Visual protocol fails to detect critical water quality problems

A new study finds a widely-used technique for assessing the health of freshwater streams is not effective at detecting a range of water quality problems, including those related to acidity, oxygen levels, and presence of pathogens.

This study started out as a class project, and many of us had learned about a health assessment methodology called the Stream Visual Assessment Protocol (SVAP) as ecology students. Our goal with the project was to assess the health of urban streams in the region using both SVAP and water quality tests done in a lab. And we found there was a significant disconnect between the SVAP scores and the water quality testing results."

Abigail Finch, co-author of a journal article on the work and former undergraduate at North Carolina State University

The SVAP was developed by the USDA's Natural Resources Conservation Service to serve as an accessible way for resource managers and the public to get a "snapshot" of general stream health. The SVAP involves assessing a variety of visual characteristics, such as the appearance of the water, presence of invertebrate habitat, deep spots - or pools - in the stream, and so on. The methodology is used in the U.S. and internationally as a tool for evaluating the condition of freshwater streams.

For the study, the research team used SVAP to assess four urban streams. The researchers also used instruments to collect quantifiable data on each stream's physical features and water quality parameters. Physical features included things like water depth and temperature. Water quality parameters included measures such as dissolved oxygen concentration and testing for Enterococcus, which is a fecal indicator.

The researchers found that SVAP scores were strongly correlated with measured physical characteristics, but there were few significant correlations between SVAP scores and water quality data.

"There were no visual markers associated with most of the water quality characteristics," says Erin McKenney, corresponding author of the paper and an assistant professor of applied ecology at NC State. "Dissolved oxygen concentration, pH, and the presence of Enterococcus are all critical water quality criteria, and SVAP doesn't offer any information on those characteristics."

However, the researchers found there were a handful of SVAP elements that did correlate with some water quality characteristics. Specifically, water appearance was associated with total dissolved solids and conductivity; and physical alteration of a stream's banks was associated with turbidity.

"This suggests that, while SVAP isn't sufficient to gauge stream health, the protocol may have real value in terms of identifying urban streams that could benefit from restoration efforts to re-establish ecosystem services - such as establishing vegetation on the stream banks that could serve as riparian buffers to limit erosion and filter pollutant runoff," says McKenney. "In the long term, restoring those ecosystem services could have a meaningful impact on stream health."

"Riparian buffers can also reduce the impacts of flooding, which is a significant benefit in urban environments," says Finch.

"However, the big take-away here is that - as helpful as SVAP might be - we still need water quality testing in order to get an accurate assessment of actual stream health," says McKenney.