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1. Cases of Coral Damage due to Sedimentation

Damage to reefs in the Parque Nacional Morrocoy, Venezuela, began on a large scale when, in the 1970's, construction took place on all existing keys, on many shoals, sand banks and reef flats. By May 1974, however, the Venezuelan government proclaimed the area a national park, ordered the demolition of all the construction on the keys and beaches and forbade any further developments of coastal towns within the park. Subsequent surveys conducted in 1979 and in 1980 found that deterioration had not been halted. Symptoms of the damage consisted of dead coral coverage of over 70%, and the stressing and burial of coral by sediments. An increased rate of sedimentation was found to coincide with land clearing, construction and agriculture from 1972 onwards.

Saba, Netherland Antilles, in the northeastern Caribbean, is mountainous and land-ocean access for people is through bays. The 3 main impacts are sedimentation, dive tourism and fishing . The sedimentation is primarily due to a rock-crushing plant and secondarily due to natural runoff during heavy rains.

2. Case of Seagrass Damage due to Sedimentation

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Seagrasses have declined on a global scale and at a rate that is accelerating. The Laguna Madre in Texas, USA, has lost 140 km2 of seagrass area within the last 30 years. These declines have been attributed to turbidity from sedimentation and dredging. In order to verify the effects of dredging, activities were carried out at Laguna Madre and the effects on sea grass were observed. The effects (measured by shoot density, biomass and blade chlorophyll content) were compared to those of a control site. Dredging was found to be deleterious to sea grass through sediment burial and reduction of light intensity through increased turbidity. Dredging was also found to significantly affect sea grass survival and productivity with the effect lasting for several months after the dredging activity was completed.

3. Case of Lagoons Affected by Sedimentation

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Coastal lagoons in the western Mediterranean were found to be the major recipients of sediments in the area, as is the case with most lagoons. There was found to be a serious threat to the Mediterranean lagoons from siltation. There has already been a decrease in lagoonal area from 33000 ha in the 18th century to 26000 ha in 1990 in southern France.

Sedimentation due to terrestrial runoff led to:

· reduction in overall depth of water

· land formation due to increasing sedimentation of delta fan

· transport of particulate matter to deeper waters.

The reduction of water levels was favourable to rooting of vegetation which further traps sediments and is a positive feedback process detrimental to fisheries.

4. Wetland Restoration

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The San Francisco Bay Estuary has been studies extensively since 1972. Diverse wetland restoration projects have been implemented by opening barriers and restoring tidal action. The projects have been successful in transforming mudflats into mature vegetated marsh plain and a decrease of wind and wave erosion has been observed.

The area has also undergone regular physical monitoring since 1986, thus, building up a comprehensive evolutionary history of the site and site restoration since the start of the project. Data such as sediment accretory rates and rates of vegetation colonization have been collected and are extremely useful in rehabilitation and restoration projects elsewhere.

5. Mangroves

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Very few quantitative studies have been carried out in the field of relating the presence of mangrove habitats with coastal harvests. One of these studies has been carried out by Yanez-Arancibia et al (1985) which shows a clear positive correlation between commercial finfish catches and total area of coastal vegetation, mangroves in particular. The researchers also verified that one of the principal factors affecting fish catches was river discharge. The authors also point out that it is not known whether the presence of the mangrove itself is a causal factor or whether it is due to other related factors such as large area of shallow sea and coastline, intertidal area, organic matter, etc.

Researchers measured accretion rates of mangroves in developed watersheds and compared them with those of undeveloped watersheds in Micronesia. They found that human development is leading to increased sedimentation. The cause of increased sedimentation needs to be determined, long-term survival of the ecosystem needs to be considered and finally remediation strategies need to be implemented.

6. Rehabilitation of Rural Habitats

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Participatory Upland Conservation and Development (PUCD) projects of the FAO have provided technical assistance in areas where required. In Burundi the problem concerned sustainable rural development. High population density and limited farm size are serious problems where sustainable development is concerned. The area was difficult to cultivate due to the topography of steep hills and ploughing had led to the loss of soil fertility through erosion. Green manuring, contour line cultivation, planting of tree and fodder species were implemented in order to increase soil fertility and prevent erosion.

Similar problems were seen in Bolivia where slash-and-burn techniques were found to cause soil loss. The PUCD project provided assistance for the implementation of logs and branches to establish self-forming terraces, contour line planting and the planting of nitrogen fixing fodder species to improve soil retention.

A project in Louisiana is currently assessing the value of in enhancing fishery production through providing sheltered areas for planktonic and juvenile forms of marine life. Ridges or terraces are formed on subtidal bottom sediments in order to convert shallow subtidal areas into marsh. They were arranged in a checkerboard pattern with open corners and planted with marsh vegetation. Long term studies are presently being conducted.

7. Effect of River Damming and Deficit of Sediment Flux on the Continental Shelf: A Case Study of the Nile Delta

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Man’s intervention in the flow of the Nile in Egypt dates back to Pharaonic times. Modern intervention began with the construction of the "Delta Barrage" near Cairo in 1861. The practice was developed with the low Aswan Dam constructed in 1902. The Aswan High Dam is the second dam to be built in the vicinity of the Nile’s first cataract at Aswan. Its construction began in 1960. The Nile was closed around a temporary structure in 1965, the dam was completed in 1967. Sediment once transported by the Nile River to the coast, average of 100x10 6 t yr-1, is now almost cut off.

The intervention of the River Nile and continued modification of the delta is expected to result in the increased erosion of the surficial shelf sediments.

This paper discusses the effect of river damming and the deficit of sediment budget on the continental shelf off the Nile Delta. Details of this paper are found at the URL given below:

http://ioc.unesco.org/iochtm/w089/w089ww12.htm

8. Effect of Damming on the Colorado River

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This article details the effects of damming and over utilization of the Colorado river, including the effects on downstream marine life. Details of this paper are found at the URL given below:

http://www.msnbc.com/news/320003

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