Scientist emeritus for the United States Geological Survey Rachel Claire Muir recently gave a presentation titled “Restoring the French Broad River Watershed, One Species at a Time” for the Asheville Museum of Science at the Collider.
Muir launched her presentation with a photograph of not the river, but the mountains. “That’s precisely because I’m talking about watersheds. When we talk about a river, you can’t talk about it in isolation to the land it drains. When you talk about a river, you talk about the wetlands that are found next to it. When you talk about the streams that feed into a river, you talk about the groundwater that is a principal component of the water that eventually makes its way into the channel,” she said.
Thus, to restore or conserve a river, the watershed must be restored. Muir said she would discuss several elements of restoration, and focus on the self-sustaining biological restoration of rivers and aquatic ecosystems. The watershed for the French Broad River is about 2,800 square miles and includes a number of tributaries including the Little River, Davidson River, Mills River, Pigeon River, the Nolichucky River, and primary, secondary, and tertiary streams. “The French Broad River runs northwest through the oldest mountains in the world, and it’s one of the oldest rivers in the world. This river predates these ancient mountains,” she said.
The three components for undertaking the restoration of a watershed are physical and hydrologic, water quality, and biological elements. Dams diminish the hydrological flows, which reduces flooding but also has some adverse environmental effects. There are many species that depend on the occasional scouring of the riverbed in order to create their habitat. Other physical modifications that impact our watershed are infrastructures such as buildings and roads, and the loss of tree cover.
Dams also block passage for migratory species like sturgeon and accumulate silt upstream, but dams can be modified. For example, in Tennessee, the Normandy Dam on Duck River released very cold water from below for many years that was good for trout, but a majority of native organisms that were not cold-water species died off for a couple hundred miles downstream. When the dam was modified to spill warmer water, it resulted in the restoration of these native species.
The primary threats to our rivers right now are land use including agriculture and urbanization. Water running off of impervious surfaces such as parking lots often contains chemicals that can cause adverse impacts when the water reaches our rivers. The Clean Water Act of 1970 did much to eliminate chemicals from factories being drained by pipes directly into the French Broad River.
The maintenance of buffer zones beside rivers and a reduction in the use of pesticides and herbicides are other ways to improve water quality. “When I do a chemical analysis of the water, the first way for me to separate urban from non-urban environments is to identify the pesticide signature. Urban environments have the more prominent pesticide signature, primarily because of excessive use on lawns and gardens. The principle markers for agricultural areas are generally nutrients like fertilizers, and herbicides,” Muir said.
“We are in the most diverse aquatic temperate ecosystem in the world,” she said. “There are more native tree species in the Great Smokey Mountains National Park than there are native to all of Europe. We have more species of crayfish and salamanders in the southeast than the rest of the world combined, and one-third of all freshwater mussels.”
Muir said Virginia Spiraea is a rare flowering plant native to the southern Appalachian Mountains. She explained that to take root it requires the periodic scouring of the riverbed associated with flooding which the dams have abated. The freshwater mussel population has been another casualty of our water conditions. The middle section of the French Broad River is historically home to at least 27 species of freshwater mussels, but only six can be found in our watershed today, and they are scarce. To facilitate biological restoration and improve water quality, common species are first are reintroduced. They, in turn, improve the habitat, creating the conditions for the return of more rare species.
Muir explained one clever way mussels manage to advance their populations in an unlikely direction. “One of the greatest inventions in the history of mollusks was the ability to get upstream. Freshwater systems did not include any large clams until about 80 million years ago when one family of mussels learned a trick. They modified their lifecycle to hitch a ride. Once the microscopic fertilized eggs of baby clams reach a stage where they develop little barbs, the mother clam shoots them out at a fish so the larvae can attach themselves to the gills and scales of the fish that can subsequently swim upstream.”
In a particularly dramatic image, Muir showed two 20 gallon aquariums side by side. The water in the tank on the left is murky and green, and the water in the tank on the right is crystal clear. “Mussels and plants are environmental engineers that improve water quality,” Muir explained. “Both tanks were the same ten hours before this picture was taken. There are half a dozen mussels in the tank on the right, and in that short time the mussels have entirely cleaned out the water. They have an extraordinary impact on sedimentation, turning it into food for other plants and animals.”
Muir finds inspiration in the wise words of her ancestor John Muir (1838-1914) who was an early advocate for the preservation of wilderness in the United States. “When we try to pick out anything by itself, we find it hitched to everything else in the universe,” John Muir said. “The organisms that reside in rivers and streams on the landscapes are environmental engineers. Let them loose and they will do the work for us,” said Rachel Muir.
As part of her ongoing advocacy for environmental science and science literacy, she is the acting coordinator for the Greater Asheville Science-For-All Book Club. Find out more about the book club meetings on their Facebook page.