The Implications of Observer Variation for Existing Macrophyte Recording Methods

Abstract

The scale of observer variation recorded during the Western Cleddau sampling trials has implications for all of the established methods of river macrophyte recording, and in this chapter we look at the implications for two of the methods associated with Water Framework Directive (WFD) monitoring in the UK, namely Common Standards Monitoring (CSM) and the LEAFPACS macrophyte methodology. We also look at the implications for Mean Trophic Rank (MTR) recording.

The sampling trial results suggest that high levels of observer variation are associated with all of the methods currently used for monitoring river macrophytes in the UK. In summary, the surveyors would have classified the 500 m section as five different river community types, with only one of the eleven datasets corresponding to the river type defined during the 1980s; the master dataset passed the CSM macrophyte criteria for Favourable Conservation Status, whereas the datasets of all eleven surveyors failed these criteria; almost 50% of the LEAFPACS species had a detection rate of >25%; MTR scores covered a range of 21 points on the MTR scale.

As the sampling trials took place under optimal conditions, the results represent the minimum range of observer variation that we might expect to find in macrophyte data collected by professional surveyors. The options for minimising the levels of observer variation associated with recording macrophyte data are discussed.