The key to measuring dangerous levels of nutrients in freshwater streams might lie in the microscopic organisms swimming through them.

A colorized scanning electron microscope image of a diatom.

A team largely of researchers from the Academy of Natural Sciences (namely research scientist and professor in the College of Arts and Sciences Don Charles, researcher Thomas Belton, and former rsearch scientist Sonja Hausmann) analyzed data from 1,400 freshwater Mid-Atlantic streams to see whether a group of tiny algae called diatoms might be efficient indicators of overly high nutrient levels, termed “eutrophication.”

Eutrophication — caused by runoff of agricultural fertilizer, sewage and other forms of pollution — feeds algae and plants in water to the point of overgrowth. The algal blooms can cause low dissolved oxygen and fish kills.

The team found a new way to use diatoms’ particular sensitivity to nutrients as a measuring stick.

They call it the Diatom Biological Condition Gradient, or BCG. “The BCG has an advantage over other nutrient indicator metrics because it can be used to identify boundaries along the nutrient concentration gradient that separate unimpaired from impaired sites,” says Charles.

The Academy-based team’s research found that the composition of diatom species correlated with New Jersey water quality. Diatom species in waters considered unimpaired were largely made up of surface-attached species; diatoms in water considered impaired were motile — having the ability to move. The changeover occurred primarily at the split between level three and level four on the biological condition gradient. 

Biological condition gradients methods were created by the U.S. Environmental Protection Agency to provide objective standards for assessing the health of freshwater systems. The scale ranges from level one, a pristine waterway, to level six, which stands for the most ecologically stressed habitats.

Without a uniform scale, states are left to their own devices to grade their water.