Deceptive ecological status of urban streams and rivers-evidence from diatom indices

Our findings indicate that streams degraded in their upper course may exhibit desired changes in diatom assemblages further downstream, even if human pressure intensifies, which suggests that the streams compensate for the symptoms of urban degradation

Ewelina Szczepocka; Paulina Nowicka-Krawczyk; Andrzej Kruk

2018

Scholarcy highlights

  • The Industrial Revolution of the 18th and 19th centuries resulted in the ecological degradation of freshwater ecosystems around the world
  • Apart from the Łagiewniczanka, which has been subjected to the least anthropogenic impact, all have been transformed by channel straightening, closure into underground sections, having banks or bottoms covered with concrete slabs, being impounded or by the construction of artificial reservoirs
  • Our assessment of the ecological status of streams in the city of Łodz revealed considerable differences between the studied sites, which results from the diverse taxonomical composition of the diatom assemblages
  • This has been attributed to their short reproductive cycle, which allows them to quickly rebuild their assemblages, the composition of which reflects environmental changes; as a result, a number of biomonitoring studies based on diatom indices have been performed globally
  • The assessment of the ecological status of the streams examined in the present study varied depending on the applied diatom index
  • Indicator value allows for the identification of indicator diatom taxa for each self-organizing map output layer region, that is, taxa significantly associated with each SOMcluster of real diatom samples
  • Polish biomonitoring studies most commonly use the IO index; it does not allow water quality to be differentiated in streams at individual sites, as it exhibits a low sensitivity to changes caused by pollutant inflows
  • The regulation of the streams and the enclosure of their beds within underground concreted channels resulted in altered environmental conditions, that is, rapid current, low water temperature, and high dissolved oxygen concentration, favoring certain species sensitive to organic pollution

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