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    Water - Water Quality
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Introduction

Water quality refers to the concentration of dissolved gases and solids, suspended solids, hydrogen ions, heat and pathogens in a given amount of water (Dingman, 2002). The chemicals are a water-quality issue depending on their intrinsic toxicity, persistence, bioaccumulation in aquatic organisms, interaction with other chemicals, how they are transported from soil and air to water, and potential for transformation into other more dangerous chemicals (Walker et al., 2006). Assessing water quality as good or bad is not absolute; it depends on its intended use or fate (Revenga et al., 2000; WRI, 2000); therefore, water quality can also be defined simply as the suitability of water to serve several uses or processes (Meybeck et al., 1996). This chapter focuses on the analysis of water quality from the standpoint of human uses, as its relation to aquatic ecosystems is discussed in the chapter on Biodiversity.

All human activities that depend on water, both consumptive (agriculture, households and industry) and non-consumptive (recreational, fishing, power generation, aquatic transportat), require the concentration of some of the constituents that determine its quality remain within certain limits. When the concentration of any of these constituents exceeds the threshold above which it affects the suitability of water for a specific use, this constituent is considered a pollutant (Meybeck et al., 1996; Dingman, 2002).

At higher volumes extracted to meet the consumers’ demand, the volume of wastewater generated also increases, with the potential to affect and degrade the quality of water supply sources, as most uses affect water quality (Jackson, 2001). Additionally, domestic, industrial, agricultural and livestock-raising wastewaters are generally untreated but discharged directly into surface water bodies (CNA, 2001) which, besides, serve as sinks for other point or diffuse pollution sources. Point sources encompass a relatively small area, such as industrial, municipal and farm wastewater, open dumps, septic tanks, leaking storage tanks, leaking oil wells and pipes, and chimneys. Diffuse sources encompass large areas, such as agricultural and livestock land, quarries, urban areas and deposition of air pollutants (Carpenter et al., 1998; Dingman, 2002). Rain, runoff and infiltration wash the air and soil, carrying pollutants towards surface water bodies and aquifers (Carpenter et al., 1998; Dingman, 2002). Groundwater pollution may pose a risk for human consumption. Vulnerability is the risk of water to be polluted. There are two types of vulnerability: intrinsic and specific. The first type corresponds to pollutants generated by human activities; the second one refers to a specific pollutant or group of pollutants and involves both the pollutants’ properties and their relationship to intrinsic vulnerability (Pérez and Pacheco, 2004).

Chemicals that are either volatile or carried by air as particulate matter are an important component of water pollution. Persistent organic compounds such as mercury, pesticides and polychlorinated biphenyls (PCBs), as well as inorganic nutrients -phosphorus and nitrogen, for example- are among the air pollutants that affect water quality as a result of their impact on both aquatic ecosystems and the health of all types of organisms, from algae and invertebrates to humans (Baselice et al., 2002; Swackhamer, 2004; MPCA, 2007). For all these reasons, soil chemical, eolic and hydric degradation and air quality are factors that, albeit indirectly, affect water quality, which is why this chapter is closely related to the Soil and Atmosphere chapters.

Declining water quality is an issue that adds to the increasing scarcity due to overconsumption and rising supply costs, given the need to treat water before use (Carpenter et al., 1998). Many measures to reduce water pollution have been implemented in recen years. Increasing efforts are being made to improve control and treatment of industrial and domestic waste discharges to curb pollutant emissions into the atmosphere and control solid waste disposal and the use of agrochemicals in the field, as well as to monitor the quality of water bodies and restrict their use when they fail to meet the standards for each type of use.

A set of indicators are provided below to account for the main pressures affecting water quality in our country, the state of water supply sources and the performance of measures that have been taken in an attempt to solve this issue. Importantly, for the correct interpretation of some of these indicators, particularly the pressure and state indicators, it should be considered that water quality varies continuously over time due to natural factors such as seasonal changes in rainfall frequency and intensity, as well as temporal variation in socioeconomic activities that affect it. This is particularly true in water bodies where water supply, currents and turnover occur continuously (Conagua, 2008a). Some indicators are presented in terms of annual national or regional averages, and may differ significantly from local values ​​at any given time.

 

 

References

Baselice, A., R. García, I. Saavedra, G. Giner. Análisis de la distribución y el transporte del mercurio en ríos bajo explotación minera con aplicación a la cuenca del Caroní. Revista de la Facultad de Ingeniería de la U.C.V. 17:83-95. 2002.

Carpenter, S., N. F. Chair, D. L. Caraco, Correll, R. W. Howarth, A.N. Sharpley y V.H. Smith. Nonpoint Pollution of Surface Waters with Phosphorus and Nitrogen. Issues in Ecology. 3:1-12. 1998.

Conagua. Estadísticas del Agua en México. 2008a.

Dingman, S.L. Phisical Hydrology. Prentice Hall. Nueva Jersey. 2002.

Jackson, R. B., S. R. Carpenter, C.N. Dahm, D. M. McKnight, R. J. Naiman, S. L. Postel y S. W. Running. 2001. Water in a Changing World. Issues in Ecology. No. 9.

Meybeck, M., E. Kuusisto, A. Mäkelä y E. Mälkki. Water Quality. En: UNEP/WHO. Monitoring - A Practical Guide to the Design and Implementation of Freshwater Quality Studies and Monitoring. Programmes. 1996. Disponible en: http://www.who.int/water_sanitation_health/resourcesquality/wqmonitor/en/ Fecha de consulta: 30-10-2012.

MPCA. Phosphorus rule: Report to the legislatura. As required by Minnesota session law 2006, chapter 251 section 16 (b). Minnesota Pollution Control Agency. USA. 2007.

Pérez C.,R.  y J. Pacheco A. 2004. Vulnerabilidad del agua subterránea a la contaminación de nitratos en el estado de Yucatán. Ingeniería 8: 33-42.

Revenga, C., J. Brunner, N. Henninger, R. Payne, y K. Kassem. Pilot analysis of global ecosystems: Freshwater systems. WRI. Washington, D.C. 2000.

Swackhamer, D.L., H. W. Paerl, S. J. Eisenreich, J. Hurley, K. C. Hornbuckle, M. McLachlan, D. Mount, D. Muir y D. Schindler. Impacts of Atmospheric Pollution on Aquatic Ecosystems. Issues in Ecology12:1-24. 2004.

Walker, H.C., S.P., Hopkin; R. M., Sibly y D. B., Peakall. Principles of ecotoxicology. 3th edition. Taylor & Francis Inc. British. 2006.

WRI. Pilot analysis of global ecosystems: freshwater systems. USA. 2000.