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Why the Amazon’s small streams have a major impact on its grand rivers

Researcher Guilherme Cabral

Researcher Guilherme Cabral, from the Federal University of Pará (UFPA), is working to collect an unprecedented temporal study of Amazonian aquatic ecosystems. The first phase took place in 2010 and now scientists are once again covering 100 streams in forests, pastures and agricultural production areas between the municipalities of Santarém and Paragominas. Image by André Dib.

  • An unprecedented time-series study in the basin of the Tapajós River, a major tributary of the Amazon, assesses the level of degradation of small rivers threatened by agribusiness expansion.
  • Researchers from several universities will assess the conservation status of 100 streams spread between the municipalities of Santarém and Paragominas, at the confluence of the Tapajós and the Amazon, which were first analyzed in 2010.
  • The impact of dirt roads and their network of river crossings, which causes sediment load, siltation, erosion and changes in water quality, was one of the factors that caught researchers’ attention in the initial time-series study.
  • Experts say that local development models should ideally start from water to land, rather than the other way around, given the importance of water for the rainforest, its biodiversity, and the inhabitants who depend on both.

TAPAJÓS NATIONAL FOREST, Brazil — We have to walk fast inside the forest to keep up with the scientists and their local guides. It’s the dry season, and the heat in the Amazon Rainforest is suffocating. An hour and a half later, after going up and down several slopes, some so steep that a helping hand is needed from the colleague ahead, we arrive at the stream. Relief. The pure and crystal-clear water of this small river branch isn’t just perfect for quenching our thirst after the walk; it’s the very subject of the scientists’ research.

In Brazil’s Tapajós National Forest, in the state of Pará, students and professors from different universities are assessing the conservation status of streams as part of a research project that includes 100 small streams spread between the cities of Santarém and Paragominas, which were analyzed for the first time in 2010.

The word used in Brazil for these streams, igarapé, comes from the Tupi-Guarani language and means “canoe path.” Igarapés run from springs toward lakes and rivers, and although much narrower and shallower than the latter, they’re navigable by small boat, as the name suggests. “The great rivers of the Amazon would not exist without those streams, which are their headwaters,” says Cecília Gontijo Leal, an ecologist at the University of Lancaster, U.K., and the Sustainable Amazon Network (RAS). She heads the Understanding and Conserving Tropical Freshwater Ecosystems project.

Now, returning to the same sites of the 2010 study, the group of 19 professors and students want to understand the impact of human activity on these aquatic ecosystems and their fish communities since then. The goal is to find solutions to protect Amazonian biodiversity and influence preservation policies and best land-use practices.

“There are not many time-series studies in the Amazon, and that is a gap in scientific information. Therefore, we decided to come back to see how change had taken place in the landscape and its effects on those streams,” Leal says.

The study is a pioneering assessment of the change in the condition of the streams over the past decade, using modern methods that will help elucidate recent environmental stress factors. The project will run until 2029 and cover forests in the municipalities of Santarém, Belterra, Mojuí dos Campos and Paragominas.

A river flanked by forests.
The word used in Brazil for these streams, igarapé, comes from the Tupi-Guarani language and means “canoe path.” Image by André Dib.

The region has changed a lot in the last 13 years, Leal notes, highlighting deforestation and an increase in activities such as the conversion of pastures to mechanized agriculture. “The streams are impacted by these changes, which deteriorate water quality and alter wildlife,” she says. The consequences are seen in larger rivers already affected by major construction works and reflect on the Amazon Basin as a whole — up to 90% of its water bodies are streams. “Headwater streams are much more numerous than larger rivers,” Leal says.

The health of the biome is closely linked to aquatic biodiversity, to the point that some species, referred to as bioindicators, reflect its level of conservation. Aquatic plants and dragonflies are among the important ones. The more aquatic plants, or macrophytes, the stronger the change in the environment. Streams that are more exposed by deforestation receive more light, which means more plants grow there. Fewer of these plants, or the existence of some specific species, indicates a healthy environment. Dragonflies, in turn, known in the forest as jacinas or jacintas, are insects sensitive to changes in the aquatic environment. The presence of species from the suborder Zygoptera is usually a sign of a well-preserved environment, while the presence of Anisoptera dragonflies often reflects disturbances such as vegetation loss.

