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symbol for the element poloniumpolonium
, radioactive chemical element; symbol Po; at. no. 84; mass no. of most stable isotope 209; m.p. 254°C;; b.p. 962°C;; sp. gr. about 9.4; valence +2 or +4. Polonium is an extremely rare element found in uranium ores (about 0.1 gram per ton).
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(pō, It. pô), Latin Padus, longest river of Italy, c.405 mi (650 km) long, rising in the Cottian Alps of Piedmont, NW Italy. It winds generally east in a wide valley, past Turin, Pavia, Piacenza, Cremona, and Ferrara, to enter the Adriatic Sea through several mouths. Its marshy delta is constantly expanding eastward. The Dora Baltea, Tanaro, Ticino, Adda, and Oglio rivers are its chief tributaries; hydroelectricity is produced there. The Po River is navigable for small craft c.300 mi (480 km) upstream, but seasonal variations in flow hamper navigation. It is extensively used for irrigation. The Po valley is densely populated and is the most important industrial and agricultural region of Italy. Grains, sugar beets, livestock, and fruits are raised. Turin, Asti, Milan, Brescia, and Verona are the chief cities of the Po valley.



the largest river in Italy. The Po measures 652 km long and drains an area of about 75,000 sq km. Originating in the Cottian Alps, it flows primarily through the Po-Venetian Plain from west to east and empties into the Adriatic Sea, forming a marshy delta about 1,500 sq km in area; the delta is expanding at an average rate of 60 hectares a year. The largest left tributaries are the Dora Riparia, Dora Baltea, Ticino, Adda, and Oglio. Originating on the southern slopes of the Alps, they carry the greatest volume of water. The Po’s right tributaries, which originate mainly on the northern slopes of the Etruscan Apennines and in the Maritime Alps, usually carry little water but considerable suspended alluvia.

Below the mouth of the Tanaro River, the largest right tributary, the Po, which is 300–350 m wide here, is leveed to protect the adjacent lands from flooding. Some of the Po’s tributaries within the Po-Venetian Plain are also leveed. Despite this, there are numerous floods caused by rises of the water level by as much as 5 to 10 m, mostly after heavy downpours, in the Po and its tributaries. In the 20th century the largest floods occurred in 1951 and 1966, which inflicted great damage and led to mass evacuation.

The Po’s average discharge at the mouth is 1,460 cu m per sec. The left tributaries contain the greatest volume of water in the spring and summer, when seasonal snows and glaciers in the Alps melt. Hence, the upper Po has an alpine regime. The right tributaries have more water in the spring and fall. This produces two flash-flood periods in the middle and lower Po: one in May or June and one in October or November. In the winter the river usually has a low volume of water. Annual sediment discharge is estimated at 13 to 15 million tons.

The Po’s waters are used for irrigation, and series of hydroelectric power plants have been built on a number of left tributaries. The river is navigable to the city of Piacenza and is linked by canals with Milan and the lagoon of Venice. The Po is linked with several large lakes, including Lakes Como, Maggiore, and Garda, by canals and the Adda, Ticino, and other tributaries. The cities of Turin, Piacenza, and Cremona are situated on the Po.


Galkina, T. A., and N. A. Sysoeva. Italiia. Moscow, 1972.
Romanova, E. P. “Vodnye resursy rek Italii i ikh ispol’zovanie.” In Vestnik MGU: Seriia 5—Geografiia, 1968, no. 2.





Abbr. for “purchase order.”


a river in N Italy, rising in the Cottian Alps and flowing northeast to Turin, then east to the Adriatic: the longest river in Italy. Length: 652 km (405 miles)