A new index measures the human impacts on Amazon waters

Over the past 30 years, the Amazon has lost 12% of its surface water — a total of 11,046 square kilometers (4,265 square miles), an area 14 times the size of New York City. That’s according to a study released in September 2021 by the MapBiomas collaborative network. According to the project, “Land use dynamics based on the conversion of forest for cattle farming and agriculture together with dam construction result in reduced water flow.”

The Amazon Water Impact Index (AWII), developed by Ambiental Media with funding from the Instituto Serrapilheira, points in the same direction: 20% of the aquatic ecosystems in the Brazilian Amazon have been significantly impacted.

These numbers shed light on the real scope of the damage already done to the Amazon’s aquatic ecosystems, and indicate that Brazil’s ongoing freshwater crisis is more serious than it seems. “Environmental water conservation policy is in need of urgent revision,” says biologist Cecília Gontijo Leal, a scientific consultant who worked on the Aquazônia project, another initiative focusing on the issue.

Built to contribute to the discussion, the AWII isn’t aimed at being a precise academic tool, but rather a scientific journalism tool based on the available data. Its goal is to offer clear visual information about the regions and basins that are most affected, together with qualified opinions. This makes the index a reference platform for understanding the impacts of human activity on the aquatic ecosystems of the Amazon River Basin, which covers 7 million km2 (2.7 million mi2) over eight nations and holds approximately 18% of all the freshwater that reaches Earth’s oceans.

Beyond its colossal proportions, water in the Amazon is what connects everything. Spilling down from glaciers in the Andes, it forms the rivers that along their way feed human communities and irrigate forests and plains rich in fauna and flora. The evapotranspiration from the vegetation produces new water in an annual cycle of rainfall that feeds back the stock in the biome and then travels across Brazil. These so-called “flying rivers” irrigate crops and guarantee water supply for urban centers further south.

Climate, economy, science, culture, ecology, energy, politics and biodiversity: all are part of the water forest.

Assessing threats to the basin

For decades, the international debate on conservation of the Amazon biome has focused on the threats to its vegetation: fires, deforestation, mining, cattle ranching, soybean farming. The Amazon is seen as a source of raw materials. Aquatic ecosystems also suffer from human activity — loss of forest affects the hydrological cycle — but the damage is more difficult to identify and understand.

Urban waste isn’t the only form of pollution affecting bodies of water. “When we talk about fire or forest degradation, it’s not just about the air or the soil: it also means there will be problems in the aquatic environment,” says Leal, a biologist at the University of São Paulo’s (USP) Luiz de Queiroz College of Agriculture. “When measuring an undertaking’s impact on a river, we often only look at the problems associated with riverbank vegetation.

“Even though most of the impacts measured in the index happen on land, our focus has turned to the location, intensity and amount of pressure these impacts exert on the bodies of water in each micro basin,” Leal adds.

In developing the index, a certain amount of flexibility was necessary to assess environmental impacts, either due to the lack of data or to the fact that each micro basin is an individual ecological complex with its own environmental or legal peculiarities. For example, the impacts caused by a hydroelectric dam or deforestation are fairly clear, but the same can’t be said of the networks of thousands of small clandestine roads cutting through the web of waterways running throughout the forest.

“In the Amazon, impacts change depending on the characteristics of each ecosystem,” Leal says. “Deforestation has harsher effects on the floodplains and igapó [flooded blackwater] forests. On the other hand, damming up an igarapé [small forest stream] changes an environment’s dynamics: the flow of organic matter and the distribution of species within it.”

Equally challenging was gauging the target, range, and intensity of each factor putting pressure on the environment. Are the impacts worse for local human populations or for flora and fauna? This is hard to determine, as effects are different for each species. Migratory fish, for example, suffer the effects of hydroelectric dams, but other species don’t.

And while it’s not yet possible to pinpoint where the heaviest impacts are being felt, it’s clear they’re greater where several of them overlap.

“The most degraded regions are those where the pressures add up,” says Laura Kurtzberg, a professor at Florida International University and an expert in data visualization. “When we zoom in on watersheds, we can see that the impact on water is as strong as it is on land. It’s a silent drama.”

Then, the even less tangible impact of climate change is factored in into the AWII. The index’s final result offers a concrete overview of existing threats to the Amazon Basin, but with clear limitations in the modeling.

Data gaps in a watery world

“The farther we move into the waters of Amazonia, the less knowledge we have,” says Angélica Resende from USP’s Tropical Forestry Lab.

This isn’t only because of the lack of existing research, but also the challenges involved with monitoring the environment.

