Temporal Variation The effect of time on water quality data (page 3)

SEASONAL VARIATION
Lake water quality is dynamic, so we have to collect samples throughout the season to accurately estimate nutrient and algal chlorophyll concentrations. The exact number of samples depends on various factors, including: stability of water quality in a given lake (because of hydrology, some lakes are more variable than others); length of the sample period (e.g. spring-fall vs. summer only); and the desired precision of our estimates. In general, the more samples collected, the stronger our estimate of water quality.

Even sampling just once every three weeks, LMVP is able to detect much of the variation in water quality that occurs during the sample season (Figure 2). Revisiting Little Dixie Lake, which has been part of the LMVP for nine years, we find that the maximum measured nutrient values are generally twice the minimum values. On average, phosphorus ranges from 40 to 80 μg/L and nitrogen ranges 620 to 1200 μg/L. During some years the ranges are larger than this 2-fold range. Chlorophyll is more variable, with the maximum value averaging about five times the minimum (average range 12.4 to 46.8 μg/L). To account for the variable nature of water quality, we need to collect a sufficient number of samples to allow for a strong estimate of average conditions.

By collecting the eight scheduled samples each season, volunteers ensure sufficient data points to allow an accurate estimate of water quality. We could go into the statistical explanation of why more is good, but that would make for a boring article. Trust me, more data result in a more accurate estimate of conditions. While there is no such thing as too much data, we find the gains in accuracy associated with collecting more than eight samples per year are relatively small.

Previous Page <===> Next Page

Back to the Water Line

Brought to you by the Lakes of Missouri Volunteer Program