Effects of variations in water quantity and quality in the structure and functions of invertebrates’ community of a Mediterranean urban stream

Abstract

Urban streams provide important ecosystem services to cities’ population, from the maintenance of urban biodiversity, temperature, humidity and air quality to improving aesthetics and provision of natural areas for recreation. However, these streams are under multiple-stressors, including artificialization of the channel and flow, poor water quality and cut of riparian vegetation which puts in risk their ecological integrity and consequently their services. In this study, we aimed to understand variations in macroinvertebrate communities and in biological condition as a response to flow and water quality, by following a Mediterranean urban stream over 8 months (December–July). With a monthly periodicity, we sampled invertebrate communities and characterized in situ water physicochemical parameters. The urban stream studied showed a high variation of environmental factors over time. Invertebrate communities were generally poor, with some Ephemeroptera (Baetis sp.) but was dominated by Chironomidae and Oligochaeta that changed over time alongside with environmental conditions. Biological quality based on the Portuguese Invertebrates Index (IPtIS) varied between poor and bad. Multivariate community patterns (at genus level) showed variations in communities over time, as well as in their biological trait patterns (invertebrates’ maximal size, reproduction mode, resistance form, feeding habits and locomotion mode). Periods displaying worse biological quality, less diverse communities and lower functional richness corresponded to peaks of discharge, higher conductivity and hardness while the best quality communities were found under lower nitrate concentrations. Our study points out that the detection of impacts or recovery in urban streams through invertebrate communities might require at least the use of genus level as family level does not detect smoother changes. Communities reflect the complex interplay of environmental variables affecting structural and functional natural patterns and ultimately the biological condition of this urban stream. Rehabilitation measures should carefully consider this complex interplay of variables to enhance quality and ecosystem services.