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River Types: The Freestone River

The Freestone River Gallery

The first major river type, the freestone river, exhibits typical meanders created by centuries of eroding the substrate over which it flows. Luna Leopold observed in his book, A View Of The River, that:

The river is the carpenter of its own house

The Colorado River at Grand Canyon
Photo by George H. H. Huey
Sierra Club, Engagment Calendar 2003

This is especially true for freestone rivers. They have predictable widths and intervals between meanders, regardless of where they occur, making them favorite subjects for stream ecologists and geologists, alike. This river type comprises the majority of the world’s free flowing cold waters. Rock and rubble characterize their riverbeds, known as the benthic zone, with additional input from the occasional landslide or avalanche. The rocks within the confines of the river eventually become eroded and are reduced to freely moving, smooth stones, gravel and sand, hence the term “freestone.” The configuration of these elements within the riverbed contributes significantly to its flow characteristics. Water also seeps down into the sand and gravel substrate of the riverbed and creates a reservoir for stream life. This is called the hyporheic zone and has recently attracted the attention of a new generation of stream ecologists.

Due to their relatively cold temperatures and rapid rate of mixing with the air, these waters are highly oxygenated (7-10mg/liter), and the life forms in them lead a highly aerobic life style.Typically, freestone rivers are slightly acidic in nature, and are found in mountainous areas. The water that will eventually form them (snow melt, springs, etc.) increases in volume and pace as it progresses down steep gradients towards the lower elevations. Eventually they coalesce into rivulets, creeks, streams, and then rivers. Taken together, these running waters form a watershed, carving their way through the substrate of the mountains that gave rise to them. 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 nervous system. Typically, rivers empty their waters into the sea, creating an extensive fresh water-salt water interface referred to as an estuary. These interfaces between fresh and salt water (ecotones) are among the most productive in the world in terms of total biomass, rivaled only by the tropical rain forest and coral reef. The largest river systems, such as the Mississippi-Missouri, Amazon, Nile, Yangsee, Hudson, and Murray Rivers, all began as small rivulets high up in the mountain ranges that spawned 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 their tolerance limits.

Livingston River, Alberta, Canada

Jumbles of rock, swiftly flowing riffles, twisting currents and back eddies, and deep, dark pools surrounded by hardwood forests typify the freestone river. Some begin as glacier melt, high up in the mountains, contributing to the freestone river’s hydrological cycle. Many others start as springs, fed by rainwater that seeps into and refreshes the aquifer. Whatever their origins, freestone rivers are wonderful places to visit, often flowing through unaltered natural landscape. Most of the freestone rivers of the northern hemisphere harbor significant populations of trout. 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 “remedied” during the late 18th and early 19th centuries when the British stocked rivers that they considered part of their empire. Today, trout can be found wherever their biological requirements are met. What else makes a cold, running body of water suitable for trout?

Magalloway River, Maine

As mentioned, freestone rivers are highly oxygenated and this characteristic, alone, allows for a diverse population of macro invertebrates 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 predominate. Trophic refers to energy processing (ingesting and digesting food of various sorts) 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, just as if a Lazy Susan filled with varying and tasty cuisines had been installed at our favorite restaurant. When a trout feels the urge to feed, often cued by the hatching of some insect (e.g., mayfly, caddis fly, or stonefly), they swim from their hiding place to a nearby feeding site. However, as nice as all this may appear to us, the life of a trout in a freestone river is anything but idyllic. The changing of the seasons conspire to select out only the hardiest individuals with the genetic potential to meet the river’s changing flow rates and fluctuating water temperatures. Anchor ice that forms on the submerged rocks during a particularly cold winter, and spring-time 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 or at mouths of feeder streams. There they are vulnerable to predation and/or 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 the primary source of food for macro invertebrates. 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.

Castle River, Alberta, Canada

On top of all these natural seasonal variations, vast stretches of freestone rivers are now in danger of extinction through the construction of dams. Over 75,000 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. In addition, the same things that threaten to eliminate limestone streams - nutrient loading due to over-use of fertilizers and grazing of cattle along river banks - also endanger the 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 alter a river’s bio-productivity for long periods of time. It takes approximately 150 years for the average hardwood tree to reach full maturity, and often less than 20 minutes to cut it down. Add to all of this the unrelenting effects of acid deposition. Many eastern United States streams have been severely impacted by this invisible form of air pollution. In extreme cases, such as the one that exists in the Shennadoah Valley of Virginia, an entire drainage system was nearly rendered sterile 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 Shennadoah River. In that region of the United States, the buffering capacity of calcium and other metal ions in the bank-side rock and soil have been depleted by acid deposition well below the level needed to neutralize it.

Ausable River, New York

 

Beaver Kill River, New York

As with all other things, if something is valued enough, we always find a way to preserve it. Currently, there is a ground swell 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, and The Sierra Club, 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 reverse this environmental disaster and return our freestone rivers to a semblance of their original level of bio-productivity.

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