Research Paper

The Values and Important Functions of Riparian Zones

and the Effects on Water Quality

The one thing that separates this planet from any other in this solar system is the presence of water. Most humans take this precious resource for granted, however it is necessary for the survival of all flora and fauna. As C. Benezech says, "Water is the structural and functional basis of living beings."(qtd. in Rondiere 67) It is no wonder then that creatures are drawn to rivers and streams and great masses of vegetation spring up along the banks. This riparian zone is as essential to the stream and its quality as the water is to it.

Riparian is based off the Latin ripa, meaning bank and vegetation, and a riparian zone is the area that contains that vegetation. (Riley 95) These riparian zones are important structures of the streams. They protect the streams from pollutants, direct sunlight, larger unnatural floods, and contribute nutrients and fodder to aquatic life. All of these functions affect the streams' water quality, which, if poor, can lead to potential human health problems.

When a stream's banks are bare, the first types of vegetation to appear are grasses, and other small wetland plants. This forms a meadow-like area with a shallow root system of sun-loving plants. The second stage includes the entrance of sun-loving trees and small shrubs looming over the present grasses. Once these plants become established, a shadow is cast down on the bank and the ground floor, no longer allowing the sun-loving saplings to prosper. This allows shade-tolerant trees to take over the situation and become dominant. (Beck 56) According to Philomath High School Ecology teacher Jeff Mitchell, Ponderosa Pines (Pinus ponderosa) were the dominant streambank species in the Willamette Valley many years ago. The present riparian dominant species are far from any similar coniferous evergreens. They consist of Bigleaf Maples (Acer macrophyllum)(Field 532), Black Cottonwoods (Populus trichocarpa)(345), Red-osier Dogwoods (Cornus stolonifera)(573), willows (Salix)(358), Red Alders (Alnus rubra)(377) and White Alders (A. rhombifolia)(376). All of these either require or prefer moist to very wet soil, are shade tolerant, and grow from 10 feet to 110 feet tall forming large canopies of shade over streams and banks.

Since the range of size is so great between these dominant species, the ecology of all these and other less common plants is very complicated and requires a significant amount of space to perform all the necessary ecological functions. Under the Forestry Practices Act, a recommended size for a riparian zone is 20 to 100 feet, although the Natural Resources Conservation Service only recommends thirty-foot buffer on either side of the stream. At least twenty feet is desirable because that is the minimum width of area that is needed for the vegetation to perform its functions that affect the water quality of the adjacent stream. (Riley 7)

Among the many purposes of a riparian zone are stream shading, filtering pollution, bank stabilization, providing wildlife habitat, and acting as a sponge aiding in floods. (Beck 133) All of which contribute to the quality of the stream, both chemically and aesthetically.

Shade is the most noticeable function and is provided by the many canopies of trees located in the riparian zones. Even in the winter when most leaves are absent, the skeletons of the trees still provide a little shade for the more rarer than not sunny days during this season. It's an obvious observation that shade reduces temperature, and this is important because when temperature decreases, dissolved oxygen (D.O.) increases. Dissolved oxygen is essential to the survival of the stream and all of its components. Fish need to breath and dissolved oxygen is their mainstay. Just like humans, the less oxygen that is available, the more uncomfortable and stressful the situation, the higher respiration of the fish. This scenario is very unhealthy for fish and could be ameliorated by plenty of trees providing lots of shade. (Mitchell)

Dissolved oxygen is also important in encouraging aquatic microorganisms to grow. A healthy population of algae and bacteria will keep the food web in perpetual motion. Algae are an important food source for many aquatic organisms and bacteria is needed to break down deceased organisms. Algae and bacteria are the start and end of the food chain respectively. (Mitchell)

A higher amount of dissolved oxygen also benefits humans. Not only do humans get to experience finding masses of fish swimming in the water, they also can swim in a nice refreshingly cold water source on a hot summer day, knowing that they are swimming in healthy safe water. Although most people don't drink water straight from streams, there have been radio advertisements claiming that by pouring water from glass to glass and back again, oxygen has been added to the water and that dissolved oxygen actually improves the taste of the water. This is all because of the shade from the riparian zone.

