Lake Trasimeno
Lake Trasimeno, also referred to as Trasimene, Trasimeno Lake, or Thrasimene in English, is a lake in the province of Perugia, in the Umbria region of Italy on the border with Tuscany. The lake has a surface area of, making it the fourth largest in Italy, slightly smaller than Lake Como. Only two minor streams flow directly into the Lake and none flows out. The water level of the lake fluctuates significantly according to rainfall levels and the seasonal demands from the towns, villages and farms near the shore.
Description
Trasimeno is shallow, muddy, and rich in fish, including pike, carp, and tench. During the last 10 years it has been 5 meters deep, on average. Lake Trasimeno is an apparently endorheic body of water with no natural above-ground outlet. However, the Romans dug an artificial drainage tunnel in the San Savino area, which was restored in the Renaissance; a modern canal, the Emissario del Trasimeno, was built in 1898, flowing into the Caina, the Nestore, and eventually the Tiber.The shallow waters meant that malarial mosquitoes prospered. To combat malaria, some mosquito larvae-eating fish were imported from the United States during the 1950s. These fish are widely scattered, and some live in the lakes near Trasimeno. Although billions of larvae are eaten, there are still many mosquitoes and other insects.
The lake's water quality is still very good, as a study by conservation group Italia Nostra showed in 2005. This is believed to be largely due to the small population and a lack of large farms in the area.
A proposal to drain the lake to solve the problems of malaria and depth changes was rejected. At the end of the 19th century, the level changes were solved by building a channel near San Feliciano. This also lessened the malaria problem.
Origins and early history
The lake environment of Trasimeno Lake dates back to the Middle Pleistocene but the geological history of the Trasimeno area began a few million years earlier, in the Miocene.Historically, Trasimeno was known as the Lake of Perugia, being important for northwestern Umbria. In prehistoric times, this lake extended almost to Perugia. Trasimeno is a mythological figure, joined with Agilla, a nymph born in Agello, now a hill midway between Perugia and Trasimeno, formerly an island in the lake.
The first civilization to inhabit this area was the Etruscans; three of the main Etruscan cities as Perugia in Umbria, Chiusi and Cortona in , are within of the Trasimeno Lake. Little physical evidence remains from the period of Etruscan or later Roman settlement. Castiglione del Lago has some Roman ruins and its main streets are structured like a chessboard in the Roman style.
The Battle of Lake Trasimene occurred on the northern shore of the lake in June 217 B.C. during the Second Punic War. The exact location of the battle is unknown because the lake then extended further north; the battle was fought in the territory of Tuoro sul Trasimeno near the hills overlooking the lake.
Near Cortona is a place called 'Ossaia', in Italian meaning ossuary. Another place with reference to the battle is the place named Sanguineto, whose name is connected with the Italian term sangue meaning "blood" or, probably, "bloody place."
Local climate
The Trasimeno climate is fairly warm, with moderate winters. Summers can be very warm and humid, but in general the lake moderates the climate both in cold and warm conditions because even shallow water gives a moderate thermic inertia. From May to September, the temperature is high enough to allow swimming. In 1929, a cold winter froze the whole of the lake's surface, and cars could be driven over the ice. Cold winters in 1957, 1985 and 2002 caused heavy damage to the olive trees nearby. A less severe freeze happened in 1991. Given the latitude of the lake, freezing remains a rare occurrence.Water level
The water level of the lake is very dependent on the amount of seasonal rain and can change significantly from one year to the other. The water level is usually at its minimum level after summer and at its highest during spring.Trasimeno has high hills to the east, which help to capture rain and partially protect the lake from cold eastern winds. Most of the water in the lake comes from the network of streams on the western side of the lake.
The reference water level of the lake is set at 257.33 AMSL. This level corresponds to a maximum depth of around 6m. Actions are planned to reduce the water level when it climbs above 257.60 AMSL, but since the maximum level was set the lake has reached that height only occasionally.
