engleski

Bedrock Influence on Geochemical Background of Soils in Istria - a Statistical Approach

The complex and polygenetic nature of the soils landscapes of Istrian Peninsula is reflected in their geochemical signatures that combine geogenic and anthropogenic signals to varying degrees. Criteria for identifying asymmetrical contribution of both inputs, as well as for marking the baseline limits, may be sundry, but the fate of major and trace elements involved in various soil-forming processes can be very effectively studied via the character of their probability distribution curves (or proxy histograms). The geochemical background is effortlessly calculable by the statistical methods regardless of the soil type or any of the natural or anthropogenic factors under consideration, though the study clearly shows that idealistic impression of simple, linear cause-and-effect relationship between geochemical or any other soil features is plainly nonexistent. The two main issues can be summarized by this work in respect to the geochemical background: the first is that the greater part of all measured concentration values fall within the normal range of data whose thresholds can be determined by simple mathematical computations ; the second is that the soil complexity resists building a stable, symmetrical probability distributions complying to the Gaussian law, even within the calculated background limits. Skewness of elemental distribution curves is the first and foremost signal of non-linear response to various, especially external, factors that disturb the soil system, because it indicates non-equilibrium dynamics reflecting either accumulation or depletion of an element involved in some soil forming or human-affected process. It explains complex and irregular temporal and spatial patterns caused by multiple responses in the soil evolution and by various modes of adjustment. The hope for their disentanglement is unsubstantiated without posing some limits as regards particular soil forming factors. In this work the setting had been cleared from the start by sequestering the two types of parent material that is considered as the most significant contributor to the specific behaviour of elements and character of their probability distributions. Thus the carbonate-derived and flysch-derived soils differ considerably from each other both in their background ranges and character of their elemental probability distributions, which is the result of different character of soil forming processes in the uppermost part of the soil horizon. The "immaturity" of the soils developed on the flysch parent material is seen in the low variation from the natural background - a consequence of frequent reversal of developmental trends from progressive to regressive and vice versa. The normal range of the postulated geochemical background is not invariably followed by normal distribution of values within its limits, which suggests the presence of multi-modality. The latter points to instability of the main population due to the unyielding influence of more than one process on the local distribution of the given element. The "mature" or evolved soils overlying the carbonate parent rock show greater variation from the geogenic background and much more pronounced skewness being, though, more under the influence of anthropogenic sources often overprinting to a considerable degree, or even obliterating the natural signal. Outliers as the principal cause of skewed distribution are related specifically to these soils (their upper horizon) due to the fact that geogene processes cannot keep the pace with recent, rapid anthropogenic change. Just on the contrary, undeveloped soils on flysch bedrock suppress the outlier outbreaks because of the dilution effect caused by weathering and transport of the easily erodible parent material and its subsequent mixing with already formed regolith. In both cases, the anthropogenic and natural signals are mixed together creating a multiple-causality problem which enhance development of complex nonlinear soil dynamics. Since only the topsoil is taken into consideration the conclusions reached in this work inevitably suffer from the lack of data necessary for deeper evolutionary insight. Nevertheless, much can be deduced from the obtained results as regards the human impact on its environment, so that the calculated geochemical background (with its upper limit) offers trustful and plausible information on the natural, or geogene limits of element content within the local boundaries of the study area.

geochemical background; topsoil; parent material; geogene influence; human impact; normal distribution; normal range; Istria; Croatia

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