The only way to carry out large-scale monitoring in the Amazon is by remote sensing (satellite imagery), but “the challenges of working with water are different from those of working with the rainforest and deforestation. It’s more complex,” says Cláudio Barbosa from INPE, Brazil’s national space agency, and coordinator of the agency’s Aquatic Systems Instrumentation Lab (LabISA).

The international community has expressed concern about the loss of standing forest in the Amazon since INPE began measuring deforestation via satellite in 1988. According to Barbosa, Brazil’s first sensors allowed only for analysis of the margins and ground cover in cases of deforestation and mining.

Technologies making it easier to measure bodies of water began to appear in 2016. But not enough time has passed to reach many conclusions from the data, Barbosa says. In the meantime, INPE is already working with algorithms that allow for estimating sediment variation in water. “This system, which we call CADE, measures the composition of light in the water column,” Barbosa says. “That light is the energy that feeds phytoplankton and allows for diversity of fish species.

“To analyze water quality, we have to work with the concentration of sediment, chlorophyll and dissolved organic matter,” he adds. “We can already map these three parameters by satellite.”

The absence of more consolidated data on water creates challenges for awareness, scientific focus, public policy and conservation projects. Edgardo Latrubesse is a fluvial geomorphology specialist — someone who studies how rivers form and change over time — at Goiás Federal University. He says public policies on water management already exist. “We have a strong Water Resources Law and basin regulating committees. The problem in Brazil is that, despite having the legislation, no one respects it.”

But Cecília Leal says the existing legislation views aquatic ecosystems merely as resources — that is, exclusively for human use. As a result, broader ecological factors like biodiversity are left out. At the National Water Agency, rivers are measured and viewed according to their utilitarian potential for purging pollution. “It is an important service, but we can’t think of water bodies only in terms of their ability to dilute waste,” Leal says.

Without data on the current situation of the Amazon’s water resources, it’s impossible to plan the future of ecosystems that are constantly transforming, says Leandro Castello from Virginia Tech in the U.S. And as a result, we lacking long-term references. “What is ‘a lot of fish’ for us today is nothing compared to what was ‘a lot of fish’ for our grandparents,” Castello says.

“Rivers today are completely different than they were 40 years ago — but we don’t have data on how they are different.”

There’s an established method for researching standing forest on dry land. When describing land organisms, biologists can identify species by following sound trails — of birds and amphibians, among others — and observing traces left behind. As for fish in rivers, “you have to collect them, because the water is usually cloudy or black. Data on direct observation is rare,” says Jansen Zuanon, from the National Institute of Amazonian Research (INPA).

Furthermore, land organisms are more homogeneously distributed, spread out over a more or less two-dimensional surface, Zuanon says. Fish, on the other hand, live in waterways that branch out as they flow through the basin. As they travel toward headwaters, niches of increasingly smaller habitats are formed in creeks and streams, and the fauna start to change longitudinally.

Since 2015, Zuanon has participated in the Amazon Fish project, a broad database on water species in the Amazon. The project has logged nearly 2,700 species so far, distributed by factors such as climate, topography, hydrography and rainfall. One piece of data already established is that there are more endemic species present in the western part of the Amazon Basin, in the Peruvian Andes. “Biodiversity tends to fall off as you move toward the mouth of the river,” Zuanon says. “It’s surprising because the river widens near the mouth in the lower basin, and we would expect an accumulation of species.”

One hypothesis for this points to the ancient past: Between 8 million and 10 million years ago, the Amazon River flowed into the Pacific Ocean. When the Andes began to rise, the river changed direction and began flowing into the Caribbean. “As the Andes were established, that region rose more and the river began to drain into the Atlantic,” Zuanon says. “Apparently, the process didn’t allow enough time for all the environments in the lower part of the river to be colonized.”

Zuanon also studies the gradual and subtle effects of climate change on aquatic environments. A study by INPA in the Central Amazon analyzed fish from a reserve near Manaus, the largest city in the Brazilian Amazon, where rainfall has increased in recent years. There, researchers detected changes in the stream species within a 10,000-hectare (25,000-acre) protected area​​. Rainfall increase has affected the accumulation of banks of dead leaves and the amount of sand in environments not affected by deforestation or pollution. “Changing the structure of the substrate means changing the composition of the fish fauna,” Zuanon says. “It’s not a local extinction, but we have already seen changes inside even protected systems.

“Extreme events like droughts and floods impact fish production and the ability to predict ways to get around on waterways,” he adds. “It’s not just about biodiversity, but also about people’s lives.”