After World War II, the lake's shores retreated a kilometre in the west. In 1958 the water of the lake reached the lowest recorded level, at -2.63m vs reference level. Since 1958 the level increased again to reach reference level in June 1989. After the water level started again to fall, and in 2003 the shore retreated over and the level fell in October 2003 to -1.85m vs reference.
From 2004 to the summer of 2006, there was plenty of rain. of rain fell during the last 20 days of August 2005 and over during the remaining part of the year. During the following five years rain was insufficient so by October 2012 the water level was -1.51 m vs the reference. Fortunately, since 2012 the winters have been very rainy so the level of the lake has progressively increased to reach in February 2014 the reference level. In April 2014 the water level increased further to reach 0.30 m above the reference.
A channel from the reservoir at Montedoglio in Tuscany to supply agriculture and lakeside towns was opened in 2012.
Conservation
The inhabitants of the communes around Trasimeno and the Umbrian people have successfully protected their lake, whose waters are fit for swimming and whose valleys and islands are intact environments.In 1995 a natural park was established over the entire surface and the shores. A bicycle path was opened in 2003 around the lake that allows tourists to explore it. There are also cross-country paths, especially over the hills on the eastern side.
The lake is inhabited by 19 species of fish, of which 15 are introduced exotics. The impact of non-native species in the lake has been heightened by the effects of climate change, which consist primarily of decreasing water levels due to lowered precipitation and increased evaporation rates, alongside reduced transparency, less dissolved oxygen and higher salinization caused by the gradual warming and shrinking of the lake. As the exotic species mostly have wider habitat preferences than the native species, the changing environmental conditions have allowed them to further establish themselves as the native fishes decline. Decline of native species is also affected by the reduction in the lake's native vegetation, such as macrophytes and the reed Phragmites australis.
Commercially important native species include southern pike, tench, and European eel. The southern pike has been declining as a result of reduction in the lake's aquatic vegetation, as pikes use water plants for cover during hunting and as a substrate for laying their eggs. The increased water turbidity is also harmful to their hunting, as pikes are primarily visual predators. Efforts to counteract the southern pike's decline include a ban on its fishing, which has been in effect since 2011, and controlled restocking of juvenile specimens. Eels are also considered to be locally at risk due the presence of artificial dams and weirs impeding their ability to migrate between the lake and the Mediterranean Sea; restocking programs have been implemented in response to this.
The rovella and the spined loach have historically been native to the lake, but have not been recorded in modern samplings and are considered to be locally extinct. The extinction of the rovella is linked to the introduction of non-native pumpkinseed, which competed with it for food and habitat, and to decreasing rates in dissolve oxygen in the water.
Goldfish were introduced to the lake in 1988 and today make up the most common species in its fish community. Their presence has caused significant disruptions to the lake ecosystem, as their feeding on the lake bottom destroys hydrophyte coverage and stirs up sediment into the water column, increasing turbidity and causing phytoplankton blooms. They are also known to negatively impact tench populations due to competing with them for food and habitat. Other introduced species include the largemouth bass, European perch, big-scale sand smelt, topmouth gudgeon and common carp. The growing populations of goldfish, carp and gudgeon are linked to their greater tolerance for more turbid, higher-temperature water with less dissolved oxygen. Pumpkinseed has been introduced to the lake and was recorded in large numbers in 1966, but is considered to be a locally rare species in the present.
Surroundings
Half of Trasimeno is surrounded by hills, rich in olives that are an important agricultural resource. On the western shore, near Tuscany, there are vineyards, and fruit and vegetables are grown. The hills are much lower and the climate is warmer. Monte Subasio near Assisi, about to the east, and Monte Amiata, about to the west, can be seen. The vegetation includes pines, willows and poplars around the shores, many over 30 m tall.The main towns are Passignano sul Trasimeno, Tuoro, Monte del Lago, Torricella, San Feliciano, San Arcangelo, Castiglione del Lago, and Borghetto. Castiglione del Lago has the longest shore, being on the only significant peninsula of the lake. This may have been an island that was joined to the shore by the Romans.
Surrounding the lake are old small towns, and isolated castles, like Zocco castle and a tower near Passignano. Monte del Lago was originally built to control the road from Trasimeno to Perugia.