Nav: Home

Urbanization and agriculture are land uses that most affect Brazil's rivers

September 09, 2020

Brazil has more freshwater than any other country, but this resource is dwindling because of climate change, rising consumption and inadequate treatment, among other factors. Worse, Brazil's rivers are increasingly polluted due to a lack of proper land use planning.

Agriculture and urbanization are the main culprits, closely followed by mining. Although mining occupies a small percentage of Brazil's territory, it has a huge impact on water quality, according to a literature review by a group of researchers published in Journal of Environmental Management.

The review was led by Kaline de Mello, a biologist at the University of São Paulo's Institute of Biosciences (IB-USP). Mello is supported by São Paulo Research Foundation - FAPESP .

Researchers affiliated with the Federal Universities of the ABC (UFABC), Minas Gerais (UFMG) and São Carlos (UFSCar) in Brazil and the University of Massachusetts (UMass Amherst) and Oregon State University (OSU) in the United States also participated.

This study is the first to provide a nationwide overview of the impact of land use on water quality. "Most research offers projections of the impact of land use changes on the amount of water available and not on water quality. We set out to see what water quality will be like 30 years from now," said Ricardo Hideo Taniwaki, a professor at UFABC and a coauthor of the published article.

The authors evaluated the impacts of all possible future scenarios, ranging from worst-case to best-case scenarios for the impact of changes in land use on water quality while also considering climate change.

Extensive survey

The analysis was divided into stages. First, having collected land use and land cover data from the platform Mapbiomas, the researchers observed conservation of native vegetation and the extent of activities potentially affecting water quality, particularly agriculture, pasture, silviculture (forestry), mining and urbanization.

"Next, we separated the field studies that assessed the effects of the activity in question on nearby rivers in the various Brazilian biomes," Mello said. The parameters used to measure water quality included fecal bacteria, sediment, nitrogen, phosphorus, heavy metals, and other pollutants.

The second stage showed that degradation varies according to the scale or dimension used to evaluate it and that this should be taken into account when conservation action is planned. Land use impacts on water quality are evaluated in one or all of the following spatial dimensions: at the water sampling site, in the riparian vegetation and in the entire catchment area. "Catchment analysis appears to best reflect overall water quality," Taniwaki said.

The temporal dimension involves rainfall and other seasonal variations, such as temperature. "This is important in the context of climate change," Taniwaki said. "Heavier precipitation and longer droughts are expected. In the absence of best agricultural practice, river pollution will increase."

Finally, the article discusses mathematical models that predict future water quality. "We highlight models available in Brazil that can be used to simulate the impact of positive and negative measures, as well as the data required to do so," Mello said.

Impact by soil type

Pasture and cropland account for 28.8% of the territory and are found mainly in the Cerrado (42% of the total) and Atlantic Rainforest (62%) biomes. "In areas of pasture, soil compaction by animals affects water absorption. Surface runoff increases, and so does the volume of polluted water entering streams and rivers when it rains," Mello said.

Agricultural activities also affect runoff dynamics and increase the amount of pollutants such as nitrogen, phosphorus and other chemicals in water courses. "It's worth recalling that Brazil is one of the world's largest consumers of fertilizer and agrochemicals, which have a significant impact on surface water and groundwater," Mello said.

In urban areas, there are two main problems. "The soil is almost entirely sealed and made impervious by concrete and tarmac, so that runoff with pollutants of all kinds including heavy metals enters the water courses when it rains, and Brazil has few stormwater treatment programs," Taniwaki stated.

Although urban areas occupy only 0.6% of Brazil's land mass, cities are major drivers of water quality degradation due to untreated sewage, which fills rivers with fecal bacteria, organic matter and other pollutants. Some 48% of the population is not connected to a domestic sewerage network, and only 10% of the largest cities treat more than 80% of the domestic and industrial waste they collect.

Mining also occupies a small percentage of the territory but has an enormous local impact on water quality, discharging heavy metals that are toxic to plants and animals as well as humans into water courses. This impact was evidenced by catastrophic tailings dam failures in Mariana and Brumadinho, in the state of Minas Gerais.

The Mariana disaster polluted more than 650 km of the Doce, one of Brazil's major rivers, affecting over 1 million people. Analysis of water from Paraopeba, one of the rivers affected by the Brumadinho disaster, showed that after the accident, levels of lead and mercury were 21 times those acceptable.

"More than 40 mine tailings dams are at risk of similar accidents up and down the country," Taniwaki said.

Most endangered biomes

Loss of native plant cover is the main threat to water sources in all biomes, Mello noted, citing the state of rivers and streams in the Atlantic Rainforest biome, where 65% of the population lives. Only 26% of the original vegetation remains in this dwindling biome, and water quality is considered good in only 6.5% of its rivers.

The Amazon biome and the Cerrado are also cause for concern. Although much of the Amazon's native vegetation is still in place, it is distinctly endangered. "In 2019, the Amazon suffered its greatest forest cover loss in ten years, according to the National Institute for Space Research [INPE]," Mello said.

Deforestation in the region grew 108% in January 2020 compared with the same month of 2019. Only 19% of the original vegetation survives in the Cerrado. "More research is needed on water quality in these two biomes, which are suffering the most from the advance of the agricultural frontier," Mello said.

The future of water in Brazil

Public administrators and researchers can use the mathematical models available in the literature to predict future water quality in their regions and help make a decisions on the kind of intervention that will be most effective to deal with the specific situation. One of the tools highlighted in the article is multicriteria assessment, an approach that uses participation by civil society and private enterprise to partner with the state in prioritizing areas to be restored at a time of financial austerity.

