net – сеть, чистый

Read the international words and give their Russian equivalents:

major, history, effect, million, transport, hydrogeological, engineer, decade, problem, planet, serious, tragedy, national, central, fundamentally, balance, natural, hectar, canal, application, reservoir, filtration, system, result, accelerate, block, separate, western, portion, stabilize, kilometer

There are two major environmental disasters in the recent history of the former Soviet Union: Chernobyl and the Aral Sea. In 1960 the land-locked Aral Sea was the world's fourth largest lake, but now, due to increased irrigation demands on its two main inflowing rivers, it is now half the size, 16 m lower and three times as salty. The effect on the 3 mln people who needed the lake for its water, fish and transport has been slowly devastating. Sadly, the huge hydrogeological changes which engineers have unwittingly triggered will take decades to reverse. This paper investigates the nature, causes and consequences of the Aral Sea problem and discusses proposed solutions.

One of the planet's most serious environmental and human tragedies is unfolding in the basin of the Aral Sea. Over the past 40 years, the huge lake has shrunk considerably as expanding irrigation has reduced river inflow to it.

The Aral Sea is located among the deserts of Central Asia. A terminal lake (i.e., without surface inflow ), its level is fundamentally determined by the balance between surface inflow from two large rivers and net evaporation ( i. e. evaporation from its surface minus precipitation on it), which is estimated to be around 874 mm per year. Net ground water exchange plays a secondary role and data on it are approximate.

Five former republics, now independent nations, lie wholly or partially in the sea's basin: Uzbekistan, Kazakstan, Kyrgyzstan, Turkmenistan and Tadzhikistan. The Aral Sea drainage basin encompasses all of Uzbekistan and Tadzhikistan, all but the nothern part of Kyrgyzstan, the eastern half of Turkmenia and the two southern oblasts of Kazakstan. It also includes part of nothern Iran and Afganistan. The flow of the Amu-Dar'ya arises primarily from the Pamir Mountains and the flow of the Syr-Dar'ya primarily from the Tien-Shan Mountains. The population of that part of the Aral Sea basin lying in the former Soviet Union was around 35 mln in 1990.

The Aral Sea was the world's fourth largest lake in the area in 1960. Although somewhat saline the lake was populated mainly by fresh water species and had a productive fishery as well as serving as a major regional transportation route. The vast deltas of Amu-Dar'ya and Syr-Dar'ya not only had major ecological significance, with a diversity of floral and faunal species but great economic importance related to irrigated agriculture and animal husbandry, hunting and trapping, fishing and harvesting of the reeds that grow in abundance in the numerous wetlands and lakes found here.

Over the past 40 years the sea has steadily shrunk. The reason is a huge and growing diminuation of discharge from the Amu-Dar'ya and Syr-Dar'ya, caused primarily by the expanding irrigation in their basins.

Irrigation expantion in the Aral Sea basin after 1960 required much more water per hectar as long canals were extended into the desert; poorer, more saline soils were irrigated, requiring heavier water applications. Giant reservoirs were built that required filling and which increased evaporative losses, and new irrigation systems discharged their water into the deserts rather than back to the rivers.