Water resources: Multiple uses and resulting conflicts

The multiple uses of surface and groundwater and Brazil’s economic development generate conflicts in the following areas:

Source: Alto Adige Südtirol – Rio dei Gamberi Krebsbach biotope – Photo by Giovanni Ussi

• Uses of water in agriculture and urban water supply. Pressure on surface water resources and groundwater affects the supply sources for urban populations.
• Public water supply can be impacted by agribusiness development and multiple uses in industry, affecting water quality, aquifer recharge and increasing treatment costs for the production of drinking water.
• The expansion of solid waste disposal in the urban system affects surface and underground water, impacting water quality.
• The increased discharge of wastewater from urban populations (untreated sewage) has a huge impact on the quality of surface and groundwater. Currently ANA data (2011),
indicate that only 35% of sewage water in Brazil is treated.
• Contamination by toxic substances, heavy metals, fertilizers, pesticides and herbicides used in agriculture is another factor that impacts the quality of surface and groundwater.
• Constructions of reservoirs in watersheds affect hydrological, biological and hydrosocial cycles.
• There is a permanent impact on human health and the collective safety of the population as a result of contamination, loss of quality and lack of availability of water resources.

Impacts on water resources and contamination

Our post summarizes the main impacts on watersheds and their consequences on water resources, aquatic biodiversity, treatment costs and loss of aquatic ecosystem services. As can be seen from this figure there is a chain and a set of interrelations and consequences that not only affect aquatic ecosystems and their components, but also the regional economy, human health, water availability and the loss of ecosystem services. There are direct and indirect effects of processes resulting from impacts.

Source: The La Mesa Watershed Reservation as viewed from space. NASA, 2021.

A list of impacts and their consequences show a diverse set resulting from the intensive uses of hydrographic basins, land uses and the production of residues that contaminate air, water and soil, surface water and groundwater. This list of impacts has numerous economic, social, environmental consequences and generates collective insecurity in populations, public health problems and deterioration of water resources, increasing the cost of water treatment for better potability, and high costs in recovery and protection of surface and groundwater reserves (Martinelli et al 2010). The main impacts and their consequences are:

• Deforestation and soil erosion.
• Increased nitrogen and phosphorus load and eutrophication from agricultural areas and untreated urban waste.
• Sedimentation of lakes, rivers and dams.
• Atmospheric pollution and contamination of air, soil and water.
• Biodiversity changes due to toxicity.
• Biodiversity changes due to the introduction of exotic species.
• Contamination of surface water, sediment and groundwater by toxic metals.
• Acidification.
• Organic Pollution (Persistent Organic Pollutants).
• Removal and destruction of flooded areas.
• Degradation of rivers (construction of canals, construction of reservoirs, waterways).
• Degradation of floodplains.
• Thermal pollution.
• Depletion of fish stocks.
• Pollution from fuel dumps.
• Industrial solid waste dumps.
• Municipal solid waste dumps.
• Toxic waste dumps.
• Salinization of reservoirs in the semi-arid region.
• Increased bacterial contamination and formation of bacteria-clay organic aggregates.
• Increased geographic distribution and incidence of waterborne diseases.
• Increased risks to public health and the collective insecurity of populations.

This set of impacts is distributed in all hydrographic basins in Brazil, with greater or lesser intensity, depending on the urban density, the volume of industrial and agricultural activities. Four fundamental problems are consequences of impacts: increased toxicity of surface and groundwater and aquatic biota; the increase in water treatment costs for the production of drinking water; the impacts on human health, generating more economic expenses with treatments and hospitalizations; increased vulnerability of human populations. The synergy between hydrological extremes, for example, and excessive land use, with a reduction in vegetation cover and removal of flooded areas, resulted in large-scale urban and peripheral area disasters, causing accidents with deaths and generating social instability.

