The Pantanal, one of the world’s largest freshwater wetlands, could face ecological, economic and social collapse due largely to the cumulative effects of seemingly isolated development decisions, four researchers warned in a letter published this month in the journal BioScience.

In their letter, published May 4, the Brazilian scientists said there “is still hope” for the Pantanal, which occupies an enormous geological depression in South America’s upper Paraguay River basin. But they warned of the collective impact of existing and planned development projects, pointing specifically to the construction of upstream dams and to a planned river-dredging project aimed at easing grain-barge transport through the region.

“[The Pantanal’s] sustainable use must not be challenged by the consequences of small, mistaken decisions that fail to consider their cumulative impacts, compromising the future of sustainable cattle ranching, fishing, ecotourism, traditional communities, biodiversity, and ecosystem services,” they wrote.

The letter was coauthored by scientists from Embrapa Pantanal, a research unit of Brazil’s Agriculture Ministry; ICMBio, an arm of the Environment Ministry that oversees federal protected areas; the Institute of Ecological Research (IPÊ), a Brazilian research nonprofit; and the Brazilian office of Panthera, a global wildcat conservation group.

Although the Pantanal comprises 179,000 square kilometers (69,112 square miles) in Brazil, Paraguay and Bolivia, the letter focuses on the biome’s Brazilian portion, which faces the greatest development pressure.

That portion, located in western Brazil, accounts for 80% of the Pantanal overall, covering 140,000 square kilometers (54,050 sq. miles)—an area roughly the size of New York state. It is bracketed by the Cerrado, a sprawling savannah just south of the Brazilian Amazon and, more specifically, by the Cerrado plateaus of the upper Paraguay River basin, a four-country network of rivers.

Rainwater runoff from the Cerrado, most of whose precipitation originates in the Amazon region, swells rivers flowing into and around the Pantanal. Water covers up to 80% of the Pantanal several months a year, with the timing of the flooding varying from location to location.

Prominent among the causes of the Pantanal’s environmental threats is the array of small and large dams that have been built in the Brazilian portion of the upper Paraguay River basin, the four researchers said in their BioScience letter. Over the last two decades, private developers and the government have built a total of 50 dams in the region, taking advantage of the elevation change at the edges of the plateaus to generate hydropower.

Seven of these 50 dams are classified as large, with an installed capacity of over 30 megawatts; 24 as small, with five to 30 megawatts of installed capacity; and 19 have an installed capacity of five megawatts or less, according to Ecology and Action (Ecoa), a Brazilian environmental research and advocacy nonprofit. Another 13 small dams are being built, and a further 125 dams—two of them large, 96 of them small and 27 under five megawatts—are planned but not yet approved by the government, Ecoa says.

Scientists blame the dams for blocking the flow of sediments into the Pantanal—both the inorganic variety, such as waterborne sand and clay, and the organic kind from, for instance, decomposing wood and plants. They point out that the dams also cut the floodplain’s upstream supply of nutrients such as nitrogen, phosphorus, potassium and magnesium.

“Diminishing this floodplain’s lifeblood starves the Pantanal and reduces its biodiversity,” says Pierre Girard, a professor of ecology at the Mato Grosso Federal University (UFMT), who specializes in Pantanal hydrology.

Experts say the size of Pantanal fish could decline as a result, compromising the health of the fish as well as their numbers. That, in turn, would compromise the food source for fish-eating birds and the livelihoods of commercial fishers in the region. Further threatening fish populations is the role dams play in preventing them from migrating and spawning upstream.

The reduced flow of nutrients also constricts the growth of native grasses. These serve as pasture for cattle-raising operations and for native herbivores such as deer—a key food source, in turn, for jaguars and pumas.

In harming the Pantanal ecosystem, dams add to other pressures that are threatening what some experts view as a unique coexistence of economic activity and natural processes amid one of the richest concentrations of wildlife in the world.

“The Pantanal is one of the few large-scale biomes, in or outside Brazil, where sustainable economic development, be it cattle ranching or commercial fishing, can thrive alongside biodiversity conservation,” Rafael Morais Chiaravalloti, an IPÊ researcher who coauthored the BioScience letter, told EcoAméricas. “But the land-use changes that have occurred in the biome in the last two decades, mainly the damming of upper Paraguay basin rivers for hydropower, along with droughts and record Pantanal fires in 2020, have altered the natural dynamics of the biome and now threaten its survival.”

