River Types: The Freestone River
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?
 |
|
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.
