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Plitvice Lakes

The shape of Plitvice Lakes and the surrounding terrain closely reflect the underlying geological structure. The Upper Triassic dolomites underlying the Upper lakes are relatively impermeable and allow retention of the accumulated water. As a result, the upper lakes are nested in a gently sloping valley. The bedrock of the lower lakes is the Upper Cretaceous limestone that was more susceptible to karstification processes. The lower lakes are narrower, and situated in a deep canyon. The contact between the dolomite and the limestone is a fault that determines the NW– SE strike of lake Kozjak. The lakes are separated by natural dams constructed of a porous carbonate deposit called calcareous tufa, or cold-water travertine. The Plitvice system is complex and dynamic, and as such is an instructive model of bio-geo-chemical interactions ranging from microscopic to global in scale. The processes involved deal with the physico– chemical conditions of carbonate dissolution and precipitation, both strongly modified by biological processes, primarily respiration and photosynthesis. There are several requirements for the formation of tufa: (1) the supersaturation of the water with respect to calcium carbonate ; (2) the presence of photosynthesizing organisms (cyanobacteria, algae and plants) ; (3) the cleanliness of the water with a low organic matter content.The formation of calcareous tufa is a complex process that proceeds through phases of carbonate dissolution, precipitation, crystal nucleation and sediment formation. Organisms participate to different degrees in each of these phases, depending on, and interacting with, concurrent physical and chemical environmental conditions.

Plitvice, geology, travertine, calcareous tufa, biocalcification

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