“Fish regenerate forests by dispersing seeds,” says Rogério Fonseca, coordinator of the Fauna and Forest Interactions Laboratory at Amazonas Federal University. “Water connects everything: it is the bloodstream of the system, spreading nutrients and allowing plants and animals to propagate from one region to another.”

Fewer fish for the table

The approximately 30 million Brazilians living in the country’s Amazonian region have among the highest rates of fish consumption on the planet. The United Nations’ Food and Agriculture Organization (FAO) estimates average global consumption to be 20.3 kilograms (44.8 pounds) per person per year; in some communities in Brazil’s Amazonas state, it can be as high as 150 kg (330 lbs).

Although the Amazon’s fish population is great — and only about 50% of the system’s sustainable potential is exploited, according to Leandro Castello — impacts from pollution and overfishing threaten fishing stability. Local populations suffer from a lack of fish at certain times of the year, and it’s estimated that today, more than half the riverbank communities along the Amazon and its main tributaries, like the Madeira and the Purus, use community management to ensure they have enough to eat.

Such management isn’t only valuable for food and economic security, but also for conserving resources. “These are humble communities of 50 people, often located 300 kilometers [190 miles] from the nearest town,” Castello says. “But they will always be the pillars of any conservation action.”

One of the most successful examples comes from the Mamirauá Sustainable Development Reserve, in the Mid-Solimões River Basin in Amazonas state, which centers on a species that has become a symbol of the forest: the pirarucu, or Arapaima gigas.

The model is simple: fishermen count how many of these giant fish are present in the lake and set a fishing quota. The amount increases when fishermen comply with established size limits. A predictable supply of fish means the market is organized and the locals can profit more. According to Castello, some 450 communities have already adopted the model.

Is water a low-impact energy source?

A report published by WWF in September 2021 named the Tapajós, a tributary of the Amazon, one of the 10 most threatened rivers in the world. This, because of a series of projects to dam its waters — an obsolete energy strategy, according to WWF, given the resistance of successive governments to invest in lower-impact, renewable alternatives.

The Tapajós and the Xingu, another Amazon tributary, are cratonic rivers, which means they have a very gentle gradient and thus have little lateral mobility and carry little sediment. Communities along this type of river are highly dependent on the flood pulse.

“The Tapajós project is absurd,” says Edgardo Latrubesse. “It is a system of large waterfalls and a continuum of hydroelectric plants which regulate the river and create a 1,000-kilometer-long [620-mi] artificial lake. All this in an area of ​​great diversity and scenic beauty.

“The natural heritage of the Brazilian river system is being neglected,” he adds. “The Tapajós is a symbol, and it must be saved.”

Successive Brazilian governments have clung to the idea that the country’s rivers would provide the perfect energy matrix because water is a renewable resource with low carbon emission. “This discourse was aligned with the international community, but they simplified the complexity of the problem,” Latrubesse says. “A river that has a thousand species of fish is a unique treasure. Carbon in the atmosphere and the discussion of climate change are irrelevant topics in terms of building a hydroelectric plant on a river like this because the impact is immediate.”

But hydropower already accounts for 62.7% of the electricity feeding into Brazil’s grid, and it continues to be endorsed by most public managers as a geographical asset for new development projects. Renewable sources like solar, wind and biomass currently comprise only 22.7% of the total energy mix.

“Planning dams in series without considering the cumulative effects is a recipe for disaster,” says Cecília Leal. “A plan that makes it possible to prioritize certain places for generation and others for conservation, with free rivers, would be an alternative.”

The Ministry of Mines and Energy’s National Energy Plan (PNE 2050) calls for increased power generation from hydroelectric plants to be a priority. The goal is to increase installed capacity from 98 gigawatts at present to 168 GW by the end of 2030, with much of this power coming from the river basins of northern Brazil.

But this is a scenario that has played out many times before, often to a tragic end. The Balbina dam, built in the 1980s on the Uatumã River, another Amazon tributary, is one of many examples. The creation of its reservoir flooded such a large area of forest that today it emits more greenhouse gas per unit of electricity produced than a coal-fired power plant. It also forced the displacement of an Indigenous group from their native lands.

In a study published in 2021, researcher Thiago B.A. Couto, together with the National Geographic Society and Florida International University’s Environmental Institute, showed that small hydroelectric dams in the Amazon cause the loss of river connectivity and prevent migratory fish from completing their life cycles.

“Indigenous groups and riverbank communities depend on being able to fish migratory species for their livelihood,” Couto wrote. “Nine small hydroelectric dams on the Juruena River, a tributary of the Tapajós in Mato Grosso, already affect several peoples, such as the Enawenê-Nawê.”