The high diversity of fish caught the attention of researchers as early as 2010, says Paulo Pompeu, professor of ecology and conservation at the Federal University of Lavras (UFLA). While streams in southeast Brazil typically have five to 15 species of fish, those in the Santarém area host 30-40 species. At one point in Paragominas, a municipality of more than 100,000 inhabitants a few hours from the state capital, Belém, 48 species were found — greater aquatic biodiversity in a single stream than in entire countries such as England. According to the researchers, the variety of fish species in streams in certain small areas isn’t seen often elsewhere in the Amazon. “How can such a small environment support so many species at the same time? We want to understand how local diversification occurs,” Pompeu says.

Among the new approaches of the 2023 study is the collection of water samples to test for environmental DNA. This will give an indication of the species present in the water, via DNA in the tissues and droppings that they shed. Another new task for the researchers is to collect samples of what the fish feed on, such as algae, terrestrial and aquatic insects, and leaves and fruits from trees. This will help them identify what resources sustain the fish community, and the differences in nutrient sources between a preserved area and a degraded one.

The scientists will spend up to four years in the laboratory analyzing the samples they collect. The results should show the health status of streams in the Santarém plateau — a snapshot of what’s happening to small rivers throughout the so-called Arc of Deforestation in the southern Amazon. At the same time, they’ll serve as the basis for planning new actions to minimize or even reverse the negative impacts caused by changes in land use in the biome.

A damselfly and a dragonfly.
With wide-set eyes and smaller, thin bodies, damselflies (suborder Zygoptera) (image on the left) generally live in preserved environments, while dragonflies (suborder Anisoptera) (right), with more robust bodies and eyes close together on the top of the head, tend to reflect altered environments. Dragonflies are among the species considered bioindicators, as they reflect the level of conservation in a region. Images by André Dib.

A biological treasure at risk

The Tapajós River Basin covers an area of 48.9 million hectares (121 million acres), or 7% of the entire Amazon Basin. With its headwaters close to the municipality of Cuiabá, in Mato Grosso state, the clearwater river runs nearly 2,000 kilometers (1,200 miles) before it joins the Amazon River near Santarém. The Tapajós is the Amazon’s fifth-largest tributary.

Archaeologists estimate that human occupation in the area where the rivers meet dates back 7,000 years. Modern-day Santarém was established over sites of pre-Columbian peoples, and reports of European pioneers exploring the Amazon region — such as Francisco de Orellana’s expedition of 1542 that successfully navigated the length of the Amazon — already mentioned the existence of a village with thousands of people at the confluence of those two major rivers.

The effects of centuries of accumulated human actions on the Amazon Basin’s waters, especially in recent decades, are evident from the Amazon Water Impact Index (IIAA), developed by Ambiental Media under the Aquazônia project. While 20% of the microbasins in the Brazilian Amazon are highly impacted, that figure rises to 40% specifically in the Tapajós Basin.

The impact of dirt roads and their network of river crossings was one of the factors that caught researchers’ attention in the time-series study. The roads that cross the channels increase sediment load, causing siltation, erosion and changes in water quality. “A road crossing a stream may seem like an isolated impact, but the accumulated adverse effects are relevant,” Leal says.

The scientists are still working on mapping the Santarém area, but data for the entire biome compiled by Aquazônia indicates 9,778 points where roads intersect rivers of all sizes, not just streams. The number is likely an underestimate due to the difficulty in mapping.

At the northern entrance to Tapajós National Forest, two streams called Jamaraquá and Jaguarari are now closed because of the same road. In a 2020 technical note, the Chico Mendes Institute for Biodiversity Conservation (ICMBio), the federal agency in charge of managing protected areas, said that from December 2004 to March 2005, the Belterra municipal government opened the Transtapajós road without authorization, environmental license or previous study.

The construction of the 12-km (7.5-mi) route to connect the national forest’s riverine communities was included in the municipality’s management plan, but City Hall didn’t follow the recommendations from the army’s engineer corps, which called for a different route. The road ended up damaging the streams. IBAMA, the environmental protection agency, issued a notice of violation and embargoed the road section, while a court ordered the municipality to come up with a recovery plan to prevent erosion, stabilize soils and desilt streams.

