The living indicators of river health

It was the first rain of the year, and I stood in my long, green raincoat watching the medium-sized raindrops fall onto the grounds of an old paper mill. I was in this industrial section of Antioch to capture the rain event in a water sample – a sample that would tell us what chemicals the rain had picked up and released into the San Joaquin River. I attached the first bottle onto a six-foot pole and lowered it into the manhole, listening as the great rush of water, trapped in underground pipes, made its way into the largest river of central California. The paper mill is just one of hundreds of industrial, urban, and agricultural sites that line the banks of this 366-mile long river. I soon packed 16 bottles into an ice chest, covered the manhole, and headed to the lab.

After three years as an environmental consultant, I still didn’t really understand what it meant to find an arsenic concentration of 0.05 mg/L in a sample of water being released into the river. Sure, I could write a report about whether this arsenic concentration, along with a suite of many other chemicals, exceeded the “maximum contaminant levels” for drinking water or the “total maximum daily loads” for the San Joaquin.  But, what did it really mean for the river? I wanted to understand how freshwater organisms and ecosystems respond to the chemical soup in which they live. And before I even knew what a caddisfly was, I decided to study biological monitoring with an aquatic entomologist.


Caddisfly, of the genus Neophylax, inside it’s tiny case built from pebbles. Photo by Tina Mendez.

Scientists have been using aquatic insects and other freshwater organisms as indicators of water pollution since the start of the industrial revolution, when it first became a widespread problem. And, it makes sense. We can’t chemically test for most of the pollutants that enter our streams and rivers. Nor do we know the synergistic effects of multiple contaminants. But the fish, bugs, and algae live submersed in the water. If chemicals are toxic or if they significantly alter the chemistry of the water, the community of critters and plants in the stream will respond. We now have accumulated decades of research on tolerance levels for individual species.

As it happens, tolerant insects that are able to thrive in polluted waters are also the most repulsive – the worms, fly larvae and mosquitoes. The rat-tailed maggot, for example, can live in raw sewage by sticking a long snorkel-like apparatus out of oxygen-depleted water to breathe air. In contrast, I soon found myself describing many of the more sensitive insects- the mayflies, stoneflies, and caddisflies- as “cute.” The centimeter-long mayfly has three tails to help it move in the water and a series of tiny gills along its abdomen that it moves back and forth, like the pectoral fins of a very small fish, to get oxygen from the water.  The caddisflies are perhaps the most charming as they construct tiny cases around their bodies from tiny pebbles, sticks or leaves. One species makes a case of evenly cut twigs, and looks like a teeny-tiny basket inching along the surface of a cobble. Each of these guys hatch from an egg in the water and spend their first weeks, months, or even years in the stream habitat before they emerge to mate, reproduce, and start the cycle again. These bugs can tell us something about how the river is doing, and I intend to keep listening.


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