This is a key finding, given that small plants make up 80% of the 275 hydroelectric plants installed in the Amazon. Their licensing is less regulated and they tend to avoid the kind of public scrutiny that larger undertakings face.

The Belo Monte dam, on the Xingu River, has over the past decade become emblematic of the issue. It’s located near the municipality of Vitória do Xingu in Pará state, and just a few years after going into operation, the dam has become more famous for its environmental and social liabilities than for the energy it generates. It uses what’s supposed to be a more river-friendly model, the run-of-the-river system, in which the turbines lie horizontally at the bottom of the river, the reservoir area is reduced, and the volume of water that enters the plant is essentially the same as the volume that leaves. From an environmental point of view, it should have less of an impact.

“The problem with this model is that it doesn’t protect water enough. It remains very vulnerable to heavy droughts, which happened in 2021,” Jansen Zuanon says. “So there will be more pressure for new reservoir projects or reservoirs in series, like we have on the Tapajós.”

To make things worse, climate models point to changes in rainfall patterns, with less rain in the eastern part of the Amazon — precisely where Belo Monte is located. Zuanon says that in order to maintain minimum turbine function, more water will have to be diverted from Volta Grande, the highly scenic region flooded by the dam.

A survey carried out by the Instituto Socioambiental together with the Juruna Indigenous people evaluated the recent hydrological cycle of the Xingu and found, among other issues, a drop in fruit production in the local igapós, the flooded forests. This resulted in less food for turtles and tambaqui fish (Colossoma macropomum), meaning less food for the people living there.

“For the Indigenous people, the question is basic: if there is no more food for the fish, there will be no more fish to eat,” says biologist Camila Cherem Ribas from INPA’s Board of Biodiversity and Scientific Biological Collections Program.

The Madeira River is another giant waterway facing the threat of hydroelectric dams. The huge Jirau and Santo Antônio dams have been operating near Porto Velho, capital of the state of Rondônia, over the past decade, and two new hydroelectric plants are included in the 2050 National Energy Plan as part of binational agreements between Brazil and Bolivia.

According to the Dam Environmental Vulnerability Index (DEVI), developed by geologist Latrubesse and other scientists, the Madeira is the most vulnerable river in the Amazon. And a study by Latrubesse published in Nature in 2020 identifies 16 hydroelectric projects threaten the upper stretches of the Madeira.

Gold: A dream turned into environmental nightmare

The Madeira region around Porto Velho was once one of the world’s most productive regions for alluvial gold mining. But construction of the dams left the mining areas flooded and made licensing of mining projects impossible.

This means there are still hundreds of dredgers in the city or upriver that continue to scour the riverbed without mining authorization or environmental licensing. In this illegal mining model, dredgers suck material from the riverbed to filter out and separate the gold using mercury. The contaminated water is then dumped back into the river.

This “Floating Gold Rush” intensified with the 2020 economic crisis precipitated by the COVID-19 pandemic, amid shrinking fish stocks and a lack of environmental enforcement. In the Humaitá region, many fishermen quit their trade to take up gold mining, which is both more profitable and more polluting.

The mercury used to separate out the gold ends up contaminating the water and destroying the food chain. “Mercury tends to accumulate in the bodies of organisms and grow exponentially in the chain,” Zuanon says. “Predators accumulate more. Then problems spread throughout the basin, resulting in lost diversity and ecological functions in every local community.”

Latrubesse is among those who defend the presence of a regulated activity subject to certain limits, laws, protocols and quotas. He says the problem is not the mining itself, but the techniques that illegal miners use to extract the gold and the fact that they do it inside conservation areas and Indigenous lands.

“The system could be changed to lessen the impact. Techniques for extracting gold without using mercury exist,” says Valdenira Santos, a professor at Amapá Federal University (UNIFAP) and researcher at the state’s Institute for Scientific and Technological Research (IEPA).

It’s a complex and sensitive debate: history has shown that what happens in the real world of mining never corresponds with good theories. In February of this year, the federal government launched a program to formalize and bolster artisanal mining in the Amazon — an initiative that drew an immediate outcry from scientists and environmentalists.

“Although mining can be done without using mercury, it’s still completely distant from the reality in the Amazon,” Cecília Leal says. “Without a major change in mining culture, the activity will tend to continue generating significant environmental and social impacts.”

Flooded forests: Legendary landscapes of the Amazon

The dams of the big hydropower plants pose an especially serious threat to the Madeira because of a vital element for the health of the biome: sediments. Almost 90% of the sediment in the Amazon system comes from the Andean tributaries. “The most important sedimentary portion of the entire Amazon Basin is located in the Ucayali, Marañon and Madeira rivers,” Latrubesse says.

