The Unique Blackwater River (Earthcache) EarthCache
The Unique Blackwater River (Earthcache)
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Located on the sandy shoreline of the Blackwater River in the Blackwater River State Park. A short walk along dirt and wooden pathways.
As of 10/2009 there is a $4 charge for parking/entrance.
The Blackwater's soft sandy bottom and large sandbars are a sharp contrast to the dark tannic water that gives the river its name. The Blackwater River is the ONLY pristine sand river left in the United States - so unique that the State of Florida purchased and designated it as a State Forest. The Blackwater State Park was certified a Registered State Natural Feature in 1980, for possessing exceptional value in illustrating the natural history of Florida. The average depth of the Blackwater River is 2 ½ feet, average speed is 5 miles per hour (no white water). You may notice a similarity of the soft, sugar-white sandbars to the snow white beaches of the Emerald Coast - it's the quartz sand!
"Pristine" River
The permeable nature of the terraced, layered sand of the Blackwater gives rise to some unusual features. Its water is filtered by layers of sand between impervious layers of clay which creates the river's clear "pristine" waters but there are other reasons that will be presented as well. Except during floods, the water is clear and flows in clean channels of sand and gravel.
Steepness of Stream Heads
The heads remain steep longer than they would otherwise because there is little surface erosion and the headward growth of the streams is caused by springs. A gradient of 3.4 ft/mile for the Blackwater, whose main tributaries all have steeper gradients than the main stream, is indicative of the swiftness of the stream and is also the source of energy that keeps the shifting sands in almost constant motion.
What Is A "Steephead"
A steephead is a deep, narrow, flat bottomed valley ending (or starting) abruptly by a wall or cliff. Such valleys arise in karst (soluable, irregular limestone) landscapes, where a layer of permeable rock lies above an impermeable substrate such as marl (clay and carbonate mixture). They are created by a stream flowing within the permeable rock and eroding it from within, until the rock above collapses opening up a steep narrow valley which is then further eroded by the stream running across the impermeable valley floor. At the head of the valley the stream emerges from the rock as a spring. It is because of this that most of the normal flow of the River is ground water, not runoff water (surface drainage). This results in a tempering effect on extremes of temperature, keeping this stream cooler in summer and warmer in winter than waters of other origin.
Rarity of Aquatic Plants
The unusual biological features of the Blackwater River are a reflection of the combined chemical, physical, and geological features.
Chemically the river water is extremely soft and but slightly mineralized. This is due to the above mentioned ground water filtering by the layers of sand and clay. The effects of this carry over into the stream itself, bedded, as it is, in the same sands and clays, thus having little opportunity to increase mineralization. The water is low in dissolved nutrients, a fact that is reflected in sparse growths of aquatic plants. Aquatic plants, common in many Florida rivers, are rare in the freshwater portion of the Blackwater River.
Diverse Aquatic Fauna (Animal Life)
Certainly streams with shifting sand bottoms are widespread within the Southeastern Coastal Plain Province but the shifting sands of the Blackwater are biologically productive; most others are not. The aquatic fauna is greatly diversified in the Blackwater River.
But Why the Black "Tea-Like" Color; Meet Mr. Tannin
If the water is so 'Pristine' then why is it so dark? Blackwater is a translation of the Creek Indian work oka-lusa (as in Okaloosa County.) which means water black. A blackwater river is a river with a deep, slow-moving channel that flows through forested swamps and wetlands. As vegetation decays in the water, tannins are leached out, resulting in transparent, acidic water that is darkly stained, resembling tea or coffee. Blackwater rivers' waters are much lower in nutrients and much more acidic than white water rivers. Tannins are a group of pale yellow to light brown substances found in plants. Tea is an example of a plant said to have naturally high tannin content but tea "tannins" are chemically distinct from other types of plant tannins.
Tannins are used chiefly in tanning leather, dyeing fabric, and making ink when mixed with ferric chloride (either blue, blue black, or green to greenish black) according to the type of tannin. Tannins are used industrially to clarify wine and beer, and they have also had some medical uses and have shown potential antiviral, antibacterial and anti-parasitic effects. They are found in wine, particularly red wine, as tannins are found in grape skins and seeds. Pomegranate's tannin content is found to be a major component responsible for pomegranate juice's antioxidant and health benefits. Tannin is found in various berries, nuts and spices. Tannins may play a role in inhibiting microbial activity, thus resulting in the natural durability of the wood. Many plants employ tannins to deter animals. It has not been determined whether tannin was produced for another purpose, e.g. as a pesticide, or whether it evolved specifically for the purpose of inhibiting predation. Most animals that consume excessive amounts of these plants will fall ill or die.
To Log:
Post a short paragraph telling about your trip to the Blackwater River area and with your log post a picture of you (and your GPS) at the specified coordinates with a picture displaying the color of the Blackwater River as best you are able.
Send answers to the following questions to me via my profile; do not put the answers in your cache log.
1. Near the posted coordinates, you will find between the two railings a request to perform a 'Green' activity; what is the sign requesting?
2. During your visit to the 'pristine' waters, fill a clear plastic water bottle from the river. Describe the coloration of the bottled water compared to how the water looks in the river itself. Did you observe any particles in the water, if so describe them.
3. From the information presented, what feature do you feel provides the biggest reason for the water being so 'pristine'?
References:
Florida Adventuring:
(visit link)
Chemical and Phyical Aspects of the Blackwater in NorthWest Florida by William Beck:
(visit link)
Blackwater River, wiki:
(visit link)
absoluteastronomy, Tannin:
(visit link)
Steephead valley, wiki:
(visit link)
Additional Hints
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