## 4 Results
### Tufa Facies  
Four tufa facies are recognized herein. They range from moss, algal, stromatolitic laminated, and phytoclastic tufa facies. Moss tufa is the most common facies at studied localities. Mosses are widespread, especially in the SRB, where they usually occur at the steep sides and waterfalls (Figure 2a,b). The moss filaments are generally randomly oriented (Figure 3b). Moss tufa consists dominantly of micrite, but sparite and microsparite are also observed (Figure 4c). The size of the individual crystals varies, but, in general, they are less than 0.1 mm and, most commonly, isometric or elongated. Oval-shaped or irregular voids, which are usually empty, are the most abundant in moss tufa. Further magnification showed that moss tufa usually consists of rhombohedron calcite crystals (Figure 5c), as well as dagger-like, elongated crystals with sharp edges (Figure 5d). Figure 4: Optical photomicrographs of thin sections. (**a**) Algal tufa. Note regular oval-shaped voids, surrounded by spherical calcite crystals (white arrows); (**b**) Algal tufa. White arrow points to void, filled by sparry calcite crystal; (**c**) Moss tufa built by micrite and sparrie; (**d**) Phytoclastic tufa dominantly built by micrite; (**e**) Fan-shaped sparry calcite crystals in stromatolitic laminated tufa; (**f**) Micritic laminae (white arrow) alternates with sparric laminae (pink arrow) in stromatolitic laminated tufa. Figure 3: Samples of the most representative tufa samples. (**a**) Algal tufa; (**b**) Moss tufa; (**c**) Phytoclastic tufa; (**d**) Stromatolitic laminated tufa. Algal tufa is usually found at the river bottom, which is intensively occupied by algae (Figure 2i). At some places, it occurs as a thin crust above the host rock. Algal tufa is brownish and, usually, very porous and friable (Figure 3a). It is dominantly built by clotted micrite, with scarce traces of sparite and microsparite, which locally surround micritic grains, forming a rim. Secondary sparry calcite crystals are usually found inside voids of different thicknesses (Figure 4b). Calcite grains are about 0.1 mm in size, and, in this facies, they are generally equal in size and shape. Regular oval-shaped voids are commonly present, surrounded by spherical calcite crystals (Figure 4a). It is observed that algal tufa usually displays massive or clotted textures and does not contain well-developed crystals (Figure 5b). Figure 5: SEM images of tufa samples. **(a)** White arrows point to sylvite crystals; **(b)** Massive calcite aggregate in algal tufa; **(c)** Crystals of a primitive homobhedron in moss tufa; **(d)** Dagger-like calcite crystals in moss tufa; **(e)** Massive calcite aggregate with well-developed cleavage; **(f)** Scalenohedron calcite crystals; **(g)** Photoclastic tufa. Note the leaf imprint (white arrow); **(h)** Tubular cavities in calcite left by loss of bacterial filaments. Stromatolitic laminated tufa is exclusively fossil tufa, usually found in a lower altitude. Stromatolitic laminated tufa is non-porous, very compact, and consists of about 1.5 mm thick light sparitic and dark mricitic laminas (Figures 3d and 4f). Usually, light and dark laminas are of equal thickness, but some variations were noted. Respectively, sporadically light sparitic laminas are thicker than the micritic ones. Lamination is horizontal or wavy. In these facies, columnar and fan-shaped or needle-shaped sparitic crystals are found in laminas (Figure 4e). Calcite crystals are perpendicular to lamination and occasionally reach 1 mm in length. SEM analyses showed that stromatolitic laminated tufa consists of coarse scalenohedron calcite crystals (Figure 5f) with well-developed cleavage (Figure 5e). found among the whole river flow, especially at the barrages. Finally, the least present facies was stromatolitic tufa, and all of those tufa samples were considered fossil ones. In general, moss tufa was dominantly found in high energy conditions, whereas algal tufa and phytoclastic tufa were found in lower energy environments.