If you have ever fly-fished a blue ribbon river in the Rocky Mountains or perhaps waded through a deep green forest stream, you know somewhere inside that rivers are the life-blood of our earth. Teeming with creatures from little mayflies to foot-long trout, rivers are supported by life and in turn, support more life. Yet, these vital ecosystems are suffering some of the greatest loss of biodiversity due to human activities and climate change. Dire as it is, this situation is far from hopeless. Read on to learn the story of rivers, their inhabitants, and how you can play a part in preserving the natural flow.
An Underwater Savannah
Snap on your old swim goggles and peek under the waves of your local river. You might be surprised by what you find: just beneath the water's surface is a savannah of which few people are aware. Draped across the rocks and pebbles are vast velvety mats of algae. Herds of tiny mayflies and caddisflies roam like wildebeest and gazelles; grazing, trimming, scraping away the algae, often unaware that in crevices nearby, lurk predators, patiently awaiting an opportunity to strike. Welcome to the home of aquatic insects. In this watery realm mayflies are the most plentiful herbivores. Tiny as they are, they play vital roles as the stewards of the stream.
Just like the iconic bison of the American West that keep grass growth in check, mayflies carefully manicure mats of algae (called periphyton) with their comb-like mouths, preventing it from choking the stream by growing too large too quickly. Stoneflies are some of the largest aquatic insects and are tactile (touching) predators. They feel around with their legs and antennae in the cold rushing water, swallowing whole any unsuspecting mayfly that comes too close. Of course, many other aquatic insects larvae make their home in rivers; caddisflies, dobsonflies, and true flies to name a few. Eventually−months for some, years for others−they will sprout wings and on a single day, emerge at the surface of the river and fly off in search of a mate. On a mid-summer day you may have noticed tiny tornadoes of newly-emerged mayflies swirling above the water. During these insect “hatches”, trout and other fishes congregate to share the river’s bounty and prey upon the emerging insects. Not far off, waiting silently for the fish are birds and bears and other animals hungry for their share. As you can see, on the miniscule shoulders of these little creatures, rests the success of a much larger food chain. Clean, cold rivers are the only habitats for most aquatic insects, and the greater the diversity of insects, the healthier the river ecosystem.
Rivers in Our Hearts
Supporting life is just one of the river’s many vital features. They are also sources of inspiration and hold spiritual meaning for many of us. In fact, there is an uncanny resemblance between a river delta and the blood vessels of the human heart; we really do have rivers in our hearts. I've come to know rivers intimately through my PhD work studying the effects of climate change on these biologically rich ecosystems. Apart from their obvious beauty, some primordial force draws me to rivers.
They tell me stories. Old dried up channels tell tales of how a river once ran; large boulders in pools speak of ancient floods that had the power to move them; meanders in the channel foreshadow paths that have yet to be taken. If we pay attention, rivers teach us lessons too. As environmentalist David Brower once said, "there are many ways to salvation, and one of them is to follow a river." We can learn to flow gracefully past obstacles in our path, to know that, as a river runs ultimately to the ocean, we are finding our own ways to our goals.
When a River Dies
Despite our deep connection to rivers, these ecosystems are jeopardized by many human activities. The looming threat of global warming can only exacerbate the detrimental effects of our exploits on rivers. Overdrawing of water for irrigation and human consumption has reduced flows to all-time lows. After decades of overdrawing, the Colorado River delta is a mere impression of water that once gushed for miles and miles. In the wake of climate change, small rivers and streams are especially in danger of becoming too warm, or worse, drying up altogether. A recent study found that when water returned to a Sonoran desert stream after a long drought, very few aquatic insect inhabitants recolonized it. In effect, the insects went extinct in the area. In my own work I have found that tropical aquatic insects are very sensitive to increases in temperature, so the warming of tropical streams can decimate populations of aquatic insects that have important roles in the ecosystem. Without a rich diversity of aquatic insect inhabitants, a stream would lose other life forms like fishes and frogs, and eventually become lifeless. In fact, the influence of a river is not confined to the wetted parts of the landscape, but has far-reaching effects on land as well. Scientists in Japan, for example, found that when freshwater insect numbers fell in a particular stream, bird population sizes dwindled. This was because the spiders that ate emerging insects along the banks starved and perished, and the birds that relied on a healthy meal of spiders were left without food.
It has long been known that damming can kill a river too. Besides preventing the seasonal migration of various fishes, dams raise the temperatures of rivers, hinder the natural pulse of spring floods, and reduce the diversity of life in all its forms and functions4. Because tropical mayflies, stoneflies, and caddisflies can only handle a narrow range of temperatures, dammed tropical rivers may be even more imperiled than previously thought. Rivers in temperate areas like the U.S. are not far behind. By damming a river, we are also damning the biodiversity it supports, and ultimately robbing ourselves of a precious, irreplaceable resource.
"Boundaries Don't Protect Rivers, People Do"
— (Brad Arrowsmith, Landowner along the Niobrara National Scenic River, Nebraska)
From the mayflies’ ephemeral existence to the powerful rapids that gouge rocks over millennia, river ecosystems are in need of our protection. We can in our own way reduce the negative impacts we have had on rivers and streams. Here are some examples of what people can do to support their local rivers: Organize river clean-ups as this community did for the Merrimack river in Massachusetts; Teach children to preserve rivers starting with the tiny insects that inhabit them (e.g. my presentation booth at City of Fort Collins’ Annual Children’s Water Festival); Make changes to our life styles to conserve water, like the residents of city of San Antonio Texas; And finally, write to and urge politicians to pay attention to the science of dams and their effects*. No endeavor to protect rivers can be too small. So what will your part be in letting our rivers run clean and free?
*As of this writing, a new study published in the journal Science (Poff, N.L. & Schmidt, J.C. 2016) shows that with certain modifications to dam infrastructure, natural flows can be restored. This is one way in which dam engineers and politicians could incorporate scientific studies to inform their decisions.