Lacerda & Malm (2008) consider two large groups of pollutants that damage ecosystems. The first comes from organic effluents in large urban areas, associated with inadequate treatment of solid waste (garbage) and domestic sewage. The organic matter that it contaminates rivers, estuaries, dams and coastal areas, it produces an increase in BOD and eutrophication, which promotes the growth of cyanobacteria with toxic strains (Azevedo 2005).

Source: “MODIS image of Lake Erie” by NOAA Great Lakes Environmental Research Laboratory. NOAA Great Lakes Environmental Research Laboratory, 2021.

The anoxia resulting from this process affects aquatic organisms and also produces methylation of mercury or others metals. Large Brazilian capitals with dense urban populations are areas in which these processes occur, whose costs to public health are not yet fully accounted for (Marins et al 2002). The other group of pollutants is toxic metals, organic pollutants and greenhouse gases that affect regions, resulting from activity for long periods and can contaminate the atmosphere (Mastrine et al 1999). The response of natural ecosystems to chronic exposure to these contaminants is still little known according to Lacerda & Malm (2008).

Different human activities pollute the natural environment with metals. Toxic concentrations of metals such as Arsenic (As) and Mercury (Hg) can accumulate in the water column, sediment and organisms (Barky et al 2003). Mercury water pollution is associated with methylation of its inorganic form Hg2+ by bacteria. Through these biological and biogeochemical routes, mercury can accumulate and undergo biomagnification, affecting the food chain and man after ingestion of aquatic organisms with a high concentration of metal in muscles (Lacerda & Salomons 1998, Lacerda et al 2001, Malm 1998).

Mercury contamination in Amazonian rivers and in the atmosphere, due to mining activities (amalgamation with metallic mercury is the process used in the pre-concentration and extraction of gold), is a classic example of this process. Mercury concentrations have been attributed to gold mining, the presence of soils with high concentrations of naturally occurring mercury and atmospheric transport and deposition of anthropogenic mercury (Malm et al 1990, Lacerda 1995, Pfeiffer & Lacerda 1988, Nriagu 1992, Roulet & Lucotte 1995).

Also the construction of reservoirs in Amazonas offers conditions for additional sources of mercury methylation (Palermo et al 2002, 2004a, 2004b). Combinations of mercury gradients in reservoirs with changing fish eating habits affect upstream conditions and downstream of the dam. Figure 8 illustrates the different mercury concentrations along the Madeira River.

In several estuaries in Brazil, contamination by metals, especially mercury, was recorded. Work carried out in the Sepetiba basin, Rio de Janeiro, by the Millennium Institute of Estuaries, show that 30% of the mercury load that reaches the Sepetiba basin comes from the waters of the Paraíba do Sul river (Molisani et al 2007).
The possible export of bioavailable forms of mercury from the Sepetiba basin to the adjacent area of ​​the continental shelf, discussed by Lacerda & Malm (2008), shows the continuous contamination process that can occur from continental watersheds to estuarine and coastal areas ( Lacerda et al 2007).


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LACERDA, L. D. and MOLISANI M. M. Three decades of Cd and Zn contamination in Sepetiba Bay SE Brazil: evidence from the mangrove oyster Crassoscrea rhizophorae. Mar. Poll. Bull. Vol. 52. pp. 969-987. 2006.

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MARTINELLI, L. A. et al Dissolved nitrogen in rivers: comparing pristine and impacted regions of Brazil. Braz. J. Biol. Vol. 70, nº 3 (suppl.) pp. 709 – 722. 2010.

MARINS, R. V. et al. Caracterização hidroquímica, distribuição e especiação de mercúrio nos rios Ceará e Pacoti, Região Metropolitana de Fortaleza Ceará, Brazil. Geochimica Brasiliensis. Vol. 16. pp. 37-48. 2002.

MASTRINE, J. A. et al. Mercury concentrations in surface waters from fluvial systems draining historical precious metals mining sites in southeastern USA. Applied. Geochemistry, v. 14, p. 147-58. 1999.

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