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WETLANDS MANAGEMENT

Water availability in the Zambezi Basin is closely linked to its 66,000 sq km of wetlands or surface waters. These floodplains, lakes and reservoirs provide extensive storage holding about 100,000 million cu m of water a year and that the total volume of water available, excluding net losses is about 110,000 million cu m per year.

Wetland habitats, productivity and biodiversity as well as ecological processes are dependent on the availability of water. It has been estimated that the minimum water requirement to maintain the wetlands is 3,840 cu m per second, a figure based on average evapotranspiration from the wetlands.

Benefits and services provided by wetlands

Water and wetland resources of the Zambezi Basin provide numerous benefits to the riparian states for social and economic development. Their management is important to sustain the various sectors of the economy that are dependent on the water resources and the wetlands. About 20 million people, constituting about 52 percent of the population in the basin, are concentrated around wetlands and many of them are dependent on hand-dug wells for the supply of potable water.

Some of the benefits and services provided by the water resources and the wetlands of the basin include but are not limited to: energy, flow regulation, plant and animal products, conservation, tourism, and recreation.

Energy

The high runoff and 1,000-metre fall in elevation from the source to the sea make the Zambezi River well suited for hydropower generation. This is also true for some of the tributaries. At present, 15 power stations generate 32,800 GWh a year in the Zambezi Basin. However, low water levels caused by frequent droughts threaten reliable electricity generation in the basin. Generation levels can fall by as high as 12.2 percent depending on the severity and persistence of the drought.

Flow regulation

Wetlands regulate flow and attenuate floods. Flood-plains store water during the wet seasons, slowly releasing it throughout the dry periods. This helps to maintain flow in perennial rivers such as the Zambezi and its tributaries. This function of wetlands is dependent on a number of parameters such as the size of the wetland, number of wetlands located in the basin, soil type and depth, and the vegetation in the wetland, among others. Plants in marshes and swamps control erosion as roots hold the soil and trap sediments. Wetlands, therefore, play an important role in flood control and erosion prevention. Well vegetated rivers and floodplains are excellent flood absorbers. The variations in flooding create fertile soils used to support intensive agriculture in floodplains. About 520,000 sq km of land is annually cultivated within the basin, a proportion of which is subsistence floodplain farming dependent on the seasonal replenishment of nutrients within wetlands.

Plant and animal products

The wetlands of the Zambezi Basin support a diversity of plant and animal species. Wetlands are principal habitats for fish species, providing cover as well as suitable breeding and feeding grounds. Wetlands support subsistence, artisanal, ornamental and commercial fisheries. The most notable commercial fisheries are on Lake Malawi/Nyasa, Zambezi Delta/Sofala Bank and Cahora Bassa, and at Itezhi-tezhi, Kafue and Lake Kariba. The fisheries of these areas depend on the availability of relatively nutrient-rich water provided by the wetlands. On Lake Kariba, the main commercial fishery activity is the offshore sardine fishery. This freshwater sardine or kapenta, has also established itself in Cahora Bassa where its exploitation is still limited. However, potential catches are estimated at 15,000 tonnes per year. By 1993, the annual yield from Lake Kariba was about 30,000 tonnes valued at US$55 million.

Fish is a major protein source in the basin states. There are 85 fish species in the Upper Zambezi alone and the potential yield is estimated at 14,000 tonnes per year, while fish catches average 7,500 tonnes annually. The Zambezi Floodplains fisheries support about 300,000 people and act as a food store for a great variety of fish-eating birds.

Earlier fish yields from the eastern Caprivi, between 1970s and early 80s, are estimated to have been as high as 800 tonnes annually for Lake Liambezi and an additional 700B900 tonnes a year from the Zambezi, Chobe and Kwando rivers. However, reduction in floodplains due to inadequate floods, particularly of the shallow seasonal breeding areas, and overfishing has contributed to a decline in the fishery. The annual value of the fish catch in Caprivi is about US$1.8 million and total fish production about 1,500 tonnes.

At the delta, a thriving shrimp fishery contributes significantly to the Mozambican economy. In Angola, it is estimated that 50,000 people are seasonally employed in the floodplain fisheries near the headwaters of the Zambezi. In Malawi, the major fishing industry is on Lake Malawi/Nyasa where the "Chambo" fish dominates the industry. Elsewhere in the country, the Lower Shire is known to yield 10,000 tonnes of fish annually.

Wetland resources can, to some extent, buffer the effects of poverty. Poor rural communities living close to wetlands and having access to a variety of "free" wetland resources such as reeds, thatching grass, timber, fish, crabs and edible plants, are often healthier and have a better quality of life than those subsistence communities who do not have access to wetland resources.

