This river type comprises the majority of the world’s free flowing cold waters. The freestone river exhibits typical serpiginous (snake-like) meanders (Figures 9, 10, 11) created by centuries of eroding the substrate over which it flows. Luna Leopold (his father was Aldo, author of A Sand County Almanac) wrote A View Of The River. In it he observed: “The river is the carpenter of its own house.” How true this is for the freestone stream. Sinuous river beds with predictable widths and intervals between meanders are the result of this activity. Rock, gravel and sand characterize their riverbeds, known as the benthic zone (Figure 12), with additional input from the occasional landslide or avalanche. The in-stream rocks eventually become eroded and reduced to free moving, smooth stones, gravel and sand, hence the term “freestone.” In fact, the bottom of the freestoner is in constant motion, altering the very structure of its banks. As the result, its flow characteristics and geomorphology are in constant flux. Perhaps that is what attracts us to them in the first place. Heraclitus, the most knowledgeable of all the Greek philosophers, had this to say about rivers: “The river that you set your foot just now is gone, those waters giving way to this, then this” (reference: Fragments) (Figure 13). I am sure he meant it to apply to freestoners!
Water seeps down into the sandy substrate of the freestone riverbed and creates a reservoir for stream life. This is called the hyporheic zone (Figure 14) and has attracted the attention of a new generation of stream ecologists. Due to their cold temperatures and rapid rate of mixing with the air, freestoners are highly oxygenated (7-10mg/liter), and the life forms in them lead a highly aerobic life style. Typically, these rivers are slightly acidic in nature, and have their headwaters in mountainous areas. The water that will eventually form them increases its volume and pace as it progresses down steep gradients towards lower elevations. Eventually they coalesce into creeks, streams, and rivers defining a single watershed or catchment basin (Figure 15). The pattern of coalescence for all of these levels of moving water is dendritic, resembling the root system of a plant, or that of a mammal’s nervous system. Typically, they all eventually culminate into a large, solitary river that empties into the sea (although not always), creating an extensive freshwater-salt water interface (i.e., ecotone, a zone that forms the border between two or more ecosystems). Estuaries (Figure 16) and deltas form at these zones and are among the most biologically productive areas in the world, rivaled only by the tropical rainforest and warm ocean coral reef. The largest river systems, such as the Mississippi-Missouri, Amazon, Nile, Yangtze, Hudson, and Murray Rivers, all begin as small rivulets high up in the mountains that birthed them. Somewhere along the gradient, most freestone rivers in temperate zones cease to support the life forms associated with trout, largely because of the change in temperature, which goes up as the river slows down and widens, becoming exposed to greater and greater amounts of direct sunlight. It is temperature more than anything else that determines how much oxygen can dissolve into the water, and salmonids require high amounts of that essential element. Aquatic niches that have less than 5 mg/liter fall below the tolerance limits of all cold-water dwelling salmonids.
Ecology of the Freestone River
Jumbles of smooth rock, swiftly flowing riffles (Figure 17), twisting currents and back eddies, and deep, dark pools surrounded by hardwood forests typify the freestone river. Some begin as glacial melt, contributing to the freestone river’s hydrological cycle (Figure 18). Many others start as springs, fed by rain that seeps into the aquifer. Whatever their origins, freestone rivers are truly wondrous places, often remote and untamed, flowing through the steepest valleys of the world's mountain ranges. Most of the freestone rivers of the northern hemisphere harbor significant populations of trout, products of post-glacial teleost evolution. Yet, many of the thousands of streams that drain the watersheds of the Himalayas, and all those of the southern hemisphere had no native trout species. This was, however, quickly remedied during the late 18th and early 19th centuries when the British stocked rivers that they considered part of their “Empire.” Today, trout are found wherever their biological requirements are met. In these situations, they thrive and reproduce. It is largely due to the presence of freestone rivers that the world's cold running water ecosystems have been transformed into trout fisheries. What else makes a cold, running body of water suitable for trout?
As mentioned, freestone rivers are highly oxygenated and this characteristic, alone, allows for a diverse population of macroinvertebrates (Figure 19) that can interact, forming complex food webs. While rivers that begin as glacial melt are sterile at their sources because they lack nutrients, their lower, tree-lined reaches provide the necessary ingredients for life in the river. For a trout, finding food in this zone is not a problem.
