The Idaho, Florida, and Utah RCWP projects found that monitoring upstream and
downstream from BMP implementation on a subwatershed scale was effective in
documenting water quality improvements associated with the RCWP land treat-
ment.
Multiple Watersheds and Pre- and Post-
Comparison of Multiple Watersheds was a common design in the RCWP. This
may be useful when comparingsimilarsubwatersheds, especially when combined
with the
and/or the above and below designs. Although there is no
experimental control, observing water quality changes of similar directions and
magnitudes occurring with land treatment changes across several watersheds
serves to substantiate the evidence for BMP effectiveness. For this design to be
truly effective, approximately one-half of the subwatersheds need to remain
untreated for the entire monitoring period to be used as comparisons. An effective
design would allow for about 15 treated and 15 untreated subwatersheds over
several years.
The multiple watershed approach was used successfully in the Utah, Florida, and
Vermont RCWP projects. Detection of predicted water quality trends and patterns
over multiple drainage areas improves documentation that the changes in water
quality were attributed to
Coverage Through Time
Baseline monitoringduringpre-land treatment implementation is usually required
to detect a trend or impact or to show causality. Two years of pre-implementation
monitoring and two to five years of post-implementation monitoring are typically
needed. Less time may be needed for edge-of-field studies, when hydrologic
variability is known to be less than typical for largeragricultural systems,
a paired watershed design is used. Sufficient baseline data are required for impact
assessment because:
historical or baseline monitoring is fundamental to the study of the problem,
system function, and variability;
NPS control projects have difficulty detecting a statistically significant
treatment effect, in part attributable to insufficient baseline; and
n adequate historical or baseline data may be the most reliable and significant
design of the monitoring program if a control is not monitored successfully.
Watershed Site
There are three spatial scales for watershed monitoring, edge-of-field,
shed, and watershed outlet. Criteria for selecting the spatial scale are the monitor-
Monitoring
ing objective, the location and intensity of treatment, funding, and availability of
sampling equipment.
Edge-of-Field
Monitoring pollutant export from a single-field watershed is the most sensitive
scale since the direct effects of implementation can be detected without pollutant
trapping in afield border or stream channel. Edge-of-field monitoring is also ideal
for demonstrations and pilot studies. However, edge-of-field results may not be
directly extrapolated to larger areas (e.g., subwatersheds).
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