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

Abstract

Urbanization directly affects the ecological status of streams and rivers: Their beds and drainage basins are often heavily transformed and their habitat conditions disturbed. The aim of the study was to evaluate the extent of human impact in streams in the city of Łódź, Central Poland (~700,000 inhabitants), by pattern recognition analysis of benthic diatom assemblage samples using a Kohonen artificial neural network, principal component analysis, and indicator species analysis. The study also determined the ecological status of the streams using five diatom indices: Multimetric Diatom Index, Specific Pollution Sensitivity Index, Generic Diatom Index, Biological Diatom Index, and Trophic Diatom Index. The samples demonstrated considerable variation in ecological status. Examples of poor and bad ecological status were observed, clearly resulting from strong human pressure; however, good status and moderate status were also recorded, both at natural sites and, unexpectedly, those which were severely transformed, whose beds were covered with concrete and which were located downstream from combined sewer overflows. Such sites demonstrated high water conductivity of up to 1440 μS/cm, but this was accompanied by other more favorable conditions: The water flowed from upstream stretches enclosed in downtown underground canals with a fast current, low water temperature, and high average concentration of dissolved oxygen (approximately 10 mg/dm3). These conditions had a mitigating effect, shaping the diatom assemblages to a specific form with the highest species richness and the highest number of indicator taxa observed in the study. In summary, the hydromorphological transformation of streambeds may result in seemingly good ecological status at heavily degraded sites. Therefore, conclusions based on diatom‐based biomonitoring of urban streams and rivers should be drawn with caution.

Critical multi-stranded approach for determining the ecological values of diatoms in unique aquatic ecosystems of anthropogenic origin

“…Planothidium frequentissimum is an eurytopic species that occurs globally in a variety of habitat types, from natural springs to rivers in urban areas with high levels of pollution. Its value as an indicator is low, as confirmed by the Shade Plot analysis, which found it to significantly affect the degree of similarity observed between samples from different environments (Siver et al, 2005; Levkov et al, 2007; Żelazna-Wieczorek, 2011; Kulikovskiy, Lange-Bertalot & Kuznetsova, 2015; Szczepocka, Nowicka-Krawczyk & Kruk, 2018).…”

Peer Review #1 of "Critical multi-stranded approach for determining the ecological values of diatoms in unique aquatic ecosystems of anthropogenic origin (v0.1)"

“…Planothidium frequentissimum is an eurytopic species that occurs globally in a variety of habitat types, from natural springs to rivers in urban areas with high levels of pollution. Its value as an indicator is low, as confirmed by the Shade Plot analysis, which found it to significantly affect the degree of similarity observed between samples from different environments (Siver, et al 2005;Levkov et al 2007;Żelazna-Wieczorek 2011;Kulikovskiy, Lange-Bertalot & Kuznestova 2015;Szczepocka, Nowicka-Krawczyk & Kruk 2018). Recently P. frequentissimum was divided into several different species.…”

The performance of diatom indices in assessing temporal changes in water quality in a large lowland river ecosystem

“…The structure of algae assemblages and their autecology have been studied, and algae community indices have been developed and used worldwide (Prygiel & Coste, 2000; Kalyoncu, Çiçek, Akköz, & Yorulmaz, 2009; Rakowska & Szczepocka, 2011; Tan, Sheldon, Bunn, & Zhang, 2013; Xia, Zhang, Zhao, & Bunn, 2014; Hassan & Shaawiat, 2015; Szczepocka, Nowicka‐Krawczyk, & Kruk, 2018; Tokatli, Solak, Yilmaz, Arici, & Doyioğlu, 2020). Watanabe's Index (WAT) (Watanabe, Asai, & Houki, 1986) was originally developed in Japan to assess organic pollution in aquatic ecosystems (Watanabe et al, 1986).…”

“…The diatom‐based eutrophication/pollution index (EPI‐D) has been reported to be sensitive to Cl − and nutrients (Dell'Uomo, 1996; Prygiel & Coste, 2000). The Biological Diatom Index (IBD) (Prygiel & Coste, 2000) has been widely applied in Europe (Prygiel & Coste, 2000; Kalyoncu et al, 2009; Rakowska & Szczepocka, 2011; Szczepocka et al, 2018; Tokatli et al, 2020) and has been found suitable for evaluating the trophic status and ionic content in water quality assessments in subtropical rivers (Yangtze River basin) in China (Tan et al, 2013). The Pampean Diatom Index (IDP) was developed and used for assessment of rivers and streams in Argentina (Gómez & Licursi, 2001).…”