Methodological development of an index of coastal water quality: Application in a tourist area

With the aim of obtaining an index of coastal water quality, a methodologic al procedure based on numerical classification and discriminant analysis is presented. The procedure was applied to nutrient data (ammonia, nitrite, n itrate, and phosphate) analyzed along the coastal waters of a Spanish touri st area. Using numerical classification, three levels of nutrient loading w ere revealed, characterizing oligotrophic, mesotrophic, and potentially eut rophic waters. Discriminant analysis was shown to be an effective methodolo gical tool in the discrimination between trophic groups. For every group, t he discriminant procedure generated the centroids. The centroids representi ng oligotrophic and potentially eutrophic conditions were used to establish the two extremes of the continuum of mesotrophic conditions in these coast al waters: Standardizing values from -1 to I,the centroids for oligotrophic and potentially eutrophic waters yielded an interval that defined the rang e of mesotrophic conditions. This interval is proposed as a water quality i ndex. The ability of the coastal water quality index to successfully predic t mesotrophic conditions was proved with random samples.