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#10469 Igarapé do Aturiá, Rio Negro Basin, Amazonas, Brazil

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Brazil, Amazon, Santa Isabel do Rio Negro

The Aturiá Stream (Igarapé do Aturiá), in the middle Rio Negro basin, Amazonas, Brazil, is a pristine blackwater igapó (flooded forest) ecosystem. The habitat features extremely acidic, nutrient-poor waters stained tea-dark by humic acids and shaded by a dense forest canopy. Its underwater structure is defined by fine white sand, thick layers of natural leaf litter, and an intricate network of submerged tree roots. This structure provides vital refuge and foraging grounds for specialized acid-tolerant fish. The biotope is highly representative of the Rio Negro’s biodiversity, dominated by massive wild schools of Paracheirodon axelrodi (Cardinal Tetra). These fish rely entirely on the shaded root tangles and leaf litter for protection from predators, swimming among the fallen branches in their natural social behavior, perfectly adapted to this unique low-visibility environment.

Submitted by
Arthur Carvalho Valgueiro
GPS
-2.5730000, -60.3724670
Geographical region
South America
Drainage Basin
Amazon Basin
River catchment
Rio Negro
Water body type
Igarapè
Water body name
Igarapé do Aturiá
Water body part
Channel
Water body course
Lower course
Water body: tributary of
Rio
Tributary name
Rio Negro

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Water Chemistry

Water information

Water type
Freshwater
Water color
Black water
Water transparency
Medium
Concentration of sediments
Low
Water temperature
27 °C
Water flow/curent
Slow

Chemical parameters

pH
5.0
Conductivity
23.7
GH
0
dGH
KH
0
dKH
Dissolved Oxygen
78.4 %

Substrate in nature

Sand
Beige
Pebble/Gravel
None
Stone
None
Stone form
Silt/Mud
None
Leaves
Adundant
Driftwood
Many
Submerged terrestrial vegetation
Yes

Aquatic Biotope

Date of collecting
Collecting area
Water depth
Air temperature
Sunlight

Environment

Environment
Untouched
Surrounding area

The Aturiá Stream (Igarapé do Aturiá) is a small blackwater tributary located in the middle Rio Negro basin, Amazonas, Brazil. The surrounding area is characterized by dense, pristine Amazonian igapó forest (flooded forest). The riparian vegetation consists of large trees, shrubs, and terrestrial plants adapted to the seasonal flood pulse, during which water levels fluctuate significantly throughout the year, partially submerging the forest margins.

Underwater landscape

The underwater landscape is defined by a slow-moving current and a very dark, tea-colored water column rich in dissolved tannins and highly acidic. The substrate consists predominantly of fine, light beige quartz sand, heavily covered by a thick layer of leaf litter, fallen branches, and large seed pods. There are no rocks or stones; instead, the complex structure is formed entirely by a dense network of submerged tree roots, fallen logs, and flooded terrestrial vegetation along the shallow margins.

Fish:

Paracheirodon axelrodi (Characidae)

Threats to ecology

Although the area remains relatively remote, the main ecological threats to this biotope include climate change, which disrupts the natural flood cycle (causing extreme droughts or unseasonal floods), and localized river traffic. Additionally, potential deforestation throughout the Rio Negro basin and unregulated ornamental fish collecting or overfishing could pose risks to the delicate balance of this acidic, low-nutrient ecosystem.

Riparian zone

Trees near the aquatic habitat
Many -

Sitography

→ Amazon Waters
→ FishBase
→ INPA