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Increasing the number of standing water environments due to deforestation is called slowing and affects biodiversity in the Amazon

Edited and resized image by A. Duarte, available on Flickr under CC BY-SA 2.0 license

Human interventions in the Amazon may be causing the region's water resources to go through a “slowdown” process. In deforested areas, still water environments – ponds, puddles, floodplains and dams – would be becoming more frequent than those with running water such as rivers and streams. The finding comes from a survey by USP carried out in the Alto Xingu Basin, in Mato Grosso. In addition to changes in Amazonian landscapes in areas of pasture and agricultural cultivation, the researchers also observed an impact on biodiversity. In “lentic” environments, there was a proliferation of some species (amphibians and fish) well adapted to these habitats.

“The 'slowdown' phenomenon does not necessarily imply an expansion of high-quality standing water environments. On the contrary, many of these environments are heated, silted and contaminated by fertilizers and pesticides”, explains Professor of Environmental Management Luis Schiesari, from USP's School of Arts, Sciences and Humanities (EACH) and coordinator of the study to the USP Journal. The field research took place between 2011 and 2013 and an article on the subject, entitled Ponds, puddles, floodplains and dams in the Upper Xingu Basin: could we be witnessing the 'lentification' of deforested Amazonia?, was published in June 2020 in the magazine Perspectives in Ecology and Conservation.

According to the researcher, in the Amazon, there are at least three combined factors that would be influencing this process: the construction of dams and wells (pools for accumulation of water for cattle herds); the elevation of the water table and the compaction of the soil, resulting from deforestation.

Studies cited in the article show that in addition to large dams built for the purpose of power plants, such as Belo Monte, the Alto Xingu Basin has, alone, about 10,000 small dams built in deforested areas to supply water to cattle and generate electricity for local consumption. Another study also reports the existence in the Amazon Basin of 154 hydroelectric dams in operation, 21 under construction and 277 planned. “Both the large dams and the small ones change the water flow regime. These are recognized as the most important factors that lead to ‘ slowing ’”, says the researcher.

The other factor is the elevation of the water table or elevation of the surface limit of groundwater. Schiesari explains that in deforested environments, replacing large trees, with deep roots and leafy crowns, with grass and soybeans reduces evapotranspiration (loss of water from the soil through evaporation and loss of water from the plant through transpiration). “Under these conditions, a larger fraction of rainwater accumulates as groundwater, promoting an expansion of the stream floodplains and the many puddles connected to them”, he says.

And, last but not least, is the compaction of soils in deforested areas, says the researcher. These are associated with the trampling of cattle, machinery traffic and road construction. “Soil compaction in animal pasture areas is 8 to 162 times greater than in forests, which favors the formation of temporary puddles,” he says.

Toads, frogs and tree frogs

With the damming of water, the tendency is for the fauna and flora to be impacted. To demonstrate that the “slowing down” of the waters would be affecting biodiversity, the researchers carried out a survey of typical species of standing water. In this search, it was possible to observe an increase in the population of amphibians (toads, tree frogs and frogs) and fish such as yams, lambaris and rivulids, which commonly live in very shallow aquatic environments isolated from rivers. “Amphibians are excellent indicators of hydrological changes because most species reproduce in still water environments,” reports the article.

In temporary puddles formed by soil compaction in deforested plateaus (elevated surfaces), 12 species of amphibians were found - the tree frogs boana albopunctata and the frogs Physalaemus cuvieri, for example, – which did not occur on forested plateaus. In floodplains diverted from streams, the abundance of fish Melanorivulus megaroni doubled compared to forested environments.

Schiesari also remembers the relationship between the impact of biodiversity and human health. According to him, maintaining healthy ecosystems in balance with food production is humanity's greatest challenge. The constant and long human interventions in nature imply the emergence of the spread of diseases. According to the researcher, “the reorganization of biodiversity that occurs with "slowdown ’ can favor the population increase of species responsible for the transmission of diseases such as schistosomiasis and malaria, scourges of colonists in deforested environments", he concludes.