2. Development of BMP Cost-Effectiveness Values
Table 2-16. Cost Data for
Conversion
1,200 ha
7.116
3 % of
10
Crop
5,705
conversion
base cost
to grass
1,833 ha
7,457
3% of
10 years
Crop
$
122,486
base
cost
conversion
The effectiveness of
conversion in reducing nutrient loads to the stream
is highly dependent on a variety of site specific factors. First is the location of the
converted area in relation to the cropped land. if situated at the bottom of a slope,
and the stream, the converted area can potentially function
between the
as a filter strip. However, if the converted area is
of the rest of the
cropland, little filtering of runoff will be achieved. Size and shape of the converted
area also play a role. If the converted area constitutes a substaptial portion of the
in a given field, nutrient reductions would obviously be higher than those
where only a small portion was converted. Similarly, if the converted area is of
the shape to allow dispersed overland flow, it could be much more effective as a
filter strip than one that promotes concentrated flow. Another key factor is the
pre-conversion use of the field. If the converted area was previously planted in
row crops with high runoff and intensive fertilization, the reduction obtained by
conversion could be quite high. On the other hand, if the area was previously
planted in closely-planted small grains or hay, the reduction may not be as
substantial. A final consideration is the type of vegetation which grows after
conversion. Over a long period of time, trees are generally more effective than
grass in sequestering nutrients and encouraging key processes such as
denitrification (National Research Council, 1993).
Any of the factors discussed above has the ability to dramatically affect the
conversion in reducing nutrient loads to the stream.
effectiveness of
Each these factors is highly
and generalizations for the Tar-Pamlico
basin cannot be made with currently available data. It appears that effectiveness
of
conversion could range from essentially zero, to perhaps 90% (the
upper bound for a vegetated filter strip).
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