One night, singer-songwriter-comedian Jack Black was walking down a dark and lonely road with his axe-slinging bandmate, Kyle Gass. There, they encountered a shiny demon who threatened to eat their souls if they could not immediately perform the “greatest song in the world.” The duo — known as Tenacious D — took one look at each other and then spontaneously began to play the first song that came into their heads which, by good fortune, just so happened to be the best song in the world.
Having vanquished the demon, they returned home to their studio to record this epic song…but, being mere mortals, they had already forgotten it. Although true greatness had slipped through their sieve-like minds, they instead recorded a tribute to that song. While “Tribute” rocks hard, we are left to ponder what was lost. But at least they did record an homage that preserves glimpses of the wonder for posterity.
What can we learn from this story? Besides that there should be an iPhone app for recording spontaneous soul-saving, demon-defeating songs? What can this story teach us, say, about river conservation?
First, just as Tenacious D would have done had they had an app for that, save the original greatness if you can. In the river-conservation context, this means the main-stem river that functions as the spine or aorta of a great river basin. A massive dam or dams built across the main-stem river severs the connections between everything upstream of the dam and everything downstream — the lower river, the estuary, the ocean.
Globally, we have far too many examples — such as the Colombia River — of how the health and productivity of river basins decline after these connections are severed. The imperative to save this “original greatness” is what drives those who have organized to stop a proposed series of main-stem dams on the Mekong River that would sever its incredibly important biodiversity and fisheries productivity.
But in many places where The Nature Conservancy and others work, the main rivers have already been severed and much of the original greatness has been lost. We are left with the job of maintaining or restoring tributes that can capture the essence of the original, even if they can’t hope to ever quite equal it.
For example, on the Penobscot River, a coalition of partners developed a plan to remove two main-stem dams and greatly improve fish passage on a third, significantly increasing the amount of the river basin accessible to migratory fish. Although the future restored Penobscot likely will not quite equal its pre-development fisheries abundance, it will be a worthy tribute to that river.
In other river basins, the most important conservation options may lie with tributaries. Though generally much smaller, tributaries often encompass scaled-down versions of the flow patterns and habitat features of their master rivers. As suggested by their shared etymology, they are tributes to the original, if you will.
In a recent paper, the University of Nebraska’s B. M. Pracheil and co-authors reported that in river systems where the main-stem river is dammed and heavily regulated, tributaries can help maintain fish populations.
They analyzed 40 years of data on the population size of young-of-year (i.e., baby) paddlefish, an endangered fish whose reproduction is strongly influenced by river flow patterns. Their study site was an intensely regulated stretch of the Missouri River, within which dams had turned natural flow patterns upside down. However, the mostly free-flowing Niobrara River enters the Missouri within their study site (in photo below, the muddy Nibrara, at bottom of photo, flows into the clear Missouri).
Using the Indicators of Hydrological Alteration, a software program developed by the Conservancy that analyzes river flow patterns, the researchers determined that the natural flow patterns of the Niobrara had a much stronger influence on the population size of young paddlefish than did the flow patterns of the regulated Missouri, despite the fact that the Missouri has approximately 14 times more flow than the Niobrara.
The tributary still provided the hydrological “spawning cue” — rising river levels in the spring — that told paddlefish when to reproduce. The Niobrara likely also provided some of the important spawning and rearing habitat that was now no longer available in the simplified channel of the Missouri.
Pracheil’s paper, along with other recent papers, identifies the importance of tributaries to river ecosystems, and the outsized importance they may take on when main-stem rivers are dammed. These insights should guide our work in large, developed river basins. For example, we can try to identify those tributaries that are best suited to providing the necessary flow and habitat conditions that the main river can no longer provide.
The job of river conservation boils down to this: If at all possible, save the original; create or save tributes where you can’t.
(Top image: Junction of the Heng Jiang (smaller tributary river in lower half of photo) with the Upper Yangtze River, or Jingsha Jiang. Just upstream (to the left) of the junction of the rivers lies the town of Shuifu and the construction site for Xiangjiaba Dam, a 6,400 MW hydroelectric dam being built across the Upper Yangtze. Image credit: Google Earth.)
(Lower image: Junction of the Niobrara River (from below) with the Missouri River. Note that the undammed Niobrara still carries sediment (indicated by brown water), which is important for forming river habitat features, while the Missouri runs relatively clear due to upstream dams that trap sediment. Both the Missouri River system and Yangtze River system support the only two species of paddlefish in the world, the American and Chinese paddlefish, respectively. Both species are endangered in part due to dams on main-stem rivers, and tributaries may be essential to their persistence. Image credit: Google Earth.)