Function of Wetlands

Wetlands play a key role in the hydrology of a river basin, including a number of socio-economic development benefits to the riparian states, including among others:

Flow regulation
Erosion control
floodplain farming
Plant and animal products
Conservation
Tourism and recreation
Water Quality
Carbon sinks

Therefore, careful and appropriate management is important to sustain the various sectors of the economy that depend on wetlands and their effect on water resources. Much of the population in the basin is concentrated near wetlands and many depend on associated springs and shallow wells for potable water.

In addition to socio-economic benefits, wetlands can provide significant biophysical benefits, including groundwater recharge and improved water quality.

Flow Regulation

Besides serving as sources of streams in certain cases, wetlands also regulate flow and attenuate floods. Wetlands located on flood-plains store water duringwet seasons, slowly releasing it throughout the dry periods. This helps to maintain flow in the perennial rivers of the basin and in some of their tributaries.

This function of wetlands depends on a number of parameters: the size and shape of the wetland, number of wetlands located in a particular sub-basin or the entire basin, soil type and depth, and the vegetation in the wetland.

Plant and Animal Products

The nutrients in the wetland environment of the basin support diverse plant and animal species. Wetlands are also principal habitats for fish species, providing cover as well as suitable breeding and feeding grounds.

Many wetland areas are often used by local people as pasture for livestock and the areas around wetlands in the Limpopo River basin are often converted to agricultural fields. Water from wetlands is also often withdrawn for irrigating crops.

Examples from a study by Masiyandima et al (2005), from across the Limpopo River basin illustrate the widespread conversion or modification of wetlands to support livestock and arable agriculture. The study provides examples from the Intunjambili wetland in Tuli, Botswana, the Motlapitsi wetland in the Olifants River in South Africa and the Chibuto wetland in the Changane River, in Mozambique.

International Recognition for Conservation

The rich biodiversity and natural beauty of wetlands make them an important focus for conservation. Protected areas make up 8 % of the Limpopo River basin (Revenga 1998). Many of the national parks and conservation areas in the basin are wetlands which support large numbers of wetland birds of diverse species.

Threats to the wetlands of the Limpopo River basin include modification of flows caused by droughts, water abstractions and infrastructure developments, in addition negative impacts from aquatic weed infestation, increased nutrient load from agricultural return flows, and other forms of physical and chemical pollution.

Tourism and Recreation

The wetlands of the basin play a role in sustaining flow in the rivers, particularly in the lower Limpopo and Changane Rivers and support fish biodiversity.

The Limpopo River basin is one of the focal points for eco-tourism and nature reserves in the SADC region, including many of the large and famous parks, including Kruger, Limpopo, Gonarezhou, Manjinji Pan, Malipati, Madikwe, Pilanesberg, Mapungubwe, Mashatu, Soutpansberg and Sabi-Sand. Many of these parks include wetlands as they present opportunities for viewing animals and birds that inhabit these ecosystems.

Groundwater Recharge

Depending on the soil, geology, and landscape of a wetland ecosystem, wetlands can contribute to groundwater recharge if water can filter down to the groundwater system. This function of wetlands can be very important where communities rely on groundwater resources for drinking water. Due to their storage capacity, wetlands often retain water during wet periods and release water during periods of drought, contributing to stream flow during these dry periods. See below for a conceptual diagram of the groundwater component of the water cycle.

Water Quality

Wetlands play an important role in improving surface water quality by filtering out suspended material (e.g., organic or inorganic sediments) and by retaining nutrients and pollutants. Both physical and chemical processes are important in this process. Wetland vegetation can help to trap suspended material, and the slower-moving or static waters in wetlands allow suspended particles (and any adsorbed chemicals) to settle out. Nutrients dissolved in water inflows can be used as resources by aquatic organisms or vegetation within the wetland, and can, along with pollutants and other chemicals, be chemically altered, stored within plants, or attached to wetland sediments. The benefits of water quality improvement to downstream ecosystems can include prevention of eutrophication, removal of water-borne pathogens and toxic chemicals, and protection of fish health and navigation routes as the load and deposition of suspended sediments is reduced. However, the processes responsible for water quality improvement can themselves be degraded by water pollution, depending on the specific characteristics of the soil, vegetation, and aquatic organisms and the nature of the water inflows (Hatfield Consultants 2006).