2.2.2.3 Elements of Monitoring Needed to Link Land Management Modifications with Water
Quality Changes
Experimental Designs for Water Quality and Land Treatment. An appropriate
experimental design for water quality and land treatment monitoring is essential to document a clear
relationship between land treatment and water quality changes. The best designs to demonstrate linkage
are those that can isolate the effects of the land treatment from other land use and climatic changes.
Such designs include: 1) paired watershed (Clausen and Spooner, 1993); 2) upstream-downstream
sites monitored before, during, and after land treatment; and 3) multiple watershed monitoring.
The paired watershed design is the best method for documenting BMP effectiveness in a limited
number of years (three to five). Two or more similar subwatersheds (drainage areas) are monitored
before and after implementation of BMPs in one of the subwatersheds (the treatment subwatershed).
Paired drainage areas should have similar precipitation and runoff patterns and should exhibit a
consistent relationship in terms of the magnitude of pollutant losses with changes in hydrology and
climate. Analysis of paired pollutant data from treatment vs. control areas should show a statistically
significant correlation. Ideally, a paired watershed monitoring program is characterized by:
Simultaneous monitoring at the outlet of each drainage area;
Monitoring prior to land treatment to record the relative hydrologic
response of each
drainage area (calibration period);
Calibration period of one to three years, depending on the consistency of
the data
relationships between drainage areas;
Subsequent monitoring where at least one drainage area continues to serve as a control (that
is, receives significantly less land treatment than the other drainage area); and
Similar land management in both drainage areas both before and after BMP implementation
(for example, similar crops), except for BMPs implemented in the treatment drainage area.
Land Management and Water Quality Monitoring Before and After BMP
Implementation. Monitoring for several years both before and after BMP implementation is essential
for documentation of water quality changes. The pre-BMP period is the time prior to installation of new
land treatment practices. Monitoring of water quality and land use prior to BMP implementation is
required to establish baseline data for statistical comparison with post-implementation data. The
post-BMP period starts once BMPs have been implemented on critical areas and are reducing
pollutant delivery to the water resource.
2.2-3
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