The BioScience letter highlights other development decisions that could further jeopardize the region’s environment. These include a proposed 1,272-km (789-mile) dredging project to enable barge-transport of soybeans and corn south through the Pantanal along the Paraguay River, to the Paraná River and, further downstream, transshipment from Argentina or Uruguay to export markets. The dredging is slated to be heavy along the northern 680 kilometers (422 miles) of that stretch and lighter along the lower 592-kilometer (367-mile) portion. Construction of a river port is also planned for a site 60 kilometers (37 miles) north of the area slated for dredging so grains from Brazil’s Cerrado region can be trucked there and loaded onto barges for the trip south.

The governments of Brazil and two Brazilian states on the river route’s northern portion, Mato Grosso and Mato Grosso do Sul, support the project. But ecologists point out that because the work would deepen the Paraguay River and in certain areas straighten its course, thereby speeding its flow through the Pantanal, the giant wetland’s water levels—and, thus, its seasonal inundations—would diminish.

That would mean a decline in sediments and nutrients, shrinking fish habitats and other negative ecological knock-on effects says Alcides Faria, executive director of Ecoa.

Chiaravalloti says the impacts would be far-reaching: “Because nutrient- and sediment-bearing inundations are the source of the Pantanal’s life, diminished flooding caused by the planned waterway would threaten the biodiversity of this wetland.”

He and the other coauthors of the BioScience letter also take issue with decision-making on the proposed river port. The port, to be named Barranco Vermelho, or Red Ravine, has won preliminary approval from Mato Grosso state authorities and is slated to be built by a consortium of private developers. “[A]lthough the [port’s] approval has followed the legal process, the ecosystem-scale consequences of the port were ignored; the analysis was rather focused on the port’s local, isolated impacts, despite the fact that the port will be viable only if the engineered waterway is implemented,” the letter says.

Letter coauthor Fernando Tortato, a researcher with the Brazilian arm of Panthera, argues that the port and dredged barge route must be viewed in a broader context.

“In the last two decades, regionally approved infrastructure like dams have already impacted the Pantanal, reducing its biodiversity,” Tortato says. “If other projects like the port and waterway are implemented, they will create a synergy of adverse environmental shocks to the biome that will further threaten biodiversity and sustainable economic activities, such as cattle ranching and commercial fishing.”

Analysts find such blows especially worrisome amid the growing pressure being exerted on the Pantanal by climate change, drought and dry-season wildfires. In 2020, the largest number of wildfires ever recorded in the Brazilian Pantanal burned 26% of the biome. (See "Once again, devastating dry-season fires in Brazil" —EcoAméricas, September 2020.) The next year, another outbreak of wildfires blackened an additional 12.6% of the Brazilian Pantanal.

The blazes are attributed mainly to brutal drought conditions in the Pantanal in recent years, a phenomenon that climate experts associate in part to climate change. Also cited are the burns Pantanal ranchers and farmers conduct on pasture and cropland for nutrient release and for brush and weed control.

Experts say most Pantanal ranchers and farmers manage their land sustainably and respect fire regulations such as the 120-day nationwide burning ban that the federal government declared, belatedly in July 2020, halfway through the April-to-October dry season. Because of the severe drought, however, many of those who attempted controlled burns—whether legally before the ban was declared or illegally after it was imposed—were unable to contain the blazes.

In their BioScience letter, the researchers portrayed the pressures on the Pantanal as multilayered, with decision-making on such activities as dam construction and river dredging a crucial variable in an overall picture that also includes drought and fires.

“[L]and-use changes [add] to the global, continental and regional-scale threats to challenge the Pantanal’s conservation status,” the letter states. “…[I]n such a multi-scale context, regional and local decisions are key to mitigating the negative impacts of broader, difficult-to-access threats.”

Numerous Brazilian scientists are expressing agreement with the BioScience letter, arguing that it is past time for government bodies to recognize the collective impact that piecemeal development decisions have on prized ecosystems such as the Pantanal’s.

Says Philip Fearnside, a senior researcher in Amazon Ecology at the government-run National Institute of Amazon Research (INPA): “The Pantanal is in dire straits because existing and planned dams, and a planned waterway going through it, as well as climate-change-generated impacts, like devastating fires, are converging on the biome, greatly limiting its capacity to recover.”