For four months each year during the rainy season, floodwaters spill over the banks of the Niger and Bani Rivers and the Inner Niger Delta swells to an area of about 20,000 square kilometers (km2). The swamps, lakes, and channels of the delta provide vital habitat for migratory Palearctic birds and West African manatees. The delta is also an essential resource for Malians, supporting livelihoods in fishing, farming, and pastoralism in an otherwise arid country. These floodplains support the highest livestock density in Africa, and are increasingly threatened by a variety of anthropogenic pressures and unsustainable uses.
Location and General Description
The Inner Niger Delta is located in central Mali in the semi-arid Sahelian zone, just south of the Sahara Desert. The huge dunes of the Erg Ouagadou funnel the waters of the inner delta north and east through Mali. A diverse mix of channels, swamps, and lakes, the delta expands to cover 20,000 km2 during the rainy season and contracts to 3,900 km2 during the dry season. The delta extends for 425 km with an average width of 87 km, tapering into a braided river near Timbouctou where the Niger River curves to the east. The floodplain is remarkably level, dropping only 8 meters (m) over its course. Delta topography is a complex mix of submerged lower areas and higher, unflooded areas known as tougérés. The floodplain consists of a vast network of river channels with leveés separated by low, clay-based floodplains. As waters flow through the delta, they pass over Pleistocene and recent alluvium overlying Paleozoic sandstone.
The floodwaters of the delta come primarily from the Niger River, its main tributary the Bani River, and smaller streams that flow down from the Dogonland Plateau. The Niger River is the longest river in West Africa and the third longest in Africa. Originating in the Fouta Djalon highlands of Guinea, the river extends for 4,100 km before flowing into the Atlantic Ocean on the Nigerian Coast. The Bani River is 1,100 km in length with sources in Côte d’Ivoire and Burkina Faso. Dogonland streams provide an insignificant contribution to the delta but do fill the southwestern lakes. Dry, landlocked Mali is completely dependent on these rivers for its water resources.
Precipitation over the delta varies in duration and volume with latitude. In the south, the rainy season lasts from July through October, with mean annual precipitation of 750 millimeters (mm). In the north, the rainy season extends from July through September, with a mean annual precipitation of 250 mm. This local rainfall has a negligible impact, and the flood regime of the inner delta is dependent on rainfall in the Niger and Bani headwaters. Rains fall at the Niger’s headwaters from May through September, creating a surge that reaches the inland delta in October. This surge dissipates as it continues through the delta, with nearly two-thirds of the Niger’s water volume lost to seepage and evaporation. The extensive swamps and vegetation of the delta filter silt and salt from the water so that the water leaving the delta is clear, low in dissolved salts and silt-free.
A diverse mix of vegetation grows in the Inner Niger Delta. Three main plant associations have been identified: submerged and floating plants in shallow or stagnant water, partially submerged and marginal vegetation dominated by grasses, and plants that grow on seasonally exposed sand. Algae blooms are common on the lake and greatly reduce the water transparency.
The southern half of the delta is low-lying floodplain with grasses such as Acroceras amplectens, Echinochloa pyramidalis, E. stagnina, and Eragrostis atroviriens. Along the heavily grazed outer fringes, Andropogon gayanus, Cynodon dactylon, and Hyparrhenia dissoluta dominate. A gallery of Mimosa asperata and Salix chevalieri grows along watercourses above a Cyperus maculatus understory. In the south, sparse gallery forest extends into the delta along watercourses. Trees such as Diospyros sp. and Kigelia africana grow on higher levées, their density increased due to human activity. The northern half of the delta is characterized by emergent sand ridges and the palms Hyphaene thebaica and Borassus aethiopum that occur in higher frequency near villages. Other trees and shrubs of elevated areas include Acacia nilotica, Guarea senegalensis, Mimosa asperata, and Ziziphus mauritiana.
