## 4 Results  
### Tufa Morphology and Petrology  
Both localities are characterized by both active and fossil tufa precipitation, due to the changed direction of the river flow. Tufa is actively forming throughout the entire river flow at: waterfalls, cascades, and at the river bottom. Finally, deposition of the phytoclastic material led to the formation of dams and barrages, which locally surround pools. Dams and barrages are developed transverse to the watercourse. At those dams, barrages, and pools, there is also active tufa precipitation. The size of the barrages ranges from 10 cm to a few decimeters in height, and they are usually irregular or tongue shaped. They occur as single or as several piled-up barrages (Figure 2e). Figure 2: **(a)** The tallest, multi-step waterfall at the River Sopotnica with active tufa precipitation; **(b)** Curtain-type waterfall at the River Sopotnica; **(c)** Fossil tufa, with visible traces of exploitation; **(d)** The main waterfall at Gostiljska River with active tufa precipitation; **(e)** Several tufa barrages, surrounding swallow pools; **(f)** Fossil tufa outcrop; **(g)** Limestone fragments mixed with tufa debris; **(h)** Stromatolitic laminated fossil tufa; **(i)** Algae occupying the river bottom; **(j)** “Dry” waterfall; **(k)** Fossil tufa. The pools vary in length and width from a few decimeters to 3 m, and water depth is around a few decimeters, up to one meter maximum. Tufa outcrops differ in size; sometimes they reach 12 m in height (Figure 2f). Outcrops are well preserved, and their lateral extension varies, but it usually is less than 100 m. Fossil tufa is white, very hard, compact (Figure 2k), and contains less organic matter. On the other side, recent tufa is brownish, more porous, and has many plants' remains. The thickness of tufa bodies is variable, sometimes reaching 20 m. Older, allochthonous tufa is sporadically present as debris. In some places, tufa debris is mixed with fragmented limestones (Figure 2g). On the riverbanks, fossil tufa sometimes displays well-developed lamination (Figure 2h). Tufa accumulations of the Sopotnica River appear in the village of the same name at the western slopes of the mountain Jadovnik, at 1100 m.a.s.l. Although it flows shortly, at about 3.5 km, the Sopotnica River creates a series of waterfalls all the way down before its confluence with the Lim River, due to having constant stream throughout the year. The tallest waterfall is 25 m in height (Figure 2a), and, generally, it is a multi-step waterfall [43]. Locally, the waterfalls display features of both a segmented and curtain type (Figure 2b). The other waterfalls are on average 19-23 m in height. Some of the smaller waterfalls are active only during spring, while they are dry during other months (Figure 2j). The deposition of tufa starts beneath the limestone cliff Podstijenje at 1120 m.a.s.l. and continues down to 850 m.a.s.l., i.e., within 270 m in vertical directions and, for some, 500 m over melange rocks. The deposition of tufa was disrupted at the middle of the river flow, due to exploitation (Figure 2c). Tufa accumulations of the Gostiljska River are located approximately 25 km from the center of Zlatibor Mountain, at 867 m.a.s.l. Despite its short flow (about 2 km), the Gostiljska River creates tufa accumulations along the whole flow, as well as numerous waterfalls and small cascades. The biggest of them is 22 m high and it is created just before the end of the river flow, before its confluence with the Katusnica River (Figure 2d). Water drops abruptly from a 22 m high limestone cliff, forming further in the course of river, a several smaller tiered waterfalls and rapids yet to its confluence with the Katusnica River. Those waterfalls and rapids are always covered with hanging stems, moss, and grass. According to the results obtained by XRD investigations, the dominant constituent of all tufa samples is low-Mg calcite (LMC).