Sampling frequency and collection must be consistent across seasons and years. Year-to-year
variability is often so large that at least two to three years each of pre- and post-implementation
monitoring is required to indicate a consistent water quality change following implementation and
maintenance of BMPs. Documentation of changes over multiple years increases confidence that
observed water quality improvements are due to land treatment.
Short-term monitoring is seldom effective because climatic and hydrologic variability can mask
water quality changes. However, in small watersheds affected by relatively few large pollutant sources,
the monitoring period may be shorter. Longer duration monitoring is necessary where water quality
changes are likely to occur gradually, such as large watersheds with lakes in which lag times may occur
due to buffering effects of long hydraulic residence times and pollutant recycling.
Quantitative Monitoring of Land Management. The importance of recording the amount
and type of land treatment cannot be overlooked when trying to establish documented water quality
improvements. Best management practices must be targeted to treat specific sources of pollutants
causing the water quality impairment; these pollutants, in turn, must be monitored in the water resource.
A high level of appropriate NPS pollution control implementation in critical areas is usually required to
achieve substantial water quality improvements.
Monitoring of land treatment and land use is needed to quantify the pollutant reduction impacts
of BMPs. Quantitative monitoring of BMP implementation facilitates documentation of land treatment
trends and is a necessary step in linking water quality to land treatment. Methods of reporting and
quantifying land treatment and land use should be consistent throughout a project.
Careful planning is required to determine which land treatment variables should be monitored to
best reflect the extent of actual changes in agricultural practices. Land treatment data must be reported
in quantitative units that reflect BMP effectiveness and changes from previous practices. Examples of
quantitative units include: application method, tons of manure spread per acre, pounds of fertilizer
applied per acre, acres served by each BMP, and acres served by each BMP system. The acres
served unit includes all treated acres (those acres with actual implementation) plus all acres whose
pollutant delivery is being reduced by the BMP. Documenting the assumptions used in calculating the
acres served is important so that these units can be calculated consistently from year to year, thus
ensuring valid year-to-year comparisons.
When reporting acres served, care should be taken to avoid double counting acres when
multiple BMPs are serving the same acres, as this could artificially inflate the reported number of acres
served. In addition, correction should be given for differences in the effectiveness of the BMPs in
controlling pollutant delivery.
Operation, management, and maintenance of BMPs should be tracked because these factors
affect BMP effectiveness and, therefore, the water quality impacts of the land treatment.