Deforestation increases water treatment costs 100-fold

In places where vegetation has been damaged, chlorine alone is not enough. A Brazilian researcher says that coagulants, pH correctors, fluorite, oxidants, disinfectants and algaecides increase the cost of the process.

By Karina Toledo

Agência FAPESP – In addition to altering the rainfall cycle, compromising the replenishment of underground aquifers and consequently reducing the water resources available to humans, deforestation of watershed vegetation is having a huge impact on the quality of the water itself, making the treatment required to turn it into potable water 100 times more expensive.

This warning was issued by researcher José Galizia Tundisi of the International Institute of Ecology (IIE) during a lecture presented at the third meeting of the 2014 Biota-FAPESP Education Conference Cycle held on April 24 in São Paulo.

“In areas with well-protected riparian forest [contiguous to water flow], it is enough to add just a few drops of chlorine per liter to obtain good quality drinking water. But in areas with damaged vegetation, such as the Lower Cotia system [the Cotia River watershed in the São Paulo metropolitan area], you have to add coagulants, pH correctors, fluorite, oxidants, disinfectants, algaecides and substances to remove taste and odor. The entire filtration service provided by the forest needs to be replaced by an artificial system, and its cost exceeds R$2 (about US$0.83) to R$3 (US$1.25) for every 1,000 cubic meters, for totals of R$200 (US$83) to R$300 (US$125). This amount needs to be added on to the costs of deforestation,” Tundisi stated.

When there is adequate plant cover in the watershed area – including not only the riparian forest but also flooded areas and other areas of native vegetation – the evapotranspiration rate is higher; in other words, a larger amount of water is returning to the atmosphere and encouraging precipitation.

In addition, Tundisi explained, storm water runoff occurs more slowly, reducing the process of erosion. Some of the water is absorbed into the soil through trunks and roots that work like biofilters, replenishing the aquifers and ensuring the sustainability of the springs.

“In bare soil, the rainwater drainage process occurs much more quickly, and there is a considerable loss of soil surface, which ends up in the bodies of water. This suspended organic matter completely alters the chemical characteristics of the water, both on the surface and underground,” Tundisi explained.

According to the researcher, the change in the chemical composition of the water is even more accentuated in the presence of cattle breeding or when fertilizers and pesticides are used along the banks of the rivers. There is then an increase in turbidity and in the concentration of nitrogen, phosphorous, heavy metals and other contaminants, which has a strong impact on the aquatic biota.

Tundisi noted that in addition to ensuring water for human consumption, the aquatic ecosystems offer a series of other services of major economic significance, such as the generation of hydroelectricity, irrigation, transport (waterway), tourism, recreation and fishing.

Measuring the value of these ecosystem services is the goal of the project led by Tundisi, “Long-term ecological research in the watershed of the Itaqueri and Lobo rivers and UHE Carlos Botelho Dam, Itirapina, SP, Brazil (PELD),” with funding from FAPESP and from the National Council for Scientific and Technological Development (CNPq).

“They are strategic services that are essential to São Paulo State development. Their valuation is of fundamental importance in implementing green economy projects that emphasize the conservation of these structures of vegetation and flooded areas,” he said.

Carbon cycle

In the second lecture of the meeting, Maria Victoria Ramos Ballester, a researcher at the Center for Nuclear Energy in Agriculture (CENA) at the University of São Paulo (USP), presented FAPESP-funded studies conducted in the Amazon that revealed the importance of the rivers in the carbon balance of the Amazon River basin, including the forest and soil. Some of the findings of these studies were published in an article that appeared in the journal Nature.

“We’ve always believed that nearly all the atmosphere’s carbon absorbed by the Amazon Forest remained in the soil, but we have demonstrated that a significant portion of it goes into the rivers in the form of leaves, branches and sediments. This material is decomposed by microorganisms and returns to the atmosphere,” Ballester explained.

According to the researcher, river waters process nearly the same amount of carbon on the global level as that estimated for earth systems – approximately 2.8 petagrams (2.8 billion tons) per year.

Studies by the group have demonstrated that the quantity of carbon in the waters of the central portion of the Amazon River basin was nearly 13 times higher than that discharged into the ocean.

“Isotopic composition analyses have shown that the carbon comes primarily from young plants, approximately 5 years old. It is quickly metabolized in the river and returns to the atmosphere. Carbon metabolism occurs even more quickly in small rivers,” Ballester said.

However, the intense process of occupying the Amazon region and the resulting changes in the patterns of land use have altered nutrient cycling in the rivers, increasing the amount of carbon and reducing the dissolved oxygen, the researcher warned.

“The increased amount of organic matter suspended in the water along with the greater penetration of light as a result of the removal of trees encourages the growth of a grass known as paspalum, which increases oxygen consumption and carbon dioxide (CO2) flow into the atmosphere,” she said.

The effects of the changes in river habitat on the biota were assessed in a study conducted under the scope of the thematic project, “The role of Amazonian fluvial systems in regional and global carbon cycles: CO2 evasion and land-water interactions,” led by researcher Reynaldo Luiz Victoria.

The CENA group analyzed the nitrogen transfer and biodiversity of the fish from two interconnected basins in the state of Rondônia, which both measured 800 meters and had the same physical conditions. One of the basins was surrounded by cattle pastures and the other by native forest.

The researchers observed that the river whose vegetation coverage was modified had only one species of fish, whereas the river whose native forest was maintained had 35 species. There was also a significant difference in the diversity of invertebrate species observed.

The imbalance in access to abundant existing water resources in Brazil was the theme of the third and final lecture at the meeting, given by Humberto Ribeiro da Rocha from the Institute of Astronomy, Geophysics and Atmospheric Sciences (IAG/USP).