For 15 years, volunteers have dutifully collected and processed lake samples spring through fall, and then waited patiently for LMVP staff to report back with water quality data. Among the various graphs and tables, the annual data reports always list mean values for the monitored parameters. These values are used to summarize lake water quality.

Have you ever wondered just how well these numbers represent lake conditions? The answer to this question depends somewhat on you, the volunteer. The mean values that we report are nothing more than estimates, and the accuracy of the estimates hinges on a number of factors, starting with proper sample collection. The LMVP sampling protocol is designed to account for natural variation in nutrient, chlorophyll and suspended solids concentrations over time. In this article we consider the different scales of temporal variation and review what you, the volunteer, can do to ensure data quality. In the next issue of the Waterline we’ll look at spatial variation in water quality.