Long term urban impacts on the ecological status of a lowland river as determined by diatom indices

Abstract

This study determined changes in the ecological status of a lowland river under the impact of an urban agglomeration after modernizing the wastewater management. For 174 years the Ner River was loaded with pollution from expanding industry. Construction of the Group Sewage Treatment Plant (GOŚ) in 1994 and its subsequent modernization should have improved the water quality. After 20 years of proper sewage treatment the ecological status of the river hasn't improved. Study sites were established on the river above and below sewage disposal from GOŚ, and the ecological status was assessed on the basis of benthic diatoms. Diatom indices: IO, GDI, IPS were calculated in order to determine the ecological status and water quality. Hierarchical cluster analysis and multivariate analysis of diatom assemblages were used to reveal differences of the study sites. It was revealed that the river is divided into two sections: the first is above the sewage disposal and the second is below it. In the first section, domination of species sensitive to organic pollution Meridion circulare and Ulnaria ulna was noted, while in the second section species resistant and tolerant to organic pollution, Hippodonta capitata and Navicula gregaria, were noted. The ecological status at the first section was moderate to poor, while at the second it was poor to very poor. The division of the urban river into two sections with different ecological status stems from the history of water management. The present location of the GOŚ outflow served in the past as a dump of untreated sewage from the industry of the Łódź Agglomeration. Development of the city led to the degradation of the ecosystem. Modernization of wastewater management did not reverse the degradation of the river. The persistence of accumulated industrial pollution in sediments caused by the long-term impact of urban agglomeration almost completely destroyed the ecosystem of the river.

Diatom communities and ecological status classification in the upper Po River basin

“…Recently, homogenization of diatom communities has also been observed in response to hydrological alterations and urbanization in Mediterranean rivers which also led to significant species loss at both local and regional scales (Falasco et al, 2021a) and a reduced role of diatoms in the total benthic chlorophyll-a (Piano et al, 2016). Moreover, the present study confirmed the high trophic value of some species, mainly collected in the R-C macrotype, such as N. gregaria (Hicks and Taylor, 2019;Hausmann et al, 2016;Szczepocka et al, 2016), Nitzschia palea (Licursi et al, 2016;Szczepocka et al, 2016;Yang et al, 2015), Gomphonema parvulum (Lu et al, 2020;Szczepocka et al, 2016) and C. euglypta (Trábert et al, 2020). S. nigri was confirmed as one of the most tolerant diatom species (see Hausmann et al, 2016 as Eolimna minima;Yang et al, 2015).…”

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

“…However, it has been reported that in natural rivers, the IPS may significantly underestimate the actual ecological status (Szczepocka et al 2014). The TDI index, used to assess the trophic conditions, is usually very precise and is believed to reflect the true trophic state of river ecosystems in Poland (Szczepocka et al 2016), as presented in this study.…”

“…, Szczepocka et al. , , Żelazna‐Wieczorek and Nowicka‐Krawczyk ). However, it has been reported that in natural rivers, the IPS may significantly underestimate the actual ecological status (Szczepocka et al.…”

“…The TDI index, used to assess the trophic conditions, is usually very precise and is believed to reflect the true trophic state of river ecosystems in Poland (Szczepocka et al. ), as presented in this study.…”

“…Industrialization and urbanization impoverished aquatic ecosystems by increasing the concentrations of municipal and industrial pollutants within them; these negative effects were compounded by the lack of effective sewage systems at the time, and these effects persist today. Even when sewage management improves, the pollutants accumulated in sediments and the valley are released during increased rainfall and discharge and often prevent downstream sections of streams and rivers from achieving a good ecological status (Sekabira et al 2010, Luo et al 2014, Tszydel et al 2015, Szczepocka et al 2016.…”