European Diatom Database-Surface Waters Acidification Programme

The Surface Waters Acidification Programme (SWAP) calibration training set included initially 178 surface sediment diatom assemblages and the associated environmental variables from 170 sites. Data-screening reduced these to 167 lakes, which using weighted averaging give superior results in terms of lowest root mean squared errors of prediction in cross-validation (Birks et al. 1990a; Birks et al. 1990b).

The refined diatom/water chemistry training set used within the SWAP project is derived from five regional datasets (number of samples in parentheses) from Sweden (30), Norway (51), Scotland (60), Wales (32) and the English Lake District (5). These sites represent upland lakes in Britain and both upland and lowland lakes in Scandinavia with a bias towards acidic waters. Using gravity or a piston corer, surface sediment samples were usually taken from the deepest point in each lake and in all cases the top 0.5 cm was used for diatom preparation.