Environmental factors affecting aquatic invertebrate communities were assessed using Daphnia magna
in situ bioassays and biological indices based on community assemblages of benthic macroinvertebrates.
Investigations were carried out in two heavily industrialized and urbanized river basins from the NE of
Spain (Llobregat and Beso´ s).Measures of energy consumption (i.e. algal grazing), and of specific biochemical
responses (biomarkers)were conducted on individuals transplanted upstream and downstream from
effluent discharges of sewage treatment plants. In both rivers there was a clear deterioration of the ecological
water quality parameters and benthic communities towards downstream reaches. In all but one
of the 19 locations studied, transplanted organisms were affected in at least one of the five measured
responses. In three of them, significant effects were detected in most of the traits considered. Principal
Component and Partial Least Square Projections to Latent Structures regression analyses indicated that
the measured responses in D. magna in situ bioassays and those of macroinvertebrate assemblages were
affected by distinct environmental factors. From up to 20 environmental variables considered, seven of
them including habitat degradation, suspended solids, nitrogenous and conductivity related parameters
affected macroinvertebrate assemblages. On the other hand, levels of organophosphorus compounds and
polycyclic aromatic hydrocarbons were high enough to trigger the responses of D. magna in situ bioassays.
These results emphasize the importance of combining biological indices with biomarkers and more
generalized and ecologically relevant (grazing) in situ responses to identify ecological effects of effluent
discharges from sewage treatment plants in surface waters.
Environmental factors affecting aquatic invertebrate communities were assessed using Daphnia magna
in situ bioassays and biological indices based on community assemblages of benthic macroinvertebrates.
Investigations were carried out in two heavily industrialized and urbanized river basins from the NE of
Spain (Llobregat and Beso´ s).Measures of energy consumption (i.e. algal grazing), and of specific biochemical
responses (biomarkers)were conducted on individuals transplanted upstream and downstream from
effluent discharges of sewage treatment plants. In both rivers there was a clear deterioration of the ecological
water quality parameters and benthic communities towards downstream reaches. In all but one
of the 19 locations studied, transplanted organisms were affected in at least one of the five measured
responses. In three of them, significant effects were detected in most of the traits considered. Principal
Component and Partial Least Square Projections to Latent Structures regression analyses indicated that
the measured responses in D. magna in situ bioassays and those of macroinvertebrate assemblages were
affected by distinct environmental factors. From up to 20 environmental variables considered, seven of
them including habitat degradation, suspended solids, nitrogenous and conductivity related parameters
affected macroinvertebrate assemblages. On the other hand, levels of organophosphorus compounds and
polycyclic aromatic hydrocarbons were high enough to trigger the responses of D. magna in situ bioassays.
These results emphasize the importance of combining biological indices with biomarkers and more
generalized and ecologically relevant (grazing) in situ responses to identify ecological effects of effluent
discharges from sewage treatment plants in surface waters.
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