According to ICMBio environmental analyst Bruno Delano, the embargo was lifted in 2022 so that Belterra officials could carry out the repair work, but little has been done so far. The mounds resulting from erosion were removed, as well as some of the siltation in the waters. However, the embankments haven’t been revegetated, banks weren’t reforested, and the bridge over the Jamaraquá stream has yet to be repaired; the wood for this purpose is there, waiting to be used before it rots.

The roadworks violated environmental legislation and impacted not only the ecosystem but also the local economy, given that Jamaraquá is the most popular community in the national forest. “Local income suffers and also the national forest, which has visitation data to be monitored,” Delano says. “As long as the stream is deteriorated, we can’t allow people to access that area.”

Despite the impacts on these two watercourses, the national forest still fulfills its role of protecting water bodies. The springs are inside the forest, and some of the water flows west to the Tapajós River and then east to the basin of the Moju River, another tributary of the Amazon. The latter area is crossed by the BR-163 highway and under pressure from expanding soy and corn fields, which is where the streams begin to be severely damaged.

The Cuiabá-Santarém section of the highway, opened in the 1970s, is one of the main Brazilian routes for moving grain, whose cultivation continues toward northern Pará, at the confluence of the Amazon and the Tapajós.

Transtapajós, the road opened without authorization from ICMBio that cuts through Flona do Tapajós
Residents use Transtapajós, the road opened without authorization from ICMBio that cuts through Flona do Tapajós, to reach basic health services. The community of Acaratinga does not have access to public transport, which reinforces the need to readjust the road with environmental damages. Image by André Dib.
Tapajós National Forest
Created in 1974, the Tapajós National Forest is home to 24 traditional communities that depend on sustainable timber forest management, community-based tourism, oil, fruit and rubber production, in addition to subsistence farming and artisanal fishing. Image by André Dib.

Changes in land use

In the Amazon region, the cycle of illegal deforestation that causes areas to be cleared for pastures or plantations follows a widely known order. It begins with selective logging, followed by deforestation and then fires — a sequence that causes drastic impacts on streams. “Vegetation provides shade and organic matter, influencing the entire dynamics of waters and species,” Leal says. “If you remove riparian vegetation [near water bodies], that material won’t enter.”

Fish are the first to feel the impacts. According to researcher Gabriel Brejão, who holds a Ph.D. in animal biology from São Paulo State University (UNESP), while terrestrial vertebrates can stand about 60% of deforestation in a given area before they begin to decline, some species of fish suffer when that rate reaches 10%. On the other hand, when more than half of the forest is cut down, the presence of fish species that thrive in altered environments begins to increase.

In this scenario, “high diversity changes to very homogeneous wildlife, with few species dominating the area,” Brejão says. When it becomes homogeneous, in addition to declining numbers, several species unique to the biome go extinct.

The village of Takuara on the banks of the Tapajós offers a prime example of how this deterioration plays out. It’s late afternoon when we arrive by canoe after a half-hour paddling through the blackwater-flooded forests known as igapó. The atmosphere is magical, with light filtering through the canopy and reflecting the twisted shapes of the trees on the water’s mirror-like surface.

The fishers from the Indigenous Munduruku community cast their nets while we wait in the boat. The crescent moon is already visible when we return to check on their catch. Only 15 fish were caught: banded aracu, spotted sorubim, piau, and a single peacock bass.

“Thirty years ago there used to be lots of tambaqui, arapaima, peacock bass. We didn’t need to go far to fish. We used longlines to catch three or four tambaqui to eat during the week,” says Leonardo Pereira dos Santos, chief of this Munduruku village inside Tapajós National Forest. “Now arapaimas are virtually gone,” he adds, referring to one of the world’s largest freshwater fish.

Munduruku people in a boat.
In the igapó forests, on the banks of the Tapajós River, in Santarém, Indigenous people from the Munduruku community who live in the Takuara village go fishing frequently, but the quantity and variety of fish have decreased in the last three decades. Image by André Dib.

The low number and variety of fish reflect changes in upstream land use, especially as a result of deforestation and illegal mining, as well as fishing by large boats known as geleiras (ice boxes). On the banks of the river, residents of Tapajós-Arapiuns Extractive Reserve and Tapajós National Forest have seen their way of life and food security affected by companies that arrive from other cities and states to buy tons of valuable fish.

