Plitvice Lakes National Park
Plitvice Lakes National Park is one of the oldest and largest national parks in Croatia. In 1979, Plitvice Lakes National Park was inscribed on the UNESCO World Heritage list, for its outstanding and picturesque series of tufa lakes, caves, and connected waterfalls.
The national park was founded in 1949 and is in the mountainous karst area of central Croatia, at the border with Bosnia and Herzegovina. The important north–south road that passes through the national park area connects the Croatian inland with the Adriatic coastal region.
The protected area extends over. About 90% of this area is part of Lika-Senj County, while the remaining 10% is part of Karlovac County.
Area
The national park's lakes are arranged in cascades. Sixteen lakes can be seen from the surface.The lakes are renowned for their distinctive colors, ranging from azure to green, grey or blue. The colors change constantly depending on the quantity of minerals or organisms in the water and the angle of sunlight.
Etymology
The name Plitvice was first mentioned in a written document in 1777 by Dominik Vukasović, the priest of Otočac. This name was designated because of natural phenomena that have created the lakes. Nature formed shallow basins, which have been filled with water. For centuries, water has changed the limestone and thus the landscape of this area. The emerging travertine barriers decelerated and retained the flowing water. These dams are continuously growing in height.Location
Routes and distances
The area of Plitvice Lakes National Park extends across two political subdivisions or counties. Its area is divided between Lika-Senj County and Karlovac County, hence the national park authority is under national jurisdiction. The overall water body area is about. The two largest lakes, Prošćansko jezero and Kozjak, cover about 80 percent of the overall water body area. These lakes are also the deepest, with a depth of respectively. None of the other lakes in the park exceeds in depth. The elevation drop from the first lake to the last is.Topography and geology
Terrain
The availability of water, influenced by the configuration of the terrain, has a great impact on the biodiversity of this area. The Plitvice Lakes are surrounded by various mountains. The western side of the national park area is enclosed by the Mala Kapela mountain, while the eastern side is enclosed by the Lička Plješivica mountain, which also represents the border with Bosnia and Herzegovina. Plitvice Lakes National Park is situated in the Plitvice plateau which is surrounded by three mountains that are part of the Dinaric Alps: Lička Plješivica mountain, Mala Kapela mountain, and Medveđak.The afforested mountain slopes serve as reservoirs. They are also a refuge for many animal species. The large difference in altitude in a narrow space between the mountains in the south and the Korana river in the north represents a significant criterion for biodiversity in this region. The overall difference in elevation within the national park area is 912 m.
Rivers
The Plitvice Lakes originate in the south of the park area at the confluence of Bijela Rijeka and Crna Rijeka. These rivers originate south of the municipality of Plitvički Ljeskovac and unite at one of the bridges in this village. From this place onwards to the lakes, the water masses are referred to as Matica. At the bay of Liman, a part of Prošćansko jezero, another small river flows into the lakes. This river is fed by permanent springs; the water quantity, however, varies. Temporarily, water from other, usually dry, creeks reaches Prošćansko jezero from the west.Properties of the underground
sediments have been formed from the Pleistocene onwards in sinkholes or depressed areas between the surrounding mountains. Generally seen, the underground of the Plitvice Lakes could be categorized into two zones. The Upper Lakes in the south predominantly consist of dolomite rock. The Lower lakes in the north predominantly consist of limestone rock. Dolomite rock is slightly harder than limestone. Though fragile upon physical influence, dolomite rock has lower water permeability properties. In contrast, limestone rock is more compact and massive, but has a higher water permeability.Climate
On average, the annual precipitation rate at the Plitvice Lakes is. Usually, in spring and fall the largest rain quantities are measured. The average relative air humidity is 81.8 percent. In January, the average temperature is 2.2 °C. During the summer months of July and August, the temperature rises to 17.4 °C. The general average annual temperature is 7.9 °C. Snow falls from November until March. Usually, the lakes are frozen during December and January.The dissolution and creation of rock
The lakes of Plitvice are a result of century-old processes and the sedimentation of chalk, which is abundantly available in the waters of this karst area. These sedimentations are called tufa or travertine.Alteration processes
In geological terms, the actual phenomena molding the Plitvice Lakes are quite young. The complex processes of dissolution and sedimentation of limestone require specific climatic preconditions. These have only existed since the end of the ice age about 12,000 to 15,000 years ago, according to tufa radiocarbon datings.Apart from weather and temperature factors, the water quality and other natural factors are significant for the creation of these natural phenomena, prevailing at the Plitvice Lakes. By passing through the limestone underground the karst rivers dissolve chalk, which concentrates in the water. The saturation level of calcite within the frontal flows is thus very high. The water becomes significantly mineralized, super-saturated with calcium and magnesium-hydrogencarbonate.
