Lençóis Maranhenses National Park is located in northeastern Brazil. The park includes 43 mi of coastline and an interior composed of rolling sand dunes. During the rainy season, the valleys among the dunes fill with freshwater lagoons, prevented from draining due to the impermeable rock beneath.
Lençóis Maranhenses National Park is located in Maranhão state in northeastern Brazil, just east of the Baía de São José. The 155,000 ha (380,000 acre) park includes 70 km (43 mi) of coastline and an interior composed of rolling sand dunes. During the rainy season, the valleys among the dunes fill with freshwater lagoons, prevented from draining due to the impermeable rock beneath.
While much of the park has the appearance of a desert, the area receives about 1,200 mm (47 in) of rain per year, while deserts, by definition, receive less than 250 mm (10 in) annually. About 70% of this rainfall occurs between the months of January and May.
The sand is carried to the park from the interior of the continent by the Parnaíba and Preguiças rivers, where it is then driven back inland up to 50 km (31 mi) by winds, creating a series of sand dunes rising as much as 40 m(130 ft) tall.
During the rainy season, between the months of January and June, the rainstorms fill the spaces among the dunes with fresh water lagoons of up to 100 m (330 ft) in length and 3 m (10 ft) in depth, and together comprising as much as 41% of the area of the park. The water in the lagoons is prevented from draining by a layer of impermeable rock located beneath the sandy surface.
The lagoons typically have a temperature between 27.5 °C (81.5 °F) and 32 °C (90 °F), pH of between 4.9 and 6.2, and low levels of dissolved nutrients. When the dry season returns, the pools quickly evaporate, losing as much as 1 m (3 ft) of depth per month.
In the interior of the park are located two oases or restingas, Queimada do Britos, covering an area of 1,100 ha (2,700 acres), and Baixa Grande, covering an area of 850 ha (2,100 acres).
The area of the park has an average annual temperature of between 26 °C (79 °F) and 28.5 °C (83.3 °F) and an annual temperature variation of about 1.1 °C (2 °F).
The lagoons in the park are often interconnected with one another, as well as with the rivers that run through the area. They are home to a number of fish and insect species, including the wolf fish, which burrows down into wet layers of mud and remains dormant during the dry season. Besides the dunes that form the centerpiece of the park, the ecosystem also includes area of restinga and mangrove ecosystems.
The park is home to four species listed as endangered, the scarlet ibis (Eudocimus ruber), the neotropical otter (Lontra longicaudis), the oncilla (Leopardus tigrinus) and the West Indian manatee (Trichechus manatus). The park also includes 133 species of plants, 112 species of birds, and at least 42 species of reptiles.