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Natural History of the Eau Claire River in the Eastside Hill Area

Submitted by Editor on April 7, 2010 – 6:11 am | Print or Email »No Comment

by Rob Kuchta

The suspension bridge over the Eau Claire River offers the pedestrian two views into the natural world that forms the northern boundary of the East Hill. One of these views gives us a glimpse of what the world was like millions and millions of years ago when the East Hill alternated between being beach front property or the bottom of an ancient ocean. The other shows us a natural world that uses the river today.

It is difficult to imagine that our neighborhood, safe from the floods of the Chippewa and Eau Claire rivers, was once under hundreds of feet of water. An uplifting of the ocean beds in this area raised the rock above sea level and turned the ocean sediments into dry land. However, the sandstone cliffs along the Eau Claire River, and the river’s bottom, give testimony to the long marine history of this area.

The various size of sand grains within the rock layers give us clues as to the depth of water when these rocks began to form. Small sand grains and flakes of clay travel great distances and remain suspended in the water for long periods of time. These particles slowly settle to the bottom of deep water. The layers of small sand grains and shale show us the remnants of deep water areas where the still water allowed these light particles to settle out.

Layers of large sand grains are the remnants of near shore areas where wave action would keep the smaller particles in suspension and only the heavier, larger sand grains would fall to the bottom. These would have been shorelines or shallow areas where wind, wave, or river currents would stir things up.

Some layers of the rock contain fossils. Most of these are small clam-like organisms. Fossils are rare in most of the rock. Remember the agitated water that wouldn’t allow fine sand grains and clay particles to settle? That moving water was pretty wicked and potential fossils were broken up or transported to quieter and deeper areas. If you want to see whole fossils or the tracks of long dead sea animals, look for the layers of rock made of fine sand particles. Sometimes the broken shells of these creatures form layers that contain more shell fragments than sand.

Regardless of grain size, sandstone is very porous and can contain lots of water. Sometimes we can see ground water oozing out of cliff faces. We see the water trickling out from the rock where the downward moving water encounters a clay-like layer that blocks the water’s downward passage, and the water flows along this waterproof layer until it drains from the cliffs along the Eau Claire River. The rock is porous not only to water but to pesticides, fertilizers, and nearly any liquid put into the ground.

The soft sandstone is also susceptible to erosion from water and vegetation. Tree roots winding their way into cracks in search of water and nutrients exert enough pressure to break huge chunks off the cliff face. Water freezing in the rock creates enough force to split the rock apart, sending large sandstone boulders into the river.

The best place to view the rocks is from the middle of the river, looking around on all sides and at your feet. The second best place is along the trail to Archery Park from the old Uniroyal parking lot. There you can get a close glimpse of the rocks and touch stone that was formed in a world much different than the one that surrounds you today.

Today, the Eau Claire River cuts through ancient sea beds on its way to meet the Chippewa River. At first glance the river appears to be a sterile, shallow stream running between sandstone cliffs and a thin ribbon of forest. Watch the river and its surroundings patiently, because life is there.

With your back to the sun, look into the water for flashes of gold or silver. It may take a while for your eyes to adjust to looking into the river depths. The gold or silver flash in the shallow, fast water is the side of a carp or sucker reflecting sunlight as the fish rolls from side to side, dislodging insect larvae or plants growing on the rocks. The fish, headfirst into the current, are part of a complicated food web that relies on material from outside the river as the ultimate food source.

Lakes and ponds have, as their food base, the plants and microscopic organisms that turn the energy of the sun, carbon dioxide, and water into food. The Eau Claire River is too swift and rocky for large plants to anchor themselves and too nutrient poor for lots of algae. Yet, there is a large population of fish that must feed on something. Where does most of the energy come from that supports this population?

The answer comes from the trees and other plants lining the river corridor. Plant parts (mostly leaves) find their way into the river. There, small organisms work on the leaves. Some insect larva chew the leaves but, being messy eaters, allow chunks of leaves to wash down- stream. Downstream other organisms, insects and other creepy crawlies, feed on the leaf bits that wash their way. Some larva even stretch out nets spun from silk to trap these tasty morsels.

Another source of energy is the algae and moss that grow on the rocks in the shallow swift current. These organisms provide not only needed energy and nutrients but, along with bubbling rapids, supply the organisms of the river with needed oxygen.

The deep pools are where decomposition of dead material takes place. Photosynthesis can only occur when there is a supply of carbon dioxide. A river with nothing but shallow rapids will have lots of dissolved oxygen but very little production from algae or plants because there is too little carbon dioxide for photosynthesis.

Pools also serve as nurseries for fish. The slow currents that allow the dead plant and animal material to settle to the bottom also provide a safe haven for small fish that can’t fight the current in the swiftly moving shallows. Other riverdwellers or river visitors will prey upon these young fish or, depending on the size of the predator, prey on the fish that prey on the young fish.

Those bright flashes we saw from the bridge are fish adapted to swift currents. Their body form lets the current flow over and actually pushes them closer to the river bottom. Take a moment to watch their movements. Their struggles against the current must pay off by the amount of food they gather or else they wouldn’t be there. You may see them break the surface with a slap of their tails as they fight against the current.

Keep in mind that what you see from the bridge is only a small part of the life within the river. What appears, at first glance to be lacking life, is actually teeming with life. We only need to take a moment to find it and acknowledge it.

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