The Streams of Life Around Us

by Brian T. Lynch, MSW

“Don’t it always seem to go that you don’t know what you’ve got ‘til it's gone?” - Joni Mitchell

Lamington Tributary (aka Shawn Brook,) Mine Hill, NJ

More than ever, I see environmental matters from a viewpoint best expressed by Joni Mitchell’s lyrics in this song. Too often, we don’t see the environmental damage we cause until it's too late. Mitchell spotted this truth back in 1970… the same year we first celebrated Earth Day. But it’s the flip side of this lament that motivates me here. Let’s find out what we have before we do more harm than good. Environmental damage is most often the result of ignorance than of malice. Let’s learn what we can about streams and rivers and raise public awareness of the good and beautiful places worth preserving.

A recent article in Scientific American highlights this point. It is a story about the science of trying to bring back long-dead streams in Seattle, Washington. It taught me a great deal, and it has local implications.

For more than a century, people viewed streams as little more than drainage ditches for excess rainwater. Little regard was given to them when rerouting, modifying, dredging, channeling, damming, or even burying streams in concrete pipes whenever it facilitated development. Watershed networks were treated as transit systems for disposing of residential and industrial waste, which is still true in many places. Wetlands were coveted as wasted space suitable for development. The critical importance of these habitat areas was never imagined before we learned what we know today.

Despite what we have learned, the news media calls catastrophic flooding that results from our ignorance of river systems “acts of nature” rather than manmade disasters that they usually are. Climate change exacerbates the problems we created and is itself a manmade disaster. We still engineer solutions to control floods that, in many cases, only make matters worse. At the same time, we are losing an even more important environmental battle that most of us don’t know we are waging against our children’s future.

Here is the point. Natural rivers and streams are just as essential for terrestrial life as the rain itself. They are complex physical and biological systems. What you see standing beside a stream, the vegetation along its banks, its water, rocks, riffles, sediments, aquatic plants, animals, etc., are all important elements. But what lies beneath a stream is just as integral and more extensive than what we see on the surface. While rain fills a stream from above, groundwater also fills it from below. This does more than keep streams flowing during dry spells.

HYPORHEIC ZONES
The subsurface layer where groundwater and surface water meet is called the hyporheic. It is what scientists refer to as an ecotone, a transition zone between two larger ecosystems where species from both zones mingle and where only unique organisms exist. In a big river, the hyporheic can be many miles wider than the river, and it is dozens of feet thick. In a smaller stream, the hyporheic will extend out beyond its banks. It will be thicker and deeper than the sediment layers. The lateral flow of water through the hyporheic layer flows in the same direction as the surface water but at a much slower rate. This serves an important filtration function. The upward flow of groundwater in this zone brings oxygen needed for fish eggs to develop. The upward flow of groundwater is also cooler than the surface water in the summer and warmer in the winter, so it moderates stream temperatures.

The hyporheic layer is full of life in healthy streams. Crustaceans, worms, and aquatic insects move between this zone and the stream bottom. Nematodes, copepods, rotifers, and tardigrades burrow up and down within the zone, creating pathways for groundwater and surface water to mix. Microbial life thrives throughout the hyporheic layer. They metabolize inorganic compounds to create food for other tiny organisms. They transport nutrients between the hyporheic and the stream bed sediments. Their function is like the bacteria in our gut which are essential to probiotic health. The hyporheic and its microbes also filter out and metabolize many of the pollutants introduced by stormwater runoff. 

From a systems perspective, scientists consider the hyporheic layer to be like the liver of streams and rivers because it regulates the physical, chemical, and biological processes. It facilitates aeration, oxygenation, and temperature modulation. It helps clean up pollution and create food for other organisms. It plays an essential role in the nitrogen, phosphorous, and carbon cycles within a stream's ecosystem. But the hyporheic layer is often damaged by many unwise human interventions.

HYPORHEIC THREATS

If you treat a stream or river as a stormwater drainage ditch, that is what it will become.

In the Scientific American article I referenced, manmade channeling and dredging drained the flood plains in the urban Seattle area for development purposes. Stream beds were straightened and narrowed. Riparian vegetation that stabilizes stream banks was removed, and some streams were rerouted through underground conduits and storm drains. The result was flooding, erosion, and the scrubbing away of the stream bottoms. This caused thinning of the hyporheic layers below the sediment until the hyporheic disappeared. The ecosystem collapsed along with the salmon that had sustained the native populations for thousands of years. All recent efforts to revitalize and restore the streams to a life-sustaining habitat failed until those efforts included attempts to restore the hyporheic layer below the streams. Success so far has been modest but encouraging. More research and experience are needed to improve the methodology.

Once we see something, we can’t unsee it. At least, I hope that is true in this case. Seeing our local streams, rivers, and watersheds as complex natural systems essential to sustaining life on land is something I hope everyone can see for our children’s sake.