engleski

The role of simuliid and trichopteran silk structures in tufa formation during the Holocene of the Plitvice Lakes (Croatia)

Fluvial tufa formation was studied using artificial substrates, over a 1-year period on barrages of the Plitvice Lakes (Croatia). Significant differences in tufa deposition rates were found between the source springs and upper and lower lakes throughout the year. During the summer we recorded the highest tufa deposition rates - probably caused by the influence of temperature on CO2 outgassing. On 13% of artificial substrates simuliid (Insecta: Diptera) and hydropsychid caddis-fly (Insecta: Trichoptera) larvae created silk structures, which were encrusted by calcium carbonate, thus contributing to tufa formation. Simuliid silk pads had a measurable role during the winter, when tufa deposition rates were low, while during the rest of the year their influence was undetectable. In contrast, hydropsychid silk formation was not recorded during the winter on the artificial substrate, whereas at other times of year they created nets and retreats, which became calcified. Techniques involving drying, weighing and dissolving tufa deposits on artificial substrate and on silk, revealed that when present, silk structures of caddis-flies, accounted for on average 71.0% of the total depos-ited calcite. During the winter, simuliid silk pads had on average 48.5% of total calcite crystals on their sur-face. Both investigated groups are rheophilic, and preservation of their silk structures in fossil tufa might serve as an indicator of palaeohydraulic conditions.

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