Chironomidae communities from the Mazafran watershed as bioindicators of water quality and biodiversity with implications for global freshwater ecosystems

This study investigates the use of Chironomidae communities as bioindicators to evaluate biodiversity and water quality in freshwater habitats. A crucial sub-basin in a north African coastal area, it is subject to severe pollution and urbanisation pressures, which makes it a perfect model for comprehending how human activity affects aquatic ecosystems. We performed physico-chemical assessments of water quality indicators, in addition to monthly sampling of Chironomidae larvae and macroinvertebrates at 13 sites during a one-year period. Chironominae and Orthocladiinae emerged as the leading subfamilies among the 55 Chironomidae taxa, which comprise 30,145 individuals. As a result, downstream stations showed indications of severe contamination, but upstream stations had the maximum species diversity. The Canonical Correspondence Analysis (CCA) demonstrated the sensitivity of Chironomidae to habitat conditions by revealing robust connections between environmental variables and species distribution. While Orthocladius rubicundus was a critical signal of high-water quality upstream, the Dominant Species Chironomid Index (D.S.C.I.) further confirmed considerable water quality degradation downstream, in contrast to the biological balance observed upstream. These results highlight the usefulness of biotic indices based on Chironomidae for biomonitoring and offer important management insights for freshwater ecosystems in areas affected by pollution and urbanisation.