On their way out, they discard fish that for them has no commercial value, thereby depriving local communities of a valuable source of nutrition. “Predatory fishing destroys what we have. Soon we will be eating chicken every day or canned stuff that is not good for our health,” Santos says.

The riverine communities, however, managed to fight predatory fishing by official means: a fishing agreement approved by the Pará state government. Initiated by ICMBio in 2016, in partnership with civil society, the process resulted in rules in late 2022 that imposed limits on large boats operating in this stretch of water. To assess the impact of the agreement and adopt future measures, ICMBio trained residents of both the extractive reserve and the  national forest to act as supervisors. During each step of the hydrological cycle — ebb, drought, flow and flood — fishers must record several characteristics of the fish they catch, such as species and size, to gain an idea of how the species are responding to external pressures.

“If we don’t preserve it, in the future our children won’t know the local fish. We’ll have to go to the market in Santarém to buy fish to eat. So we must organize while there is still time,” Santos says.

He also recommends that people avoid drinking water from the Tapajós or swimming in it, citing concerns about mercury contamination from illegal gold mining in the river. The muddy color of the naturally clear river also indicates high levels of sediment washed by rain into streams and rivers, from soils that were exposed after the native vegetation was cut down.

“What we see in the Tapajós is an increase in suspended particulate matter due to numerous land-use activities,” says Daniele Kasper, a biologist at the Federal University of Minas Gerais (UFMG), who has studied the impact of mercury on the waters and soils of the Amazon for 20 years.

Rafael Pereira Leitão, from UFMG, and Cecília Gontijo Leal, from U.K.'s University of Lancaster
Rafael Pereira Leitão, from UFMG, and Cecília Gontijo Leal, from U.K.’s University of Lancaster, are part of the group of 19 researchers who seek to understand the impacts of human actions on streams and their fish communities; one of the objectives is to develop solutions and influence public policies and conservation practices. Image by André Dib.

Various contaminants like mercury clump together in these suspended particles. Mercury pollutes rivers and may alter their natural colors. It also affects fish, thus finding its way up the food chain to humans. A 2022 study conducted by researchers at the Federal University of Western Pará (UFOPA) and the Oswaldo Cruz Foundation, Brazil’s leading public health research institute, examined 462 residents of eight riverine areas and one urban zone in the municipality of Santarém: more than 75% of participants had mercury levels in their blood above the safe limit recommended by the World Health Organization.

Exposure was higher in riverine dwellers (90%) than in the urban population (57%). Fish, too, will exhibit varying mercury levels depending on what they eat, “since the element accumulates throughout the food chain,” Kasper says.

The mercury that winds up in the river doesn’t come only from mining. The element is easily absorbed by organisms in its organic, naturally occuring form known as methylmercury, which develops under low-oxygen conditions — in hydroelectric reservoirs and flooded areas of igapós and floodplains, for example, as shown by Kasper and other scientists. Thus, any activity that causes erosion will supply the aquatic system with mercury stored in certain soils.

Many of these harmful actions — deforestation, fires, new roads — are associated with agribusiness. Not surprisingly, of all the impact factors analyzed by the Amazon Water Impact Index, none is more widespread than agriculture and livestock: these activities impact 88% of the total 11,000 microbasins that make up the Brazilian Amazon. “It’s quite clear that the great damage in the area has been the increase and intensification of large-scale agribusiness on large properties,” says Leal, the study’s coordinator.

Such changes in land use also have a profound impact on the way of life of riverine and Indigenous populations. Under pressure from the unrestrained expansion of agribusiness, the idyllic past of clear Amazonian rivers serving the leisure and everyday needs of communities has become just a memory for people born and raised in the region.

Biologist Thiago Couto (in the foreground), from Lancaster University, analyzes specimens collected in the Santarém region.
Biologist Thiago Couto (in the foreground), from Lancaster University, analyzes specimens collected in the Santarém region. The continuing research will help evaluate the environmental stress factors to which Amazonian streams are subjected. Image by André Dib.

Profit first

Archaeologist Anne Rapp Py-Daniel is a professor at UFOPA and studies the establishment of Indigenous and Afro-Brazilian Quilombola communities in the Santarém area. She uses people’s reports, memories and traces of occupation to reconstruct that past and understand today’s identity and reality.

