Monitoring Program Design
The Vermont RCWP project found that the paired watershed design was the most
effective for documenting a linkage between land treatment and water quality
changes on a farm field-watershed over a short (3-5 years) time period.
Upstream/Downstream and Pre-and Post- BMP
Single watersheds can be monitored above and below the pollutant sources.
Monitoring above a site
Monitoring above a site can be used to correct for varying incoming pollutant
sources not related to the changes in land treatment in the study area. Varying
can be used to correct for
of consumptive water use between monitoring points, however, may make
varying incoming pollutant
technique is applicable to PS monitoring and may also
be useful in monitoring the impact of NPS controls when a high correlation exists
sources not related to the
between concentrations of the pollutant over time measured at the
changes in land treatment
above and below BMP implementation. It should be emphasized that this
technique is inappropriate and ineffective unless it is combined with `before and
in the study area.
after' monitoring. The effect of the land treatment cannot be determined unless
there is a comparison between the pre- and post-treatment period. Figure 4.2
shows an idealized upstream/downstream and pre- and post- BMP design. Station
A would be used to monitor upstream of land treatment and station B would be
used to monitor below land treatment.
Figure 4.2. Upstream/down-
stream and pre- and
Year-to-year variability in water quality variable concentrations/loads is often
greater than the BMP-induced change in water quality in any given year or season.
At least two to three years are required (for both pre- and post- BMP periods) to
account for year-to-year variability.
In a pre- and post-monitoring design for monitonng BMP implementation
effectiveness with no control watershed, the changes observed over time may be
primarily due to climate and therefore very difficult to attribute to the NPS
controls. To substantiate a cause-and-effect relationship, the explanatory variable
can adjustforchanges in hydrologicand meteorologicvariability betweenseasons
and years and should be monitored and used as an explanatory variable in the trend
analysis (e.g., in analysis of covariance).