EXPLORING A MORE ELEGANT WATER QUALITY INDEX - DO WE DARE?

It has been over 50 years since the concept of a water quality index (WQI) was proposed by Brown and others. Since that time the metric has been adopted and used by government entities, scientists, and the media, to summarize multiple water quality parameters and to communicate about the aggregate water quality of a water body. Despite widespread WQI use there are many challenges faced by users of this venerated metric. Flow variability, diel variations in some parameters, and sampling bias can result in index values which do not provide a valid means of comparison between different water bodies or even different locations along the same river or stream. Flow variability, especially after precipitation and runoff events, can result in increases in some parameters, such as total suspended sediment; while others such as chloride, can be diluted by rainwater depleted with respect to chloride. Some parameters, such as dissolved oxygen and temperature, exhibit diel variation as a result of solar insolation and biologic activity. These parameters are often heavily weighted in water quality index calculations amplifying the introduced error. Water quality sample collection along a river system can introduce bias as a result of changes in flow along the river and sampling a moving medium. Sample collection moving upstream or downstream can introduce sampling bias which will in turn impact water quality index values and subsequent interpretations. The only way to overcome these challenges is to craft more elegant and nuanced WQI calculators which can reduce geochemical and sampling biases.