The estuaries of the Saloum River, near the coast in Senegal, are surrounded by mangrove forest. These images show the forests dying between 1972 and 1992, turning from dark red to gray. The likely cause is a persistent drought, which may have increased the estuary's salinity beyond the mangroves' tolerance.

A dying forest

The coastal wetlands of Senegal are centered on the Saloum River and a myriad of estuaries and tidal flats that make up this complex ecosystem. The estuaries are generally bordered by dense, vigorous stands of mangroves (dark red tones in the Landsat images). A major portion of this ecosystem enjoys full protection as the Saloum Islands National Park. The wetlands are critical habitats for wintering Palearctic birds, as well as many species of fish and mollusks.

The mangrove vegetation is made up of several species, some of which form low canopies and others of the Rhizophora genus are among the tallest in the world, attaining heights of up to 40 meters. They grow in habitats that are periodically flooded by sea water (tidal influence) and river water. They are halophytes, plants which grow in salty environments.

Since the late 1960s, it has become apparent that many of the mangrove forests are dying. One theory is that there is a serious mangrove disease which is systematically wiping them out. However, most evidence indicates that the mangrove die-off is related to the widespread Sahelian drought, which has plagued the region since 1968. The lack of rainfall has led to an accumulation of salts, exceeding the tolerance levels of the mangroves.

The die-off is particularly acute in the northern half of the Saloum River wetland complex (note the change in tone on the Landsat imagery, from dark red to dark gray). Today, there are vast areas of standing dead mangrove carcasses; many of these areas have been reduced to barren mud flats. Only in the southern reaches of the wetland complex does one still see healthy stands of mangrove forests.

References

Remote Sensing Institute, 1986, Mapping and remote sensing of the resources of the Republic of Senegal; a study of the geology, hydrology, soils, vegetation and land use potential: Brookings, South Dakota, South Dakota State University, 655 p.

Thanks to Gray Tappan, USGS EROS, for photographs and written material used in this article.

Satellite images

LM1220050007231090 (Landsat 1 MSS, 5 November 1972)

LT4205050009230510 (Landsat 4 TM, 31 October 1992)

Map

Defense Mapping Agency, 1984 (compiled 1965, aeronautical and CHUM information revised 1984), Operational Navigation Chart K-1: edition 5, scale 1:1,000,000.

Photographs:

All photographs for this article were taken by Gray Tappan, USGS EROS.

How to cite this article

Campbell, Robert Wellman, ed. 1998. "Saloum River, Senegal: 1972, 1992." Earthshots: Satellite Images of Environmental Change. U.S. Geological Survey. http://earthshots.usgs.gov. This article was released 1 January 1998.