The recent EU requirement to use macrophytes to monitor the status of lakes necessitates the separation of lakes into types in order to partition natural variability. This allows ecological change to be detected more easily (CEC 2000, Refcond 2003). Many factors are known to influence macrophytes; however, the main determinants, at least for macrophyte richness, have been identified as alkalinity and transparency (Vestergaard Sand-Jensen 2000). Environmental boundaries of types are often set using discriminant analysis of biological groupings of reference sites (sites minimally affected by anthropogenic activity) (Clarke et al. 2003). With limited availability of reference lakes, discriminant equations may be more descriptive of the sample rather than the lake population as a whole. One approach may be to place boundaries to types at positions of natural change in the environment or at positions of biological relevance. The principal factors affecting macrophytes, alkalinity and light penetration, may be open to this. Large differences in alkalinity may be found between limestone and siliceous catchments, owing to the higher weathering rate of limestone (Johnson et al. 1994). The exponential decline of light in water may allow a boundary to be placed at a zone of rapid change.
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