Thursday, 19 April 2012

Contraction of Wetlands and Drying Up of Lakes

Wetlands, often referred to as earth’s kidney, has played a vital role in sustaining ecosystems that serves millions of lives. They act as an enormous sponge slowly releasing water into rivers all round year.

The fresh water wetlands on the Tibetan Plateau are distributed in an area of around 1,33,000 With their wealth of stored carbon, these wetlands provide a potential sink for theatmospheric carbon. It was also observed that the role of wetland as a carbon sink was closely related with the water table and the amount of precipitation.

The warming climate has resulted in the drying-up of thousands of lakes across the Tibetan Plateau. Most of them are considered sacred. These lakes have no outlet and depend entirely on local streams and underground sources to maintain their water level. Already a large number of lakes have disappeared due to warming climate and human activities in the past few decades. This is now accelerating.

Dagze Tso is one of many inland lakes in Tibet. In glacial times, the region was considerably wetter, and lakes were correspondingly much larger, as evidenced by the numerous fossil shorelines that circle the lake and attest to the presence of a previously larger, deeper lake. Over millennia changes in climate have resulted in greater aridity of the Tibetan Plateau. Image Credit: NASA/GSFC/METI/ERSDAC/JAROS, and U.S./Japan ASTER Science Team
The subsequent release of Carbon dioxide, Methane and Nitrogen dioxide from these contracting wetlands further adds up to the yearly GHGs emission. Total Carbon dioxide emission from the Tibetan Plateau wetlands due to prolonged permafrost thawing season is estimated to be around 10 million tons, which is roughly equivalent to Carbon dioxide emitted by 10 million average automobiles in China for two months. The wetlands of Lhalu on the northwest edge of Lhasa, with its total area of 6.2 sq. km could absorb 78,800 tons of Carbon and produce 57,300 tons of oxygen annually.

Tso-Ngonpo or Kokonor Lake shrank considerably between 1959 and 2005.

The contraction in the wetlands due to climate change led to reduced flows of the Drichu (Yangtze) and Machu (Yellow) rivers. The warming climate has resulted in the drying-up of thousands of lakes across the Tibetan Plateau over thousands of years.

According to Chinese Academy of Sciences, the wetlands on the Tibetan Plateau have shrunk more than 10% overall in the past 40 years, with biggest shrinkage occurring at the source of the Drichu (Yangtze) and Machu (Yellow).

The surface area of lake Nam-Tso has decreased by 38.58 sq. km from 1970 to 1988 at a rate of 2.14 Sq. km per year. Similarly, the water level of Tso-Ngonpo has reportedly lowered by 3.62 meters and its water surface shrank by 342 sq. km between 1959 and 2005. The decline in the lake level of Tso-Ngonpo has led to many environmental problems in this watershed such as grassland degradation, deterioration of water quality, wind erosion and expansion of sandy land.

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