Particulate matter from different mineral origins, like erosion or decomposing organisms, sediments work as natural fertilizer in a watershed and serve vital functions such as transporting nutrients and controlling lateral migration rates. In the Amazon, they’re responsible for the fertility of the floodplains, unique ecosystems that cover about 14% of the basin.

The floodplains and flooded forests, known as várzeas and igapós, respectively, are unique to this immense tropical environment and have been protecting its life and habitats for millennia. They depend on the local flood pulse, which is determined by rainfall at the headwaters of the basin’s main rivers. This determines the levels of annual floods and droughts.

“These have always been the environments most occupied by human populations in the Amazon because of the nutrient-rich soil, even in pre-Columbian periods,” says Jochen Schongart, an associate researcher on INPA’s Board for Environmental Dynamics Research (CODAM). These fertile inland regions are where most of the rural communities lie.

Flood regions are particularly vulnerable to deforestation or overfishing, as well as climate change and El Niño and La Niña phenomena, which intensify the levels of rainfall and drought. MapBiomas data released in September 2021 point to an increased drought trend in floodplain areas.

“When we don’t have the forest that mitigates them, droughts and floods become more intense,” says Raimunda Lucineide Gonçalves Pinheiro, a professor at Western Pará Federal University’s Institute of Education Sciences. “If the stream silts up, it overflows even more.

“The floodplain is plentiful,” he adds. “It has many fish and is fertile for growing food: bananas, watermelon, melons, vegetables. During the flood season, the lakes where fish are caught mix with the river, which floods over into the forest. Fish go into the forest to spawn and feed on the fruits that fall from the trees.”

The amount of sediment deposited at the mouth of the Amazon is estimated at 1.2 billion metric tons per year. Part of the material released by the river feeds the coast up to Venezuela, forming the largest belt of mud bars in the world. Part of this is retained on the platform in Amapá.

“If the amount of sediment decreases, there is a deficit of material on the platform and along the coast of neighboring countries,” says Valdenira Santos. Less sediment, combined with strong hydrodynamics in the ocean, will accelerate erosion processes near the mouth of the largest river on the planet.

Biodiversity tries to adapt to these changes in morphology, drainage network and hydrology. “But invasive species, such as the Malaysian shrimp, which are brought in with ballast water on cargo ships, are already being seen at the mouth of the river. This can have an impact on the redistribution of species,” Santos says.

Experts’ main concern is with the retention of sediments by large dams, especially in the Madeira Basin. “If the entire flow of sediments from the Andes were blocked,” Latrubesse says, “the Amazon system could die completely.”

The future: A coordinated effort by the basin

In the intricate plot of evolution in the tropics, “South America has the most diverse cast of species,” researcher Michael Goulding wrote in his book The Fishes and the Forest: Explorations in Amazonian Natural History. “The Amazon Basin provided ideal conditions for the irradiation of life in an almost unbelievable number of niches.”

A comprehensive assessment of degradation on a continental scale is a challenge for scientists. There’s no coordinated data network for the entire Amazon hydrological system, much less an institution or government agency working to conserve the entire basin. And data surveys or eventual conservation plans need to include more than just the Brazilian Amazon. Any activity in anoy of the other countries that also make up the basin — Bolivia, Colombia, Ecuador, Venezuela, Guyana, French Guiana, Peru and Suriname — will affect Brazil, as the water flows through to the Amazon.

Within the basin, areas protected by national legislation remain one tool of conservation. Another is environmental licensing regulations. Leandro Castello says these are important, but they’re not designed to protect aquatic ecosystems. “It’s a big puzzle,” he says.

The lack of a channel for dialogue between scientists and policymakers makes the scenario even more complex. In Valdenira Santos’s view, the solution lies in joining three complementary forces: inspection and monitoring; watershed and land use by companies and the population; and research. “Without joining these efforts and interests, there will be no change,” he says.

“We need solutions, because we clearly have problems,” Leal says, adding that focusing on regions whose natural characteristics are still intact is key. “It is much easier to preserve than to restore. Impacts are difficult to reverse.”

Recent studies, Leal says, show that the conservation of freshwater environments helps maintain biodiversity, including species on land. “It is time that we look at aquatic ecosystems not just as water resources, but in a more generous and integral way.”

This story was first published in Portuguese on Ambiental Media on May 4th, 2022. 

Banner image: In one of the best-preserved areas of the Amazon, rivers and forests mix in the region of the Japurá River, which starts in Colombia and crosses the Brazilian state of Amazonas until it flows into the Solimões River. Image by André Dib.