Igarapé do Daracua near Barcelos, Brasil

Environment

Environment

Affected by human activity

Affected by human activity

Deforestation

Deforestation

Advanced

Surrounding area

Igarapé do Daracuá is located within a primary Amazonian igapó flooded forest, approximately 10 km upstream of Barcelos, Amazonas, Brazil (0°58′ S, 62°55′ W). It forms part of the middle Rio Negro Basin within the Brazilian Amazon.

The surrounding vegetation consists of dense flooded forest with more than 90% canopy cover, dominated by Mauritia flexuosa (buriti palm), Euterpe precatoria, Hevea brasiliensis, and Leopoldinia piassaba. The igarapé experiences approximately six months of seasonal flooding each year.

Annual rainfall exceeds 2,500 mm, while temperatures remain between 27-29 °C throughout the year, with relative humidity typically above 85%. The nearest human settlement is the municipality of Barcelos. There are no roads, agriculture, or industrial activities within approximately 50km.

The area is protected under the Brazilian Forest Code as a Permanent Preservation Area and provides important habitat for migratory birds and endemic blackwater fish species.

Underwater landscape

The underwater habitat consists exclusively of allochthonous organic material, with no exposed mineral substrate. The streambed is formed by 15-30 cm deep accumulations of decomposing leaf litter, seed pods, and submerged branch tangles. True submerged macrophytes are absent due to less than 1% surface PAR penetration and the acidic water (pH 3.8-4.5).

The water is tea-coloured by dissolved tannins, with a conductivity of 8-12 µS/cm and visibility of less than 30 cm. A flow velocity of less than 5 cm/s creates stagnant leaf-pack microhabitats that become isolated during the dry season.

Paracheirodon axelrodi occupies these leaf-litter zones in monospecific schools exceeding 50 individuals/m³, using the detritus for predator avoidance and foraging on fungal and bacterial biofilms (Knöppel, 1970). No sand, gravel, or rock is present within this cardinal tetra microhabitat.

Threats to ecology

The primary regional threats include deforestation within the Rio Negro Basin for cattle ranching and soy cultivation, reducing the allochthonous input of palm fronds and other organic material essential for habitat structure. Climate change is increasing the frequency of extreme drought events, which can isolate igarapés, leading to hypoxia and the local loss of Paracheirodon axelrodi populations.

Illegal gold mining upstream introduces mercury contamination, which has been documented as a source of sublethal stress for Rio Negro fish communities. Although ornamental fish collection targets cardinal tetras, current harvest levels are considered sustainable under the Project Piaba model. Most igarapés lack formal protected status, making them vulnerable to hydrological alteration. The leaf-litter microhabitat itself has low resilience to disturbance because decomposition is slow, typically requiring 6-8 months.

Riparian zone

Trees near the aquatic habitat

Many -

Bibliography

• → SPB Academic Publishing, The Hague, Netherlands. 1988. - Rio Negro, Rich Life in Poor Water: Amazonian Diversity and Foodchain Ecology as Seen Through Fish Communities by Goulding, M., Carvalho, M.L., & Ferreira, E.J.G.
  ISBN 978-9051030208
  

Sitography

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