Recovery dynamics in invertebrate communities following water-quality improvement: taxonomy- vs trait-based assessment
Abstract
Sewage effluents are recognized as one of the most common sources of river degradation. However, very few investigators have tried to evaluate ecosystem recovery after cessation of wastewater treatment plant (WWTP) discharge. Our goals were to: 1) analyze invertebrate community responses to chemical water quality and habitat changes after wastewater treatment improvement, and 2) evaluate the abilities of taxonomy-based and trait-based approaches to detect and explain community recovery processes in a multistressor context. We studied the benthic macroinvertebrate community of 3 sites of a heavily impaired stream (the Vistre River, France) during a 4-y period that included the decommissioning of a deficient WWTP (WWTP-A) and the commissioning of a new one (WWTP-B). We assessed the recovery of the benthic community by comparing observed taxonomic and trait-based (i.e., functional) metrics at the study site to values estimated with information from least-impaired reaches of the same river type. Most taxonomy-based characteristics of benthic communities subjected to WWTP-A recovered in 3 mo, but the recovery time of several trait-based characteristics was ∼2 y. No change was observed in taxonomic and trait-based diversity during the 4-y study. Taxonomy-based metrics detected the first signs of river reach recovery rapidly, but combinations of trait-based metrics and taxonomic abundance-based metrics are more likely to identify functional recovery of invertebrate assemblages faced with water-quality improvement, even when multiple stressors impaired upstream reaches.