Quality Control:
Chlorophyll Filter Comparison

pie chart of 2012 chlorophyll filter pairsThe procedure for processing samples for chlorophyll analysis involves filtering a volume of water through a glass fiber filter and properly storing the filter. Chlorophyll filters are prepared in duplicate. By having two filters we can compare the values of each and, if the filters replicate well, average them for our estimated lake chlorophyll concentration. If the filters don't replicate well, we discard both values and leave a blank in the data set. No data are better than bad data!

Each year we compare the values obtained from the analysis of the replicates to estimate how well volunteers are performing this task. If the two values are consistently different from one another, then we need to examine the volunteer's technique. This is just one of the LMVP quality control methods we employ regularly.
The pie chart to the right shows the results from comparing the 874 filter pairs from the 2012 data. Filter pairs differing by 5% or less are considered "Excellent," those differing by 6% to 10% are considered "Good." Results show that 89% of 2012 filter pairs were either "Excellent" or "Good."Percent of excellent and good filters since 1992

This year we examined the data from previous years to see if there has been a change in volunteer performance since the LMVP began monitoring lakes in 1992. According to our analysis, the long-term average percent of "Excellent" and "Good" filters is 89.9%, ranging from 85% in 1995 to 98% in 1997, just two years later. As the number of volunteers has increased, the number of filter pairs has also increased. The number of filter pairs tripled from 1999 to 2012. The higher sample number is probably contributing to the lower variability seen in the last decade.

To examine how well the volunteers perform compared to professionals, we scored our own laboratory staff using the same methods used for volunteers. We looked at data collected by summer staff for our Statewide Lake Assessment Project over the past 20 years. While the numbers varied somewhat from year-to-year, the difference in volunteer filter pairs was less than 1% greater than the difference in MU staff filter pairs, indicating volunteers performed just as well as MU field staff.Number of filter pairs since 1992

Not all filter replication problems are the fault of the volunteer. In lakes with very little algae, just a few more cells on one filter versus another will result in a much larger difference (when expressed as a percentage) than would be found in lakes with even a moderate amount of algae. In some cases we have observed large zooplankton on the filters with bellies full of algae. These "packets" of chlorophyll could certainly result in large differences between the filters, depending on how many zooplankton are on each filter and how much they have eaten.

In most cases, vigorous shaking is the best way to improve the chlorophyll comparison score. A good rule is to shake the sample bottle (with the lid on, of course!) each time you pick up the bottle. It will soon become second nature to shake the sample several times during processing.

Our volunteers are doing a fantastic job with sample collecting and processing. Examining filter pairs is just one of our quality control checks to ensure that LMVP data are of high quality and reliable.


The volunteers at the following sites had all "Excellent" filters. All of the filter pairs varied by 5% or less.


Lake and Site

Mike Gambill and Greg Hoeltzel Alpine Lake, Site 1 (dam)
Russ Duffer Blue Springs Lake
Larry Bradshaw, Steve Hurst, Chris and Brad Hazel Creek Lake, Sites 1 and 2
Kurt Hentschke Hunnewell Lake
Bob Steiert Lake Jacomo
Bart, Anne and Kyle Gulshen Lake of the Ozarks, Site 31.1
Sandy and Larry Triplett Lake of the Ozarks, Site 61
Marti, Pat and Marijane Everett Pomme de Terre Lake, Site 5
Jim Riffe, Easton Parks Prairie Lee Lake
Geri Blakey Rothwell Lake
Joe Wolf Lake Sherwood
Charles and Mona McCormack, Angie North, Jason Kloeppel Spring Fork Lake, Site 1 and Site 2
Lynn Fair and Frank Fillo Sugar Creek Lake, Site 1 and Site 2
David Cassaletto Table Rock Lake Site, 12
Renny Buckaloo, Kristine Stein, Young, Bush Lake Tapawingo
Dan Wollaeger Wanderfern Lake


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