“Over the last three decades, Santarém and other municipalities in Pará state have encouraged the arrival of soy farms,” she says. “That encouragement has taken several forms, such as proposals to create soy and fuel ports on Lake Maicá; changes in the city’s master plan to increase farming-ready areas; and authorization to deforest land on the Santarém Plateau. These actions, focused mainly on the economic sector, have been carried out without prior assessment of impacts on the environment and traditional communities.”

The Açaizal stream, which runs through the Indigenous village of the same name, is an example of that impact, which started at the turn of this century. Since then, the flow of streams has decreased, the color of the water has changed, and lagoons have dried up. “There used to be many fish and lots of alligators,” says Josenildo dos Santos Cruz, the village chief. “The stream is no longer good. Leisure spaces are gone; Brazil nut, souari nut and other trees were cut down.”

The environmental impact is reflected in Indigenous culture itself. “The forest makes us stronger. When a tree falls, our people become spiritually ill,” dos Santos Cruz says.

In 2009, residents started submitting complaints to the Federal Prosecution Service, which filed a public civil action against the Pará state government and the municipality of Santarém for failing to enforce environmental laws and demanded the restoration of the silted stream. Filed in 2019, the lawsuit received a favorable opinion from the Regional Prosecutor’s Office in September last year.

This sets an important precedent for communities facing the same problem in other parts of the river basin. The four Munduruku villages located on the Santarém Plateau — Açaizal, Amparador, Ipaupixuna and São Francisco da Cavada — are surrounded by large plantations. “From 2021 to 2022, 809 hectares [2,000 acres] were deforested between Açaizal and Ipaupixuna alone,” Py-Daniel says. “Soy has already reached people’s backyards.”

Soy fields affect not only Indigenous peoples but also family farming communities on the plateau. Farmer and artisan Maria Emília dos Reis Pinto guides us along a dirt road that crosses some streams. None of them has clear water. The first stream we cross is covered in aquatic plants and the water smells strange. A little further on, the stream is an opaque green and filled with aquatic plants that are bioindicators of pollution. It gets worse in another section of the stream, where the water is brown. Pinto stopped using the stream that crosses her land six years ago. “People are afraid to use their wells because of the pesticides,” she says.

Mechanized corn harvesting in a deforested area of the Amazon forest in the municipality of Belterra, Pará.
Mechanized corn harvesting in a deforested area of the Amazon forest in the municipality of Belterra, Pará. Of all the factors analyzed in the Amazon Water Impact Index (IIAA), none surpasses agriculture and livestock in terms of spatial distribution. These activities impact 88% of the total 11 thousand micro-basins that make up the Brazilian Amazon. Image by André Dib.
Grain storage silos
Scientists point out that changes in land use since the last decade in the Santarém region, where the conversion of pastures into mechanized agricultural planting areas was intense, threaten local waters and biodiversity. The grain storage silos (above) are an indication of the volume of monoculture-based production.

Their fear is well-founded. To assess the impact of agribusiness on the rural area of Santarém, geologist Moema Morgado, an associate researcher at the Federal University of Mato Grosso, analyzed samples of groundwater from wells, surface water from rivers and streams, and bottom sediments. The results indicate the presence of herbicides such as atrazine, glyphosate and metolachlor, as well as several metals, both in the water and sediments. She also found traces of insecticides banned in Brazil, such as DDT and endosulfan.

Just like mercury, some pesticides accumulate throughout the food chain. This happens because they can form insoluble complexes: instead of breaking down, they settle in the sediment. Glyphosate, one of the most popular pesticides in Brazil, is a perfect example. Brazilian law allows levels of glyphosate residue in drinking water that are 5,000 times higher than Europe’s. It forms complexes that are insoluble in waters rich in aluminum and iron oxides. “The composition of sediments and soil in the Amazon is perfect for that,” says Morgado, who found glyphosate in all sediment samples analyzed and in 40% of water samples, where the water-soluble pesticide is diluted.

