Effects of anthropogenic pollution and hydrological variation on macroinvertebrates in Mediterranean rivers: A case-study in the upper Tagus river basin (Spain)

• Published in: The Science of the total environment 2021-04, Vol.766, p.144044, Article 144044
• Main Authors: Arenas-Sánchez, Alba, Dolédec, Sylvain, Vighi, Marco, Rico, Andreu
• Format: Article
• Language: English
• Subjects: Animals; Biodiversity and Ecology; Biological traits; Environmental Monitoring; Environmental Sciences; Functional diversity; Hydrological variation; Invertebrates; Pollution; Rivers; Spain; Water Quality
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2020.144044

Seasonal hydrological variation and chemical pollution represent two main drivers of freshwater biodiversity change in Mediterranean rivers. We investigated to what extent low flow conditions can modify the effects of chemical pollution on macroinvertebrate communities. To that purpose, we selected twelve sampling sites in the upper Tagus river basin (central Spain) having different sources of chemical pollution and levels of seasonal hydrological variation. The sites were classified as natural (high flow variation, low chemical impact), agricultural (high flow variation, high agricultural chemical inputs) and urban (limited flow variation, high urban chemical inputs). In these sites, we measured daily water discharge, nutrients, and contaminant concentrations, and we sampled benthic macroinvertebrates, in spring, summer and autumn. Significant differences related to toxic pressure and nutrient concentrations were observed between the three groups of sites. Seasonal patterns were found for some water quality parameters (e.g. nitrites, ammonia, suspended solids, metal toxicity), particularly in agricultural sites. Taxonomic and functional richness were slightly lower in the polluted sites (agricultural and urban), particularly during low flow periods (summer and early autumn). Functional diversity was significantly lower in sites with seasonal flow variation (agricultural sites) as compared to the more constant ones (urban sites). The frequency of traits such as large size, asexual reproduction, aquatic passive dispersion and the production of cocoons increased in response to pollution during low flow periods. This study shows that the impacts of anthropogenic chemical pollution on taxonomic and functional characteristics of macroinvertebrate communities seem to be larger during low flow periods. Therefore, further studies and monitoring campaigns assessing the effects of chemical pollution within these periods are recommended. [Display omitted] •We assessed the effect of varying flow conditions and pollution on invertebrates.•Stronger functional diversity response to pollution during low flow periods.•Traits representative of pollution and low-flow conditions have been identified.•Late summer monitoring is recommended to tackle maximum ecological disturbance.