One of the most basic things we do—protecting water quality—is rooted in the Clean Water Act’s “fishable and swimmable” target uses. We’re looking out for aquatic habitats and our own health at the same time. But what is it we’re actually measuring when we determine how safe the water is?
A recent study shows that how we set up a test, even if it seems pretty straightforward, can produce tremendously varied results. And the health of the species swimming in the waters we’re protecting depends not just on the pollutants we allow—or don’t allow—to get through, but very much on the species themselves.
Researchers at Washington State University collected stormwater runoff from the western part of the state, near Puget Sound. They took the runoff from roadways, which is likely to contain high levels of hydrocarbons and metals. They then placed two species of salmon, coho and chum, into tanks containing the runoff and observed them for signs of distress or illness, removing them if they seemed to be in trouble. No fish was left in the tanks for more than four hours, and blood from all the fish was sampled after exposure to the water.
The coho salmon, the researchers found, were the lightweights; few of them made it for the full four hours. The chum salmon, on the other hand, looked fine, and none had to be removed from the tanks. Results of the blood tests showed just how the coho were affected: “The team found a significant increase in lactic acid concentrations and their blood was thicker and more concentrated. Their blood pH was thrown off and the amount of salt in their plasma decreased significantly,” according to a summary of the research in Science Daily (www.bit.ly/2HkrA5m). The blood of the chum salmon showed none of these changes. In a follow-up test, some of the chum salmon were left in the water for four days with no problems at all. The difference is puzzling, because the two species are closely related, both belonging to the genus Oncorhynchus.
What do the results mean? The researchers admit they don’t know what physiological differences in the two closely related species make one more vulnerable than the other, nor which specific substances in the water affected the coho. Heavy metals and hydrocarbons are the prime suspects, but because actual stormwater runoff was used, many other constituents were present—the whole gamut of things you’d find in almost any urban or highway runoff. Further research might expose the fish to a more limited array of constituents at one time to narrow down the possibilities. With more research, we might also be able to identify the more vulnerable species in a given geographical region and perhaps focus our efforts, such as the development of TMDLs, on the pollutants to which those species are most susceptible.
But the disturbing thing is that if the researchers had chosen only chum salmon for this study, they might easily have concluded that stormwater is harmless to fish. An obvious long-term implication is that we need to look at a greater variety of species when making determinations about water quality.
The study also included researchers from the NOAA-National Marine Fisheries Service and the US Fish and Wildlife Service. The study was published in the journal Environmental Pollution.