Lakes and Floodplain Habitats

The landscape of the Amazon flood plain is a palimpsest written by the recent erosions and depositions of the rivers. Land is cut and re-laid to maintain an intricate mosaic of forest, scrub, marshes, lakes and channels. Due to the annual flood regime, all habitats flood occasionally. Most habitats flood every year, some submerging by up to 11 metres. Some floating communities do not submerge but are still subject to mixing and disruption by the floods.

All habitats are dominated by the physical activities of the river. Much of the 'land' begins as ridges alternated with swamps or lakes. The ridges are created by annual floods and sedimentation at the sides of major channels. As land distances from the main channels, fine deposits in-fill this relief and poor drainage in low-water season forms backswamps. In such interior areas the vegetation cannot progress to the high forest of levees and sand-bar ridges but forms lower swamp forest (chavascal). Subsequently, this land is recut by the return of the previous channel or another. Therefore in sharp contrast to the adjacent unflooded forest no climax vegetation type is ever reached (Salo et al., 1986). Likewise, no old water bodies develop, most lacks and channels are less than 1000 years old.

The Andean rocks supply both the sediments from which the floodplains of the Amazon river are formed and the dissolved nutrients which allow their high biomass productivity. Lower productivity blackwater lakes which are fed by nutrient-poor forest streams exist on the margin of these floodplains. These two types of seasonally flooded habitat occurring inside and outside of the outermost levees of the river and known respectively as várzea and igapó are often sharply contrasted even though spatially close (Prance, 1979). Igapó is not confined to the neighbourhood of the floodplain; it is also found around the edges of the sometimes very large impeded ('blackwater') lakes and tributaries (the whole lower stretch of the Rio Negro is one example) and is scattered as poorly drained and temporarily flooding patches within the matrix of non-flooding terra firme forest. In contrast, várzea habitats and vegetation are strictly confined to silty 'white-water' floodplains.

The River Amazon floodplain - whitewater habitats
Within the general category of várzea it will be useful to distinguish the habitat sub-types described in the following table:

Floodplain habitats, equivalent local names in italics.
Mainly terrestrial: Wholly or mainly aquatic:
Island and point sand bars = praias Main river channels =Rios.
Levees = restingas
(silt-heightened riverbanks and bars, on which grows tall forest)
Lesser river channels = paranas
(usually flowing but sometimes static during low water)
Low swampy woodland = chavascal
(usually behind levees)
Lake channels = canos
(as above but connecting to lakes rather than to other channels)
Whitewater floodplain = várzea
Blackwater floodplain = igapó
(i.e. around lakes and streams outside the flanking levees of a várzea)
Lakes = lagos
(i.e. water bodies of variable shape and size but usually fluvial in origin holding static or slow moving water)
Never inundated land = terra firme
(land flanking the floodplain)
 
It is inevitable that all the named landscape features intergrade and contrasting the simplicity of the table to the complexity of the actual floodplain as shown by satellite and aerial photographs shows this classificatory system to be too simple to describe all water bodies. A rapid-flowing parana at flood season may transform to a series of lakes at low water; lakes are often elongated like paranas and may be not much wider than their own channels; and so on. At high water the entire floodplain can be under water that is for the most part nearly static. At such a time only the pattern of the emergent vegetation allows the different types of water bodies to be distinguished. Even when not all is covered, it is useful to remember that all land has been deposited by the river and therefore várzea includes nothing, excepting upper parts of substantial trees, that is never flooded.

The time scales of different process involved in the formation of the floodplain (varzea)



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The Pareto plot of lake area distribution within the triangle of floodplain within the Rios Solimões and Japurá and the Parana Aranapu
The Pareto plot of lake area distribution within the triangle of floodplain within the Rios Solimões and Japurá and the Parana Aranapu

The Pareto plot of lake area distribution within the triangle of floodplain within the Rios Solimões and Japurá and the Parana Aranapu
The Pareto plot of lake area distribution within the triangle of floodplain within the Rios Solimões and Japurá and the Parana Aranapu

Water depth at Tefe
Water depth at Tefe

Aerial view of the Rio Solimoes in the vicinity of Tefe showing varzea floodplain forest. Note the abandoned river channels and the scole-swale topography of the forest.
Aerial view of the Rio Solimoes in the vicinity of Tefe showing varzea floodplain forest. Note the abandoned river channels and the scole-swale topography of the forest.

Aerial view of varzea forest within the Mamiraua reserve. The picture shows two of the most important types of water body, a channel running from top to bottom, and in the foreground, a varzea lake. The lake has floating meadow around its periphery.
Aerial view of varzea forest within the Mamiraua reserve. The picture shows two of the most important types of water body, a channel running from top to bottom, and in the foreground, a varzea lake. The lake has floating meadow around its periphery.

Aerial view of Lago Mamiraua and surrounding varzea habitat. In this low lying area of the floodplain there are few trees and extensive areas of floating meadow.
Aerial view of Lago Mamiraua and surrounding varzea habitat. In this low lying area of the floodplain there are few trees and extensive areas of floating meadow.

False colour satellite image of the varzea floodplain in the Mamiraua reserve at the confluence of the Rios Solimoes and Japura.
False colour satellite image of the varzea floodplain in the Mamiraua reserve at the confluence of the Rios Solimoes and Japura.

False colour satellite image of central Amazonia.
False colour satellite image of central Amazonia.

Flowering trees on the edge of a floodplain whitewater lake in the vicinity of Tefe
Flowering trees on the edge of a floodplain whitewater lake in the vicinity of Tefe
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View towards the edge of a varzea lake in the floodplain of the Rio Japura
View towards the edge of a varzea lake in the floodplain of the Rio Japura

The edge of a varzea lake showing typical white water inundation forest
The edge of a varzea lake showing typical white water inundation forest

Vegetation along the edge of a white water inundation lake in the floodplain of the Rios Solimoes and Japura near Tefe
Vegetation along the edge of a white water inundation lake in the floodplain of the Rios Solimoes and Japura near Tefe

View towards the forest across Lago Mamiraua in the floodplain of the Rios Solimoes and Japura near Tefe
View towards the forest across Lago Mamiraua in the floodplain of the Rios Solimoes and Japura near Tefe

A caiman swimming across Lago Mamiraua during the low water season
A caiman swimming across Lago Mamiraua during the low water season

A view across the Rio Japura at high water
A view across the Rio Japura at high water

View across a varzea lake at high water as a storm approaches
View across a varzea lake at high water as a storm approaches

View across a varzea lake at high water
View across a varzea lake at high water

Storm clouds over a varzea lake
Storm clouds over a varzea lake

Storm clouds over a varzea lake
Storm clouds over a varzea lake

A varzea lake
A varzea lake

  

Sunset over a varzea lake
Sunset over a varzea lake