Dr. Conservation

Stream Health; Clear as Mud

Dear Doctor Conservation,

The phrase “looks can be deceiving” is coming back to haunt me as I try to understand the quality of streams. There are two creeks in my county that I have seen repeatedly and they are almost always clear, so I thought they were clean. Now I find out that both are on a list of streams considered unhealthy. How can this be?
Confused,
Phyllis

Dear Phyllis,

Yes, when it comes to determining the health of streams, their ecosystems, and their composite watersheds, looks certainly can be deceiving. While it is true that a visual inspection of water will reveal something about the stream’s overall health, there are other factors that impact ecosystem health not detectable by clarity. Certainly, streams tainted by heavy pollution resulting in various colors, opaque water or scum are obviously degraded, but in other cases clear water can be a bad or indeterminate signal.

However, ultimately the concern is with the patient, not symptoms. After all, it is not the water itself that we are the most concerned with when we think about streams, it is stream life. Our conservation interests are generally focused on stream species, populations and their ecosystems. These same elements are also often the best indicators of the health of the stream. The most sensitive species are typically thought of as the “mine canaries” of aquatic habitats. If their health is threatened by impacts to the stream or its watershed, then we can surmise that the stream ecosystem itself is unhealthy. Sometimes such conditions are present even when the water is clear. In other cases, a stream can be as clear as mud, but it is still healthier than a crystal clear one. Again, the story is told by the condition of the insects, mollusks, fish and plants - the health indicators.

So what are examples of clear, albeit unhealthy, streams? Those stressed by acid deposition (“acid rain”) where their watersheds have no acid buffering capacity. Many of Pennsylvania’s mountain streams fall into this category. The water is clear and often otherwise pure, but the brook trout and stonefly populations are depressed or absent due to low pH (acid) conditions and sometimes the associated release of metals into the stream by the acids. Another acid example is related to coal mining. Abandoned mine drainage occurring well upstream might not deposit the telltale orange staining on rocks in lower reaches, where the water is clear with a somewhat greenish cast. These acidified ecosystems are not in prime condition and harbor less aquatic life.

Also, more is not better. Some aquatic ecosystems suffer from too much water rushing into them during storm events where the landscape has been cleared and does not impede sheet flow. Stream “flashing” can include so much energy that the bottom of the stream is disrupted. Again, even though the water is clear, populations of sedentary freshwater mussels become uprooted or buried.

I hope this helps you think about streams and their conservation.

Sincerely,
Dr. Conservation

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