Not only are trees' leaves important for shading, they also contribute to the food web of the aquatic/terrestrial ecosystems. (Beck 135) Keystone invertebrate species feast on alder leaves in the fall after they have fallen in the water to gain valuable nutrients to live off of. Deer and elk have also been heard to consume Red Alder leaves. Finally, the leaves that fall to the ground surrounding the trees become the humus layer of the soil. (Mitchell)

This humus layer is the uppermost layer of the soil. It consists of mostly leaves and some other organic matter. The significance of the humus is especially noticeable in riparian areas. The solids that are in this layer and also those deeper within the soil capture and hold pollutants (such as herbicides and pesticides), preventing these nasty things from entering the water table that drains into streams. (Beck 133) This system works well because of the bacteria that are present within the roots of these trees. Pollutant-consuming bacteria can make their home quite easily under the soil in the protection of a complicated root system. (Mitchell)

When a riparian zone has a variety of trees, it also has a variety of root systems that all combine together to create one massive frame for holding soil together. A sturdy bank and surrounding area is not only supportive of the existing and future plants, but also makes an aggressive attack against the mighty forces of the river that create erosion. (Beck 133) Erosion is harmful to water quality in numerous ways; two of these ways are increasing turbidity of the water (making the water muddier) and not being able to support a healthy riparian zone that gives so much back to the stream. (Riley 104) It has been found that steeper banks (that could be formed by erosion) are less likely to support vegetation and more susceptible to even more erosion, continuing the vicious cycle of erosion. (Platkin 5-9)

If there are stream banks that are subject to such aggressive erosion, it seems the only thing to do is to add more vegetation. Accomplishing this would also increase the diversity and quantity of wildlife present in the area. Trees, shrubs, and herbaceous plants create many habitats for a variety of animals. Red Alders in particular are important to amphibian populations. The wood of Red Alders rots very quickly, but while doing so it holds large amounts of water and holds it very well, making a very convenient home for amphibians. Any pieces of trees that happen to fall in the stream itself are also extremely important to the survival of wildlife; more specifically fish. Large woody debris creates cool hidden pools for fish to rest and live in and slows the flow of the river to a more comfortable speed in places. (Mitchell)

Because riparian zones are so good at holding soil within the trees' roots, they can also hold water sufficiently. A function such as this comes in mighty handy during flood season. The soil between the roots acts as sponge and holds water better than, say, a large grassy lea. A sturdy riparian zone will also help prevent erosion during flood season, by continuing to hold that soil within the roots of its trees. (Beck 58) As mentioned earlier, the roots also perform a very important purpose of encouraging helpful bacteria to prosper to consume percolating pollutants.

With the lack of riparian zones, the unhealthy status of the water quality can adversely affect human health. Humans are dependent on water to live, and numerous cities' water supplies are drawn from nearby rivers and streams. If the water temperature is high, it allows bacteria and other organisms that can be harmful to humans (such as E. coIi) to develop. A study of forty-three rivers in Oregon, done by the Western Ecology Division of the Environmental Protection Agency, found a direct relationship between the low numbers of E. coli present and the high amount of streamside vegetation. The research also stated that road disturbance and total fecal coliform bacteria were in variation of the number of E. coli that existed. ("Public") Therefore, the fewer number of trees, the less leaves present, the more direct sunlight on the water, the higher the water temperature that encourages harmful bacteria (E. coli) to reproduce that could potentially cause some major health issues.

In order for riparian zones to be successful in the future the general public needs to be aware of their importance in protecting streams and in turn saving people the threat of dangerous water. Most anyone would prefer a shaded, vegetated stream bank as opposed to a ten foot slump of eroded soil, regardless if this person was ignorant of the importance of those beautiful plants or not. That vegetation is not present simply for aesthetics, but also for the ecology of the terrestrial and aquatic ecosystems nearby. Even the United States' government admits, "No other ecosystem is considered more important to the survival of the nation's fish and wildlife resources."(qtd. in Riley 96) It's not just the fish and wildlife at stake here; humans encounter water every day and live off of it. Therefore, it's imperative to keep water supplies healthy and pristine.

Works Cited

Beck, Gregory Gilpin. A Practical Handbook for Healthy Water. Buffalo, New York: Firefly Books, 1999.

Field Guide to North American Trees, Western Region. National Audubon     Society. New York: Alfred A. Knopf, Inc, 1980.

Mitchell, Jeff. Personal interview. 21 May 2002.

Platkin, James L., et al. Rapid Bioassessment Protocols for Use in Streams and Rivers, Benthic Macroinvertebrates and Fish. Washington D.C.: US EPA, May 1989.

"Public Health Indicators Appear Useful in Stream Monitoring."    19 September 2001. 18 May 2002 http://www.epa.gov/wed/pages/news/nov99/hendricks.htm

Riley, Ann L. Restoring Streams in Cities, A Guide for Planners, Policymakers, and Citizens. Washington D.C.: Island Press, 1998.

Rondiere, Pierre. Purity or Pollution, The Struggle for Water. New  York: Collins Publishers Franklin Watts, Inc, 1971.

Contact me at bcwaterquality@hotmail.com