički značajno manji udjel minerala kvarca i veći udjel minerala klorita i feldspata u odnosu na sedimentne stijene.The highly complex lithological structure as well as topographic characteristics of the Medvednica area are responsible for its profound vegetational, micro-climatic and pedophysiographic diversity. In view of the quality of the original soil-forming material, the first place is taken by rocks and their detritus which directly govern soil physical composition. The best indicators of soil physical composition are its depth, colour, skeletal nature, particle size distribution, soil density, density of soil solid phase, total porosity, water capacity, air capacity, structure and hydraulic properties. On Medvednica, these vary greatly and play the main role in defining soil quality. The success of ecosystem management depends on the knowledge of the above factors. The goal of this research is to determine how the lithological base, or parent material, primarily affects physical (horizon thickness, profile depth, skelet proportion, soil texture, soil structure) and mineral soil properties.A total of 80 pedological profiles were opened in the Medvednica Nature Park area and evenly distributed so as to comprise all the representative lithological units. Samples of physically altered soils were taken from genetic horizons, as well as a fragment of rock, i.e. parent material, for the purpose of determining the lithological rock affiliation. Soil samples has been analayzed in the humus-accumulative (A horizon) and first under mineral horizon (mostly B horizon). The differences between the topsoil humus-accumulative and B horizon were statistically analyzed per lithological units. The samples were prepared (ISO 11464 2006) and analyzed in the laboratories of the Faculty of Forestry of the University of Zagreb and at the Croatian Geological Institute in Zagreb. According to FAO (2006), the following was determined in situ: the proportion of skelet per genetic horizon, horizon thicknesses and total profile depth. Laboratory analyses of the samples taken from genetic horizons included the particle size distribution according to ISO 11277:2009, stability of structural microaggregates according to Pernar et al. (2013) and mineral soil composition (XRD) using the X-ray diffraction method on X-ray diffractrometer X’Pert PRO MPD.For the needs of statistical analysis, parent material was divided into six characteristic units, leaning in part on the classification of Halamić et al. (2001) used during geochemical research of stream sediments on Medvednica. The lithological unit LIT1 is represented by metamorphic rocks, predominantly greenschists, muscovite chlorite and quartz-muscovite schists. The lithological unit LIT2 is represented by metamorphic rocks, predominantly phyllites. The lithological unit LIT3 consists of igneous rocks, predominantly diabases and spilites. The lithological unit LIT4 are Mesozoic clastic rocks of Lower Cretaceous age, and comprise sandstones, siltites and shales. The lithological unit LIT5 consists of Mesozoic and Tertiary clastic rocks dominantly represented by marls. LIT6 is made up of Tertiary carbonate rocks represented by lithotamnic limestones together with clay limestones (Figure 1).Statistical analysis was performed with Statistica 7 software. Descriptive statistics was made for all the analyzed variables, including the number of samples, arithmetic means and standard deviation. Differences between the analyzed variables by lithological units were tested with a one-way analysis of variance (ANOVA), on condition that the assumption of homogeneity of variance was satisfied. For those variables in which the test of homogeneity of variance was not satisfied, the Kruskal-Wallis non-parametric test was used. Type I error (a) of 5 % was considered statistically significant.The following soil types were identified in the opened pedological profiles: dystric cambisol, eutric cambisol, calcaric cambisol, stagnosol, regosol and luvisol (the percentage ratio by representation is 62 % – 19 % – 10 % – 4 % – 3 % – 2 %).Based on the comparison of soils formed in six different lithological units, it can be concluded that physical and mineral soil properties depending on type of litological units. Silty to clay loam is the most represented textural class in Medvednica Nature Park. It was found on metamorphic rocks above greenschist and phyllite, igneous rocks, sandstones and marls, whereas on easily weathered limestones the textural class ranges from silty clay to clay. The analysis of particle size distribution (content of individual fractions) showed that the profiles developed on silicate lithological parent material have on average higher sand content compared to the profiles developed on carbonate rocks, which is conditioned by the manner of parent rock weathering. Higher clay content above easily weathered limestones eventually led to variability of the textural class in relation to other lithological units. In all the investigated lithological units in terms of structural microaggregate stability, the soils in Medvednica Nature Park manifest highly stable microaggregates. In relation to the B-horizon, the humus-accumulative horizon revealed higher stability of structural microaggregates, which can be attributed to higher content of organic matter in the topsoil horizon. The soils above igneous and metamorphic rocks have significantly lower content of the mineral quartz and higher content of the minerals chlorite and feldspar in relation to the soil above sedimentary rocks. There was no difference in muscovite/illite contents in lithological substrates. Soil was the deepest above marl rocks and the shallowest above dolomitised limestones, which is primarily conditioned by the manner of parent material weathering.Our research highlights all the complexity and heterogeneity of the geological-lithological structure of Medvednica. In combination with other pedogenetic factors, it manifests even higher soil heterogeneity, which eventually causes problems in the processing and interpretation of the results.This research provides reference data on physical and mineral properties of soils in Medvednica Nature Park in the most represented lithological units. However, these data should be taken with caution and should be compared with the results of other similar studies, since the same lithological parent material may give rise to the formation of soils of different taxonomic affiliation, depending on the changes in the constellation of other pedogenetic factors (climate, vegetation, relief)