Selecting indicator-diatom taxa and its application for simplifying trophic diatom index for biological water quality assessment

Background : : Trophic diatom index (TDI) should have been conducted annually by 'water environment conservation act' since 2008 in South Korea. However, its application had difficulties in identification such as fine structures and diversity of diatoms. In this study, it is proposed that a new water quality assessment method called simplified-TDI (S-TDI) for reducing the difficulties of identification using indicator-diatom taxa. Results : : The indicator-diatom taxa were selected using relative abundance and frequency of occurrence. The one criterion was above 10% of the minimum relative abundance of diatom species occurred in each station and the other was above 2% of the minimum frequency of occurrence of diatoms among the total station. Appeared species in 1,999 stations for study was 412 and 115 species were selected as the indicator-diatom taxa. The criterions were verified using statistic assessment method as below similarity, paired sample t-test and root mean square error (RMSE). Species excluded from indicator-diatom taxa were identified two methods. They were identified up to genus level and received the average sensitivities and indicator values of the genus in TDI. Even they were not able to be identified genus level, identified them to 'unidentified group' and received the average sensitivities and indicator values of total diatom species in TDI. This method was newly proposed as S-TDI in this study. To verify the application of S-TDI, its values were compared with original TDI values from 60 sampling stations considering various aquatic environments. The similarity between S-TDI and original TDI values were very high degree of 0.999, the paired sample t-test indicated no statistically significant difference and RMSE was 1.52 below the threshold. Conclusion : s: These results showed S-TDI can be applied to the water quality assessment instead of original TDI.