Wetlands are also important in sustaining life during droughts. Both people and wildlife converge on wetlands for water and food during droughts. For example, during the 1969-70 drought that affected Zimbabwe, 84 percent of the farmers with dambo fields were able to support their families.

Conservation

The natural beauty and rich biodiversity of wetlands make them an important focus for conservation. Eight percent of the Zambezi Basin consists of protected areas. Many of the national parks and conservation areas in the basin are wetlands. Most of the wetlands support large numbers of wetland birds, consisting of more than 500 species.

Despite the numerous and important products and values provided by wetlands they have not been accorded the conservation status that they require. Only one Ramsar site exists in the whole basin, and this is the Lochnivar Wetlands in the Kafue Flats. Of the eight riparian states, only five are parties to the Ramsar Convention. Tanzania ratified only in 1998 while Angola, Mozambique and Zimbabwe have not. The convention accords international conservation status to important wetlands.

Wetlands are an important focus for conservation, tourism, recreation and education. The ecological value of the Zambezi Basin wetlands has been estimated to be US$15,000 per hectare per year. The mangrove wetlands and estuaries of the delta are worth between US$10,000-100,000 per sq km per year.

Threats to wetlands

Threats to the Zambezi Basin wetlands include reduced flows caused by droughts and water abstractions, aquatic weed infestation, pesticides especially dichloro-diphenyl-tricholoroethane (DDT), infrastructure development such as dams, overexploitation of resources due to human pressure, uncontrolled fires, pollution and deforestation, among others.

Wetlands such as the Elephant Marsh in Malawi, the Zambezi Delta in Mozambique, the Kwando/ Linyanti/Chobe system draining down into the Caprivi and the Zambezi and the Kafue floodplains of Zambia are among the most environmentally sensitive areas in the basin. All are rated as "very high" in terms of environmental sensitivity.

There are indications of declining wetland productivity in the Zambezi Floodplains due to a combination of reduced flows and increased exploitation of natural resources as a result of increasing population pressure.

Further downstream, the proposed abstraction of water to supply the city of Bulawayo and for irrigation in Zimbabwe, could adversely impact the ecology of downstream wetlands such as the Mana Pools. At Livingstone, Victoria Falls and Tete, raw untreated sewage is discharged into the Zambezi River, causing pollution and posing health risks to downstream users.

The growth of problem aquatic plants such as Kariba weed and water hyacinth is correlated to increased nutrient levels in rivers, sewage effluent, as well as fertiliser-rich runoff from agriculture. New dams such as the hydropower development proposed at Batoka Gorge and downstream of Cahora Bassa need to be carefully assessed in terms of their potential impact on river ecology. The existing large dams have already drastically reduced the vital floodplain areas in the Zambezi Basin.

On Lake Kariba, there is a problem of aquatic weeds, originally Kariba weed and more recently water hyacinth. Also of concern is that the fishing regulations for the lake are different in Zambia and Zimbabwe. For example, in Zimbabwe gill net mesh may not be smaller than 100 mm while in Zambia the size limit is 75 mm.

In the Lower Zambezi and the Lower Shire Valley, wetlands are under pressure due to dense human settlement. Evidence exists that water regulation from Cahora Bassa has substantially reduced the Zambezi Delta wetland area, affecting wetland productivity in Mozambique and even offshore shrimp catches. Salt-water intrusion is a serious problem in the delta due to reduced freshwater flows and the lack of substantial seasonal floods. New infrastructure development proposed downstream of Cahora Bassa will worsen the already declining ecological situation in the delta. The environmental impacts of dams on the ecology and water needs of the downstream communities especially in Mozambique have not been fully assessed.

Pollution and the drying of floodplains have also caused habitat damage and species loss, especially in the Caprivi. Since the beginning of the 1990s, the Kwando River has been experiencing reduced water flows, resulting in wetland loss and reduction in wetland-dependent species. Pollution from industrial and domestic sewage, has in recent years been increasing due to growing urban centres along the Zambezi River, such as Mongu, Senanga, Katima Mulilo, Kasane-Kazungula, Sesheke, Livingstone, Victoria Falls, Kariba, Siavonga, Chirundu and Tete. Most of these urban centres including cities such as Blantyre, Bulawayo, Harare and Lusaka and the mushrooming tourist facilities along the river, discharge effluents into the river and its tributaries.

Overfishing in the wetland areas of the basin has also led to the depletion of some fish species. Over-exploitation of riverine vegetation such as reeds and grasses is threatening wetland ecosystems, ultimately leading to habitat loss.

As human population densities in the Zambezi Basin increase, the available land share per capita decreases, forcing more and more people to move into floodplains to settle. The most striking example of this is in the Lower Shire Valley where even the smallest island is now cultivated and conflicts with wild animals such as hippos and crocodiles are a serious problem.

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