The Inner Niger Delta provides essential habitat for huge numbers of wetland birds, including Afrotropical resident species and migrants that spend the Palearctic winter in Africa. Approximately 500,000 garganey (Anas querquedula) and up to 200,000 pintail (Anas acuta) winter here, along with large numbers of ferruginous duck (Aythya nyroca), white-winged tern (Chlidonias leucopterus), ruff (Philomachus pugnax), black-tailed godwit (Limosa limosa) and other waterbirds. One Ramsar site, Lac Horo, often holds more than 50 percent of the West African wintering ferruginous duck population. It is also nationally important for breeding African spoonbills (Platalea alba) and purple swamp-hens (Porphyrio porphyrio).
The Inner Niger Delta is also known for its large waterfowl breeding colonies, with 80,000 breeding pairs of birds within 15 species of cormorant, heron, spoonbill, and ibis. The Inner Niger Delta is also a breeding stronghold for the endangered West African subspecies of black-crowned crane (Balearica pavonina pavonina). The delta is essential waterfowl habitat because it remains wet in the dry season long after other areas dry up. A notable non-wetland bird species is the endemic Mali firefinch (Lagonosticta virata), which is found only in Mali and largely confined to the delta area. The river prinia (Prinia fluviatilis) is considered near-endemic to this ecoregion. The vast floodplains also provide habitat for the Nile crocodile (Crocodylus niloticus).
Mammal species are a mixture of Sahelian species, and those of more mesic environments that occur here because of the delta wetlands. Populations of all larger species have been greatly reduced by human population pressures, and some species have been extirpated from the area. Sahelian savanna species found in the Inner Niger Delta: Libyan striped weasel (Ictonyx libyca), African civet (Civetticutus civetta), caracal (Felis caracal), serval (Felis serval), striped hyena (Hyaena hyaena), patas monkey (Erythrocebus patas), sand fox (Vulpes pallida) and African wild cat (Felis silvestris). A number of other mammal species are more closely linked to the wetlands of the Inner Niger delta. The delta harbors the largest surviving population of West African manatees (Trichechus senegalensis), although they are prized for their meat and ease of capture and are thus heavily hunted. Hippos (Hippopotamus amphibius) are increasingly rare and have been regarded as nearly exterminated. Antelope populations have been seriously reduced by the bushmeat trade and because of conflicts with grazing livestock. Buffon’s kob (Kobus kob kob) was once numerous in the Inner Niger Delta, but is no longer present. Bohor reedbuck (Redunca redunca) and waterbuck (Kobus ellipsiprymnus defassa) have also probably been eliminated from the area. Small populations of roan antelope (Hippotragus equinus), red-fronted gazelle (Gazella rufifrons), dorcas gazelle (Gazella dorcas), and dama gazelle (Gazella dama) are believed to still exist. Warthogs (Phacochoerus africanus) are still found in the delta, Cape clawless otter (Aonyx capensis) and spotted-neck otter (Lutra maculicollis) are common, and elephants (Loxodonta africana) migrate from Burkina Faso to the Diaka River.
A rich fish fauna of 110 different species is found in the inner delta, but few species are endemic because the Niger River was linked to the Chad and Nile systems at various times. Two of the endemic fish found here are Syndodontis gobroni and a cichlid, Gobiocichla wonderi. Many species migrate upriver and downriver as well as laterally out on to the floodplain as the water rises. When the waters recede, the fish move upriver or risk becoming trapped in small, isolated ponds. Some fish species can survive in these dwindling pools by aestivating or by breathing air.
Three Ramsar sites were declared in 1987: Lac Horo, Lac Debo, and the Séri floodplain complex, comprising 1,620 km2. The Ramsar sites are owned by the state and are utilized by local villagers for drinking water, fishing, seasonal agriculture, and livestock rearing. Lac Horo is separated from the Niger by a dam and a sluice gate. The rest of the area is unprotected and heavily used for different forms of human activity.
