Calculation of Water Quality Index and Its Use for Water Quality Assessment in Lake Sevan

Abstract

The article gives an example of the choice and implementation of a method for water quality assessment for a large high-mountain lake with long-term unstable level regime and variable morphometry (artificial level decrease by 19 m followed by an increase by 4 m and more). The choice of a procedure for water quality assessment for such a water body requires non-standard solutions. This is made with the use of a modern modification of the Delphi expert panel method. This method gives a quantitative estimate of water quality relative to the initial/desirable state that all managers strive for in order to achieve and maintain water quality. The index of Lake Sevan water quality index SWQI is based on seven priority characteristics with the weight of each of them taken into account. The long-term dynamics of this index confirmed the managerial impact of lake level rise on water quality: a poor water quality (a minimal value of SWQI = 20) was recorded in the years of the lowest level (1976–1990), while a good water quality (the maximal value of SWQI = 69), in the years of highest level (2016–2020); (the coefficient of correlation was 0.82). The advantages of the used index SWQI include the relatively low dependence of the index on the availability of a database and the possibility to use the estimate for balancing the environmental and socioeconomic interests. The general approach to SWQI model can be used to evaluate the water quality of such lakes all over the world.