# 9639 Rio Do Sono, Tocantins, Brazil

Environment

Environment

Affected by human activity

Affected by human activity

Surrounding area

The Rio do Sono biotope is characterized by lush riparian vegetation (gallery forests) lining its banks. These areas feature dense tree cover, shrubs, and various emergent plants, mirroring the rich biodiversity of the Cerrado and Amazon transition biomes. The banks often present exposed light-colored sandy beaches (praias fluviais) or gradual slopes of soil and rock, leading down to the water. The sky is typically clear, reflecting vividly on the water’s surface, creating a vibrant tropical river landscape.

Underwater landscape

Below the surface, the Rio do Sono’s bed is predominantly composed of fine, light-colored sand, forming gentle undulations and expansive sandy stretches, which are vital for bottom-dwelling species. These sandy areas are often punctuated by scattered stones and pebbles and intricate formations of complex snag piles (‘galhadas’). These snag piles are crucial elements, consisting of submerged fallen branches, logs, and exposed tree roots from the riparian forest. Accumulations of leaf litter are also common in calmer sections, providing additional micro-habitats. The water itself is clear to slightly amber-tinted, reflecting the low suspended sediment concentration and the presence of natural tannins from organic matter.

 

Fish list:

• Geophagus sveni (Cichlidae)
• Acarichthys heckelii (Cichlidae)
• Pseudacanthicus pitanga (Loricariidae)
• Panaque armbrusteri (Loricariidae)
• Platydoras armatulus (Doradidae)
• Myleus maculatus (Serrasalmidae)
• Mesonauta festivus (Cichlidae)

Wetland plant:

• Epipremnum aureum (Araceae)

Threats to ecology

The ecological balance of the Rio do Sono biotope, like many rivers in the Araguaia-Tocantins Basin, faces several significant threats:

Deforestation and Agricultural Expansion: The primary threat comes from the rapid conversion of surrounding natural vegetation into agricultural land (especially for soy cultivation and cattle ranching). This leads to increased soil erosion, silting of the riverbed, and alteration of the hydrological cycle.
Agrochemical Pollution: Runoff from large-scale agriculture introduces pesticides, herbicides, and fertilizers into the river, leading to water contamination, algal blooms, and oxygen depletion, severely impacting aquatic life.
Hydropower Development: While the Rio do Sono itself may not have large dams, the broader Tocantins Basin has numerous large hydroelectric dams (e.g., Tucuruí, Estreito, Lajeado). These dams alter natural flow regimes, block fish migration routes, change water temperature and oxygen levels, and fragment habitats throughout the basin, indirectly affecting its tributaries.
Illegal Mining and Siltation: In some areas of the Tocantins Basin, illegal gold mining (garimpo) contributes to heavy metal contamination (especially mercury) and excessive siltation, degrading water quality and destroying aquatic habitats.
Urbanization and Waste Disposal: Uncontrolled growth of human settlements along the river’s banks can lead to untreated sewage discharge and improper waste disposal, further polluting the water.
Unsustainable Fishing Practices: While traditional fishing is often sustainable, increased commercial fishing pressure and the use of destructive fishing methods can lead to overfishing and depletion of fish stocks.

Riparian zone

Trees near the aquatic habitat

Few -