Summer 2016

TABLE 1 | Minimum Width For Vegetative Filter Strips Where Soil Is Tilled. 1
Slope (%)
Minimum Width in Feet
1–3 25
4–7 35
8–10 50
1
Standards and specifications No. 393, USDA-NRCS field office guide, 2004.
TABLE 2 | Effectiveness Of Filter Strips In Reducing Fecal Coliform Levels Under
Fecal Coliform
Reduction (%)
Slope (%)
Varying Conditions. 2
Buffer Width
In Feet
Runoff Source
43 -74 9 30± Poultry Litter On No-Till Cropland
>99 4 3 -82 Manure On Improved Pastureland
2
Mike Marshall, Texas A&M-Institute of Renewable Natural Resources.
capacity of ponds and lakes.
Water from precipitation also percolates or moves downward
through soil pores to replenish underground aquifers. Pores
in bare ground become sealed and there is essentially no
water percolation; so sparsely covered soil negatively impacts
groundwater supplies.
A covered soil holds more water by binding it to organic
matter and loses less water to runoff and evaporation. The
amount of organic matter increases in soil when it is covered
by vegetation and dead plant material residue. Organic matter
holds 18 to 20 times its weight in water and recycles nutrients for
plants to use. One percent organic matter in the top six inches of
soil holds approximately 27,000 gallons of water per acre.
“Big trees growing along streams can shade the water and
provide good fish and wildlife habitat,” Nelle continues. “Their
massive, far-reaching root systems reinforce the banks against
flood damage and help provide stability. Depending upon the
area, riparian trees can include pecan, elm, cypress, sycamore,
cotton wood, willow or oak.
“Invasive exotic plants such as giant cane, saltcedar, Chinese
tallow and others may sometimes dominate riparian areas. These
plants may form near monocultures and crowd out native plants.
In these cases, selective control measures are warranted.”
PROTECTIVE MANAGEMENT
Selective control measures can involve mechanical removal of
unwanted species leaving the desirable plants undisturbed.
Mechanical methods include various types of saws and
tree grubbers or excavators. A second option is individual
plant treatments (IPT) with herbicides, which includes basal
treatments and stem/leaf sprays. Read and understand the
product label before using any herbicide. Ensure that the
target plants are listed on the label and pay special attention
to any precautions or restrictions on use of the particular
herbicide around water.
“It’s important to avoid overgrazing riparian areas in order
to keep them in healthy condition,” says Marshall. “Animals
may need to be fully excluded from these areas or only given
access for short periods. If the creek, lake or pond is used for
watering livestock, consider other water sources.”
“Grazing is the most important factor that influences
riparian vegetation,” says Nelle. “Heavy and prolonged
grazing damage riparian vegetation and render it ineffective
at retaining sediment. Management in riparian settings
should strive to provide short livestock grazing periods
followed by long rest periods to maintain or enhance desired
plant communities. Only two to four weeks of grazing each
year with a large number of animals may be appropriate
for maintaining good riparian vegetation. This type of flash
grazing can take advantage of large volumes of high quality
forage while still retaining good riparian vegetation. Separate
riparian pastures combined with an observant and diligent
manager will permit this kind of specialized grazing.”
Fencing livestock out of lakes, creeks and rivers reduces
water contamination from soil, manure and urine. Total or
partial exclusion of livestock also helps maintain dense
vegetation to catch and stabilize sediments. For animal
access to water, areas can be graveled where banks are less
likely to erode. These watering areas should be fenced to
prohibit livestock from moving further into the stream.
“Grazing animals with unrestricted access to riparian areas
may remove streamside vegetation, compact or disturb soils,
and break down banks, resulting in both channel incision and
widening of stream beds. Additionally, when grazing animals
have free access to riparian areas, their manure is deposited
or washed into streams. This results in excessive nutrients,
organic matter and pathogenic organisms,” says Machtinger.
“If grazing is managed, livestock manure and urine are
deposited in thick vegetation where it is lodged in place,
quickly decomposed and used by plants,” says Nelle.
“Very little manure and urine get into the water when the
riparian area is heavily vegetated.”
In addition to over-grazing, humans degrade riparian
zones by heavily manicuring and mowing, grading or
paving stream and river banks. Constant use of all-terrain
vehicles (ATVs) and other equipment in riparian areas
and deposition of trash and other foreign material into
rivers and streams are also detrimental to these systems.
Dysfunctional riparian zone characteristics include exposed
soil or gravel on banks and in the floodplain, a wide channel with
shallow water, increased flood flows and excessive erosion often
resulting in stream bank collapse. Other signs of a degraded
riparian system are lack of shade or over-hanging vegetation and
absence of large wood or downed trees in the stream bed. This
results in the loss of fish and wildlife habitat and the dominance
of non-native invasive plants and/or upland species.
In most cases, recommendations by NRCS and other
land management agencies on repairing dysfunctional
riparian zones are to cease or alter damaging practices
and then let nature take its course. Nelle states that
some heavily disturbed riparian plant communities,
especially where the water table has been lowered or
flows interrupted, may not recover in our lifetime. But
most are extremely resilient and can recover as long as
they have time, rest, and adequate water.
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