One case stood out in the municipality of Belterra, near Santarém. On Feb. 6, 2023, 30 people, including students and staff of the Vitalina Motta school, went to the health center with symptoms such as itchy skin and eyes, sore throat, nausea, vomiting and fainting. A few days later, the doctor who examined them told IBAMA inspectors that there were signs of pesticide poisoning, since everyone had similar and collective symptoms and described a strong smell and feelings of suffocation.

Schoolteacher Heloise Rocha says that when she arrived at the school that morning, she noticed a strange smell. By around 9 a.m., the children began to complain of burning eyes and shortness of breath.

“Soy farmers have always done this, but it was never so aggressive,” she says of the liberal use of agrochemicals. “We don’t know whether they changed the poison or increased the amount.” The soy field, planted with corn in the off-season, is located behind the school. Before a wall was built, the plantation almost merged with the school’s vegetable garden.

When crops from the field across the road are harvested, soot stains the school walls and causes allergies and inflammation. “Locals are permanently in contact with the poison. We’re not sure whether the water is contaminated or not, but the pesticide is thrown directly into the soil, and most people here have wells, including the school,” says Rocha, who has lived in the area for eight years.

The teachers filed a complaint with the Federal Prosecution Service, and IBAMA fined landowner Renato Zambra more than 1 million reais ($200,000). It also ordered him to cut down a 100-meter (330-foot) stretch of the plantation nearest the school and replant native vegetation in the area. As of August 2023, however, there was only a single row of grass growing close to the wall.

Vitalina Motta school
In the beginning of 2023, students and staff of the Vitalina Motta school reported symptoms of poisoning that started after the use of pesticides in the soybean plantation adjacent to the teaching unit. Image by André Dib.

For the right to be an igarapé

Since communities began reporting health problems linked to the water, the Saúde e Alegria project, a nonprofit operating in the Brazilian Amazon to promote and support sustainable community development, has been working on the installation of solar-powered water supply microsystems and distributing nanotechnology filters. More than 6,000 people have already benefited in five municipalities in western Pará. “If there is no garbage collection, no sewage system, no treatment facilities, it’s clear that groundwater can be contaminated in towns,” says the NGO’s founder, Eugênio Scannavino.

In the Santarém urban area, the degraded streams take on a new shade: gray. In Bela Vista do Juá, an area occupied by landless people next to the road to the airport, the strong smell of sewage tells of the failure of the nearby waste treatment facility, where the 3,081-family housing project Residencial Salvação was built in 2016.

From the top of a gully, a 2-m (6-ft) erosion hole filled with trash, water trickles toward a small stream that flows into Lake Juá, in front of the Tapajós River, where a white sand beach can be seen at this time of year. The small watercourse is an igarapé. It doesn’t have an official name yet because it didn’t even exist for most residents of the occupied area, despite being mapped by the federal government in 1983 as an intermittent drainage area: a flow of water that appears in the rainy season and disappears in the dry season. A canal was excavated during the construction of the housing project on the other side of the avenue, says UFOPA geography professor João Paulo de Cortes, who has been working for the recognition of the stream since 2018.

Around 100 families live in the area, the largest and most recent housing project in the city. There’s a lot of debate about the environmental impact of the irregular houses, as people arrived and cleared the vegetation to settle in the area, at about the same time as the housing project was built. Without proper infrastructure, some houses risk collapsing, which led UFOPA to submit a report to the Federal Prosecution Service.

The university monitors risks and carries out environmental education activities with the community. “What we want is formal recognition of the stream in the municipality’s planning instruments — of the stream and the basin,” Cortes says. According to him, official identification is the first step to recover the canal by treating the sewage thrown there.

Public authorities follow what he calls “urban counterplanning,” that is, management based on the logic of the use of public space, which ends up exhausting water assets. “In the Amazon, urban streams are very sensitive, due to the combination of intense rainfall and terrain that is poorly consolidated from a geological point of view. The waters drain into lakes and rivers, which have important social uses and ecological functions. These drainage areas must not suffer irreversible impacts,” Cortes says.