Types and Severity of Threats
Mali is among the poorest countries in the world, with 65 percent of its land area desert or semi desert. Economic activity is largely confined to the riverine area irrigated by the Niger, and fish makes up 60 percent of the total animal protein consumed by Malians. Approximately 580,000 permanent residents inhabit the delta, with a population density 2.7 times greater than the national average. Despite this large population, the delta normally produces a surplus of fish, rice, and livestock to be exported to surrounding countries. However, the Niger River is not a constant resource, with fluctuating rains altering economic circumstances dramatically from year to year. Fish landings and rice production may be halved, or further reduced, during years with low rainfall. The region remains economically unstable as a result, and foreign aid has had little effect. Since 1972, some US$100 million has been spent in the region, as the area’s economy worsened.
In recent times, a combination of low river floods, limited rains, increasing human populations and changing administrative practices has increased pressure on the delta. While people have intensively exploited the Niger Delta over the last 1,000 years, resource use was dictated by a complex traditional system of management. A half-dozen different ethnic groups used the delta, engaging in pastoralism, fishing and farming, synchronizing their movements with the annual river flood. Today, the traditional systems of management have been discontinued, replaced by ineffective and confusing governmental regulations. In one case, the Malian laws actually encouraged deforestation.
Without traditional management of fisheries, more people are fishing (previously only two ethnic groups fished), and fish diversity is decreasing. Several economically important species are declining or extinct, causing grave financial hardship for fishermen. Many fish species disappeared after serious droughts in 1994, but the decline has been compounded by water management projects and overharvesting. Traditional methods of catching fish are still used, with intensive harvesting taking place during the dry season as fish become trapped in dwindling channels and lakes. Fishermen follow fish as they migrate throughout the delta. Modern gear, such as nylon nets, is increasingly available.
Traditional management systems once regulated pastoralists as well. Pastoralists move the herds on to arid, rain-fed lands as waters rise, and then they move livestock back on to the floodplain to graze on protein-rich grasses as water recedes. Livestock are numerous here, with as many as 2 million cattle and 3 million sheep found in the highest density livestock herds in Africa. Excessive grazing combined with the severe droughts of the past two decades has resulted in land degradation and pasture loss. Habitat degradation is also caused by deforestation, erosion, and agricultural mismanagement in the Niger watershed. Erosion leads to increased sand deposits that then fill in small pools and streams, eradicating aquatic vegetation and mollusks. Deforestation in the delta decreases bird habitat by removing roost and breeding trees. At one point in the 1990s, the combination of drought and deforestation had led to the disappearance of two-thirds of the bird colonies.
Water levels, bird populations and fish catches have increased in recent years with adequate rain, but river waters are still threatened by water management projects. The Selingue Dam and other smaller dams have a negative impact on fisheries, cutting off fish migrations and altering the timing of the annual delta flood. Within the delta, rice, millet, maize, and wheat are cultivated in the rich floodplain soils. Farming varies from basic subsistence level to larger, irrigated projects such as the Food and Agriculture Organization of the United Nations (FAO) special program for food security pilot project in the Mopti region. Large rice irrigation projects would have a number of adverse effects on floodplain ecology. These projects require total hydrological control and would upset the natural distribution of fish, insect, and bird species. Some fish, such as Alestes baremose and Tilapia zillii, eat rice plants and could flourish, while other fish and bird species may decline as a result of environmental modifications. Irrigation projects may also encourage pesticide use to control insects and other pests such as the red-billed quelea or dioch (Quelea quelea).
Justification of Ecoregion Delineation
The distinctiveness of this area, particularly in terms of its role for migrating birds, is the justification for defining the area as a separate ecoregion. The linework for this ecoregion follows the ‘mosaic of edaphic grassland and aquatic vegetation’ unit of White.
Additional Information on this Ecoregion
- For a shorter summary of this entry, see the WWF WildWorld profile of this ecoregion.
- To see the species that live in this ecoregion, including images and threat levels, see the WWF Wildfinder description of this ecoregion.
- World Wildlife Fund Homepage
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