A comparison of water sampling and analytical methods in western Lake Erie

Monitoring the water quality of large water bodies requires the efforts of many organizations. However, monitoring organizations often use a variety of sampling and/or analytical methods to measure important parameters such as chlorophyll a (chl a) and total phosphorus (TP) concentrations that may result in incompatible data sets. In order to assess the compatibility of collection and analytical methods used in Lake Erie, we compared four water sampling methods in side-by-side fashion and conducted a round-robin comparison of field replicates that were analyzed for TP and chl a by several laboratories using several methods. For samples collected under mixing conditions, linear regressions among the four sampling methods resulted in nearly 1-to-1, highly correlated (R2 > 0.90) relationships. The methods were less compatible, however, when surface cyanobacterial scums were present. All TP data reported by the different laboratories were in agreement. Chl a data from 4 of the 6 laboratories were in agreement (< 20% relative difference) despite the use of different combinations of organic solvents, cell lysis, and quantification methods. In conclusion, we found that sampling methods and TP and chl a data from multiple organizations examined were generally compatible. These results should build confidence in the compatibility of data sets generated by Lake Erie monitoring organizations and should be beneficial to any combined analysis of historical, long-term data.