Orange River Ecosystem

• Category: Inland Aquatic Biomes.
• Geographic Location: Southern Africa.
• Summary: The most vital river in southern Africa, the Orange, supports agriculture, tourism, and a wide variety of animal life.

The Orange River, the fourth-longest river in Africa, flows some 1,400 miles (2200 kilometers) across southern Africa in a westerly direction, through four countries—Botswana, Lesotho, Namibia, and South Africa. The Orange River starts in the Maloti Mountains in northern Lesotho, where it is known as the Senqu, then flows southwest through Lesotho. It meanders northwest and west through central South Africa, forming the southwestern boundary of Free State and part of the South Africa-Namibia border, then through the southern part of the Kalahari and Namib Deserts, before entering the South Atlantic Ocean at Oranjemund by the Alexander Bay.

In Lesotho, at the source, the river receives up to 79 inches (200 centimeters) of precipitation per annum; as evaporation rates increase, and rainfall decreases, precipitation can be as little as 2 inches (5 centimeters) per year at the river’s mouth. In dry years, water does not even reach the mouth. The total catchment area of the Orange River system is approximately 376,000 square miles (973,000 square kilometers), equal to three-quarters of the entire land area in South Africa.

Wildlife

The ecology of the Orange River does not have true estuarine communities, as the sea hardly enters the river, and there are few salt-tolerant plants. The Ramsar designation, indicating a wetland of international importance, is comprised of sand banks and channel bars covered with pioneer vegetation, a tidal basin, a narrow floodplain, pans, the river mouth, and a salt marsh on the south bank of the river mouth.

The wetland vegetation includes wetland marshes, salt marshes, islands, and bank vegetation, mainly freshwater species. The predominant presence of freshwater species in the island and bank vegetation results from the present regulated flow through the Orange River mouth system. The salt marsh on the southern bank of the Orange River mouth system is cut off from the rest by the embankment of an access road to the mouth.

Invertebrates in the Orange River include the sand prawns or bivalves that would normally be expected to dwell in the mud flats of estuaries. There are predominately freshwater fish species in the river. As far as fish life is concerned, this system cannot be regarded as an ecologically important system. One endangered fish species, the largemouth yellowfish, is found only in the lower reaches of the Orange River. It is a popular sport fish.

The Orange River mouth is regarded as the sixth-most-important coastal wetland in southern Africa, in terms of the number of waterfowl it supports. The river mouth, mudflats, interfluvial marshlands, islets near the mouth, and adjacent pans provide a sizable area of sheltered shallow water suitable for concentrations of wetland birds, which use these habitats for breeding purposes or as a stopover on migration routes. The bird population can be as high as 20,000 to 26,000 individuals.

Of the fifty-seven wetland species recorded, fourteen are listed as either rare or endangered in one or both of the South African and Namibian Red Data Books. At times, the area supports more than 1 percent of the world population of three species endemic (not found elsewhere) to southwestern Africa: the Cape cormorant, Damara tern, and Hartlaub’s gull. The site also supports thirty-three mammal species, including the Cape clawless otter and one of the tourist attractions, the manatee.

Human Impact

Robert Jacob Jordan named the river after the Dutch Royal House. Although the river does not pass through any major cities, it plays an important role in the South African economy by providing water for irrigation, as well as hydroelectric power. Shoals, falls, irregular flow, and a sandbar at its mouth limit navigation, but the river is used extensively for irrigation. It is also used for rafting, fishing, and other recreational and tourism activities.

The South African Orange River Project, which includes the Gariep and Vanderkloof dams, provides water for irrigation, hydroelectric power generation, and municipal water supplies. The Orange feeds the Gariep dam, creating the country's largest reservoir at 318 billion cubic feet (6 billion cubic meters). This dam, near Colesburg, is the primary storage structure on the Orange River. Considering the generally dry climatic conditions characterizing the sub-continent, it is essential for this freshwater resource to be utilized to the most significant benefit of the region and its people.

Pollution due to human activities is a concern. Researchers have found heavy metals in sediment in the lower river region. In descending order, iron, manganese, chromium, and arsenic were the most common elements found. Most samples contained significant amounts of arsenic, chromium, and iron. New research also suggests the presence of microplastics and microfibers from urban centers within the river. 

The Orange River Project increased the value of South African agricultural production: it has provided for the establishment of a large number of irrigated farms, and stimulated the production of meat, wool, milk, citrus, cotton, wheat, raisins, beans, and peas. The project has also promoted economic activity and development in the areas directly involved, counteracted the migration of the rural population to the cities by creating stable farming communities, created recreational facilities in the center of the interior and promoted tourism, leveled off moderate flood peaks in the course of the river, and, in the process, safeguarded riparian communities and irrigation schemes downstream.

South Africa is particularly vulnerable to climate change because, among other things, a large proportion of the population has low resilience to extreme climate events (poverty; high disease burden; inadequate housing infrastructure and location). Large parts of South Africa already have low and variable rainfall, and a significant proportion of surface water resources are already fully allocated.

Some effects of climate change may already be occurring, manifested as changes in rainfall (droughts and floods), temperature extremes, and cholera outbreaks. These have each been associated with extreme weather events, especially in poor, high-density settlements. Agriculture and fisheries are important for food security and local livelihoods; those in poverty will be the most impacted.

Bibliography

Jacobs, Nancy J. Environment, Power, and Injustice: A South African History. Cambridge University Press, 2003.

Pitiya, Regean, et al. "A Pilot Study on the Concentration of Heavy Metals in Sediments from the Lower Orange River, //Karas Region, Namibia." Journal of Materials Science and Chemical Engineering, vol. 10, no. 3, Mar. 2022, doi.org/10.4236/msce.2021.103001. Accessed 8 Nov. 2024.

Weideman, Eleanor A., et al. "Little Evidence That Dams in the Orange-Vaal River System Trap Floating Microplastics or Microfibres." Marine Pollution Bulletin, vol. 149, 2019, doi.org/10.1016/j.marpolbul.2019.110664. Accessed 8 Nov. 2024.