Igarapé near Rio Daraá, tributary of Rio Negro, Amazonas, Brazil

_th place in Biotope Aquarium Design Contest 2020

Volume: 200 liters
Dimensions: 100x40x50 cm
List of fishes: Pterophyllum scalare, Heros efasciatus, Mikrogeophagus ramirezi, Corydoras aeneus, Panaque nigrolineatus
List of plants: N/A
Description of decorations: Roots, trunks and branches and river sand.
Water parameters: Temperature: 26 ±1ºC , PH: 6.4, GH: 5, TDS: 7
Additional info: TPA 20% weekly


Description of the area surrounding the biotope: The Rio Daraá is a leftbank tributary of the middle Rio Negro, just past the city Santa Isabel do Rio Negro in Amazonas state in Brazil.
To know more about the Rio Daraá, we first have to understand the Rio Negro. The Rio Negro rises in Colombia, where it is known as the Guainía, before joining with the Casiquaire on the border with Venezuela. After flowing for about 1700 km, it flows into the Amazon at Manaus, Brazil. The Rio Negro is the world’s largest tributary and the world’s largest blackwater river. Its annual flow exceeds that of all the rivers of Europe combined. The Rio Negro is a seasonal river in the sense that it has fairly predictable seasonal fluctuations in water level during most years. It begins raining earlier in the lower Rio Negro drainage than in its upper reaches. The rainiest months in the lower Rio Negro are between December and May, whereas in the middle course they are between March and July. At the Rio Daraá, February is the month with the heaviest rainfall and October is the month with the least rainfall. Water level usually varies about 7 meters from low to high tide, but a maximum difference of 16 meters is possible. During low water periods you can find entire beaches formed by fine, almost white sand. Some cataracts are confronted within 20-30 km of the mouths of the left bank tributaries of the upper Rio Negro, and they indicate the presence of the Guiana Shield. Upstream the Rio Daraá there are also some waterfalls flowing over big granite rocks like the ‘cachoeira do Aracu’. Along the riverbanks of Rio Daraá and the surrounding forests a lot of trees and bushes are growing, like palmtrees (Leopoldina pulchra and Astrocaryum jauari), Smilax regelli, locally known as ‘sarsaparillas’, Pseodobombax munguba and Eschweilera tenuifolia. There are also many bushes like Licania stewardii, also known as ‘acará-acú’ and Myrciaria dubia, known as ‘camu-camu’. Many fish can be found along the riverbanks to find their shelter between these bushes and fallen branches and to eat the fruits and seeds carried by these plants. Its hard seedpods are cracked open by monkees and some fall into the water which form part of the diet of the fish who live here. During the period of inundation small fishes move upstream within the river’s tributaries and then laterally into the flooded forest itself to feed and reproduce, before returning to the tributaries when the waterlevel drops. As you move deeper into the dense ‘terra firme’ forest you can find many small shallow rivers or forest streams, also known locally as an ‘igarapé’, slowly flowing through the dense forest. There is a presence of overhanging riparian vegetation and many fallen leaves and twigs on the ground. You can hear many birds singing in the background. The coordinates of this particular igarapé are 0.4S and 64.8W. It is close to the mouth of the Rio Daraá.
Description of the underwater landscape of the biotope: The Rio Negro and its many tributaries, like the Rio Daraá, are stained by humic acids or compounds due to immense layers of leaves and twigs. Igarapés are characterised by thick, often overhanging, riparian vegetation and substrates covered in fallen branches, tree roots and leaf litter. Therefore it has its unique dark color, ranging from light brown to almost entirely black. The tropical sun is streaming in through the canopy just to light up a few places in the water. The water is shallow, less than 1 meter in most places, and the bottom is thoroughly covered with leaf litter. The sheer density of fish is therefore incredible. It’s also likely that just a few dozen kilometers further down there is another igarapé that contains a completely different set of species from the previous one, and often including species not found anywhere else in the Amazon. It happens that igarapés are extremely diverse in aquatic fauna and very distinct from one another.