The quality of the available data must be improved in order for this analysis to be performed more assertively, but the researchers also argue that the quantity is insufficient and that far more data are needed. "It's hard to make predictions with the water quality and land use data we have now, and predictions are vital to public policy formulation," Taniwaki said.

"The estimates now available point to severe water quality degradation unless deforestation is halted and basic sanitation improves in the years ahead," declared Mello. The long-term negative consequences include increased public spending to treat polluted water before it is used or to transport it from more distant areas. This extra cost will have to be passed on to consumers in their water bills. Drastic changes in the other environmental services provided by rivers will also be required.

"On the other hand, simulations of restoration in Permanent Conservation Areas [APPs in Portuguese, mainly riparian forest] resulting from compliance with the Brazilian Forest Code point to increased water quality due to a reduction in sediments, nitrogen and phosphorus," according to Mello.

Hence, it is important to enforce environmental legislation and planned agricultural and urban expansion. "The literature we reviewed also shows the negative effects of lowered standards, watered-down legislation, and less investment in research," Taniwaki said.
About São Paulo Research Foundation (FAPESP)

The São Paulo Research Foundation (FAPESP) is a public institution with the mission of supporting scientific research in all fields of knowledge by awarding scholarships, fellowships and grants to investigators linked with higher education and research institutions in the State of São Paulo, Brazil. FAPESP is aware that the very best research can only be done by working with the best researchers internationally. Therefore, it has established partnerships with funding agencies, higher education, private companies, and research organizations in other countries known for the quality of their research and has been encouraging scientists funded by its grants to further develop their international collaboration. You can learn more about FAPESP at and visit FAPESP news agency at to keep updated with the latest scientific breakthroughs FAPESP helps achieve through its many programs, awards and research centers. You may also subscribe to FAPESP news agency at

Fundação de Amparo à Pesquisa do Estado de São Paulo

Related Climate Change Articles:

Mysterious climate change
New research findings underline the crucial role that sea ice throughout the Southern Ocean played for atmospheric CO2 in times of rapid climate change in the past.
Mapping the path of climate change
Predicting a major transition, such as climate change, is extremely difficult, but the probabilistic framework developed by the authors is the first step in identifying the path between a shift in two environmental states.
Small change for climate change: Time to increase research funding to save the world
A new study shows that there is a huge disproportion in the level of funding for social science research into the greatest challenge in combating global warming -- how to get individuals and societies to overcome ingrained human habits to make the changes necessary to mitigate climate change.
Sub-national 'climate clubs' could offer key to combating climate change
'Climate clubs' offering membership for sub-national states, in addition to just countries, could speed up progress towards a globally harmonized climate change policy, which in turn offers a way to achieve stronger climate policies in all countries.
Review of Chinese atmospheric science research over the past 70 years: Climate and climate change
Over the past 70 years since the foundation of the People's Republic of China, Chinese scientists have made great contributions to various fields in the research of atmospheric sciences, which attracted worldwide attention.
A CERN for climate change
In a Perspective article appearing in this week's Proceedings of the National Academy of Sciences, Tim Palmer (Oxford University), and Bjorn Stevens (Max Planck Society), critically reflect on the present state of Earth system modelling.
Fairy-wrens change breeding habits to cope with climate change
Warmer temperatures linked to climate change are having a big impact on the breeding habits of one of Australia's most recognisable bird species, according to researchers at The Australian National University (ANU).
Believing in climate change doesn't mean you are preparing for climate change, study finds
Notre Dame researchers found that although coastal homeowners may perceive a worsening of climate change-related hazards, these attitudes are largely unrelated to a homeowner's expectations of actual home damage.
Older forests resist change -- climate change, that is
Older forests in eastern North America are less vulnerable to climate change than younger forests, particularly for carbon storage, timber production, and biodiversity, new research finds.
Could climate change cause infertility?
A number of plant and animal species could find it increasingly difficult to reproduce if climate change worsens and global temperatures become more extreme -- a stark warning highlighted by new scientific research.
More Climate Change News and Climate Change Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Listen Again: The Power Of Spaces
How do spaces shape the human experience? In what ways do our rooms, homes, and buildings give us meaning and purpose? This hour, TED speakers explore the power of the spaces we make and inhabit. Guests include architect Michael Murphy, musician David Byrne, artist Es Devlin, and architect Siamak Hariri.
Now Playing: Science for the People

#576 Science Communication in Creative Places
When you think of science communication, you might think of TED talks or museum talks or video talks, or... people giving lectures. It's a lot of people talking. But there's more to sci comm than that. This week host Bethany Brookshire talks to three people who have looked at science communication in places you might not expect it. We'll speak with Mauna Dasari, a graduate student at Notre Dame, about making mammals into a March Madness match. We'll talk with Sarah Garner, director of the Pathologists Assistant Program at Tulane University School of Medicine, who takes pathology instruction out of...
Now Playing: Radiolab

What If?
There's plenty of speculation about what Donald Trump might do in the wake of the election. Would he dispute the results if he loses? Would he simply refuse to leave office, or even try to use the military to maintain control? Last summer, Rosa Brooks got together a team of experts and political operatives from both sides of the aisle to ask a slightly different question. Rather than arguing about whether he'd do those things, they dug into what exactly would happen if he did. Part war game part choose your own adventure, Rosa's Transition Integrity Project doesn't give us any predictions, and it isn't a referendum on Trump. Instead, it's a deeply illuminating stress test on our laws, our institutions, and on the commitment to democracy written into the constitution. This episode was reported by Bethel Habte, with help from Tracie Hunte, and produced by Bethel Habte. Jeremy Bloom provided original music. Support Radiolab by becoming a member today at     You can read The Transition Integrity Project's report here.