Po River

Category: Inland Aquatic Biomes.

Geographic Location: Europe.

Summary: The longest river in Italy, the Po supplies water for irrigation to Italy’s primary agricultural region, but is threatened by pollution and overuse.

The Po is the longest river in Italy, at about 410 miles (650 kilometers), and also has the largest river basin, encompassing more than 27,000 square miles (70,000 square kilometers), about half of which drains montane regions, and the rest draws flow through plains. The Po basin in general constitutes a broad plains area between two mountain ranges, the Alps and the Apennines; it is the largest region of fertile agricultural land in Italy. Almost one-quarter of the population of Italy, or about 16 million people, live in this region.

The Po rises in the Cottian Alps in northwest Italy and flows through the regions of Lombardy, Liguria, Piemonte, Emilia Romagna, Veneto, Valle d’Aosta, and the province of Trento; it has 141 tributaries including the Adda, Dora Riparia, Dorea Baltea, Mincio, Oglio, Tanaro, and Ticino. The Po originates as a mountain stream on Monte Viso in the Alps; most of its vertical drop occurs between its source and Piacenza, after which it becomes a marshy and heavily diked river, with many meanders. In the upper Po plain, numerous lakes are created by the natural dams formed by low moraines; two of the largest are Lake Garda and Lake Como. The Po enters the Adriatic Sea in a wide cuspate delta southwest of Venice, created in part by the considerable sediment transported by the river.

The Po River Valley has a mild continental climate to a humid subtropical climate, depending on the section of valley. Summers and winters are both more extreme in the lower elevations along the river. Average temperatures here range between 50 and 59 degrees F (10 and 15 degrees C). The precipitation range is 25–45 inches (63–115 centimeters) per year. Generally, the precipitation amount increases in the region moving from south to north and from east to west. The Po’s waters are highest around the month of May, because of snowmelt from the Alpine region, and November, due to rainfall.

Wildlife

The Po River Delta has been protected by the institution of two regional parks in the region of these wetlands: the Veneto and the Emilio-Romagna. The Po Delta Regional Park in Emilia-Romagna is the larger of the two, and in 1999 was designated a World Heritage Site by the United Nations Environmental, Scientific, and Cultural Organization (UNESCO). The park contains wetlands, forest, dunes, and salt pans. It has a high biodiversity, with 1,000 to 1,100 plant species and 374 vertebrate species, of which 300 are birds.

The ecoregion’s wetlands are very important breeding and resting grounds for many bird species. Commonly seen here are egret, tern, heron, cormorant, and globally threatened ferruginous duck (Aythya nyroca). Several endemic (found nowhere else) species of fish are present, and the upland valleys of the Po River function as spawning grounds for many species, including some that are rare and/or threatened.

Human Impact

Although humans have been making modifications to the Po since ancient times, the most significant changes in the Po began in the 1950s. From this time forward, human activities altered the Po in several ways, including dredging to deepen the riverbed, forcing the river into channels, and erecting embankments (argini); the latter now exist along more than half the length of the river. Another major source of alteration in the river is sediment mining for construction purposes. In 2002, it was estimated that 33 million cubic yards (25 million cubic meters) of gravel and sand were removed annually from the river.

The Po River is used primarily for irrigation rather than for transport, and its floodplain provides a good growing environment for crops such as rice, maize, and sugar beets. Agricultural development in the area preceded the Romans. Today, about half the land in the Po Valley is irrigated, and some 12,000 square miles (31,000 square kilometers) are cultivated. As of 2003, about 70 percent of water withdrawn from the Po was used for agriculture, amounting to some 26 billion cubic yards (about 20 billion cubic meters) annually.

As there are no effective plans to promote efficiency or reduce water use, inefficient methods of irrigation continue to be practiced. In addition, about 4.2 million head of cattle and 5.2 million hogs are raised in the area. The natural vegetation of the Po has also been altered; along about one-quarter of its length, natural vegetation has been replaced by poplar trees grown to be harvested for cellulose.

The Po basin is hugely important in the nation’s economy, as 38 percent of the production of Italy is generated in this area, and 42 percent of the national workforce is employed here. Major industrial cities within the Po River biome include Cremona, Ferrara, Pavia, Piacenza, and Turin—and the metropolis of Milan is connected to the Po through a series of channels. The demands of this economic productivity have placed high burdens on the environment, while cultural and organizational factors have made it difficult or impossible to engage in effective resource management.

The combination of dense human population, agriculture, and animal husbandry produces a high organic load, and has created eutrophication (nutrient overload) in segments of the river with low flow rates. Although there is a permit system for point-source pollutants, it is not effective in controlling the problem. Pollutants from the many industrial installations in the area also contribute to a degradation of water quality in the Po. Although the Po Basin Authority is responsible for planning in the region, implementation is the responsibility of many other institutions (e.g., city councils, provinces) that often favor local interests, complicating the execution of an integrated management plan. One result is that many regulations that are in place are not enforced.

Major changes in water use will be necessary in northern Italy’s economically strategic Po River basin because of climate change. Scientists are predicting that rising sea levels, reduced rainfall, and lack of snow in the Alps will combine over the next few decades to render the last 60 miles (100 kilometers) of the river useless in many cases, mainly because of saltwater intrusion. Aspects of the change are clearly well underway. Meteorological records indicate that the total number of rainy days in Italy decreased by 14 percent from 1951 to 1996.

Because so much of the water from the Po is used for agriculture, farming techniques, especially those dealing with irrigation, will have to be altered to become more efficient. At the same time, mitigation efforts, barriers, and other contingency plans will have to be developed to preserve the ecological function and habitat support capacity of the delta and estuary segments of the Po River.

Bibliography

Grove, A. T. and Oliver Rackham. The Nature of Mediterranean Europe: An Ecological History. New Haven, CT: Yale University Press, 2003.

Marchi, Enrico, Giorgio Roth, and Franco Siccardi. The November 1994 Flood Event on the Po River: Structural and Non-Structural Measures Against Inundations. Genoa, Italy: Instituto di Idraulica, 1995.

Zwingle, Erla and W.A. Allard. “Italy’s Po River. Punished for Centuries by Destructive Floods, Northern Italians Stubbornly Embrace Their Nation’s Longest River, Which Nurtures Rice Fields, Vineyards, Fisheries—and Legends.” National Geographic 201, no. 5 (2002).