If the goal is to document changes at the entire watershed level, a monitoring station must be located at the watershed outlet. Matching of Land Treatment and Water Quality Data on a Temporal Scale Water quality and land treatment data should be collected during the same time periods so both data sets are temporally related . Actual implementation of land treatment needs to be recorded at least seasonally or annually. Water quality samples are usually collected weekly or biweekly. Alternatively, water quality data can be aggregated to the same time scale as the land treatment data for analysis.
Data aggregation is particularly useful for plotting and explanatory data analysis.
Monitoring Explanatory Variables Accounting for all major sources of variability in water quality and land treatment data increases the likelihood of isolating water quality trends resulting from BMPs. Correlation of water quality and land treatment changes by itself is not sufficient to infer causal relationships. Accounting for variability in water quality due to known causes also decreases variation in adjusted water quality data, facilitating documentation of statistically significant trends. Explanatory variables should be monitored at the same frequency as the principle water quality variables. Summary A good experimental design for water quality and land treatment monitoring is essential in order to provide clear documentation of the relationship between land treatment and water quality changes.