Ducks and other riparian
wildlife benefit when wooded or grassy streambanks and wetlands keep excess
nitrate and phosphorus from entering streams. Soil core in middle photo shows,
at right, a dark, upper soil layer rich in organic matter that helps break down
these nutrients. Skunk cabbage, bottom photo, is an example of wetland
vegetation that takes up and uses the nutrients. Click the images for more
information about them. |
Evaluating Riparian Buffers' Effectiveness
By Don
Comis October 25, 2005
A specially designed field chamber has proved to be a good tool when
used together with a computer model to evaluate how effectively riparian
buffers filter out pollutants before they can reach streams or other bodies of
water.
That is the finding from a series of systematic studies of a riparian
grass buffer zone by scientists at the Agricultural Research Service's (ARS)
Henry A. Wallace Beltsville (Md.) Agricultural Research Center (BARC).
After success with a prototype chamber in the laboratory, BARC soil
scientists
Jim
Starr,
Ali
Sadeghi and
Yakov
Pachepsky installed a field version of the chamber in a tall fescue grass
buffer near a forested stream and wetland area. The chamber has no top or
bottom and encases the four sides of a 3-by-3-foot block of soil down to 4
feet.
The scientists injected water with dissolved nitrate into one side of
the soil chamber. Then, as water flowed horizontally and out the other side,
they monitored rates of lateral water flow and loss of nitrate due to its
breakdown by soil microbes.
Riparian buffers are wooded or grassy streambanks or wetlands that
filter out pollutants such as nitrate from fertilizer and other chemicals, as
well as sediment. The slow movement of nitrate through highly organic riparian
areas provides ideal conditions for soil microbes to break down or transform
the nitrate into safer compounds.
The scientists used the two-dimensional computer model "HYDRUS-2D" to
simulate water flow and transport of chemicals within the riparian zone soil.
Overall, the model-chamber combination provided good results.
The experimental chamber is essential for the accurate use of the
growing number of computer models being developed to assess the effectiveness
of riparian buffers. Once a model gets this information for a particular
location, it can predict nitrate loss rates.
A paper on this study will appear in the November-December issue of
the Soil Science Society of America
Journal.
ARS is the U.S. Department of
Agriculture's chief in-house scientific research agency.