engleski

Role of humic and fulvo acids in carbonate weathering, example from SW part of Vis Island

Carbonate rocks cover more than 50% of Croatian territory. Together with tectonics, carbonate weathering is the main driver (most important process) of karst relief formation. For area of investigation south-western part of the Vis Island was selected. Vis Island represents symmetric anticline ; east-west orientated, and is built of Cretaceous carbonate sediments, clastic sediments with gypsum and anhydrite in association with pyroclasts as well as spilites and diabases of Triassic age, and quaternary cover. Due to intensive agricultural production, surface of Vis Island is almost completely covered by thin soil cover, with anthropogenic terra rossa, calcocambisol and colluvium as most common soil types. Since, surface of the Island is covered by soil cover, percolated water that reaches carbonates in the base is enriched by dissolved humic and fulvo acids from organic matter. That dissolution causes carbonate weathering that results in different morphological forms compared to those exposed only to meteoric conditions. Three locations in the south-western part of the Vis Island were selected ; one covered by calcocambisol, and two by anthropogenic terra rossa. Soil analyses included determination of humus content (Tjurin method), composition of humus (Schnitzer, 1982) and E4/E6 ratio by UV- VIS spectrophotometer. Humus content varied from 4, 9 to 8, 7 % on first location (calcocambisol), 1, 8 to 4, 8 % on second (anthropogenic terra rossa) and from 3, 5 to 7, 2 % on third location (anthropogenic terra rossa). In all samples E4/E6 ratio exceeded 5, which indicates fulvo acids domination, therefore increases carbonate weathering. Since soil layer that covers carbonate rocks retents more moisture, time of rock exposal to such solution is prolonged. Therefore, weathering of those rocks results in different morphological forms compared to those exposed only to meteoric conditions.

Vis Island ; humic and fulvo acids ; soil cover

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