ABSTRACT

A review is presented of the hydrology and water resource values of humid tropical wetlands and lakes. Issues discussed in relation to natural lakes are long-term changes in water levels, aquatic weeds and modelling lake/river interactions. The status of tropical wetland research is presented with reviews of different modelling strategies, empirical water balance studies, and wetland influences upon downstream flows. Current issues involving wetlands in the water resource arena are discussed, and strategies for optimal wetland management and research strategies are identified.

INTRODUCTION

Wetlands occupy approximately 6% of the earth's land surface, and can be found on each of the tropical continents. Table 1 illustrates that tropical wetlands are most extensive in South America, with similar areal extents between Asia and Africa. Balek (1977) reports that the 340 000 km2 of wetlands within Africa are composed of some 104 to 105 individual wetland systems alone. Table 2 illustrates that wetlands can cover up to 10% of individual countries on the African continent and up to 30% on the Asian continent. Early estimates of wetland proportions in the tropics are being revised upwards as improved surveys are carried out in more isolated regions of the world (Maltby, 1988). Furthermore, consideration of wetland extent in the past has tended to under-represent the number of small seasonal wetlands, such as the dambo, pan and black clay types (Howard-Williams & Thompson, 1985), which can occupy over 25% of the land surface areas in many regions of southern Africa.