Emily Clarke
The Absorption of Nutrients in Riparian Forests
Emily Clarke
English 2, Biology 3, Technology 4
1
Emily Clarke
Riparian forests are defined as “vegetation directly adjacent to rivers and streams”
(Naiman et al., 1998). These zones appear wherever there are bodies of water and flora.
Some of the benefits that environments receive from these riparian zones are sediment
control, habitat for fauna, and reduced pollution in water. Riparian forests appear all over
the United States. Several tributaries of the Potomac River run through Riverbend Park,
located in Falls Church, Virginia. Large portions of the park are considered riparian
zones.
The key to understanding how riparian forests affect Riverbend Park is to
understand more about Riverbend's streams. Streams that run through riparian forests are
vital to the health of the surrounding land. Riparian forests often act as filters to catch
possible harmful nutrients or pesticides (R. Lowrance, 1984). The condition of these
streams has been getting worse over the last decade, sparking concern from many
scientists, government officials, and activist groups. In the 1960s, it was reported that
“two-thirds of the U.S. Waterways were polluted”. In response to that crisis, the Clean
Water Act was passed in 1972. For about 30 years, it appeared that the state of America's
rivers was improving. In 2005, however, the Environmental Protection Agency (EPA)
reported that the conditions of the streams were reverting back to their damaged state. If
this trend continues, “U.S. rivers will be as dirty in 2016 as they were in the mid-1970s”.
It is unknown how polluted the streams that run through Riverbend Park have become or
what effect pollution is having on the riparian zones in the park (Palmer and Allan, 2006)
Several examples of the predicaments faced by riparian forests that have recently
been brought to light by the popular media. Many people are familiar with the current
2
Emily Clarke
move to protect America's wetlands. Most people, however, are not aware that the
Florida Everglades or the Chesapeake Bay are really just riparian zones. Even though
laws such as the aforementioned Clean Water Act or the policies put into place by the
Chesapeake Bay Program (Riparian forest buffer initiative/Stream releaf, 1996) have
been put into place to protect our riparian zones and wetlands, the forests are still not
completely protected from modern industry. Many companies choose to place their
factories close to streams or to denude a large area. Not only do pollution and
deforestation destroy habitat, they can also cause many ecological problems formerly
held at bay by riparian forests. Examples of ecological problems include erosion, excess
sediment, and decreased biodiversity (Whiting, P. J., 2002). Lawmakers are among the
groups currently working hard to combat pollution. For example, in Fairfax County,
Virginia, a law was passed in 2003 to keep construction around rivers minimal (Views on
streambed protection run deep, 2003).
The destruction of riparian forests can cause some serious side effects on the
environment. Various past disturbances of wetlands have shown that their removal can
cause serious water quality problems, as well as depopulation in the surrounding
environment. Scientists are currently studying exactly what roles riparian forests play in
the environment. Another popular set of studies is the condition of the streams. An
example of a stream condition study would be measuring sediment levels using stream
channels(H. Becker, 1994). Both studies are often directed towards the government to
lobby for more or better protection laws for wetlands and riparian zones. Sometimes
studies are released to the general public to increase their knowledge of riparian forests.
3
Emily Clarke
Larry J. Puckett and W. Brian Hughes conducted a study to analyze how much
and in which way nitrate and pesticides traveled from an agricultural field to an adjacent
creek. The site chosen was a dairy farm off of Cow Castle Creek in Orangeburg County,
South Carolina. Forests and unfarmed fields surrounded the site of the study. To help
with drainage, the farmers had added various drains or planted pine trees (Pinus sp.) in
the surrounding forests. A water table, or an area of soil through which water flows,
made up of limestone, sand, silt, and clay lay under the site studies. Fifteen shallow
water-sampling wells made of 5 centimeter diameter PVC pipe were placed on a transect
parallel to the ground water flow. A total of 27 sampling ports made of 1.5 meter PVS
slotted screens were inserted in the wells. A streamgaging station was also built
downstream from the farm. Water samples were collected from October 1995 through
September 1998 at the wells and streamgaging station. Collected samples were then
analyzed for sediment, nitrate, and pesticides using a series of chemical tests conducted
by the United States Geological Survey.
Only one of two hypotheses was supported by the results. The first hypothesis
was that nitrate would be removed due to ditrification in the riparian forest. Collected
data showed that denitrifacation played only a minor role in the removal of nitrate from
stream water in the studied area. Varied amounts of nitrate were detected in the water
samples. The scientists hypothesized that the lack of denitrifacation would cause
problems in the future. The second original hypothesis was that pesticides and their
degradates would be nearly undetectable in water samples. This hypothesis was proved
4
Emily Clarke
to be more or less true. By the time that the water was checked for pesticides, the level of
pesticides was approximately a third of the amount originally used. (2005)
In a study by P. J. Mulholland et al., scientists used a radioisotope to trace how
nitrogen flows through a system for a better understanding of organisms and their uptake
of important nutrients. The stream into which a 15-nitrogen-labeled ammonium tracer
was added was a 125 m section of a forested stream called West Branch in eastern
Tennessee. Stations were set up at intervals along the stream bank for collections of
organisms, detritus, and water. The samples were collected, filtered, and then carefully
analyzed for traces of the 15N tracer. Other samples, such as macrofauna, sediment, and
chlorophyll, were collected before the tracer was added to compare with the samples that
were affected by the tracer.
