Orinoco wetlands

• Category: Inland Aquatic Biomes.
• Geographic Location: South America.
• Summary: This still-pristine ecoregion provides habitats for several endangered animal and plant species, but industrial and agricultural development plans threaten the ecological balance.

The Orinoco delta region in northeastern Venezuela extends from near the Araya and Paria Peninsula southward to the Amacuro Delta, the world’s seventh-largest river delta. There, vast floodplains were created by fluvial-marine sediments. The delta’s distributaries, called caños, spread like a fan over an area of about 2,300 square miles (6,000 square kilometers), branching out from the main distributary, called the Rio Grande, and the second major distributary, Caño Manamo. The delta region of the Orinoco River has been declared an internationally significant wetland.

In this ecoregion, the climate is tropical. Precipitation varies throughout the area from 39 to 79 inches (100 to 200 centimeters) annually, with a wet season from April or May until December. The United Nations Educational, Scientific, and Cultural Organization (UNESCO) added this ecoregion in 2009 to the World Network of Biosphere Reserves (WNBR). A reference map categorizes the forest subregions of the Orinoco Delta as inundated woodland savannas (with palms) of the Upper Delta, wetlands of the Middle Delta, and swamp wetlands of the Lower Delta.

Large permanent wetlands such as swamps, marshlands, tuberas (peatlands), swampy plains, and mangroves occur in patterns with seasonally flooded freshwater swamp forests. While the peatlands are dominated by water extensions with rich organic soils, supporting a herbaceous vegetation, moriche palms, and forests, the wetlands are subdivided by networks of fluvial and tidal channels. Westward, these flooded grasslands become drier, forming the llanos, and eventually retain stands of evergreen broadleaf trees. Common species of the riparian forests include bloodwood, peramán, Guiana chestnut, chaguaramo palm, coral trees, and jobo. Salt marshes are formed close to the coastal streams in the east. The mangroves in this region represent an important sink for atmospheric carbon dioxide gas.

Biodiversity and Conservation

The Orinoco basin, together with the Gulf of Paria, comprise the world’s largest manatee refuge. Nonetheless, the Venezuelan government had to order a resolution to ban manatee hunting to prevent extinction of these marine mammals. Further threatened or endangered species are the Brazilian tapir, giant anteater, Orinoco crocodile, yellow-footed tortoise, Amazon River dolphins (grey and pink), jaguar, bush dog, Orinoco goose, and harpy eagle.

Other wildlife inhabiting the delta include: the river otter, crab-eating fox, howler monkey, capuchin monkey, parrots, toucans, scarlet macaws, rufous crab-awk and the muscovy duck. There are reptiles such as the caiman, iguana, turtles and sea turtles, lizards, and many snake species. Fish include the lau-lau, catfish, piranha, tarpon, morocoto, coporo, sardine, rays, and a variety of coral reef fish. There is also an abundance of crab, shrimp, and other crustaceans, and mollusks.

The delta region has many species of birds, mainly shorebirds, many of which are migratory. The delta provides habitat for nesting, breeding, and stopovers. The endemic scarlet ibis is found here, as is the black skimmer, gull-billed tern, short-billed dowitcher, lesser and greater yellowlegs, black-bellied whistling duck, and tricolored egret.

Conservation and Threats

At the beginning of the 1990s, several protected nature and indigenous areas were established, including the United Nations Environment Programme (UNEP) Delta del Orinoco Biosphere Reserve, Delta del Orinoco National Park, Turuïpano National Park, and Mariusa National Park, protecting a combined area of approximately 5,965 square miles (15,500 square kilometers). Endangered species (as listed in the Convention on International Trade in Endangered Species of Wild Fauna and Flora—CITES—Appendix I) include manatees and giant otters.

Although some nature-reserve actions are already enforced and the Orinoco Delta is still largely untouched and intact, human activities already influence the ecosystems in this region. Current threats to the area include water construction projects such as water diversion and damming, and increasing demands of a growing human population. Upstream, in the northwestern delta, the constructions of the Volcán dam and the Raul Leoni dam (on Caroní River) are two examples. Dams provide water reservoirs and increase areas for farming and cattle ranching, but interrupt essential seasonal flooding.

Reduced water levels in the upper delta caused a chain of ecological consequences. The region became tidal, resulting in water levels that rise and fall by 3–7 feet (1–2 meters) daily. As a result, the dramatically increased salinity affects the flora and fauna.

The potentially greatest threat, however, is oil extraction—mainly by the Venezuela Oil Corporation (Corporación Venezolana de Petróleo), but also by transnational petroleum companies that explore and exploit abundant resources in the Gulf of Paria. Major sources of hydrocarbons include Lago de Asfalto de Guanaco and Caño La Brea in the delta of the San Juan River.

The floodplains of large rivers are not only among the most productive ecosystems, but also are most vulnerable to changes in water quality. If economic development—including agriculture, mining, oil exploration, and navigation of the rivers—accelerates, environmental risks also accumulate, such as saltwater intrusion in the delta, degradation of aquatic and floodplain habitat, reduction of ecosystem capacity, and interference with groundwater systems. Another consideration for this area is future impact to the coast due to climate change. Studies are already indicating rising sea levels, increased frequency and severity of storm surges, and changes in precipitation patterns. Rising sea levels could further impact the salinity of the area.

Venezuela’s government plans the construction of large navigation facilities. The Orinoco River system is still relatively pristine, so it is possible to avoid fatal disruption of the ecology of the river system and, thus, long-term costs of economic development. One successful application of new approaches is the model of a privately owned conservation network for the Orinoco river system. This is adapted from the llanos area. About 10 percent of the llanos ecosystem is conserved by families and corporations that mix ecotourism with cattle ranching in sustainable management schemes. Thus, gallery forests, rivers, and streams will stay protected as biological corridors, and the land can be maintained in a natural, balanced state even while facing economic growth.

Bibliography

Dinerstein, E., et al. A Conservation Assessment of the Terrestrial Ecoregions of Latin America and the Caribbean. Washington, DC: World Wildlife Fund and The World Bank, 1995.

Lasso, Carlos A., Leeanne E. Alonso, Ana Liz Flores, and Greg Love, eds. “Rapid Assessment of the Biodiversity and Social Aspects of the Aquatic Ecosystems of the Orinoco Delta and the Gulf of Paria, Venezuela.” The Rapid Assessment Program (RAP) Bulletin of Biological Assessment 37 (2004).

Neild, Andrew F.E., Maria Eugenia Losada, and Keith R. Willmott. "A Distinctive New Subspecies of Moschoneura Pinthous (Linnaeus, 1758) (Lepidoptera: Pieridae: Dismorphiinae) from the Orinoco Delta, Venezuela, with Comments on the Species-Level Taxonomy." Tropical Lepidoptera Research, July 2021. DOI: 10.5281/zenodo.4966791. Accessed 25 Nov. 2024.

Seeliger, Ulrich, and Björn Kjerfve, eds. Ecological Studies 144: Coastal Marine Ecosystems of Latin America. New York: Springer, 2001.

Westlake, D. F., J. Kvet, and A. Szczepanski, eds. The Production Ecology of Wetlands: The IBP Synthesis. Cambridge, United Kingdom: Cambridge University Press, 1999.