The quantity of calcium hydrogencarbonate dissolved in water depends on the quantity of dissolved carbon dioxide in the water. Generally, the following could be said: The colder the water, the higher the quantity of dissolved calcium hydrogencarbonate. Depending on the conditions for the alteration processes, scientists identified limestone dissolution rates of 0.01 to 4 millimeters a year.
Preconditions for sedimentation
Measurements of carbon dioxide quantities in the water show that they correspond with continuous sedimentation processes in the Plitvice Lakes area. Carbon dioxide quantities at the springs are about twenty times higher than in the atmosphere. The quantity of carbon dioxide decreases along the water route. The Plitvica river, for example, loses even up to 97% of its original quantity of carbon dioxide along its route.The area of a river, in which the formation of tufa occurs, is called precipitation area. Along the Korana river, for example, measured from its origins, tufa is being formed only along the first 10 to, even if according to pH measurements the conditions would be favorable further down the river. At the ground of Lake Kozjak a constant yearly sedimentation of 0,8 millimeters during the past 3,000 years has been ascertained. Yearly, the barriers are growing up to 13 millimeters in height. Tufa formation processes thus surpass erosion activities, which would destroy the sensitive barriers of the lakes. It is estimated that the tufa sedimentations at the ground of the lakes date back 6,000 or even 7,000 years.
The precipitation of calcium carbonate, however, does not occur right at the springs of the rivers that flow into the Plitvice Lakes. For the precipitation of carbonate chalk the water needs to reach a certain mineral saturation level. At the springs this saturation level is about 1. For the precipitation, the water saturation level needs to be higher than 3. At the same time, the pH value of the water needs to be above 8,0.
Thresholds become barriers
In the course of time, older barriers can be flooded by rising water levels since other barriers have outgrown the older ones. 400 years ago, there were two lakes in place of today's Kozjak lake. In the lowest third of the lake, at the level of Matijaševića draga, a crown of an underwater barrier that is 40 m high, is stretching 4 m below the water surface. This barrier certainly formed a magnificent waterfall in the past. The travertine barrier at the Kozjak bridges at the current end of the Kozjak lake, however, grew faster. Thus, 400 years ago two lakes merged in one. That is why the greatest depths of Kozjak lake are in its lower basin.Influence of vegetation
Mosses, algae and water plants play a major role in forming the unique landscape of the Plitvice Lakes and its tufa barriers. Up until the 21st century, it was supposed by scientists, including the botanist who initially argued for conservation efforts at Plitvice in 1926, that plants extract carbon dioxide from the water for photosynthesis purposes and that in return oxygen is released, thus resulting in the sedimentation of hydrogen carbonate phytogenesis.Recent scientific evidence indicates that vegetation is not primarily responsible for the extraction of carbonate from the flowing water. However, plants indirectly contribute to tufa formation. For sedimentation to occur it is essential that the water be decelerated, aerated and sprayed. The mosses of the Plitvice Lakes waterfalls provide a substrate for sedimentation, generating travertine. Depending on the species found locally, various biological types of travertine can be differentiated.
Photosynthesis by algae and mosses, however, fosters the crystallization of sediments because of the extraction of carbon dioxide.
The young shoots of mosses are green and soft. They are mostly without travertine, while older shoots are encrusted by a thin and fragile yellow layer, completely covered and petrified by plant-formed travertine. The mosses foster not only the creation of tufa barriers, but also become part of the barrier. The moss becomes encrusted with travertine and fresh moss grows further out. First a crag is formed but later a cave roof forms under the crag. If the water continues flowing, the cave becomes progressively bigger. Older travertine is filled with fossilized algae and mosses. This type of tufa rock typical of the Plitvice Lakes is called "phytogeneous tufa."