The 15N tracer showed the importance of nitrogen uptake in an environment. In
the stream studied, both the ammonium and nitrification rates were high. Most of the
loss of nitrogen downstream was in the form of nitrate and was controlled by the amount
of N needed by trees and the amount of ammonium in the water. Nitrification was shown
to be an important in the removal of ammonium from stream water. "Nitrate production
via coupled regeneration/nitrification of organic N was about one-half as large as
nitrification of stream water ammonium". The results of this experiment were consistent
with the results of other such experiments using similar methods to study the same
system.
As stated in the above introduction, several streams run through Riverbend Park,
an eastern deciduous forest in Fairfax County, Virginia. The area of the park surrounding
5
Emily Clarke
those streams is considered riparian forest. A survey of how riparian forests affect tree
growth could be easily and efficiently done in Riverbend Park using random sampling
along several transects both close to and far from a stream or several streams. Using a Ttest, the results would show whether tree growth in riparian forests was significantly
different from those in other parts of the park. Sediment samples could also be analyzed
using chemical tests in a manner similar to that in the study by Mulholland.
The proposed study would help us better understand the benefits of riparian zones
as well as the absorption of nutrients in riparian forests. Other students could use these
studies in the future to form their own hypotheses on streams and tree growth. The tree
growth data collected could also be used in future surveys for comparison and contrast to
other collected data of the same sort. Finally, knowing the exact role that riparian forests
play to the Potomac River could better increase our knowledge of how to conserve the
Chesapeake Bay.
References
Becker, H. (1994, July). Streambed erosion. Agricultural Research, 42(7), 10-11.
Retrieved December 12, 2005, from ProQuest database.
Several tool for measuring sediment in streambeds, including stream channels
and stream samplers, are contrasted and described in details.
Lowrance, R. (1984, June). Riparian forests as nutrient filters in agricultural watersheds.
Bioscience, 34(6), 374-377.
Riparian forests help agricultural watersheds by acting as filters and buffers.
6
Emily Clarke
Riparian forest buffer initiative/Stream releaf. (1996, October 10). Retrieved January 17,
2006, from http://www.dnr.state.md.us/forests/programapps/ripfbi.html
The Chesapeake Bay Program developed a set of policies in October of 1996
to protect riparian forests and streams.
Mulholland, P. J., Tank, J. L. et al. (2000, August). Nitrogen cycling in a forest stream
determined by a 15N tracer addition. Ecological Monographs, 70(3), 471-494.
Retrieved October 27, 2005, from ProQuest database.
After adding a 15N-labeled ammonium tracer to a stream, scientists carefully
observed how nitrogen was taken up by the trees in an eastern deciduous
riparian forest in Tennessee. The results showed ammonium retention and
nitrification rates were high, and most of the nitrogen lost downstream was in
the form of nitrate. Author qualifications include a PhD in Biology and a
current job as an aquatic ecologist in the Environmental Sciences Division of
Oak Ridge National Laboratory.
Naiman, R. J. et al. (1998). Chapter 12: Riparian forests (R. J. Naiman & R. E. Bilby,
Eds.). In River ecology and management: Lessons from the Pacific coastal
ecoregion (pp. 289-323). New York: Springer-Verlag. Retrieved February 1,
2006, from
http://www.fish.washington.edu/people/naiman/CV/reprints/chapter_12.pdf
This is a reprinted chapter containing basic information on riparian forests.
Author qualifications include a professorship at the School of Aquatic and
Fishery Sciences.
7
Emily Clarke
Palmer, M. A., & Allan, J. D. (2006, Winter). Restoring rivers. Issues in Science and
Technology: Washington, 22(2), 40-48. Retrieved January 17, 2006, from
ProQuest database.
Palmer and Allan stress the important of riparian forests in the fight against
pollution in American rivers. Author qualifications include professorship at
various universities.
Puckett, L. J., & Hughes, W. B. (2005, November/December). Transport and fate of
nitrate and pesticides: Hydrogeology and riparian zone processes . Journal of
Environmental Quality, 34(6), 2278-2292. Retrieved January 17, 2006, from
ProQuest database.
A study was done in Cow Castle Creek in Orangeburg County, South Carolina
to observe the flow of nutrients and pesticides downstream from a corn (Zea
mays) field. The results showed that riparian zones have an important role in
filtering the flow of said nutrients and pesticides. Author qualifications
include current jobs with the United States Geological Survey.
Riparian forest buffers. (2005, November 7). Retrieved January 17, 2006, from
http://www.chesapeakebay.net/ripar1.htm
Riparian forests, acting as buffers, are beneficial to the Chesapeake Bay
watershed in multiple ways.
Views on streambed protection run deep. (2003, July 3). The Washington Post, t.05.
Retrieved December 12, 2005, from ProQuest database.
8
Emily Clarke
A ruling in Fairfax County, Virginia, that would protect streambeds in eastern
deciduous forests from construction shows why streambeds are vital to the
forests around them. This article also shows what dangers streambeds are in
from commercial development.
Whiting, P. J. (2002). Streamflow necessary for environmental maintenance. Annual
Review of Earth and Planetary Sciences, 30, 181-207. Retrieved October 27,
2005, from ProQuest database.
The author describes the importance of streams and the water they carry in
various fields of biology, including ecology, geomorphology, and hydrology.
9