Land degradation a threat to environment

By Waqas Manzoor Bhutta



LAND degradation implies that the land has become less productive and supportive of human life and livestock or is unable to fully renew its natural vegetation.
It is, therefore, a major concern for those who care about land and environment. In Pakistan, land degradation encompasses deforestation, desertification, salinity and sodicity, soil erosion, water-logging, depletion of soil fertility and negative nutrient balances.

The country is located in arid and semi-arid climatic zones. Generally high evapo-transpiration in semi-arid and arid zones is the basic cause for salt accumulation on soil surface. The average summer temperature is about 40°C and the minimum winter temperature between 2°C to 5°C. The annual rainfall varies between 100 mm to 700 mm. The evaporation rate is generally very high and exceeds that of precipitation.

Thus, the insufficient rainfall followed by high evaporative demand and shallow ground water depth, enhances the movement of salts towards soil surface which leads to salinity and erosion of soils. Accumulation of rain and floodwaters in natural depressions is the major cause of primary salinity. Secondary salinity due to man-made causes is related to seepage from canals, lack of drainage, use of poor quality groundwater for irrigation, and insufficient leaching and poor land management practices.

Salinity and sodicity: At country level, 6.28 million ha is affected with salinity and sodicity. The majority of salt-affected soils are saline-sodic in nature.These salt affected soils are causing potential reduction in yield.

Soil erosion: Soil erosion implies loss or removal of surface soil material through the action of moving water, wind or ice. About 13.05 million hectares are affected by water erosion and about 6.17 million hectares are affected by water erosion. Soil erosion is taking place at an alarming rate and is mainly due to deforestation in the north. Water erosion is prominent on steep slopes such as the Potohar track and surrounding areas, an area extensively used for cultivation. The highest recorded rate of erosion is estimated to be 150-165 tons/hectare/year. The Indus River carried the fifth largest load of sediment (4.49t/h) in the world in 1990. According to some estimates, the Indus is adding 500,000 tons of sediment to the Tarbela Reservoir every day, reducing the life of dam by 22 per cent and the capacity of reservoir by 16 per cent.

Wind erosion has a relatively lower impact than water erosion. However, the combination of the two is more devastating. This reduces the productivity of the land by 1.5-7.5 per cent per year. This affects almost one-fifth of Punjab.

Water logging: It appears that problem of water logging may not be as serious now as it was in the past. The problem has been reduced due to prolonged drought and excessive mining of ground water.

The extent of the mentioned problems in terms of area is presented in the table below.

All of the above environmental issues are summarily taking Pakistan towards more economic instability. According to a conservative estimate, the impacts of degradation and biodiversity loss on productivity and public health are in the tune of three per cent of GDP per year. It would be higher if toxic waste disposal, biodiversity, river and coastal resource depletion were taken into account.

It is therefore necessary for the sustainable economic future and a friendly environment to cope with land degradation problem on basis of war-footing. Productive lands and healthy environment are precious gifts worth passing to our next generations.

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