Description of the parameters of the habitat: The Rio Negro drains three principal geological formations, that is, the ancient Guiana Shield, late Cretaceous to early Tertiary Lowlands and Quaternary Lowlands. In general the rocks, and derived soils, of the Rio Negro basin are acidic and extremely poor in chemicals associated with nutrients. The Rio Negro is chemically one of the poorest rivers in the world. It is also referred to as ‘slightly contaminated distilled water’, according to Sioli (1967). In the absolute concentrations of major elements, Rio Negro is very similar to rainwater (Gibbs, 1971). The blackwater rivers are extremely poor in dissolved nutrients because the geology it drains had very impoverished soils. The rivers are very poor in nearly all of the major elements, especially phosphorous, calcium and potassium. The conductivity is somewhere between 8-10 µS/cm. The most striking chemical characteristic of the Rio Negro is its low pH or high acidity. The pH ranges from about 3.6-5.8, depending on the exact site and time of the year. No exact measurements are known from this particulair igarapé, but it is similar to those known of the Rio Daraá (pH 3.9). The transparency ranges between about 0.9-1.5m. Because it is darker in color than for example clearwater rivers of the Amazon, it absorbs more solar radiation and is thus slightly warmer. The water temperatures are about 28-31 degrees Celsius. During the low water period, when many lakes and pools become shallow, super-heating can take place and temperatures have been recorded in excess of 35 degrees Celsius. The waters can become very deoxygenated due to thermal stratification, decomposition or organic matter and because of super-heating.
List of fishes and invertebrates occurring in the nature biotope: Ancistrus sp, Abramites hypselonotus Characidae, Pterophyllum altum Cichlidae, Aequidens pulcher Cichlidae, Pterophyllum scalare Cichlidae, Mesonauta festivus Cichlidae, Heros severus Cichlidae, Acarichthys heckelii Cichlidae, Apistogramma macmasteri Cichlidae, Apistogramma uaupesi Cichlidae, Apistogramma cacatuoides Cichlidae, Apistogramma regani Cichlidae, Apistogramma guttataCichlidae, Carnegiella strigata Characidae, Pseudoplatystoma fasciatumSiluriformes, Glyptoperichthys gibbiceps Siluriformes, Chalceus macrolepidotus Characidae, Chilodus punctatus Characidae, Corydoras adolfoi Siluriformes, Corydoras aeneus Siluriformes, Corydoras melini Siluriformes, Corydoras sterbai Siluriformes, Corydoras metae Siluriformes, Corydoras habrosus Siluriformes, Corydoras tukano Siluriformes, Hemiodus gracilis Characidae, Satanoperca jurupari Cichlidae, Piaractus brachypomus Characidae, Metynnis hypsauchen Characidae, Colossoma macropomum Characidae, Panaque nigrolineatus Siluriformes, Panaque maccus Siluriformes, Platydoras costatus Siluriformes, Nannostomus marginatus Characidae, Nannostomus trifasciatus Characidae, Nannostomus unifasciatus Characidae, Pimelodus pictus Siluriformes, Serrasalmus rhombeus Characidae, Pygocentrus nattereri Characidae, Phractocephalus hemioliopterus Siluriformes, Hemigrammus rodwayi Characidae, Pristella maxillaris Characidae, Mikrogeophagus ramirezi Cichlidae, Hemigrammus rhodostomus Characidae, Paracheirodon axelrodi Characidae, Hyphessobrycon bentosi Characidae, Cichla temensis Cichlidae, Dicrossus filamentosus Cichlidae, Moenkhausia pittieri.
List of plants found in the nature biotope: Cabomba, Cabomba furcata, Mayaca fluviatilis, Eichhornia azurea, Echinodorus diversifolia, Ludwigia inclinata, Nymphaea rudgeana, Echinodorus horizontalis, Echinodorus tenellus, limnobium laevigatum, Pistia stratiotes, Eichhornia crassipes
Threats to the ecology: There are many threats to the Amazon rainforest, like goldmining, hydroelectric dams and agriculture, which cause massive deforestations and endangering the lives of local populations. Goldmining is generally very destructive to the environment. In order to mine, trees and vegetation are cleared and burned. With the ground completely bare, large scale mining operations use huge bulldozers and excavators to extract the metals and minerals from the soil. Agricultural expansion and intensification are also major threats to tropical biodiversity. In addition to the direct removal of native vegetation, agricultural expansion often elicits other human‐induced disturbances, many of which are poorly addressed by existing environmental legislation and conservation programmes. This is particularly true for tropical freshwater systems, where there is considerable uncertainty about whether a legislative focus on protecting riparian vegetation is sufficient to conserve stream fauna.
But there are also threats on local scale. Recent studies demonstrate that small bodies of water are much more important than scientists previously supposed. Because igarapés are extremely diverse in aquatic fauna and very distinct from one another, it is important to conserve these wonderful places. Igarapés provide potable water for human and livestock consumption; irrigation for valuable fruit and vegetable crops; fish for consumption and ornamental trade. A threat to igarapés are so called ‘dirt roads’. These are roads made of sand which cross and cut off the small forest stream. It creates a small dam, leading to sand and clay accumulates and the stream flooding its banks. Interruption of the water flow results in a barrier to the movement of fauna. Fewer fish species live upstream of small dams. There is erosion and silting up of the rivercourse on the other side of the dirt road and little river beds are exposed. This will eventually cause loss of habitat diversity; less vegetation and therefore loss of fish species.
Sources of information:


Comments of the members of the jury of Biotope Aquarium Design Contest 2020