Located in one of the most remote areas inhabited by human populations in the Amazon, Santarém has become an important urban center in western Pará
Located in one of the most remote areas inhabited by human populations in the Amazon, Santarém has become an important urban center in western Pará, but the development model based on the expansion of predatory agribusiness generates wealth, income concentration and environmental degradation. Image by André Dib.
Most of the members of the 100 families living in the Bela Vista occupation in Santarém have never seen the stream near the urban community clea
Most of the members of the 100 families living in the Bela Vista occupation in Santarém have never seen the stream near the urban community clean. Only the oldest residents remember when the water of the stream was clean: “it hurts my heart. We had a bath here, the water was beautiful, and now it is polluted by sewage,” says a resident. Image by André Dib.

A chance for the future

Centuries after the arrival of the first Europeans, the colonial logic of exploiting the territory’s resources continues to threaten Indigenous peoples and degrade the most biodiverse rainforest on the planet, a biome sustained and shaped by water. The rain cycle fills and then empties lakes and rivers, establishing drought and flood periods that regulate the way of life of populations. In floodplains and igapós, the flood-prone areas with species adapted to seasonal flooding, planting, harvesting and means of transportation are dictated by that ebb and flow.

According to this regular and powerful natural dynamic, local development models should ideally start from water to land rather than the other way around, experts say.

To help with environmental restoration, biologist Gabriel Brejão advocates adding structures to the aquatic ecosystem. “If fish like to hide behind branches, trunks and leaves, these elements can be introduced to improve structural diversity that allows a variety of species to circulate.” Other arrangements could allow the fish to migrate from one environment to another when the area has been altered by a dam or a road.

Restoration of ecosystems as well as their destruction cause cascading effects on the biome as a whole, as there are countless connections within a river basin. “Each species plays its specific role in the environment and is performing services,” Brejão says.

Along the course of the river, he says, the headwaters provide nutrients for larger water bodies. For example, intact headwater streams support the fishing chain on the Tapajós River: when fruit is produced and food consumed in the chain, terrestrial energy is transferred to the aquatic environment. These nutrients, in turn, sustain large fish consumed by human populations. Homogenization of aquatic wildlife caused by land degradation creates an imbalance in this nutrient cycling, which can cause ecosystems to collapse, affecting local supply chains. “Preserved headwaters and wildlife diversity guarantee economic activity and health for human communities,” Brejão says.

A baby agami egret in a floodplain lake where the Tapajós and Amazon rivers meet.
A baby agami egret in a floodplain lake where the Tapajós and Amazon rivers meet. The main threat to this species is the acceleration of deforestation in the Amazon Basin. Image by André Dib.

Altogether, the effects of degradation on streams and small rivers will, at some point, be reflected in the large rivers that cross the Amazon, inevitably affecting people. “Everything that passes through the streams — animals and plants, sediments, organic matter — will accumulate downstream,” Cecília Gontijo Leal says.

Minimizing these impacts involves improving water protection laws, considering specific aspects of each environment, investing in scientific dissemination, and getting traditional communities involved in decision-making. “There are several Amazons within a larger Amazon. We must work a little in each region to reach the whole,” says Luciano Montag, a professor at the Federal University of Pará and a researcher on the time-series study of streams.

After completing all the analyses, which will generate dozens of scientific studies, the findings could help environmental agencies in managing ecosystems. “Pará has several restoration targets, which can be met in a way that better encompasses aquatic environments,” Leal says.

For her, the paradigm that governs humanity’s relationship with water needs rethinking: rivers, lakes and streams must be seen as the source of biodiversity rather than resources for exclusive human use. “Our usual view is utilitarian: people think about the quantity and quality of water. But species play a crucial role. There is no healthy river without its species.”

Life wouldn’t survive without water, and in the Amazon, its endless and powerful cycle sustains and regulates the existence not only of the rainforest but also of the entire planet.

Banner image: Researcher Guilherme Cabral, from the Federal University of Pará (UFPA), is working to collect an unprecedented temporal study of Amazonian aquatic ecosystems. The first phase took place in 2010 and now scientists are once again covering 100 streams in forests, pastures and agricultural production areas between the municipalities of Santarém and Paragominas. Image by André Dib.


This story was reported by Ambiental Media and first published here on Dec. 4, 2023, and republished here by Mongabay Brazil on Dec. 27, 2023.


Coordination: Thiago Medaglia

Editing: Ronaldo Ribeiro and Fernanda Lourenço

Data check: Marina Martinez

Translation: Roberto Cataldo

Overexploitation threatens Amazon fisheries with collapse, study warns

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