In most freestone rivers, four trophic levels (Figure 20) predominate. Trophic refers to energy processing (ingesting and digesting food) by the various forms of life found there. Freestone rivers offer ideal resting places for both food supplies and trout, because of the turbulent currents that wrap around the myriad rocks and other rubble that lie in their stream beds. The currents each day present the fish with a varied menu, as if a Lazy Susan had been installed at our favorite restaurant. When a trout feels the urge to feed, often cued by the hatching of some morsel (e.g., mayflies, caddis flies, and stoneflies; see: Galleries – Macroinvertebrates), they relocate from their place of safety to a feeding site often within close proximity.
However, as idyllic as all this may appear, the life of a trout in a freestone river is anything but. Seasons conspire to select only the hardiest individuals with the genetic potential to meet the river’s changing flow rates and fluctuating water temperatures. The anchor ice of a particularly cold winter, and severe springtime floods conjure up a surreal world compared to ours. Because of rapidly changing conditions in summer months, fish are often forced to seek out the cooler waters of spring holes (Figures 21, 22), or mouths of feeder streams, making them vulnerable to predation and starvation. In these stressful situations, bank-side trees help to modulate water temperatures by providing shade. In addition, trees supply leaves to the freestone river in the fall, serving as an essential source of food for macroinvertebrates. Bank-side foliage and in-stream plant life constitutes the first level of the four tropic levels of the energy flow scheme common to all trout streams. From the perspective of the trout, the freestone river is a more variable, less enjoyable place to live than the smaller but ecologically more stable limestone stream. This is especially true when the hot weather and lack of rainfall conspire to endanger the lives of all the creatures that live in them.
In addition to natural seasonal variations, vast stretches of freestone rivers have been in danger of extinction through the construction of dams (Figure 23). Over 80,000 dams have been erected in the last hundred years within the continental United States, alone. More dams are planned, as groundwater grows more scarce due to over-use or contamination. The good news is that some have already been decommissioned and removed. This is especially the case for the state of Maine. Removing dams also encourages the return of anadromous fish species. In addition, the same things which threaten to eliminate limestone streams - nutrient loading due to over-use of fertilizers, and grazing of cattle long river banks - also endanger life in the freestone river. Defoliation of riparian ways by harvesting bank-side trees represents a unique set of problems that have the potential to reduce a river’s bioproductivity for long periods of time. It takes approximately 150 years for the average hardwood tree to reach full maturity, and less than 20 minutes to cut it down. Erosion is another unwanted consequence of cutting down the trees along the riverbank (Figure 24). Add to all of this the unrelenting effects of acid deposition. Many eastern United States streams are severely impacted by this outgrowth of industrialization. In extreme cases, such as the one that exists in the Shennadoah Valley of Virginia, an entire drainage system was nearly sterilized by acid snow melt, which mobilized aluminum from the surrounding soils, killing most of the stocks of native brook trout in the feeder streams that lead into the Shenandoah River. The buffering capacity of calcium and other metal ions in the bank-side rock and soil have long been depleted by acid deposition below the level needed to counteract this situation. Fortunately, the Shenandoah River watershed has been the target of many conservation-minded groups, including Trout Unlimited and the University of Virginia. Creative remediation schemes to the acid deposition problem employing limestone chips and diversion towers filled with large chunks of limestone have neutralized the acid headwaters and allowed the return of brook trout and black nose dace, the primary food of the brook trout. Re-wilding these feeder streams has met with great success, so that today, angling for the centennial-strain Salvelinus fontinalis (Brook trout – see: Galleries - Trout) is now a sporting possibility once again (http://www.virginiaplaces.org/watersheds/).
As with all other things, if something is valued enough, we always find a way to preserve it. Let us value rivers so much so that those that are still intact will remain that way. Currently, there is a groundswell of national programs sponsored by environmental groups such as The National Fish and Wildlife Foundation, The National Arbor Day Foundation, Trout Unlimited, The Nature Conservancy, The Audubon Society, The Sierra Club, and American Rivers whose major aim is to restore (remediation is the ecologist’s term) the country’s rivers to a clean and productive state. Tree planting, bank restoration, environmental planning with enlightened land developers, educational programs aimed at the general public and children in schools throughout the country, all play important roles in raising community awareness regarding these issues. More effort is needed to insure the success that is required to return our freestone rivers to a semblance of their original level of bio-productivity.