A Water Quality Index Applied to an International Shared River Basin: The Case of the Douro River

Abstract

A Water Quality Index (WQI) is a numeric expression used to evaluate the quality of a given water body and to be easily understood by managers. In this study, a modified nine-parameter Scottish WQI was used to assess the monthly water quality of the Douro River during a 10-year period (1992-2001), scaled from zero (lowest) to 100% (highest). The 98,000 km(2) of the Douro River international watershed is the largest in the Iberian Peninsula, split between upstream Spain (80%) and downstream Portugal (20%). Three locations were surveyed: at the Portuguese-Spanish border, 350 km from the river mouth; 180 km from the mouth, where the river becomes exclusively Portuguese; and 21 km from the mouth. The water received by Portugal from Spain showed the poorest quality (WQI 47.3 +/- 0.7%); quality increased steadily downstream, up to 61.7 +/- 0.7%. In general, the water quality at all three sites was medium to poor. Seasonally, water quality decreased from winter to summer, but no statistical relationship between quality and discharge rate could be established. Depending on the location, different parameters were responsible for the episodic decline of quality: high conductivity and low oxygen content in the uppermost reservoir, and fecal coliform contamination downstream. This study shows the need to enforce the existing international bilateral agreements and to implement the European Water Quality Directive in order to improve the water quantity and quality received by the downstream country of a shared watershed, especially because two million inhabitants use the water from the last river location as their only source of drinking water.

Application of fish index of biological integrity (FIBI) in the Sanmenxia Wetland with water quality implications

“…As a consequence of rapid urbanization, economic growth, intensification of agricultural productivity, and water scarcity (Bordalo et al, 2006), the contamination of riverine wetlands with nutrients as well as trace metals and organic xenobiotica has increased, especially in developing countries, resulting in a deleterious effect on aquatic organisms and their structures (Allen and Hansen, 1996;Singh et al, 2007). Thus, a series of evaluating methods were promoted to conduct scientific assessments of water and sediment quality, such as the water quality index (WQI), sediment quality guidelines, and sediment pollution index (SPI).…”

“…WQI was first developed in 1965 (Horton, 1965), as a simple and understandable tool for decision makers to evaluate the quality and possible uses of riverine wetlands (Cude, 2001), then this approach was modified and applied with multiple variations and comparative water quality evaluations for different riverine wetlands (Bordalo et al, 2001(Bordalo et al, , 2006Cude, 2001). The role of sediments, as the sinks of pollutants in wetlands, was not recognized until the 1970s; sediment quality guidelines have been promoted since that time, as well as sediment quality criteria, index of geoaccumulation, and ecological risk assessment methods (Shea, 1988;Chapman and Mann, 1999).…”

Evaluation of the ecological status of an impaired watershed by using a multi-index approach

“…A modified version of the Scottish water quality index (WQI; SDD 1976) was used to assess water quality, adapted to temperate and tropical environments (Bordalo et al 2001(Bordalo et al , 2006. We used the original SDD version adapted to temperate environments with a reduced number of parameters (nine parameters compared to 10).…”

Assessment of Quality of Groundwater in Certain Villages nearby Krishna River, Krishna District, Andhra Pradesh, India

“…WQI attempts to provide a mechanism for presenting a cumulatively derived numerical expression defining a certain level of water quality [4]. There are several reports in literature in which WQI was determined in order to assess the quality of water at different places and different sources [5][6][7][8][9][10][11][12][13]. The present investigation of the quality of groundwater from various villages of Krishna district of Andhra Pradesh state has been carried out, based on the above background.…”