Response of diatom indices to simulated water quality improvements in a river.

摘要

Various diatom indices are routinely used in European countries to monitor water quality in waterways. In order to assess their sensitivities and their integration interval after a sudden and lasting environmental change, epilithic diatom biofilms were transferred from several polluted rivers to an unpolluted stream. To monitor the changes of the index values, the biofilms were sampled in a first experiment 20 and 40 days after transfer, and in a second experiment 30 and 60 days after transfer. Sensitivities of the indices to the water quality improvement were assessed calculating the differences between the index values of the reference and the transferred assemblages. Some indices have intermediate sensitivities (BDI, GDI, ILM, SLA), others higher sensitivities (CEE, EPI, ROT, SPI, TDI). The integration interval of these indices was 40-60 days. Some differences were observed between the indices, but their results were homogeneous when compared to those obtained with other metrics such as Bray-Curtis or Chord distances, used to assess the difference between the transferred and the reference diatom assemblages. These other metrics showed that even after 60 days, the transferred assemblages still differed from the reference. This underlines that metrics do not have the same integration intervals and do not assess the same stresses; the choice of the metric used to assess water quality is of prime importance..