Taxonomic concentration of diatom index uncertainty
Under Consideration at Environmental Monitoring and Assessment (EMA)
Abstract
Diatom assessments retain genus information when finer taxon labels are unresolved, yet the fraction of unresolved valves alone cannot specify assessment precision. We quantified the precision retained by genus identity and located the taxa contributing most to the remaining uncertainty. Using 6,588 fully scored assemblages from an English river archive, we concealed fine taxon labels while preserving counts and correct genera. The compatible Trophic Diatom Index range and its additive genus contributions were calculated in catchment-disjoint development and confirmation populations. At 20% random label loss, genus information reduced mean width from 20.00 to 10.92 points in the 4,153-record confirmation population across 240 catchments. Ten-point attainment reached 41.2% of catchment-weighted cases (95% confidence interval, 37.7–44.7%). Navicula, Gomphonema and Nitzschia accounted for 53.2% of residual width from 31.0% of masked abundance. Their combined width share remained between 53.0% and 53.4% when each confirmation catchment was omitted. Random-loss point estimates had a mean absolute error of 0.46 points. The entire feasible range resolved one derived sample class in 31.6% of weighted cases with eligible alkalinity. Genus composition therefore determines how much trophic precision incomplete identification preserves, with residual uncertainty concentrated in a few genera with substantial unresolved abundance and broad trophic score ranges. Recording unresolved genera and counts quantifies that precision and identifies the taxonomic contributions that finer identification can remove.
