engleski

Reactivated channels on Skradinski buk tufa barrier – an example of interdisciplinary approach for sustainable management

Tufa barriers are a unique hydrological and geological phenomenon. They provide specific and diverse hydromorphological conditions thus creating heterogeneous habitats for periphyton. The growth and development of tufa barriers is very sensitive to changes in physico-chemical or biological factors that play a role in the tufa building process. Uncontrolled growth of vegetation can result with barriers drying out, and consequently cessation of tufa formation. The latter was the case in the Krka National Park, Croatia. Despite numerous actions ensured by the National Park protection category, uncontrollable growth of an invasive plant species Ailanthus altissima (Mill.) SWINGE resulted with dried water channels along the final and longest tufa barrier – Skradinski Buk. Removal of A. altissima reactivated five channels that had been dried for decades. The aim of the research was to develop a multi- criteria model for sustainable management of the Skradinski Buk barrier after the invasive species removal. Periphyton and tufa samples were collected monthly in the period from October 2017 to December 2018 along the established experimental reach comprising of seven sites. In the frame of multidisciplinary research, physico- chemical, biological and geological parameters were measured. Reactivated channels displayed higher nitrites concentration, lower pH and dissolved oxygen concentration probably caused by higher organic matter content originating from forest soil developed on tufa barrier during dry phase. Periphyton community showed more diversity in reactivated streams in comparison to control, presumably due to lower competition and predatory rates and/or intensive organic matter decomposition processes. Here we put focus on results of granulometric and mineralogical analysis. In order to determine granulometric characteristics of samples at seven stations, combined method of wet sieving and sedigraph analysis was used. Granulometric analysis displayed variations in grain size in different seasons. Gravel fraction (particles ˃ 2 mm) was composed dominantly of broken tufa pieces and it was observed that ratio of gravel fraction was lower in May and June, somewhat higher in September and highest during November and December. Accordingly, ratios of sand (2 - 0, 063 mm) and mud fraction (silt and clay ; ˂ 0, 063 mm) were lowest during November and December. During autumn and winter, more intensive rainfall and higher erosion by streams probably washed away loose sandy and muddy particles and only lithified tufa remained on all stations. In warmer and drier months, finer sediment was also present. In order to determine what these fine particles were composed of, the qualitative mineral phase composition by the X-ray diffraction technique was performed on the Philips X’pert powder diffractometer with CuK radiation. No differences were observed among sampling sites or among sampling seasons. A predominant mineral phase in all samples was calcite. Aside from analysis of a mud fraction, all samples were treated with the hydrochloric acid solution (1:10), drop by drop, in order to remove carbonate component and collect insoluble residue, for further XRD analyses. Quartz was a predominant phase in the residual part of all samples, with micas as probable additional phase, which, due to the small amount was not possible to determine with certainty. Obtained results suggest that the removal of Ailanthus altissima enabled microfauna colonization and re-commencement of tufa formation. We emphasize the need for continuous monitoring, interdisciplinary research and sustainable management of this environmentally sensitive area.

tufa, barrier, periphyton, multidisciplinary research, monitoring

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