Response indicators

Population with access to sewerage

Together with water sanitization and drinking water coverage, efforts to increase the population with access to sewerage are part of a sanitation strategy to reduce the incidence of disease and generally improve the population’s life quality (Conagua, 2008b; Guerrero, 2008). As a response to reduce the pressure on the quality of water supplies, sewerage coverage represents only the first step: the collection of municipal wastewater for treatment before reuse or discharge into natural water bodies. To note, wastewater collection coverage in Mexico includes sewerage in septic tanks and drainage to gullies, crevices, rivers, lakes or seas (Conagua, 2008b). The World Bank includes access to sewerage among its Poverty-Environment Indicators. The OECD includes sewer connection as part of the indicator of connection to wastewater treatment, which breaks down sewer and treatment types (OECD, 2008). The UN includes the population with access to adequate sewerage among its sustainable development indicators (UN, 2007).

Treated wastewater

Pollutants in municipal and industrial wastewater are harmful to human health and hamper the different uses of water bodies. Aquatic and terrestrial ecosystems are, to some extent, able to process or dilute these pollutants and render them innocuous for humans and other animal and plant species. However, ecosystems have a limited capacity for processing pollutants and, when this is exceeded, ecosystems are no longer able to provide this environmental service, as frequently pollution itself ends up affecting their functioning (Daily et al., 1997).

The increase in pollution and the destruction of ecosystems worldwide are affecting the water-purification ability of nature (Daily et al., 1994; Revenga et al., 2000). One of the most effective response measures to address this issue is the treatment of municipal and industrial wastewater, which aims to remove water pollutants to make it suitable for reuse or for safely discharging it into water bodies. The indicator Treated wastewater denotes the efforts made to reduce pressure on the quality and availability of natural waters, as this allows water to be reused for some activities, depending on the type of treatment administered. The OECD uses the percentage of population with connection to wastewater treatment (broken down by connection to sewerage and types of treatment) in its Key environmental indicators and Core Set of environmental indicators, as does the EEA (OECD, 2008; EEA, 2009d).

AREA INCORPORATED TO THE PAYMENT FOR HYDROLOGICAL ENVIRONMENTAL SERVICES PROGRAM

The economic contribution that the hydrological ecosystem services provided by natural ecosystems make to human activities is estimated to be in the order of billions of dollars (Daily et al., 1997). However, this contribution has traditionally been insufficiently recognized in market economies, as the value generated is frequently not reflected in the prices of goods the production or exploitation of which depends, one way or another, on proper water availability and quality. Until very recently, there were no economic instruments to finance the conservation of ecosystems whose functioning significantly influences the regulation of hydrological and nutrient cycles, soil retention, and degradation and assimilation of other pollutants that affect water quality. In 2003, Mexico implemented the Payment for Hydrological Environmental Services Program (PSAH, for its acronym in Spanish), in which government money is used to retribute owners of land that includes well-preserved woods and forests for the public benefits implicit in their conservation (Conafor, 2009, Semarnat, 2009). This program focuses specifically on forest land, not only for its importance from the hydrological standpoint, but also because it offers owners an alternative to clearing the land for agriculture and livestock ranching, which are the main drivers of the loss of natural vegetation cover in the country.

Trees in temperate and tropical forests provide hydrological services in various ways (Daily et al., 1994; Dudley and Stolton, 2003; Semarnat 2009; Manson, 2004; GWP-CA, 2006): they promote less variability in local rainfall by continuously pumping water from the soil up into the atmosphere through transpiration. When it rains, trees retain a significant amount of water in the foliage which also evaporates, and their roots and litter maintain adequate conditions in the soil for the gradual infiltration of rainwater, thus favouring both aquifer recharge and the maintenance of rivers and springs. This, in turn, prevents the occurrence of massive flash surface runoff which often results in waterfloods downstream. Because trees in temperate and tropical forests regulate infiltration and runoff, they contribute to the maintainance of water quality, as they retain sediments and allow plants to assimilate nutrients and degrade or filter, along with soil, anthropogenic pollutants carried by water (Daily et al., 1994; Manson, 2004).

Other types of ecosystems also provide valuable hydrological services but have not yet been formally included in the environmental services market. Wetlands, for example, can remove 20 to 60 percent of metals in water, retain 80 to 90 percent of sediments in runoff and absorb 70 to 90 percent of nitrogen. For their part, riparian forests trap sediments and process nutrients and pollutants carried by water from adjacent land; they can reduce nitrogen loads by as much as 90 percent and phosphorus loads by as much as 50 percent (Ramsar Convention, 2004; Schuyt and Brander, 2004; ESA, 2005).

Other government actions, currently in place, aimed at protecting vegetation cover and terrestrial ecosystems also positively influence water quality and availability, for the same reasons stated above. This is the case of Protected Natural Areas (PNA), Management Units for the Conservation of Wildlife (Uma¹), the Conservation and Sustainable Management of Forest Resources project (Procymaf¹), the Forest Development Program (Prodefor¹), the Commercial Forest Plantations Program (Prodeplan¹), the Conservation and Restoration of Forest Ecosystems Program (Procoref¹), the Program to develop the environmental services market for carbon sequestration and those derived from biodiversity, and the promotion of the establishment and improvement of agroforestry systems (PSA-CABSA¹) and Ecological Land-Use Planning (OET¹), all of which are discussed in more detail in the chapters on Biodiversity and Forest Resources.

¹ For its acronym in Spanish