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Last week in this column we presented a wide range of economic, social and environmental benefits that can be derived from wetland ecosystems.  Using wetlands wisely, in a manner which does not harm the ability for future generations to also benefit from the wetland, will maintain these functions and the provision of products. However, unsustainable exploitation of wetlands, and river basins as a whole, still occurs on a large scale.  This has often resulted in higher frequency and severity of flooding, drought and pollution. The degradation and loss of wetlands and their biodiversity imposes major economic and social losses and costs. 

Threats to Wetlands

1. Fishing and hunting destroys a wetland if too many animals are caught or hunted, as there will not be enough left to reproduce and to replace the ones that are removed.  In order that hunting and fishing be sustainable, the number of animals caught or hunted should not exceed the capacity of the population to renew itself.

2. Burning is a threat to the wetland as some fires burn soil and plants below the ground, which can destroy the plants.  Burning can also damage the wetland by increasing the risk of erosion.

3. Mowing and harvesting of plants by hand  (like picking of reeds) tends to have much less of a negative impact on the indirect benefits of wetlands than cultivation.  Cutting plants has similar effects to grazing and generally increases habitat diversity, provided that extensive areas are not mown or cut at one time. 

4. Timber production from wetlands could lead to extinction of useful trees and lead to a habitat change.  Moreover the wetland itself may be lost due to timber production since plantations have a high impact on the water storage function of wetlands.

5. Grazing may have both positive and negative effects on the indirect benefits of wetlands.  Grazing may be particularly helpful in wetlands, which have some areas grazed short and other areas left tall, often the diversity within such a habitat is increased.  On the other hand in wetlands which are completely grazed short, the diversity of that habitat is decreased.

6. Wetland erosion: since wetlands are characteristically areas where the movement of surface water is slowed down and sediment is deposited, erosion occurs when more sediment is removed that is deposited.  Erosion of wetlands may result in deep gullies, which drain the water rapidly from the wetland and make the water regime much less wet, thus reducing the value of the wetland.

7. Drainage occurs when wetlands are converted to agricultural cropland and leads to most of the indirect benefits of the land being lost.  Drained wetlands are less effective at regulating stream-flow and purifying water because the drainage channels speed up the movement of water through the wetland.  Drainage also increases the danger of erosion by concentrating water flow thus escalating the erosive power of the water.  Furthermore, drainage significantly reduces the biodiversity of wetland areas.

8. Damming is useful in performing certain wetland functions, for instance sediment trapping and water storage. However invasive damming damages other functions of wetlands, and also impacts upon the habitat required by specialised wetland dependent species.

Next week we will conclude this series on wetlands by examining how integrated wetlands management can help to reduce these threats, and the role of the Ramsar Convention.  Before then we will be celebrating World Wetlands Day, this coming Wednesday (2nd February); please have a look at http://www.ramsar.org/wwd2005_index.htm if you are interested in learning more.

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